Monday Morning Key
26 ODP related abstracts
Section Session Location Title Author Time
Marine Controlled Source Electromagnetics MCC level Schwalenberg, K GP11 A for Gas Hydrate Evaluation on the Cascadia 8:00 2 et al. Margin: Correlation Between Resistivity Anomalies and Seismic Blank Zones Age Offsets of the Matuyama-Brunhes MCC level Polarity Transition in Records From the GP11 B Clement, B. et al. 8:00 2 Atlantic: Lock-in Depth Variations or Site Dependent Field Behavior? Paleomagnetic and Rock Magnetic Geomagntism Investigation of Leg 210 Cores, Liu, Q et al. 8:00 and Newfoundland Basin Paleomagnetism Paleomagnetic and Rock Magnetic Signature of Upper Oceanic Crust Generated Acton, G. et al. 8:00 by Superfast Seafloor Spreading: Results MCC level from ODP Leg 206 GP11 D 2 Paleomagnetic Paleolatitudes of the Ontong Java Plateau From 120 Ma to 55 Ma: Hall, S. et al. 8:00 Implications for the Apparent Polar Wander Path of the Pacific Plate.
Magnetic Properties and Paleointensity of a Hawkins, L. et al. 8:00 Mid-Miocene Gabbro from the Costa Rica Accretionary Wedge, ODP Leg 170 Calibration of Mobile NMR Instruments in Mineral and Rock MCC level MR11 A Respect to Porosity and Pore Size Arnold, J et al. 800 Physics 2 Distribution of Drill Cores
New Insights into Inferring Climate Variability from Records of Planktonic Greaves, M. et al. 8:00 Foraminiferal Mg/Ca, Oxygen Isotope and Shell Weight in the Southern Ocean Paleoceanography MCC level and PP11 A 1 Paleoclimatology Changes in Deep Sea Temperature and Ice Volume Based on Paired Measurements of Healey, S L 8:00 Benthic Foraminiferal Mg/Ca and d18O: Evidence from ODP Site 849, Equatorial Pacific for Marine Isotope Stages 1-3 Section Session Location Title Author Time
The Nature of the d13C of Periplatform Swart, P K 8:00 Sediments: Implications for stratigraphy Orbitally Paced Climate Variability During the Middle Miocene: High Resolution Stable Isotopes and Fe Holbourn, A 8:00 Records From the Western and MCC Southeastern Pacific PP11 A level 1 Middle Eocene to early Oligocene paleoceanography of the Southern Ocean Bohaty, S et al. 800 from foraminiferal stable isotope and Mg/Ca records Cenozoic variations in the South Atlantic carbonate saturation profile: Schellenberg, S 800 Insights from the Walvis depth-transect and Nielsen, J (ODP Leg 208) New Data On The Distribution Of Calcareous Nannofossils During And Raffi, I 800 Paleoceanography After The Paleocene/Eocene Transition and Paleoclimatology Depth Dependant Variations in Benthic McCarren, H et Foraminiferal Assemblages and Stable 800 Isotopes Across the P-E Boundary, al. Walvis Ridge (ODP Leg 208) Marine carbonate dissolution event across the Eocene/Oligocene boundary: Liu, Z et al. 800 the Walvis Ridge transect, South MCC PP11 B Atlantic (ODP Leg 208) level 1 Tracers of Productivity across the Quartini, J C et PETM, Walvis Ridge, ODP Sites 1262 800 al and 1263 The Composition and Flux of Terrigenous Material from the late Nicolo, M J 800 Paleocene to the early Eocene in the Indian Ocean Extreme Acidification of the Deep Sea at the Paleocene-Eocene Boundary: New Zachos, J et al. 800 Constraints From Ocean Drilling Program Leg 208 Section Session Location Title Author Time Paleoceanographic changes in the western tropical Atlantic during the late Paleocene (59-55 Romano, M et al. 800 Ma): high-resolution stable MCC isotope records from ODP Leg PP11 B level 1 207 Site 1258 Paleoceanography Decoupled Shelf-Ocean and Phytoplankton Productivity Gibbs, S J et al. 800 Paleoclimatology Responses Across the Paleocene- Eocene Thermal Maximum Late Quaternary Biosiliceous Laminated Marine Sediments MCC P11 C From Antarctica: Seasonality Pike, J et al 815 2004 During a Period of Rapid Climate Change Ice shelf drill sites proposed to study Pre-Late Oligocene climate and tectonic history, Coulman Decesari, R et al. 800 High, Southwestern Ross Sea, MCC T11 A Antarctica. level 2 Evidence That Early to Middle Miocene ice Streams From West Sorlien, C et al. 800 Antarctica cut Into Southeastern Tectonophysics Ross Sea Continental Shelf Holocene Turbidite Recurrence Frequency off Northern Nelson, H et al. 1205 California: Insights for San MCC Andreas Fault Paleoseismicity T12 B 3002 Cascadia Great Earthquake Recurrence: Correlation Evidence Goldfinger, C et 1050 for Repeated Margin Wide al. Rupture Monday Afternoon Key
21 ODP Related abstracts
Section Session Location Title Author Time LGM to Holocene African Marriott climate variability and the Sr, Nd, Union U14 A Cole, J et al. 1700 Salon 7 and Pb isotope ratios of eolian deposits off northwest Africa Data Management for the Ridge Chayes, D et al. 1340 2000 Program MCC Evidence for Along-Strike Biogeoscience B13 A level 1 Hydrothermal Circulation Within Young Oceanic Crust on the Hutnak, M et al 1340 Eastern Flank of the Endeavour Axis, Juan de Fuca Ridge Teaching Biostratigraphy Using Real Cores and IODP Data: The use of Information Technology on Hilding- Education 1340 MCC Spatial Visualization Skills, Kronforst et al. and ED13 E level 2 Motivation and Transfer of Human Resources Undergraduate Science Majors
Writing and Visualization for Thomas, S F 1340 Teaching Plate Tectonics Geomagnetism and MCC Weitemeyer, K GP13 A A Pilot Marine EM Study of 1455 Paleomagnetism 3112 Hydrate Ridge, Oregon. et al. Timing of Late Quaternary sea surface temperature change: Evidence from high-resolution {\it Pak, D et al. 1300 Globigerina bulloides} Mg/Ca records from the California Margin Primary Productivity Changes in MCC the subtropical western North PP13 A level 1 Atlantic During Marine Isotope Poli, M et al. 1340 Paleoceanography Stages 11-12: Inferences from and Benthic Foraminifera Paleoclimatology MILLENNIAL-SCALE CLIMATE VARIABILITY IN THE SUBTROPICAL Gibbons, F et al 1340 ATLANTIC DURING THE MIDDLE PLEISTOCENE MCC PP13 B Tripati, A 1455 2004 Sea-surface and deep-sea Section Session Location Title Author Time Calcareous Nannofossils and Orbitally Tuned Cyclostratigraphy Raffi, I 1425 MCC in the Cenozoic PP13 B 2004 Meynadier, L Paleoceanography Oxygen Isotopic Stratigraphy and and 1440 and Geomagnetic Field Intensity Valet, J Paleoclimatology Revisiting ODP Site 690 to Assess the Responses of Marine Carbonate Chemistry to the Kelly, D et al 1645 MCC PP14 A Paleocene-Eocene Thermal 2004 Maximum Multiple Early Eocene Thermal Roehl, U et al. 1615 Maximums
MCC Airborne Gravity Gradiometer T13 A Talwani, M 1340 level 2 Survey Over the San Andreas Fault Magnetic Properties of Ocean Crust from the Walls of Endeavor Richmond, R et Deep: Implications for the Source 1340 al. Layers of Marine Magnetic MCC T13 B Anomalies Tectonophysics level 2 Structure of the Upper Crust Exposed at Endeavor Deep: Popham, C et al. 1340 Implications for Crustal Accretion at Ultra-Fast Spreading Rates Analysis of the Growth of Active Detachment Folds Applying the Gonzalez-Mieres, MCC T14 C new Thickness Relief Method, R and 1650 3002 With Examples From the Tien- Suppe, J Shan and Nankai Trough Along Strike Hf-Nd Isotopic Composition of Aleutian Arc Gerseny, M et al. 1340 Lavas Volovanology, The Hf-Nd isotopic diversity of Vervoort, J et al. 1340 Geochemistry, V13 B MCC subducting oceanic sediments Petrology level 2 Characterizing Sedimentary Carbon and Nitrogen Subduction Li, L Fluxes in the Central America and 1340 Convergent Margin (ODP Legs Bebout, G 170, 205) Tuesday Morning Key
13 ODP Related abstracts
Section Session Location Title Author Time MCC Union U21 A Late Pleistocene Paleoclimate Record Shackford, J 800 level 2 From the SW African Margin Carbon Biogeochemistry of Marine MCC Biogeoscience B21 D Sediments at the ODP Leg 204, Hydrate Li, Y et al. 800 level 2 Ridge Education Experiences and Results from the and MCC Integrated Ocean Drilling Program ED21 C Rice, J et al. 800 Human level 1 (IODP) Teacher at Sea Program, Resources Expedition 301 MCC An Experiment on GPS/A Seafloor Fujimoto, H et Geodesy G21 A Positioning in the Central Part of Kumano- 800 level 1 nada, Central Japan al. Authigenic Dolomite in Marine MCC Vasconcelos, C OS21 A Marginal Sediments: An Indicator of 800 level 2 et al. Fossil Microbial Activity Ocean Sciences Slope Instability and Gas Hydrates in the MCC OS21 E Hudson Canyon Region, U.S. Atlantic Rona, P et al 930 3011 Continental Margin MCC OS22 B Size and Age Characteristics for West Lee, H et al. 1120 3011 Coast Tsunamigenic Landslides Long-Term Observations of Active MCC Von Damm, K Tectonophysics T21 C Hydrothermal Processes on the Gorda 800 level 1 Ridge: The Sea Cliff Hydrothermal Field et al. and Escanaba Trough
Volcanology, Tephrochronology of North Pacific Prueher, L 850 Geochemistry, Volcanic Arcs - data from ODP Leg 145 Petrology MCC V21 C 3008 Terrestrial-marine Correlation of the 24 kyr BP Dawson Tephra: Implications for Beget, J et al. 820 Dispersal and Preservation of Alaskan Tephra Deposits Section Session Location Title Author Time An ocean floor prospecting: Implications from the petrological insights of the abyssal chromitites from ODP Leg 209, Abe, N 1055 MAR 15 20 N FZ
Volcanology, MCC Geochemical Study of Mid Atlantic Geochemistry, V22 A 3008 Ridge Peridotites From 15\deg N: Godard, M et al 1125 Petrology Preliminary Results From ODP Sites 1272 and 1274
Upper Mantle Geochemistry at Suhr, G Peridotites of Site 1274 (ODP Leg 209): and 1140 Relation to Melt-Rock Reaction and Paulick, H Processes at the Base of the Lithosphere Tuesday Afternoon Key 15 ODP Related abstracts
Section Session Location Title Author Time Marriott MIS 11 and the mid-Brunhes Dissolution Union U23 A Barker, S et al. 1440 Salon 7 Interval Geomagnetism Hotspot motion, scales of mantle MCC and GP24 A convection and the long-term history of the Tarduno, J 1610 3024 Paleomagnetism geydynamo Secondary Teachers and Their Students; MCC Ocean Sciences OS23 A Why you Need Them, Where to Find Them Peart, L 1340 level 2 and How to Make Them Your Number One Audience!Do Tropical SST Changes Lead High Latitude Climate Change, Or Are Our Dekens, P et al. 1340 Proxies Misleading Us? High Latitude and Tropical Climates Linked Prior to the Onset of Northern PP23 A Lawrence, K et al. 1340 Hemisphere Glaciation: Evidence From MCC the Eastern Tropical Pacific level 2 Liu, Z Early Onset and Origin of 100-kyr Cycles and 1340 in a Tropical Pleistocene SST Record Herbert, T Paleoceanography Detrital Sediment Supply And Late and Quaternary Environmental Changes Off Hofmann, J et al 1340 Paleoclimatolgy Taiwan, ODP Site 1202
High resolution paleoceanography of the central Gulf of California during the past Barron, J et al. 1340 15,000 years Pleistocene North Atlantic Deep Water Production; A Southern Hemisphere Foote, J et al. 1340 PP23 B Perspective MCC
level 2 Optical Dating of Marine Sediment From ODP Core 658B - An Intercomparison Armitage, S et al. 1340 With an Independent AMS 14C Chronology Fulfilling the Promise of the DSDP/ODP Legacy with Multiparameter Logging of Schultheiss, P et al 1340 Archive Cores New insights into serpentinization at Atlantis Massif, 30° N Mid-Atlantic Ridge, Singh, S et al. 1340 using wide-angle seismic method Magnetization Of Gabbroic Rocks and Peridotites Recovered From Mid Atlantic Kikawa, E et al. 1340 Volcanology, Ridge 14N - 16N, ODP Leg 209 MCC Geochemistry, V23 B level 1 Lithium and strontium isotope Petrology compositions of serpentinite-hosted carbonate veins from the MAR (ODP Leg Rosner, M et al. 1340 209): Records of different stages of seafloor metamorphism Extensional Faulting at 15\deg North on the Schroeder, T et al. 1340 Mid-Atlantic Ridge, ODP Leg 209 Wednesday Morning Key
11 ODP Related abstracts
Section Session Location Title Author Time MCC Warmer tropics during stage 11 - evidence Union U31 A Lea, D level 1 from the Cariaco Basin Rack, F MCC Out To Sea: Life as a Crew Member Aboard a ED31 A and 800 level 2 Geologic Research Ship'' - Production of a Education Video and Teachers Guide. Tauxe, K and Learning Activities Developed at The Human Resources MCC University of Texas at Austin Institute for ED31 C Bailey, D et al. 800 level 2 Geophysics Using Ocean Drilling Science, Technology and Data
Volcanic Influence on the Susceptibility Salome, A et al 800 Geomagnetism and Signal: a Case Study in Indian Ocean GP31 B MCC Paleomagnetism level 2
Rock Magnetic Properties Across Paleocene- Lippert, P et al. 800 Eocene Boundary Sediments from the North Atlantic, South Atlantic, and Eastern Pacific
Evidence For Deep-water Production In The Thomas, D 800 North Pacific During The Early Cenozoic MCC PP31 B Paleoceanography 2000 and Planktonic Foraminifera Study at Site ODP 999A (Caribbean Sea): Insights into Oceanic Vautravers, M et Paleoclimatology 800 Exchange and Paleocirculation During the last al. 450 Kyrs. Tracking Warm Saline Deep Water on Maud Martin, E et al. 815 Rise Using Nd Isotopes MCC Structure of the Penultimate Deglaciation PP32 A 2000 Cannariato, K et Along the California Margin and Implications 1120 al. for Milankovitch Theory Evidence for Extremely Large Lava Flows on MCC Ontong Java Plateau from High Precision Volcanology, V31 A Michael, P 800 level 2 Measurements of Volatiles and Major Geochemistry, Elements in Natural Glasses Petrolgy Gabbro fracturing and elemental analysis in MCC V31 B the Costa Rica margin (ODP Leg 205): Core- Thu, M et al. 800 level 2 log integrated high-resolution study Wednesday Afternoon Key
16 ODP Related abstracts
Section Session Location Title Author Time Rapid true polar wander: A Cottrell, R et 1340 quixotic search? al. Union U33 A MCC Paleomagnetic Data From level 1 Ontong Java Plateau are Sager, W 1340 Anomalous $\sim$ Did the Plateau Form on Another Plate? Testing the Molecular Clock MCC Using the Best Fossil Record: Biogeoscience B33 B Steel, B et al. 1340 level 1 Case Studies from the Planktic Foraminifera Determination of Relative Geomagnetism Contributions from Marine and MCC Verosub, K et and GP34 A Terrestrial Sediment Sources in 1630 2000 al. Paleomagnetism the Cariaco Basin using a Magnetic Mixing Model Holocene and Glacial Variability MCC of the Hydrologic Cycle in the OS33 A Dulski, P et al 1340 level 1 Tropical Atlantic: Evidence from the Cariaco Basin Sediment Accumulation Rates of Late Quaternary Deposits in San Normark, W Pedro Basin, the Gulf of Santa 1340 et al. Catalina, and San Diego Trough, Offshore Southern California Ocean Sciences OS33 B MCC level 1 Relations Between Basement Tectonics, Sediment Deformation Zuehlsdorff, and Fluid Flow at the Eastern Juan L and 1340 de Fuca Ridge Flank: Results Spiess, V From Very High Resolution Seismic Data Mechanism for free gas migration Liu, X and through South Hydrate Ridge 1630 Flemings, P MCC hydrate system OS34 B 3010 Structural Controls on Hydrate Weinberger, J Distribution and Morphology at 1615 and Brown, K Hydrate Ridge, Oregon Section Session Title Author Time Grayson, R et An Excess $^{226}$Ra 1340 Geochronology for Saanich Inlet al Differentiation of Cenozoic PP33 A Eolian Dust Sources in the Stancin, A et Paleoceanography MCC 1340 and level 2 Eastern Pacific by Nd-Sr-Pb al. Paleoclimatology Radiogenic Isotopes High Resolution Record of Zylberberg, D Seawater Osmium Isotopes Over 1340 et al the Last 100,000 Years High Resolution Calcareous MCC Nannofossil Fluctuations Across PP33 B McGonigal, K 1340 level 2 the Oligocene/Miocene Boundary, ODP Hole 1168A Trace Element and Isotopic (Re- Os, O) Systematics of Roberts Victor Eclogites: Evidence for 3 MCC Shirey, S et V33 E Ga Subduction-Incorporation of 1340 level 2 al. Archean Oceanic Lithosphere into the South African Kaapvaal Volcanology, Craton Keel Geochemistry, Plume-Ridge Interaction on the Petrolgy Cocos Plate (ODP Leg 205, Costa Chavagnac, V 1630 Rica): Implication for Fluid et al. V34 B MCC Circulation 3006 Hawaiian Hotspot - Spreading Ridge Interaction in the Late Keller, R 1745 Cretaceous: A Fair and Balanced Look at the Evidence Thursday Morning Key
17 ODP Related abstracts
Section Session Location Title Author Time Data Acquisition, High Tech High School Interns Develop MCC Staudigel, Management, SF41 A a Mid-Ocean Ridge Database for 800 level 2 D et al. Display Research and Education
Education and Marriott Undergraduate Student Research with the Hawkins, L ED41 C 900 Human Resources Salon 4 Integrated Ocean Drilling Program on et al. Expedition 301 Field Geometry During the Iceland MCC Basin Event Observed from the North Laj, C et al. 830 2000 Atlantic Ocean, North Pacific Ocean and the South China Sea GP41 B A 300 kyr Record of Geomagnetic Geomagnetism and Excursions and Paleointensity From the Paleomagnetism Irminger Basin: Candidates for Mono Channell, J 815 Lake, Laschamp, Iceland Basin, Jamaica and Pringle Falls? A paleomagnetic record of the last 640 kyr from an eastern Mediterranean piston Oda, H et 945 core and a review of geomagnetic al. excursions in the Brunhes Estimation of Free Gas Saturation Using AVO Analysis on 3D Seismic Data at Xun, H et 800 MCC South Hydrate Ridge, Cascadia al. OS41 C level 1 Accretionary Complex Analysis of Sonic Velocity in an Active Guerin, G Gas Hydrate System, Hydrate Ridge, 800 Ocean Sciences et al. Offshore Oregon Medusa-Isosampler: A modular, network-based observatory system for MCC combined physical, chemical and Schultz, A OS42 A 1135 3011 microbiological monitoring, sampling et al. and incubation of hydrothermal and cold seep fluids Late Cenozoic reduction in Antarctic Paleoceanography MCC Circumpolar Current flow from analyses Hassold, N and PP41 A 800 level 1 of drift deposits along the Antarctic et al. Paleoclimatology Peninsula, ODP Site 1095 Section Session Location Title Author Time Enriched MORB in the Northeastern Pacific, Petrological and Geochemical Haraguchi, S 800 Features of igneous Basement at Site et al. MCC T41 A 1224, ODP Leg200 level 2 Atlantis Bank as a Key to Understanding Matsumoto, T the Nature of the Moho and Crust-Mantle 800 et al. Boundary Varying Rates and Modes of Subduction Kukowski, N 800 Erosion Along the Peruvian Margin et al. T41 C MCC Structural vergence variation and level 2 clockwise block rotation in the Cascadia Johnson, J et 800 accretionary wedge, offshore central al. Tectonophysics Oregon Metamorphic Tectonites and Differential MCC Exhumation Reveal 3D Nature of T41 C Little, T et al. 800 level 2 Extension and Lower Crustal Flow in the Active Woodlark Rift, Papua New Guinea Distribution of Post-Rift Sills on the Newfoundland Nonvolcanic Margin Shillington, D Around the ODP Leg 210 Transect From 800 MCC et al. T41 E Waveform Inversions and Synthetic level 2 Seismograms Opal diagenesis and sediment properties Spinelli, G et 800 in the Nankai Trough, Japan al. Stratigraphic Control on Excess Pore MCC Underwood, T42 B Pressure at the Plate Boundary Fault of 1120 3000 M et al Nankai Trough Thursday Afternoon Key 19 ODP Related abstracts Section Session Location Title Author Time Late Miocene-Recent Magnetic Polarity Stratigraphy and Astro-Chronology From ODP Evans, H et al. 1340 Sites 1207, 1208, 1209, 1210, 1211 and 1212- Shatsky Rise 30 Myr of polarity stratigraphy and relative Geomagnetism paleointensity from Equatorial Pacific and Lanci, L et al. 1340 GP43 B sediments (ODP Sites 1218 and 1219, Leg Paleomagnetism MCC 199) level 2 Deep-tow Study of Magnetic Anomalies in the Tominaga, M 1340 Pacific Jurassic Quiet Zone et al. Holocene relative paleointensity and Richter, C et paleosecular variation from the Southern 1340 al. Okinawa Trough (ODP Hole 1202B) Different magnetostratigraphic approaches: Lake Baikal sediments and the J/K boundary Pruner, P et al. 1340 strata in the Tethyan realm MCC Global Distribution of Microbial Alteration of OS43 A Josef, J et al. 1340 level 2 the Ocean Crust A Three-Dimensional Subseafloor Observatory Network for Cross-Hole, Hydrogeologic Ocean Sciences Fisher, A et al. 1340 MCC Experiments Established in the Northeast OS43 B level 2 Pacific Ocean Geology of Smooth Ridge: MARS-IODP Jordahl, K et 1340 Cabled Observatory Site al. Excess Aluminum and the Quantification of MCC Murray, R. et PP43 A Terrigenous Material in Pelagic Biogenic 1340 level 1 al. Sediment: An Update and Eye for the Furture Antarctic Timing of Surface Water Changes off Chile and Patagonian Ice-sheet Response Lamy, F et al. 1340 Based on ODP Site 1233 Pliocene Shoaling of the Central American Seaway and its Effect on Caribbean and Steph, S et al. 1410 Paleoceanography Tropical East Pacific Upper Ocean and Stratification Paleoclimatology Regime Shifts in Climate Forcing of Peru Altabet, M et 1440 Denitrification al MCC PP43 B 2000 Paleoproductivity and Paleoclimate off Abrantes, F et 1455 Southern Chile During the last Deglaciation. al. Diatom and Phytoliths Records from Site 1233 Linking Global Climates Between Hemispheres and Ocean Basins: Millennial- Scale Temperature and Isotopic Variability of Mix, A et al 1510 Intermediate and Mid-Depth Watermasses of the Equatorial and Southeast Pacific. Paleomagnetic Results From ODP Leg 202: Stoner, J et al. 1525 The Chilean Margin Sites MCC Deep Ocean Temperature and Salinity at the Adkins, J and PP44 A 1600 2000 Last Glacial Maximum Schrag, D Friday Morning Key
32 ODP Related abstracts
Section Session Location Title Author Time
Education and MCC USIO-IODP Developing a New Castner, A et ED51 C 800 Human Resources level 1 Fellowship for HBCU Students al. Data Modeling, Development, Installation and Operation of the ACEX Offshore Drilling Information Conze, R et al 800 System for the Mission Specific Global Climate MCC GC51 D Platform Expedition to the Lomonosov Change level 2 Ridge, Arctic Ocean. A Test for Extending the High- Hopkins, S et Resolution Global Climate Record in 800 al. Santa Barbara Basin Jack Dymond's "Fingerprints" on MCC Leinen, M Ocean Sciences OS52 A Sediment Chemistry, Biogeochemical 1055 3011 et al. Fluxes, and my Career Duration of Pliocene Ice-Rafting MCC Events Offshore of Prydz Bay, McAuley, A et PP51 A 800 level 2 Antarctica, Derived From al. Extraterrestrial Helium-3 Radiolarian and Sedimentologic Paleoproductivity Proxy Record From Bittniok, B 800 MCC the Benguela Upwelling System, Et al. PP51 B level 2 DSDP Site 532, 0-6 Ma The Late Miocene Carbon Isotope Shift Diester-Haass, 800 and Marine Biological Productivity. L et al. The early Eocene in the Southern Ocean; an integrated dinocyst and Deltrap, R et al. 800 Paleoceanography geochemical analysis of ODP Leg 189 and sites 1171 and 1172, Tasman Sea. Paleoclimatology Eocene-Oligocene Southern Ocean Paleo-bathymetry maps generated with Brown, B et al 800 geophysical, sedimentological and microfossil data. MCC PP51 D Radiolarian and Sedimentologic level 2 Evidence for Late Eocene Origin of Lazarus, D et al 800 Southern Ocean Environments Evolution of North Atlantic Via, R Thermohaline Circulation: From the and 800 Greenhouse to the Icehouse Thomas, D Orbital forced sea level fluctuations Warnaar, J et during the Middle Eocene (ODP site 800 al. 1172, East Tasman Plateau) Friday Afternoon Key
21 ODP Related abstracts
Section Session Location Title Author Time Poroelastic Parameters of Peru Margin MCC Sediments: Implications for Flow and Gettemy, Biogeosciences B53 A 1340 level 2 Transport at Multiple Scales in the Marine G et al. Biosphere Late Quaternary Paleoenvironmental History Global Climate MCC Lamy, F GC53 A of the Peru-Chile Current System and Adjacent 1340 Change 3020 et al. Continental Chil Marine Sedimentary Record of Cenozoic MCC Hydrology H53 E Monsoon Intensity Preserved in the Asian Clift, P 1525 3009 Marginal Seas $^{15}$N depleted nitrogen isotope values in Junium, C Cretaceous black shales: paleoceanographic and 1340 event or diagenesis Arthur, M Evaluation of Geochemical Proxies Preserved Gallego- MCC in the Sapropel Record from the Eastern PP53 B Torres, D 1340 level 2 Mediterranean Within the Pliocene-Holocene et al. Time Interval Implications of Mn-Mg-rich Contaminant Pena, L et Phases for Mg/Ca Past Temperature 1340 al. Paleoceanography Reconstructions and The evolution of atmospheric carbon dioxide Pagani, M Paleoclimatology since the middle Eocene: a biomarker 1355 et al perspective MCC A Cenozoic terrestrial isotope record and the Gr”cke, D PP53 D 1410 2000 evolution of C$_{4}$ photosynthesis et al. A 10 Million Year, High-Resolution Record of Huang, Y C4 and C3 Plant Evolution from Arabian Sea 1530 et al. ODP Site 722 Scher, H Evidence for an Open Drake Passage in the and 1600 Late Middle Eocene Martin, E Exploring the Carbonate MCC Flores, J PP54 A Production/Dissolution Paradox in the Mid- 1615 2008 Bruhnes of the Southern Ocean Using Coupled et al. Records of Biological and Chemical Dynamics Two Highly-Resolved Geochemical Records Kryc, K et of Holocene Variability: A Comparison 1655 al Between West and East Antarctica Section Session Title Author Time Paleoceanography and Paleoclimatology of the MCC Warnke, PP54 A Southern Ocean: A Synthesis of Three Decades 1710 2008 D et al. of Scientific Ocean Drilling Stickley, Timing and Nature of the Deepening of the 1620 Paleoceanography Tasmanian Gateway C and Moran, K Paleoclimatology ACEX: A first Look at Arctic Ocean Cenozoic and MCC 1635 PP54 B History Backman, 2000 J From Greenhouse to Icehouse: Evidence for Late Early Eocene Concomitant Cooling of Brinkhuis, 1650 Southern Ocean Surface Waters and Global H et al. Deep Waters From Dinoflagellate Endemism Extremely Rapid and Localized Erosion in the MCC Stewart R Tectonophysics T53 A Himalaya Recorded in Sediments of the Bengal 1340 level 1 et al. Fan Thallium Isotope Constraints on Hydrothermal MCC Rehkamper V53 B Water Fluxes at Mid-Ocean Ridge Axes and 1455 3006 , M et al. Flanks The Mantle Plume Hypothesis Pro and Con: Ingle, S MCC Volcanology, V53 C Evidence from Earth's Most Voluminous Large and 1425 3008 Geochemistry, Igneous Provinces Coffin, M Petrology Pb and Other Trace Elements in Melt Beaudoin, Inclusions From Modern Seafloor Tectonic 1615 Y et al. Settings V54 B MCC Deep Marine Sediment Diagenesis of 3006 Froelich, Germanium, Silica, Lithium and Lithium P and 1730 Isotopes in ODP-177: The "Missing Oceanic King, S Ge Sink" HR:14:40h AN: U23A-05 TI: MIS 11 and the mid-Brunhes Dissolution Interval AU: * Barker, S et al.
AB: The mid-Brunhes dissolution interval (MBDI) represents a prolonged period of marine carbonate dissolution centred around Marine Isotope Stage 11 (MIS 11). The MBDI has been observed in all the major ocean basins and at all water depths. We present a 1Myr foraminiferal shell weight record from ODP site 982 in the North Atlantic (57.5N, 15.9W, 1134m) which is strongly affected by dissolution over this period, demonstrating the vulnerability of even shallow sites to the effects of dissolution. From a compilation of carbonate mass accumulation rates (MARs) we suggest that a global increase in marine carbonate production was responsible for the carbonate crash at this time. This is a variant on the basin to shelf hypothesis which argues that enhanced growth of shallow water carbonates in low latitudes during MIS 11 resulted in a global dissolution event. We model the effects of the proposed increase in carbonate production within the constraints of observed atmospheric CO2 variability. HR: 1340h AN: U33A-0024 TI: Rapid true polar wander: A quixotic search? AU: * Cottrell, R D et al.
AB: Studies in the 1960's emphasized that polar wander could be a significant component of apparent polar wander curves. These concerns were assuaged when subsequent tests revealed that polar wander components were very small and overwhelmed by plate motion. Nevertheless, the concept of large and rapid polar wander has been surprisingly resilient. It gained new support in the 1980's when polar wander was defined in a fixed hotspot frame of reference and called ``true polar wander" (TPW). This new TPW was correlated to a wide variety of phenomena, from the rate of geomagnetic reversals to anomalous volcanism, but the linkages often differed sharply between studies. And renewed investigations, including paleomagnetic studies of the Emperor seamounts (ODP Leg 197), have emphasized that hotspot drift can be relatively rapid (over 40 mm/yr). We trace problems in some past and recent TPW hypotheses to an overreliance on the hotspot reference frame. The failure to scrutinize independently the two key components (APWPs and hotspot tracks) in directional space has led to illusory short-term spurts of TPW and overestimates of long-term rates. We review tests that can be used to detect these artifacts. The exclusion of hotspot drift reduces total ``TPW" displacements so that they are near the level of other competing explanations that might account for variation in global paleomagnetic pole positions (e.g. reconstruction uncertainities and inadequate geomagnetic field averaging). This vanishingly small amount of polar wander suggests that locally developing mantle mass heterogeneities may have been naturally balanced by global mantle flow in the post-Jurassic Earth. 0800h AN: U31A-0011
TI: Warmer tropics during stage 11 - evidence from the Cariaco Basin AU: * Lea, D and Peterson, L EM AB: Marine Isotope Stage (MIS) 11 stands out as the most extreme interglacial episode of the last million years. But evidence for unusual warmth in the tropics at this time remains equivocal. A proxy SST record from the equatorial western Pacific (ODP 806B - Lea et al., 2000; Medina et al., this meeting) suggests that MIS 11 was the warmest time interval of the last million years. A key question that directly addresses the hypotheses proposed to explain MIS 11 is whether anomalously warm SSTs were a common feature of the tropics at this time. The Cariaco Basin, an anoxic marine basin on the northern shelf of Venezuela, preserves a unique high resolution climate record of the southeastern Caribbean/tropical Atlantic. This record is continuous through the last 580,000 years and includes multiple varved intervals. Records from this basin have been instrumental in establishing ties between tropical climate records and high latitude ice core and oceanic records. Paleothermometry based on planktic foraminiferal Mg/Ca works well in the Cariaco Basin because of the presence of a wide range of planktic species and superb preservation of carbonates, including pteropods. We have analyzed Mg/Ca in samples from ODP Hole 1002C (10ø42.73'N, 65ø10.18'W, 893ÿm water depth) that span MIS 11. Our preliminary results, covering the interval 402-409 ky BP, from surface dwelling Globigerinoides ruber yield Mg/Ca values of 4-5 mmol/mol, equivalent to SSTs of 26.5- 28 degrees C. For comparison, Mg/Ca values in the Holocene range from 4-4.5 mmol/mol, equivalent to SSTs of 26-27.5. We are in the process of adding further results to evaluate how systematic this difference is. Poore and Dowsett (2001) reported oxygen isotope results from the same sequence and species and found that MIS 11 values were 0.3 permil more depleted than the Holocene. Our preliminary Mg/Ca-SST results suggest that most of this difference is not due to higher SST, suggesting either lower Cariaco salinity at this time and/or a negative shift in mean ocean O18 related to higher sea level during MIS 11. These findings will be considered in light of the unusual climate state that prevailed during MIS 11. HR: 17:00h AN: U14A-04 TI: LGM to Holocene African climate variability and the Sr, Nd, and Pb isotope ratios of eolian deposits off northwest Africa AU: Cole, J M et al. EM: AB: Abrupt changes in African climate from the last glacial period through the Holocene have been documented in a core located off Cap Blanc, northwest Africa, ODP Hole 658C (deMenocal et al, 2000). Large changes in terrigenous sedimentation to the ocean, due in large part to humid-arid shifts in terrestrial vegetation, are observed in the percent terrignous and Th-230 normalized terrigenous flux measurements. While there is overall high biogenic and eolian terrigenous sedimentation, terrigenous input decreased during the African Humid Period (AHP, 14.8-5.5 kyr). Additionally sea surface temperatures were lower during that time compared to the later Holocene. Others have shown that radiogenic isotope isotope ratios of terrigenous deposits from marine and ice cores vary over time and provide provenance information. Alternatively, it has been suggested that changes in Sr isotope ratios of dust may relate to the degree of chemical weathering. We sampled the <63 micron detrital fraction to measure the Sr, Nd and Pb isotope ratios in order to quantify the eolian dust proportion and potential source regions. Nd and Pb measurements record source area contributions. However, Sr isotope data indicate a clear shift toward less radiogenic values during the African Humid Period, where as there is no corresponding change in Nb and Pb values. Additionally, we observe an abrupt termination of the AHP and other rapid events. This research seeks to enhance our understanding of African and low-latitude responses to global climate forcings over the last deglaciation. \
HR: 0800h AN: U21A-0704 TI: Late Pleistocene Paleoclimate Record From the SW African Margin AU: Shackford, J K et al.
AB: Late Pleistocene sediments recovered from ODP Leg 175, Site 1085 are used to generate a high-resolution (500 yr) record of continental climate change in Southern Africa. Sedimentological, geochemical, and clay mineralogical variations of the Cape Basin sediments for the last 200 k.y. are used to determine transport pathways of terrigenous load and continental climate change in southern Africa. The location of Site 1085, the SW African continental slope, provides a continuous hemipelagic section with a significant terrigenous component. Terrigenous sediments are either fluvial or eolian, with fluvial load possibly being controlled by monsoonal circulation and insolation (Christensen et al., 2002; Murray et al., 2002) and eolian by glacial intensification of trade winds. Analyses, including grain size (transport), color reflectance (terrigenous input), biogenic sediment geochemistry including %CaCO3, % organic carbon, and C:N (terrigenous input, productivity), bulk sediment geochemistry (continental climate, terrigenous sediment source, and productivity), benthic foraminiferal stable isotopes (chronology), and clay mineralogy (source, continental climate, transport pathways), are used to identify continental climate conditions in southern Africa, and to address possible forcing mechanisms of climate change in the region during the last 200 k.y. Analyses indicate significant glacial and interglacial variation. Color reflectance and %CaCO3 covary down section, with highest values during MIS1, while there is an inverse correlation between color reflectance, median grain size and C:N ratios, with greatest terrigenous carbon during MIS 1. Peaks in median grain size are associated with boundaries between MIS 1 and 2 as well as MIS 2 and 3. Our results differ from Stuut et al. (2002), who find increased eolian sediments from grain size within glacial stages on the Walvis Ridge, north of the Cape Basin, rather than at the boundaries. Clay mineralogy, determined after removal of calcite, indicates the presence of smectite, different from the modern regional maps of Petschick et al. (1996). Presence of smectite downcore may attest to increased continental weathering and possibly a more humid climate in Southern Africa. D
HR: 1340h AN: U33A-0032 TI: Paleomagnetic Data From Ontong Java Plateau are Anomalous $\sim$ Did the Plateau Form on Another Plate? AU: * Sager, W W EM AB: A recent study of Ocean Drilling Program basalt core paleomagnetic data from Ontong Java Plateau (OJP) found paleolatitudes that disagree with previous estimates of the Early Cretaceous Pacific APWP, a result attributed to poor quality of data used in prior pole calculations [Riisager, P., S. Hall, M. Antretter, X. Zhao, Earth Planet. Sci. Lett., 208, p. 235, 2003]. My compilation of paleomagnetic data from Cretaceous Pacific basalt cores drilled by the Deep Sea Drilling Project and Ocean Drilling Program shows that paleocolatitude data in of ages 118-129 Ma display greater scatter than other age bins. The only factor that allows this data group to be coherently subdivided is whether or not the coring site is located on OJP. Without OJP data, paleocolatitude scatter is much less and gives a similar pole position (48.9$\deg$N, 327.1$\deg$E, N=40) to data in the 110-118 Ma interval. Data from the plateau give a pole that is 15$\deg$ farther north (64.9$\deg$N, 323.4$\deg$E; N=37), indistinguishable from late Jurassic and earliest Cretaceous skewness poles. The OJP and non-OJP poles are distinct at the 95$%$ confidence level despite having indistinguishable mean ages of 121.6 $\pm$1.1 Ma (OJP) and 123.4 $\pm$4.1 (non-OJP). Because Ontong Java Plateau data come from 6 different sites spread over the northern plateau, tectonic tilting is not a likely explanation for the difference. Also unlikely are systematic errors such as incomplete averaging of secular variation (large number of independent magnetic units sampled), inaccurate radiometric dates (many high quality dates), or inadequate paleomagnetic techniques (detailed studies by several different investigators). Rapid true polar wander does not seem a plausible explanation because global true polar wander curves have a different trend. Perhaps the simplest explanation is the one often used when anomalous data are found within a plate: the anomalous region had a different history of tectonic drift. In this scenario, OJP formed on a separate plate that drifted southward relative to the Pacific plate before becoming attached. This finding is similar to the AŸ’'A+ƒ_TAŸƒ_sA,A›AŸ’'A,A›AŸA›A›ƒ_sAªA.A_AŸƒ_sA,AªAŸ’'A›ƒ,ªA_AŸA›A›ƒ _sAªA.ƒ_oStealth PlateAŸ’'A+ƒ_TAŸƒ_sA,A›AŸ’'A,A›AŸA›A›ƒ_sAªA.A_AŸƒ_sA,AªAŸ’'A,A_AŸƒ_s A,A¨AŸƒ_sA,A« hypothesis [Larson, R. L., and W. W. Sager, Proc. ODP, Sci. Res., 129, p. 471, 1992], which was formulated to explain a similar angular difference between skewness-derived paleolatitudes from the Hawaiian and Japanese magnetic lineations relative to the Phoenix lineations. The most significant challenge for this hypothesis, however, is to account for the space and plate boundaries. If true, this hypothesis implies either that much of the Jurassic Quiet Zone seafloor was created by Pacific-Stealth spreading or that an unknown plate boundary near OJP separated the plateau from the rest of the Pacific plate. HR: 0800h AN: SF41A-0764 TI: High Tech High School Interns Develop a Mid-Ocean Ridge Database for Research and Education AU: Staudigel, D et al.
Ridges (MOR) represent one of the most important geographical and geological features on planet Earth. MORs are the locations where plates spread apart, they are the locations of the majority of the Earths' volcanoes that harbor some of the most extreme life forms. These concepts attract much research, but mid-ocean ridges are still effectively underrepresented in the Earth science class rooms. As two High Tech High School students, we began an internship at Scripps to develop a database for mid-ocean ridges as a resource for science and education. This Ridge Catalog will be accessible via http://earthref.org/databases/RC/ and applies a similar structure, design and data archival principle as the Seamount Catalog under EarthRef.org. Major research goals of this project include the development of (1) an archival structure for multibeam and sidescan data, standard bathymetric maps (including ODP-DSDP drill site and dredge locations) or any other arbitrary digital objects relating to MORs, and (2) to compile a global data set for some of the most defining characteristics of every ridge segment including ridge segment length, depth and azimuth and half spreading rates. One of the challenges included the need of making MOR data useful to the scientist as well as the teacher in the class room. Since the basic structure follows the design of the Seamount Catalog closely, we could move our attention to the basic data population of the database. We have pulled together multibeam data for the MOR segments from various public archives (SIOExplorer, SIO-GDC, NGDC, Lamont), and pre-processed it for public use. In particular, we have created individual bathymetric maps for each ridge segment, while merging the multibeam data with global satellite bathymetry data from Smith & Sandwell (1997). The global scale of this database will give it the ability to be used for any number of applications, from cruise planning to data HR: 0800h AN: B21D-0908 TI: Carbon Biogeochemistry of Marine Sediments at the ODP Leg 204, Hydrate Ridge AU: * Li, Y et al. EM AB: ODP Leg 204 was drilled on the Oregon continental margin to determine the distribution and concentration of gas hydrates in an accretionary ridge. The microbiological communities and biogeochemical properties of the hydrates are of special interest. Our goal was to study carbon biogeochemistry in the marine sediments collected from boreholes 1245B, 1245C, 1250D, 1244E and 1244F. The total organic carbon of all boreholes had a narrow range of \delta$^{13}$C values (-21.3 to - 22.3\permil), indicating the predominance of a homogeneous source. Lipids were extracted from bulk sediment and separated into neutral-, glycol- and polar-fractions using silicic acid columns. The polar lipids were treated further for analyses of phospholipids fatty acids (PLFA) and compound-specific carbon isotope ratios. Total PLFA was low (less than 80 pmol/g) in boreholes 1245B and 1245C and generally decreased with depth. Total PLFA in borehole 1250D, however, increased with depth, ranging from 33 pmol/g at 30.24 mbsf (meters below seafloor) to 426 pmol/g at 134.7 mbsf. On the other hand, total PLFA in boreholes 1244E and 1244F were high (338.1 to 444.2 pmol/g) but without any obvious trends with depth. Overall, saturated fatty acids were predominant (less than 45% to 82%) in these borehole sediments and terminally branched fatty acids, indicative of sulfate-reducing bacteria, were up to 15% of total PLFA. In borehole 1250D, saturated fatty acids decreased from greater than 80% at the top of the core to less than 45% at depth. Meanwhile, the monounsaturated fatty acids increased from several percent to more than 20% with depth. The \delta$^{13}$C values of PLFA ranged from -45\permil to -50\permil, which were significantly lower than bulk organic carbon. It is unclear, however, whether these low values are attributed to the anaerobic oxidation of methane, which is known to occur in other gas hydrates of the Hydrate Ridge and Gulf of Mexico. DE HR : 1340h AN: B13A-0158 INVITED TI: Data Management for the Ridge 2000 Program AU: * Chayes, D N et al. EM AB: Since the start of this effort (September 1, 2003) we have developed a data base schema, selected and installed a relational data base management system (PostgreSQL), designed, developed and, deployed a draft set of metadata forms, ingested data from ten Ridge2000 cruises as of September 2004 and deployed a web accessible Ridge2000 data portal: http://www.marine-geo.org/ridge2000/ . At the portal, one can get content using with pre-constructed queries for survey targets and deployed instruments at each of the R2K Integrated Study Sites. Alternatively, our data link allows spatial, temporal and keyword searches to identify and download data. The current metadata forms have been used for 6 cruises and we have received constructive feedback (in addition to the actual metadata) from all three R2K integrated study sites. We are working on incorporating this feedback into an updated set of forms which we expect to release early in 2005. Other recent include substantial improvements to GeoMapApp, links to other data repositories, a major update of our web site, integration with data from Arctic, Antarctic, Margins data sets and the pre-constructed queries on the R2K portal page. Our plans for 2005 include: A second major revision of the metadata forms in early '05, improvements in the metadata ingestion process, enhanced authentication using LDAP, continued active participation in the broader data community developing interoperability as well as implementing direct interoperability with a number of complementary databases including the underway geophysical and multibeam databases at National Geophysical Data Center, the National Deep Submergence facility at Woods Hole, the Geological Data Center of the Scripps Institute of Oceanography, and the databases of the ODP (JANUS at TAMU, and Borehole Geophysics at LDEO) UR
HR: 1340h AN: B13A-0183 TI: Evidence for Along-Strike Hydrothermal Circulation Within Young Oceanic Crust on the Eastern Flank of the Endeavour Axis, Juan de Fuca Ridge AU: * Hutnak, M et al. EM AB: Many geological, geophysical, and geochemical indicators at spreading centers suggest that the dominant direction of fluid circulation may be along-strike, subparallel to the primary orientation of neovolcanic and near-ridge faulting. Researchers are beginning to identify additional evidence from young ridge flanks for along-strike fluid (and heat and solute) flow. We present newly-compiled thermal, swath-map, and seismic data collected on young crust east of the Endeavour Segment of the Juan de Fuca Ridge. Hydrosweep data reveal several prominent basaltic outcrops just north of the ODP Leg 168 drilling transect, within an area experiencing a hydrothermal transition (HT) from exposed to sediment-covered basement. Seafloor heat flow is strongly suppressed 20 km east of the spreading center, and the pattern of thermal rebound with increasing distance from the ridge has been interpreted as evidence for dominantly across-strike hydrothermal circulation. We show that within one part of the hydrothermal transition, located on 1.2-1.3 Ma seafloor, the data are at least as well explained by along-strike fluid circulation, with cold seawater recharging through outcrops to the north of the HT area. Application of a simple analytical model for coupled heat and fluid flow suggests specific discharge in basement on the order of 1 m/yr, a rate consistent with earlier estimates of across-strike circulation, and with independent estimates of driving forces and crustal permeability. Dominantly along-strike circulation has also been inferred on 3.5 Ma crust to the east of the HT area, suggesting that this mode of fluid transport may be the rule, rather than the exception, on this young ridge flank. Since primary flow paths are likely associated with tectonic processes that occur during and soon after the crust is formed, it seems probable that along-strike fluid flow is also important today at the Endevaour Segment. DE HR: 1340h AN: B53A-0985 TI: Poroelastic Parameters of Peru Margin Sediments: Implications for Flow and Transport at Multiple Scales in the Marine Biosphere AU: * Gettemy, G L et al. EM AB: As part of a broader investigation of the deep marine subsurface environment, the first biosphere-focused drilling expedition, Leg 201, of the Ocean Drilling Program (ODP) occupied five unique sites in the Peru Margin (in a 1200 km$^2$ region centered at 10 S, 80E). These sites represent the entire range of shallow biogeological conditions associated with this convergent margin:deep-water, mixed clay-pelagic sediments ocean- ward of the trench; slope-apron and prism toe sediments at the deformation front; and several distinct lithostratigraphic sequences on the continental shelf. Microbial enumeration and pore-water geochemistry results show that each particular site is both consistent and unique--consistent in terms of general biotic quantity and activity as predicted by energy flux and redox potential given the depositional environment and sedimentary record, but unique at key biogeological boundaries such as lithologic and/or physical property interfaces. This research addresses questions related to our understanding of how and why these boundaries form by looking at poroelastic and hydrologic parameters measured at multiple scales, from sub-millimeter to several centimeters. The issue of measurement scale, especially in regard to permeability and diffusivity characterization, is vital to interpreting observations of biologically-mediated diagenetic fronts (e.g., dolomitic lenses, depth- or time-varying barite fronts). These parameters are derived from (i) hydrologic and wave propagation experiments, (ii) SEM images, and (iii) shipboard split-core measurements, and structured in a modified Biot poroelasticity framework. This approach also allows quantification of the local heterogeneity of these parameters at the scale applicable to (and controlled by) microbial life; these results can then be used to formulate predictive models of the impact of biogeochemical processes. Ultimately, these models could then be used in interpretation of new remote-sensed data (e.g., from borehole tools, high-frequency backscatter devices), a fundamental challenge for all types of biospheric imaging everywhere. DE
HR: 1340h AN: B33B-0265 TI: Testing the Molecular Clock Using the Best Fossil Record: Case Studies from the Planktic Foraminifera AU: * Steel, B A EM AB: Criticism of molecular clock studies often centres on inadequate calibration and a perceived lack of correlation between reproductive isolation and recognisable morphological evolution. Since many major groups (e.g. birds, mammals, reptiles) have a poor fossil record, it is often difficult to test and refute these limitations. Planktic foraminifera represent an exception to this rule. Deep-sea sediments are super-abundant in foraminifera, and large numbers of specimens and occurrences are easily garnered from Ocean Drilling Programme cores. Planktic foraminifera therefore represent an ideal model group with which to test and refine molecular clock studies. Since the 1990AŸA›A›ƒ_sAªA›ƒ_zA›s, genetic sequences (principally 18S r-RNA) have been extracted from living planktic foraminifera, and a large genetic library has developed. Our study attempts to contextualise and test molecular data, particularly AŸA›A›ƒ_sAªA<"molecular clockAŸA›A›ƒ_sAªA›ƒ_zA› dates, utilising material from two ODP cores (Site 926A (Atlantic) and 806 (Pacific), to examine the evolutionary history of two sibling-species complexes (Globigerinella siphonifera and Globigerinoides ruber, both common shallow-water species and both of considerable palaeoceanographic utility). Recent genetic studies have suggested that these two AŸA›A›ƒ_sAªA<"super- speciesAŸA›A›ƒ_sAªA›ƒ_zA› in fact consist of a number of isolated forms, with contrasting ecologies and longevities, which in Recent and sub-Recent sediments can be distinguished either on the basis of pore ultrastructure (Gl. siphonifera) or test colouration (Gs. ruber). In both cases, molecular clock estimates are indicative of ancient (7-11 Ma) intra-species cryptic divergences, which seem to be considerably older than fossil dates. In particular, the calculated molecular split between the two forms of Gs. ruber (AŸA›A›ƒ_sAªA<"whiteAŸA›A›ƒ_sAªA›ƒ_zA› and AŸA›A›ƒ_sAªA<"pinkAŸA›A›ƒ_sAªA›ƒ_zA›) of around 11 Ma is considerably discordant with the fossil date of around 0.7 Ma. At first glance, this may appear to be a classic case of molecular over-estimation, often a feature of clock models, especially where, as in the foraminifera, substitution rates may vary widely. However, there is good reason to suspect that fossil range of the derived AŸA›A›ƒ_sAªA<"pinkAŸA›A›ƒ_sAªA›ƒ_zA› form may have been artificially truncated by diagenetic degradation of the meta-stable test pigmentation. The deep molecular splits for Gl. siphonifera (around 7 Ma for the two main morphologically distinguishable sub- types), whilst not so obviously at odds with the fossil record, still belie the very small amount of morphological evolution observed within the plexus. We have used morphometric methods on a large (over 2000 pooled specimens) dataset in an effort to independently test the molecular clock, using SEM-based measurement of pore metrics (for Gl. siphonifera) and a multivariate analysis of whole-test characteristics (for Gs. ruber). Comparison of results for the two species suggests interesting patterns; whilst the two cryptic sub-types of Gl. siphonifera seemingly can be traced through time and seem to respond to external oceanographic forcing, the sub-types of Gs. ruber appear to be truly cryptic, and cannot be distinguished in the fossil record beyond 0.7 Ma. This raises two important points; firstly, the molecular clock (at least for foraminifera) bears considerable scrutiny, appears to be relatively robust to substitution bias and is seemingly broadly in accordance with morphological data; and secondly, the relationship between form and function in planktic foraminifera appears to be ill-defined, raising important questions for functional morphology. HR: 0800h AN: ED31A-0734 TI: ``Out To Sea: Life as a Crew Member Aboard a Geologic Research Ship'' - Production of a Video and Teachers Guide. AU: * Rack, F and Tauxe, K EM AB: In May 2002, Joint Oceanographic Institutions (JOI) received a proposal entitled "Motivating Middle School Students with the JOIDES Resolution", from a middle school teacher in New Mexico named Katie Tauxe. Katie was a former Marine Technician who has worked aboard the R/V JOIDES Resolution in the early years of the Ocean Drilling Program (ODP). She proposed to engage the interest of middle school students using the ODP drillship as the centerpiece of a presentation focused on the lives of the people who work aboard the ship and the excitement of science communicated through an active shipboard experience. The proposal asked for travel funds to and from the ship, the loan of video camera equipment from JOI, and a small amount of funding to cover expendable supplies, video editing, and production at the local Public Broadcasting Station in Los Alamos, NM. Katie sailed on the transit of the JOIDES Resolution through the Panama Canal, following the completion of ODP Leg 206 in late 2002. This presentation will focus on the outcome of this video production effort, which is a 19 minute-long video entitled "Out to Sea: Life as a Crew Member Aboard a Geologic Research Ship", and a teacher's guide that can be found online. UR: 1340h AN: ED13E-0747 TI: Writing and Visualization for Teaching Plate Tectonics AU: * Thomas, S F EM AB: The Theory of Plate Tectonics is probably the most important paradigm for understanding the workings of our planet. As such it is an integral part in any Introductory Geology course. Whereas geology majors usually easily embrace the Theory of Plate Tectonics, the enthusiasm for the coherence and elegance of this theory appears to be much more subdued among the majority of non-science majors. While visual and electronic media certainly support the teaching of the theory, pretty pictures and animations are not sufficient for many non-science majors to grasp the concepts of interacting lithospheric plates. It is well known that students do better in learning scientific concepts if they create their own understanding through research and inquiry- based learning, by working in the field, manipulating real earth-science data, and through writing. Writing assignments give instructors the opportunity to assess their students' learning and to clarify misconceptions yet they also have to be willing to teach students how to craft a science paper. Most electronic media and textbook-added CD-ROMs are not useful for making the structure of a science paper transparent. I found many of the necessary ingredients for effectively teaching plate tectonics in the interactive CD-ROM, "Our Dynamic Planet", developed by Wm. Prothero together with G. Kelly (University of California at Santa Barbara). It allows students to select and manipulate real earth- science data of plate-tectonically active regions, and provides an electronic interface that lets students create graphical representations of their collected data. A downloadable Teacher's Manual provides suggestions on teaching students to write a scientific argument, rooted in sound pedagogy. Originally designed for a large oceanography class, the material was modified for use in a small introductory geology class for non-science majors. Various assignments were given to instruct students in writing a scientific argument based on their own collected data and observations. The main goals are for students o To see the relationship between data and the development of a scientific theory o To understand the elements of scientific discourse o To learn how to derive conclusions from interpretations and observations o To back interpretations with observations o To be able to write a scientific argument o To understand the Theory of Plate Tectonics, and o To gain a better understanding about how science works The results of several surveys will be presented that confirm that most of the expected outcomes continue to be met. 0800h AN: G21A-0139 TI: An Experiment on GPS/A Seafloor Positioning in the Central Part of Kumano-nada, Central Japan AU: * Fujimoto, H et al. EM AB: Kumano-nada, northeast of Kii Peninsula in the central part of Japan, is a seismogenic zone of the M-8 class Tonankai earthquakes that occurred repeatedly at an interval of about 100 years. The MEXT (Ministry of Education, Culture, Sports, Science and Technology, Japan) initiated a 5-year program in 2003 for seafloor observations in and around Kumano-nada. Nagoya and Tohoku Universities initiated experiments on GPS/A seafloor positioning to monitor crustal deformation in the subduction zone with a focus on investigation of the effect of sound velocity structure in the ocean on seafloor positioning (e.g., Tadokoro et al., this meeting). Tohoku group deployed five precision acoustic transponders (PXPs) jointly developed with Scripps Institution of Oceanography in the central part of Kumano-nada at depths of about 2,000m. The deployed PXPs A, B, C, and D form a diamond on the seafloor, and PXPs C, D, and E form a triangle. Although three typhoons were in the way of our 12-day cruise in August this year, we carried out GPS/A observation for several days. After an observation for locating the precise position of each PXP, we tried to keep the buoy near the center of the diamond or the triangle. The vessel held the position within 20-30m from the center, and the buoy_fs position was kept with 100m from the center. Kinematic GPS positioning is now under processing with GEONET data observed in Kii Peninsula. We also tried monitoring the sound velocity structure with 3 sets of inverted echo sounders (IESs) deployed near the PXPs C, D, and E. The IESs can monitor temporal and spatial variation in the sound velocity structure in the triangle array of PXPs. We plan to carry out the second GPS/A observation in November. The result is worthy of notice. Strange earthquakes of magnitude 6.9, 7.4, and 6.4 occurred on the nearest Nankai Trough axis on September 5- 7, 2004. Co-seismic crustal deformation observed by the GEONET was about 4 cm near the coast of Kii Peninsula. The seismogenic zone is in the list ocean drilling under the IODP (Integrated Ocean Drilling Program). HR: 08:30h AN: GP41B-03 TI: Field Geometry During the Iceland Basin Event Observed from the North Atlantic Ocean, North Pacific Ocean and the South China Sea AU: Laj, C et al. EM AB: The Iceland Basin event (IBE), which is named for a record from ODP Site 983 in the North Atlantic Ocean (60.5øN), is a focus of growing interest in our community. This geomagnetic excursion is coeval with the marine oxygen isotope (MIS) stage 7/6 boundary at about 190 ka according to the orbitally tuned SPECMAP time scale. We have detailed new records of this excursion at two new sites from the North Atlantic (core MD99-2247; lat. 59øN, long. 31øW and core MD99-2242; lat. 59øN, long. 47øW), at one site from the North Pacific (ODP Site 884; lat. 51.5øN, long. 168.3øE), and in two others from the South China Sea (ODP Site 1146; lat. 19.5øN, long. 116.3øE and ODP Site 1145; lat. 19.6øN; long. 117.6øE). For all five sites, the event is identified at the MIS 7/6 boundary, which confirms its potential as a precise stratigraphic marker. The average sedimentation rate for this portion of the cores is 7.5, 10 and 15 cm/kyr in North Atlantic, North Pacific and South China sea cores, respectively, which allows high- resolution studies in this time interval. The event is characterized by a marked minimum in the relative paleointensity (sometimes with a double feature) and by large swings in inclination and declination. The VGP latitudes reach 78øS and 45øS for ODP sites 1146 and 1145, respectively, 37øS for ODP Site 884, and 74øS and 41øS for cores MD99- 2247 and MD99-2242, respectively. The VGP paths for the four records from the North Atlantic and South China Sea cores are highly similar. For the most detailed of these records, the poles first pass over Africa, then they proceed to Antarctica and return northward over Australia. The paths are less well resolved for ODP Site 1145 and core MD99-2242, for which the poles cross the southern Indian Ocean rather than reaching Antarctica. The VGP paths for the two most detailed records (ODP Site 1146 and MD99- 2247) are highly similar and are also similar to the path for ODP Site 983, which also has a high sedimentation rate and is precisely dated. In contrast, but in common with other published records of the IBE, the VGP path for ODP Site 884 loops in the opposite sense and passes from North to South America and then over the Pacific Ocean before returning to high northern latitudes. The striking similarities between multiple records for two observed sets of differing VGP paths for the IBE at locations spanning the northern hemisphere provides evidence for a non-dipolar, but relatively simple, HR: 08:15h AN: GP41B-02 TI: A 300 kyr Record of Geomagnetic Excursions and Paleointensity From the Irminger Basin: Candidates for Mono Lake, Laschamp, Iceland Basin, Jamaica and Pringle Falls? AU: * Channell, J E EM AB: Sediments recovered at ODP Site 919, off east Greenland, record geomagnetic directional excursions at 33 ka and 40 ka (Mono Lake and Laschamp), and at 187 ka (Iceland Basin), 208 ka (Jamaica?) and at 220 ka (Pringle Falls). U-channel records are augmented by 1-cm discrete samples collected back-to-back alongside the u-channel troughs. Deconvolution of the u-channel records yields records that can be closely matched to the discrete sample data. The age-model based on planktic oxygen isotope data (St. John et al., Marine Geology, in press) is consistent with the relative paleointensity record and the recognition of Ash Layer 2 (55 ka). The results indicate that the Mono Lake and Laschamp excursions, and the Iceland Basin and Pringle Falls (and perhaps also Jamaica), are distinct excursions, rarely recorded together in individual stratigraphic sections. Why are they recorded at ODP Site 919? Mean sedimentation rates are 22 cm/kyr in MIS 3 where Mono Lake/Laschamp are recorded, but sedimentation rates do not appear to be especially high in MIS 7 (13 cm/kyr) where candidates for Iceland Basin/Jamaica/Pringle Falls are recorded. DE HR: 1340h AN: GP43B-0854 TI: Late Miocene-Recent Magnetic Polarity Stratigraphy and Astro-Chronology From ODP Sites 1207, 1208, 1209, 1210, 1211 and 1212- Shatsky Rise AU: * Evans, H F et al. EM AB: ODP Leg 198 to Shatsky Rise recovered a total of ~768 meters of Late Miocene to Recent sediments from 6 Sites. Neogene sediments at the sites consisted mostly of light gray to pale orange nannofossil oozes with varying amounts of clay, radiolarians and diatoms. Site 1208 was drilled on the Central High and provided a Late Miocene to Recent sequence with sedimentation rates ~4-5 cm/kyr. Sites 1209, 1210, 1211 and 1212 were drilled on the Southern High and yielded shorter sequences of Late Miocene to Recent sediments with sedimentation rates ~1-2 cm/kyr. Clearly interpretable magnetic stratigraphies have been obtained from all six sites based on shipboard data. These results have been augmented using discrete sample cubes (7cc) collected shipboard and measured post-cruise. Astrochronologies for Sites 1207 to 1211 were based on cycles seen in reflectance data from shipboard measurements. The reflectance data for these cores were measured using a digital imaging track system equipped with a line-scan camera. ODP Leg 198 was the first cruise after installation of the track, and these measurements provided a high-resolution stratigraphic record of color variations for visible wavelengths. These data were placed on an initial age model by pattern fit of the polarity zones to the geomagnetic polarity timescale (GPTS) of Cande and Kent (1995). Power spectra calculated using this initial age model often show concentration of power at orbital frequencies, particularly around the 41 kyr obliquity cycle, although the orbital power is more pronounced in some parts of the section than in others. The reflectance record was tuned to the astronomical solution for obliquity from Laskar et al. (1993). Astronomically tuned ages were estimated for polarity reversals in the 1-9 Ma interval at Site 1207. At Sites 1208 and 1209 tuning was performed in the 1-7 Ma interval and at Sites 1210 and 1211 in the 1-5 Ma interval. Cross spectral analysis on the tuned age model indicated significant coherence between the astronomic solution and the reflectance data. The tuned timescales are compared with other published ages for this part of the GPTS and indicate that the Shackleton et al., (1995) ages from ODP Leg 138 in the 8-9 Ma interval are too young by ~100 kyrs. The astronomical timescales are in better agreement with the timescale of Hilgen et al., (1995) in this interval. DE HR: 0800h AN: GP11D-0869 TI: Paleomagnetic and Rock Magnetic Investigation of Leg 210 Cores, Newfoundland Basin AU: * Liu, Q et al. EM AB: Leg 210, the final leg of the ODP, was devoted to studying the history of rifting and postrift sedimentation in the Newfoundland-Iberia rift. Two sites (Sites 1276 and 1277) were drilled in the central Newfoundland Basin that are along a transect exactly conjugated to the ODP Leg 149/173 drilling sites on the Iberia margin. Site 1276 was cored from 800 to 1739 m below seafloor with excellent recovery of Albian-lower Oligocene sediments and sills (estimated to be 100-200 m above basement). Site 1277 is located about 40 km southeast of Site 1276. Recovered cores from the upper part of basement at this site represent an assemblage of basalt flows, slivers of gabbro, serpentinized peridotite, and sediments. Below these rocks, basement is serpentinized peridotite with veins of gabbro. Stable components of magnetization are revealed in the results of detailed thermal and AF demagnetization on the sediments and diabase sills from Site 1276 and serpentinized peridotites from Site 1277. Azimuths of the maximum anisotropy axis of magnetic susceptibility are used to evaluate the fidelity of the natural magnetic memory of the serpentinized peridotites. Combining the age information available from other Leg 210 studies, we estimated paleolatitudes vs. time for the Newfoundland drill sites. Results from a series of rock magnetic measurements show that (titano)magnetites are present in the diabase sill and serpentinized peridotites, whereas maghemite is mainly responsible for the magnetic signatures displayed in the sedimentary and volcanic succession at Site 1277. These results, in concert with previous paleomagnetic characterization of serpentinized peridotite samples from ODP Legs 149 and 173, provide an inter-basin correlation of the magnetic properties of the peridotite rocks. The magnetic signatures of the serpentinized peridotites recovered from both sides of the Newfoundland-Iberia rift appear not to conflict with the notion that conjugate margins will have generally similar crustal structure and evolution history. DE HR: 1340h AN: GP43B-0855 TI: 30 Myr of polarity stratigraphy and relative paleointensity from Equatorial Pacific sediments (ODP Sites 1218 and 1219, Leg 199) AU: * Lanci, L et al. EM AB: ODP Sites 1218 and 1219 yielded an exceptional record of the direction and relative intensity of the geomagnetic field during most of the Miocene and Oligocene. The sedimentation rate in the Oligocene and the lower Miocene carbonate-rich pelagic sediments is > 10 m/Myr, and measurements on u-channel samples allowed a high- resolution magnetostratigraphy to be resolved. Moreover, the sediment has uniform magnetic properties that made it suitable for relative paleointensity estimates. Relative paleointensity was computed using the slope of thenatural remanent magnetization (NRM) versus anhysteretic (ARM) and isothermal remanent magnetizations (IRM) during AF demagnetization. ARM and IRM were AF demagnetized using the same alternating fields used for NRM demagnetization This high-resolution record of magnetic polarity and relative paleointensity has been used to determine whether small-scale magnetic anomalies on the ocean floor (cryptochrons) represent short polarity subchrons, intensity fluctuations of the geomagnetic field, or both. DE: HR: 0800h AN: GP11D-0868 TI: Paleomagnetic and Rock Magnetic Signature of Upper Oceanic Crust Generated by Superfast Seafloor Spreading: Results from ODP Leg 206 AU: * Acton, G and Wilson, D EM AB: During Ocean Drilling Program (ODP) Leg 206, Site 1256 ($6.736\deg$N, $91.934\deg$W) was cored deep into a 15-Ma section of oceanic crust that is part of the Cocos Plate formed by superfast spreading ($>$200 mm/yr) at the East Pacific Rise. Three holes penetrated through 250 m of sediment and into igneous basement, with the two deepest holes, Holes 1256C and D, reaching 88.5 and 502 m sub-basement, respectively. The igneous section consists of an uppermost massive ponded flow that is $>$70 m thick, underlain by thin flows ($<$3 m thick), massive flows ($>$3 m thick; some of which may be dikes), pillows, and hyaloclastites. The uppermost units, particularly the massive ponded flow, record an anomalously steep paleomagnetic direction for this near equatorial site and commonly retain only a few percent of their natural remanent magnetization (NRM) after being demagnetized in peak alternating fields (AF) of only 20 mT. The steep direction appears to be the characteristic remanent magnetization (ChRM) as it can be separated from an even steeper drilling overprint. Units below this have shallow inclinations and retain 5% to 15% of their NRM after 20 mT AF, both characteristics being more typical of what would be expected for near equatorial oceanic basalts. Rock magnetic results based on hysteresis, FORC, and thermomagnetic measurements indicate that there are insignificant differences in the paleomagnetic carriers for the units with steep and shallow inclinations. In both cases, pseudo-single domain titanomagnetite and titanomaghemite are the main carriers. This supports the interpretation that the uppermost basalts were extruded in a weak transitional or excursional field. Given that the site was cored 5 km east of the transition zone between marine magnetic anomalies 5Bn.2n and 5Br, the massive ponded lava most likely recorded this transitional field after traveling ~5 km from the spreading axis. DE
HR: 16:30h AN: GP34A-03 TI: Determination of Relative Contributions from Marine and Terrestrial Sediment Sources in the Cariaco Basin using a Magnetic Mixing Model AU: * Verosub, K L et al. E AB: The Cariaco Basin, an anoxic basin off the coast of Venezuela, acts as a depocenter for sediments of both marine and terrestrial origin. Sedimentation rates for the upper 170 m of sediment recovered during ODP Leg 165 at Site 1002 average 35 cm/k.y. and are fairly constant over the entire 600-k.y.-long interval cored. We have used a magnetic mixing model to identify and quantify the contributions to the sediment at this site from marine and terrestrial sources during the past 27,000 years. Our approach is based on a broad array of environmental magnetic parameters. Using the appropriate statistical methods, we first determine the extent to which different pairs of parameters are interrelated. In the case of the Cariaco Basin, many of the parameters can be shown to vary coherently. We then use the extremal values of each particular magnetic parameter to determine the magnetic signature of two hypothetical source materials. A magnetic mixing model is used to calculate the contribution at any point in the core from each of the sources. The magnetic signatures of the two hypothetical sources can be compared to actual source materials that have contributed sediment to the basin. For the Cariaco core, recent geochemical studies have shown that variations in Ti and Fe content correlate with precipitation and that wetter intervals are associated with more riverine (terrigenous) input and higher Ti and Fe content while dryer intervals are associated with more marine (biogenic) input and lower Ti and Fe content. The relative contributions from our two hypothetical sources, as determined by the magnetic mixing model, show a good correlation with variations between higher and lower Ti and Fe content. This suggests that we have successfully determined the magnetic signatures of the marine and terrestrial components in the sediment. DE HR: 0800h AN: GP11B-0831 INVITED TI: Age Offsets of the Matuyama-Brunhes Polarity Transition in Records From the Atlantic: Lock-in Depth Variations or Site Dependent Field Behavior? AU: * Clement, B M et al. EM AB: A number of high -resolution Matuyama-Brunhes transitions have recently been obtained from deep-sea sediments in the Atlantic Ocean. Three of these transition records were obtained from sites on the Blake-Bahama Outer Ridge and the Bermuda Rise as part of depth transect drilled during ODP Leg 172. The polarity transition records from these sites are remarkably similar, both during the reversal and in excursions that occurred prior to the reversal. Previous work has shown that in this region initial magnetic susceptibility records provide a useful proxy for marine isotopic stages. However, using the shipboard susceptibility records as a correlation tool, it becomes apparent that while the transition records exhibit very similar features, these features are offset relative to the susceptibility records at ODP Sites 1060, 1061 and 1063. The distance between Sites 1060 and 1061 is insignificant on a geomagnetic scale, implying that the differences are not likely due to time transgressive field behavior. Instead, the offset of the magnetization record relative to the susceptibility record may result from a difference in the lock-in depths at these sites. A possible explanation is that the different water depths at the sites affect the amount of organic matter that is oxidized before reaching the sea-floor. This in turn would lead to different depths of the redox boundaries within the sediment column. If the remanence lock-in zone is related to processes associated with the redox boundary, the difference in water depths may explain the offsets. To test this hypothesis, we compare the other Matuyama-Brunhes records from the Atlantic with the positions of the reversal relative to the marine isotopic stages, including the record from Site 1083, which was recorded in anoxic sediments. DE: HR: 16:10h AN: GP24A-01 TI: Hotspot motion, scales of mantle convection and the long-term history of the geodynamo AU: * Tarduno, J A EM AB: The Hawaiian-Emperor hotspot track has a prominent bend which has served as the basis for the theory that the Hawaiian hotspot, fixed in the deep mantle, traced a change in plate motion. However recent data from ODP Leg 197 define an age-progressive paleolatitude history, indicating that the Emperor seamount trend was principally formed by the rapid motion of the Hawaiian hotspot (81 to 47 Ma). Recognition of this motion affects models of mantle convection and plate tectonics and our understanding of terrestrial dynamics. For the future, the study demonstrates how paleomagnetism can be used to record large-scale mantle flow. Defining the nature of this flow is an important prerequisite to our understanding of core-mantle boundary processes, and their ultimate relationship with the geomagnetic field. While great progress has been made understanding secular variation and reversal frequency, long-term paleointensity records have remained elusive. Studies of feldspars containing magnetic inclusions indicate that the mid-Cretaceous field was remarkably strong, stable and dipolar. Superchrons may represent times when the nature of core-mantle heat flux allows the geodynamo to operate at peak efficiency. On billion-year time scales, spanning initiation of inner core growth, the paleomagnetic record is sparse. The use of lasers to derive directions and paleointensities from oriented silicate minerals holds significant promise for understanding the nature of the Archean geodynamo and its potential relationship with environmental conditions of the early Earth. UR HR: 14:55h AN: GP13A-05 TI: A Pilot Marine EM Study of Hydrate Ridge, Oregon. AU: * Weitemeyer, K et al. EM AB: It has long been proposed (e.g. Nigel Edwards, U.\ Toronto) that EM methods may be able to detect and map gas hydrate, which is more resistive than host sediments and thus provides an electrical target. While the base of hydrates often produces a distinctive seismic signature (the bottom-simulating reflector, or BSR), the gradational upper surface is less well imaged using seismology, and some hydrates are known to exist without a prominent BSR. In August of 2004 the Scripps Institution of Oceanography Marine EM Lab collected magnetotelluric (MT), dipole-dipole controlled source electromagnetic (CSEM), and controlled source magnetotelluric (CSMT) data across Hydrate Ridge, about 70 km offshore Newport, Oregon. Three component electric field data and two component magnetic field data were recorded at 25 evenly spaced sites along a 14.4 km east-west line that coincides with 2D and 3D seismic transects and ODP Leg 204 well-log data. Forward calculations of models with conservative resistivity contrasts suggest that radial mode CSEM electric fields at frequencies of 5 Hz (and up to the 7th square wave harmonic of 35 Hz) will give a measurable electric field response to shallow hydrates at source-receiver ranges between 500 m to 2500 m. An important part of this experiment is to compare well log data with electrical conductivity estimates of hydrate {\it in situ}, unmodified by either drilling or sample collection. We will present the CSEM and (CS)MT data from this new experiment along with preliminary interpretations. UR HR: 1340h AN: GP43B-0856 TI: Deep-tow Study of Magnetic Anomalies in the Pacific Jurassic Quiet Zone AU: * Tominaga, M et al. EM AB: The Jurassic Quiet Zone (JQZ) is a region of low-amplitude, short-wavelength, difficult-to-correlate magnetic anomalies located on Jurassic seafloor and thought to represent a time of decreased field strength and rapid reversals. We collected new deep- tow magnetic data over the Pacific JQZ that complement 2 deep-tow profiles reported in Sager et al. (J. Geophys. Res., vol.103, p. 5269, 1998). Our primary goals were to extend the correlation of deep-tow magnetic anomalies farther back in time, crossing ODP Site 801 (where Jurassic ocean crust has been drilled and cored), to evaluate the correlation of anomalies, and to refine the Jurassic geomagnetic polarity reversal time scale developed by Sager et al. (1998). These new data include: (1) closely spaced lines around M34 and Site 801, (2) two long lines extending from the previous survey, across Site 801 to the southeast, and (3) one line between the previous lines in the area of difficult-to-correlate anomalies. Systematic changes in anomaly amplitudes occur along the deep-tow lines, perhaps indicating changes in field strength. From northwest to southeast (i.e., increasing in age) anomaly amplitudes and wavelengths decrease, become nearly constant, and then increase slightly. The zone of smallest, shortest wavelength anomalies corresponds to a period of ~4 m.y. that appears to have an abrupt end. Comparing anomalies between lines, correlations were excellent on the closely-spaced profiles over M34 and around Hole 801C. Correlation over supposedly older seafloor to the south of Site 801 was also good. However, anomaly correlation in the region between M34 and Site 801 was difficult. As with other studies of magnetic profiles, it is impossible to uniquely determine which anomalies are caused by reversals and which are not. Many of the larger anomalies are likely caused by changes in polarity, whereas smaller anomalies may be intensity fluctuations. The new deep-tow data, being closer to the source than the previous lines, show more short-wavelength anomalies in some areas, particularly the area where anomaly amplitudes are least. This observation suggests that many of these short-wavelength anomalies may result from intensity fluctuations. To construct a reversal time scale, we limit short wavelengths by modeling magnetic profiles upward continued to mid-water depth. DE HR: 0800h AN: GP11D-0867 TI: Paleomagnetic Paleolatitudes of the Ontong Java Plateau From 120 Ma to 55 Ma: Implications for the Apparent Polar Wander Path of the Pacific Plate. AU: * Hall, S A et al. EM AB: Paleomagnetic analyses of Late Cretaceous- early Tertiary deep-water carbonates obtained during ODP Leg 192 drilling have been used to document the latitudinal motion of the Ontong Java Plateau (OJP). Paleolatitude estimates were obtained for the following periods: magnetochrons 25n-25r (55.9-57.5 Ma), 27r-31n (61.3-68.7 Ma), 32n-32r (71.1- 73.6 Ma) and 33n (73.6-79.1 Ma). The broad agreement between our new sedimentary paleomagnetic data and those recently obtained from OJP basement rocks suggests that possible compaction-induced inclination shallowing in the studied sediments is negligible. Anisotropy of anhysteretic remanent magnetization measurements further support this argument, yielding magnetic fabrics that appear poorly correlated with individual characteristic remanent magnetization inclinations. \ Our results when combined with other OJP paleomagnetic data yield an internally consistent data set that describes the northward motion of the plateau from its formation $\sim$120 Ma until 55 Ma. Between 120 Ma and 76 Ma the plateau is located near $24\deg$S and is either stationary or exhibits a slow northward movement. From 76 Ma until 68 Ma the plateau moves rapidly through approximately $10\deg$ of latitude to $\sim10\deg$S. From 68 Ma until 56 Ma the plateau is again almost stationary before moving slowly northward. Our data therefore support previous suggestions for a Cretaceous "standstill" of the Pacific plate and provide additional constraints upon proposed episodes of rapid plate movement. Our new OJP paleomagnetic paleolatitudes are generally lower than those predicted by indirect data from seamount magnetization studies and deskew analyses for chron 27r/31n but are higher than those predicted from deskew analyses for chrons 32 and 33n. More direct paleomagnetic data are necessary to define Pacific plate motion, drift of hotspots, and possible true polar wander events. We suggest that deep-water carbonates, if carefully analysed, can yield reliable paleomagnetic inclinations. DE: HR: 0800h AN: GP31B-0835 TI: Volcanic Influence on the Susceptibility Signal: a Case Study in Indian Ocean AU: * Salome, A et al. EM AB: Magnetic susceptibility of sediments is now widely used as a climate proxy in paleoclimatic and paleoceanographic studies. The correlation between the susceptibility and the oxygen isotopic variations is either positive or negative and thus cannot be only caused by carbonate dilution. So far no convincing model has been proposed to entirely explain the dependency of the two signals. Many studies used the fact that the weathering products, which are transported by rivers or by winds to the sea, keep the signature of their source. In order to evaluate the contribution of magnetic particles from different origins to the budget of susceptibility signal, we measured mass normalized susceptibilities for sands and suspended load from the world major rivers and from rivers draining volcanic lithologies. We found that weathering products transported by rivers which drain volcanic terrains have a susceptibility signal which is 10 to 100 fold higher than for granites. Taking into account the size of river basins, their lithology and the fact that the weathering rates of basalts are much higher than that of continental silicates, the contribution of volcanic particles to the susceptibility of oceanic sediments is estimated to be 100 to 1000 fold stronger than the contribution of particles eroded from granites. Thus we infer that the susceptibility signal of oceanic sediments is mostly dominated by basaltic inputs to the sea. With this assumption in mind, we can compare the carbonate- free susceptibility signals of several cores collected in the Arabian Sea [1,2], the Somali Basin [3] and from the Ninety East Ridge (ODP Leg 121). The time-depth calibration was based on the oxygen isotopic variations measured in the same cores. In addition we measured the susceptibility of individual samples to improve and validate the calibration between different cores with different material. Comparison of absolute values from carbonate-free sediments to our river sands data should allow us to estimate the contribution of the volcanic input for each area. Ultimately this approach should lead us to retrace the amount of alteration of volcanic terrains through time. 1 P. DeMenocal, J. Bloemendal and J. King, 1991, Proc. Ocean Drilling Program Sci. Results 117, 389-401. 2 M.W. Hounslow and B.A. Maher, 1999, J. Geophys. Res. 104, 5047-5061. 3 L. Meynadier, J.P. Valet and F.E. Grousset, 1995, Paleoceanography 10(3), 459-472. DE: HR: 0800h AN: GP31B-0840 TI: Rock Magnetic Properties Across Paleocene-Eocene Boundary Sediments from the North Atlantic, South Atlantic, and Eastern Pacific AU: * Lippert, P C et al. EM AB: We present new rock magnetic data from Wilson Lake, NJ (N. Atlantic continental shelf), ODP Site 1262, (Walvis Ridge, S. Atlantic), and Lodo, CA (continental shelf, coastal California) in an effort to evaluate the comet-impact trigger hypothesis (Kent et al., 2003) for the carbon isotope excursion (CEI) associated with the Paleocene-Eocene Thermal Maximum (PETM). The comet-impact trigger hypothesis is based primarily on anomalous magnetic properties in outer shelf Paleocene-Eocene boundary sediments from the New Jersey continental margin; proponents of this hypothesis suggest these magnetic properties indicate the presence of extraterrestrial nanoparticles of magnetite. Our results suggest that these nanoparticles of magnetite may be terrestrial, not cosmic, in origin. Changes in magnetic hysteresis properties (e.g., Mr/Ms and Hc/Hcr) across the Wilson Lake section are similar to those from other regional stratigraphic sections (re: Kent et al., 2003), but similar changes are not observed at S. Atlantic or coastal California sites; thus, there may be a regional rather than global source of magnetic material. Squareness plots (Tauxe et al., 2003) and Day plots (Day, 1977) of hysteresis data suggest that Wilson Lake magnetite is single domain (SD flower structure to SD cubic), but the grain size of magnetite from the other two sites is mixed, possibly with a significant component of pseudo-single domain grains. Weak-field high temperature susceptibility experiments suggest that the primary magnetic mineral in these sections is magnetite. Low-temperature zero- and strong-field saturation isothermal remanent magnetization (SIRM) experiments indicate that the fine-grained magnetite is partially oxidized, probably to maghemite. More significant, however, the low-temperature experiments suggest that the fine-grained magnetite from the CIE portion of the Wilson Lake section may have a biogenic origin. Although it is clear that intact chains of magnetosomes are not preserved, the single-domain magnetite in the Wilson Lake section may have a significant population of isolated magnetosomes or other biogenic magnetite. We present additional comparative studies of low-temperature data to better assess the component of biogenic magnetite in the Wilson Lake section. We also present geochemical data to better understand the redox conditions that could favor or inhibit the production of biogenic magnetite at the three sampling sites. DE HR: 0800h AN: GP11D-0870 TI: Magnetic Properties and Paleointensity of a Mid-Miocene Gabbro from the Costa Rica Accretionary Wedge, ODP Leg 170 AU: * Hawkins, L K et al. EM: AU AB: Samples of gabbro from cores recovered by the Ocean Drilling Program Leg 170 have been analyzed for magnetic mineralogy and paleointensity using a Thellier-Thellier method. The cores are from the Costa Rica Accretionary Wedge, Site 1039, Hole C at a minimum depth of 423 meters below the sea floor. This gabbroic unit is younger than 16.49 Ma based on nannofossils in the intruded oozes. This makes it ideal for a paleointensity study because few paleointensity data exist for this time period in this region. Rock magnetic investigations included continuous low field thermomagnetic analysis, alternating field (AF) demagnetization, optical microscopy, scanning electron microscopy (SEM), and element analysis. AF demagnetization paths are straight to the origin on orthogonal vector endpoint diagrams suggesting that the magnetization is single component. Optical microscopy and SEM observations identified titanomagnetites as the most abundant magnetic mineral in the samples; occurring as either coarse- or fine-grains with euhedral shape. Titanomagnetite composition, estimated from weight percents provided by element maps from the backscattered electrons, are both low and high titanium, TM22 and TM74. Reversible susceptibility vs. temperature curves from low field thermomagnetic analysis to 710$\deg$C suggests that the minerals do not alter in an argon atmosphere. Curie temperatures below 200$\deg$C and above 400$\deg$C calculated from these curves are consistent with the SEM results. The modified Thellier technique used a 0.4 uT field and an argon atmosphere. Low temperature demagnetization before and after some temperature steps was used to look for different behavior of the large and small magnetite grains. Based on Thellier and thermal experiments, most of the samples have about equal contributions from low and high Curie temperature titanomagnetite. Although alternating field demagnetization produced straight line paths on demagnetization diagrams, thermal results show that the two magnetites carry different components. We are currently exploring the reasons for the difference, e.g., the contribution of drill string remanence, and whether either magnetite can be used to determine the paleomagnetic field intensity. DE HR: 1340h AN: GP43B-0864 TI: Holocene relative paleointensity and paleosecular variation from the Southern Okinawa Trough (ODP Hole 1202B) AU: * Richter, C et al. EM AB: We investigated u-channels from the top 36 meters of Hole 1202B collected in the Southern Okinawa Trough during Ocean Drilling Program Leg 195. Detailed rock magnetic data demonstrate that the sediments preserve a high resolution record of paleosecular variation and a paleointensity signal spanning almost the entire Holocene. The sediments consist of homogenous, slightly calcareous, bioturbated clayey silt with isolated sandy intervals and fine sand laminae. An age-depth model was established through C-14 accelerator mass spectrometry dating of planktonic foraminfera. The studied section spans almost the entire Holocene (0-9.4 kyr) and exhibits sedimentation rates close to 400 cm/kyr. The magnetic properties are dominated by stable, pseudo- single domain low-titanium magnetite with a Curie temperature of about 540 deg C. High-field hysteresis data and the grain-size sensitive ratio of anhysteretic remanent magnetization (ARM) to low field magnetic susceptibility indicate a narrow range of grain sizes and concentrations. Key magnetic parameters vary by less than a factor of four, thereby fulfilling the criteria for relative paleointensity determinations. The relative paleointensity was extracted by normalizing the intensity of the natural remanent magnetization (NRM) by the ARM and by the low field magnetic susceptibility. Both normalizations yield very similar results. Spectral analysis indicates that the record is not significantly affected by local environmental conditions. Comparison of this Western Pacific paleointensity curve with other curves suggests a geomagnetic origin for the observed variations. Millennial-scale features in our record correlate with variations of the archeomagnetic dipole moment, which implies that the sediment from Hole 1202B recorded changes of the geomagnetic field over the investigated time interval. DE: HR: 1340h AN: GP43B-0860 TI: Different magnetostratigraphic approaches: Lake Baikal sediments and the J/K boundary strata in the Tethyan realm AU: * Pruner, P et al. EM AB: Rock magnetic and paleomagnetic parameters were studied on two cores drilled in the Academician Ridge, Lake Baikal, Russia. The rock magnetic parameters were used to identify variations in the concentration, grain size and mineralogy of the magnetic material. Three intervals of deviating declinations and inclinations with steep totally reversed inclinations are clearly present in the cores. The ChRM directions were clearly dominated by normal polarity indicating the Brunhes Chron age of the sediments. The observed excursions were interpreted as the Blake excursion, the Iceland Basin excursion and the Biwa II excursion. The reversal excursions fall within the intensity minima. On the basis of the identification of excursions we correlated the magnetostratigraphic results (relative paleointensity and polarity) from the Lake Baikal sediments to comparable data sets from ODP site 984. Data obtained from the cores indicate the age of deposits up to 300 ka. Comparing the variations of the paleointensity records the mean sedimentation rate in the range of 3 - 4 cm/ka can be estimated. The result of magnetostratigraphic and micropalaeontological investigations of the Jurassic/Cretaceous boundary strata in the Tethyan realm (Brodno - Slovakia, the Bosso Valley - Italy, and Puerto Escano - Spain) can be reasonably intercorrelated. Reverse subzones proposed to be named "Kysuca Subzone" in M20n and "Brodno Subzone" in M19n were precisely localized in all studied profiles. All the magnetozones and subzones can be related to the M-sequence of marine magnetic anomalies. At the locality of Brodno, the interpreted duration of the transition between N - R (R - N) polarity falls into the range of 5 - 10 ka. Stratigraphically significant calpionellid events occupy an identical position in relation to magnetozones and subzones derived in all the three sections. The base of the calpionellid zone Crassicolaria coincides with the base of the "Kysuca Subzone". Appearance of the species Calpionella grandalpina represents a significant horizon; it lies immediately below the base of the magnetozone M19r in all sections. The base of the standard zone Calpionella was used for the definition of the J/K boundary in calpionellid stratigraphy. UR HR: 0800h AN: GP11A-0813 TI: Marine Controlled Source Electromagnetics for Gas Hydrate Evaluation on the Cascadia Margin: Correlation Between Resistivity Anomalies and Seismic Blank Zones AU: * Schwalenberg, K et al. EM AB: The gas hydrate deposits on the Cascadia Margin have been the focus of a vast number of projects and marine experiments to investigate the distribution and concentration of this potential future energy resource. Gas hydrate or frozen gas consists mainly of methane and water molecules. It is stable at low temperatures and high pressures and forms in pore space within the hydrate stability zone in marine sediments. Hydrate itself is electrical insulating and replaces conductive pore fluid, which subsequently increases the bulk resistivity of a hydrate formation. Accurate measurements of the seafloor resistivity can be a useful tool for hydrate estimation, which is essential for resource and environmental hazard evaluation. The instrument - a development of the University of Toronto - is basically an inline dipole-dipole configuration dragged along the seafloor. It has been successfully applied in previous experiments on the Cascadia Margin and on the Chilean Margin. Here we present a promising new data set collected in summer 2004. Measurements have been conducted along three profiles. For the first time data have been collected with the marine controlled source electromagnetic method in water depths shallower than required for hydrate stability (i.e. below 500m). These data are important as a reference site for hydrate assessment. The second profile covers the bullseye, a vent site in vicinity of ODP site 889B that correlates with a region of seismic blanking and recovered hydrate outcrops. The 7km long profile also covers another series of seismically identified vent sites. The average amplitudes of the measured electric fields and thus the related apparent resistivities along the first profile (no hydrate) are smaller than along the second profile (vent sites). This is consistent with the idea of an increased resistivity in hydrate rich zones. Two pronounced anomalies occur along the second profile in spatial agreement with the bullseye and the other series of vent sites. The third profile intersects the second profile at the bullseye. However, beside of a careful lowering procedure, the array was likely tangled on the seafloor for most parts of the deployment which complicates or even inhibits the interpretation, but points out the importance of a careful coordination of ships navigation and instrument deployment as well as weather and sea conditions for a successful experiment. UR HR: 09:45h AN: GP41B-08 TI: A paleomagnetic record of the last 640 kyr from an eastern Mediterranean piston core and a review of geomagnetic excursions in the Brunhes AU: * Oda, H et al. EM AB: Core KC01 (25.93 m long) was taken from a small ridge on the lower slope of the southern Calabrian Ridge (Pisano Plateau, 36deg15.25'N, 17deg44.34'E, 3643m water depth) during cruise MD69 of the French R/V Marion Dufresne in June-July 1991. The sediment consists of hemipelagic sediments with intercalated sapropel and tephra layers. They form an alternation of grey, greenish, olive-coloured, yellowish, white and beige shades. Sapropel layers are black to dark green. Paleomagnetic samples (6.4 cm3 cubes) were taken from the half split cores and measurements of the natural remanent magnetization was conducted at Utrecht University with a DC SQUID magnetometer (2G Enterprises model 740-R). Stepwise alternating field demagnetization was done at 8-11 steps up to 60-80 mT on each sample. Core KC01 (37.04 m long) was taken as a companion core from core KC01B at the same locality, earlier subjected to magnetostratigraphic work (Langereis et al., 1997). Langereis et al. (1997) established an age model based on the matching of (ghost-)sapropels with insolation minima. They applied the 65degN summer insolation calculated from the astronomical solution La90 (Laskar 1990; Laskar et al., 1993) as target curve and included a time lag of 3-kyr - based on the age difference between the radiocarbon dated midpoint of S1 at 8.5 ka and the insolation maximum at 11.5 ka following the method by Lourens et al. (1996). Lourens (2004) modified the astronomical chronology established by Langereis et al. (1997) and investigated the sapropel chronology on KC01B and KC01 based on high resolution colour correlation with ODP Site 964, which is 1 km away, and constructed an improved age model, which gives a better estimate for these two cores. Langereis et al. (1997) reported four excursions (CR0, CR1, CR2, CR3) with ages of 261, 318, 515, and 573 ka based on the chronology of sapropels on Core KC01B. Lourens (2004) revised the chronology of Core KC01B and redated the excursions as 260, 319, 543, and 593 ka. In this study, these four excursion records were confirmed and dated as 258-263, 313-319, 541-542, 592-594 ka based on the new chronology. Also Laschamp, Norwegian- Greenland Sea, Iceland Basin and Jamaica excursions were found at ages of 41-43, 77, 193-194 and 212-213 ka. Finally, we conducted a review of published excursion records and identified a maximum of 23 excursions and a minimum of 16 excursions in the Brunhes. HR: 13:40h AN: GC53A-01 INVITED TI: Late Quaternary Paleoenvironmental History of the Peru- Chile Current System and Adjacent Continental Chile AU: * Lamy, F et al. EM AB: A combined analysis of terrigenous and biogenic compounds in marine sediments from the Chilean continental margin allows detailed reconstructions of the paleoclimatic and paleoceanographic history of this region during the last ca. 120,000 years. Based on several sediment cores recovered during two German cruises and ODP Leg 202 (Site 1233), we found evidence for changes both in continental rainfall, most likely induced by latitudinal shifts of the Southern Westerlies, and marine productivity as well as sea surface temperature and salinity changes within the Peru-Chile Current system on time scales ranging from Milankovitch to centennial-scale. On Milankovitch time-scales, we found strong evidence for precession-controlled shifts of the Southern Westerlies implying for example generally more humid conditions during the LGM and a trend towards more arid climates during the deglaciation culminating in the early Holocene. These shifts are paralleled by paleoceanographic changes indicating generally higher productivity during the LGM mainly caused by increased advection of nutrients from the south through an enhanced Peru-Chile current. North of 33øS, these general productivity patterns are complicated by additional impacts from the tropics resulting in maximum paleoproductivity during the deglaciation and prior to the LGM. On shorter time-scales, extremely high resolution sediment cores from the southern Chilean margin provide evidence of significant short-term Holocene climate variability with bands of variability centred at ca. 900 and 1500 years, periodicities also well known from Northern Hemisphere records. Recently drilled ODP Site 1233 allowed to prolong these records into the last glacial. The available data show millennial-scale SST changes that closely follow the temperature pattern known from Antarctic ice-cores. Including other records from the Southern Hemisphere mid-latitudes, our data suggest a quasi-hemisphere-wide response that is consistent with the bipolar see-saw mechanism but may also imply a more prominent role of the Southern Hemisphere in the origin and transfer of millennial- scale climate variations during the last glacial. In addtion, Site 1233 offers the excellent opportunity to compare continental and marine paleoenvironmental signals within the same well-dated archive suggesting a lagged response of the terrestrial signal most likely related to climate inertia of the Patagonian ice-sheet. DE: HR: 0800h AN: GC51D-1078 TI: A Test for Extending the High-Resolution Global Climate Record in Santa Barbara Basin AU: * Hopkins, S E et al. EM AB: ODP Site 893 in Santa Barbara Basin recovered high-resolution global climate data extending back to ~160 ka at 200 m sub-seafloor. Safety concerns though have prevented deeper drilling at this site. Santa Barbara Basin is, however, tectonically active. As a result, continuous late-Quaternary strata deposited in the deep paleo-bathymetric basin were uplifted and folded across the Mid-Channel Trend, and strata as old as ~450 ka (OIS 12) appear to be exposed at the seafloor where they are now accessible to piston coring. This project will test the accessibility along the anticline of these older stratigraphic sequences through detailed basin correlation of high-resolution seismic stratigraphy and subsequent coring. In preparation for coring in summer 2005, grids of high-resolution MMS analog, industry multichannel, and 2D USGS high-resolution seismic reflection data (collected in 2002) are being used to correlate dated reference horizons at ~120 ka, ~160 ka and ~1 Ma along with several intervening seismic sequence boundaries across the Mid-Channel Trend. Results provide the basis for modeling the structure and stratigraphy in 3D, and to precisely locate suitable sites for coring. Subsequent core analyses will be used to verify the predicted outcrop pattern and basin-wide sequence stratigraphic interpretation. Thus, in addition to its contributions to Quaternary climate history, this project will help document the nature and evolution of the Mid-Channel anticline, and the local interaction between tectonics, climate, and sea-level change. To date, our results show that the Mid-Channel Trend has propagated from east to west as previously proposed. South of Santa Barbara harbor, folding on the anticline began about 1 Ma, while 10 km farther west, folding began after ~450 ka. Furthermore, our results confirm that older strata (extending back to inferred OIS 12) of the paleo-Santa Barbara Basin have been folded, and are present at or near the seafloor. HR: 15:25h AN: H53E-08 TI: Marine Sedimentary Record of Cenozoic Monsoon Intensity Preserved in the Asian Marginal Seas AU: * Clift, P D EM AB: Climate models predict that the intensity of the Asian monsoon is largely controlled by the elevation of the Tibetan Plateau. However, the elevation of Tibet and the erosional response to monsoon intensification is contentious. Compilation of seismic data from the marginal seas of East Asia now shows that sedimentation rates sharply increased across the region, and especially in the Red River catchment after around 33 Ma and continued to increase until around 11 Ma. The dating of potassic magmatism and strike-slip faulting on the eastern flanks of the Tibetan Plateau starting at 35-30 Ma suggests that this tectonism may accompany a period of accelerating surface uplift in Tibet. At present few climate records exist for this time period, though the monsoon might be expected to have strengthened in stages since that time. Most notably new data from ODP Site 1148 in the northern South China Sea show a sharp increase in clastic and carbonate mass accumulation rates associated with a change in clay mineralogy to greater illite dominance (physical weathering) starting around 17.2 Ma. I interpret this to reflect a change to a more erosive, more monsoonal climate starting at that time in southern China. Falling sedimentation rates at 11-8 Ma and lasting until 4 Ma indicate drier conditions across Asia at that time, also recorded by strong eolian sedimentation in the North Pacific, slower sedimentation on the Indus and Bengal Fans, and change to a more smectite dominated mineralogy on both these fans, indicating a less erosive environment. Only in the Mekong does erosion increase after 8 Ma, driven by local tectonic uplift in the Vietnamese Highlands. Faster sedimentation and a return to an illite dominated mineralogy after 4 Ma accompanies a series of proxies that indicate a stronger summer monsoon at that time, and a return to faster erosion driven by rains in East and South Asia. The evidence shows a broad positive correlation between monsoon strength and erosion over long periods of geological time. Pulses of sediment caused by faster erosion do not appear to be strongly dampened over time scales >100 kyr by sequestering in continental sedimentary basins, but mostly reach the continental margins of the South China Sea. UR 0800h AN: MR11A-0916 TI: Calibration of Mobile NMR Instruments in Respect to Porosity and Pore Size Distribution of Drill Cores AU: * Arnold, J et al. EM AB: The focus of our research is set on the calibration of two different and new developed light weight mobile NMR scanning systems: (1) the NMR-MOUSE and (2) the HALBACH device for measuring porosity and pore size distribution of different drill cores recovered from the International Ocean Drilling Program (IODP). Further goals are to adapt current NMR processing techniques, the development of new measurement routines, and to evaluate precision and accuracy of this method. Transverse relaxation on water-saturated drill cores were measured using a CPMG sequence. A regularized Laplace transform analysis based on the UPEN program yields the distribution of transverse relaxation times. The signal amplitudes and the integrals of distribution correlate directly to the core porosity. The main advantage of our mobile NMR scanning systems compared to conventional methods is their small size and weight, which is particularly attractive for the shipboard use and on any drilling platform envisioned for IODP. Both tools, the NMR-MOUSE and the HALBACH scanner are suitable for routine measurements of porosity and pore-size distribution of drill core sections. In contrast to the NMR-MOUSE, the HALBACH tool has a sufficiently homogeneous magnetic field and is more sensitive. It can determine porosities as low as 3 %. While the NMR- MOUSE can be applied on core sections of any geometry, the Halbach tool is especially designed for the size of standard drill cores recovered from the deep sea ocean floor by the IODP. Combined with a mobile NMR spectrometer and special software for porosity and pore size distribution measurements, both light and mobile devices are particularly attractive for the use on research vessels and logging platforms and thus alow to determine prosity and permeability on very fresh material. HR: 1340h AN: OS43A-0526 TI: Global Distribution of Microbial Alteration of the Ocean Crust AU: * Josef, J A et al. EM AB: Early evidence for a deep subsurface biosphere in ocean crust came from unusual alteration textures within petrographic thin sections. The textures are attributed to microbial activity within basalt minerals and glass. Microbial textures have now been found in DSDP and ODP holes and in sea floor surface basalt from around the globe. These samples revealed a variety of unique alteration textures, and our hypothesis is that similar textures are the result of similar conditions in ocean crust environments. One- hundred and five petrographic thin sections from DSDP and ODP drill cores from the Pacific, Atlantic, and Indian Oceans as well as the Mediterranean Sea were used to create a library of images of microbial alteration textures. Prevalent textures include straight, curving, segmented and angular twisting tunnels, mushroom shaped structures, and fungus-like groups of alteration. We are using Lossless Compression Analysis on our library of images to distinguish and classify the variety of alteration textures. Currently we are classifying textures both down-hole and across ocean basins and correlating the occurrence of similar textures with measured drill-hole properties, including age, location of the sample, water depth, basalt temperature, type and amount of sediment cover, depth within the basalt, and secondary minerals. DE: HR: 16:30h AN: OS34B-03 TI: Mechanism for free gas migration through South Hydrate Ridge hydrate system AU: * Liu, X and Flemings, P EM AB: At southern Hydrate Ridge, offshore Oregon, free gas vents through hydrate-bearing sediments where free gas coexists with gas hydrate and brine in shallow subsurface. To establish three-phase (liquid, hydrate and gas) equilibrium within the gas hydrate stability zone (GHSZ), salinity must increase from a baseline value of 3 wt.% at the base of the GHSZ to about 12 wt.% at the seafloor. This predicted salinity profile is similar to in situ pore water salinity calculated at ODP Site 1249. We interpret that the upward increase in salinity is driven by rapid hydrate formation in the case of high methane flux from below. As hydrates form, dissolved ions are excluded and pore water salinity rises. Ultimately, salinity rises to the point where three-phase equilibrium is reached and additional methane exists in free gas phase. By assuming that there is no transport of water or salt, we can estimate the hydrate amount from change in salinity relative to the baseline. Hydrate volume faction would increase from 0 below the GHSZ to 70% at the seafloor. This predicted hydrate distribution is consistent with resistivity log- and PCS- derived hydrate occurrences at Hydrate Ridge. Thus, both observations and calculations of three-phase equilibrium suggest that the formation of marine methane hydrate is a self- equilibrating process at locations where methane supply is abundant. This provides a mechanism whereby free gas migrates through the GHSZ without being converted into hydrate. DE: HR: 1340h AN: OS33B-0587 TI: Sediment Accumulation Rates of Late Quaternary Deposits in San Pedro Basin, the Gulf of Santa Catalina, and San Diego Trough, Offshore Southern California AU: * Normark, W R et al. EM AB: A multiyear program of seismic-reflection profiling and sediment coring has focused on understanding the history of late Quaternary sedimentation within the inner basins of the California Borderland. The objective of this study has been to develop a high-resolution seismic stratigraphy primarily for the Last Glacial Maximum and the Holocene that can be used to understand depositional processes, sediment budgets, and deformation within the basins. The Santa Barbara and Santa Monica Basins in the northern Borderland are closed basins and both were cored during the Ocean Drilling Program (ODP) in support of paleoclimatic studies. In contrast, the inner basins in the southern Borderland that are the focus of this report are open-ended basins that have not been the subject of scientific drilling. We present the preliminary results of sediment coring at 21 sites in San Pedro Basin, the Gulf of Santa Catalina, and San Diego Trough. Initial estimates of sediment-accumulation rates for these basins are based on 48 previously unpublished radiocarbon dates. During the Holocene, average sediment- accumulation rates are generally less than 0.5 m/ky on the basin floors where turbidite deposition locally continued at reduced rates from those of the OIS 2-lowstand interval. This rate is nearly an order of magnitude less than was documented for the Holocene by ODP coring at Site 1015 in Santa Monica Basin reflecting, in part, the loss of sediment in the non-closed basins. Background hemipelagic rates range from 0.01 to 0.1 m/ky, with the lowest rates on mid-basin highs, e.g., Lasuen Knoll. More dating is currently underway for some of the core sites to determine the rate of change in sediment accumulation during the Holocene. DE: HR: 1340h AN: OS33B-0583 TI: Relations Between Basement Tectonics, Sediment Deformation and Fluid Flow at the Eastern Juan de Fuca Ridge Flank: Results From Very High Resolution Seismic Data AU: * Zuehlsdorff, L and Spiess, V EM AB: In summer 2004, IODP Leg 301 was drilled on the eastern flank of the Juan de Fuca Ridge as a successor of ODP Leg 168 (1996). The main subject of the new leg was to study the properties of an active ridge flank hydrothermal system, which is for a big part isolated beneath a low permeable sediment cover. During the Leg 301 seismic pre-site survey, which was carried out during R/V Sonne Cruise SO 149 (2000), this sediment cover was imaged in a multi-frequency seismic data set at high and very high resolution. Folds, faults, and the layer structure were carefully mapped to show that forced folding is a dominant process affecting sediment physical properties and fluid flow. By comparing data from areas of different basement age and integrating seismic and borehole data, the importance of basement tectonics on sediment deformation and fluid flow, depending on crustal age and sedimentation processes is investigated. Preliminary results show that growth faults characterized by upwardly decreasing offsets reflect off-axis tectonic crustal reorganization. Growth fault propagation at Second Ridge ceased about 0.28 Ma ago at the base of a major sediment transport channel, whereas tectonic activity at First Ridge was more recent. Forced folding at First Ridge controls creation and maintenance of a subsurface plumbing system for vertical fluid flow through the sediments. Indications for forced folding are also found at Second Ridge though vertical fluid flow likely is much less affected. DE: HR: 0800h AN: OS41C-0492 TI: Estimation of Free Gas Saturation Using AVO Analysis on 3D Seismic Data at South Hydrate Ridge, Cascadia Accretionary Complex AU: * Xun, H et al. EM AB: In 2000 we conducted a high-resolution 3D seismic survey of a 4x10 km2 region on south Hydrate Ridge on the Oregon continental margin. The objective of the survey is to characterize the regional pattern of fluid and gas migration and its relationship to hydrate accumulations on Hydrate Ridge. These data were acquired with a high-resolution seismic source with source-receiver offsets of up to 644 m, which results in incidence angles of up to 20 degrees. In 2002 new 2D seismic data with source-receiver offsets of up to 1500 m, producing incidence angles of up to 40 degrees, were collected during R/V Ewing Cruise EW0208, which was coordinated with Ocean Drilling Program (ODP) Leg 204. Prior to AVO analysis, we conducted true amplitude recovery by using the seismic range equation, and true amplitude processing through prestack time migration. We also calibrated the 3D data by using the 2D data to remove unfavorable acquisition effects in the 3D survey. On prestack-migrated gathers, we measured the seismic amplitude from the three surfaces associated with free gas accumulations: 1) the bottom simulating reflection (BSR), 2) Horizon A, and 3) Horizon B'. Horizon A is a ~4-m-thick turbidite interval where it was drilled during ODP Leg 204 and it is identified as a primary conduit along which free gas migrates from deep sources to the summit of Hydrate Ridge. Horizon A focuses gas hydrate formation and feeds gas vents near the southern summit of Hydrate Ridge. Horizon B' is a volcanic glass-rich horizon that is also a stratigraphically defined gas conduit. Intercept and slope are obtained from AVO fitting, and the Poisson's ratio is obtained by using intercept and slope with the constraints of well-log data. Gas saturation for the three surfaces is estimated by fluid substitution technique. The distribution of free gas inferred from AVO analysis shows that the highest free gas concentrations lie directly beneath the highest gas hydrate concentrations estimated from Leg 204 core data. For Horizon A, the gas saturation increases toward the summit as Horizon A shallows. Free gas within Horizon A is distributed in isolated pockets rather than in continuously connected veins. DE HR: 0800h AN: OS41C-0494 TI: Analysis of Sonic Velocity in an Active Gas Hydrate System, Hydrate Ridge, Offshore Oregon AU: * Guerin, G et al. EM AB: One of the best recognized and most intuitive influence of gas hydrate on its host sediment is the change in its mechanical and elastic properties. This is identified through an increase in acoustic velocity, which is partially responsible for one of the most distinct signatures of gas hydrate presence, the Bottom Simulating Reflector (BSR). The unstable nature of gas hydrate makes the in situ recording of their properties by downhole logging the best way to identify and quantify its distribution. During ODP Leg 204 on Hydrate Ridge, offshore Oregon, acoustic logs were recorded in seven holes and vertical seismic profiles (VSP) were acquired successfully in four holes. These data, recorded within a wide range of frequency and scales provide a unique and extensive survey of the acoustic properties of a dynamic gas hydrate system. Because of the poorly consolidated nature of the Hydrate Ridge sediments, automatic picking of velocity was only partially successful and a complete post cruise reprocessing of the sonic waveforms was necessary to draw accurate compressional (Vp) and shear velocity (Vs) logs. Synthetic seismograms generated with the Vp and density logs allow to confirm the nature of the main reflectors identified in a 3-D seismic survey of Hydrate Ridge, such as the BSR and various faults underlying the southern Hydrate Ridge system. Despite the highly heterogeneous distribution of gas hydrate, the Vp logs and interval velocities calculated from the VSP clearly identify the presence of gas hydrate and the eventual presence of free gas directly underneath the hydrate stability zone or within the faults feeding the ridge system. We use various elastic models to try to estimate gas hydrate and free gas saturations from sonic velocity and from bulk moduli. The best agreement with independent estimates derived from resistivity logs and other methods indicate that gas hydrate interact with the host sediment through cementation, which contributes also to a significant energy loss in the recorded waveforms. DE: HR: 11:20h AN: OS22B-05 TI: Size and Age Characteristics for West Coast Tsunamigenic Landslides AU: * Lee, H et al. EM AF: AB: Multibeam bathymetric imagery is now available for a number of well-defined submarine landslide deposits along the west coast of the United States. Several of these landslides are known to have caused damaging tsunamis and others are of sufficient size to have generated tsunamis when they occurred, assuming that their motion was rapid. These failures are located off Palos Verdes Peninsula, California, and within Santa Barbara Channel, California, Commencement Bay, Washington, Resurrection Bay, Alaska, and Port Valdez, Alaska. For two of these failures, ages were determined by identifying acoustic reflectors in the vicinity of the failed masses that either clearly postdate or predate the landslide events. The ages of the reflectors are determined by tracing them to the locations of nearby ODP borings or to piston cores dated using radiocarbon methods. Three of the landslides produced tsunamis during historic time (post 1750 AD) so the ages are well constrained. High-resolution subbottom reflection profiles also allow us to estimate the dimensions of the failed masses. Although the examples selected clearly do not represent all scales of tsunamigenic west coast landslides, this information is useful in providing input to statistically based models of landslide-induced tsunamis. DE: HR: 0800h AN: OS21A-1204 TI: Authigenic Dolomite in Marine Marginal Sediments: An Indicator of Fossil Microbial Activity AU: * Vasconcelos, C et al. EM AB: Dolomite formation under Earth surface conditions remains a long-standing enigma in Earth science. Although it is abundant in the rock record, dolomite does not commonly form in modern marine sedimentary environments and attempts to precipitate dolomite in the laboratory at Earth surface conditions have been largely unsuccessful. In recent years, however, microbial mediation of dolomite formation has been tested in cultural experiments and in natural environments. A new microbial factor has been added to the list of factors, which are thought to promote dolomite precipitation. This microbial model for dolomite formation has found wide acceptance and has been applied to explain modern and ancient dolomite formation. In particular, deep-sea margin sediments provide an ideal setting to apply the microbial dolomite model. With the discovery of dolomite in Quaternary deep-sea sediments in the late 1970's, e.g. during Deep Sea Drilling Program (DSDP) Legs 63 and 64 on the California Margin and in the Gulf of California, a new environment for dolomite formation was recognized. We have applied the microbial dolomite model in two different marine marginal settings and will present the results of SEM, isotopic and mineralogical studies of the recovered dolomite. The discovery of a field of dolomite chimneys strewn on the Gulf of Cadiz seafloor provided an opportunity to study the fossil microbial activity, which had mediated dolomite formation in the flow path of upward migrating methane on this tectonically active margin. In contrast, modern microbial activity was investigated in organic carbon-rich hemipelagic sediments recovered in drill cores obtained from the Peru Margin during ODP Leg 201, which was dedicated to the study of the deep biosphere. The microbial impact on the pore-water geochemistry could be linked directly to the diagenetic processes occurring in the sediments, i.e. dolomite formation. Combining the results obtained from our two study areas, we propose that dolomite formation in marine marginal settings is probably directly linked with microbial activity associated with the geochemical transition between the zones of sulfate reduction and methanogenesis. DE HR: 1340h AN: OS33A-0578 TI: Holocene and Glacial Variability of the Hydrologic Cycle in the Tropical Atlantic: Evidence from the Cariaco Basin AU: * Dulski, P et al. EM AB: Climate variability in the Central American tropics is largely forced by changes in the intensity of the Hadley circulation and the strength and position of the Intertropical Convergence Zone (ITCZ). The two most direct consequences of seasonal ITCZ motion for Cariaco Basin and its sediments are the pronounced alternation between the upwelling that occurs in the winter-spring and the increased river runoff that takes place in the summer-fall. This seasonal contrast, coupled with the lack of bioturbation during anoxic phases of deposition in the basin, has produced a high deposition rate (ca. 30 to $>$150 cm/kyr). Sediment sequence in most portions consisting of mm-scale, annually-paired plankton-rich biogenic laminae and terrigenous detrital-rich laminae. The built-in seasonal clock that results from ITCZ movement has allowed development of annually- resolved chronologies over intervals where laminae are distinct enough to reliably count yielding nearly unparalleled temporal resolution for a marine sequence. In a series of recent papers, we have utilized measurements of sedimentary Ti and Fe contents as proxies for the total terrigenous fraction of Cariaco Basin sediments. Downcore variations in Ti and Fe have been adopted as indices of past regional hydrologic change, with higher values interpreted to reflect increased rainfall, river discharge, and terrigenous sediment delivery to the basin. Bulk Ti and Fe and other major element patterns in sediment recovered from IMAGES core MD03-2621 and Ocean Drilling Program (ODP) Hole 1002C were measured at a 50 to 500 um spacing, which reflects a temporal spacing of up to 10 measurements per varve, using a new profiling x-ray fluorescence scanner located at GFZ Potsdam. Here, we present a new data set spanning the Holocene and parts of the last glacial period. DE
HR: 16:15h AN: OS34B-02 TI: Structural Controls on Hydrate Distribution and Morphology at Hydrate Ridge, Oregon AU: * Weinberger, J and Brown, K AB: Analysis of resistivity-at-the-bit (RAB) images from nine sites drilled during Ocean Drilling Program (ODP) leg 204 to southern Hydrate Ridge reveals a complex pattern of fracture orientations that correlate with the structural location of the borehole on the ridge. Sites 1244 and1245 on the eastern and western flanks of the ridge, respectively, have concentrated zones of resistive fractures within the gas hydrate stability zone that exhibit a preferred orientation orthogonal to the regional direction of plate convergence and crustal shortening. The mean orientation of the identified fracture planes at Site 1244 strikes N10W and dips $40\deg$E, and the mean fracture plane at Site 1245 strikes N15W and dips $33\deg$E. Higher on the eastern ridge flank, at site 1246, fracture planes exhibit a transitional behavior from clustering on the flanks to a less well organized pattern at the ridge crest. Poles to structural planes at the ridge crest sites (1247-1250) are evenly distributed, though their typically shallow dips (i.e. steeply dipping planes $>$ $30\deg$) create a girdle pattern in stereographic projections. The steeply dipping planes at the ridge crest occur in zones of chaotic resistivity in the RAB images and correlate to zones of massive hydrate in the cores. Simple planar relationships can be obscured in these zones by hydrate growth patterns and morphology. Bedding plane dips were also measured and are consistently sub horizontal at all sites. Little change in bedding dip occurs with depth at sites on the ridge crest and flanks, though the basin site shows bedding dips increase below $\sim$ 200 mbsf. As expected, few fracture planes were documented in the basin site images where hemipelagic sedimentation dominates. Results of the RAB image analyses indicate that the orientation and morphology of hydrate filled fractures is controlled by structural position on the ridge. At the ridge crest, undergoing extension, migrating aqueous fluid and free gas have the potential to hydrofracture the sediment creating a network of steeply dipping, but randomly oriented fractures with massive hydrate accumulations. Along the ridge flanks where fluid flow is controlled primarily by lithology, hydrate filled fractures maintain a preferred orientation that parallels that of the uplifted sedimentary section and is oriented perpendicular to the regional maximum compressive stress. DE: HR: 09:30h AN: OS21E-07 TI: Slope Instability and Gas Hydrates in the Hudson Canyon Region, U.S. Atlantic Continental Margin AU: * Rona, P et al. EM AB: The continental slope and the upper rise centered on Hudson Canyon offshore New York and New Jersey lie within a major gas-hydrate province. This region exhibits evidence of gravitational mass movements and possible methane expulsion, as inferred from our bathymetric and water-column surveys conducted in 2002 with support from NOAA/OE, and prior data. The bathymetric data cover our study area (200 km by 110 km; 37\deg40'N to 39\deg50'N, 70\deg00'W to 72\deg30'W) from the inner edge of the continental slope (depth 200 m) seaward to the middle rise (c.3500 m). The world's largest hub of submarine telecommunications cables partially passes through this area. Evidence of gravitational mass movements and of probable gas release is extensive. Examples of the former include: (1) blocks of landward-dipping strata up to 2-km wide and 150-m high that lie at the base of the continental slope (water depth 2100-2200 m) seaward of an over-pressured zone beneath the continental slope (639 mbsf in ODP Hole 1073A; water depth 650 m; Dugan and Flemings, 2000); (2) boulders of Eocene chalk that litter the lower slope and upper rise; (3) a semicircular, tabular glide block, about 20 km in diameter, which thickens to about 150 m at its seaward margin; the block is centered at 39\deg23.5'N, 71\deg10.0'W between 2450 and 2600 m depth on the upper rise, about 15 km downslope from a congruent scarp at 2200 m on the lower slope; (4) apparent penecontemporaneous faulting and gliding in strata inclined sub-parallel to the seafloor along the upper rise; 5) apparent clogging of Hudson Canyon with hummocky sediment at a right-angle turn of the axis (depth 3368 m; 38\deg39.6'N, 71\deg01.8'W); 6) changes in stratification from the upper to middle rise; uneven layering beneath the upper rise (seafloor mean inclination 0.75\deg down to 2700 m) is inferred to reflect disturbance by gravitational mass movements; even layering parallel to the seafloor beneath the middle rise (inclination increase seaward from 0.25\deg to 0.76\deg) may reflect less disrupted hemipelagic sedimentation. Evidence of gas release includes: (1) a zone of irregular pits, each up to 500-m in diameter and spaced kilometers apart, that extends along the upper rise (2600-2650 m); (2) a line of eight depressions each 50-70 m in diameter with several meters relief and spaced 100-120 m apart that trends NNW (2150 m; near 39\degN, 71\deg52'W)and that may indicate gas or porewater escape along a local fault; 3) a plume of sediment suspended in fluid that is discharging through the seafloor and rising about 1 m at 2625 m depth on the SW margin of Hudson Canyon (38\deg52.4'N, 71\deg31.0'W) recorded on deep-towed video; and 4) three zones of regional, water-column, methane anomalies, which exceed background values, deeper than 2500-m depth, centered at 1200-m depth, and near 200-m depth. These features indicate past and present dissociation of gas hydrates and/or venting of free gas. They also indicate that coherent gravitational mass movements over low seafloor slopes (< 1\deg) have been facilitated by excess fluid (water and/or gas) pressures. The continental slope and rise in the Hudson Canyon region comprise a natural laboratory in which to study slope instability in a gas hydrate province and to assess the hazards to telecommunications cables. Dugan, B. and P.B. Flemings (2000), Overpressure and fluid flow in the New Jersey continental slope: implications for slope failure and cold seeps, Science, 289, 288-291. HR: 1340h AN: PP33B-0946 TI: High Resolution Calcareous Nannofossil Fluctuations Across the Oligocene/Miocene Boundary, ODP Hole 1168A AU: * McGonigal, K L EM AB: Ocean Drilling Program (ODP) Leg 189 drilled five sites around Tasmania to investigate the timing and nature of the development of the Tasmanian Seaway. The Oligocene/Miocene interval at Site 1168, located on the western continental slope of Tasmania, was relatively expanded with an average linear sedimentation rate of 5 cm/k.y. A high resolution study of calcareous nannofossils was conducted at a 5 k.y. sample interval. Fluctuations in nannofossil assemblages, diversity, absolute abundance and flux were calculated across the Oligocene/Miocene interval at Site 1168. These data were combined with physical property data to further elucidate changes across this interval. Multivariate statistical analysis was conducted on several time slices through the 2 m.y. interval of interest in an effort to identify paleoceanographic fluctuations. DE HR: 0800h AN: PP51F-1377 TI: Orbital and suborbital variability in Coccolithophore assemblages in the eastern tropical and equatorial Pacific Ocean (7§N to17§S) for the last 500 ka (ODP Leg 202) AU: * Flores, J et al. EM AB: Ocean Drilling Program Leg 202 covered a South-North transect in the eastern Pacific Ocean, providing excellent material to reconstruct variations in surface and subsurface water dynamics in selected time-slices. The main goal here is to investigate the evolution of coastal and equatorial upwelling systems and their relationship to global and/or regional climate processes such as El Nino or related features. Based on a preliminary age-model using calcareous nannofossil-calibrated datums, a quantitative analysis in the Coccolithophore assemblages was carried out to investigate orbital variations in surface water dynamics during the last 500 kys. Here we present data from four ODP sites: Site 1237 situated in the west South America upwelling system; Sites 1240 and 1241 in the equatorial Pacific upwelling system, and Site 1242 close to the Costa Rica margin. The ratio between the shallow and deep coccolithophore dwellers is used to reconstruct fluctuations in the nutricline/thermocline position, and consequently, monitor variations in the upwelled waters. Our preliminary results show a orbital periodicity (ca. 100, ca. 40 and ca. 20 ka periodicity), together with an obvious millennial signal in the above mentioned proxy. Moreover, other well-defined patterns are overprinted in all sites, allowing us to differentiate three intervals without a clear orbital relationship. Periods of well defined upwelling alternate with other intervals where surface and subsurface waters appear better stratified. This model seems to respond to regional and almost synchronous variations linked to variations in like-El Nino-La Nina periods of orbital range. DE
HR: 0800h AN: PP41A-0588 TI: Late Cenozoic reduction in Antarctic Circumpolar Current flow from analyses of drift deposits along the Antarctic Peninsula, ODP Site 1095. AU: * Hassold, N et al. EM AB: All waters from the Earth's oceans flow into and are mixed in the Antarctic Circumpolar Current (ACC). Thus the ACC has a major effect on the transport of heat in the oceans and the Earth's climate. Sediment drifts, which form along the Antarctic Peninsula under the influence of the ACC, record the history of this flow. We examined samples from cores drilled during Ocean Drilling Program (ODP) Leg 178 along the Antarctic Peninsula to determine paleocurrent strength changes. Both paleomagnetic cubes and sediment samples were taken from cores from ODP Site 1095 ($66\deg$59'S, $78\deg$29'W, 3814m). Factor analysis using major element chemistry indicates a two- component system between terrigenous and biogenic opal. The terrigenous fraction of 236 sediment samples was isolated and the grain size measured to determine the terrigenous mass accumulation rate (MAR), the median grain size ($\phi$50), the $>$63 $\mu$m MAR and the biogenic opal MAR. Terrigenous mass accumulation rates reflect the overall MAR's at the site, decreasing in a series of steps at 9 my, 5.5 my, and 2.5 my. Median grain size changes occur at 5.5 my (sharp decrease followed by a slight increase) and 2.7 my (decrease). The magnetic fabric, as determined for 324 samples by anisotropy of magnetic susceptibility (AMS), decreases sharply at 5.7 my and again at 2.7 my. We interpret these step-like changes as indicating a decline in the current strength over the last 6 my, with specific decreases occurring around 5.5 my and 2.5 my. DE: HR: 0800h AN: PP11A-0547 TI: New Insights into Inferring Climate Variability from Records of Planktonic Foraminiferal Mg/Ca, Oxygen Isotope and Shell Weight in the Southern Ocean AU: * Greaves, M et al. EM AB: Temperature is the dominant control on foraminiferal Mg/Ca, although other factors are important and can bias paleoceanographic reconstructions. In order to investigate the controls on Mg/Ca, we compare records from two sites at different water depths located north and south of the Subtropical Convergence in the Southern Ocean (ODP Site 1123 and MD97-2120). Mg/Ca, d18O, and shell weight were obtained from two narrow size fractions (250-300 and 300-355 um) of the planktonic foraminifer Globigerina bulloides. Combining these data allows us to investigate the effects of hydrography, dissolution and foraminiferal habitat as controls on Mg/Ca. Differences are observed between the records from these locations. Comparison of Mg/Ca records from both size fractions at MD97- 2120 implies similar calcification temperatures. In contrast, Mg/Ca-derived paleotemperatures from the 250-300 um fraction at ODP Site 1123 are higher than in the larger size fraction. Mg/Ca records from both size fractions at MD97-2120 are similar across Termination 1 and imply a glacial-interglacial temperature change of 8 degrees C. The temperature record from the 250-300 um fraction from ODP Site 1123 shows a glacial-interglacial temperature change of 4 degrees across Termination 1, whereas in the 300-355 um fraction no temperature change is observed. At ODP Site 1123, the contrast between size fractions in Mg/Ca-derived temperatures is even more striking across Termination 2. The differences in Mg/Ca records are associated with offsets in d18O and shell weight records from both size fractions. The larger fraction exhibits heavier d18O and larger weight variability. Possible explanations for these observations include hydrographic differences between the two sites, foraminiferal habitat, dissolution susceptibility, and preservation history. DE: HR: 0800h AN: PP51F-1365 TI: Alkenone Sea-surface Temperature Variations in the Southeast Pacific Ocean Inferred from a High-Resolution Record of the past 200,000 Years (ODP Site 1234) AU: * Chen, M and Huang, C EM AB: High sedimentation rate records with millennial to centennial resolution were recovered from ODP Site 1234 in the southeast Pacific. SST reconstructions by using alkenone unsaturation indices measured from the sediments recovered from this site allow assessment of climate variability pattern in the surface ocean of the southeastern Pacific. Site 1234 SST records also provide opportunity to establish a high-resolution record that is sensitive to eastern Pacific climate, and allow a comparison with a SST record from a more southern (ODP Site 1233) near the glacial extension of Patagonian Ice Sheet in southern Chile. The record from Site 1234 can be compare further with a western Pacific record (MD972151) over the last two glacial-interglacial cycles and be used to identify any basin-scale type of climate variability pattern in the Pacific. In this study, we present (~10cm mcd sampling intervals, ~200 years resolution) alkenone SST reconstruction that covers the past ~200,000 years. Based on our preliminary results, the SST record from Site 1234 reveals large oscillations from ~17-11›FXC and patterns of high frequency changes which open a room for further correlations with Greenland and Antarctic ice cores. Large amplitude oscillations in SSTs are also observed from the MIS 5 interval of the record and appear to parallel to the variations of benthic oxygen isotopes measured from the same core. A long-term trend of alkenone concentration decreases is clearly observed from MIS 5 to the present, suggesting that at this site calcareous productivity was decreased or siliceous productivity / terrestrial sediment supply was increased since MIS 5. Accurate chronological controls by using AMS 14C, paleomagnetic and oxygen isotope stratigraphies will provide opportunity to assess the timing of these climatic events into a global framework. DE HR: 15:25h AN: PP43B-08 INVITED TI: Paleomagnetic Results From ODP Leg 202: The Chilean Margin Sites AU: * Stoner, J et al. EM AB: ODP Leg 202 sediments provided the unique opportunity to derive paleomagnetic records that range from sub-centennial to tectonic timescales. Paleomagnetic studies are ongoing with the most complete results to date from the Chilean Margin Sites (1233, 1234 & 1235) and Site Survey cores. Shipboard data from these sites suggest that they contain an unprecedented record of geomagnetic field behavior for the last 70 kyr. Progressive alternating field (AF) demagnetization of u-channel paleomagnetic samples from the Holocene section of Site 1233 (41.0. S, 74.26W, water depth 838 m) indicated that these sediments preserve a strong (10-2 A/M), stable, well-defined, low coercivity magnetization. Component directions show that inclinations vary around the expected GAD values for the site latitude, declinations show variations consistent with PSV. The u-channel results attest to the general robustness of the shipboard data. Comparisons between ODP cores, multi cores and gravity cores demonstrate that Site 1233 preserves the upper most sediment and records the distinct shallow inclination and eastward declinations of the historical field off South America. By splicing u-channel and shipboard data and calibrating it to the historical record a long geomagnetic timeseries is reconstructed. Augmented by twenty-seven radiocarbon dates from Site 1233 and nearby cores show that the normalized intensity records capture millennial scale variability that can be correlated to the highest resolution relative paleintensity records globally. We have developed a composite chronostratigraphy for the last 75 kyr and will begin the exploration of the spatial coherence of the paleomagnetic secular variation record. These and other results will be discussed. DE HR: 0800h AN: PP11A-0545 TI: Changes in Deep Sea Temperature and Ice Volume Based on Paired Measurements of Benthic Foraminiferal Mg/Ca and $\delta$$^{18}$O: Evidence from ODP Site 849, Equatorial Pacific for Marine Isotope Stages 1-3 AU: * Healey, S and Thunell, R EM AB: Most continuous records of sea level changes are based on benthic foraminiferal δ18O, which is a measure of both the δ18O of seawater and temperature. New calibrations [Martin et al., 2002; Lear et al., 2002] between temperature and Mg/Ca ratios in benthic foraminiferal calcite provide a means to differentiate the separate effects of temperature and global ice volume on the benthic foraminiferal δ18O signal. We have measured the Mg/Ca ratio of the benthic foraminifera species, Cibicidoides wuellerstorfi, throughout Marine Isotope Stages (MIS) 1-3 (0-60 Ka) in sediments from Eastern Equatorial Pacific, ODP Site 849 (0$\deg$11'N, 110$\deg$ 31'W; 3851 m). Using published Mg/Ca - temperature relationships for this species, we estimate a 2.5$\deg$C increase in bottom water temperature at this location over Termination 1. The change in benthic foraminiferal δ18O associated with this deglaciation is ~1.6$\permil$ [Mix et al., 1995]. Using a conversion factor of 0.23 $\permil$ per 1$\deg$C [Kim and O'Neil, 1997], the $\delta$$^{18}$O change accounted for by a 2.5$\deg$C change in temperature is approximately 0.58$\permil$, suggesting a residual 1.02$\permil$ change to be accounted for by the change in global ice volume over Termination 1. This is consistent with previous estimates of the global δ18O change of seawater due to melting of continental ice sheets since the Last Glacial Maximum. DE: HR: 0800h AN: PP11B-0559 TI: New Data On The Distribution Of Calcareous Nannofossils During And After The Paleocene/Eocene Transition AU: * Raffi, I EM AB: Major changes occur among calcareous nannofossil assemblages at the transition from Paleocene to Eocene. In most known P/E boundary sections with complete sediment records, the changes are associated to the brief, intensive interval of global warming, the Paleocene-Eocene Thermal Maximum (PETM), and a concomitant huge perturbation of the global carbon budget, the Carbon Isotope Excursion (CIE). Changes in nannofossil assemblages include: (A) occurrence of {\it Rhomboaster} spp. - {\it D. araneus} correlative with the CIE; (B) decrease in diversification of {\it Fasciculithus} spp. at the CIE onset; (C) occurrence of {\it Zygrhablithus bijugatus} and {\it Fasciculithus} spp./ {\it Z. bijugatus} abundance cross-over within the upper part of the CIE-PETM interval; and (D) extiction of the Paleocene genus {\it Fasciculithus} just above the CIE, an event that is closely followed by the further evolution of {\it Rhomboaster - Tribrachiatus} plexus. The genus {\it Tribrachiatus} subsequently radiates over the next $\sim$1 million years, a time interval showing further steps in the evolutionary history of calcareous nannofossils (speciations among discoasters and sphenoliths) during the Eocene. Quantitative analyses of selected calcareous nannofossils in deep-sea sections recovered from the Atlantic (DSDP Site 550, ODP Site 929, and ODP Sites 1262 and 1263 of Leg 208) and paleo-equatorial Pacific (ODP Sites 1215, 1220, 1221 of Leg 199) provide new informations about calcareous nannofossils across the Paleocene/Eocene transition interval. The distinctive {\it Rhomboaster} spp. - {\it D. araneus} association (RD) was previously considered to have a marked provincialism, restricted to the Atlantic Ocean and partially extending to the Tethys seaway and westernmost Indian Ocean. Detailed study of Leg 199 sections (from equatorial Pacific) and preliminary analyses at the P/E boundary of ODP Site 929 (from Ceara Rise in western equatorial Atlantic) and ODP Sites 1262 and 1263 (from Walvis Ridge in southern Atlantic) indicate some difference in the RD distribution. The sudden appearance and short co-existence of {\it R. calcitrapa} gr. and {\it D. araneus}, and the lowermost occurrence of {\it R. cuspis} at the onset of CIE clearly can be extended to the equatorial regions of the Atlantic as well as the Pacific Ocean. The genus {\it Fasciculithus} undergoes a substantial decrease in diversification at the onset of CIE, and perish completely shortly afterwards. This significant turnover appears to represent a global event observed in all the known P/E boundary sections from different oceans and paleo-latitudes. The abundance cross-over between Fasciculithus spp. and Z. bijugatus has been observed to occur within the the CIE-PETM interval in several deep-sea sections. In the central paleo-equatorial Pacific Ocean, however, Z. bijugatus specimens were not present at all, whereas a marked increase in abundance of {\it R. cuspis} was observed in conjunction with the final decline of {\it Fasciculithus} spp. Data from the western paleo-equatorial Atlantic Ocean (Site 929) shows only few {\it Z. bijugatus}, implying that this particular early Eocene turnover is absent in these equatorial regions. {\it Thoracosphaera} spp. shows a short abundance peak immediately above the carbonate barren interval at the P/E boundary, during the CIE, at paleo-equatorial Pacific Site 1220, which probably reflects a stressed surface water environment. DE HR: 0800h AN: PP11B-0564 TI: Depth Dependant Variations in Benthic Foraminiferal Assemblages and Stable Isotopes Across the P-E Boundary, Walvis Ridge (ODP Leg 208) AU: * McCarren, H et al. EM AB: The Paleocene-Eocene Thermal Maximum (PETM) ($\sim$55 Ma), was characterized by extreme global warming, a negative carbon isotope excursion, intensified carbonate dissolution, and a severe mass extinction of benthic foraminifera. The lack of continuous, undisturbed cores over a wide depth range has limited efforts to place constraints on key aspects of the PETM event, such as changes in ocean redox and carbon chemistry, and depth dependent patterns of the benthic extinction. The P-E boundary was recovered in multiple holes at 5 sites from Walvis Ridge in the southeastern Atlantic (ODP Leg 208). We document changes in benthic assemblages and stable isotopes across the PETM at ODP Leg 208, and compare these with data from other PE boundary sections, including DSDP Sites 525 and 527 previously drilled on Walvis Ridge. Faunal assemblage analyses show a distinct drop in diversity coincident with the base of the clay layer at all sites. There is a clear relationship between water depth and magnitude of the benthic foraminifera isotope excursion along the Walvis Ridge depth transect. Site 1263 (2717m) records excursion values of -2.2 $\delta$$^{13}$C and -2.5 $\delta$$^{18}$O; whereas Site 1262 (4759m) has values of -0.2 $\delta$$^{13}$C and -0.8 $\delta$$^{18}$O at the height of the excursion. This difference implies truncation of the record at deeper sites by carbonate dissolution, possibly as well as a depth dependent difference in water mass chemistry and temperature during the PETM. Several benthic foraminiferal species such as {\it Nuttallides truempyi} and various abyssaminid species that may indicate low nutrient availability increase in abundance at the onset of the isotope excursion, while the percentage of biserial and triserial species, used as high food/low oxygen indicators, decreases. There are thus distinct changes in ocean chemistry over the 2.3 km paleodepth range of the Walvis Ridge transect during the PETM event. DE HR: 0800h AN: PP51F-1369 TI: A Reconstruction of Millennial-scale Changes in Sub-surface Watermasses Off of Central Chille AU: * Phipps, M and Mix, A EM AB: Here we examine millennial scale changes in subsurface watermasses off central Chile during the last ice age, based on stable carbon and oxygen isotopes from benthic foraminifera. ODP sites 1235: (489m water depth) and 1234 ( 985 m water depth) bracket the modern extent of Antarctic Intermediate Water. The core top \delta 18O at 1235 and 1234 are 2.7 \permil and 3.3 \permil respectively. This 0.6 \permil difference between the two cores corresponds to a modern 2.4 $^{\circ}$ C temperature offset between sites. Variations in \delta 18O from Site 1234 resemble similar high-resolution records from the deep Atlantic, which suggests Southern Ocean linkage of deep ocean temperatures in the two ocean basins. High amplitude \delta 18O variations at Site 1234 indicate a larger change in temperature in the intermediate Southeast Pacific than the deep North Atlantic, whereas Site 1235 varies with lower amplitudes. If glacial ice volume accounts for 1.1 - 1.3 \permil of the observed change in benthic foraminiferal \delta 18O, Site 1235 may have experienced temperature changes of 2 - 3 $^{\circ}$ C and that Site 1234 experienced changes of 3-4 $^{\circ}$ C. DE
HR: 0800h AN: PP51D-1353 TI: The early Eocene in the Southern Ocean; an integrated dinocyst and geochemical analysis of ODP Leg 189 sites 1171 and 1172, Tasman Sea. AU: Deltrap, R et al. EM AB: The early Eocene is known as the warmest and most extreme long-term greenhouse interval of the Cenozoic. Superimposed on these conditions, short-lived 'hyperthermal' events, apparently caused by the fast input of carbon in the ocean-atmosphere system, are associated with dramatic changes in ocean chemistry, the global hydrological cycle and bio-provincialism and evolution. The `Paleocene/Eocene Thermal Maximum' or PETM event (55 Ma) is the most extreme hyperthermal event, but recently similar events within this time period have been identified. Many relatively complete late Paleocene through early Eocene sequences have by now been reported from around the world, but most are from ancient low- to mid-latitude sites. ODP Leg 189 in the Tasman Sea recovered the southernmost successions ever encountered from this critical phase in Earth's history at the marginal marine Sites 1171 and 1172 (at 70\deg to 65\deg S paleolatitude). On the basis of more detailed investigations of downhole and core logging data, in combination with bio- (dinocysts) magnetostratigraphy and organic stable isotope geochemistry, we have identified the PETM, and possibly also the younger Elmo event (see Sluijs et al., AGU fall meeting abstract volume 2004) and provide correlation and analysis of the late Paleocene through early Eocene in terms of completeness and paleoenvironment. DE HR: 0800h AN: PP51F-1366 TI: Alkenone and planktic foraminifer sea-surface temperature reconstructions at ODP Site 1240: 500-900 kya AU: * Yu, P EM AB: One of the objectives of ODP Leg 202 is to retrieve high-resolution sediment cores from the eastern equatorial Pacific, an area in which modern interannual-scale climate are dynamically fluctuating. In this study we aimed to reconstruct paleoceanographic records from the ODP Site 1240 (0o1.311'N; 86o27.758'W; WD: 2921m) from the Leg 202. One of our objectives in the paleoceanographic reconstructions is to better understand how tropical oceans interact with global climate over orbital time scales, and focus on testing hypotheses of ENSO-like oscillation and of extra-tropical forcing prevailed in long-term climate variations in the tropics. We are especially interested in examining an abnormally "warm and wet" climate in glacial MIS 14 shown in Chinese loess and South China Sea marine records and looking for any tropical origin of forcing or feedback for explaining the abnormality. Site 1240 was chosen for this purpose as this site is ideal for monitoring upwelling and circulation changes in the eastern equatorial Pacific, and is likely very sensitive to if any ENSO-like oscillations occurred in this particular time interval. In this preliminary study, the age model of cores from Site 1240 was constructed primarily based upon 4 calcareous nannofossil datums at the top 80 meters composite depth (mcd) and the average sedimentation rate is ~10cm/kyr. We have also generated alkenone SSTs from an interval of 500-900 kya of the cores. Initial observations indicate that high alkenone concentrations are associated low SSTs and vice versa at this interval. Alkenone SSTs calculated from Prahl's equation show an amplitude ~$4-5\deg$C variations over major glacial-interglacial periods in this interval and suggest a dynamic climate pattern in the EEP. Comparison of the alkenone SSTs and relatively low-resolution planktic foraminifer fauna MAT-SSTs also indicates that these two estimates appear to be of similar amplitudes, though the MAT-SSTs are apparently warmer than alkenone SSTs by ~$1-2\deg$C. In the interval equivalent to MIS 13-15 based on our very initial age model, both SST proxies show large cooling (~$4\deg$C) which suggest a strong equatorial circulation at this time. DE: HR: 0800h AN: PP11B-0571 TI: Marine carbonate dissolution event across the Eocene/Oligocene boundary: the Walvis Ridge transect, South Atlantic (ODP Leg 208) AU: * Liu, Z et al. EM AB: Sediments recording the response of South Atlantic to global cooling and marine carbonate dissolution during the Eocene-Oligocene transition were recovered across a broad range of depths of five sites on the northeastern flank of Walvis Ridge during ODP Leg 208. Although the Eocene/Oligocene (E/O) boundary is not well preserved biostratigraphically, especially at two deepest sites (Sites 1262 and 1267), oxygen and carbon stable isotopes of benthic and/or planktonic foraminifers have determined the exact boundary position for most of sites. High-resolution carbonate content and foraminiferal grain size combined with coarse fraction and siliciclatic element geochemistry reveal that the strongest carbonate dissolution event occurred just above the E/O boundary, leading the global Earliest Oligocene Glacial Maximum (EOGM). This carbonate dissolution event may take up abundant atmospheric CO2 into the deep ocean by the calcium carbonate pump system, and then induces the global cooling during the earliest Oligocene. The recovery of the foraminiferal preservation does not appear to be immediate with rapid cooling; however, it lags behind about 500 kyr, implying that the shift in carbonate preservation was triggered by changes in climate. The carbonate dissolution event is associated with deepening of carbonate compensation depth (CCD) and falling of sea level. Moreover, the event has a close relationship with continental weathering rates indicated by element geochemistry, implying the possible carbon cycle- forced global cooling event across the E/O boundary. DE: HR: 14:55h AN: PP13B-06 TI: Sea-surface and deep-sea temperatures and seawater d18O in the Southern Ocean over the last 440,000 years AU: * Tripati, A et al. EM AB: The circulation of Antarctic Bottom Water is one of the controlling factors in the Earth's heat budget, and therefore Southern Ocean paleoceanography is critical to understanding glacial-interglacial climate change. Ocean Drilling Program (ODP) Site 1123 (3290 m water depth) on Chatham Rise (41ø 47.15' S, 171ø 28.94' W) is located just north of the present-day Subtropical Convergence, below the Pacific Deep Western Boundary Current, within the depth range of Antarctic Bottom Water. The recovered sedimentary sequence from ODP Site 1123 contains a record of Southern Ocea, hydrographic variations over several glacial-interglacial cycles: We present a 440,000 year record of surface and deepwater hydrographic variability based measurements of Mg/Ca and stable isotope ratios in planktic and benthic foraminifera. Planktic Mg/Ca- based temperatures indicate a maximum glacial-interglacial temp. change of 7.5øC. The planktic record shares many features in common with a record from a shallower site located just south of the Subtropical Convergence excepth that temp. changes across Termin. 1 and 2 aren't seen at Site 1123. Possible reasons for this include hydrographic differences between sites, foraminiferal habitat, and dissolution artifacts. Glacial- interglacial benthic Mg/Ca differences are variable through the record, with coldest temperatures inferred for Stages 8 and 10. Deep-water temps. based on Mg/Ca indicate LGM values of -0.8øC (calibration of Martin et al. 2002) and a seawater d18O of 1.0 per mil (VSMOW), similar to the porewater-based reconstruction at this site (Adkins et al. 2002). DE HR: 1340h AN: PP23B-1408 TI: Pleistocene North Atlantic Deep Water Production; A Southern Hemisphere Perspective AU: * Foote, J et al. EM AB: Faunal counts and stable isotopes of planktonic foraminifera are used to identify glacial-interglacial and millennial scale change in Pleistocene Atlantic interhemispheric transport. The sampling site, ODP Site 1085, has a sedimentation rate of approximately 5 cm/k.y. Samples were taken every 2 cm throughout the sections of the core representing the last 200 k.y., giving the site a resolution of approximately 500 years, high enough to observe glacial-interglacial variation, Dansgaard/Oeschger temperature cycles, and Heinrich events, within the Nyquist frequency. {\it Globigerina bulloides}, found in cold, nutrient-rich water, is used as a proxy for upwelling (Girardeau 1992). At Site 1085, {\it G. bulloides} peaks both during glacial and interglacial periods. The interglacial peaks covary with peaks of terrigenous sediment greater than 10 microns, an indicator of aeolian transport (Stuut et al. 2002), indicating a link between upwelling and wind strength at that time. The glacial peaks broadly correlate to a low C/N ratio, indicating a probable marine cause for the upwelling, such as an enhanced Benguela Current. Additionally, there is higher-frequency (sub-Milankovitch) variability through both the glacial and interglacial periods. DE: HR: 15:10h AN: PP43B-07 TI: Linking Global Climates Between Hemispheres and Ocean Basins: Millennial-Scale Temperature and Isotopic Variability of Intermediate and Mid-Depth Watermasses of the Equatorial and Southeast Pacific. AU: * Mix, A et al. EM AB: Analysis of stable isotopes and trace metals in benthic foraminifera from rapidly accumulating sediments in the Equatorial and Southeast Pacific recovered on ODP Leg 202, reveal remarkably high amplitude variations on millennial scales at water depths of $\sim$500-1500 m. Presence of climate signals that mimic variability in ice cores provides a strategy for inter-hemispheric and interocean correlation. Surprisingly large variability in subsurface watermass properties in this region mimics signals found in the mid-depth Atlantic. This variability in the Pacific suggests a role for global-scale ocean circulation in interhemispheric and interocean linkage. DE
HR: 1340h AN: PP23A-1396 TI: Early Onset and Origin of 100-kyr Cycles in a Tropical Pleistocene SST Record AU: * Liu, Z and Herbert, T AB: The large 100-kyr cycles evident in most late-Pleistocene paleoclimatic records still lack a satisfactory explanation. Many climatic records show that the period of Pleistocene glacial cycles changed from 41-kyr, dictated by orbital obliquity, to 100-kyr during the mid-Pleistocene transition (MPT). Careful documentation and consideration of how this transition occurred may help resolve the puzzle of late Pleistocene 100-kyr cycles. One hypothesis is that strengthened semi-precession cycles (about 10-kyr) originating in the tropics propagated to high latitudes around 1.5 Ma and triggered the sustained 100-kyr glacial cycles. A 2-Myr SST record from ODP Site 846 in the eastern equatorial Pacific (EEP) indicates that an early onset of 100-kyr cycles did occur in the tropics. However, the record also provides an alternative view of the MPT. Substantial spectral power near the 100-kyr period occurs in early Pleistocene tropical, but not extra-tropical SST records. This spectral power is derived from the subharmonics (multiple integers, about 120-kyr and 80-kyr) of obliquity cycles. In addition, as shown in evolutionary SST spectra, the two subharmonics converge into the late-Pleistocene pseudo 100-kyr period. Therefore, we argue that the subharmonics of obliquity cycles in the early Pleistocene represent a _rprototype__ of the late Pleistocene 100-kyr cycles, and that the pseudo 100- kyr cycles are a nonlinear response to orbital obliquity forcing. This view can potentially resolve some existing Pleistocene climate puzzles: (1) the transition from 41-kyr to 100- kyr periodicity during the MPT, (2) the dominance of late-Pleistocene 100-kyr cycles, and (3) weakened late Pleistocene 41-kyr power in some climate records, despite the expected ice-albedo amplification of high latitude insolation forcing. DE: HR: 0800h AN: PP51A-1328 TI: Duration of Pliocene Ice-Rafting Events Offshore of Prydz Bay, Antarctica, Derived From Extraterrestrial Helium-3 AU: * McAuley, A et al. EM AB: The sediment record of ODP Site 1165, located 400 km offshore of Prydz Bay, Antarctica, contains layers rich in ice-rafted debris (IRD) dating from the Early Miocene to the present. The IRD represents pulses of icebergs from the Lambert Glacier and the Antarctic coast west of the site. If the duration of the ice-rafting events is short, they are likely to represent relatively rapid deglaciations of the continent. Alternatively, the IRD could be concentrated in these layers by winnowing or a reduced sedimentation rate. In order to distinguish between these possibilities we have measured helium isotopes across two of the layers. Interplanetary dust particles (IDPs) are enriched in helium-3 compared to terrestrial materials and they are deposited at a relatively constant rate, thus providing a means of determining the (relative) duration of the ice-rafting event. IDPs and helium- 3 are diluted one of the Pliocene IRD-rich layers, indicating relatively fast deposition and increased iceberg flux, probably during deglaciation.
HR: 0800h AN: PP51F-1371 TI: Sedimentary Characteristics through Glacial/Interglacial Transitions at ODP Site 1233 AU: * Joseph, L H EM AB: ODP Site 1233, located shoreward of the Chile Trench on the Chilean continental slope ($\sim$38 km offshore; $41\deg$0.005'S, $74\deg$26.992'W, 838 mbsl), recovered a 136 mcd-thick continuous and extremely high-resolution sedimentary sequence that extends through 70 ka, providing the potential to significantly enhance our knowledge of Southern Hemisphere climates. The sediment collected originates in an area where the erosion and transport of sediment to the continental margin is enhanced by alpine glaciation and heavy rainfall. This study investigates glacial/interglacial sediment variations in through the use of magnetic fabric (anisotropy of magnetic susceptibility, AMS), terrigenous grain size, and flux calculations. Site 1233 consists primarily of homogenous nannofossil clay, nannofossil silty clay, and nannofossil-bearing silty clay. Ninety-one samples were taken at approximately 1.5-meter intervals from a composite splice. On average, one sample was obtained for every $\sim$800 years. Bulk magnetic susceptibility values range from 3.4 x 10$^{-4}$ to 4.6 x 10$^{-3}$ SI with an average of 3.0 x 10$^{-3}$ SI. Values of AMS parameter P' (the strength of the magnetic fabric) range from 1.005 through 1.058, with an average of 1.025 while T values (shape factor) fall almost exclusively within the oblate realm, especially when samples from noted intervals of diagenesis are disregarded. The depositional environment, as indicated by P' and T, plots within the field of low to mid-velocity currents, indicating some current influence at this site. The strength of the magnetic fabric (P') varies through time, with maxima present at $\sim$38 and 13 ka, and may represent fluctuations or changes in the surrounding AAIW. Analyses of terrigenous grain size and flux are on-going and will facilitate further interpretation of the magnetic fabric results. DE
HR: 0800h AN: PP11B-0562 TI: Tracers of Productivity across the PETM, Walvis Ridge, ODP Sites 1262 and 1263 AU: Quartini, J et al. EM AB: The rapid and extreme global warming across the Paleocene-Eocene Thermal Maximum (PETM) is unmatched in Earth's history. We are using sedimentary phosphorus concentrations and geochemistry, along with barium and trace metals, to reconstruct nutrient burial, primary productivity, and paleoredox state across a depth transect for Walvis Ridge. We have chosen Ocean Drilling Program (ODP) Sites 1262 (4755 m water depth) and 1263 (2717 m water depth) at a sample resolution of $\sim$ 1- 2 kyr for 5 Ma centered at 55 Ma. We are characterizing the nutrient burial history during the PETM by recording the associated short-term changes in ocean chemistry and circulation. We have measured Ba excess, a good indicator of export productivity in marine sediments underlying oxic conditions, for Site 1262 samples. Ba excess concentrations range between $\sim$ 2-5 umol Ba/g prior to the warming event and decrease to zero at the boundary (140.04 mcd). Ba excess gradually recovers but does not greatly exceed pre-event concentrations ($\sim$ 2-5 umol Ba/g). Uranium and manganese enrichment factors (EF) were determined during this event for Site 1262. U ranges from 0.9 -1.1 relative to crustal averages pre-event, 0.7- 0.8 during the event, and 0.9 -1.1 after the rapid warming. Uranium data shows consistent recovery with calcium carbonate deposition over a depth range $\sim$ 0.5m. Mn EF values range between 3.7 - 8.6 prior to the event, suggesting an oxygenated depositional environment. At the boundary, Mn EF values drop to 1.3, then gradually return to pre-event values with a peak at 139.76 mcd of 13.2. We will compare our geochemical results with Site 1263 data. DE HR: 0800h AN: PP51F-1367 TI: Phosphorus and Barium Tracers of Productivity, Nazca Ridge ODP Site 1237, Southeast Pacific Paleoceanographic Transects AU: * Chun, C and Delaney, M L EM AB: Phosphorus, biogenic barium, and trace metal concentrations have been measured in sediments recovered from Ocean Drilling Program (ODP) Leg 202 Site 1237, Nazca Ridge. Our work has been to understand how these tracers of productivity and sedimentary redox conditions may have responded to the tectonic and climatic evolution of the Southeast Pacific. Changes in lithology as the site moves from a pelagic to hemi- pelagic depositional setting with past plate motion are important when applying paleoproductivity proxies. This unique record extends to 31 Ma over 360 mcd, with a sampling resolution of $\sim$ 0.2 m.y. throughout the sequence. Reactive phosphorus, an indicator of nutrient burial, shows increasing concentrations toward the modern, peaking at 25.3 umol P/g at 15.34 mcd. Biogenic barite, a proxy for export productivity, peaks at 36.90 mcd at a concentration of 3.8 umol Ba/g. Reactive P/Ba excess ratios display lower than expected values for the upper $\sim$ 180 mcd with a sharp increase to higher ratios starting at $\sim$ 270 mcd. Biogenic barite (determined by sequential extraction) defined as Ba barite, were performed on select samples to compare with Ba excess measurements. We found that estimates of biogenic barite from Ba excess are greater than those from barite extraction for these samples. Uranium and manganese enrichment factors (EF) were determined for the entire record. U EF all exceeds crustal values. Dramatic changes in Mn EF at $\sim$ 162 mcd and the observed color change from grayish white to a fairly homogeneous pale brown at this depth lead us to believe that a change in source material, not redox conditions caused this event. We will need an improved age model to generate accumulation rates and to test nutrient burial history at this site. DE HR: 08:00h AN: PP31B-01 INVITED TI: Evidence For Deep-water Production In The North Pacific During The Early Cenozoic AU: * Thomas, D J EM AB: The evolution of Cenozoic climate began with a long-term warming trend culminating in peak warmth during the Early Eocene. This was followed by intense cooling that ultimately led to the onset of the "icehouse" climate of the late Cenozoic. Changes in poleward heat transport via thermohaline circulation may have played a role in the general evolution of Cenozoic climate. To investigate the relationship between the evolution of global climate and thermohaline circulation over the interval $\sim$70 to 30 million years ago (Ma), I generated paleo-seawater neodymium isotopic records from Ocean Drilling Program (ODP) sites in the present-day northern Pacific Ocean. Fish debris Nd isotope data from ODP Sites 1209 and 1211 (paleodepths $\sim$2300m and $\sim$2900m) indicate that $\epsilon$$_{Nd}$ values in the deep waters of the central subtropical Pacific were characterized by a composition of $\sim$-4.5 to -5 during the latest Cretaceous and the Early Paleocene ($\sim$70 to 64 Ma). Beginning $\sim$64 Ma, the composition of Pacific deep waters became more radiogenic ($\sim$-3 to -3.5), and remained so for the next $\sim$20 million years. From $\sim$46 to 33 Ma, deep-water $\epsilon$$_{Nd}$ values subsequently became more nonradiogenic ($\sim$-4.5 to 5). The similarity in the overall $\epsilon$$_{Nd}$ trends at both sites indicates that they were bathed by a common deep-water mass. Nd isotopic data from ODP Leg 199 Sites (1215, 1219, and 1221; north-central Pacific), which lie $\sim$6000 km to the west and south of Shatsky Rise, demonstrate a trend similar to the upper portion of the records from Shatsky Rise. Although the basal age of sediments from the Leg 199 Sites is younger than 56 Ma, $\epsilon$$_{Nd}$ values from Sites 1215, 1219 and 1221 demonstrate the shift from relatively radiogenic (North Pacific) values of -3.5 at 53.7 Ma to more non-radiogenic (Southern Ocean) values of -4.9 by 44.8 Ma. The $\sim$1.5 epsilon unit shifts toward more radiogenic values recorded at both sites reflect a fundamental change in the source of deep waters bathing the northern Pacific sites from $\sim$65 to 45 Ma, involving a switch in deep-water production from the Southern Ocean to the North Pacific. Production of North Pacific deep waters lasted $\sim$20 million years, and coincided with the warmest climatic interval of the Cenozoic Era. The timing of the deep-ocean circulation changes lagged changes in global temperatures implying that climate exerts long-term control over thermohaline circulation patterns. Thus Cenozoic thermohaline circulation patterns evolved in response to long-term changes global climate, and were not the cause of extreme Cenozoic warmth. DE
HR: 1340h AN: PP23B-1434 TI: Optical Dating of Marine Sediment From ODP Core 658B - An Intercomparison With an Independent AMS 14C Chronology AU: * Armitage, S et al. EM AB: We demonstrate the potential of optical dating of detrital quartz silt from marine sediments via a chronological intercomparison for samples from ODP Site 658, which range in age from 0 to 140ka. ODP Site 658 is located off Cap Blanc, Mauritania. It has a high sedimentation rate (18 cm/ka), due to high regional surface productivity and large inputs of windblown Africa dust. This windblown dust provides both the substrate for optical dating and a proxy for North African aridity. The AMS 14C chronology is based on monospecific foraminiferal (Globigerinoides bulloides) samples. This is the first large-scale, systematic application of optical dating to marine sediment, and demonstrates that the technique has considerable potential for the age estimation of otherwise undateable deep-sea material. Optical dating techniques measure the total ionising radiation dose that a mineral grain has received since its last exposure to sunlight (i.e. during burial). The resulting optical age is essentially calibrated via a knowledge of the environmental dose rate, yielding the burial period. The environmental dose rate is derived from the decay of radioisotopes in the sediment (K, U and Th). In terrestrial sediments, the uranium and thorium decay chains can be assumed to be in equilibrium. In the marine realm this assumption is not valid, and unsupported uranium decay series exist on deposition. Consequently, the environmental dose rate changes with sample age. This problem was circumvented by quantifying U and Th decay series disequilibrium, using an MC-ICP-MS. The evolution of the environmental dose rate during burial was modelled, and ages for each sample calculated. The 14C and optical ages are generally in good agreement, indicating that the latter technique can provide equally robust chronologies for marine sediments. Although the maximum age attainable using optical dating is sample specific, the dose rate and luminescence characteristics of the samples analysed in this study indicate that marine sediments ranging from 0-200ka should be dateable. Very precise (1-3%) burial doses and radioisotope concentrations were obtained, although ultimately precision is limited to about 10% due to uncertainties in the moisture content, source calibrations and dose rate conversion factors. However, over the timescales that optical dating is applicable, these overall errors are not inconsistent with the rarely quoted precision accorded to orbitally tuned records. Optical dating should provide a valuable geochronological tool for marine sediments extending well beyond the time range of 14C dating, and for dating marine sediments that contain no dateable carbon. DE: HR: 14:10h AN: PP43B-03 TI: Pliocene Shoaling of the Central American Seaway and its Effect on Caribbean and Tropical East Pacific Upper Ocean Stratification AU: * Steph, S et al. EM AB: Multispecies planktonic \delta$^{18}$O records and Mg/Ca-temperature reconstructions from ODP sites 999, 1000 and 1241 were used to assess changes in Caribbean and tropical East Pacific upper ocean stratification in response to the progressive closure of the Central American Seaway. Our studies focus on the time interval from 5.5 to 2.5 million years. Previous studies suggested that the sill depth of the Panamanian Gateway shoaled to less than 50 m by about 4.6 Ma as indicated by an increase in Caribbean sea surface salinity (SSS), reflecting the development of the modern Atlantic-Pacific SSS contrast. At site 1241, the general increase of \delta$^{18}$O and Mg/Ca temperature gradients between the mixed-layer dweller {\it G. sacculifer} and deeper dwelling foraminifers {\it N. dutertrei}, {\it G. limbata} and {\it G. tumida} suggests a shoaling of the tropical East Pacific thermoline from 5.5 Ma to 3.3 Ma. At Caribbean sites 999 and 1000, both \delta$^{18}$O and Mg/Ca temperature gradients indicate a warming of subsurface water masses after 4.4 Ma. The direct comparison of subsurface water signatures from Caribbean sites (999, 1000) and tropical East Pacific site 1241, however, points to a deeper leakage in the Central American Seaway that persisted at least until 3.3 Ma, just before the onset of the Northern Hemisphere Glaciation. The increase in Caribbean SSS after 4.6-4.2 Ma is interpreted to reflect a diminished eastward volume transport of less saline Pacific water masses through the gateway, rather than a shoaling of the gateway to a water depth of less than 50 m. Similar and stable Mg/Ca temperatures at sites 999 and 1241 paralleled by a \delta$^{18}$O increase at both sites display a salinity increase in Caribbean and tropical E-Pacific subsurface waters from 4.4 Ma to 3.3 Ma, possibly indicating reversed throughflow at greater water depths. DE:
HR: 1340h AN: PP33A-0914 TI: An Excess $^{226}$Ra Geochronology for Saanich Inlet AU: * Grayson, R et al. EM AB: When examining past environmental and climatic change the ability to date both freshwater and marine sediments is essential. Numerous methods are currently available, however where present techniques fail, novel dating techniques are required to overcome these obstacles. In particular the use of $^{14}$C to date sediments over the Holocene period can be severely limited where there are significant hard-water and reservoir effects and where reworking of organic matter occurs. The use of unsupported or excess $^{226}$Ra offers a potential dating tool in such depositional contexts over the Holocene time period as a result of its half-life of 1600 years. Indeed, the technique has been applied to a number of environments since first being proposed by Koide et al. (1976). However, numerous question marks still surround the application of the technique, particularly with reference to the dating of sub-aqueous sediment deposits. As part of wider research into the applicability of excess $^{226}$Ra to date lake sedimentary environments, deep-sea samples from Saanich Inlet were obtained from the ODP (Leg 169S) in order to validate the dating technique. Saanich Inlet is an anoxic fjord located on the coastline of Vancouver Island, British Colombia, the sediments of which have been shown to be comprised of lamina-scale alternations between diatom-rich and diatom-poor clays and silts representing annual. Using digital sediment colour analysis Nederbragt and Thurow (2001) constructed a varve chronology for the last 6000 years. Alpha-spectrometry was successfully used to measure $^{226}$Ra, $^{230}$Th and $^{234}$U in sediment samples collected from Saanich Inlet during ODP Leg 169S. These activities were used to determine an excess $^{226}$Ra geochronology for Saanich Inlet. This radiometric chronology compares well with dates obtained from the varve record, and spans two different phases of sediment accumulation. DE HR: 08:45h AN: PP51G-04 TI: Nitrogen isotopic composition of ammonium released during diagenesis of organic matter under steady-state and non-steady state conditions in marine anoxic sediments AU: * Prokopenko, M et al. EM AB: The d15N of organic matter in marine sediments has been successfully used as a paleoceanographic proxy. However, diagenesis may alter the original isotopic ratio. One approach to evaluate the sign and magnitude of the diagenetic impact is to measure the isotopic composition of ammonium that is produced during the degradation of nitrogenous organic matter (N-org). If diagenesis of organic matter is the only process affecting ammonium concentration and its isotopic composition, the $\delta$15N of ammonium should reflect the isotopic ratio of the N-org plus fractionation, if any. We evaluated the impact of diagenesis on $\delta$15N of N-org on a time scale of few thousand years in two California Borderland Basins, Santa Barbara (SBB) and San Nicolas (SNB). We found ammonium to be about 2.5 \permil heavier than the bulk N- org. One interpretation is that N-org consists of multiple, isotopically distinct fractions of organic matter with variable lability. The most labile fraction must be 2.5 \permil heavier than the bulk N-org. The relatively large loss of N-org in SNB (50 %) should have resulted in a 2 \permil shift in $\delta$15N of N-org downcore, while in SBB, higher accumulation rates led to smaller loss of N-org (15%) and little change in its isotopic composition. Sediment from the Peru-Chile margin, collected during ODP Legs 201 and 202, was used to evaluate the diagenetic impact on a time scale of millennia to millions of years. In rapidly accumulating anoxic coastal sediments with constant $\delta$15N in the N-org , we found diagenetic fractionation is less than 1 \permil. Several other ODP sites are also strongly influenced by non-steady state conditions, and the isotopic composition of pore water ammonium primarily reflects changes in $\delta$15N of the source organic matter through time. Preliminary model results show that isotopically heavy ammonium released from organic matter deposited within the last 12-15 Kyr has diffused about 30 m into the sediments. This result underscores the importance of recognition and proper evaluation of non-steady state conditions. DE HR: 0800h AN: PP11B-0566 TI: The Composition and Flux of Terrigenous Material from the late Paleocene to the early Eocene in the Indian Ocean AU: * Nicolo, M J EM AB: Stable isotope records of both marine and terrestrial origin constructed from numerous widespread locations show a characteristic sequence of large amplitude variations in \delta $^{18}$O and \delta $^{13}$C between ca. 60 and 50 Ma, suggesting major changes in global climate and carbon cycling from the late Paleocene to the early Eocene. Continental weathering and atmospheric circulatory systems should have varied in response to these global fluctuations. In this regard, the flux, composition and grain- size of both eolian and hemipelagic (terrigenous) components of oceanic sediments should be affected by the intensity of atmospheric circulation and changes in terrestrial climate and weathering respectively. Deep-Sea Drilling Project Site 215 (near Ninety- East Ridge), Ocean Drilling Program Site 752 (Broken Ridge), and Ocean Drilling Program Site 762 (Exmouth Plateau) are located in the Indian Ocean, have well-dated early Paleogene sections, and are applicable to these systems in different ways (e.g. are varied by latitude and type of terrigenous material they likely received during the time interval of interest). Following early work at ODP Site 215 (Hovan and Rea, 1992), here we present records of the terrigenous component at these sites, including mass accumulation rate (MAR), grain-size, and mineralogy (XRD). These records coupled with future work in the southern Atlantic and southern Pacific oceans provide a basis for understanding early Paleogene climate changes in the Southern Hemisphere, as well as constraints for future modeling. DE
HR: 16:30h AN: PP44A-03 TI: Glacial ITCZ Shifts Recorded by Tropical Salinity Reconstructions in the Pacific and Caribbean AU: * Spero, H et al. EM AB: A variety of data from terrestrial, marine and modeling studies indicate that the tropical Atlantic and Pacific ITCZ was shifted considerably south of its current position during the last glacial period. The effect of such a shift on the glacial ocean would be to increase surface salinity (relative to today) in regions that are currently influenced by the ITCZ and to decrease salinity in regions that are currently south of the modern ITCZ but within the influence of the glacial ITCZ. Here we compare a previously published 380 ka \delta$^{18}$O$_{sw}$ reconstruction (a proxy for salinity) for the western equatorial Pacific (WEP) at ODP Site 806B ($0.33\deg$N, $159.34\deg$E) (Lea et al. 2000) with a new Caribbean \delta$^{18}$O$_{sw}$ reconstruction at ODP Site 999A ($12.75\deg$N, $78.75\deg$W) that was derived from Mg/Ca (a proxy for SST) and \delta$^{18}$O data from a surface dwelling foraminifera, {\it Globigerinoides ruber}. These reconstructions indicate the WEP was considerably fresher during past glacial periods with surface \delta$^{18}$O$_{sw}$ 0.3 to 0.4 \permil lower than today after removal of ice volume. Using modern \delta$^{18}$O$_{sw}$ vs salinity relationships, this geochemical change suggests glacial surface salinities in the WEP at Site 806B were ~1-1.5 psu lower than today. In contrast, Caribbean surface waters were much saltier during the last glacial period with \delta$^{18}$O$_{sw}$ 0.5 \permil higher than modern after removal of ice volume. This \delta$^{18}$O$_{sw}$ shift translates to a glacial surface salinity $>$2 psu higher than today (after the influence of ice volume was removed). Reconstruction of surface salinities across 3 glacial cycles back to 380 ka at these two sites demonstrate that the Caribbean and WEP were antiphased with large salinity differences during glacials and nominal differences during interglacials. Tropical western Pacific sediment trap data indicate the maximum {\it G. ruber} flux is during the summer months. Hence, we interpret these data to indicate that the glacial summer ITCZ was located over the equator in the WEP, considerably farther south than its current position at $8-10\deg$N. In contrast, the elevated Caribbean salinities support terrestrial and coastal Cariaco Basin data that indicate the ITCZ was situated over the over South America during the summer months. We are optimistic that future \delta$^{18}$O$_{sw}$ records from adjacent tropical sites will permit us to reconstruct the continuous migration of the ITCZ through time. DE: HR: 1340h AN: PP33A-0911 TI: Differentiation of Cenozoic Eolian Dust Sources in the Eastern Pacific by Nd-Sr-Pb Radiogenic Isotopes AU: * Stancin, A et al. EM AB: DSDP, ODP and piston core samples from the eastern Pacific provide a temporal and spatial context for mapping changing sources of eolian dust during the Cenozoic Era (65 Ma to present). We examined core sites from ODP Sites 469, 495, 853, 885/886, DSDP Sites 32, 319, 320, and piston core sites EW9709-01, 07 for Pb, Sr and Nd isotopic provenance. Isotopic analyses were performed on the $<$63 micron extracted detrital component following reductive cleaning to remove all authigenic and biogenic components. Downcore comparison of continental margin sites with those dominated by pelagic clays from north and south of the equator was facilitated by factor analysis using two programs. Multivariate factor analysis was performed with both CABFAC and Minitab. Three factors were identified and accounted for 98.4% of the variance. Factor 1 (epsilon Nd and Pb 207/206) defines the dominant late Cenozoic Asian dust source and accounts for 44.1% of the variance. Factor 2 identifies a South American dust source based on $^{87}$Sr/$^{86}$Sr and Pb 206/204, 208/204 and 207/204 and accounts for 36.5% of the variance. Factor 3 identifies a North American dust source ($^{87}$Sr/$^{86}$Sr, Pb 208/206, and Pb 207/206) and accounts for 17.8% of the variance. We conclude that in the eastern Pacific, late Cenozoic Asian dust sources can be quantitatively differentiated from both North American and South American continental sources. We are attempting to extend this record back to 65 Ma, with the ultimate goal being to reconstruct long-term Cenozoic atmospheric circulation and wind patterns across major climate transitions. DE HR: 0800h AN: PP11A-0556 TI: The Nature of the $\delta$$^{13}$C of Periplatform Sediments: Implications for stratigraphy AU: * Swart, P et al. EM AB: The carbon isotopic composition ($\delta$$^{13}$C) of bulk carbonates, obtained from a transect of sites drilled through platform and periplatform sediments of Holocene to Early Miocene age, have been compared to ascertain whether changes in the $\delta$$^{13}$C can be correlated between sediments of equivalent ages and whether such changes can be related to global changes in the $\delta$$^{13}$C of the dissolved inorganic carbon in the oceans over this time period. Five of the sites were drilled during Leg 166 of the Ocean Drilling Project (1003-1007) in a transect ranging from five km to 25 km away from the platform margin and penetrating sediments of Holocene to Oligocene age that are contained in 17 depositional sequences (A-Q). Two shallow water sites, Clino and Unda were situated on a extension of the same transect on Great Bahama Bank in a water depth of 10-15 m. With the exception of Unda and Clino, the $\delta$$^{13}$C of the carbonates range in isotopic composition from +5% in the younger sequences to +1% in the Early Miocene. In each of the sites the $\delta$$^{13}$C is strongly positively correlated with the percentage of aragonite. As a consequence the $\delta$$^{13}$C of sequences A through F is strongly correlated, reflecting the decreasing amount of aragonite with increasing depth. In the two platform sites, the $\delta$$^{13}$C is significantly more negative in the younger portions of the cores as a result of the influences of meteoric diagenesis during repeated exposure during the Pleistocene. Although the $\delta$$^{13}$C of the individual sequences can be correlated in most instances between the ODP holes, the changes are not related to global changes in the d13C of the oceans which in contrast to the $\delta$$^{13}$C of the platform sediments become isotopically more negative towards the present day. Instead the $\delta$$^{13}$C appears to be related to varying contributions from $\delta$$^{13}$C rich bank-top sediments. While the results from this study may not be universally applicable to all carbonates associated with shallow water platforms formed throughout geological time, they certainly cast a note of caution that apparently related changes in the carbon isotopic composition can be caused by mechanisms other than global changes in the carbon cycle. DE HR: 0800h AN: PP11A-0550 TI: Orbitally Paced Climate Variability During the Middle Miocene: High Resolution Stable Isotopes and Fe Records From the Western and Southeastern Pacific AU: * Holbourn, A et al. EM AB: We present continuous high resolution middle Miocene benthic foraminiferal isotope ($\sim$ 4-ky) and XRF scanner Fe ($<$ 1-ky) records from two deep-sea cores in the western and southeastern Pacific (ODP Sites 1146 and 1237). These records provide new insights into the pacing of climatic variability across the middle Miocene climate transition. Spectral analyses of the $\delta$$^{13}$C records from Sites 1146 and 1237 and the Fe record from Site 1237 reveal spectral power concentrated in the eccentricity band (400-ky, 100-ky) over the time interval from 13 to 17 Ma. In the $\delta$$^{18}$O records, a switch occurs at $\sim$ 14.9 Ma from predominant 100-ky eccentricity to 41- ky obliquity periodicity, suggesting a shift in the ocean-climate response to orbital forcing from the low to the high latitudes. The $\delta$$^{18}$O obliquity signal, mainly attributed to the waxing and waning of an expanded southern polar ice sheet, is pervasive in the $\delta$$^{18}$O records until $\sim$ 13.9 Ma, when a sharp increase in $\delta$$^{18}$O values indicates a further climatic transition (major expansion of East Antarctic Ice Sheet). This critical step into the "icehouse-world" coincided with a further switch in the $\delta$$^{18}$O records from the obliquity (41-ky) to the eccentricity (100-ky) band. DE HR: 1340h AN: PP23A-1397 TI: High Latitude and Tropical Climates Linked Prior to the Onset of Northern Hemisphere Glaciation: Evidence From the Eastern Tropical Pacific AU: * Lawrence, K et al.
AB: The last major climatic transition in Earth's history occurred between the Pliocene and Pleistocene epochs. This transition witnessed a substantial increase in the variance of Earth's climate in response to changes in orbital obliquity at $\sim$3 Ma, approximately coincident with the onset of Northern Hemisphere glaciation. A recent theory suggests that the start of this transition also marks a fundamental shift in the ocean's heat budget from a state of local equilibrium prior to $\sim$3 Ma, to a state in which heat absorbed in low latitude upwelling zones is balanced by heat removed at high latitudes after $\sim$3 Ma. In this remotely balanced state, changes in the distribution of high latitude insolation due to changes in orbital obliquity can be communicated from the high to low latitudes via the thermocline. To evaluate this theory, we use the alkenone organic proxy on sediments from Ocean Drilling Program (ODP) Site 846 ($3\deg$S, $91\deg$§W) in the Eastern Equatorial Pacific (EEP), documenting orbital scale variations in sea surface temperature (SST) and productivity in the largest upwelling zone on Earth over the past 5 Myrs. Our U$^{k'}$$_{37}$ temperature record shows that SST decreased by $\sim$$1\deg$C/Myrs from a high of $28\deg$C in the early Pliocene to a low of $20\deg$C in the late Pleistocene. A dramatic increase in paleoproductivity occurred $\sim$3 Ma followed by a sharp decline $\sim$1.5 Ma. Evolutive spectral analysis of sea surface indices and benthic oxygen isotope data from ODP Site 846 show that before 1 Ma all three proxies were dominated by obliquity variations and that these variations were modulated by the 1.2 Myr obliquity envelope. Evolutionary cross-spectra further indicate that in the obliquity band, the phase relationships between these three climatic indices remain essential constant throughout the entire 5 Myr interval, with EEP SST and paleoproductivity essentially in phase and both of these proxies leading benthic $\delta$$^{18}$O by $\sim$4 kyrs. The constancy of phase between SST, paleoproductivity, and ice volume implies that the physical mechanisms governing the climate of the EEP have persisted for at least the past 5 Myrs and that the high latitudes and the tropics were linked at least 2 Myrs before the onset of Northern Hemisphere glaciation. These results do not rule out a major reorganization of the sources and sinks of the Earth's heat budget, but suggest that if it occurred, it took place prior to 5 Ma. However, the EEP was not entirely unaffected by the onset of Northern Hemisphere glaciation. The major increase in productivity and cooling of SST at $\sim$3 Ma suggest a dramatic strengthening of the EEP upwelling system at this time. DE: HR: 0800h AN: PP11B-0561 TI: Extreme Acidification of the Deep Sea at the Paleocene- Eocene Boundary: New Constraints From Ocean Drilling Program Leg 208 AU: * Zachos, J et al. EM AB: A negative carbon isotope excursion and a rise in global temperature at the Paleocene-Eocene boundary have been attributed to the rapid release of as much as 2000 Gt of methane. In theory, the subsequent oxidation and uptake of this carbon by the ocean should have lowered deep-sea pH and carbonate ion content ([CO3]), thereby triggering a relatively rapid (~10-20 kyr) shoaling of the oceanic lysocline and calcite compensation depth (CCD) followed by more gradual (~40 kyr) recovery via silicate weathering of continental rocks. Here, we provide inorganic carbon, carbon isotope, and other physical property and geochemical data from a vertical array of deep-sea cores that constrain the timing and magnitude of CCD migration during the Paleocene-Eocene Thermal Maximum (PETM). The cores, Sites 1262, 1263, 1265, 1266, and 1267, were recovered from between 2.7 and 4.8 km water depth on the flanks of Walvis Ridge in the South Atlantic during ODP Leg 208. In each section, the Paleocene-Eocene boundary is marked by an abrupt transition from carbonate-rich ($>$90%) chalk or ooze to a clay rich layer ($<$1% CaCO3), the thickness of which increases (5-35 cm) from the shallowest to deepest core. With high-resolution carbon isotope and other records, we correlate the carbon records to each other and to the carbon isotope record of ODP Site 690, one of the more expanded marine P-E boundary sections. The comparison shows that the CCD shoaling was relatively fast coinciding with the initial phase of the carbon isotope excursion, while the recovery of the CCD over the 2 km transect took between 30-50 kyr. The rapid shoaling and gradual descent support the hypothesis that an anomalously large mass of carbon was rapidly released at the Paleocene-Eocene boundary. We also posit that this extreme decline in oceanic carbonate saturation to paleodepths shallower than 1.4 km contributed to the mass extinction of benthic foraminifera. UR
HR: 14:25h AN: PP13B-04 INVITED TI: Calcareous Nannofossils and Orbitally Tuned Cyclostratigraphy in the Cenozoic AU: * Raffi, I EM AB: The well known reputation of calcareous nannofossils as powerful biostratigraphic and dating tools has been improved in the last two decades, with a decisive advance towards consistently successful biostratigraphy. This has been obtained by improving the nannofossil database, following the pioneering paper of Backman and Shackleton (1983), with the application of a strategy that combines quantitative data-gathering techniques with high resolution sampling. The effort to optimize the analytical methodologies, in the study of an increasing numbers of suitable sedimentary successions, has generated excellent results for different intervals of geological time. The improvement of database is linked to improvements in the quality of sedimentary successions, as the high-quality sediment cores recovered by the Ocean Drilling Program (ODP). It has been proved that high-quality biostratigraphic data provide the potential for high resolution calibration between nannofossil biohorizons and the other records used for dating as, specifically, orbitally tuned cyclostratigraphy. In this way the accurate time resolution, which distinguishes this data sequence, is transferred to the biohorizons, and a precise biochronology is obtained. On the other hand, detailed nannofossil biostratigraphy can be used to provide preliminary control points for the astronomical tuning of cyclostratigraphic records. This rigorous approach in the study and use of calcareous nannofossils has been greatly stimulated by Nick Shackleton. The introduction of orbitally tuned time-scales has been crucial for the chronological precision of nannofossil biohorizons, and has provided an accurate chronologic framework which is continuously improved, in various intervals of the Cenozoic. Furthermore, an accurate database on ancient nannofossil communities provides informations useful for clarifying their possible paleoceanographic meanings and their paleoecological affinities, and for describing the evolutionary "behaviour" of nannofossils during prominent climatic episodes and climatic transitions. DE HR: 0800h AN: PP11B-0567 TI: Paleoceanographic changes in the western tropical Atlantic during the late Paleocene (59-55 Ma): high-resolution stable isotope records from ODP Leg 207 Site 1258 AU: * Romano, M et al. EM AB: High-resolution isotopic records are being developed for the late Paleocene (59-55 Ma) from cored materials from ODP Leg 207 Site 1258 to evaluate oceanographic changes leading up to the Paleocene/ Eocene Thermal Maximum (PETM). Site 1258 is located on the western slope of the Demerara Rise, $\sim$380 km north of Suriname. It was drilled in 3,192 meters of water and is the deepest water site of the paleoceanographic transect drilled for Leg 207. Site 1258 contains an exceptional sedimentary archive of late Paleocene oceanographic and climate changes based on high sedimentation rates and pristinely preserved benthic foraminifers, providing the requisite material to study deep-sea changes in the western equatorial Atlantic. The late Paleocene $\delta$$^{18}$O record at Site 1258 contains low values from 58 Ma until near the PETM at Site 1258, which are consistent with bottom water temperatures of up to 10$\deg$ to 12$\deg$C. These low $\delta$$^{18}$O values result in a significant gradient (up to $\sim$1$\permil$) between the equatorial Atlantic and the southern ocean (e.g., Site 690) bottom waters. This suggests at least two bottom water sources existed during this time, one originating from the southern ocean region and another from either the Tethys Sea or somewhere near the equatorial Atlantic regions. A number of isotopic excursions occur in both the $\delta$$^{13}$C and $\delta$$^{18}$O records between 57 Ma and before the PETM. These are characterized by $\delta$$^{13}$C changes of over 1$\permil$ and $\delta$$^{18}$O changes of up to $\sim$0.7$\deg$ (equivalent to $\sim$ 3$\deg$ C). Similar events were previously identified in records from the North Pacific Ocean Site 577, which were interpreted to be restricted to the Pacific basin. Although limitations in age control cannot unequivocally show whether these events were synchronous at both sites, these results indicate that these brief abrupt deep-sea warming events occurred in both the Atlantic and Pacific basins, indicating that they were global in nature. DE HR: 1340h AN: PP13A-0599 TI: Timing of Late Quaternary sea surface temperature change: Evidence from high-resolution {\it Globigerina bulloides} Mg/Ca records from the California Margin AU: * Pak, D et al. EM AB: The role of the Pacific Ocean in climate evolution remains a fundamental question in paleoceanography of the late Quaternary. High-resolution sedimentary sections from the California margin provide a valuable opportunity to address the mechanisms of how heat is transmitted through the extra-tropical Pacific by closely examining the phasing of sea surface temperature relative to ice volume changes in a region far removed from the direct effects of continental ice sheets. We present high-resolution {\it Globigerina bulloides} Mg/Ca records from two sites on the central California Margin. ODP Site 1017E (off Point Conception, California; 955 m) provides a millennial-scale sea surface temperature record to 60 kyr; MD2504 (Santa Barbara Basin; 440 m) provides a centennial-scale record through the Last Glacial Maximum. These records, together with oxygen isotopic data, provide a window into the timing of sea surface temperature change on the deglacial as well as during short-term climate events in Marine Isotope Stage 3. At Site 1017E temperature oscillations in MIS3 were synchronous with $\delta^{18}$O and had an amplitude of as much as $6\deg$C, on average $2\deg$C larger than those inferred by $\delta^{18}$O. Comparison between the Mg/Ca records from the two sites indicates that within the resolution of the age models, the amplitude and timing of SST changes were equivalent between Santa Barbara Basin and Point Conception, suggesting that there was not a strong local overprint on temperature change along the California margin. Mg/Ca records indicate that full glacial sea surface temperatures were approximately $8\deg$C. Both sites show a prominent pre-Bolling temperature oscillation of 2-$3\deg$C, followed by an abrupt glacial-interglacial temperature change of 7-$8\deg$C that occurred synchronously with $\delta^{18}$O. DE: HR: 0800h AN: PP51F-1373 TI: Surface and Thermocline Variability of the Eastern Equatorial Pacific During the Last 80,000 yr: Results from ODP Site 1240 AU: * Cacho, I et al. EM AB: Recent hypothesis consider low latitudes as the source region for past global rapid climatic changes. In this sense, the Eastern Equatorial Pacific (EEP) is an area with great potential to trigger global changes due to its active role in the El Ni€o-Southern Oscillation (ENSO). Here we present results obtained from ODP 1240 (Leg 202, 0§ 01.31'N, 86§ 27.76'W, 2921 mbsl) on paired stable isotopes (d18O, d13C) and trace elements (Mg/Ca) on planktonic foraminifera. Multiple species with different dwelling preferential depths were studied to reconstruct both surface and thermocline characteristics. Core-top Mg/Ca inferred temperatures are in good agreement with current mean annual sea surface temperature (SST) and deep thermocline temperatures (DTT) as recorded from available data from hydrographical stations. Our reconstruction covers the last ~80 kyr, including the entire last glacial period, the glacial-interglacial transition and the Holocene. Chronostratigraphy is currently in progress, but initial results evidence strong changes in sedimentary rates. Higher accumulation rates are recorded during the glacial time and deglaciation, likely reflecting changes in the intensity of the upwelling system (cold tongue expansion). In general, sedimentation rates are relatively high for the region (8-15 cm/kyr) which makes Site 1240 particularly valuable for the study of rapid climatic variability. Results are still preliminary but several rapid oscillations of about 1- 2C are observed during MIS 3 in both, SST (G. ruber) and DTT (N. dutertrei) records. Thermocline structure also changed in relation to these oscillations. Last deglaciation is seen as a SST (G. ruber) warming of about 4§C, while lower DTTs (N. dutertrei) increase only about 2§C. This early warming preceded the isotopic depletion of the last deglaciation. A middle deglaciation abrupt cooling event of about 3§C (SST) and 1§C (DTT) interrupted the gradual warming and nearly returning to full glacial conditions. During the Holocene two main periods are easily distinguishable in both d18O and Mg/Ca records. Early Holocene is characterized by higher Mg/Ca and relatively high d18O values whereas Late Holocene presents lower Mg/Ca and lower d18O levels. DE HR: 0800h AN: PP11B-0558 TI: Decoupled Shelf-Ocean Phytoplankton Productivity Responses Across the Paleocene-Eocene Thermal Maximum AU: * Gibbs, S et al. EM: AB: Significant transformations in the global biosphere accompanied dramatic global warming and profound perturbation of the carbon cycle during the Paleocene Eocene Thermal Maximum (PETM, $\sim$55 Ma). These abrupt changes have been linked to a massive release of light carbon into the ocean-atmosphere system. Increased phytoplankton productivity has been cited as a mechanism responsible for subsequent CO$_{2}$ draw-down. However, interpretations of geochemical and biotic data differ on where this increased productivity occurred. Here we constrain the loci of increased productivity using highly detailed nannofossil assemblage data. Calcareous nannofossils provide an excellent basis to monitor changes in primary production during the PETM given their sensitivity to surface water conditions, especially availability of nutrients. We present nannofossil assemblage records from productivity end-member environments: a central gyre setting (ODP Site 1209, Shatsky Rise, paleo-equatorial Pacific), a high- latitude, open-ocean setting (ODP Site 738, Indian Ocean sector of the Southern Ocean) and a neritic setting (USGS Wilson Lake drill hole, New Jersey). Nannofossil assemblages at all three sites display a pattern of continuous reorganization during the PETM. In particular, assemblage shifts at Shatsky Rise demonstrate a short-lived interval of extremely low productivity coincident with the carbon isotope excursion. In contrast, assemblages at Wilson Lake suggest a transient shift to more mesotrophic conditions. Combined with published planktonic assemblage records, these data produce a global picture of productivity change across the PETM with shelf areas and the open ocean clearly decoupled regardless of latitude. Open ocean sites demonstrate a global but transient increase in oligotrophy which may have resulted from a widespread deepening of the thermocline. Shelf productivity increase is localized with mesotrophic communities spatially restricted to areas close to nutrient sources via increased precipitation and runoff. DE: HR: 1340h AN: PP23B-1432 TI: Fulfilling the Promise of the DSDP/ODP Legacy with Multiparameter Logging of Archive Cores AU: * Schultheiss, P et al. EM AB: Since 1968, the Deep-Sea Drilling Project (DSDP) and the Ocean Drilling Program (ODP) have been storing their recovered sediment and rock cores in purpose-built, refrigerated repositories. Approximately 300 km of core was recovered by DSDP and ODP at an estimated average cost of $2,000,000/km. Half of every core recovered is kept as an archive half, normally only available for viewing (subsampling requires special permissions). Sound archiving policies and storage techniques over the years have ensured that these half cores have remained well preserved for analyses that were not made, or were not technically possible, at the time of recovery. The archive half-cores are well suited for automated non-destructive geophysical measurements ("core logging"), including many of those that provide essential data for reconstructing Earth's climatic history, such as high-resolution magnetic susceptibility, natural gamma spectroscopy, and UV/VIS/IR spectrophotometry. Most of the cores have either not been logged for all the relevant parameters or have not been logged at the spatial intervals necessary for high resolution climatic studies. Consequently, a very large, untapped reservoir of paleoclimatic and other data awaits extraction from these well-preserved archive half- cores. Recently we used a new Geotek MSCL-XYZ core logger at the IODP West Coast Repository to log archive core halves recovered by D/V Glomar Challenger in 1983. We wished to obtain a high-resolution paleoclimate record for DSDP Site 594, east of New Zealand, Southwest Pacific, to complement the record obtained more recently from nearby ODP Site 1119, cored in 1998. The new MSCL-XYZ system is specifically designed to allow multiparameter, non-destructive geophysical data to be collected easily at high spatial resolutions from archive core halves. Because the data acquisition from archive cores can be slow, either because of the measurement itself or the frequency at which the data is required, the system holds multiple 1.5 m-long core sections (currently up to 9) and can be left to run unattended for hours or days at a time. We obtained complete data sets of natural gamma, magnetic susceptibility, spectral color and RGB digital line scan images for the top 150m of the sediment column at Site 594 . No useful core log data was previously available for this site. The data set of primary interest was natural gamma, which will be compared with the downhole natural gamma record from Site 1119. To our knowledge this is the first time that a high-resolution natural gamma data log has been recovered from an archive core half. Detailed magnetic susceptibility records were also obtained despite low signal levels, using 10 sec sampling time throughout. The excellent quality of the spectral color and RGB image data, despite the partially ephemeral nature of these properties, is a testament to the core storage techniques employed over 21 years. As core working halves become depleted, pressure is mounting to allow subsampling from the archive core-halves. The community now has the tools necessary to take advantage of what could be a final opportunity to collect continuous geophysical data on ocean cores drilled over the past three decades. DE HR: 0800h AN: PP51B-1333 TI: The Late Miocene Carbon Isotope Shift and Marine Biological Productivity. AU: * Diester-Haass, L et al. EM AB: The late Miocene global carbon isotope shift of approximately 1 per mil is not well understood. Is it linked to ocean-related processes such as the AŸA›A›ƒ_sAªA.ƒ_oBiologic BloomAŸA›A›ƒ_sAª \(Farrell et al., 1995\), or to changes in type \(C3/C4 plants\) or cover of terrestrial vegetation? Here we examine the evolution of marine biological productivity during the isotope shift at ODP Site 846 \(Pacific equatorial upwelling, where the AŸA›A›ƒ_sAªA.ƒ_oBiologic BloomAŸA›A›ƒ_sAª has been first described, Farrell al, 1995\) and at Indian Ocean Site 721 \(monsoon-driven upwelling\), and compare their productivity history with non upwelling locations in the Atlantic Ocean. The onset of the carbon isotope shift is accompanied at all locations by an increase in paleoproductivity derived from benthic foraminiferal accumulation rates \(expressed as gC/cm2 * ky; Huerguera, 2000\) and increased abundance of Uvigerina spp.. At the equatorial upwelling sites the increase is comparable to half present-day values to present-day values; in the Atlantic Ocean paleoproductivity increases from present-day up to 3 times present-day values. But the productivity maxima are not concurrent. The carbon isotope shift is accompanied by severe carbonate dissolution and reduced ventilation of bottom waters, as reflected in the occurrence of pyrite and good preservation of cartilageous fish debris. Carbonate preservation is good since about 6 Ma despite high productivity. We discuss changing deep water circulation patterns, increased weathering and continental nutrient delivery, as well as erosion of terrestrial vegetation as possible factors to explain our findings. DE:
HR: 16:00h AN: PP44A-01 INVITED TI: Deep Ocean Temperature and Salinity at the Last Glacial Maximum AU: * Adkins, J and Schrag, D AB: Sediment pore fluids from the deep ocean contain a record of the bottom water salinity and $\delta$$^{18}$O due to the last glaciation. Storage of water on land as glacial ice imparts a global signal of increased salinity and enriched oxygen isotopic values in the abyssal ocean and changes in deep circulation patterns can impart an additional local signal. In the mean this signal was about 3.5% in salinity and about 1.0\permil in $\delta$$^{18}$O, but has been diffusing and advecting away over the last 20,000 years. Today, high resolution sampling (every 1.5 meters) coupled with high precision geochemical analyses of pore fluids from a single core can be used, in conjunction with a 1-D pore fluid diffusion model, to reconstruct the Last Glacial Maximum (LGM) salinity and $\delta$$^{18}$O at that site. We have done this analysis for several globally distributed Ocean Drilling Program (ODP) holes including some new unpublished data from the equatorial Pacific. In addition, benthic foraminiferal measurements of modern and LGM CaCO$_{3}$ $\delta$$^{18}$O, coupled with the water $\delta$$^{18}$O reconstruction, can be used to constrain the deep-water temperature change from LGM to today. Plotted as a T/S diagram for the LGM, our data show that the entire deep ocean cooled to about $-$$1.0\deg$C potential temperature. This relative homogeneity in temperature is contrasted by much larger than modern salinity gradients in the deep. Due to increased sea ice export, the Southern Ocean was by far the saltiest water mass in the LGM, and as a result the modern salinity contrast between NADW and AABW was reversed. Stratification of the LGM deep ocean was largely controlled by salinity (as opposed to temperature today) and this feature has important implications for the stability of the LGM overturning circulation. With salty waters filling the deep LGM Ocean, it is difficult for fresh water changes at the surface of the North Atlantic to alter the abyssal circulation. Before freshwater forcing can trigger circulation changes, some other forcing must first increase the buoyancy of the deep Southern Source waters. In addition, the combination of our water $\delta$$^{18}$O data and a global database of benthic $\delta$$^{18}$O imply that the deep Pacific was warmer than the deep North Atlantic at the LGM. DE
HR: 08:15h AN: PP31B-02 INVITED TI: Tracking Warm Saline Deep Water on Maud Rise Using Nd Isotopes AU: * Martin, E et al. EM AB: Evidence for the production and export of Warm Saline Deep Water (WSDW) to the southern high latitudes during the Paleogene is equivocal and widely debated. The strongest support for WSDW in the Southern Ocean are discrete intervals of benthic $\delta$$^1$$^8$O inversions between vertically offset sites on the Maud Rise, ODP sites 689 (2080m) and 690 (2914m), which were interpreted as temperature inversions. During these intervals a warm bottom water mass is believed to have occupied site 690. Nd isotopes in fossil fish teeth reflect water mass mixing and are unaffected by changes in temperature, salinity, nutrients, or productivity. We present Nd isotope records for sites 689 and 690 that cover the middle Eocene to the late Oligocene and which have been correlated by Sr isotope chemostratigraphy. The Nd isotope data support the incursion of a distinct water mass at depth in the middle Eocene and portions of the Oligocene. During these intervals $\epsilon$$_N$$_d$ values at site 690 are 1$\epsilon$ unit less radiogenic than those at site 689, reaching minimum values of -9.3 to -10. The $\epsilon$$_N$$_d$ minima at site 690 coincide with $\delta$$^1$$^8$O inversions. In the Paleogene, potential sources of deep water masses characterized by such nonradiogenic $\epsilon$$_N$$_d$ values include the North Atlantic, Southern Ocean, and Tethys Sea. However, the North Atlantic is an unlikely source of such a strong signature to the high latitude Southern Ocean and Paleogene $\epsilon$$_N$$_d$ values of Southern Ocean deep waters are too radiogenic to account for the Maud Rise Nd data. Further, we argue that a Southern Ocean water mass should influence both sites, and the data clearly support instances when more than one water mass was present. The Maud Rise Nd isotope data is best explained by the export of Tethys sourced WSDW to the Southern Ocean. Authigenic shelf deposits from obducted Tethys margin sediments indicate that shallow Tethys seawater had $\epsilon$$_N$$_d$ values of -9.2 to -9.7, suggesting that deeper waters were less radiogenic. These values are also consistent with modern Mediterranean outflow (-9.4). The pulsed export of WSDW to the Southern Ocean from a low latitude source accounts for the coincidence of $\epsilon$$_N$$_d$ minima at site 690 with $\delta$$^1$$^8$O inversions between sites 689 and 690. DE
HR: 1340h AN: PP13A-0601 TI: Primary Productivity Changes in the subtropical western North Atlantic During Marine Isotope Stages 11-12: Inferences from Benthic Foraminifera AU: * Poli, M et al. EM AB: The time interval referred to as Marine Isotope Stage 11 (MIS 11, ~423 to 362 ka) is characterized by a configuration of earth's orbit similar to that of the Holocene, and is therefore a good analog for our current interglacial. MIS 11 was probably the warmest and longest interglacial of the last 500 kyrs, characterized by sea level possibly 20m higher than today and a maximum in NADW production. In contrast, during MIS 12, sea level was about 140m below present, and the production of NADW was severely reduced. We have examined benthic foraminiferal assemblages in sediments from ODP Site 1058 (Blake Outer Ridge, 3000m water depth), and Site 1063 (Bermuda Rise, 4584m water depth) spanning the MIS 11-12 time interval at a time resolution of 500 to 3000 years. At both sites the glacial-interglacial transition is accompanied by changes in faunal composition; however, bottom environmental conditions appear to have undergone the most dramatic change at Site 1058. Here, infaunal taxa indicative of organic carbon-rich sediments dominate during glacial MIS 12, and are replaced during MIS 11 by epifaunal species indicative of oligotrophic environments. The beginning of the MIS 12 and MIS 10 glaciation is characterized by large, rapid increases in the relative and absolute abundances of {\it Epistominella exigua} both at Site 1058 and Site 1063. In the modern ocean, this species inhabits seasonally deposited aggregates of phytodetritus produced during spring plankton blooms, thus suggesting an increase in surface ocean primary productivity at these times. DE:
HR: 1340h AN: PP13A-0600 TI: MILLENNIAL-SCALE CLIMATE VARIABILITY IN THE SUBTROPICAL ATLANTIC DURING THE MIDDLE PLEISTOCENE AU: * Gibbons, F et al. EM AB: We are generating Globigerinoides ruber (white, ss) oxygen isotope and Mg/Ca records from ODP Site 1058 to assess relative climate stability in subtropical northwestern Atlantic during the mid Pleistocene, Marine Isotope Stages (MIS) 11-22. Currently, our records span MIS 11 (a portion only) through MIS 15 with a temporal resolution of about 800-1000 years. The paired Mg/Ca and d18O records allow us to reconstruct fluctuations of sea surface temperatures (SST) and the regional oxygen isotopic composition of surface water on millennial time scales during one of the most extreme glacial-interglacial transitions of the Pleistocene. Our ultimate goal is to test the hypothesis that relative climate stability is linked to the extent of continental glaciation (ice volume). The d18O record displays rapid, high amplitude variability during glacial MIS 12 and the MIS 12 to MIS 11 deglaciation. The Mg/Ca results show that the long- term trends in the temperature record follow the general glacial-interglacial pattern implying SST changes concurrent with large-scale climate change. Portions of the Mg/Ca record generated at higher resolution reveal SST variability similar in timing to variability observed in the d18O record, particularly during MIS 13 and the MIS 13/12 transition. The total amplitude of SST changes implied by the Mg/Ca data is ~6øC, with absolute temperatures ranging from about 24 to 30øC. The current records show that this site is sensitive to millennial-scale variability during the extreme glacial MIS 12 and the MIS 12/11 deglaciation, but not in the older portion of the oxygen is record (MIS 14) thus far generated. Ultimately, the entire record will show if other glacial extremes such as MIS 16 contains similarly high variability, which would further support the hypothesis that ice sheet size plays an important role in determining the amplitude of millennial-scale climate change. DE:
HR: 0800h AN: PP51F-1368 TI: Continental and Marine Climate Records from Chile and the Southeast Pacific: Joint Pollen, Oxygen Isotope, and Radiolaria Records from ODP Sites 1233 and 1234 AU: * Heusser, L et al.
AB: Rapidly-deposited sediments (1-3m/kyr) from ODP Site 1233 (41ø0.005'S, 74ø26.992'W, 838m water depth) document millennial-scale changes in the response of Chilean plant communities to atmospheric circulation in the southeast Pacific over the past 60ka. Pollen data from the upper 95m of Site 1234 (36ø13.153'S, 73ø40.902'W) replicate and extend the terrestrial record through the last glacial cycle (MIS 1-MIS5e), thus providing the first record of vegetation and climate from the last interglacial in temperate South America. Both Sites monitor a major discontinuity in Chilean climate - the transition between northern semi-arid, summer dry-winter wet climate and southern year-round, rainy, cool temperate climate. Downcore changes in diagnostic pollen from xeric and mesic vegetation (Lowland Deciduous Beech forest, Valdivian Evergreen Forest, and Subantarctic Evergreen Forest and Parkland) reflect frequent latitudinal shifts of the southern westerlies during MIS 2 and MIS 3. During most of the last glacial, cool, mesic rainforests composed of evergreen beech (Nothofagus dombeyi) and conifers, such as the endangered Prumnopitys andina, characterized coastal Chile. Late Pleistocene, intervals of heavy rainfall and lower temperatures inferred from expansion of Subantarctic Parkland correspond with regional glacial events, and the structure and variability of southern Chilean vegetation and climate correspond with changes in marine surface waters offshore and in Antarctic ice core data. In the last 140,000 years, only during MIS 5e was vegetation of southern Chile similar to that of the Holocene. At the MIS 6/5e transition, coeval with the rapid shift to light isotopic values, glacial vegetation was rapidly replaced by plant communities associated with Mediterranean climate. An increased prominence of halophytic vegetation suggests that MIS 5e was more arid and possibly warmer than MIS 1. Lowland Deciduous Beech Forest (N. obliqua) extended well into the interval of ice growth of MIS 5d, thus interglacial conditions in southern Chile were not synchronous with global ice volume. DE HR: 13:40h AN: PP43B-01 INVITED TI: Antarctic Timing of Surface Water Changes off Chile and Patagonian Ice-sheet Response Based on ODP Site 1233 AU: * Lamy, F et al. EM AB: ODP Site 1233 off southern Chile is situated in an ideal location to study Southern Hemisphere millennial-scale climate variations during the last glacial. We present records of surface ocean conditions in the southernmost Peru-Chile Current and associated changes in the extent of the Patagonian ice-sheet in adjacent southern Chile covering the last ca. 70,000 years. Sedimentation rates at this continental margin site are extraordinarily high (in the order of 1-3 m/kyr) consistent with strong fluvial discharge in response to heavy continental rainfall in southern Chile and the proximity to the Patagonian ice-shield (PIS) that advanced towards the Chilean Lake District (directly onshore Site 1233) during the last glacial providing terrigenous material via glacial erosion. This proximity to the ice-sheet provides the excellent opportunity to compare continental and marine paleoenvironmental signals within the same well-dated archive. Millennial-scale SST changes closely parallel the temperature changes recorded in Antarctic ice-cores. Including other records from the Southern Hemisphere mid-latitudes, our data suggest a quasi-hemisphere-wide response that is consistent with the bipolar see-saw mechanism but may also imply a more prominent role of the Southern Hemisphere in the origin and transfer of millennial-scale climate variations during the last glacial. Compositional changes in the terrigenous sediment input, interpreted to primarily represent changes in the extent of the PIS, show a similar pattern as SST changes but reveal a lagged response of the terrestrial signal most likely related to climate inertia of the PIS. During the deglaciation, paleosalinity data suggest that meltwater input from the ice-sheet started up to ca. 1000 years after the onset of deglacial warming. During early isotope stage 3. however, a lag between SST and PIS changes appears to be absent. Spectral analyses suggest that both proxy records are characterized by higher short-term variability in this interval. Though the general pattern of the records is still very similar to the Antarctic records, we speculate that the short-term variability may origin from the tropics during warmer intervals of the last glaciation. DE HR: 0800h AN: PP31A-0887 TI: Planktonic Foraminifera Study at Site ODP 999A (Caribbean Sea): Insights into Oceanic Exchange and Paleocirculation During the last 450 Kyrs. AU: Vautravers, M et al. EM AB: A recent micro-palaeontological study of a core from the South Atlantic (Peeters et al., Nature. 430, 661, 2004) stresses the importance of the Agulhas leakage intensity as a key control on North Atlantic Thermohaline operation. Planktonic foraminifera counts were conducted on the Colombian Basin core ODP 999A ($12\deg$N, $74\deg$W, 2878 m); results are presented on a SPECMAP-based age model (Schmidt et al., in prep 2004). At present both climate and surface circulation are driven by the motion of the Intertropical Convergence Zone (ITCZ), which governs dry/wet seasons and upwelling intensity. Caribbean surface water originates from both the south Atlantic, which re- circulates Indian Ocean water, and the north Atlantic subtropical gyre. Similarly the deep-water is a mixture of AAIW and UNADW, originating in the southern and northern hemispheres respectively. A CaCO$_{3}$ preservation index, which is deduced from planktonic fragments and pteropod remains, is used to trace changes in the intermediate water mixture. This study confirms that the sediments are better preserved during glacial times. Furthermore, it shows that the sediments of MIS11 are intensely dissolved, suggesting a maximal contribution of AAIW. Over the last 450 kyr, we observe a decreasing contribution of the AAIW during both interglacial and glacial times. In addition, the Holocene appears unusual, with a low AAIW to UNADW ratio in comparison to previous warm intervals. An examination of the percentages of the surface Indo-Pacific species {\it G. menardii} seems to confirm part this result, identifying MIS11 as a time of maximal Indian-Atlantic exchange via the Agulhas 3valve_. It also confirms that during MIS2, 3 and 4, Caribbean surface waters were unusually unfavourable for this species and/or that the Agulhas connection was absent. The % of {\it G. Hexagona}, another Indo-Pacific species, which lives in deeper thermocline waters, peaks during MIS11, MIS9e, MIS7c and MIS5e but is absent during the Holocene and MIS7e. This observation suggests a slightly different scenario for the intermediate water flowing through the 3valve_. This confirms the peculiarity of the Holocene as was found on the basis of benthic \delta$^{13}$C measurements in the North Atlantic (Raymo et al., Paleoceanography. 19, PA2008, 2004). Finally, on the basis of the species mentioned above in the Caribbean Sea we cannot find evidence of enhanced exchange between the Indian and the Atlantic at the end of the past five glacial as found in the Agulhas area. This disagreement and the factors controlling the late reappearance of these species in the Caribbean Sea need further investigation. DE HR: 17:15h AN: PP44A-06 TI: Gulf Stream Salinity Variation During MIS 3 and its Link to D-O Cycles AU: * Schmidt, M et al. EM AB: Paleoclimate archives indicate that Marine Isotope Stage 3 (MIS 3) was characterized by a highly variable climate, expressed in the Greenland ice cores by the Dansgaard-Oeschger (D-O) fluctuations associated with large temperature changes (Johnsen et al., 2001). However, the question remains as to the trigger for these abrupt Northern Hemisphere climate swings. A popular theory implicates thermohaline circulation instability as a driver for D-O cycles, suggesting that salinity variability in surface waters delivered to the sub-polar North Atlantic via the Gulf Stream may have played a role in driving millennial-scale oscillations in glacial thermohaline circulation (Broecker et al., 1990; Zaucker and Broecker, 1992). In order to investigate the relationship between Gulf Stream salinity variation and D-O cycles, we combine Mg/Ca measurements (a proxy for the temperature of calcification) with ($\delta$$^{18}$O) analyses of shells from the surface-dwelling foraminifera {\it Globigerinoides ruber} (white var.) from ODP site 1060 located beneath the Gulf Stream on the Blake Outer Ridge (36.77$\deg$N, 74.47$\deg$W; 3480 m; 20-53 cm/kyr sed. rate) to produce a high-resolution record of $\delta$$^{18}$O$_{SEAWATER}$ ($\delta$$^{18}$O$_{SW}$) during MIS 3 (49.5- 59.2 kyr, corresponding to Interstadial 13 to 16 on the SSO9sea time scale). The Mg/Ca-temperature (SST) record from 1060 shows minimal variability ($\pm$3$\deg$C) between stadials and interstadials. Average interstadial Mg/Ca-SSTs (25.2$\deg$C) agree with faunal August SST reconstructions (Vautravers et al., 2004), but stadial Mg/Ca-SST reconstructions are warmer than faunal estimates. The calculated $\delta$$^{18}$O$_{SW}$ record co-varies with the Greenland ice core $\delta$$^{18}$O record (Johnsen et al., 2001), and indicates high stadial salinities, similar to MIS 3 Caribbean salinity reconstructions (Schmidt et al., 2004), followed by abrupt decreases in $\delta$$^{18}$O$_{SW}$ up to 0.9$\permil$ occurring in less than 250 years on the transition to interstadials. We hypothesize that the input of isotopically light freshwater from melting North American ice sheets during interstadials accounts for the rapid, large decrease in Gulf Stream $\delta$$^{18}$O$_{SW}$. Our $\delta$$^{18}$O$_{SW}$ reconstruction from ODP 1060 therefore suggests that D-O cycles directly impact Gulf Stream salinity during MIS 3, with elevated salinities occurring during stadials followed by a rapid decrease of salinity into interstadials in response to Northern Hemisphere warming. DE HR: 16:00h AN: PP54A-01 TI: Evidence for an Open Drake Passage in the Late Middle Eocene AU: * Scher, H and Martin, E E EM AB: Circulation of the Antarctic Circumpolar Current (ACC) appears to require an unimpeded circumpolar path, thus arguments for initiation of the ACC hinge on the timing of tectonic gateway development in the Southern Ocean. However, timing of the onset of seawater exchange between the Pacific and Atlantic oceans through the Drake Passage is widely debated, with estimates ranging from the late Eocene to the early Miocene. Hiatuses and productivity increases in South Atlantic sediment records imply that ocean currents accelerated during the Eocene and Oligocene, though there is not yet independent and unequivocal evidence for Pacific seawater entering the Atlantic Ocean during the Paleogene. Nd isotopes in fossil fish teeth reflect water mass mixing and are unaffected by changes in temperature, salinity, nutrients, and productivity. We present the first Nd isotope record from the Atlantic sector of the Southern Ocean that covers the entire range of estimates for the opening of the Drake Passage; from ODP site 1090. The record indicates that a water mass with a Nd isotopic composition typical of Pacific seawater appeared in the Atlantic sector at 39 Ma, as illustrated by a rapid transition to radiogenic $\epsilon$$_N$$_d$ values ($\epsilon$$_N$$_d$ = -5.8). Pacific seawater was the only volumetrically significant water mass with such a radiogenic Nd signature during the Paleogene. A second transition to radiogenic $\epsilon$$_N$$_d$ values occurs at 28.5 Ma. Pronounced peaks in productivity at site 1090 coincide with the $\epsilon$$_N$$_d$ transition at 39 Ma. The data support the opening of the Drake Passage to shallow depths at 39 Ma. Moreover, the association of productivity peaks with this event implies that a shallow opening may have enabled a precursor to the modern ACC. The data also support establishment of a deep-water connection at 28.5 Ma. The interpretations imply that tectonically induced changes in ocean circulation preceded large shifts in global climate during the Paleogene. $\epsilon$$_N$$_d$ values during the late Oligocene to early Miocene covary with benthic $\delta$$^1$$^3$C values at this site, confirming the capability of Nd isotopes as a tracer of past changes in ocean circulation. DE:
HR: 0800h AN: PP51F-1375 TI: the Pliocene Evolution of E-Pacific and Caribbean SST Reveals the Final Phase of the Closure of the Panamanian Gateway. AU: * Groeneveld, J et al. EM AB: We used samples from ODP Sites 999 ($12\deg$44N, $78\deg$44W, 2828m waterdepth) and 1241($5\deg$50N, $86\deg$26W, 2027m waterdepth) to investigate the development of the sea surface temperature (SST) gradient between the East-Pacific and the Caribbean for the Pliocene interval 2.2-4.8 Ma. For Site 1241 we constructed new benthic and planktonic $\delta$$^{18}$O-records. The benthic $\delta$$^{18}$O-record was used to construct an orbitally tuned age model to which the age model of Site 999 was tuned. SST was determined by applying Mg/Ca-analyses on the planktic foraminifer Globigerinoides sacculifer. The spatial resolution for the SST-records averages 5 kyr, for the $\delta$$^{18}$O-records 3 kyr. An open gateway, permitting the throughflow of water from the Pacific into the Caribbean, leads to equal SSTs on both sides of the Isthmus. When the gateway reached the final phase of the closure, the Caribbean started to warm up and the E-Pacific cooled down, resulting in an increasing SST-gradient (E- Pacific-Caribbean SST difference). Before 4.6 Ma the Caribbean was slightly warmer than the E-Pacific by about $1\deg$C, suggesting the inflow of Pacific water into the Caribbean. After 4.6 Ma, average SST at Site 999 decreased by about $2\deg$C, while at Site 1241 average SST remained the same. This implies that no longer the same watermass is bathing both Sites, suggesting a cooler watermass, probably originating from the Peru-Chile Current, to penetrate into the Caribbean. The final phase of the closure is indicated by a change in Caribbean-Pacific SST relationships. Positively correlated SST fluctuations persisted from 4.8Ma until about 3.2Ma, before larger-scale sea level fluctuations became important in response to the amplification of the northern hemisphere glaciation. After about 3.2Ma, glacial stages (indicative of sea level low- stand) are associated with Pacific minima in SST (Site 1241) and maxima in Caribbean SST (Site 999). Thus, the cessation of the throughflow during glacials terminated the imprint of cooler Pacific surface waters in the Caribbean and allowed Caribbean temperatures to increase. This documents the final phase of the closure of the Central American Isthmus, when sea level fluctuations on the order of 50-70 m start to control the Pacific water inflow into the Caribbean. DE HR: 1340h AN: PP23A-1395 TI: Do Tropical SST Changes Lead High Latitude Climate Change, Or Are Our Proxies Misleading Us? AU: * Dekens, P et al. EM AB: Initial reconstruction of the last glacial maximum (LGM) sea surface temperature (SST) estimates showed little to no change in the world's tropical oceans. More recently, several studies have shown that the tropics were 1 to $6\deg$C cooler during the LGM and previous ice ages. These observations, as well as the timing of the SST changes, has led some researchers to hypothesize that the tropical Pacific may have played an important role in glacial/interglacial (G/IG) climate change during the late Quaternary. Uncertainty remains about the magnitude of the SST change, the spatial pattern of the changes, and the timing of tropical SST changes relative to high latitude climate transitions. For example, in the eastern equatorial Pacific (EEP) geochemical proxy data indicate that during the LGM SST was only 1 to $2\deg$C cooler at the equator , but was 2 to $3\deg$C cooler just north of the equator and in the central equatorial Pacific compared to today. Additionally, the sites on the equator record a significantly larger lead in SST compared to ice volume than one site just north of the equator. These records have been reconstructed using different SST proxies however, leading us to question if the observed geographical differences in the magnitude and timing of SST changes during recent glacial cycles could be explained by the different uncertainties inherent in each of the proxies. The EEP is a critical region because SST in this region is sensitive to changes in upwelling, and is therefore indicative of the state of the tropical Pacific, which has known air sea feedbacks that can affect global climate. A clear picture of the timing of SST changes and ice volume is needed if we are to understand the potential role of the tropical Pacific in G/IG climate change. We have generated high resolution ($\sim$2-4 k.y.) SST records at ODP site 847 ($0\deg$12'N, $95\deg$19'W, 3346m water depth) using the U$^{k'}$$_{37}$ and Mg/Ca paleothermometers extending back 500 k.y. This site provides an excellent opportunity to compare Mg/Ca and alkenone records, as it is located above the lysocline, thereby minimizing the effect of dissolution on Mg/Ca in foraminifera, and has relatively high organic matter content. The U$^{k'}$$_{37}$ SST record shows a G/IG amplitude of $\sim$$2\deg$C through MIS 8, and a larger ($\sim$5- $6\deg$C) amplitude from MIS 9-12. SST leads ice volume changes at all glacial to interglacial transitions, but the magnitude of the lead varies. Comparing the variability in these two proxies at this site over the last ~500 k.y. will increase our understanding of the behavior of these two proxies in this region, and dramatically increase our confidence in our climatic interpretations. DE HR: 15:30h AN: PP53D-08 TI: A 10 Million Year, High-Resolution Record of C4 and C3 Plant Evolution from Arabian Sea ODP Site 722 AU: * Huang, Y et al. EM AB: The Siwalik paleosol sequence in Pakistan and India and the Bengal Fan sediments indicate a major expansion of C4 plants during the late Miocene, approximately 8 to 5 Ma. However, the depositional environments of paleosol sequences and deep-sea fans result in uncertainties in chronology and sediment discontinuities. The paleosol isotopic data are also local in nature. Here, we report new high-resolution carbon and hydrogen isotopic measurements of higher plant biomarkers from sediments in the Arabian Sea (ODP 722B). This site is situated at 2000 m water depth on the Owen Ridge, isolated from turbidite deposition on the adjacent Indus Fan. Continuous deposition allows more accurate age control, based on oxygen isotope and nannofossil stratigraphy. The principal source of terrestrial input to the site is from aeolian sources associated with monsoon circulation, which results in the transport of plant leaf waxes from adjacent continental regions, especially the Arabian Peninsula, the Middle East, and the Indian subcontinent. Therefore, our data represent the first continuous integrated large scale records of C3 and C4 plants for these continental regions. We analyzed ca 200 samples over the last 10 My. Our results show that C4 plants were already present by 10 Ma. Assuming end member d13C values for C3 (-34 %) and C4 (-20 %) plant leaf waxes, C4 plant percentage input increased from 25 to 45 percent from 10 to 7.5 Ma. Surprisingly, however, the C4 input decreased to 15 percent from 7.5 to 6.8 Ma. The major rise of C4 plant inputs occurred between 6.8 to 5 Ma, when the C4 percentage input increased from 15 to 65 percent. C4 percentage continued to rise slowly from 5 Ma, reaching 75 percent at 0.7 Ma. A C4 decrease from 57 percent took place from 0.7 Ma to present. Our hydrogen isotopic ratios of leaf waxes suggest a major increase in continental aridity between 8 to 6 Ma, which is followed by a slower rate of aridity increases from 6 to 0.7 Ma. Both carbon and hydrogen isotopic ratios become more variable on shorter time scales after 6 Ma than before 8 Ma. Notably, a decrease in C4 plants by ca. 15 percent, just prior to the major expansion of C4 plants, was also observed in published Siwalik paleosol carbonate d13C record. This pattern of C4/C3 plant evolution has not yet been observed in other continents, suggesting important regional climatic control, rather than a global change in atmospheric pCO2 may have played a key role on the rise of C4 plant during the late Miocene. DE: HR: 14:10h AN: PP53D-03 INVITED TI: A Cenozoic terrestrial isotope record and the evolution of C$_{4}$ photosynthesis AU: * Gr”cke, D et al. EM AB: Our understanding of C$_{4}$ plant evolution and expansion has predominantly relied on site-specific fossil teeth, paleosols, and pedogenic carbonates carbon-isotope records and suggests a global dominance between 15-6 Ma. However, more recent techniques using bulk and compound-specific carbon-isotope ratios from terrestrial organic matter and other biomarker evidence suggest C$_{4}$ plants may have evolved multiple times. Furthermore, C$_{4}$ plants may have been present in terrestrial environments much earlier than the late Miocene expansion, but owing to their environmental preference and low preservation potential may not have been preserved in the terrestrial sedimentary record, and/or such latitudinal sites have not been fully explored. An additional implication is that the carbon-isotope composition of CO$_{2}$ (\delta $^{13}$C$_{CO2}$) has changed through time and paleoecologic reconstructions based on teeth and carbonate isotopic signatures may not reflect accurate floral contributions. Thus, terrestrial and atmospheric carbon-isotope signatures must be integrated in order to assess the Cenozoic history of C$_{4}$ photosynthesis. Presently, we are constructing a carbon-isotope record of long-chain {\it n}-alkanes with high carbon preference indices (indicative of higher plant input) from a globally distributed set of oligotropic and marginal DSDP/ODP marine sediments. As mentioned above, an estimate of the C$_{4}$ plant proportion of total land-plant biomass requires an understanding of changes in \delta $^{13}$C$_{CO2}$ through time. Accordingly, we have constrained this parameter by establishing the carbon-isotope composition of C$_{3}$ plant organic matter from Paleogene-age shallow marine shelf and lagoonal sediments from the Isle of Wight, UK, by assuming constant carbon-isotope discrimination between CO$_{2}$ and C$_{3}$ photosynthesis. Such \delta $^{13}$C$_{CO2}$ records can be directly compared with alkenone-based {\it p}CO$_{2}$ and {\it n}-alkane based floral contribution estimates. Using integrated isotopic proxies, our preliminary data suggest that the C$_{4}$ photosynthetic pathway evolved prior to the late Miocene and was possibly driven by paleoenvironmental pressures. DE HR: 11:20h AN: PP32A-05 TI: Structure of the Penultimate Deglaciation Along the California Margin and Implications for Milankovitch Theory AU: * Cannariato, K et al. EM AB: Several studies have suggested that the penultimate deglaciation occurred earlier than Milankovitch theory predicts therefore calling into question the orbital theory of ice ages. Furthermore, the detailed structure and timing of Termination II is insufficiently defined yet critical for understanding mechanisms responsible for abrupt regional and global climate change. High-resolution climate records and a means to accurately date them independent of orbital tuning are necessary to address these issues. Here we present planktonic and benthic foraminiferal oxygen isotope records at unprecedented resolution encompassing late MIS 6 and Termination II ($\sim$150 to 120 ka) from Santa Barbara Basin (ODP Site 893) supported by additional southern California margin records (Sites 1017 and 1014), a region highly sensitive to global millennial-scale climate oscillations during the last deglaciation. These records reveal millennial- and centennial-scale climate variability throughout the interval including a prominent interstadial immediately preceding the deglaciation, a brief warm event near the beginning of Termination II, and a B$\o$lling-$\AA$ller$\o$d/Younger Dryas-like climate oscillation midway through the deglaciation. Previous work suggests the presence of millennial-scale variability over broad regions during TII including climate instability during late MIS 6 and a pause or climate oscillation during TII. Low-resolution Mg/Ca- and alkenone-derived temperature records from these sites indicate the relative timing within the sequence of local salinity and global ice volume changes. Few options exist for dating marine records during Termination II. They are typically tuned to orbital insolation, which precludes testing deglacial mechanisms. However, the distinct millennial-scale features of TII documented by the California margin records represent several widespread climate events that potentially could be correlated with well-dated high-resolution records elsewhere. For example, the $^{230}$Th-dated stalagmite oxygen isotope record from Dongge Cave, China appears to exhibit the same millennial-scale climate events as the California margin records during late MIS 6 and Termination II. This allows the adoption of the stalagmite radiometric chronology to the California margin records. This chronology supports the Milankovitch theory of deglaciation. The suborbital history of climate variability during Termination II may account for records of early deglaciation. DE: HR: 16:15h AN: PP54A-02 INVITED TI: Exploring the Carbonate Production/Dissolution Paradox in the Mid-Bruhnes of the Southern Ocean Using Coupled Records of Biological and Chemical Dynamics AU: * Flores, J et al. EM AB: The Mid-Brunhes event, an interval including MIS 9 to 11, is considered one of the warmest during the Pleistocene. This interval is also characterized by generally high carbonate concentrations (and presumably high productivity) with punctuated intervals of high dissolution in the deep ocean. The paradox of high carbonate production and high dissolution in certain intervals might be linked to nutrient available, ocean geochemistry, and upwelling. To explore this situation in the Southern Ocean, we examined calcareous nannofossil and geochemical proxies in order to estimate the degree of dissolution in the calcareous nannofossil assemblages, and examine primary production of these organisms and their relationship with surface water dynamics. In ODP Site 1089 (Cape Basin, Atlantic Ocean) the MIS 9 to 11 is characterized, as in the whole ocean, by the dominance of Gephyrocapsa caribbeanica (a small but robust and well-calcified placolith). Although the record of calcareous nannofossil is continuous, we observed fluctuations in the degree of preservation in the calcareous nannofossil assemblages, particularly periods of high to moderate dissolution during interglacial periods. Conversely, glacials are characterized by moderate to good calcareous nannofossil preservation. During Terminations IV and V we observed maxima in calcareous nannofossil accumulation, but with moderate preservation, indicating that maxima in calcareous nannofossil production occur during Terminations. One potential explanation is related to ocean geochemical mass balances and upwelling dynamics. The geochemical data from this site show that the P/Ti ratio, a paleoproductivity and P mass balance proxy, and Sr concentrations, a nannofossil production proxy, also show peaks during Terminations IV and V-thus, high production from nutrients coincides with high carbonate dissolution. In a coupled biological, chemical, and oceanographic model, low sea levels during glacials result in a basin dominance of the shelf-basin fractionation, with generally high nutrient delivery to the deep sea and increased carbonate production. During termination, the shelf reservoir of nutrients and carbonates begins to increase, but perhaps ocean stratification is diminished with higher upwelling causing greater productivity, with high dissolution the result of a switch in alkalinity with the termination. Basin production then decreases with the increase of nutrient apportionment to the shelves during higher interglacial sea levels. DE HR: 16:50h AN: PP54B-04 TI: From Greenhouse to Icehouse: Evidence for Late Early Eocene Concomitant Cooling of Southern Ocean Surface Waters and Global Deep Waters From Dinoflagellate Endemism AU: * Brinkhuis, H et al. EM AB: ODP Leg 189 drilling around Tasmania retrieved continuous Eocene records from the Southern Ocean - Antarctic Margin. The shallow marine, pro-deltaic successions of Sites 1170, 1171 and 1172 include the interval representing the onset (55 Ma) and termination (50 Ma) of the Early Eocene Climatic Optimum (EECO). The end of the EECO is globally reflected in the oceans by the onset of increasingly cooler deep-water temperatures, and marks the onset of the trend towards the Icehouse world. Here we show that a strong increase of endemic Antarctic dinoflagellates precisely matches the termination of the EECO in the Southern (Pacific) Ocean. The record of these surface- dwelling organisms thus indicates that changes of surface water parameters, notably temperature, occurred near simultaneously with global deep-water temperature changes. Moreover, the signal coincides with the return to heavier d13C-values, and atmospheric CO2 decline. Comparison of the field data with predictions from fully coupled climate model simulations, and a new basic understanding of Eocene Southern Ocean circulation, suggests that changes in carbon burial was driving changes in atmospheric greenhouse gasses, and the apparently coupled surface- and deep-water temperature signals. DE: HR: 14:40h AN: PP13B-05 TI: Oxygen Isotopic Stratigraphy and Geomagnetic Field Intensity AU: Meynadier, L and Valet, J EM AB: Nick Shackleton intellectual leadership in isotope stratigraphy had profound implications for paleoclimatology and paleoceanography. What is not so well enough known is that Nick contributed also to significant advances in studies of variations of the Earth's magnetic field. The first link between the two disciplines was certainly the paper that he produced with Neil Opdyke in 1973. About twenty years later Nick Shackleton obtained a very detailed isotope stratigraphy after analyzing the oxygen isotopes of bulk sediment of two cores from the Somali basin characterized by high resolution records of relative paleointensity for the past 140 kyr. This stratigraphy allowed us to correlate these two records with other independent data from the Mediterranean sea and to propose that the signal which was recorded at the two locations was global and thus of geomagnetic origin. The fast growing database made possible a stacking of the results for the past 200 ka and then for the past 800 kyr. The resulting curve was constructed from 33 paleointensity records and Shackleton's isotopic records were essential in many cases. Indeed without high resolution stratigraphy much information could not be retrieved due to uncertainties in correlating different records. The results revealed the very variable character of the field with large 20 to 60 kyr oscillations and changes in amplitude that can exceed a factor of five, but no apparent periodicity. Short periods of very low intensity occur at more or less regular intervals (roughly every 100 kyr) and correspond with geomagnetic excursions. The next step was to obtain a much longer record that would document the field changes across reversals and during entire polarity intervals. The opportunity was met during ODP Leg 138 with the recovery of beautifully magnetized sequences that covered at least 4 Myr of geomagnetic history. Nick was responsible for correlating sedimentary columns taken at each site. He performed a tremendeous task by orbitally tuning the density variations for thousands of meters of sediment. This allowed us to correlate the paleointensity signals from several holes and to produce the first long dataset with a very accurate time-depth control. Very recently the accumulation of data made it possible to stack records from different oceans for the past 2 Myr and to extract features of field intensity which add significant constraints to the modelling of the geodynamo. Alternatively this curve can be used as a stratigraphic reference, similarly to isotopes records. DE: HR: 0800h AN: PP51F-1370 TI: Metal Deposition Along the Peru Margin Since the Last Glacial Maximum: Evidence For Regime Change at \sim 6ka AU: * Tierney, J et al. AF AB: The Peru Margin upwelling zone plays a key role in regulating marine biogeochemical cycles, particularly the fate of nitrate. High biological productivity and low oxygen waters fed into the oxygen minimum zone result in intense denitrification in the modern system, the consequences of which are global in nature. It has been very difficult, however, to study the paleoclimatic history of this region because of the poor preservation of carbonate in Peru Margin sediments. Here we present records of trace metal accumulation from two cores located in the heart of the suboxic zone off the central Peru coast. Chronology comes from multiple AMS $^{14}$C dates on the alkenone fraction of the sediment, as well as correlation using major features of the \delta $^{15}$N record in each core. ODP Site 1228 provides a high resolution, continuous sediment record from the Recent to about 14ka, while gravity core W7706-41k extends the record to the Last Glacial Maximum. Both cores were sampled at a 100 yr resolution, then analyzed for % N, \delta $^{15}$N, alkenones, and trace metal concentration. Analysis of redox-sensitive metals (Mo and V) alongside metals associated with changes in productivity (Ni and Zn) provides perspective on the evolution of the upwelling system and distinguishes the two major factors controlling the intensity of the oxygen minimum zone. The trace metal record exhibits a notable increase in the intensity and variability of low oxygen waters and productivity beginning around 6ka and extending to the present. Within this most recent 6ka interval, the data suggest fluctuations in oxygenation and productivity occur on 1000 yr timescales. Our core records, therefore, suggest that the Peru Margin upwelling system strengthened significantly during the mid to late Holocene. DE HR: 0800h AN: PP51D-1355 TI: Eocene-Oligocene Southern Ocean Paleo-bathymetry maps generated with geophysical, sedimentological and microfossil data. AU: * Brown, B et al. EM AB: The Eocene-Oligocene transition is characterized by the cooling of the Southern Ocean region and growth of the Antarctic ice-sheet. Through this transition, changes in spatial distribution and topography of land masses and ocean basins have played a role. Our objective is to produce a set of enhanced paleo-bathymetry maps based on both plate reconstruction models for the Southern Ocean and sedimentological and microfossil data. We used paleo-age grids to create a series of paleoceanic basement-depth grids, based on a thermal boundary layer depth-age model. We further constrained these paleo- bathymetry grids, especially for continental margins, with sedimentological and microfossil data (diatoms, foraminifera, nannofossils, organic walled dinoflagellates, pollen & spores and radiolarians); derived from new and published data from land based sections and DSDP/ODP (and other) cores. In particular, we aim to map the opening of oceanic gateways (Tasmanian Gateway and Drake Passage) and changing ocean topography through Eocene-Oligocene times. It is known that the evolution of circum Antarctic current systems were strongly dependent on bottom topography, particularly the deepening of oceanic gateways and the mid-ocean ridge system. It is hoped that this work will offer a more realistic/resolved starting input for ocean basin configuration (paleo-geographic model) and topography (paleo-bathymetry model). It would be a valuable tool to assess boundary conditions for oceanographic circulation models and next generation CCM's; in particular it would help assess deep-water circulation and related climate change further back in geological time. DE HR: 0800h AN: PP51F-1379 TI: Continental and marine climate records from the Southeast Pacific as inferred from Radiolaria and pollen records from 0 to 90ka at ODP Site 1233 AU: Pisias, N et al. EM AB: Site 1233 drilled during Leg 202 of the Ocean Drilling Program provides a detailed record of oceanographic and continental climate change in the Southeast Pacific and South American continent. Splits from over 500 samples from Site 1233 were used for detailed radiolarian and pollen species population analysis. Samples were taken at 20cm interval equivalent to temporal resolution of 200 to 400 years. In each sample splits used for pollen analysis abundances of 25 species were determined while in the splits used for radiolarian studies abundances of 41 species were evaluated. Age control is provided by 25 AMS 14C dates (Lamy et al., 2004). From detailed multivariate analysis of these data sets we state the following conclusions: 1) During the past 75kyr the region of the southern Chile coast is not directly influenced by polar water from the Antarctic region. 2) Changes in ocean conditions during this time interval reflect small north-south shifts in the south Pacific transition zone and its impact on the coastal waters of Chile. 3) The ocean and terrestrial climate records extracted from Site 1233 show remarkable similarities to each other as well as to temperature records from the Antarctic. These records suggest that climate variability during the past 75kyr in the Southeast Pacific is tightly coupled at periods longer than 3000 years and not linked directly to changes in the Northern Hemisphere and; 4) the marine and terrestrial climate records from Site 1233 studied here, show no phase shift in response suggesting that ocean/continental vegetation is much more tightly coupled with regional atmospheric changes as indicated by the Antarctic temperature proxy record while the results of Lamy et al., (2004) show a time lag between ocean responses and the Patagonian Ice Sheet suggesting possibly reflecting the long response time of ice versus continental vegetation and oceanic systems. DE: HR: 16:55h AN: PP54A-04 TI: Two Highly-Resolved Geochemical Records of Holocene Variability: A Comparison Between West and East Antarctica AU: * Kryc, K et al. EM AB: Based on results from ODP Site 1098 in the Palmer Deep, we have a highly resolved record of West Antarctic Holocene climate evolution as traced by terrigenous provenance and accumulation, nutrient utilization, and surface and export production. To date, there are few comparable records from East Antarctica despite its critical role in deep ocean circulation. Here we compare results from a 25 m core recovered from Iceberg Alley on the MacRobertson Shelf of East Antarctica with the results from the Palmer Deep (PD), West Antarctica. Both cores are characterized by laminated diatomaceous muds comprising a two-component system of biogenic opal and terrigenous material. Both of these sedimentary sequences span the Holocene and capture the termination of the deglaciation event at 10kyr. The geochemical parameters we used include XRF scanned and discrete ICP-ES major and trace element analyses, biogenic opal, and carbon and nitrogen isotopes. The PD geochemical records are strongly delineated between the Holocene Climate Optimum (HCO) and the Neoglacial. Both surface and export production are elevated through the HCO, which is indicative if a warmer period. Additionally, the terrigenous provenance record of Al/Ti shows that the source of sediment during the HCO was different than during the Neoglacial. This is likely the result of water mass reorganization as a function of Westerly wind strength. The major events seen in the PD record have also been observed worldwide. In contrast, the Iceberg Alley record does not show a difference between the HCO and the Neoglacial. Rather, there are high-frequency changes that appear to vary over an unchanged average throughout the Holocene. There is, however, a large change in both the absolute values and the amplitude of the signal at 10kyr that signifies the termination of the deglaciation event. Why the Iceberg Alley records do not reflect the same structure exhibited in the PD records remains to be determined. As a first approximation, it appears that the climatic conditions differed between these two sites during the Holocene. DE HR: 17:10h AN: PP54A-05 TI: Paleoceanography and Paleoclimatology of the Southern Ocean: A Synthesis of Three Decades of Scientific Ocean Drilling AU: Warnke, D et al. EM AB: A Workshop on " Paleoceanography and Paleoclimatology of the Southern Ocean: A Synthesis of Three Decades of Scientific Ocean Drilling" Jan. 21-23, 2005 Boulder, CO Co-Convenors: D. Warnke, G. Filippelli, J.-A. Flores, T. Marchitto One of the greatest successes of the Ocean Drilling Program has been the concerted drilling efforts and exciting results recovered from the Southern Ocean (SO), which has been the focus of ten DSDP/ODP drilling legs. The SO is a critical component in the development and persistence of Antarctic glaciation, is a sensitive mixing pool of global water masses, a locus of high biological sedimentation, and contains high resolution records of climate forcing and response. As such, it is one of the most important oceanographic regions in the world. It is now an important time to mine the rich results from scientific ocean drilling over the past several decades and develop a scientific framework for future ocean drilling in this region. The focus of this Synthesis Workshop will be on the biogeochemical history of the SO, including: ú Productivity proxies, rates, records, variations, and role of climate ú Sedimentary records of organic carbon, calcium, silica, nutrients, and biogenic proxies: The role of the SO as a biogeochemical sink ú Development and dynamics of the APFZ ú Thermal structure and evolution of the SO ú The role of limiting nutrients The overall goal to integrate the various proxies into a coherent paleoceanographic picture. Such a goal will help to synthesize several decades of scientific ocean drilling in the SO, and will likely bring to the forefront the as-yet- unanswered questions about the biogeochemical history of this important oceanic system. With this goal in mind, workshop participants will submit of a short (~250 word) abstract as the Workshop application, commit to presenting a poster at the workshop based on this abstract, and contribute to one or more manuscripts that will be published after the workshop, likely as a Geological Society of America Monograph. The workshop is open to both U.S. and international scientists. Individuals interested in participating should apply by emailing a brief statement of interest and attaching an abstract (sent as a word document) of the research to be presented to [email protected]. Although the deadline for submitting abstracts will have passed at the time of the meeting, interested persons should contact [email protected] immediately to see whether space is still available. Participation will be limited to optimize workshop goals. DE: HR: 0800h AN: PP51D-1351 TI: Radiolarian and Sedimentologic Evidence for Late Eocene Origin of Southern Ocean Environments AU: * Lazarus, D et al. EM AB: Benthic foram $\delta$$^{18}$O and Mg/Ca records indicate that the deep ocean cooled by 5-$10\deg$C between the early Eocene and earliest Oligocene, although the timing, magnitude and dominant style of change (continuous vs. steps) is still debated. The largest change occurs at the Eocene/Oligocene boundary (33.5 Ma), associated with the first major Antarctic glaciation. Current debate concerns whether this glaciation was a threshold event related to long-term decline in CO$_{2}$ or was caused by opening of the Tasmanian Gateway, with thermal isolation of Antarctica and development of circumpolar circulation. The Southern Ocean, characterised by circumpolar current flows and bounded by the Polar Front, has contained since the mid Paleogene a distinct Antarctic radiolarian biota consisting of endemic forms and bipolar high-latitude taxa adapted to seasonal high productivity environments. It is also characterised by common biogenic silica in pelagic sediments. Past changes in the abundance and geographic distribution of these faunas and sediments provide qualitative proxies for the origin and development of this environment. We examine trends in radiolarian evolution, biogeography and biosiliceous facies development from the mid-Eocene to early Oligocene. We calculate diversity, speciation and extinction rates; track the origin and dispersal patterns of Antarctic radiolarian biota (percent Antarctic species at each site); and map sedimentary facies distribution changes through a series of time slices from the late Middle Eocene to the middle Early Oligocene. Data comes from numerous DSDP and ODP sites drawn from the Pacific, Indian and Atlantic sectors of the Southern Ocean. Results show maxima in rates of evolutionary change, increases in Antarctic species, and appearance of biosiliceous components in sediments in the late Middle to middle Late Eocene interval. There is little evidence for major change in, or expansion of the Antarctic radiolarian fauna; or increase of biosiliceous sediment at the time of the opening of the Tasmanian Gateway and Eocene-Oligocene glaciation. We conclude that the Antarctic environment largely developed prior to the Eocene-Oligocene boundary. DE: HR: 14:40h AN: PP43B-05 TI: Regime Shifts in Climate Forcing of Peru Denitrification AU: * Altabet, M et al. EM AB: Water column denitrification occurs in suboxic intermediate waters when bacteria transform nitrate to N2 gas, thereby removing it from the ocean's combined N inventory. Combined N availability is an important controlling factor for organic C production across much of the ocean, such that past variations in oceanic denitrification likely had repercussions for marine productivity and perhaps, at appropriate time scales, atmospheric CO2. Prior studies in the Arabian Sea and E. Tropical N. Pacific have demonstrated climatically-forced oscillations in denitrification on orbital to millennial time scales. Here we examine the Peru denitrification zone, the last of major water column denitrification zones to be studied and the only one in the S. Hemisphere. It is also the most likely to be influenced by ENSO variability. We have examined a series of high resolution cores from the upper Peru margin and developed a chronostratigraphy covering the last 60 kyr overcoming difficulties of common hiatuses and little or no preserved foraminifera. We have also examined ODP Site 1237 and associated site survey cores located in deep waters near the margin on the Nazca Ridge. A multi-proxy approach is taken including N isotopic composition to record denitrification intensity; major and minor elemental composition for sediment provenance, water column redox state, and productivity; alkenone UK37 for SST. Denitrification intensity is observed to vary at a variety of time scales. The lower resolution, 2 Ma record from site 1237 shows large orbital-scale shifts with the dominant mode shifting at the MPT. The high resolution records from the margin elucidate the nature of important forcings. The last deglaciation experienced a sharp and early rise in Peru denitrification that preceded by 2 kyr any major changes in local productivity. Forcing appears to be remote from the Peru upwelling zone, likely due to changes in either the ventilation of source intermediate waters in the Subantarctic and/or changes in the relative isolation of the `shadow zone' from the subtropical gyre circulation. The Holocene is also marked by large excursions in denitrification that are only centennial scale in duration that are unique to this region. A regime shift appears to have occurred in which local, productivity-driven forcing appears to dominate. UR HR: 1340h AN: PP53B-1395 TI: $^{15}$N depleted nitrogen isotope values in Cretaceous black shales: paleoceanographic event or diagenesis. AU: * Junium, C and Arthur, M AB: Nitrogen isotopic values of bulk sediment samples in black shales are almost exclusively near 0 $\permil$ and C/N ratios are high (20-35). Sequential extraction of exchangeable and non-exchangeable N fractions demonstrates that the inorganic N fraction is negligible and bulk sediment data reflect the organic N fraction. The trend in \delta$$^{15}$N and C/N has been observed in numerous localities and depositional environments in the mid-Cretaceous (Demarara Rise, DSDP Sites 367, 603B and 530, the Cretaceous Western Interior Seaway, Wunstorf, Germany, and Bahloul, Tunisia) as well as the Toarcian of England and in Quaternary Mediterranean Sapropels. Three explanations are considered: 1) That primary production during black shale deposition was dominated by a unique community composed of nitrogen-fixing cyanobacteria; or 2) utilization of a $^{15}$N depleted ammonium source by another set of biota; or 3) that the values are the result of diagenetic loss of N prevailing in C$_{org}$-rich strata with a low capacity for N adsorption. The depleted nitrogen isotopic values suggest that nitrogen fixation or utilization of a depleted nitrogen source (e.g. ammonium) may have been important which is plausible in consideration of nitrogen deficiencies that might characterize widespread deep-water anoxia. Secular variations in nitrogen isotope values across the Cenomanian-Turonian Boundary of ODP Site 1261, Demarara Rise, show a shift from -1 to -3$\permil$. One interpretation of the origin of the excursion could be that a fraction of the organic matter was produced utilizing a $^{15}$N depleted ammonium source, assuming that the nitrogen isotopic composition of fixed oceanic nitrogen does not change. However, it should be noted that large (greater than 1$\permil$) variations in nitrogen isotope values are observed above and below the Cenomanian-Turonian Boundary Event and have no known paleoceanographic forcing. The variations in nitrogen isotope values are matched by antithetic variations in C/N indicating diagenetic N-loss that could be interpreted as the primary control on the nitrogen isotope variations. The high C/N ratios probably result from selective removal of N-enriched compounds in the water column and during burial diagenesis. Clay-poor, C$_{org}$-rich sediments have a low sorptive capacity, allowing diffusion of dissolved N out of the C$_{org}$-rich sediments resulting in higher C/N ratios. Pore water ammonium concentrations are mM, indicating low sorption and high rates of diffusion into overlying strata. Coupled C/N and N-isotope variations occur by the removal of a $^{15}N$ enriched fraction. Protein degradation has been suggested to result in negative isotopic shifts but would not result in large increases in C/N and the isotopic shifts are limited by the protein richness of the primary organic matter and the internal isotopic heterogeneity of the organic matter pools. Although we favor an explanation that involves a primary signature, diagenesis cannot be excluded in low $\delta$$^{15}$N values. DE: HR: 1340h AN: PP53B-1396 TI: Evaluation of Geochemical Proxies Preserved in the Sapropel Record from the Eastern Mediterranean Within the Pliocene- Holocene Time Interval AU: * Gallego-Torres, D et al. EM AB: Considerable research has been devoted during the last decade to productivity and oxygenation proxies of sapropel deposition in the Mediterranean. Pliocene-Holocene sapropel layers from Mediterranean basins are considered to be an important key to assess the role of productivity vs. anoxia in organic matter (OM) accumulation. Evaluation of proxy preservation within these sediments is therefore crucial to further investigate forcing mechanism for OM deposition. With this aim, diverse layers from Pliocene, Pleistocene and Holocene sediments recovered at ODP Site 964 in the eastern Mediterranean have been analyzed. Ba excess is recognized as a reliable proxy for enhanced productivity because it derives from barite crystals originated in the water column. Additionally, their S isotope composition revealed that barite is an authigenic phase (Paytan et al., 2004). This proxy also revealed of exceptional importance in Mediterranean basins because some sapropels have been partially or totally oxidized. Assessment of productivity variations cannot be based therefore on the OM record which is strongly subjected to diagenetic preservation. Certain redox-sensitive elements as Mn were also subjected to remobilization during oxidation precipitating upon encountering the oxidation front. However some well preserved trace-element ratios, used as oxygenation proxies, are still recognized. These consistently point to a relatively oxic environment during the deposition of Quaternary sapropels while Pliocene sapropels tend to be characterized by lower oxygen conditions. Ba excess also indicates that barite accumulation rates within sapropels decreased through time, being considerable higher during the Pliocene. Thus, elevated primary export production could have enhanced oxygen consumption leading to lower oxygen levels at this time. Paytan, A., F. Martinez- Ruiz, M. Eagle, A. Ivy, and S.D. Wankel (2004) Using sulfur isotopes in barite to elucidate the origin of high organic matter accumulation events in marine sediments. Sulfur Biogeochemistry, GSA Special Paper, 379, 151-160. DE: HR: 0800h AN: PP51D-1352 TI: Evolution of North Atlantic Thermohaline Circulation: From the Greenhouse to the Icehouse AU: Via, R and Thomas, AB: A growing body of data indicates that the pattern of oceanic thermohaline circulation has varied through the geologic past. At any given time, tectonic and climatic boundary conditions will tend to dictate the operating pattern of thermohaline circulation. For example, in the Early Cenozoic prior to the opening of the northern North Atlantic basins, the Southern Ocean was the dominant source region for deep water formation. As global climate cooled and tectonic gateways changed through the Cenozoic, this mode gradually evolved into the Late Cenozoic mode, characterized by Southern Ocean and North Atlantic sources of deep water formation. To better understand how the evolution of Cenozoic thermohaline circulation related to changes in global climate and ocean basin configuration, we generated Nd isotope records from a depth transect of Ocean Drilling Program sites in the southeastern Atlantic to track deep water mass composition through time. We used fossil fish debris from ODP sites 1262-1264 (Leg 208), which span present-day water depths of 2500 m to 4750 m, to reconstruct the isotopic signature of deep waters over the past 55 Ma. The data indicate an initial transition from relatively non-radiogenic values ($\sim$-10 $\epsilon$$_{Nd}$ units) at 55 Ma to more radiogenic values ($\sim$-8.5) at 32 Ma. From 32 Ma to 3.85 Ma, the Nd signal becomes more non- radiogenic, approximately -12.3 at the top of our record. Comparison of our data with Nd isotopic records derived from a North Atlantic Fe-Mn crust show similar non-radiogenic values ($\sim$-10.5) in the 50 - 32 Ma interval and a trend toward more non-radiogenic values beginning at approximately 20 Ma. The data likely reflect an overall shift from a Southern Ocean deep water source to the ultimate incursion of deep waters from the North Atlantic. The non-radiogenic values at the base of the record reflect a Southern Ocean source of deep water. The shift toward more radiogenic values indicates an increased contribution of Pacific waters to the Southern Ocean source as the Drake Passage began to open to deep flow at $\sim$33 Ma. Though the subsequent trend toward more non-radiogenic Nd isotope values does not directly correlate to any major tectonic event, it is approximately coincident with the increase of benthic foraminiferal $\delta$$^{18}$O values, based on comparison with the Zachos et al (2001) global compilation. Thus the build-up of continental ice on Antarctica and global cooling may have altered the character of Southern Ocean deep waters during the early Oligocene. DE: HR: 0800h AN: PP11A-0541 TI: Middle Eocene to early Oligocene paleoceanography of the Southern Ocean from foraminiferal stable isotope and Mg/Ca records AU: * Bohaty, S et al. EM: AB: The middle Eocene to early Oligocene is a critical phase of Cenozoic climatic evolution, characterized by long-term cooling of deep waters and the first appearance of large Antarctic ice sheets. The Southern Ocean is a key area for monitoring Eocene- Oligocene climatic variability, and development of high-resolution paleoceanographic records from this region is crucial to evaluating possible mechanisms of long-term climate change. These records will ultimately help constrain the timing and nature of middle-to-late Eocene cooling and ice buildup on Antarctica in relation to the timing of major paleogeographic changes, especially the opening of Southern Ocean gateways, and independent records of {\it p}CO2 variability. We have generated high-resolution stable isotope records from ODP Sites 689, 702, 738, and 748 in the Atlantic and Indian sectors of the Southern Ocean. These sites are separated by considerable distances, but the records display coherent trends with several unique features. These features enable detailed site-to-site correlation and indicate that a common paleoceanographic history is shared by all study sites. The late middle Eocene records are punctuated by a strong, transient warming event at $\sim$41 Ma. This event is followed by an increase in $\delta$$^{18}$O values that culminates at $\sim$37 Ma, indicative of long-term cooling and/or growth of small ice sheets. This is followed by an inferred brief warming in the early late Eocene ($\sim$36.5-36.0 Ma), and a slight cooling step at ($\sim$35.5 Ma). A period of relative stability in the latest Eocene precedes the well-documented $\sim$1.4$\permil$ increase in $\delta$$^{18}$O (the Oi-1 event) in the earliest Oligocene. In addition to the stable isotope records, we are developing high-resolution planktonic foraminiferal Mg/Ca records. The primary goal of this work is to separate the ice-volume and temperature contributions to the Eocene-Oligocene $\delta$$^{18}$O signal. Our initial focus is on the early Oligocene Oi-1 event, which is thought to represent the first major Cenozoic buildup of large ice sheets in East Antarctica. At Site 748, Mg/Ca data from the thermocline-dweller Subbotina angiporoides indicate a significant decrease in temperature in the earliest Oligocene. These data are interpreted to represent a 2-3$\deg$C cooling at the Oi-1 transition. Removal of this temperature component from the oxygen isotope signal retains a significant ice volume signature. A minimum of 60% modern ice volume is estimated during peak Oi-1 glaciation. DE: HR: 1340h AN: PP53B-1393 TI: Implications of Mn-Mg-rich Contaminant Phases for Mg/Ca Past Temperature Reconstructions AU: * Pena, L et al. EM AB: In recent years, many paleoceanographic studies have employed the foraminiferal elemental composition as a proxy of sea water paleoenvironmental conditions. In particular, the foraminiferal Mg/Ca ratio has been widely used as a sea water paleotemperature estimator. Nevertheless, this technique is still in development and special attention needs to be focussed on those factors which can introduce potential biases in the Mg/Ca ratio and therefore leading to inaccurate reconstructions of past- oceanographic scenarios. This study aims to solve or reduce overestimations of past sea water temperatures derived from a contaminant Mg-rich phase associated to Mn- enrichments. We address this problem using samples from ODP 1240 (0§01.311'N, 86§27.758'W, 2921m water depth) from the Panama basin which is a Mn-enriched basin. By means of the LA-ICP-MS capabilities at the Research School of Earth Sciences (Australia) we have documented and identified the presence of Mn-Mg-rich contaminant phases at the inner part of the foraminifera walls. In order to asses the efficiency of the classical Mg/Ca cleaning protocols when dealing with the presence of these contaminants, we have selected a set of samples with different contents in Mn and cleaned them with both the oxidative and the full reductive methods. LA-ICP-MS and bulk ICP-MS results show that the reductive cleaning successfully removes the Mn-Mg rich layers from the samples whereas the oxidative cleaning does not effectively eliminate the contaminant phases from the selected samples. In order to test the efficiency of the different cleaning steps we have analyzed (ICP-MS) the residual fractions from each cleaning step using two sample sub-sets. The order in the reductive and oxidative step was reversed for each sub-set. Results suggest that the Mn-enrichment occurs in two different phases, one which is eliminated by either the oxidative or the reductive step but a second one which only is removed by the reductive step. This second one is also associated to Mg-enrichments. As a consequence of this contamination phase, temperature reconstructions can provide overestimations in the range of 0.5-4§C. In addition, our results clearly demonstrate that there are no significant differences in the Mg/Ca ratio when the order between reductive and oxidative steps is altered. A further insight on the nature of these Mn-Mg-rich contaminant phases has been obtained by means of complementary analytical techniques (XRD, SEM, EDX). The results obtained demonstrate that the contaminant phase is mainly a Mn-Mg carbonate known as Kutnahorite. This mineral has been previously identified in Mn-rich crusts of marine sediments but this study has been able to identify it for the first time within foraminiferal tests. DE HR: 1340h AN: PP23A-1393 TI: Detrital Sediment Supply And Late Quaternary Environmental Changes Off Taiwan, ODP Site 1202 AU: Hofmann, J et al. EM AB: During Leg 195 of the Ocean Drilling Program, Site 1202 was drilled in the subtropical northwestern Pacific Ocean beneath the Kuroshio ("Black Current") between northern Taiwan and the Ryukyu Island Arc on the northern flank of the Ilan Ridge at 1275 m water depth. The ridge separates the southwestern end of the Okinawa Trough from the basins of the Philippine Sea. The upper 120 m of the Site 1202 section, composed of dark grey calcareous silty clay, provide a high-resolution record of the last 30 kyr, deposited at high sedimentation rates between 3.0 and 5.0 m/kyr and peak values of 9,0 m /kyr between 15.5 and 11 ka. Variations in the modes and sources of detrital sediment input, as inferred from sediment granulometry, mineralogy, and element- scanner data, reflect complex changes in environmental boundary conditions related to postglacial sea-level rise, monsoon climate, tectonics, and Kuroshio variability. Between 30 and 11 ka, low portions of sortable silt show that the Kuroshio did not enter the Okinawa Trough because of low sea level. Clay-mineral tracers point to increased sediment supply from mainland China by the discharge of Yangtze sediments directly across the East China Shelf edge into the Okinawa Trough. Consistent with maximum sedimentaion rates, Yangtze discharge reached a maximum between 15.5 and 11.0 ka. High fluvial sediment supply apparently was triggered by both postglacial sea-level rise and strengthened summer monsoon in response to precessional forcing of insolation. The Holocene was dominated by sediment supply from Taiwan since 11 ka, as indicated by clay-mineral tracers and geochemistry. High proportions of sortable silt point to strong bottom currents, mediated by sea-level rise and enhanced Kuroshio activity at Site 1202. Element-scanner data reveal the presence of 200-yr cycles, possibly related to short-term climate perturbations. DE: HR: 0800h AN: PP51F-1372 TI: High-Resolution Accumulation Rate and Authigenic U Variations On The Nazca Rise , Peru Margin, Over the last 25ka AU: * Higgins, S et al. EM AB: As part of a larger regional study into ocean circulation changes along the Peru Margin over the last 25 ka, we have a developed an excess Th-230 (xsTh-230) record of sediment mass accumulation rates (MAR) and authigenic U (Uauth) at an offshore site (140km off margin) on the Nazca Rise. Over an interval between 7 and 25 ka, these profiles consists of 50 xsTh-230 and U measurements for an average resolution of ~350 yr/sample. This has allowed us to evaluate concerns about sediment redistribution affecting interpretations of other proxies, like $\delta$N-15, as well as make more direct comparisons with shallower marginal sites. The Site RR9702A-69TC (3.2 km water depth) is located at $16\deg$S $76\deg$W and has an average sedimentation rate of 5.4 cm/ka based on AMS C-14 dates and correlation to nearby locations. The xsTh-230 profile combined with estimates of dry bulk density and sedimentation rates indicates that sediment focusing (a surplus of Th-bearing sediments) is about 1.5 to 2x the expected throughout the record. Th-230 data and %CaCO$_{3}$ analyses enabled us to produce detailed records of carbonate and non-carbonate MAR. The Th-normalized detrital MAR (primarily eolian) decreases by a factor of two (1.2 to 0.6 g/cm$^{2}$/ka) across the deglacial (15 to 12 ka). In contrast, Th-normalized CaCO$_{3}$ MAR shows values increasing slowly through the LGM (0.1 to 0.15 g/cm$^{2}$/ka) then decreasing from maximum at 15ka to no Holocene accumulation by 11 ka. In addition to xsTh-230, measurements of Th-232 and Uauth (often interpreted as a total organic carbon (TOC) proxy provide us independent measures of detrital flux and productivity variations, respectively. The Th-232 derived detrital flux is consistent with estimates of eolian accumulation from nearby site ODP Site 1237 and is relatively constant through the Last Glacial Maximum (LGM). Uauth varies from 4 to 10 ppm during the LGM, decreasing through the deglacial to Holocene values of 1 to 2 ppm. However, the Th-232 detrital flux does not co-vary with Uauth concentrations (R$^{2}$ =0.2) . Instead, there is a much better correlation between CaCO$_{3}$ flux and Uauth (R$^{2}$=0.5). This indicates that the variability (factor of 4-5x) observed in Uauth was not caused primarily by dilution by terrigenous inputs. DE: HR: 16:45h AN: PP14A-04 TI: Revisiting ODP Site 690 to Assess the Responses of Marine Carbonate Chemistry to the Paleocene-Eocene Thermal Maximum AU: * Kelly, D et al. EM AB: The close of the Paleocene epoch (ca. 55 Ma) is punctuated by a transient ($<$100 kyr) global warming event referred to as the Paleocene-Eocene Thermal Maximum (PETM). In the marine realm, hallmark signatures of the PETM are a negative carbon isotope excursion (CIE) on the order of 3 per mil, widespread carbonate dissolution, and a benthic foraminiferal mass extinction. The rapid onset and anomalous magnitude of the CIE has been attributed to a sudden release of some 2000 Gt of methane into earth's surficial carbon reservoir. Presumably, oxidation of this methane elevated pCO2 levels in the atmosphere/ocean system, fueling global greenhouse warmth and carbonate dissolution. Here we revisit what is arguably the most complete deep-sea record of the PETM recovered from ODP Site 690 to explore the dynamic coupling between atmospheric CO2 levels, marine carbonate chemistry, continental weathering and global climate. The abrupt onset of the CIE is accompanied by a sharp decline in wt.% carbonate, yet wt.% coarse-fraction ($>$63 microns, foraminiferal shells) values remain fairly constant. These sedimentological shifts collectively point toward the selective removal of fine-fraction ($<$63 microns) carbonate produced by calcareous nannoplankton during peak oceanic warmth. We believe this selective pattern of "dissolution" actually reflects, in part, reduced calcification among some calcareous nannofossil taxa. An important corollary of this interpretation is that rising pCO2 levels attained a critical threshold that inhibited nannoplankton calcification. Decreased surface- ocean carbonate production triggered a shoaling of the local lysocline and concomitantly enhanced the ocean's carbon-storage capacity providing an important sink for atmospheric CO2. The character of carbonate sedimentation is reversed during the later, recovery stages of the CIE. It is within this stratigraphically expanded portion of the CIE that wt.% carbonate values and the relative proportion of wt.% fine-fraction increase markedly. This secondary shift coincides with a 5 degrees C cooling of intermediate waters and a sharp influx of kaolinite. Concurrent cooling of sea-surface temperatures is also suggested by the disappearance of warm-water microplankton. We believe these changes to be interrelated. The kaolinite spike likely reflects intensified silicate weathering on Antarctica as well as increased continental runoff. Thus, enhanced silicate weathering reactions (CaSiCO3 + CO2 -$>$ SiO2 + CaCO3) may have served as an added sink for atmospheric CO2 and a source of oceanic Ca2+ and HCO3- that drove an alkalinity overshoot thereby fostering increased carbonate sedimentation within the Weddell Sea region. The remarkable sequence of oceanic changes preserved in the Site 690 PETM record is consistent with the hypothesis that both marine carbonate chemistry and continental weathering acted as negative feedbacks to curb PETM warmth. DE HR: 1340h AN: PP33A-0917 TI: High Resolution Record of Seawater Osmium Isotopes Over the Last 100,000 Years AU: * Zylberberg, D et al. AF AB: We present a high-resolution record of the osmium isotopic composition of oceans over the past 100,000 years. The main intent of this study is to investigate the claims that the Os isotopic composition of the deep oceans varies on a glacial-interglacial timescale and consequently the mean residence time of Os in the oceans is between 8 and 10 ka (Oxburgh, 1998; 2001), about a factor of four to five less than that estimated from mass balance calculations (Sharma et al., 1997, 1999; Levasseur et al., 1999; Peucker- Ehrenbrink, 2002). At present, it is commonly believed that Os in seawater is derived from continents (rivers), submarine alteration (abyssal peridotites?), and micrometeorites. A shorter residence time would require the need to search for a yet another substantial source of Os to the deep ocean. We have measured Os isotopes in Fe-Mn fraction of core TNO57-21, which is a piston core recovered from ODP site #1089, located in the Cape Basin on the Agullhas drift ($41\deg$S, $7\deg$ E, depth = 4825 m). This site is unique in that it experienced extremely high sedimentation rates with little input of continental dust or volcanic ash. Therefore, the sediment is composed entirely of authigenic clays and carbonates. Osmium sequestered in the Fe-Mn portion of the core should yield the $^{187}$Os/$^{188}$Os ratio of ambient seawater. If Os has a residence time of 8-10 ka, we would expect to observe glacial-interglacial variations in our record reflective of variations in the intensity of continental weathering. If, on the other hand, the residence time is ~40 ka, as predicted by mass-balance equations, then the Os isotopic composition should remain essentially constant throughout the past glacial-interglacial cycle. Our data for the TNO57-21 show substantial variation during the past 100 Ka extending into the Holocene. Intriguingly, during MIS 4 and MIS 2 the isotopic composition of the oceans was more radiogenic than during much of MIS 3. Our record is relatively stable with $^{187}$Os/$^{188}$Os ratio of ~1.04 during MIS 5, 4 and 2, but shows significant variability during MIS 3: at 56 ka the $^{187}$Os/$^{188}$Os rises from 1.04 to the modern seawater composition of 1.06. It drops to a ratio of 1.0 at 40 ka and then rises to 1.04 at 36 ka. We also observe a rise in the Os isotopic composition from ~1.04 in MIS2 to ~1.06 in the most recent Holocene samples, a magnitude of change consistent with that observed by Oxburgh (1998). However, our record shows a much more recent transition to the modern seawater composition, a transition continuing into the present. It further suggests that Os is not in steady state and may be subjected to climate forcing. Indeed, Lomb-Scargle Spectrum analysis of the record shows the presence of 27 ka and 18 ka wavelengths, which have normalized spectral powers of 4 and 3.5, respectively. Further analyses are underway to understand the cause of this variation and to obtain a more complete record for the Holocene. DE HR: 14:55h AN: PP43B-06 TI: Paleoproductivity and Paleoclimate off Southern Chile During the last Deglaciation. Diatom and Phytoliths Records from Site 1233 AU: * Abrantes, F et al. EM AB: Diatom and Phytolith Accumulation Rates (DAR and PhAR) and diatom assemblage composition were determined between 23 and 8 Cal kyr B.P. for Site 1233 recovered off Southern Chile (41$^{§}$S, 74.45$^{§}$W, 837 m) during ODP Leg 202. At present, the site is located in an area where the surface forcing is dominated by strong poleward winds and heavy precipitation that generates a tongue of low-salinity water that spreads northward from the fjord region (43$^{§}$S). Oceanic circulation is dominated by the spliting of the West Wind Drift (WWD) into the Peru Current (PC) and the Cape Horn Current (CHC). Primary productivity in the region increases in winter/spring possibly associated to river input of nutrients and/or micronutrients. During the 22-8 Cal kyr B.P.time interval, both diatoms and phytoliths abundance show centennial to millennial variability. Marine Diatom AR increases as alkenone SST decreases and \delta$^{18}$O becomes heavier. Highest AR (10$^{8}$ valves/cm$^{2}$ kyr) occurs between 20 and 22 Cal kyr BP. The diatom assemblage is dominated by the genus Chaetoceros, which may be interpreted to reflect an intensification of the PC. A new average increase in DAR (to values 8*10$^{7}$ valves/cm$^{2}$ kyr) is noted from 11 to 9 Cal kyr B.Pfollowed by a sharp decrease to a minimum centered at about 8.4 Cal kyr B.P. This second maximum is accompanied by an increase in Thalassiosira spp indicating an increase in river induced productivity, and consequently stronger precipitation over southern Chile. Oceanic warm water forms reach maximum AR between 10 and 9 Cal kyr B.P. indicating a possible strong southward penetration of relatively warm subtropical waters or the poleward flowing undercurrent in the earliest Holocene. Increased PhAR occurs between 17 and 12 Cal kyr B.P. In general good agreement with a decrease in isotopic and alkenone derived salinity, this data points to an increase in grass source and continental input. Past sea-surface temperatures and productivity will be estimated on the basis of tranfer functions generated from a multivariate analysis of 232 SE Pacific surface sediment samples. DE HR: 13:55h AN: PP53D-02 INVITED TI: The evolution of atmospheric carbon dioxide since the middle Eocene: a biomarker perspective AU: * Pagani, M et al. EM AB: The carbon isotopic fractionation that occurs during marine photosynthetic carbon fixation ($\epsilon$$_{p}$) is primarily a function of surface-water [CO$_{2aq}$], growth rate, and cell geometry. Therefore, if temporal variations in growth rate and cell geometry are minimal or constrained, $\epsilon$$_{p}$ values provide the potential to evaluate paleo-pCO$_{2}$ concentrations and trends. Alkenone-based $\epsilon$$_{p}$ ($\epsilon$$_{p}$$_{37:2}$) records have been used to estimate atmospheric carbon dioxide concentrations during the Miocene ($\sim$24-5 Ma). These records provide evidence that pCO$_{2}$ was substantially lower than previously anticipated and suggest that changes in CO$_{2}$ played a secondary role in forcing global climate change during the Neogene. Alkenone $\delta$$^{13}$C values ($\delta$$_{37:2}$) for the middle Eocene to the late Oligocene were measured from six ocean locations encompassing a range of growth environments (DSDP sites 511, 513, 516, 612, and ODP site 803). Data from sites 511, 513, and 803 are limited but overlap other records. Site 516 (Southwest Atlantic Ocean) represents the most continuous record ranging from the middle Miocene to the earliest Oligocene. The Eocene portion of the record is derived largely from site 612 (Northwest Atlantic Ocean). Our results reveal a clear secular trend in $\delta$$_{37:2}$ from the early Miocene to the latest Eocene ($\sim$45 Ma), with $\delta$$_{37:2}$ values leveling off to $\sim$-32 to -33.4$\permil$ by the latest Eocene. By $\sim$25-30 Ma and older, $\delta$$_{37:2}$ values are more negative than the lowest values recorded from similar environments in the modern ocean. $\epsilon$$_{p}$$_{37:2}$ values were calculated using the $\delta$$^{13}$C values of aqueous CO$_{2}$ estimated from the $\delta$$^{13}$C of coeval planktonic foraminifera or modeled from the isotopic composition of the $<$60 um fraction. Surface temperatures were estimated from the $\delta$$^{18}$O compositions of shallow- dwelling foraminifera and/or modeled from the isotopic composition of the $<$60 um fraction. All carbonates were assumed to be influenced by secondary carbonate and thus estimated temperatures were increased by $3\deg$ to $6\deg$C to account for diagenesis. In general, $\epsilon$$_{p}$$_{37:2}$ values track $\delta$$_{37:2}$ reaching maximum values of $\sim$23$\permil$ by the late Eocene. Atmospheric carbon dioxide concentrations can be estimated if we apply the modern calibration for $\epsilon$$_{p}$$_{37:2}$ as a function of surface-water [PO$_{4}$$^{3-}$] and [CO$_{2aq}$] and assume that the range of paleo-[PO$_{4}$$^{3-}$] for each site was similar to modern distributions. These criteria lead to minimum estimates of pCO$_{2}$ that are highly dependent on our assumed ocean temperatures. Our results suggest that middle Eocene atmospheric carbon dioxide concentrations were $\sim$1000 to 1500 ppmv. Atmospheric carbon dioxide concentrations appear to rapidly decline following the Eocene/Oligocene boundary reaching modern values near the end of the Oligocene. DE: HR: 0800h AN: PP11A-0557 TI: Cenozoic variations in the South Atlantic carbonate saturation profile: Insights from the Walvis depth-transect (ODP Leg 208) AU: * Schellenberg, S and Nielsen, J
AB: Ocean Drilling Program Leg 208 Science Party (D. Kroon, J. C. Zachos, P. Blum, J. Bowles, P. Gaillot, T. Hasegawa, E. C. Hawthorne, D. A. Hodell, D. C. Kelly, J. Jung, S. M. Keller, Y. Lee, D. C. Leuschner, Z. Liu, K. C. Lohmann, L. Lourens, S. Monechi, M. Nicolo, I. Raffi, C. Riesselman, U. R”hl, D. Schmidt, A. Sluijs, D. Thomas, E. Thomas, H. Vallius) Carbonate saturation profiles are complex and dynamic products of processes operating on temporospatial scales from the "short-term local" (e.g. carbonate export production) to the "long-term global" (e.g. carbonate-silicate weathering, shelf:basin carbonate partitioning). Established, if admittedly crude, proxies for reconstructing carbonate saturation from sediments include wt% carbonate, where values of 0-20% are typically attributed to deposition below the carbonate compensation depth (CCD), and planktonic foraminifer fragmentation, where enhanced fragmentation is typically attributed to deposition below the lysocline. Ocean Drilling Program Leg 208 successfully drilled a six-site Walvis Ridge depth-transect spanning modern water depths from 2,717 to 4,755 m. Exceptional core recovery, well-constrained biomagnetostratigraphy, and standard crustal subsidence corrections provide a working age-depth framework for contouring ship-board wt% carbonate determinations and identifying the following first-order features of the regional CCD: (1) $>$3.5 km position from 60-48 Ma punctuated by a major transient shoaling to $<$2 km during the Paleocene-Eocene Thermal Maximum at $\sim$55 Ma; (2) shoaling to $\sim$2.75 km from 48 to 44 Ma; (3) subsequent deepening to $>$4.25 km from 37 to 28 Ma; (4) marked high amplitude fluctuations from 28 to 20 Ma followed by deepening to $>$4.75 km; (5) transient shoaling to $\sim$4 km around 15 Ma followed by deepening to $>$4.75 km by $\sim$12 Ma. These first-order features are broadly congruent with classic Atlantic CCD reconstructions by van Andel (1975) and Berger and Roth (1975). A wealth of higher frequency variation in carbonate saturation is clearly preserved within the Leg 208 depth-transect. Ongoing shore-based analyses aim to transform cm-scale variations in core physical properties (i.e. magnetic susceptibility, color reflectance) into synthetic records of wt% carbonate. These data, combined with other proxies (e.g., planktonic foraminifer fragmentation, stable isotopes) and placed within the evolving post-cruise biomagnetostratigraphic and cyclostratigraphic age-model, will provide valuable constraints on cyclic and secular fluctuations in the South Atlantic carbonate saturation profile and their relation to other major components of the earth system (e.g. pCO$_{2}$, eustacy). DE HR: 0800h AN: PP51E-1360 TI: Solar vs. Tidal Forcing of Centennial to Decadal Scale Variability in Marine Sedimentary Records from the Western Antarctic Peninsula AU: * Kirkwood, G et al. EM AB: Prior studies on Holocene marine sediments from the Antarctic Peninsula, including ODP Site 1098 and USAP N. B. Palmer jumbo piston cores have revealed pronounced multi-century scale variations within a number of paleoenvironmental proxies. In order to fully understand the exact timing of this signal an ultra-high resolution jumbo piston core from the Schollaert Drift was correlated with the well-known Palmer Deep record. A precise and accurate radiocarbon chronology is now available from the former site that utilizes in-situ mollusks, rather than bulk organic matter. The resulting time series spans the last 5000 years over the 20 m length of core NBP99-03 JPC28 and the surface stratigraphy of kasten core NBP01-07 KC8. The corrected and calibrated ages (with an applied reservoir correction of 1170 years) of 10 mollusks dated by the National Ocean Sciences Accelerator Mass Spectrometry Facility and the University of Arizona TAMS facility were used to construct an age-depth profile for JPC28 and KC8. A linear trend (R$^{2}$ value of 0.993) of the age-depth profile was used to extrapolate the constant time interval between magnetic susceptibility measurements, which were analyzed every 1 cm. Dominant periods in the upper 10 m of the time series were identified using the Arand Spectral Analysis Package (Howell, 2001). This analysis revealed a single pronounced maxima at 160 years, which is inconsistent with the dominant periods found in time series of climate proxies from other sites on the western side of the Antarctic Peninsula. In particular, periods of 200 and 400 years, which are dominant in the Palmer Deep site (Warner and Domack, 2002), are not present in the Schollaert Drift. The spectral peaks derived from the two records are significantly different at the 95% confidence level. The cycles in the Palmer Deep record have been associated with solar variability, where as the 160 year cycle in the Schollaert Drift is close to a 180 year cycle in tidal forces (Keeling and Whorf, 2000). We discuss these alternative forcing mechanisms with respect to: contrasts in regional processes of glacial marine sedimentation, the mechanism whereby the tidal or solar signal is transferred to the sediment column and possible cryptic stratigraphy of the Palmer Deep record (ie. missing time, Nederbragt and Thurow, 2002). Resolution of the correct forcing factor is critical to our ability to hind cast the last 100 years of paleoenvironmental data within these cores and hence to our attempts at recognizing an anthropogenic climate signal in the Antarctic Peninsula region. Howell, P. (2001), ARAND time series and spectral analysis package for the Macintosh, Brown University, IGBP PAGES/World Data Center for Paleoclimatology Data Contribution Series #2001-044, NOAA/NGDC Paleoclimatology Program, Boulder, Colo. Keeling, Charles D., and Timothy P. Whorf (2000), The 1,800- year oceanic tidal cycle: A possible cause of rapid climate change, {\it Proc. Natl. Acad. Sci., 97} (8), 3814-3819. Nederbragt, A. J., and Thurow, J. (2002) Sediment color variation and annual accumulation rates in laminated Holocene sediments, Site 1098, Palmer Deep. In Barker, P. F., Camerlenghi, A., Acton, G. D., and Ramsay, A.T.S. (eds), Proc. ODP Sci. Results, 178: College Station TX (Ocean Drilling Program). Warner, Nathaniel R., and E. Domack (2002), Millennial-to decadal-scale paleoenvironmental change during the Holocene in the Palmer Deep, Antarctica, as recorded by particle size analysis, {\it Paleoceanography, 17} (3), 8004, doi:10.1029/2000PA000602. DE HR: 16:15h AN: PP14A-02 TI: Multiple Early Eocene Thermal Maximums AU: * Roehl, U et al. EM AB: Periodic dissolution horizons signifying abrupt shoaling of the lysocline and CCD are characteristic features of deep-sea sections and often attributed to Milankovitch forcing via their diagnostic frequencies. Prominent dissolution horizons also correspond to abrupt climate events, such as the Paleocene-Eocene thermal maximum (PETM), as a result of input of significant CH$_{4}$ - CO$_{2}$ into the ocean-atmosphere system. The question arises whether other significant dissolution horizons identified in sediments of late Paleocene and early Eocene age similar to the recently identified ELMO (Lourens et al., 2004) were formed as a result of greenhouse gas input, or whether they were related to cumulative effects of periodic changes in ocean chemistry and circulation. Here we report the discovery of a 3$^{rd}$ thermal maximum in early Eocene (about 52 Ma) sediments recovered from the South Atlantic during ODP Leg 208. The prominent clay layer was named the "X" event and was identified within planktonic foraminifer zone P7 and calcareous nannofossil zone CP10 at four Walvis Ridge Transect sites with a water depth range of 2000 m (Sites 1262 to 1267). Benthics assemblages are composed of small individuals, have low diversity and high dominance. Dominant taxa are {\it Nuttallides truempyi} and various abyssaminids, resembling the post PETM extinction assemblages. High-resolution bulk carbonate \delta$^{13}$C measurements of one of the more shallow Sites 1265 reveal a rapid about 0.6 per mill drop in \delta$^{13}$C and \delta$^{18}$O followed by an exponential recovery to pre-excursion \delta$^{13}$C values well known for the PETM and also observed for the ELMO. The planktonic foraminiferal \delta$^{13}$C records of {\it Morozovella subbotina} and {\it Acaranina soldadoensis} in the deepest Site 1262 show a 0.8 to 0.9 per mill drop, whereas the \delta$^{13}$C drop of benthic foraminifera {\it Nuttallides truempyi} is slightly larger (about 1 per mill). We are evaluating mechanisms for the widespread change in deep- water chemistry, its connection to the surface-water response, and the relationship of the event, as well as the PETM and ELMO, with current astronomical solutions (Laskar et al., 2004; Varadi et al., 2003). References 1. Lourens, L.J., Sluijs, A., Kroon, D., Zachos, J.C., Thomas, E., Roehl, U., and the ODP Leg 208 Shipboard Scientific Party, 2004. An early Eocene transient warming (~53 Ma): Implications for astronomically-paced early Eocene hyperthermal events.- Abstract, 8th International Conference on Paleoceanography (ICP), 5-10 September 2004, Biarritz, France. 2. F. Varadi, B. Bunnegar, M. Ghil, Astrophysical J. 592, 620-630 (2003). 3. J. Laskar et al., Astronomy and Astrophysics (2004). DE: HR: 0800h AN: PP51D-1354 TI: Orbital forced sea level fluctuations during the Middle Eocene (ODP site 1172, East Tasman Plateau) AU: * Warnaar, J et al. EM AB: Ocean Drilling Program leg 189 was undertaken to test and refine the hypothesis (by Kennett et al., 1975), that the reconfiguration of continents around Antarctica (e.g.: the opening of the Tasmanian Gateway and Drake passage) led to the onset of the Antarctic Circumpolar Current that, in turn, would cause thermal isolation and hence cooling of Antarctica. This would possibly even cause global cooling, as suggested by the 33.3 Ma Oi1 event. The cores of leg 189, site 1172 on the eastern side of the Tasmanian Gateway provided a nearly complete succession of Eocene and Oligocene sediments. Cyclostratigraphic analysis based on XRF derived Ca and Fe records indicates distinct Milankovitch cyclicity between 40 and 36 Ma. (R”hl et al, in press). In the core- section representing magnetochron 18n-1n, the Ca record shows precession cycles in combination with obliquity, suggested to reflect sea level fluctuations (R”hl et al, in press). New datasets include microfossil data (organic-walled dinoflagellate cysts, pollen/spores and diatoms), loss-on-ignition measurements, magnetic data (environmental magnetics - ARM). Here, we aim to further investigate the proposed relationship between astronomical forcing and sea-level fluctuations. Additionally, we aim to obtain insight in the palaeoecology of the distinct endemic circum-Antarctic late Middle to Late Eocene dinoflagellate cyst assemblages. Results corroborate the concept that the cyclicity recorded by Ca and Fe measurements is the result of sea-level fluctuations. This implies that during late Middle Eocene times, astronomical forcing has modulated sea level - most likely through Antarctic ice buildup and meltdown. In turn, this would indicate the presence of significant, though probably modest, ice masses already ~40 Ma ago, well before the onset of the Antarctic Circumpolar Current. Kennett, J. P., R. E. Houtz, et al. (1975). Development of the circum-Antarctic current. Science 186: 144-147. R”hl, U.; H. Brinkhuis, C.E. Stickley, M. Fuller, S.A. Schellenberg, G. Wefer, G. Williams, Cyclostratigraphy of Middle and Late Eocene sediments from the East Tasman Plateau (site 1172), in press. DE HR: 16:20h AN: PP54B-02 TI: Timing and Nature of the Deepening of the Tasmanian Gateway AU: * Stickley, C et al. EM AB: In the late Paleogene, Australia separated from Antarctica and continued to drift northwards allowing the eventual development of the Antarctic Circumpolar Current (ACC). The exact timing and nature of the opening of this gateway during the Eocene- Oligocene (E/O) transition is of interest in respect to its apparent synchroneity with climate deterioration on continental Antarctica. The recovery of a continuous marine sedimentary record across the E/O transition at 4 sites within the Tasmanian Gateway (TG) during ODP 189, allows detailed paleoenvironmental changes to be documented at high resolution in this region. The critical sedimentary units are barren of calcareous microfossils yet siliceous and organic-walled microfossils (notably diatoms and dinocysts) are abundant and excellently preserved, allowing an integrated and detailed paleoeonvironmental analysis of the E/O transition. We present results from Site 1172 and report on the timing and nature of several step-wise deepening events and paleooceanographic changes across the E/O transition in the TG. We use integrated diatom, dinocyst, geochemical, lithological and physical property data to show that the TG deepened at 35.5 Ma, preceding the E/O Antarctic glaciation event by 2 Ma. Importantly our microfossil data indicate a pre-deepening shallow-water pro-deltaic setting characterized by highly endemic biota influenced by a cool clockwise rotating `proto-Ross Sea gyre', to a post-deepening pelagic setting in the earliest Oligocene characterized by cosmopolitan biota. Interestingly these findings indicate a warming in the TG at the exact time when, according to previous hypotheses, a cool-ACC should be influencing the region. These conclusions are corroborated independently by the modeling results of Huber et al., (in press, Palaeoceanography). DE HR: 08:15h AN: PP11C-02 TI: Late Quaternary Biosiliceous Laminated Marine Sediments From Antarctica: Seasonality During a Period of Rapid Climate Change AU: Pike, J et al. EM AB: The Antarctic ice sheet plays a key role in global oceanic and atmosphere systems. One of the most dynamic regions of the continent is the Antarctic Peninsula (AP) where ecological and cryospheric systems respond rapidly to climate change, such as the last deglaciation ($\sim$12-13 kyr BP). Here, deglacial laminated diatom-rich marine sediments are well known, e.g., Palmer Deep (64$\deg$S 64$\deg$W; ODP Hole 1098A) comprising a distinctive 3 m thick sequence of deglacial `couplet' laminations. The East Antarctic margin (EAM), however, has received less attention than the West Antarctic margin (WAM) in palaeoceanographic studies yet its role in deep ocean circulation and, therefore, the global ocean system is significant. Recent sediment cores recovered from EAM sites during NSF Polar Programs-funded cruise NBP0101 in February and March 2001 (e.g. Mertz Drift \{66$\deg$S 143$\deg$E\}, Svenner Channel \{69$\deg$S 77$\deg$E\} in Prydz Bay, Nielsen Basin \{67$\deg$S 66$\deg$E\} and Iceberg Alley \{67$\deg$S 63$\deg$E\}), reveal that a similar sedimentary facies was deposited along the EAM, in similar geomorphological settings to Palmer Deep, during the same timeframe. These rich sediment archives reveal clues about circum-Antarctic palaeoceanographic change during the last deglaciation, a time of both high silica flux and rapid climate change. Microfabrics and diatom assemblages from scanning electron microscope backscattered and secondary electron imagery analysis of coeval deglacial varves from Palmer Deep (WAM), Mertz-Ninnis Trough and Iceberg Alley (EAM) are presented and compared. The varves from these localities are characterised by laminae to thin beds of orange-brown diatom ooze up to $\sim$8cm thick alternating with blue-grey diatom-bearing terrigenous sediments up to $\sim$4cm thick. The orange-brown oozes are dominated by resting spores and vegetative valves of {\itHyalochaete Chaetoceros} spp., resulting from spring sedimentation associated with stratified surface waters promoting exceptionally high primary productivity. The blue-grey terrigenous sediments contain mixed open-water Antarctic diatoms resulting from summer/autumn sedimentation associated with increased terrigenous input and the annual trend to more oligotrophic conditions. The significance of these biogenic seasonal and annual cyclicities will be discussed in terms of interannual palaeoclimate oscillations. Sub- seasonality and a related deglacial trend are apparent within the spring lamine from the EAM and in the summer/autumn laminae from the WAM. This circum-Antarctic asymmetry indicates differences in the nature and timing of oceanographic and cryospheric systems operating around the Antarctic continent at this time. DE HR: 0800h AN: S51B-0148 TI: Permeability Measurements of Ocean Drilling Program Samples Collected From the Costa Rican Subduction Zone AU: * Hays, T et al. EM AB: Permeability is a key component in evaluating pore pressures and consolidation history in sediments. Core samples collected from the Costa Rican subduction zone were tested to determine their vertical permeabilities. The samples are from Ocean Drilling Program (ODP) Leg 205 Sites 1253, 1254, and 1255 and ODP Leg 170 Site 1040. The Costa Rican subduction zone has been shown to currently be a nonaccreting margin, and all samples are from within the underthrust sediments. The measurements were made using a constant head test by inducing a pressure gradient across the sample. Measurements were taken for three different consolidation pressures with five different pressure gradients induced across the sample in each consolidation. Two types of samples were tested; light colored, fine grained pelagic carbonates and dark colored, fine grained hemipelagic clays. Our results show two groupings of permeabilities, with the pelagic carbonates approximately two orders of magnitude higher than the hemipelagic clays. These results are consistent with permeabilities found by previous researchers. DE: HR: 0800h AN: S51B-0163 TI: Along strike changes in basement topography and sediment thickness in the northern Shikoku Basin: Variable inputs to the Nankai Trough Seismogenic Zone AU: * Ike, T et al. EM AB: The very thick terrigenous sediments in the Nankai Trough and the northern Shikoku Basin mask significant basement irregularities that will soon be subducted into the Nankai seismogenic zone. We present a new seismic reflection data set across the northern Shikoku Basin that images remarkable variations in basement relief and corresponding variations in sediment thickness and type. The basement relief has a wavelength of ~5-15 km, with the amplitude of the peaks and troughs generally ~300- 400m. Two significant troughs exist south of Shikoku that are each ~ 12 -15 km wide and 1900 m deep. These troughs strike NW-SE and are at least 40 km long. They are mostly filled with high amplitude continuous reflections that onlap the trough margins. We correlate these reflections with the mid-Miocene lower Shikoku Basin turbidite sequence drilled at ODP site 1177. Along strike approximately 125 km to the NE, off the Kii Peninsula, there is a significant basement high that is just entering the trench ~ 15 km from the base of the inner trench slope. It is roughly oval with a diameter of ~50km parallel to the trench axis and ~20 km perpendicular to the trench, with a peak that is 1400 m higher than the adjacent crust. This basement high (seamount) is covered by the hemipelagic Shikoku Basin sediments that thin from 900 m on the SW flank to 200 m at the summit. The Shikoku Basin turbidite section that fills the troughs to the SW is absent on the seamount and its flanks. Because of the variations in sediment thickness around this seamount, its bathymetric summit is only 800 m above the adjacent seafloor while the basement relief is 1400m. Between the seamount and Zenisu Ridge (~ 60 km NE), the basement deepens by 500 m and has subdued relief (compared to that SW of the seamount). Basement is overlain by the Shikoku Basin hemipelagic sequence and onlapped by young trench turbidites. These significant along strike variations in basement topography (1400m high seamounts and 1900m deep troughs), sediment thickness (200- 2000m) and sediment type (hemipelagics vs turbidites) will soon be input to the Nankai seismogenic zone and are representative of the kinds of irregularities that have been input in the geologic past. Such variations must contribute to along-strike differences in seismogenic behavior. DE HR: 0800h AN: S51B-0151 TI: Pore-Water Freshening in the Nankai Trough, Japan: Implications for Lateral Fluid Flow AU: * McKiernan, A and Saffer, AB: Pore-water freshening has been observed in ocean sediments cored along the Muroto Transect in the Nankai Trough, offshore Japan during ODP Legs 190/196. Chloride concentrations up to $\sim$11% below normal seawater values ([Cl-] $\sim$555 mM) were documented at drill site 1173, 13 km seaward of the trench. Updip, lateral fluid flow from depth, and in situ clay dehydration have been proposed as freshening sources. Placing realistic bounds on the relative contributions of these potential sources has importance for quantifying fluid and chemical fluxes in subduction zones. Here, we evaluate the hypothesis that freshening is due solely to in situ clay dehydration. We simulate the general shape and magnitude of the down hole [Cl-] anomaly observed at site 1173 using a one-dimensional model which combines sedimentation, thermal history, clay dehydration, and Cl- diffusion. Sediment accumulation during arcward transport and high heat flow for the area ($\sim$180 mW/m2), result in temperatures sufficient to transform smectite to illite + H20. The volume of released water scales with initial smectite abundance (here we assume 50% by weight based on mineralogy at site 1177, where heat flow is low and clays are less reacted). In the model, released water is added at each time step creating unstable [Cl-] profiles. Chloride diffusion is modeled implicitly in a reference frame fixed to the interstitial water column, through which consolidating sediment nodes move. Basal boundary conditions used in the model are: constant [Cl-], no-flow, and the inclusion of oceanic crust in diffusion. Simulated reaction progress matches observed clay mineralogy for site 1173. Minimum simulated [Cl-] scales with initial smectite content, ranging from 4% freshening for 20% initial smectite, to 14% freshening for 70% initial smectite. Simulated [Cl-] profiles for all boundary conditions mimic the general [Cl-] profile for site 1173, but no single boundary matches observed data exactly. A no-flow basal boundary reaches a minimum [Cl-] of $\sim$500 mM (10% freshening) but does so at the sediment-oceanic crust interface, $\sim$100 m below the observed minimum. Constant-concentration basal conditions show a return to normal [Cl- ] near the base of the section, but lack [Cl-] minima and maxima comparable to those observed. Oceanic crust is included in some models to simulate communication between basement and sediment. These models show similar behavior to no-flow and constant- concentration boundaries, differing mainly in magnitude. HR: 11:20h AN: T42B-05 TI: Stratigraphic Control on Excess Pore Pressure at the Plate Boundary Fault of Nankai Trough AU: * Underwood, M B et al. EM AB: One of the unresolved issues regarding the subduction front of Nankai Trough is the control over stratigraphic position of the decollement. The Muroto Transect area (ODP Sites 808, 1173, 1174) is atypical of the regional system because hemipelagic strata within the lower Shikoku Basin accumulated above a basement high formed by back-arc spreading and late-stage seamount volcanism. The Ashizuri Transect area (ODP Site 1177) is more characteristic of the system as a whole. Seismic reflection and coring prove that sandy turbidites are common within the lower Shikoku Basin facies, except along the Muroto Transect. Consolidation tests demonstrate that the stratigraphic equivalent of the decollement at Site 1173 is slightly overconsolidated, whereas strata below the decollement horizon are heavily overconsolidated. Samples from Site 1177, in contrast, are slightly to heavily underconsolidated within and immediately below the stratigraphic equivalent of the decollement. Mudstones within the underlying Shikoku Basin turbidite facies show moderate to strong overconsolidation. Evidently, the turbidite facies drains very effectively through a process of compaction-driven fluid flow. There is a 40-m interval of mudstone above the turbidites, however, which acts as an aquitard. Stratigraphic compartments of overpressure build up long before the subducting strata reach the deformation front, especially where the uncemented sand packets pinch out. Tectonic consolidation and up-dip fluid flow beneath the decollement exacerbate the overpressured condition. The unusually high fluid pressures reduce effective stress and provide the optimal location for propagation of the plate boundary fault. DE HR: 0800h AN: T41E-1273 TI: Distribution of Post-Rift Sills on the Newfoundland Nonvolcanic Margin Around the ODP Leg 210 Transect From Waveform Inversions and Synthetic Seismograms AU: * Shillington, D et al. EM AB: Nonvolcanic rifted margins commonly include a section of crust of uncertain affinity between normal oceanic crust and extended continental crust. The origin of this portion of the margin, often called the transition zone, is essential to establishing the symmetry of rifted margins and developing models for margin evolution. The Newfoundland-Iberia rifted margin pair is among the best-studied nonvolcanic conjugate margin pairs in the world. Drilling on the Newfoundland nonvolcanic margin during ODP Leg 210 at Site 1276 did not reach enigmatic transitional basement, but did reveal the presence of interlayered sills and sediments immediately above the inferred top of transitional crust. The presence of sills has implications for the appearance of underlying transitional basement in seismic reflection sections, the signature of this section of the margin in shiptrack magnetic data and late-stage margin evolution. Sills are estimated to be approximately 100 m.y., while rifting likely occurred ~125 Ma. Shipboard work suggests that sills encountered at Site 1276 correspond to bright reflections in the lowermost sedimentary section overlying transitional crust that are observed in coincident seismic reflection profiles collected during the SCREECH (Studies of Continental Rifting and Extension on the Eastern Canadian SHelf) experiment during 2000. These profiles also show that basement in the transition zone is essentially featureless in seismic reflection data except where it rises above these bright reflections, implying either that impedance contrasts in the deep section prevent signal transmission or that there is little contrast between interlayered sills and sediments and the underlying basement. Here, we strengthen the link between seismic reflection data and drilling data by creating synthetic seismograms from physical properties measurements made at sea aboard ODP Leg 210. Physical properties data were used in lieu of logging data, which could not be collected due to poor hole conditions. To extend the results from Site 1276 to rest of the grid of seismic lines in this region, waveform inversions were also carried out on select supergathers around the SCREECH Line 2 survey and compared with waveform inversions of data near Site 1276. This work reveals significant variability in the velocity contrasts required by deep reflections thought to be associated with sills in the transition zone, implying similar variability in the distribution of sills. Furthermore, a distinct difference is observed between bright reflections overlying transitional crust and reflections at similar depths further seaward over unambiguous oceanic crust. DE
HR: 0800h AN: T41A-1160 TI: Enriched MORB in the Northeastern Pacific, Petrological and Geochemical Features of igneous Basement at Site 1224, ODP Leg200 AU: * Haraguchi, S and Ishii, T EM AB: During Ocean Drilling Program (ODP) Leg 200, 45-Ma igneous basement was cored in the northeastern Pacific at Site 1224. The basement surface was assumed to be 28 m below seafloor (mbsf). Basement lithology down to 170 mbsf is divided into three units: Unit 1 massive flow, Unit 2 pillow breccia, and Unit 3 massive flow. The shallowest Unit 1 shows massive structure with some altered layers and vein deposits, and core recovery was 30%-50%. This unit is divided into two thick lava flows based on grain size stratigraphy and alteration layers. Intermediate-depth Unit 2 shows different characteristics than Unit 1. Core recovery was so low (<10%), and many of the small pieces retain almost circumferential alteration. Some calcite-cemented hyaloclastite layers were found. The difference in induration between the two units was so great that the drill bit broke at the Unit 1/Unit 2 boundary. The deepest Unit 3 shows features similar to Unit 1. Portions of at least two cooling units were recovered, and possibly more. Recovery in Unit 3 was lower than that in Unit 1 but higher than that in Unit 2 (20%~30%). Bulk compositions of Site 1224 rocks show interesting characteristics, the most important of which is high high-field-strength element (HFSE) content compared to typical normal and enriched mid-ocean-ridge basalts (MORB) (Sun and McDonough, 1989). Chemical stratigraphy (chemostratigraphy) differences among the three units at this site are clear. Unit 3 rocks are fractionated, and Unit 2 rocks have relatively primitive FeO/MgO ratios. Large-ion-lithophile element (LILE) content is higher Unit 2 than in Units 1 and 3. The high LILE content of Unit 2 is thought to be caused by hydrothermal alteration rather than a petrographic feature. HFSE content patterns are similar to those of FeO/MgO ratios. Unit 1 is separated into upper and lower subunits, which correspond to flow units, on the basis of HFSE content. Unit 2 has lower HFSE content and higher Y/Zr ratios, thought to result from a magma generation environment that was different from other units. The parent mantle of Unit 2 basalt was probably of a different, depleted composition compared to Units 1 and 3. Perhaps the most interesting result from this site is isotope characterization. The Sr and Nd isotope ratios are more enriched than typical Pacific MORB (Hickey-Vargas et al., 1995). These characteristics are attributed to mantle enrichment, and this enriched component is thought to still exist in the Pacific mantle. Many drill sites in the eastern Pacific show compositions similar to N-MORB (Sun and McDonough, 1989) (i.e. ODP Leg148; Brewer et al., 1996). Brewer et al. (1996) studied chemostratigraphy of the basement at from Holes 896A and 504B. They concluded that variations in chemostratigraohy were mainly caused by differentiation. When the Leg148 sites and Site 1224 results, are compared, Site 1224 basement shows more than twice the HFSE content than Sites 896 and 504, and the compositional changes is noted at Sites 896 and 504 differ from those of Site 1224. It is thought that the mid- ocean-ridge volcanism at Site 1224 was produced from more enriched mantle than that of the recent Eastern Pacific Rise and that these activities were associated with different mantle sources simultaneously. Chemostratigraphic and lithologic differences between the basement units correlate to differences in physical properties between the three units. Each lithologic unit displays different P-wave velocity, bulk density, and other physical properties. Physical properties are thought to be associated with petrological features. DE
HR: 16:50h AN: T14C-04 TI: Analysis of the Growth of Active Detachment Folds Applying the new Thickness Relief Method, With Examples From the Tien- Shan and Nankai Trough AU: * Gonzalez-Mieres, R and Suppe, J EM: AB: Active folds develop distinctive stratigraphic geometries resulting from the interactions of sedimentation and deformation, which provides a quantitative record of deformation history. Modern seismic with excellent images of growth deposits, allow us to extract this record of deformation in a detailed and quantitative way applying the new thickness-relief method. We apply the thickness relief method to growth strata of two actives detachment folds, one in Yakeng anticline of the southern Tien-Shan China and another at the front of the Nankai Trough Japan (ODP legs 190, 196). The method involves determination of areas of structural relief as a function of height based on thickness variations of all imaged horizons. This yields a high-resolution profile of shortening, as a function of height since shortening is the derivative of the area-height curve. The thickness-relief method has been successfully applied to pre-growth sequences in a number of structures. Here we extend the method to growth strata. The onset of growth is represented in the area-height plot as an upward decrease rate of growth of fold area, which is most easily analyzed through modeling. A wide variety of distinctive behaviors are expected for various ratios of sedimentation to deformation rate, depending also on the depth to detachment. Amplitude obtaining valuable information about the shortening and how this is accommodated into detachment folds. The slope of best-fit line represents shortening or displacement in the area relief graph. So, as deformation and sedimentation starts to interact the geometry of deposits change and area-relief, height, and shortening relationship is affected. Deviation from the linear trend, negative or a decrease in slope, are signatures of the growth in area relief graph, however data are restricted and theoretical models are necessary to understand the behavior of the graph. We use these models to fit real data on growth strata of Nankai and Yakeng detachment folds, which show substantially different behavior. We found that the very young and rapidly growing Nankai fold at a fast-moving plate boundary displays a sedimentation rate that is no more than 25 to 30 % of shortening rate. In contrast the Yakeng anticline in the more slowly deforming Tien-Shan of central Asia shows a sedimentation rate that is 167 % the shortening rate. We make use of available age control to transform these observations into sedimentation and deformation rates. DE HR: 1340h AN: T13B-1357 TI: Structure of the Upper Crust Exposed at Endeavor Deep: Implications for Crustal Accretion at Ultra-Fast Spreading Rates AU: * Popham, C et al. EM AB: Endeavor Deep lies at the tip of the propagating spreading center defining the Juan Fernandez/Nazca plate boundary. This 3 km-deep, amagmatic basin,which rifted into ultra-fast spread 3Myr old Nazca Plate crust, was recently surveyed and sampled with Simrad EM300, DSL-120 and ROV Jason II. Over 140 structural orientations measured from Jason II video of the south rift wall show that flows in extrusive layer 2a strike north-south and dip shallowly to the west, while dikes in intrusive layer 2b strike east- west and dip steeply to the south. Using a general model for crustal accretion in which dikes are emplaced vertically and extrusives horizontally, a rotational history is determined for the 3 Myr old crust exposed in the walls of the deep. Multiple rotations are necessary with two-fold intent, first to return structure to the original off-axis orientation prior to tectonic reorganization; second to account for rotations involved in the process of accretion. Tectonic events are first addressed with a 10-25 degree rotation about a horizontal rift parallel axis to account for flexural uplift. Next a 65-degree rotation applied about a vertical axis to return magnetic lineation 2a to its proposed paleo- off axis orientation. After rotation, intrusive and extrusive populations are strike parallel (N5E). In this orientation, dikes average 65-degree dip away from and extrusives 25- degree dip towards the ridge axis. This generally conforms to observations at Hess deep, Blanco FZ, and ODP hole 801C. The second goal of rotation is to account for off axis adjustments during crustal accretion; a 25-degree rotation about a ridge parallel, horizontal axis returns the average dike inclination to vertical and the extrusive dip to horizontal. DE:
HR: 0800h AN: T41C-1241 TI: Varying Rates and Modes of Subduction Erosion Along the Peruvian Margin AU: * Kukowski, N et al. EM: AB: At least half of the world's active margin length now is attributed to the erosive type with regard to their mass transfer modes. However, the mechanisms, loci and rates of subduction erosion still are not fully understood. Among factors contributing to subduction erosion, subduction of asperities, roughness of the downgoing plate, and rheological properties of the overriding plate are thought to be of major importance in determining its styles and amounts. The Peruvian margin, the southern portion of which has experienced collision of the Nazca Ridge, is an exceptionally suitable location to study subduction erosion. Here it is possible to compare portions of a margin that have either been affected or not affected, respectively, by the subduction of major asperities. Swath bathymetry data acquired during RV Sonne cruise SO146 reveals high, but regionally different roughness of the almost sediment free Nazca plate. RMS roughness, local dip, curvedness, and void volume, i.e. the volume between peaks and valleys potentially filled with eroded material, decrease from north to south. Recently acquired wide angle data now together with information on long-term subsidence from ODP Leg 112 Site 683 enable to estimate the rates of subduction erosion across the Peruvian margin at 9\deg S, a region which was not affected by ridge subduction. Rates are 24 to 30 km$^{3}$ km$^{-1}$ myr$^{-1}$ since the middle Miocene, 15 km$^{3}$ km$^{1}$ myr$^{-1}$ since about 40 Ma and 6.5 km$^{3}$ km$^{1}$ myr$^{-1}$ for the interval 40 to 13 Ma. These rates are considerably smaller than published long-term rates (since 40 Ma) estimated further to the south (12\deg S) or short-term (since the Pliocene) erosion rates estimated further north at about 7\deg S. However, at 9\deg S, the void volume is not much less than the eroded volume, whereas at 12\deg S, the eroded volume is about 3 times the void volume. This comparison reveals that different mechanisms of subduction erosion, which are suggested to be attributed to differences in the rheology and strength of the overriding South American plate, take place along the Peruvian margin. DE
HR: 0800h AN: T41A-1170 TI: Atlantis Bank as a Key to Understanding the Nature of the Moho and Crust-Mantle Boundary AU: * Matsumoto, T et al. EM AB: Atlantis Bank on the Southwest Indian Ridge is a key site for the study of the oceanic lower crust and mantle. It exposes an eroded oceanic core complex lying along the western flank of the Atlantis II transform. The complex exposes of huge 400+ km2 gabbroic massif that is at least 1500-m thick at ODP Site 735. Mantle peridotites are exposed on the lower slopes of the transform wall that flanks the core complex, where they locally appear to underlie the gabbro body. During the SHINKAI 6500 cruises in 1998 and 2002, seafloor gravimetry was carried out at 16 stations on the Bank to detect its precise density structure. The average density of the basement rocks on the western slope of the bank was estimated as 3.0 g/cc (lower part), 3.8 g/cc (middle part) and 3.1 g/cc (upper part), corresponding to mantle peridotite, oxide Fe-Ti gabbro and peridotite/oxide olivine gabbro collected at these sites respectively. Average density of basement rock on the eastern slope was estimated as 3.1 g/cc (lower part) and 2.6 g/cc (middle part). The southwestern slope of the bank is characterised by exposure of unaltered layered gabbro underlain by serpentinized peridotite according to observations and sampling during the 2002 survey. Average bedrock density at this site is 2.5g/cc, extremely low considering the exposure of lower crust and upper mantle rocks there. According to the seismic survey crossing the bank (Muller, et al., 1997, 2000), a discontinuity at 4 km below seafloor at the foot of the bank and at 6 km bsf at the summit was identified. P wave velocity contrast indicates that the boundary is equivalent to Moho. Their result also shows that the southwestern slope corresponds to the Layer-2 (Layer-1 is missing), and the estimated P wave velocity of 3.6 km/s is in good agreement with the basement rock density derived from seafloor gravimetry. The Moho is not necessarily identical to the petrological crust-mantle boundary and it is possible that it is the boundary between serpentinized and non-serpentinized peridotite as shown in 'Hess model', and as also suggested by Muller, et al. (1997). This hypothesis will be tested in the future IODP riser drilling. DE: HR: 0800h AN: T41E-1256 TI: Opal diagenesis and sediment properties in the Nankai Trough, Japan AU: * Spinelli, G et al. EM AB: We have measured the opal content and modeled opal diagenesis for sediment from Ocean Drilling Program (ODP) Sites 1173, 1174, and 1177 in the Nankai Trough, Japan. The porosity of the Upper Shikoku Basin facies at 1173 is nearly constant with depth from $\sim$102 to 344 mbsf. There is a step decrease in porosity across the Upper Shikoku Basin / Lower Shikoku Basin facies boundary at Site 1173; porosity decreases with depth normally in the Lower Shikoku Basin facies. Sediment physical properties suggest that the cementing of grain contacts within the Upper Shikoku Basin facies inhibits sediment consolidation, however, the nature of the cement has not been previously identified. In addition, it has been suggested that the Upper Shikoku Basin / Lower Shikoku Basin facies boundary is at least partially a diagenetic boundary. Opal comprises $<$2 wt% of the sediment at all of the sites. At Site 1173, the Upper Shikoku Basin sediment contains $\sim$1.25 wt% opal. The opal content drops abruptly to $<$0.5 wt% across the Upper Shikoku Basin / Lower Shikoku Basin facies boundary - corresponding with the drop in porosity and the return to normal consolidation behavior in the Lower Shikoku Basin facies. Secondary and back-scattered electron image analysis of sediments at this site reveals a low density, Si-rich phase that is probably opal. This material occurs as a pore-filling cement, coating grains and grain-to-grain contacts. It appears to be more common in the Upper Shikoku Basin facies than in the Lower facies. SEM analyses suggest the presence of authigenic clays in the Lower Shikoku Basin facies. We model sediment accumulation and the thermal evolution of the sediment columns for the sites. Then, we use the thermal history of the sediment and laboratory derived kinetics for the opal-to-quartz diagenetic reaction to model the opal content in the sediment column. Modeled opal content at Site 1173 decreases rapidly below 250 mbsf, where temperatures exceed 50$^\circ$C. The model results indicate that the reaction runs to completion (i.e. the last of the opal is removed) approximately at the Upper Shikoku Basin / Lower Shikoku Basin facies boundary. The model results are in good agreement with the opal measurements and suggest that opal cement may be holding open the pore space in the Upper Shikoku Basin section. It appears that during opal diagenesis the strength of the cement is lost and the pore space collapses. This apparent loss of strength is consistent with previously described loss of shear rigidity reflected in anomalous seismic velocities measured across this zone. Both this loss of strength and high dissolved silica content in sediment pore water in the Upper Shikoku Basin facies may result from the loss of opal without immediate conversion into quartz. A sharp decrease in dissolved silica across the facies bounadry may be related to the uptake of silica into authigenic clays in the Lower Shikoku Basin facies. D
HR: 0800h AN: T21C-0538 INVITED TI: Long-Term Observations of Active Hydrothermal Processes on the Gorda Ridge: The Sea Cliff Hydrothermal Field and Escanaba Trough AU: * Von Damm, K et al. EM AB: The two known sites of high temperature hydrothermal venting on the Gorda Ridge are the northerly Sea Cliff hydrothermal field and the southerly Escanaba Trough. Indications that the Sea Cliff field (GR-14) existed were first obtained from hydrographic work in 1985, and confirmed by the discovery of the site in 1988. Our cruise at the site in 2000 was the first time fluids were sampled, and we subsequently also collected fluids in 2002. One reason the Sea Cliff field is of interest is its location $\sim$3km east of the axis of spreading. It was suggested that the site might therefore be relatively 'old,' or at least located on 'older crust' at the 5.5cm/yr spreading rate. All of the hydrothermal fluids from Sea Cliff are low chlorinity, or vapor phase, contrary to its previous interpretation as an older hydrothermal system which are generally interpreted to vent fluids with chloride contents greater than seawater. Our other chemical data also support our interpretation that this system is not tapping highly altered crust. In spite of the $>$$300\deg$C measured temperatures of the vent fluids, they are strikingly clear, and have Fe contents $\sim30$ umoles/kg, about 2 orders of magnitude less than typical. The low Fe, and other transition metals, are likely a result of the slightly elevated pH (4.5 at $25\deg$C) of these fluids. Possible causes of the elevated pH include: incorporation of buried organic matter, dissolution of fracture-filling calcite, supercritical phase separation phenomena, and other reactions that may impact the proton balance in the fluids, as there is no sediment cover at this site, and no (chemical) evidence for buried sediments. The very low metal contents are in agreement with the water column signals observed in 1985, suggesting the fluids have not changed in $\sim20$ years, and that the site was not impacted by the seismic activity on the Gorda Ridge in 1996 and 2001. Hydrothermal fluids were first collected from Escanaba Trough (NESCA) in 1988, and this site was subsequently drilled by ODP in 1996. Our fluid samples collected in 2000 and 2002 have the same compositions as those collected in 1988. All of the fluids we collected venting from this site are high chlorinity (brines), while ODP also encountered low chlorinity vapors subsurface. We propose a model to explain why the brines are venting preferentially to the vapor phase at this site. Chemical stability in hydrothermal systems, as in these two cases from the Gorda Ridge, are in stark contrast to observations of variability elsewhere on the global mid-ocean ridge system. The time scales and explanations for the fundamental causes of these differences remain poorly understood. DE:
HR: 12:05h AN: T12B-08 TI: Holocene Turbidite Recurrence Frequency off Northern California: Insights for San Andreas Fault Paleoseismicity AU: * Nelson, H et a. EM AB: Numerous turbidites along the northern California continental margin are influenced by the northern San Andreas Fault (SAF). The fault parallels the coast near San Francisco Bay and further north underlies the California margin. Multiple tributary slope canyons and proximal channels join downstream into large channels, and all systems are dominated by the deposition of turbidite silt and sand beds. Our research aims to: 1) test the hypothesis that synchronous turbidites along the margin result from turbidity currents triggered by great earthquakes on the SAF and 2) thus define a paleoseismic record. Most important, we want to outline the recurrence history of paleoseismic events. Several lines of evidence suggest that there is synchronous SAF triggering of turbidites. Channels below tributary confluences are characterized by many single-event turbidite beds with multiple coarse-grained sediment pulses that contain different mineralogy from tributary source canyons. The rate of turbidite bed deposition (number/m) above and below channel tributary confluences typically is the same and not additive in downstream channels. Geotek log signatures of turbidites from different channel systems correlate along the margin and our present limited number of 14C ages suggest correlative events. The most complete and reliable turbidite record is found in Noyo Channel where the canyon head source of turbidites is directly underlain by the SAF. The five youngest turbidite 14C ages of Noyo show general agreement with the SAF paleoseismic record on land.This apparent correlation suggests that Noyo Channel may provide a much longer paleoseismic record for 24 events on the SAF during the past 6,000 yr. We utilize multiple cores with 24 correlative turbidite events from the channel to define event recurrence time between turbidites. We base this time on two independent methods: 1) hemipelagic sediment thickness (H) between two consecutive turbidites (i.e. H/sedimentation rate =recurrence time)(24 events), and 2) 14C ages (i.e. difference in ages between two consecutive turbidites= recurrence time)( 8 events). The average recurrence time we find between events is 210 yr (H method) and 180 yr (14C age method). Both methods show a minimum recurrence time of 140 yr and a maximum time of 275 yr with 75 percent of the recurrence times between 150 to 225 years. With two major assumptions that 1) Noyo Channel turbidites represent great earthquakes on the SAF and 2) the Noyo recurrence pattern continues into the future, the Noyo recurrence data suggests that we are not yet in a window for another great earthquake on the northernmost SAF. This statement is based on present evidence indicating that in the Noyo Channel area: 1) an earthquake greater than 7.2 magnitude is necessary to trigger a turbidity current, 2) minimum recurrence times are140 yr, and 3) the great earthquake in 1906 triggered the youngest turbidite. DE: HR: 0800h AN: T41C-1235 TI: Structural vergence variation and clockwise block rotation in the Cascadia accretionary wedge, offshore central Oregon AU: * Johnson, J et al. EM AB: Along the Cascadia margin offshore Oregon, the structural vergence at the toe of the accretionary wedge varies from landward vergent offshore northern Oregon to seaward vergent across the southern Oregon margin. A transition zone between these vergence domains occurs along the central Oregon portion of the wedge, centered on the Hydrate Ridge region. We examine the past variability in structural vergence across the Hydrate Ridge region through detailed structural mapping using multichannel seismic reflection data and gridded bathymetry. These data are coupled to biostratigraphic age constraints obtained from ODP drilling to constrain the timing of accretionary wedge growth since the early Pleistocene (<1.7 Ma). Our results indicate that the wedge in the Hydrate Ridge region was accreted in three structural phases: an early Pleistocene seaward vergent phase (~1.7-1.2 Ma), an early to middle Pleistocene (~1.2-0.3 Ma) landward vergent phase, and a late Pleistocene-Holocene (~0.3-0.25 Ma to present) seaward vergent phase. Age constraints on the timing of landward vergent deformation suggest coincidence with the timing of the deposition of the Astoria fan. High pore fluid pressures due to rapid fan deposition have been suggested as the likely cause of landward vergence for the northern Oregon and Washington margins. The large bathymetric expression of northern Hydrate Ridge is likely due to its history of continued seaward vergence, which permitted some sediment subduction, likely underplating and observed thrust duplexing, all resulting in an increase in the thickness of the accretionary wedge (more uplift) beneath this region. Superimposed on the accretionary wedge growth in the Hydrate Ridge region, two basement involved transverse strike-slip faults have affected the wedge development. Evidence of clockwise block rotation of the Hydrate Ridge tectonic block between the two transverse strike-slip faults appears most pronounced in the older portion of the wedge, and decreases toward the west. Constraints on the timing of propagation of the basement strike-slip faults into the abyssal plain section near the deformation front indicate that the early-middle Pleistocene landward vergent phase (~1.2-0.3 Ma) may have been terminated by this faulting. We speculate that the propagation of the strike-slip faults into the upper plate may have reduced pore fluid pressures and increased coupling along the decollement, triggering the change from landward to seaward vergence at the deformation front. DE HR: 10:50h AN: T12B-03 INVITED TI: Cascadia Great Earthquake Recurrence: Correlation Evidence for Repeated Margin Wide Rupture AU: * Goldfinger, C et al. EM AB: We are now testing correlation between turbidite event records at widely separated sites in Cascadia with radiocarbon ages and physical properties of the core sediments. We focus here on physical property correlations between sites to test for connections between sites independent of radiocarbon ages. Gamma density, magnetic susceptibility, and P- wave velocity data were routinely collected for all cores at a 2 cm interval. We find that a good stratigraphic correlation can be made between Juan de Fuca Channel (JDF, a tributary of Cascadia Channel) and Cascadia Channel based on individual event signatures, and upon the sequence of unique signatures through the Holocene record of 18 events. 16 individual event density-magnetic signatures between JDF and Cascadia Channel have correlation coefficients of 0.6-0.9, with two scores (0.16 and 0.32) for events with similar, but out of phase characteristics. Non correlated events have lower coefficients in most cases. The event sequence includes a mix of many unique signatures and some events that are similar to others. The unique sequence of these signatures limits the possibility of miscorrelation because rarely do similar events occur adjacent in time. These correlations further support the temporal correlation to great earthquake records in Willapa Bay (this session), as well as extend the record to ~ 9800 years. We find that many events can be correlated in this way between JDF, Cascadia, Hydrate Ridge (central Oregon margin), and Rogue (southern Oregon margin) core sites. The signatures vary more between sites that are not directly connected, but many robust features are preserved, including in many cases, the relative volume of the turbidite, and the number of coarse pulses in the turbidite. These features allow direct correlation between sites independent of other methods. That we are able to correlate physical property "wiggle" plots along channel systems is intriguing, given the expected chaotic nature of deposition controlled by turbid flow. However, the inter-site correlations between turbidite channels that are not connected, implies that the deposition process is influenced by more than long distance transport of event characteristics. We suggest that such correlation implies that something of the earthquake shaking signal may be contained in these records. While not all sites can be correlated on the basis of physical properties, we find that key events in the event sequence have characteristics observable at most if not all sites. Events T6, T8, and T16 are large triplets at all sites, T4 and T9 are single events, T10, T12 are small events at all sites, and T11 is a massive doublet event at all sites. These observations strengthen the correlation, and thus the inference of earthquake origin for these events. The correlations further support the un-segmented nature of most Cascadia ruptures, since direct correlation effectively eliminates this option. Currently, not all events can be correlated margin wide, leaving open the possibility of several segmented ruptures. Strengthened correlations further support a repeating pattern of Great Earthquakes in Cascadia. The pattern appears to have repeated at least four times, with the most recent AD 1700 event being the third of three events following a long interval between events T4 and T5. DE: HR: 0800h AN: T41C-1212 TI: Metamorphic Tectonites and Differential Exhumation Reveal 3D Nature of Extension and Lower Crustal Flow in the Active Woodlark Rift, Papua New Guinea AU: * Little, T et al. EM AB: The D'Entrecasteaux Islands metamorphic core complexes (MCCs) occur in the Woodlark rift, a continental region where $\sim$200 km of extension since $\sim$6 Ma has been focused into a relatively small number of normal faults, some dipping at $<$30º. Flow of a low viscosity lower crust on a time scale of $<$4 m.y. is evidenced by the narrow width of the rift zone, and the apparent large magnitude of extension (Beta ~5) , as contrasted by observed relief on the Moho ($<=$10 km). Gneisses in the footwalls of MCCs, including retrogressed eclogites, have been exhumed from depths of $\sim$30 km since ~ Ma. Our structural and thermochronometric data covers parts of the D'Entrecasteaux MCCs, including Normanby Island. These are mantled by serpentinized ultramafic rocks of the Papuan ophiolite. Remnants of this upper plate are preserved along the margins of the MCCs. In underlying mylonites, exhumation-related fabrics, microstructures and quartz lattice preferred orientations reveal a regional pattern of lineations and top-north shear inconsistent with diapir tectonics. The gently dipping mylonites were later warped by uplift of the $\sim$30 km-wide domes, perhaps in response to magmatic underplating during intrusion of dolerite dikes and granodiorites at $\sim$2 Ma. Southward across Fergusson Island, muscovite Ar/Ar ages, increase by ~2 m.y. along the detachment, suggesting footwall exhumation by top-to-the-north slip at $>$12 mm/yr. To the east, an MCC on eastern Normanby Island has top-north footwall mylonites that dip gently SW and that were exhumed during the Pliocene as part of a northward progression of normal faulting that did not arrive at the offshore Moresby Seamount until ~1.2 Ma (ODP Leg 180 site), relationships that suggest a rolling-hinge style uplift. Importantly, its detachment exposes no rocks deeper than blueschist-facies. Ductile deformation fabrics in the MCCs reveal patterns of lower crustal motion that can be evaluated against seafloor spreading-derived plate motions. Shear fabrics in MCCs closest to the Woodlark spreading ridges, including Normanby and Misima Islands are parallel to the NNE direction of 0.5-3.6 Ma Solomon Sea-Australia spreading. Farther west, lineations in the lower plates of the D'Entrecasteaux MCCs locally deflect ~40- 50ºclockwise from this direction. This obliquity is interpreted to reflect inhomogeneous lower crustal extension to the west of the Woodlark spreading ridges. A rift corridor extending $\sim$100 km to the north of Goodenough and Fergusson Islands is defined by active normal faulting and subsidence of the Trobriand margin. We infer that a previously subducted, locally eclogite-bearing, slab of thinned Australian lower crust to the north of the islands is being pulled out from beneath this zone as it is being sinistrally sheared along its eastern edge. Today the rift zone steps ~70 km south towards the Papuan Peninsula to define a right-step, an asymmetry that is enhanced by seafloor spreading east of ~151.4ºE. Published focal mechanisms suggest that N-S sinistral shear along the northern Woodlark rift is continuing. In central Normanby Island, ~2 Ma andesites may have erupted along a transverse fault bounding the deeply exhumed D'Entrecasteaux corridor. Its offshore extension trends N along a major embayment in the Woodlark Rise. HR: 1340h AN: V23B-0625 TI: Magnetization Of Gabbroic Rocks and Peridotites Recovered From Mid Atlantic Ridge 14N - 16N, ODP Leg 209 AU: * Kikawa, E et al. EM AB: ODP Leg 209 was performed from May to July, 2004 at Mid Atlantic Ridge 14N - 16N. The precruise site survey studies performed by Alvine and Shinkai 6500 submersibles indicated the existence of fresh mantle peridotites for the drilling sites. However, the recovered rocks were basalts, gabbroic rocks and peridotites few of which were unaltered. Natural remanent magnetization (NRM) intensities calculated from ODP Leg 209 gabbroic rocks and peridotites indicated very large variations from 0.001 A/m to 50 A/m. Many of the rocks recovered were observed to have drilling-induced remanent magnetizations (DIRM). The DIRM was in general easily removed by alternating field (AF) demagnetization up to 20mT, so for most of the rocks recovered, it was possible to determine stable characteristic remanent magnetization vector directions. The DIRM which was unstable against AF demagnetization showed nearly vertical direction (downward). In many cases, the DIRMs possess more than 90 percent of NRMs of the rocks recovered. The existence of the DIRM in the rocks recovered made it difficult to obtain original natunal remanent magnetization intensities not altered by drilling. So care must be taken in considering in-situ magnetization of ODP Leg 209 gabbroic rocks and peridotites before recovered from the sea-floor, specially as remanent magnetization source for overlying sea-floor spreading magnetic anomalies, though some of the ODP Leg 209 gabbroic rocks and peridotites that were not affected by DIRM indicated reasonably high magnetization of 1 - 2 A/m to contribute to lineated marine magnetic anomalies . Similar DIRMs have been found to exist among gabbroic rocks and peridotites recovered during Legs 118, 147, and 176. Non-magnetic drilling tools including drill pipes, core barrels, BHA and so on would be essential to further studies for magnetizations for deep ocean crustal rcoks and mantle peridotites that contain relatively coarse grain magnetites easily affected by DIRM of essentially isothermal remanent magnetization (IRM) origin. DE: HR: 10:55h AN: V22A-03 INVITED TI: An ocean floor prospecting: Implications from the petrological insights of the abyssal chromitites from ODP Leg 209, MAR 15 20 N FZ AU: * Abe, N EM AB: ODP Leg 209 performed to drill mantle peridotites and associated gabbroic rocks (at 8 Sites, 19 holes) along the Mid- Atlantic Ridge (MAR) from 14 to 16 N, both sides of 15 20 N FZ. Several podiform chromitites were recovered at Site 1271, both Hole 1271A and B, south of 15 20 N FZ during the cruise. These chromitites are the first sampled from the Mid-Atlantic Ridge. The primary chromites in the chromitites have moderately high-Cr# (0.52 and 0.48 for Hole 1271A and 1272B, respectively) and chromian spinels in the surrounding chromitites have similar composition. It is considered that podiform chromitite is formed by two kind of melt (melt-mantle interaction, therefore there should be plenty volume of melt in the mantle beneath this area. Abundant of gabbro and dunite were recovered from this area suggest that main volume of melt body were consumed in the upper mantle by melt-wallrock interaction. On the other hand, chromite grains have thick rims of Cr-magnetite or completely replaced by magnetite without chromite core. Cr content elevation in the Cr-magnetite rim occurred with Fe-enrichment. These chemical modifications suggest that the chromitite from Site 1271 were metamorphosed at amphibolite facies because significant Al-missing from chromite cores is taken place above 550 degree Celsius. DE
HR: 08:50h AN: V21C-04 TI: Tephrochronology of North Pacific Volcanic Arcs - data from ODP Leg 145 AU: * Prueher, L
AB: Volcanic ash layers in deep-sea sediment from the North Pacific provide a record of volcanism in North Pacific Island Arcs. 450 ash layers were counted in deep-sea cores from the Ocean Drilling Project Sites 882, 883, and 887, in order to determine frequency of eruption, ash thickness, episodes of regional volcanism, and the impact of multiple eruptions on the intensification of Northern Hemisphere Glaciation. Episodes of explosive volcanism occurred approximately at 0.2-0.5, 1.5-1.7, and 2.5-2.65 Ma in the Kamchatka-Kurile volcanic arc, and 0.15-.4, 1.5-1.7, and 2.55-2.65 Ma in the eastern Aleutian volcanic arc. Aeolian mineral grains and volcanic glass were removed from the deep-sea sediments using a method developed at the University of Michigan. A new method of heavy-liquid separation was developed to separate volcanic glass from terrestrial mineral grains. The glass was isolated in order to calculate the flux of volcanic glass in order to quantify the climatic impact of the eruptions. The amount of volcanic glass in the sediments between visible ash layers was measured and used as a proxy for sulfate aerosols in the atmosphere. Eruption ages were determined by magnetic reversal stratigraphy. Argon-argon geochronology will be used to compare the ages and to further test the usefulness of the argon-argon method for determining the age of volcanic glass. DE HR: 08:20h AN: V21C-02 TI: Terrestrial-marine Correlation of the 24 kyr BP Dawson Tephra: Implications for Dispersal and Preservation of Alaskan Tephra Deposits AU: * Beget, J et al. EM AB: The Dawson tephra, radiocarbon-dated to ca. 24,000 yr BP, is as much as 50 cm thick in Pleistocene sediments in Yukon Territory of Canada, but is not found in nearby parts of Alaska. Nonetheless, the geochemical characteristics of the tephra suggested derivation from an Aleutian arc volcano (Westgate et al., 2000). Its source was unknown until proximal deposits were recognized at Emmons Lake Volcanic Center (ELVC) on the Alaska Peninsula (Mangan et al., 2003). We have identified Dawson tephra in ODP core 880B, collected in the Northeast Pacific Ocean. The Dawson tephra also occurs in discontinuous small pods in two new localities near Fairbanks in central Alaska. Our data suggest the Dawson tephra was dispersed from the ELVC principally to the southeast over the North Pacific , and then carried to the northeast by high altitude winds. Reconstructions of the volume and distribution of individual tephras or of arc-wide explosive volcanism in Alaska must incorporate data from proximal and distal terrestrial localities, as well as marine cores.
HR: 11:40h AN: V22A-06 TI: Upper Mantle Geochemistry at Peridotites of Site 1274 (ODP Leg 209): Relation to Melt-Rock Reaction and Processes at the Base of the Lithosphere AU: * Suhr, G and Paulick, H EM AB: ODP Leg 209, Site 1274, has penetrated 156 m of upper mantle rocks plus minor gabbro intrusives north of 15\deg20' N Fracture Zone at the Mid Atlantic Ridge. The core has an unusually high amount of dunite (21%) and contains an unusual suite of opx- depleted harzburgites and dunites between 70 and 90 m depth. Between 0 and 70 m depth, harzburgites are chemically highly depleted (Cr\# in spinel 37 to 52, TiO2 in cpx $<$ 0.07% with negative correlation to Cr\#). The chemistry of these harzburgites appears to preserve evidence for progressive melt extraction. A section of 3 m dunite occurring within this interval largely shares the depleted chemical signature, though TiO2, Na2O and REE in cpx are somewhat elevated relative to the local host rocks. In the interval between 70 and 90 m depth, Cr\# are 45-57 and cpx is enriched in TiO2 (0.09 to 0.24%) and Na2O (up to 1%). Microstructural evidence for melt-rock reaction (e.g. cpx rims on opx) is pervasive throughout the core. The pristine preservation of these microstructures argues for efficient freezing during a rapid uplift. The percolating melts appear derived relatively locally because chemical indicators for foreign melts are weak. In the interval between 70 and 90 m, melt infiltration from a more remote source is suggested by the presence of strong reactive tendencies (opx depleted peridotites and dunites) and a more enriched chemical signature in all rocks. Probably, the opx-depleted rocks formed when focused melt channels failed near the lithosphere-asthenosphere boundary. In the upper part of the core, the depleted chemical signature of the dunite is interpreted as derived by melt extraction from the host into the dunite at a late stage, perhaps triggered by a fracture in the overlying lithosphere. Since locally generated melts are only weakly reactive towards opx, the formation of the dunite itself (by dissolution of opx from harzburgite) cannot be explained by locally generated melt. Instead, the early passage of more reactive melts derived from larger depth seems likely. Chemical clues to the former passage of different melts in this dunite are the occurrence of an enriched cpx inclusion in spinel in dunite and preliminary data suggesting that the internal part of the dunite may record the passage of a melt with a more radiogenic Os signatures than the highly unradiogenic harzburgites and marginal dunites. It thus appears that melt infiltration and extraction can occur in close proximity, depending on the local physical properties of the lithosphere-asthenosphere boundary. DE
HR: 1340h AN: V13B-1480 TI: The Hf-Nd isotopic diversity of subducting oceanic sediments AU: * Vervoort, J et al. EM AB: We report Lu-Hf and Sm-Nd isotopic data for sediments from several DSDP and ODP sites from the Atlantic (South Sandwich, ODP 801), Indian (Nicobar Fan, DSDP 211) and Pacific Oceans (Aleutian site 183; W. Alaskan abyssal plain, DSDP 178; Astoria Fan, DSDP 174; Central America, DSDP 495, ODP 844; S. American, DSDP 321; Tonga, 595/6; Marianas, DSDP 801; Phillippines/Ryuku, DSDP 291, 294/295). These sediments span the compositional variation that exists in the ocean basins and that are actively being transported to subduction zones on the present-day Earth. The compositions of these sediments lie between three end-member groups. One group of sediments (Central America; Aleutians) has radiogenic Hf and Nd isotopic compositions ($\epsilon$$_{Hf}$ =$^{+}$10; $\epsilon$$_{Nd}$ =$^{+}$5) that are largely controlled by ash inputs from proximal volcanic arcs. A second group of sediments (Astoria and Nicobar fans) has very unradiogenic Hf and Nd isotopic compositions ($\epsilon$$_{Hf}$ =$^{-}$20; $\epsilon$$_{Nd}$ =$^{-}$15) that reflect their derivation from mature continental crust. Both these end-members, and intermediate compositions between them, lie within the crust-mantle Hf-Nd array and have Lu/Hf and Sm/Nd ratios typical of crustal rocks. This variation in isotopic composition mirrors to a large extent the range that exists in continental sediments. The third end-member group of sediments, composed of slowly accumulating metalliferous clays, is highly anomalous in terms of both its trace element and isotopic composition. These pelagic clays are the dominant components of the Tonga and Ryuku sites and are also important in the Philippine site and, locally, the Marianas site. The clays are highly enriched in REEs (many with Nd concentrations 100 to 400 ppm), but have average concentrations of Hf. This results in extremely high, superchondritic Lu/Hf ratios ($^{176}$Lu/$^{177}$Hf up to 0.18), but Sm/Nd ratios that are typically subchondritic. In addition, nearly all of these sediments have anomalously radiogenic Hf compared to Nd ($\epsilon$$_{Hf}$ =$^{+}$10 to $^{+}$15; $\epsilon$$_{Nd}$ =$^{-}$5), which causes them to plot distinctly above the crust-mantle array. In summary, there is a wide range of isotopic compositions being delivered to subduction zones that is a function of the diversity of sediment types in the world's oceans. Although the REE rich pelagic clays have unique Hf-Nd isotopic compositions, their restricted global distribution will limit their widespread application as an isotopic tracer. DE
HR: 11:25h AN: V22A-05 TI: Geochemical Study of Mid Atlantic Ridge Peridotites From 15\deg N: Preliminary Results From ODP Sites 1272 and 1274 AU: * Godard, M et al. EM AB: During ODP Leg 209, eight sites were drilled along the Mid-Atlantic Ridge from 14\deg43 to 15\deg44 N, allowing recovery of ca. 354 meters of residual mantle peridotite intruded by gabbroic rocks (up to 25% of recovered samples). We present here the results of a whole rock major and trace element study of 28 peridotites selected among the less altered samples (those which preserved enough primary features to allow detailed petrographic and mineralogical studies), at Site 1272 and Site 1274 (respectively S and N of the 15\deg20 fault zone). Site 1272 and Site 1274 peridotites are mainly harzburgites (cpx $<$ 5%) with a few dunites. Harzburgites are characterized by highly variable opx contents (10-30 vol.%). Some samples show evidence of trapped melt (up to 3-5%). A few samples at Site 1274 show textural evidence of abundant cpx crystallization, resulting in the formation of lherzolites. All studied peridotites have been modified by alteration ($>$70% serpentinisation), leading to the addition of significant amounts of volatiles (loss on ignition $>$10 wt%). Nevertheless, except for alkali-earth elements and U, major and trace element compositions show no evidence of additional compositional changes during alteration. Site 1272 and Site 1274 peridotites are characterized by high Mg# (100 x molar Mg/[Mg + Fe]) (90.3- 92.2) and low Al$_{2}$O$_{3}$ contents ($<$0.3 wt% in dunites and ranging from 0.6 to 0.9% in harzburgites). Site 1272 and Site 1274 peridotites display flat to light Rare Earth Element (REE) depleted patterns (harzburgites : Ce$_{N}$$<$0.015; Yb$_{N}$$<$0.26 - dunites : Ce$_{N}$$<$0.001; Yb$_{N}$$<$0.04-0.08- $_{N}$: chondrite normalised). The most depleted harzburgites are observed at the southernmost Site 1272 (Ce$_{N}$$<$0.003; Yb$_{N}$: 0.045-0.1). REE allow to distinguish two harzburgites groups at Site 1274. The first one shows patterns similar to those of Site 1272 peridotites yet with slightly higher REE content (Ce$_{N}$: 0.0015-0.015; Yb$_{N}$: 0.14-0.26). The second displays on average lower heavy REE contents (Yb$_{N}$: 0.1-0.18) and more variable light REE contents (Ce$_{N}$: $<$0.002-0.05). These samples are found at the bottom of Hole 1274A where cpx display the highest Na- and Ti contents among the studied peridotite suite. Site 1272 and Site 1274 peridotites composition is similar to that of the most depleted peridotites sampled in ophiolites (e.g., Oman, Cuba) and in oceans (e.g., Izu-Bonin-Marianna). They represent the most refractory peridotites yet sampled at a slow-spreading ridge. DE AN: V31B-1435 TI: Gabbro fracturing and elemental analysis in the Costa Rica margin (ODP Leg 205): Core-log integrated high-resolution study AU: * Thu, M et al. EM AB: Costa Rica margin is an important area for studies of the seismogenic zone and subduction factory. Building on Ocean Drilling Program (ODP) Leg 170 coring and logging while drilling (LWD) at the same sites, Leg 205 drilled three sites to determine the igneous and alteration history of the upper most part of the down going plate, to characterize the hydrological regime above and within the decollement, and successfully installed long-term borehole observatories to monitor downhole pressure and temperature and sample fluids and gases. Among the several highlights from the results, coring and logging of thick gabbro zone at Site 1253 was significant to detail the fracture distribution, structure and nature of oceanic crust through core-log data integration. Even thought logging runs in the sediment section was failed due to the hole conditions, triple combination and FMS-sonic tool strings made successful measurements. Post-cruise research work included quality control on several wireline logs and processing of Formation MicroScanner (FMS), and interpreting these logging data and core sample analysis results in integrated manner. Among several downhole logging results, FMS images are used to characterize structure and fabric in the igneous units. As the hole conditions were good in most of the igneous intervals, the textural and structural variation is clear between the sections and also shows differences within the section itself. Moreover, mineralogic results from the recovered cores are combined with logging data through level-by-level multi-mineral evaluation with an optimized simultaneous equation solver and model combining method. Due to the good logging results and simple mineral composition of the single rock type, the results from the process filled mineral percentage of the no core recovery depths as well. High-resolution core-log integration in this study enhanced the understanding of structural process and nature of the oceanic crust of this particular region. DE: HR: 1340h AN: V13B-1471 TI: Characterizing Sedimentary Carbon and Nitrogen Subduction Fluxes in the Central America Convergent Margin (ODP Legs 170, 205) AU: * Li, L and Bebout, G E EM AB: We present new data regarding the C and N contents and isotope ratios of the subducting calcareous sediments from the lower section (U3) of Site 1039 and the silty sediments from the accreted section sampled by Sites 1040, 1254, and 1255. Sediments in the calcareous section contain 62 to 866 ppm N with $\delta$$^{15}$N$_{Air}$ of 2.4 to 8.5 per mil and 0.09 to 0.73 wt.% TOC with $\delta$$^{13}$C$_{PDB}$ of -25.4 to - 21.4 per mil. Integrating the upper diatomaceous ooze section (U1) and the silty clay section (U2) [Li et al., 2003], the subducting sediments along the 1100-km Central American convergent margin could carry inventories of 1.3\times10$^{10}$ g/yr N with average $\delta$$^{15}$N$_{Air}$ of 5.7 per mil, 1.4\times10$^{11}$ g/yr TOC with average $\delta$$^{13}$C$_{PDB}$ of -22.0 per mil and 1.5\times10$^{12}$ g/yr oxidized C with average $\delta$$^{13}$C$_{PDB}$ of 1.9 per mil. Sediments at Sites 1040, 1254 and 1255 contain 832 to 2398 ppm N with $\delta$$^{15}$N$_{Air}$ of 3.6 to 6.6 per mil, 0.85 to 3.06 wt.% TOC with $\delta$$^{13}$C$_{PDB}$ of -26.6 to - 21.1 per mil, and $<$4 wt.% CaCO$_{3}$ with $\delta$$^{13}$C$_{PDB}$ of -26.1 to 4.1 per mil and $\delta$$^{18}$O$_{VSMOW}$ of 30.0 to 36.4 per mil. No obvious changes in N, TOC and carbonate contents and isotope concentrations are observed in sediments in and near the fault zones and the d\'{e}collement, indicating that fluid flow in the Central American convergent margin had a minimal effect on the TOC and N concentrations and isotopic compositions of the sediments. However, the impact of fluid processes on the sediment geochemistry could be indicated by extreme $^{13}$C- depletion in minor carbonate in the sediments; this depletion could have been produced biogenetically by incorporation of methane C. Regarding the mass-balance across the Central American subduction zone, if the C and N loss in sediments due to fluid processes and early devolatilization is not significant, the large amount of subducting C and N (even without considering the potentially comparable C and N inputs in altered oceanic crust and tectonically eroded material), relative to the smaller output fluxes in arc volcanic gases, indicates significant transfer to the deep earth, likely affecting the C and N isotopic characteristics of the mantle. DE
HR: 17:30h AN: V54B-07 TI: Deep Marine Sediment Diagenesis of Germanium, Silica, Lithium and Lithium Isotopes in ODP-177: The "Missing Oceanic Ge Sink" AU: * Froelich, P and King, S L EM AB: Understanding sediment diagenetic alterations of the crustal Ge/Si ratio is important as a clue to identifying the phases and processes responsible for burying the "missing" portion of the input Ge-flux (rivers and MOR vents) that can not be ascribed to diatom Ge/Si burial. In the ocean, in diatoms, and in most low-temperature biogeochemical processes, Ge behaves much like a trace cogenor of Si, substituting for Si and displaying Ge/Si ratios that don't deviate much from crustal (10-6 mol/mol). Significant fractionation of the ratio is now recognized for continental weathering processes and hydrothermal basalt reactions. During early diagenesis in the shallow suboxic zone of marine sediments, where non-silicate phases may dominate Ge-cycling (e.g., FeOOH), pore water [Ge] also reflects uptake into authigenic phases but seldom exceeds several hundred picomolar (10-12 Molar). In this paper we present the first deep pore water Ge data from Sub-Antarctic South Atlantic Sites drilled during ODP Leg 177 across the Southern Ocean biosiliceous ooze belt. In all sites (ODP 1088-1094), pore water Ge displays steep gradients and maxima and minima that are unrelated to opal diagenesis. Deep maxima Ge-concentrations approach 120 nM, 1000-fold higher than seawater (0.1 nM). The shapes of these profiles require local diagenetic sources and sinks for Ge that are very large, and both upward and downward fluxes that far exceed those estimated for local Ge-burial in diatomaceous opal. Thus there must be other non-biosiliceous phases that carry Ge to the seafloor that are activated during deep burial diagenesis. Temperature does not seem to be a factor: deep borehole temperatures do not exceed 46-deg C. So far we have been unable to identify these reactive phases, although we suspect some combination of chert formation and clay alteration as likely culprits. In contrast, Si profiles are featureless, exhibiting near-zero Si gradients over most intervals, with Si typical of opal saturation (1-2 mM) diluted by opal/detrital sediment ratio. Pore water lithium [Li] and del-7Li display both uptake and release profiles related to aluminosilicate clay formation and destruction. Del-7Li varies from +5 to minus 25 per mil (ref seawater), while [Li] varies from sligtly below seawater values (25 uM) to about 250 uM. The downcore data are consistent with release of Li from clay minerals carrying light (7Li depleted) cations. These Li and Li-isotope data are internally consistent, but do not shed any light on the diagenetic processes affecting deep Ge diagenesis. DE HR: 17:45h AN: V34B-08 INVITED TI: Hawaiian Hotspot - Spreading Ridge Interaction in the Late Cretaceous: A Fair and Balanced Look at the Evidence AU: * Keller, R EM AB: As is so often the case in years divisible by 4, reality turns out to be quite different from reputation. The Hawaiian hotspot, often righteously promoted as the hotspot that the rest should strive to emulate, was not as stable nor as free from interactions with plate boundaries as some supporters suggest. Mounting geochemical and geophysical evidence shows that in its youth the hotspot not only inhaled, but probably snorted and did shots as well. The purpose of this presentation is to summarize what we know about the Late Cretaceous interaction between a spreading ridge and the Hawaiian hotspot from recent work on the Emperor Seamount chain. At the time of this writing, facts are a commodity to be fabricated, deleted, spun, denied, and denied-that-you-denied; but by the time of this presentation, we (hopefully) will be looking toward the future: can the Hawaiian hotspot's checkered past be treated as a bonus rather than a burden? Plate reconstructions of the Late Cretaceous northwest Pacific place a seafloor spreading center very close to, or even directly on top of, the Hawaiian hotspot. The geochemical effects of this hotspot- ridge interaction are now well documented by work on Ocean Drilling Program samples from Detroit Seamount, the next-to-oldest remaining Emperor Seamount. Basalts recovered from ODP Site 883 partway up the east side of Detroit Seamount have trace element and isotopic characteristics more akin to MORB than to Hawaiian Islands basalts. Basalts from ODP Site 884 at the eastern foot of the seamount are highly depleted tholeiites unlike anything else found so far in the Hawaiian-Emperor chain (Keller et al. 2000, {\it Nature}). Their trace element and radiogenic isotope values are essentially indistinguishable from MORB values (Keller et al. 2000), although triple- spike Pb isotope data are distinct from modern EPR MORB data (Regelous et al. 2003, {\it J. Pet.}). These characteristics were the result of the hotspot melting a greater proportion of a depleted mantle component, whether entrained from the surrounding upper mantle (Keller et al. 2000) or intrinsic to the plume (Regelous et al. 2003), while it was close to the spreading center. The Site 884 basalts are surprisingly old (81 Ma; Keller et al. 1995, {\it Leg 145 Sci. Results}) in comparison to recent results for Site 1203 basalts from near Site 883 (76 Ma; Duncan and Keller 2004, {\it G-cubed}). The unique composition and surprisingly old age of the Site 884 basalts could be due to the fact that we have not drilled a similar location deep on the flank of another Hawaiian hotspot island or seamount. However, my preferred explanation is that the temporal and spatial distribution of hotspot volcanism was also influenced by the nearby spreading center. A modern analog for Detroit Seamount may be a complex seamount platform similar to the Gal\`{a}pagos hotspot-ridge system. DE HR: 14:55h AN: V53B-06 TI: Thallium Isotope Constraints on Hydrothermal Water Fluxes at Mid-Ocean Ridge Axes and Flanks AU: * Rehkamper, M et al. EM AB: The hydrothermal circulation that occurs at mid-ocean ridge axes and flanks has profound effects on the chemical budgets of the oceans but our understanding of the relevant fluxes is incomplete. Here, we use new thallium (Tl) isotope and concentration data for hydrothermal fluids and rocks from ODP Hole 504B to obtain independent estimates of the high- and low-temperature (T) hydrothermal water fluxes at spreading axes and ridge flanks. Seawater is characterized by relatively uniform Tl isotope compositions and concentrations of $\epsilon^{205}Tl$ = -6 and 65 pmol/kg, respectively ($\epsilon^{205}Tl$ represents the deviation of the $^{205}Tl/^{203}Tl$ ratio of a sample from the standard in parts per 10,000). In contrast, high-T hydrothermal fluids from ridges axes display $\epsilon^{205}Tl = -2\pm1$, indistinguishable from unaltered mantle rocks. The correlation of Tl and Cl abundances indicates an average Tl content of 10-25 nmol/kg for high-T endmember fluids. The low-T alteration of the upper volcanic zone of ODP Hole 504B is associated with Tl-uptake from seawater. The isotope fractionation that occurs during the uptake generates Tl-rich rocks that have $\epsilon^{205}Tl$ as low as -16. The sheeted dike complex displays low Tl contents due to leaching of the rocks by high-T hydrothermal fluids. Taken together, these observations indicate that high-T vent fluids do not acquire significant Tl from the altered Tl-rich rocks of the volcanic section. With this constraint, the high-T axial water flux can be calculated, assuming that Tl is leached with an efficiency of $60-95%$ from 1.0-1.4 km of sheeted dikes and upper gabbros, which have a Tl concentration of $3\pm1$ ppb. These parameters yield a high-T water flux of 0.2-2.5 x $10^{13}$ kg/yr, equivalent to a heat flux of 0.1 to 1.2 TW. This result is in excellent agreement with other geochemical estimates of high-T water fluxes, e.g., those based on Li isotopes (Chan et al., 2002) or the Sr isotope profile of ODP Hole 504B (Teagle et al., 2003). If the total axial hydrothermal power output is about 2 TW, the geochemical data indicate that at least some heat loss at mid-ocean ridges is due to diffuse low-T fluid flow. The Tl data acquired for off-axis fluids and the volcanic zone rocks are in accord with significant ($30-80%$) losses of Tl from circulating seawater. If it is assumed that 15-35 ppb of Tl are added to the top 600 m of ocean crust, the low-T water flux of ridge flanks can be calculated as 1-5 x $10^{16}$ kg/yr, which is equivalent to an average fluid exit temperature of about $3-10\deg$C. This result is in accord with a recent Mg-based estimate (Mottl, 2003), which indicates that about $90-98%$ of the ridge flank power output occurs at cool sites with fluid temperatures of less than $20\deg$C. DE HR: 1340h AN: V23B-0626 TI: Lithium and strontium isotope compositions of serpentinite- hosted carbonate veins from the MAR (ODP Leg 209): Records of different stages of seafloor metamorphism AU: * Rosner, M et al. EM AB: Geochemical investigations of carbonate veins hosted in serpentinized peridotites drilled from the Mid-Atlantic Ridge 14$\deg$-16$\deg$N (ODP Leg 209) were conducted to gain insights into temperature and composition of the alteration fluids from which carbonates were precipitated. We have examined carbonate veins that can be grouped into low-T ($<$20$\deg$C) aragonite veins hosted in serpentinite, low-T calcite veins hosted in troctolitic rocks, and high-T (90-220$\deg$C) calcite veins hosted in talc- serpentine schists. The geochemical and radiometric characteristics of these veins is presented in a companion paper (Bach, Paulick, and Rosner) in this session. Here we report on Li and Sr isotope compositions and their relations to age, temperature, and trace element composition. Strontium isotope compositions are similar to, or slightly lower than that of modern seawater. This is consistent with young radiocarbon ages ($<$55 kyrs) and limited Sr exchange between circulating seawater and basement at low temperatures.$\delta$$^{7}$Li values (relative to L-SVEC) of the majority of aragonite samples range between 14 and 20 $\permil$. At sites 1271 and 1274 on rift valley walls of inside corner highs north and south of the 15$\deg$20N fracture zone, the $\delta$$^{7}$Li values of aragonites increase systematically with depth. At site 1274 .$\delta$$^{7}$Li shows a weak positive correlation with 14-C formation ages. Our preliminary interpretation of the Li isotope data is a decrease in the Li isotope fractionation factor as temperatures increase with increasing basement depth. This interpretation would require a fractionation factor at 2$\deg$C of about 1.016 - significantly larger than $\alpha$ =1.011 proposed for biogenic aragonite formation at 25$\deg$C. The large fractionation observed in the upper part of the drilled cores could be due to lower temperature, different precipitation kinetics, variations in fluid chemistry (e.g., strongly variable Mg/Ca), or combination of these effects. Calcite veins from Sites 1271 and 1275 display at least two compositional groups. Low T calcites range $\delta$$^{7}$Li from 22 to 27 $\permil$ and precipitated at T$<$20$\deg$C from a fluid with seawater-like Sr isotope composition. Three high-T calcite veins record an earlier and deeper stage of metamorphism associated with detachment faulting. $\delta$$^{7}$Li values between 3 and 8 $\permil$ correlate with Sr isotope ratios (as low as 87Sr/86Sr=0.70385) and indicate a prominent contribution of Li and Sr leached from the peridotite basement. DE HR: 1340h AN: V23B-0627 TI: Extensional Faulting at 15\deg North on the Mid-Atlantic Ridge, ODP Leg 209 AU: * Schroeder, T et al. EM AB: At slow spreading ridges, oceanic mantle can be uplifted and brought to the seafloor by extensional faulting, but the style of faulting and mechanisms by which this occurs remain poorly understood. We present data from faults observed in mantle peridotite and gabbro intrusions drilled at six sites on the Mid-Atlantic Ridge near the 15\deg20' Fracture Zone during ODP Leg 209. The data reveal that faulting and significant tectonic rotation can take place either via long-lived (detachment?) faults that are active through ductile and brittle regimes, or via successive series of short-lived (domino) faults. We recognize three styles of faults: a) High-temperature, mylonitic shear zones at Sites 1268, 1272 and 1274 that are overprinted by dominantly static greenschist facies alteration. These textures indicate that ductile faults were active at depth and later became inactive during denudation and are cut by brittle faults at shallow lithospheric levels. b) Brittle and semi-brittle faults that do not directly overprint ductile shear zones. These include partially- to non-cohesive serpentine mud fault gouge in zones ranging from 10 cm to several meters thick (Sites 1268, 1272 and 1274), and cohesive cataclasites and talc/tremolite schists (Site 1275). c) Ductile to brittle faults in peridotites from Sites 1270 and 1271. Strain in the peridotites at both sites appears to have been initially localized into gabbroic veins and dikes at granulite facies, and remained localized in these zones to sub-greenschist facies during long-lived faulting and denudation of peridotite. There is no apparent correlation between the faulting style and seafloor bathymetry. For example, bathymetry of Sites 1270 and 1275 indicate the presence of a detachment fault (oceanic core complex), yet 1270 displays type c faults and 1275 displays type b faults. Peridotite and gabbro from all six sites experienced significant tectonic rotation (50ø to 90ø) as interpreted from the inclination of the remnant magnetization vector (assuming horizontal axis rotations). This result is consistent with both rotation via long-lived (detachment) faulting, and/or multiple short-lived fault bounded domino systems. Variability in faulting styles and seafloor morphology along with significant tectonic rotations indicate that highly complex faulting may be typical at slow-spreading ridges. DE: HR: 16:15h AN: V54A-02 TI: Pb and Other Trace Elements in Melt Inclusions From Modern Seafloor Tectonic Settings AU: * Beaudoin, Y et al. EM AB: Evidence for the contribution of magmatic metal-bearing fluids to modern seafloor hydrothermal systems has been presented for key ore metals such as Cu, Zn, Au and Ag but not for Pb. The source of Pb in these systems can be attributed to leaching of host rocks by hydrothermal fluids and/or potentially by direct degassing of magma. We present data from 103 melt inclusions mainly in plagioclase crystals hosted in basaltic to rhyolitic lavas from 9 modern seafloor tectonic settings: oceanic back-arcs (Manus Basin including an ODP Leg 193 drill hole, Bransfield Straits), continental back-arc (Okinawa Trough), mid-ocean ridges (Explorer, MAR), seamounts (Foundation, Axial, Pito), and a transform (Garrett). Most sites host active hydrothermal systems that are producing polymetallic sulfides. Inclusions were analyzed for Pb and other trace elements by LA- ICP-MS at ETH Zurich. Although inclusion trace element compositions vary between tectonic settings, for a given setting variability between different volcanic sequences is low and follows a general mafic to felsic fractionation trend. N-MORB compositions dominate most inclusion populations with exceptions seen at Explorer (plume-ridge interaction), Garrett (near-ultramafic source) and in some Foundation samples (seamounts affected by ridge interaction). Results show high Pb concentrations in inclusions from oceanic back arc and continental back-arc settings coinciding with evolved volcanic chemistries and related in the latter to contamination from sediments or continental crust. Sulfide deposits in these back-arcs are also Pb-rich. Inclusions from primitive basalt and near-ultramafic hosted samples from MOR, intraplate seamounts and transforms have low Pb abundances. In the most Pb abundant settings, melt inclusions have Pb concentrations 1-3 times higher than that of the bulk rock or volcanic glass indicating possible Pb removal from the magma prior to eruption. This loss may be explained by direct degassing of the magma into the hydrothermal circulation. Exceptions to the behavior of Pb in the studied settings include: elevated Pb in inclusions hosted in primitive basalts TAG (MAR) and some samples from the Okinawa Trough showing low Pb with respect to bulk rock. DE HR: 16:30h AN: V34B-03 TI: Plume-Ridge Interaction on the Cocos Plate (ODP Leg 205, Costa Rica): Implication for Fluid Circulation AU: * Chavagnac, V et al. EM: AB: At subduction zone, the permeability and hydrology of the down-going igneous section play a key role on the behaviour of the seismogenic zone, which produces earthquake and tsunamis. We present, here, evidence of fluid circulation pathways in the igneous section being subducted at the Central American convergent margin (Site 1253 ODP Leg 205, Costa Rica). The geological evolution of the Cocos plate over the last 25 Ma is complicated as a result of plate boundaries re-arrangement (Silver et al., 1998). The Cocos-Nazca spreading centre (CNS) interacted with the Galapagos hotspot, which simultaneously deposited volcanic material on both side of the CNS, on the Cocos and Nazca plates. The oceanic crust of the Cocos and Nazca plates was formed along four spreading centres (Meschede et al., 1998) and the East Pacific Rise (EPR). The EPR oceanic crust has the featureless morphology and low-amplitude magnetic anomalies common to fast spreading ridge (Wilson & Hey, 1995) while the CNS oceanic crust presents a rough topography and high-amplitude magnetic anomalies (Wilson & Hey, 1995). We wish to focus on the ODP 1253 Site drilled in the Cocos plate because it samples the igneous input (rock, heat and fluid) to the Central American subduction zone. Coring at Site 1253 penetrated two separate igneous Units of which the upper one is a sill (Unit 4A) separated from the lower Unit (Unit 4B) by sediment. Both Unit 4A and 4B present similar texture, structure and mineralogy apart from the thin basaltic interval at 513 mbsf, below which Unit 4B becomes more glass-rich and altered. Unit 4B is either a sill complex with multiple intrusions related to the Galapagos volcanic activity or a series of thick slowly cooled lava flows formed at the EPR. Some of these characteristics of Unit 4B are similar to those seen in horizons recovered at Site 1256, which intersected thick-ponded lava flows. Analyses of marine magnetic anomalies indicate that the crust at Site 1253 was formed at EPR 25 Ma ago. However, its thermal gradients and conductivity yield surface heat flow anomalies of 10-40 mW\/m$^{2}$, which is $\sim$70% lower than normal cooling lithosphere of that age (Fisher et al., 2003). Off- axis magmatic and tectonic activity associated with the formation of the Cocos Ridge may have increased fluid circulation pathways within the basement structure. Mobile trace element (Ba, Sr) and Sr isotope variations in conjunction with petrographic observation help identify horizons of fluid/rock interaction, e.g. fluid circulation pathways within Unit 4A and 4B. Based on veins, fractures, and void occurrences, the Unit 4A and 4B were subdivided into two and seven subunits respectively. Along the core-depth profile, mobile element concentrations and $^{87}$Sr/$^{86}$Sr ratios vary mainly in a narrow range (0.703245 and 0.703503) but are still higher than those of EPR or the Galapagos hotspot ($<$0.703). At sub-unit interface, we observe drastic increases in Ba and Sr content and more radiogenic Sr isotope signature (up to 0.705106), especially above the thin basaltic horizon. This reflects exchange of Sr with seawater or hydrothermal fluids during alteration. Further work will determine fluid flux estimate at Site 1253. The origin, nature and structure of the oceanic crust at Site 1253 will be presented in two additional abstracts (see Dreyer and Moe, this session). DE: Subducting Crust Offshore Costa Rica: Constraints From Major, Trace Element, and Isotopic Data From ODP Legs 170 and 205
* Dreyer, B et al.
Enriched gabbro sills ($\sim$30m) intruded into post-16Ma sediments and deeper medium-grained gabbros to cryptocrystalline basalts ($>$150m) were cored on ODP Legs 170 and 205 (9\deg39$\prime$N, 86\deg11$\prime$W) on the Cocos plate near Costa Rica. Magnetic anomalies indicate that the basement is EPR lithosphere (Barckhausen et al, 2001). The units studied here may be related to overprinting by the Galapagos hotspot, consistent with the site's paleolocation. The rocks are low- to medium-K (K$_{2}$0 $<$0.44wt$%$) subalkaline tholeiities with SiO$_{2}$ 46- 50wt$%$ and Mg$\#$ 0.44-0.60, similar to Leg 206. Major and minor element variations are consistent with previous fractional crystallization of olivine, plagioclase, Fe-Ti oxides, $\pm$augite; discrete alteration is 1-5vol$%$. The small ranges in major and compatible elements largely reflect phase equilibria control, rather than source differences. However variations in incompatible trace element ratios are best interpreted in terms of two distinct magma batches with slightly different mantle sources. On a plot of Sr-Nd isotopes, Leg 205 samples ($^{143}$Nd/$^{144}$Nd= 0.512937-0.513020 $\pm$8, $^{87}$Sr/$^{86}$Sr= 0.703245-0.705106 $\pm$10) overlap the range of Galapagos Island basalts rather than EPR, except when $^{87}$Sr/$^{86}$Sr $>$0.70400. Elevated $^{87}$Sr/$^{86}$Sr is likely a result of alteration, although leachates have not yet been analyzed. The Nd-isotopic ratios cluster near 0.512950 (one value extends to 0.513020) and good correlation between the Sr-Nd isotopes of less- altered samples suggests mixing between mantle domains of variable enrichment. Rocks from Leg 205 record enrichment within EPR-generated lithosphere and may be the most northerly expressions of the Galapagos hotspot. REE patterns for Leg 170 samples form 2 distinct groups, both overlapping ranges of the Galapagos Islands and regional spreading centers (EPR and Cocos-Nazca spreading (CNS) center). The two groups (Grp 1 LREE ~60$\times$ chondrites; Grp 2 ~32$\times$, both with HREE ~16$\times$ chondrites) may correlate with depth, but their differences cannot be explained by fractional crystallization alone. Consideration of HFSE systematics and REE abundances suggest that mixing between heterogeneous sources and differing degrees of partial melting are required to generate these two groups. On a plot of Hf/Ta vs. (La/Sm)$_{N}$, CNS and EPR lavas (Hf/Ta $>$10, (La/Sm)$_{N}$ $\sim$0.5-1.5) are well separated from Galapagos lavas (Hf/Ta $<$5 and (La/Sm)$_{N}$ $\sim$1-2.5). Leg 170 rocks are within the Galapagos field, as are samples from the 14Ma Fisher Seamount SW of the ODP sites. The origin of igneous units from Leg 170, and by association Leg 205, is best explained as 10-20$%$ degree partial melting from a mantle source $<$30$%$ enriched compared to regional depleted mantle. Mantle mixing between the Galapagos hotspot and the nearby EPR and CNS ridges is recorded in off-axis volcanism offshore Costa Rica. Trace element and isotope results suggest that the spatial and geochemical influence of the Galapagos hotspot is more extensive than previously recognized, and may form a significant part of the oceanic section subducting off Costa Rica, a NSF-MARGINS focus site for studies of crustal recycling at convergent margins. HR: 0800h AN: V31A-1418 TI: Evidence for Extremely Large Lava Flows on Ontong Java Plateau from High Precision Measurements of Volatiles and Major Elements in Natural Glasses AU: * Michael, P J EM AB: Magmas of Ontong Java Plateau (OJP) display little geochemical variation, having only a few widely dispersed magma types (Mahoney et al. , 1993). (Here we define magma type as all lavas that have evolved by similar extents of melting of a similar mantle source, and have undergone similar polybaric fractionation histories). In this study, we use high precision microprobe measurements of Cl, K, S, H2O, CO2 and major elements in glasses to show that magmas from widespread locations on OJP are identical in composition and are probably from the same eruption and quite possibly from the same series of lava flows. By same eruption, we mean the quasi-continuous issuance of magma from a continuous chamber over a time period that is insufficient for further differentiation or assimilation. By same lava flow, we mean lavas that have issued from the same or nearby vents and were part of a sequence that that was continuously molten at the surface or beneath a crust. Cl concentrations are controlled by assimilation that takes place fairly late at shallow levels in the magma chamber. The amount of assimilation and Cl content of assimilated material control Cl contents of magmas, and are expected to be highly variable in this stochastic process. It is inconceivable that magmas erupted at different times would have precisely the same Cl content, even if they have the same major element chemistry from identical cotectic evolution. The clearest case of distant lavas being from the same eruption is the Kroenke-type lavas from ODP holes 1187A and 1185B, about 140 km apart. The lavas form roughly 150 flow units of about 1 meter average thickness, which we feel are multiple surges of lava from a quasi- continuous eruption. Glass compositions (major elements and volatiles) do not vary more than analytical uncertainties within each hole. Differences between the two holes are also less than analytical uncertainties. Averages of 4 samples from each of the two holes are: Cl 750 vs 732 ppm; s.d.=15 ppm. S 988 vs 969 ppm; s.d.=5 ppm. K 616 vs 608 ppm; s.d.=22 ppm. Counting precision is ñ15 ppm (2 sigma) for each element in each single glass analysis. Precision is better than accuracy. Similar CO2 contents in the glasses of the separate holes (Roberge et al., 2004), despite several hundred meters difference in their current reconstructed basement depth suggests that the lavas were erupted from the same vents and flowed for long distances: that they are not merely separate flows of a large eruptive episode that issued from a single magma chamber that had many vents. This observation does not mean that dissolved CO2 contents cannot be used to estimate paleoeruption depths, but that caution is required. The volume of the eruption exceeds that of any known submarine eruption by a great deal. If its lateral dimensions are similar to the length between the holes, then its area would be >200 km2 and its volume would be >3000 km3. That such widely separated lavas have identical chemistry means that there was virtually no cooling over 10s of km of flow. This requires an insulating layer above a rapidly flowing magma (Gregg and Fornari, 1998). We are currently evaluating whether other widely separated recoveries on OJP are also from single lava flows. Possible matches include 1185B (lower) and 1186A, which are about 150-200 km apart. They would indicate even larger eruptive volumes. It is possible that certain glasses from 807C are the same as a thin layer in 1185B. References: Gregg and Fornari, JGR 103, 27517. Mahoney et al. Proc. ODP: Sci Results 130, 3-22, 1993. Roberge et al. Geol. Soc. Lond. Spec. Pub 229, 239-257, 2004. DE HR: 1340h AN: V33E-1500 TI: Trace Element and Isotopic (Re-Os, O) Systematics of Roberts Victor Eclogites: Evidence for 3 Ga Subduction-Incorporation of Archean Oceanic Lithosphere into the South African Kaapvaal Craton Keel AU: * Shirey, S et al. EM AB: Eclogite xenoliths from the 125 Ma old, Group II, Roberts Victor kimberlite have long been of interest in studies of Kaapvaal craton evolution because of their diversity, abundance, availability in large size, occurrence with peridotite and their sometimes high carbon/diamond content. From among the coesite, corundum, kyanite, Ca-, Mg-, and Fe- rich eclogites available, we have chosen to work on those that can be classified as Group I, Group II or diamondiferous with the goal to better understand their petrogenesis, the evolution of the Kaapvaal craton keel, the role of eclogites in diamond formation and the behavior of the Re-Os system. Group I vs Group II eclogites can be distinguished by texture (isolated gt in a cpx matrix vs subhedral, interlocking gt-cpx) and mineral chemistry (higher Na$_{2}$O in gt and K$_{2}$O in cpx for GI vs lower for GII). Such differences have been thought to result from higher vs lower pressures of equilibration. Recent laser fluorination oxygen isotopes (δ18O) on gt (GI = 5.8 to 6.9; GII = 2.1 to 5.1), ion-probe trace elements (e.g. Ce chondrite normalized) on gt (G1 = 0.2 to 0.5; GII = 0.002 to 0.07) and cpx (G1 = 7 to 20; GII = 0.2 to 2) and whole-rock Re-Os (G1 Re = 0.19 to 3.41 ppb; GII Re = 0.006 to 0.38 ppb) highlight even more distinct differences between Groups I and II. These differences are likely a pre- metamorphic signature of their original protoliths and not just due to pressure differences or magmagenesis during emplacement into the lithosphere. Using the stratigraphic variation of O isotopic composition and trace element content of ophiolites and drill core from DSDP/ODP holes 735B and 504B as a guide, Group I eclogites might represent the volcanic rocks of Layer 2 of Archean oceanic crust whereas Group II might represent the cumulate, intrusive rocks of Layer 3. This idea is supported by the presence, only in Group II eclogites, of positive Eu anomalies in reconstructed ion-probe whole rock rare earth element patterns. The Re-Os sytematics of the oceanic lithosphere is poorly known, especially in the Archean, but Roberts Victor eclogite Re-Os and trace element abundances and major element compositions suggest a basaltic komatiitic protolith as might typify slightly hotter ocean ridges in the Archean. A U-Pb age of 3.061$\pm$0.006 Ga on zircon grains separated from a Group I Roberts Victor eclogite and a same-age but scattered whole-rock Re-Os isotope array containing the diamondiferous and some Group I eclogites (including the zircon-bearing eclogite), firmly date the eclogite protoliths as Meso-Archean. The direct covariation of Re content (and hence 187Re/188Os) with O isotopic composition allows the low-T alteration process occurring on the seafloor to be firmly dated at that time. For Kaapvaal craton evolution, this age is interesting because it predates by about 100 Ma the terrane collision that sutured the Kimberley block to the Eastern Kaapvaal along the Colesburg magnetic lineament, the stabilization of a thickened lithospheric mantle keel, and the generation of a widely distributed suite of eclogitic diamonds. Incorporation of these eclogites in the lithosphere is further evidence for Meso-Archean plate tectonics and the role of subduction in cratonization and diamond genesis. HR: 1340h AN: V13A-1457 TI: Along Strike Hf-Nd Isotopic Composition of Aleutian Arc Lavas AU: * Gerseny, M G et al. EM AB: The Aleutian Arc provides an ideal tectonic setting to study Hf-Nd systematics due to its along-strike tectonic and geochemical variation. Sediment load and subduction rate decrease westward along the arc with an increasingly oblique subduction angle, causing a progressive decrease westward in the flux of sediment into the subduction zone. A suite of samples collected across the length of the arc were analyzed for Hf and Nd isotopic composition. A coupled decrease in both Hf and Nd isotopic composition was observed from east to west along the arc. Piip seamount samples at 193\deg W have the highest $\epsilon$$_{Hf}$20.3 and $\epsilon$$_{Nd}$10.4. Lavas from Great Sitkin (176\deg W) and Korovin (174\deg W) have intermediate compositions of 7.4-7.9 $\epsilon$$_{Nd}$and 13.6-14.4 $\epsilon$$_{Hf}$. The lowest $\epsilon$$_{Hf}$ values obtained (12.2-13.0) were from the Cold Bay Volcanic Complex (163\deg W). Various ashes of the DSDP site 178 of the Alaskan abyssal plain have approximately the same Hf and Nd isotopic composition as Cold Bay. Clay and turbidite sequences from site 178 have lower $\epsilon$$_{Hf}$0.8-7.8 and $\epsilon$$_{Nd}$2.8-0.82 values. The change in Hf and Nd isotopic composition along the arc is consistent with a decrease in sediment flux westward. A sediment melt component in the east could mobilize Hf and Nd into the mantle wedge. Fluxing of the subducting sediment could also incorporate Nd into the melting mantle. Both these processes would lower the radiogenic signature of the source region. DE:
HR: 0800h AN: PP51B-1336 TI: Radiolarian and Sedimentologic Paleoproductivity Proxy Record From the Benguela Upwelling System, DSDP Site 532, 0-6 Ma AU: Bittniok, B et al. EM: [email protected] AF AB: The Neogene history of the Benguela upwelling system is fundamental to better understand both regional climate change and how the global ocean cycles nutrients, including carbon. We examined the 0-6 my record of the system at ca. 400 kyr spacing from Walvis Ridge DSDP Leg 75 Site 532. More than 70 radiolarian taxa were counted and two indices computed: a water depth ratio index reflecting mid water export productivity, and the URI index of species that are biogeographically restricted to tropical upwelling regions. Both proxies have been applied so far only to the late Pleistocene. Other proxies measured on the samples include BFAR, TOC, % and MAR carbonate, bulk opal and radiolarian presevation (semiquantitative), foraminiferal dissolution indices, and stable isotopes of oxygen and carbon. The radiolarian water depth index, and to a lesser degree the URI, show gradually increasing productivity in the early Pliocene and high productivity through the late Pleistocene. This general productivity pattern for the region has been established by numerous prior studies. The radiolarian water depth index is strongly correlated to TOC, and importantly is not affected by low opal concentration and poor radiolarian preservation in the basal Pliocene and late Pleistocene. Carbonate, and carbonate microfossil based indices such as BFAR by contrast show largely inverse trends to radiolarians and TOC, but are interpreted as being predominantly dissolution controlled, as indicated by the carbonate dissolution proxies. Our results show that radiolarian faunas yield useful productivity proxies in these upwelling sediments as far back as the latest Miocene. Further, radiolarian based productivity proxies are relatively robust to preservation or the supply of silica to surface waters, which is thought to affect bulk opal based measures of productivity in the region. DE HR: 10:55h AN: OS52A-03 INVITED TI: Jack Dymond's "Fingerprints" on Sediment Chemistry, Biogeochemical Fluxes, and my Career AU: * Leinen, M
AB: I first met Jack Dymond as a graduate student at Oregon State University. He wasn't my thesis advisor. He wasn't even on my committee. But his ever so gentle counsel and his low key advice did much to shape my career, as a student, as a scientist, and later as an administrator of science. At the time, Jack was wading through the analysis of a very large number of surface sediment samples from the Nazca Plate as part of an IDOE project. The number and density of sampling was extraordinary for the time and his work showed that the geochemistry of the sediments could be deconvolved to understand the contributions of sediment sources over the entire plate. I had been planning to analyze DSDP samples from the equatorial Pacific to understand the history of siliceous sedimentation in that region and I began to talk with Jack about how I could use geochemical signatures to estimate the non-biogenic fraction of the sediment. When Jack's Nazca Plate paper came out, Debra Stakes and I decided to analyze all of my sample residues for the same elements that Jack had studied. In the only piece of bad advice that he ever gave me, Jack told me that it was a waste of time because there wouldn't be high enough concentrations of transition metals in the calcareous and siliceous sediments to measure. We insisted and Jack, in typical fashion, agreed to pay for reagents and give us instrument time without charge anyway. The larger than expected concentrations, and the even more surprising match between the accumulation rates of some the metals and the accumulation rates of biogenic sediment were the subject of many discussions, all of which ended in the need for more information on the composition, fluxes and transformations of biogenic sediment in the water column and in recent sediments. This, of course, became another of Jack's specialties: his designs for sediment traps were important contributions to the evolution of this important sampling device. His studies of fluxes in a wide variety of environments - from hydrothermal vent fields to Crater Lake --were critical to the development of modern biogeochemical cycling experiments and thinking. And this, of course, was only one of the fields in which he made major contributions. DE
HR: 1340h AN: PP23B-1413 TI: High resolution paleoceanography of the central Gulf of California during the past 15,000 years AU: * Barron, J et al. EM AB: A high resolution paleoceanographic history of the central Gulf of California during the past 15,000 years has been assembled using microfossil (diatom and silicoflagellate) and geochemical proxy data from a composite section of gravity core GGC55 and giant piston core JPC56 in the western Guaymas Basin (27.5 deg. N, 112.1 deg. W, water depth 818 m) and from DSDP Site 480 (27.9 deg. N, 111.7 deg. W, 655 m water depth) in the eastern Guaymas Basin. These data argue for abrupt, basin-wide changes during the Bolling-Allerod, Younger Dryas, and earliest part of the Holocene that mirror changes documented in cores from the Pacific margins of both Baja and Alta California. Between about 10 ka and 6 ka, these central Gulf of California records became more regionally distinctive, as surface and intermediate waters resembling those of the modern- day northern Gulf became dominant and virtually no calcium carbonate or tropical microfossils were preserved in the underlying sediments. Beginning at about 6 ka, tropical microfossils returned to the central Gulf, possibly signaling enhanced El Nino- like conditions. Proxy data suggest that late winter-early spring coastal upwelling was abruptly strengthened on the mainland (eastern) side at about 5.4 ka and again at about 3.0 ka, whereas sediments from the western side of the central Gulf became increasingly diatom poor and calcium carbonate rich. An intensification of northwest winds during the late winter to early spring likely occurred in the central Gulf at about 5.4 ka. Interestingly, this proposed wind shift in the Gulf of California coincides with an abrupt 5.4 ka change to drier conditions in the Cariaco Basin off Venezuela that has been proposed to reflect a southward shift in the mean position of the Intertropical Convergence Zone in response to increasing El Nino-like conditions. DE HR: 0800h AN: V51A-0513 TI: Variations in the marine Ca cycle and implications for paleo- CO$_2$ levels over the past 24 Ma AU: * Fantle, M et al. EM AB: A detailed record of the calcium isotopic composition of bulk nannofossil ooze from DSDP Site 590, based on 40 samples measured multiple times, shows variations of $\delta^{44}$Ca over the past 24 million years between --0.2 and --0.9$\permil$, relative to bulk Earth Ca (--1.15 to --1.85$\permil$, relative to seawater). These isotopic variations are inferred to reflect changes in $\delta^{44}$Ca of seawater between +1.1 and +0.4$\permil$. Fluctuations in $\delta^{44}$Ca, which occur in 1 to 4 Ma cycles with varying amplitude, are interpreted as resulting from imbalances between the input of Ca to the oceans by weathering processes and the biogenic removal of Ca. Using a model for oceanic inputs and outputs of Ca, we reconstruct past weathering fluxes and marine Ca concentrations. Combining this information with paleo-pH of the ocean, as estimated from B isotopes, we derive a record of atmospheric $pCO_2$ levels over the past 24 Ma. The concentration of Ca in the ocean was at a minimum at $\sim$20 Ma, during the Neogene climate optimum, increased until 6 Ma, and then decreased toward the present. Maxima in the record occur at 6.4 and 4 Ma, corresponding to a generally-recognized period of enhanced marine productivity and high mass accumulation rates at Site 590. Peaks in the inferred weathering flux occur at 18, 14, 8, 5, and 1 Ma. Our derived $pCO_2$ record indicates that the highest $CO_2$ levels during the 24 Ma period under consideration occurred at 20--24 Ma and were no more than about twice the present-day (pre-industrial) levels. The maximum in the $CO_2$ record occurs during the warming that accompanied the Neogene climate optimum. The $pCO_2$ minimum occurs at 6--4 Ma, during a period of enhanced marine productivity. The calculated marine paleo-Ca and paleo-$pCO_2$ values are sensitive to the assumed $\delta^{44}$Ca value for the weathering flux, but the shapes of the derived curves do not change greatly over the range of likely input values. The reconstructed $pCO_2$ curves depend significantly on pH, but the assumption of constant pH (which only barely violates the available constraints from B isotopes) yields substantially the same result. Although the paleo-$pCO_2$ curve is likely to be revised when more data are available, the present results do not show a simple linear relationship between $pCO_2$ and high-latitude temperature as reflected in the benthic oxygen isotope records. DE HR: 1340h AN: T13B-1356 TI: Magnetic Properties of Ocean Crust from the Walls of Endeavor Deep: Implications for the Source Layers of Marine Magnetic Anomalies AU: * Richmond, R et al. EM AB: The presence of lineated marine magnetic anomalies in the ocean basins is the foundation for plate tectonics and global plate reconstructions. The relative importance of the source layers of these anomalies, however, is still poorly constrained. Identifying the source layer(s) of the magnetic anomalies is important for present-day models of crustal accretion that require crustal rotations of up to 20-30 degrees. These rotations may result in anomalously skewed seafloor magnetic anomalies, which could significantly alter global plate reconstructions. To address the question of the magnetic sources at ultra-fast spreading rates, we have measured the magnetic properties of 135 precisely located rock samples collected with JASON II from the walls of Endeavor Deep. Endeavor Deep is the tip of a propagating rift on the Nazca/Juan Fernandez plate boundary. It exposes a 70 km-long, 40 km-wide, and 3 km-deep section of ~3 Myr old upper oceanic crust (layers 2A and 2B) created at the ultra-fast spreading (~150 km/myr) East Pacific Rise. Measurements of natural remanent magnetization, magnetic susceptibility, and median destructive field define three "stratigraphic" units and are characterized relative to similar measurements by Pariso and Johnson (1991) on samples from DSDP Hole 504B. The upper 200 m of extrusives were likely altered by low temperature oxidation, and carry a relatively low magnetization (0.4 A/m). The underlying 300 m of extrusives carry a relatively high magnetization (2.1 A/m), which likely contributes significantly to the amplitude of the magnetic anomaly signal. The transition zone from extrusive layer 2A to intrusive layer 2B (pillow basalts to dykes) and possibly the upper portion of layer 2B carries an unexpectedly high magnetization (1.6 A/m) and likely contributes to the magnetic source layer as well. A dramatic increase in susceptibility is present below the base of layer 2A that has not been previously observed. DE:
HR: 1340h AN: T53A-0471 TI: Extremely Rapid and Localized Erosion in the Himalaya Recorded in Sediments of the Bengal Fan AU: * Stewart, R and Hallet, B EM AB: Vigorous erosion during mountain building is now recognized as a significant factor for integrated climate-tectonics-erosion studies in Earth system science. In this context, the ages of detrital grains in sediments both define the depositional age and provide direct evidence for the tempo of erosion. In the eastern syntaxis of the Himalaya, the youngest peak identified by BINOMFIT in detrital zircons from fluvial sediments of the modern Brahmaputra River is 0.6 Ma, and significantly, it includes 47% of the entire sand-sized zircon population. The youngest grains are ~ 0.1 Ma, and a significant subset has a peak age of 0.4 Ma. The youngest peak in apatite fission-track ages from the same samples is 0.4 Ma and includes 39% of the grains. These ages are astonishingly similar to bedrock cooling dates from their source in the Tsangpo gorge, where the Yarlung-Brahmaputra River slices through the Namche Barwa-Gyala Peri massif in southeast Tibet. The Tsangpo gorge is particularly significant because it is a region with exceptionally young bedrock ages, including zircon fission-track dates (0.2 Ma), biotite 40Ar/39Ar cooling ages (1.0 Ma), zircon [(U-Th)/He] cooling ages (0.3 Ma), and migmatite crystallization ages ($<$3.0 Ma). These data are all compatible with an estimated exhumation rate of about 7 mm/yr in the Tsangpo gorge, and provide an actualistic model for interpreting the distribution of grain ages in older sediments; clustering of grain ages from different geothermometers about the time of deposition is an indicator of exceptional exhumation rates, and, if sustained in the longterm, accompanying rapid uplift. The Bengal Fan is a repository for debris eroded from the Himalaya. Grains of K-feldspar, muscovite, and apatite are abundant in sediments of the Bengal Fan. Fission-track and 40Ar/39Ar dates on apatite, K-feldspar and muscovite recovered from DSDP Sites 717 and 718 constrain deposition on the outer fan to about the past 12 m.y. With 2 exceptions, duplicate determinations of the age of the youngest grain from identical depositional horizons within the fan are essentially concordant. This remarkable synchronicity in 40Ar/39Ar and fission-track ages requires erosion and transport from the outcrop to the fan in an astonishingly short time. It requires deposition of first-cycle material with essentially the identical age at the time of deposition, despite the significantly different cooling histories that each of these systems records. This concurrence requires exceptional erosion in a setting that exposes grains of essentially "zero-age," and provides in-situ evidence that extremely rapid and localized erosion, such as that now occurring in the vicinity of the Namche Barwa-Gyala Peri massif and the Tsangpo gorge, has been a factor in exhumation of the Himalaya for at least the past 12 m.y. DE:
HR: 0800h AN: T11A-1238 TI: Evidence That Early to Middle Miocene ice Streams From West Antarctica cut Into Southeastern Ross Sea Continental Shelf AU: * Sorlien, C et al. EM AB: The extent of the West Antarctic ice sheet during mid-Cenozoic time is controversial and important to climate models. High-resolution multichannel seismic reflection data were acquired using the RVIB Palmer along the edge of the Ross Ice Shelf across the Eastern Basin of Ross Sea, in an area where calving of the ice shelf has exposed seafloor that has not been accessible to marine geophysics in several decades. A sub-basin in the far southeast corner of Ross Sea contains a succession of sediment-filled troughs, each capped by an unconformity. These troughs range between 5 and 20 km across, and are 100 to 150 m-deep. They are cut into a sequence correlated to slightly predate ~24 Ma. The shallowest of these unconformities (named "Red" here) can be tentatively projected across the northern plunge of a basement ridge located north of Roosevelt Island (named "Roosevelt Ridge" here), and is a regional unconformity in the Eastern Basin. Reflections just below Red can be correlated to DSDP 272, where they are dated at ~14 Ma. Red is flat and level in the south, adjacent to the ice shelf edge. Older sequence boundaries beneath Red merge with it across a 70 km extent between the deep Eastern Basin and Roosevelt Ridge. Much of the late-Early Miocene and early-Middle Miocene section is missing and appears to be removed by erosion associated with the Red unconformity. There is no evidence for broad glacial troughs that predate Red west of Roosevelt Ridge. If our correlations are correct, the succession of glacial troughs must be Middle Miocene and older, and we cannot rule out the oldest being Late Oligocene without additional data. Because we do not believe that a glacier or grounded ice sheet could erode a thick interval of sedimentary rocks and still produce a smooth and level unconformity, our preferred hypothesis is that Red is a wavecut surface that has since subsided to its present 700 m depth. The fill of one 20 km-wide trough is exposed at the seafloor and accessible to Shaldrill coring to test our hypothesis. The Ross Ice Shelf is advancing over the surveyed troughs and future drilling from the ice shelf will also be possible. Finally, it may be possible to correlate the fill of the troughs to DSDP stratigraphy with acquisition of carefully-positioned seismic reflection profiles. These troughs are consistent with erosion by ice streams or glaciers fed from an ice cap over at least part of western Marie Byrd Land. An Early Miocene ice cap contrasts with the Late Miocene age for the earliest widely accepted time for grounded ice in West Antarctica. DE
HR: 0800h AN: V51B-0544 TI: Critical Evaluation of Radiometric Ages Used for Tracking Hotspots in the Pacific Ocean AU: * Baksi, A EM AB: One of the pillars supporting the plume hypothesis, is the progression of ages for numerous hotspot tracks in oceans. These ages should be based on radiometric measurements. The argon dating methods have been the tool most commonly used. Since most of the rocks selected for dating have suffered (considerable) alteration, K-Ar dates should not be used as accurate measures of the age of crystallization. 40Ar/39Ar total fusion ages, though better than K-Ar dates in general, do not pinpoint samples that (a) contain excess argon or (b) have suffered partial loss of 40Ar* due to alteration. Hence 40Ar/39Ar incremental heating studies remain as the (only) tool of choice. From such experiments, at a minimum, ages must be based on plateau and/or isochron sections that meet the necessary statistical requirements to be considered crystallization ages. Earlier (Baksi, 1999, Jour. Geol.) it has been shown that almost all the purported crystallization ages for hotspot tracks in the Atlantic and Indian Oceans, are invalid (see also www.mantleplumes.org/ArAr.html). Herein, I apply the tests outlined therein, to evaluate ages available in the literature for hotspot tracks in the Pacific Ocean. These can be divided into five main groups. (1) Those with reliable age data (e.g. Dalrymple and Garcia,1980; Dalrymple et al., 1980, DSDP 55, Hawaiian-Emperor Chain); the authors use care in selecting valid ages from their data sets. (2) Others (e.g. Pringle, 1993, AGU Monograph 77, Musicians Seamounts), most ages are statistically valid, though some fail the requisite test. In addition, many samples show high levels of atmospheric argon, suggesting the samples are (quite) altered; this could lead to incorrect plateau ages. (3) The next set (e.g. Winterer et al., 1993, AGU Monograph 77, Cretaceous guyots in the Northwest Pacific; Ozima et al., 1977, JGRAS, Western Pacific guyots; Saito and Ozima, 1977, EPSL, Western Pacific area) have few, if any, valid ages. Most plateaux/isochrons clearly fail the statistical test of reliability; many steps show high levels of atmospheric argon - the samples are (badly) altered. (4) A set of papers (e.g. Gripp and Gordon, 2002, Geophys. J. Int., young hotspot tracks; Duncan, 1985 - New Hebrides-Samoa lineament) make use of K-Ar dates, wholly or in the main. These dates should be treated as minimum estimates of the crystallization age. (5) A final set of papers (Sager et al., 1993, AGU Monograph 77, Japanese and Marcus-Wake Seamounts; Lincoln et al., 1993, AGU Monograph 77, Marshall Islands), quote ages without listing the relevant analytical data. These results are to be treated as suspect, and not used for quantitative tracking of hotspot trails. In conclusion, the purported progression of ages for numerous hotspot tracks in the Pacific Ocean does not withstand critical scrutiny. DE
HR: 0800h AN: T11A-1244 TI: Ice shelf drill sites proposed to study Pre-Late Oligocene climate and tectonic history, Coulman High, Southwestern Ross Sea, Antarctica. AU: * Decesari, R et al. EM New geophysical data were collected in front of the Ross Ice Shelf using the RVIB Nathaniel B. Palmer in January of 2003. The primary goal was to collect detailed grids of seismic data to select drill sites to investigate the climate and tectonic history of the Ross Sea region. The survey sites were located where large sections of the ice shelf have broken off, exposing previously inaccessible seafloor. A site survey at the C-19 iceberg calving site, located in 800-900 m of water adjacent to Ross Island and 120 km NE from McMurdo Station, was conducted under the premise that the ice sheet, advancing north at ~1 km/year, will in time cover the survey thereby allowing drilling into the seabed from the ice sheet. We propose an E-W transect of drill sites along the ice shelf front designed to target section where pre-Late Oligocene strata dips east allowing successively deeper stratigraphic sampling with a series of holes across strike. Cores from here may record the transition from warm climate in Eocene time to the cooler Oligocene and will test our hypothesis that extension between East and West Antarctica is recorded in sediments in this sector of the Ross Sea. Rifting in Cretaceous time resulted in widespread extension of the Ross Sea amounting to several hundred kilometers. Adare Trough seafloor spreading in Eocene-Oligocene time adjacent to the Ross Sea continental shelf resulted in about 180 km of spreading, and may project into the western Ross Sea. Syn-rift sediments of these ages may be present. The C-19 site on Coulman High is characterized by N-S trending basement half grabens filled with syn-rift sediments of unknown age truncated by an angular unconformity, and overlain by undeformed Late Oligocene and younger strata that we correlated to DSDP and Cape Roberts drill sites. We have divided the pre-Oligocene units into an upper (Early Oligocene?-Eocene?; ~ 680-1000 m below sea floor (bsf)) unit and lower (Eocene?-Late Cretaceous?; >1000 m bsf) unit, separated by an unconformity, all resting on top of acoustic basement at ~1400m bsf. We suggest that the pre-Oligocene strata are syn-rift units deposited and deformed during both Late Cretaceous and Early Eocene extension.
HR: 0800h AN: V51B-0570 TI: Widespread Synchronous Volcanism Reveals a Broad Galapagos Hotspot Melting Anomaly AU: * O'Connor, J et al. EM AB: The massive aseismic ridges and associated seamounts dominating the morphology of the Panama Basin, eastern Central Pacific, have long been attributed to a Galapagos hotspot melting anomaly linked to a deep-seated mantle plume. Although these structures can provide information about the origin of hotspots and existence, or otherwise, of mantle plumes very little is known about their volcanic histories due to a lack of direct age and geochemical information. We report here 74 whole rock and 2 plagioclase $^{40}$Ar/$^{39}$Ar ages for rocks dredged from 53 locations during the first systematic sampling of the Cocos, Carnegie, Coiba and Malpelo aseismic ridges and associated seamounts (F.S. SONNE PAGANINI expedition). In addition we also report ages for DSDP drill sites on Cocos, Carnegie and Coiba ridges and 7 Cocos Island subaerial samples. The distribution of new, and published ages for the Galapagos Archipelago-platform and NE end of the Cocos Ridge, show a general trend of increasing age with distance from the Galapagos Archipelago. A more dominant trend however is one of aseismic ridge-seamount formation in a progression of broad zones of synchronous, often overlapping volcanism created at discrete intervals. Broad zones of coeval Cocos and Carnegie volcanism once formed much larger regions of synchronous volcanism that have been split apart by the complex history of seafloor spreading associated with the Cocos-Nazca spreading center. We link these broad regions of synchronous volcanism to a correspondingly large hotspot melting anomaly. The present day, as yet unfragmented, zone of synchronous volcanism associated with this proposed broad hotspot is marked by the extensive region of recent volcanism extending across the Nazca and Cocos plates encompassing the Galapagos Archipelago-Platform and the Cocos Ridge as far north as Cocos Island. The complex tectonic history of the Cocos- Nazca spreading-center has controlled how the broad zones of synchronous, often overlapping volcanism created by the broad Galapagos melting anomaly have been fragmented between the Cocos and Nazca plates. However, interplay between the broad Galapagos melting anomaly and the Cocos-Nazca spreading center is a second-order process compared to a fundamental underlying mantle process responsible for a broad Galapagos hotspot melting anomaly exhibiting long-lived characteristics (size, time- progression, episodicity) which, on a first-order, are independent of local tectonics and lithospheric architecture. Evidence for a broad Galapagos hotspot melting anomaly and the possibility of detecting long-lived underlying mantle processes has implications for how oceanic hotspot volcanism is sampled for purposes of rigorously testing the mantle plume paradigm. A major question posed by our results is whether individual Pacific seamount chains are in fact the product of tectonic plate drift over narrow hotspots? If not, then inferring the existence and behavior of a mantle plume on the basis of age progression of volcanism produced by a narrow seamount chain could well prove to be misleading. Thus, although great leaps are being made in the theory and numerical modeling - often on a global scale - of hypothesized deep plumes, significantly more high-quality age and geochemical data are needed for oceanic hotspot volcanism that gave birth to the mantle plume hypothesis in the first place. DE: HR: 1340h AN: V33E-1500 TI: Trace Element and Isotopic (Re-Os, O) Systematics of Roberts Victor Eclogites: Evidence for 3 Ga Subduction-Incorporation of Archean Oceanic Lithosphere into the South African Kaapvaal Craton Keel AU: * Shirey, S et al. EM AB: Eclogite xenoliths from the 125 Ma old, Group II, Roberts Victor kimberlite have long been of interest in studies of Kaapvaal craton evolution because of their diversity, abundance, availability in large size, occurrence with peridotite and their sometimes high carbon/diamond content. From among the coesite, corundum, kyanite, Ca-, Mg-, and Fe- rich eclogites available, we have chosen to work on those that can be classified as Group I, Group II or diamondiferous with the goal to better understand their petrogenesis, the evolution of the Kaapvaal craton keel, the role of eclogites in diamond formation and the behavior of the Re-Os system. Group I vs Group II eclogites can be distinguished by texture (isolated gt in a cpx matrix vs subhedral, interlocking gt-cpx) and mineral chemistry (higher Na$_{2}$O in gt and K$_{2}$O in cpx for GI vs lower for GII). Such differences have been thought to result from higher vs lower pressures of equilibration. Recent laser fluorination oxygen isotopes ($\delta^{18}$O) on gt (GI = 5.8 to 6.9; GII = 2.1 to 5.1), ion-probe trace elements (e.g. Ce chondrite normalized) on gt (G1 = 0.2 to 0.5; GII = 0.002 to 0.07) and cpx (G1 = 7 to 20; GII = 0.2 to 2) and whole-rock Re-Os (G1 Re = 0.19 to 3.41 ppb; GII Re = 0.006 to 0.38 ppb) highlight even more distinct differences between Groups I and II. These differences are likely a pre-metamorphic signature of their original protoliths and not just due to pressure differences or magmagenesis during emplacement into the lithosphere. Using the stratigraphic variation of O isotopic composition and trace element content of ophiolites and drill core from DSDP/ODP holes 735B and 504B as a guide, Group I eclogites might represent the volcanic rocks of Layer 2 of Archean oceanic crust whereas Group II might represent the cumulate, intrusive rocks of Layer 3. This idea is supported by the presence, only in Group II eclogites, of positive Eu anomalies in reconstructed ion-probe whole rock rare earth element patterns. The Re-Os sytematics of the oceanic lithosphere is poorly known, especially in the Archean, but Roberts Victor eclogite Re-Os and trace element abundances and major element compositions suggest a basaltic komatiitic protolith as might typify slightly hotter ocean ridges in the Archean. A U-Pb age of 3.061$\pm$0.006 Ga on zircon grains separated from a Group I Roberts Victor eclogite and a same-age but scattered whole-rock Re-Os isotope array containing the diamondiferous and some Group I eclogites (including the zircon-bearing eclogite), firmly date the eclogite protoliths as Meso-Archean. The direct covariation of Re content (and hence $^{187}$Re/$^{188}$Os) with O isotopic composition allows the low-T alteration process occurring on the seafloor to be firmly dated at that time. For Kaapvaal craton evolution, this age is interesting because it predates by about 100 Ma the terrane collision that sutured the Kimberley block to the Eastern Kaapvaal along the Colesburg magnetic lineament, the stabilization of a thickened lithospheric mantle keel, and the generation of a widely distributed suite of eclogitic diamonds. Incorporation of these eclogites in the lithosphere is further evidence for Meso-Archean plate tectonics and the role of subduction in cratonization and diamond genesis. HR: 1340h AN: ED13E-0755 TI: Teaching Biostratigraphy Using Real Cores and IODP Data: The use of Information Technology on Spatial Visualization Skills, Motivation and Transfer of Undergraduate Science Majors AU: * Hilding-Kronforst, S et al. EM: AB: We have developed a problem-solving lab exercise using real IODP data and graphic correlation to address planktonic community change at the Eocene-Oligocene boundary. This stratigraphic interval represents a time of dramatic global cooling, but the change is expressed in different ways and to different degrees at different locations in the world's oceans. The question the students are asked to address is whether observed changes in taxonomic composition across the Eocene-Oligocene boundary are global or local responses to changes in oceanic and atmospheric circulation. First, students were introduced to graphic correlation, a quantitative biostratigraphic technique that incorporates data from many local sections into a composite reference section. Second, students were taken to the core repository of the Integrated Ocean Drilling Program on the campus of Texas A&M University to examine the Eocene-Oligocene boundary in a series of cores from the Indian and Pacific Oceans. Some cores show virtually no lithological change at the boundary, whereas others show dramatic changes in rock type. Finally, students were asked to download biostratigraphic data from the IODP on-line Janus database from the same cores that they had measured and use them to create a composite global reference section. Using their own observations of the cores, the results of their graphic correlation of the real data, and additional information they were provided by IODP scientists during their field trip to the repository, students addressed the global versus local nature of biotic change at the Eocene-Oligocene boundary. Evaluation of spatial skills and motivation were performed pre and post lab. An additional post lab exercise measured student ability to transfer conceptual knowledge. Evaluations from students will assess the effectiveness of this exercise and reflect the value of integrating technology in geoscience curriculum. DE: HR: 1340h AN: T13A-1348 TI: Airborne Gravity Gradiometer Survey Over the San Andreas Fault AU: * Talwani, M EM: AB: An airborne gravity gradiometer survey is being conducted over the San Andreas Fault drill site. The survey is over a 10km x 10km area. Forty lines will be flown in a direction parallel to the strike of topography; the lines, 250 meters apart, will each be 10km in length. Ten lines 1km apart will be flown in a perpendicular direction. The lines will be flown on a drape surface at a nominal ground clearance of 200 meters, although the ground clearance will be substantially greater in many parts of the survey because of the presence of steep topography. The principal objective of the survey is to detect density inhomogeneties associated with the San Andreas Fault which lie at a shallow depth (less than 1km). Terrain corrections are very large in the area of the survey and correct application of the corrections is essential for detection of sub-surface density variations. The survey will be carried out by Bell Geospace using its six component airborne gravity gradiometer. We expect to be able to present some preliminary results at this meeting. DE HR: 0800h AN: ED51C-0030 TI: USIO-IODP Developing a New Fellowship for HBCU Students AU: * Castner, et al. EM AB: The U.S. Implementing Organization for the Integrated Ocean Drilling Program has developed a new Fellowship for students enrolled at Historically Black Colleges and Universities. In this pilot year, the Fellowship is being offered to students enrolled at HBCUs that are in proximity to the JOI Alliance institutions: the Joint Oceanographic Institutions in Washington, DC; Texas A&M University in College Station, TX; and the Lamont-Doherty Earth Observatory of Columbia University in Palisades, NY. Selected Fellows will work closely with Alliance mentors on projects related to scientific ocean drilling in the areas of science and engineering, education and public affairs, and scientific program management. Future plans include expanding the Fellowship to include students from all HBCUs. DE: HR: 0800h AN: ED31C-0751 TI: Learning Activities Developed at The University of Texas at Austin Institute for Geophysics Using Ocean Drilling Science, Technology and Data AU: * Bailey, D et al. EM AB: NSF GK-12 Fellows at The University of Texas at Austin Institute for Geophysics (UTIG) actively contribute to K-12 education by linking K-12 students and teachers to research scientists and recent discoveries, and by developing hands-on learning activities designed primarily for secondary school learning environments. The excitement of the new Integrated Ocean Drilling Program (IODP), an international research program that explores the history and structure of the Earth by studying the sediments and rocks beneath the seafloor, has provided UTIG's GK-12 Fellows with an incentive to develop new, and revise existing, inquiry-based learning activities based on the science, technology and/or data of scientific ocean drilling. These activities, grouped into a curriculum module, address the mechanics of collecting cores, fossil identification and age relationships within a core, and the interpretation of geophysical logs. They expose teachers and students to the exciting science and advanced technology of the IODP and the achievements of the Ocean Drilling Program, which preceded IODP. UTIG scientists active in the IODP guided the development of the module's science content. The module activities are aligned with U.S. educational standards, but could be adapted for use in other countries that participate in the IODP. Where this isn't possible, they can serve as an example of educational curriculum materials that underscore the vital nature of international collaboration. UR
HR: 0800h AN: ED21C-0077 TI: Experiences and Results from the Integrated Ocean Drilling Program (IODP) Teacher at Sea Program, Expedition 301 AU: * Rice, J et al. EM AB: The IODP US implementing organization began a Teacher at Sea Program (TASP) during Expedition 301 to the eastern flank of the Juan de Fuca Ridge. The main scientific objectives of this expedition were to establish borehole observatories as part of a series of multidisciplinary experiments that will help evaluate the hydrogeologic properties of the oceanic crust, including the distribution of fluid pathways within an active hydrothermal system as well as the linkages between fluid circulation, alteration, and microbiological processes. The goals of the U.S. sponsored IODP TASP were to provide the participant with seagoing research experiences, working side-by-side with scientists, using current state-of-the-art approaches to solve scientific problems pertinent to this expedition, and gaining first-hand knowledge of the results of seagoing science. In addition, the participating teacher will use these experiences for translating scientific results into useful teaching resources, such as expedition information materials and help disseminating these resources into classrooms across the country. During IODP Expedition 301, the participating teacher spent 2 months working with shipboard scientists in processing core data and learning the different techniques used for the shipboard laboratory analyses. Several laboratory briefs targeted for middle to high school student audiences were developed during the cruise including the microbiology, chemistry, paleomagnetics, and physical properties laboratories and educational classroom activities are currently being developed. In addition, other laboratory briefs and educational activities for the underway geophysics, core, downhole measurements, and paleontology laboratories are being developed as part of the post-expedition curriculum development initiatives. The teacher also kept a daily journal detailing life at sea experiences as well as all the science and operational developments that took place during the expedition. The journal entries can be found at http://iodp.ldeo.columbia.edu/EDU/TAS/. Interaction with other middle school and high school educators while at sea was successful via a conference call where experiences and general daily operations were shared. DE:
HR: 0800h AN: MR11A-0916 TI: Calibration of Mobile NMR Instruments in Respect to Porosity and Pore Size Distribution of Drill Cores AU: * Arnold, J et al. EM AB: The focus of our research is set on the calibration of two different and new developed light weight mobile NMR scanning systems: (1) the NMR-MOUSE and (2) the HALBACH device for measuring porosity and pore size distribution of different drill cores recovered from the International Ocean Drilling Program (IODP). Further goals are to adapt current NMR processing techniques, the development of new measurement routines, and to evaluate precision and accuracy of this method. Transverse relaxation on water-saturated drill cores were measured using a CPMG sequence. A regularized Laplace transform analysis based on the UPEN program yields the distribution of transverse relaxation times. The signal amplitudes and the integrals of distribution correlate directly to the core porosity. The main advantage of our mobile NMR scanning systems compared to conventional methods is their small size and weight, which is particularly attractive for the shipboard use and on any drilling platform envisioned for IODP. Both tools, the NMR-MOUSE and the HALBACH scanner are suitable for routine measurements of porosity and pore-size distribution of drill core sections. In contrast to the NMR-MOUSE, the HALBACH tool has a sufficiently homogeneous magnetic field and is more sensitive. It can determine porosities as low as 3 %. While the NMR- MOUSE can be applied on core sections of any geometry, the Halbach tool is especially designed for the size of standard drill cores recovered from the deep sea ocean floor by the IODP. Combined with a mobile NMR spectrometer and special software for porosity and pore size distribution measurements, both light and mobile devices are particularly attractive for the use on research vessels and logging platforms and thus alow to determine prosity and permeability on very fresh material. DE:
HR: 0800h AN: GC51D-1084 TI: Data Modeling, Development, Installation and Operation of the ACEX Offshore Drilling Information System for the Mission Specific Platform Expedition to the Lomonosov Ridge, Arctic Ocean. AU: * Conze, R et al. EM AB: During August/September 2004, the Arctic Coring Expedition (ACEX) was used to trial a new Offshore Drilling Information System (OffshoreDIS). ACEX was the first Mission Specific Platform (MSP) expedition of the Integrated Ocean Drilling Programme (IODP), funded by the European Consortium for Ocean Research Drilling (ECORD). The British Geological Survey in conjunction with the University of Bremen and the European Petrophysics Consortium were the ECORD Science Operator (ESO) for ACEX. IODP MSP expeditions have very similar data management requirements and operate in similar working environments to the lake drilling projects conducted by the International Continental Scientific Drilling Program (ICDP), for example, the GLAD800, which has very restricted space on board and operates in difficult conditions. Both organizations require data capture and management systems that are mobile, flexible and that can be deployed quickly on small- to medium-sized drilling platforms for the initial gathering of data, and that can also be deployed onshore in laboratories where the bulk of the scientific work is conducted. ESO, therefore, decided that an adapted version of the existing Drilling Information System (DIS) used by ICDP projects would satisfy its requirements. Based on the existing DIS, an OffshoreDIS has been developed for MSP expeditions. The underlying data model is compatible with IODP(JANUS), the Bremen Core Repository, WDC-MARE/PANGAEA and the LacCore in Minneapolis. According to the specific expedition platform configuration and on-board workflow requirements for the Arctic, this data model, data pumps and user interfaces were adapted for the ACEX-OffshoreDIS. On the drill ship Vidar Viking the cores were catalogued and petrophysically logged using a GeoTek Multi-Sensor Core Logger System, while further initial measurements, lithological descriptions and biostratigraphic investigations were undertaken on the Oden, which provided laboratory facilities for the expedition. Onboard samples were registered in a corresponding sample archive on both vessels. The ACEX-OffshoreDIS used a local area network covering the two ships of the three icebreaker fleet by wireless LAN between the ships and partly wired LAN on the ships. A DIS-server was installed on each ship. These were synchronized by database replication and linked to a total of 10 client systems and label printers across both ships. The ACEX-OffshoreDIS will also be used for the scientific measurement and analysis phase of the expedition during the post-field operations `shore- party' in November 2004 at the Bremen Core Repository (BCR). The data management system employed in the Arctic will be reconfigured and deployed at the BCR. In addition, an eXtended DIS (XDIS) Web interface will be available. This will allow controlled sample distribution (core curation, sub-sampling) as well as sharing of data (registration, upload and download) with other laboratories which will be undertaking additional sampling and analyses. The OffshoreDIS data management system will be of long-term benefit to both IODP and ICDP, being deployed in forthcoming MSP offshore projects, ICDP lake projects and joint IODP-ICDP projects such as the New Jersey Coastal Plain Drilling Project. UR
HR: 1340h AN: V23B-0628 TI: New insights into serpentinization at Atlantis Massif, 30$\deg$ N Mid-Atlantic Ridge, using wide-angle seismic method AU: * Singh, S et al. EM AB: The Atlantis Massif is an ultramafic core complex that was formed in the last 1.5- 2.0 Myr at the intersection of the Atlantis Fracture Zone and the Mid-Atlantic Ridge near 30ø N by tectonic extension along a long-lived oceanic detachment fault. The exhumation of deep crustal and upper mantle rocks in the footwall of the fault provides an excellent tectonic window into the oceanic lithosphere. The Atlantis Massif will be the subject of a deep-drilling investigation for upcoming IODP Legs 304 and 305 (November 2004 - February 2005). Near-offset seismic reflection data (offset up to 3 km) across the core complex imaged a reflection at 0.2-0.25 s below the seafloor, which has been interpreted as an older detachment fault [Canales et al., Earth Planet. Sci. Lett., 222, 543-560, 2004]. The application of a non-conventional multichannel seismic (MCS) imaging technique allows us to include wide-angle seismic reflection data (offset up to 6 km) in the imaging process. We find that this reflection is continuous along most of the profiles and is present beneath the exposed detachment surface over an area larger than previously estimated from the near-offset MCS sections. Complementary data from on- bottom shots and ocean bottom seismometers constrain both P and S-wave velocities down to 0.5-0.6 km below the seafloor, at approximately the depth of the widespread reflection. The combined seismic data suggest that the interval between the seafloor and the reflection contains serpentinized peridotite. We quantify the amount and distribution of alteration in this layer by using an effective medium theory, and we interpret the results to shed new light on serpentinization processes at Atlantis Massif. IODP drilling results this winter will allow us to compare our interpretation to ground-truth measurements. DE
HR: 1340h AN: OS43B-0547 TI: A Three-Dimensional Subseafloor Observatory Network for Cross-Hole, Hydrogeologic Experiments Established in the Northeast Pacific Ocean AU: * Fisher, A et al. EM AB: The upper oceanic crust, composed mainly of basalt, comprises the largest aquifer on Earth. Global fluid fluxes through the upper oceanic crust are at least as large as the annual riverine flux to the ocean, and influence a diverse array of processes and properties, including the thermal state and evolution of oceanic plates; alteration of the lithosphere and the chemistry of flowing fluids; establishment and maintenance of vast subseafloor microbial ecosystems; and diagenetic, seismic, and magmatic activity along plate-boundary faults. Active experiments are needed in the oceanic crust to determine hydrogeologic properties at a crustal scale, and to quantify linkages between thermal, fluid, solute, and biological processes. The first expedition of the Integrated Ocean Drilling Program established two new subseafloor observatories within 3.5 Ma crust in the northeast Pacific Ocean, and replaced a previously-deployed observatory, in anticipation of planned cross-hole tests and related experiments. The new holes extend up to 320 m into basement and isolate distinct depth intervals. All of the new observatories are instrumented with autonomous temperature loggers, osmotic fluid samplers, and microbiological incubation substrate. Future experiments will include hydrogeologic tests to determine fluid transmission and storage properties, at cross-hole distances of 35 to 2200 m, tracer tests to quantify rates and modes of solute transport, and seismic experiments to elucidate relations between velocity and hydrogeologic anisotropy. DE:
HR: 09:00h AN: ED41C-05 TI: Undergraduate Student Research with the Integrated Ocean Drilling Program on Expedition 301 AU: * Hawkins, L et al. EM AB: I was invited to participate as a shipboard scientist on board the JOIDES Resolution during Expedition 301 of the Integrated Ocean Drilling Program (IODP). The scientific objectives of this expedition were to establish borehole observatories to evaluate the hydrogeologic properties within oceanic crust, determine how fluid pathways are distributed within an active hydrothermal system, establish linkages between fluid circulation, alteration, and geomicrobial processes and determine relations between seismic and hydrologic anisotropy. I worked as a paleomagnetics shipboard scientist with William Sager from Texas A&M University. My primary responsibility was to produce the initial paleomagnetic data through alternating field and thermal demagnetization for the sediments and basement rocks recovered during the expedition. The magnetic data obtained from samples recovered from the 220 m basaltic section that was drilled show some consistency with expected normal polarity acquired at high-mid latitudes and some reversed polarity or low inclination values which may be related to alteration. Additionally, I assisted in core curation and processing, the underway geophysics lab, and with core description. I was included in the scientific meetings discussing sample handling, preliminary results, on-going developments, and post-cruise research. My post- cruise project, under the direction of William Sager and Bernard Housen of Western Washington University, investigates magnetic properties of the basaltic rock from the upper oceanic crust. The primary goal of this work will be to refine our understanding of the magnetization process and geomagnetic field geometry recorded by young ($<$ 3.5 Ma) oceanic crust. This experience was invaluable to me as an aspiring scientist. I was participating in cutting edge research with renowned scientists who were working on subjects of global interest and I was not reading chapters out of a textbook. The scientists showed me a glimpse of what the future may be for me, including some of the challenges as well as benefits. I also received guidance for post-baccalaureate study, made contact with professors, post-docs, and graduate students outside my university, and formed life- long friendships. I cherished this opportunity and I look forward to sharing more of my undergraduate research experiences with others. DE
HR: 0800h AN: G21A-0139 TI: An Experiment on GPS/A Seafloor Positioning in the Central Part of Kumano-nada, Central Japan AU: * Fujimoto, H et al. EM AB: Kumano-nada, northeast of Kii Peninsula in the central part of Japan, is a seismogenic zone of the M-8 class Tonankai earthquakes that occurred repeatedly at an interval of about 100 years. The MEXT (Ministry of Education, Culture, Sports, Science and Technology, Japan) initiated a 5-year program in 2003 for seafloor observations in and around Kumano-nada. Nagoya and Tohoku Universities initiated experiments on GPS/A seafloor positioning to monitor crustal deformation in the subduction zone with a focus on investigation of the effect of sound velocity structure in the ocean on seafloor positioning (e.g., Tadokoro et al., this meeting). Tohoku group deployed five precision acoustic transponders (PXPs) jointly developed with Scripps Institution of Oceanography in the central part of Kumano-nada at depths of about 2,000m. The deployed PXPs A, B, C, and D form a diamond on the seafloor, and PXPs C, D, and E form a triangle. Although three typhoons were in the way of our 12-day cruise in August this year, we carried out GPS/A observation for several days. After an observation for locating the precise position of each PXP, we tried to keep the buoy near the center of the diamond or the triangle. The vessel held the position within 20-30m from the center, and the buoy_fs position was kept with 100m from the center. Kinematic GPS positioning is now under processing with GEONET data observed in Kii Peninsula. We also tried monitoring the sound velocity structure with 3 sets of inverted echo sounders (IESs) deployed near the PXPs C, D, and E. The IESs can monitor temporal and spatial variation in the sound velocity structure in the triangle array of PXPs. We plan to carry out the second GPS/A observation in November. The result is worthy of notice. Strange earthquakes of magnitude 6.9, 7.4, and 6.4 occurred on the nearest Nankai Trough axis on September 5- 7, 2004. Co-seismic crustal deformation observed by the GEONET was about 4 cm near the coast of Kii Peninsula. The seismogenic zone is in the list ocean drilling under the IODP (Integrated Ocean Drilling Program). DE
HR: 11:35h AN: OS42A-06 TI: Medusa-Isosampler: A modular, network-based observatory system for combined physical, chemical and microbiological monitoring, sampling and incubation of hydrothermal and cold seep fluids AU: * Schultz, A et al. EM: AB: The study of life in extreme environments provides an important context from which we can undertake the search for extraterrestrial life, and through which we can better understand biogeochemical feedback in terrestrial hydrothermal and cold seep systems. The Medusa-Isosampler project is aimed at fundamental research into understanding the potential for, and limits to, chemolithoautotrophic life, i.e. primary production without photosynthesis. One environment that might foster such life is associated with the high thermal and chemical gradient environment of hydrothermal vent structures. Another is associated with the lower thermal and chemical gradient environment of continental margin cold seeps. Under NERC, NASA and industrial support, we have designed a flexible instrumentation system, operating as networked, autonomous modules on a local area network, that will make possible simultaneous physical and chemical sampling and monitoring of hydrothermal and cold seep fluids, and the in situ and laboratory incubation of chemosynthetic microbes under high pressure, isobaric conditions. The system has been designed with long-term observatory operations in mind, and may be reconfigured dynamically as the requirements of the observatory installation change. The modular design will also accommodate new in situ chemical and biosensor technologies, provided by third parties. The system may be configured for seafloor use, and can be adapted to use in IODP boreholes. Our overall project goals are provide an instrumentation system capable of probing both high and low-gradient water-rock systems for chemolithoautotrophic biospheres, to identify the physical and chemical conditions that define these microhabitats and explore the details of the biogeochemical feedback loops that mediate these microhabitats, and to attempt to culture and identify chemolithoautotrophic microbial communities that might exist there. The Medusa-Isosampler system has been produced and is now undergoing initial deployments at sea. DE HR: 1340h AN: OS43B-0574 TI: Geology of Smooth Ridge: MARS-IODP Cabled Observatory Site AU: * Jordahl, K et al. EM AB: We document the geologic environment of Smooth Ridge, off shore Central California, where the deep-water node associated with the MARS (Monterey Accelerated Research Site) scientific research cable is to be deployed. The MARS cable will provide internet connections and electric power at a node in 890 m of water in support of scientific observatory development and experiments. IODP boreholes are proposed which will be connected to the MARS cable. The deeply incised channels of Monterey and Soquel Canyons flank Smooth Ridge to the SW and NE and the San Gregorio faults marks its NW and upslope boundary. However, the top of Smooth Ridge, as its name implies, only has subdued bathymetric features. These include a subtle downslope channel and one distinct slump scar. A patch of acoustically reflective seafloor on the west side of the ridge, over 5 km from the MARS site, is associated with the only known large-scale biological community on the crest of Smooth Ridge. A reflection seismic survey conducted in 2003 with a high-resolution electrical sparker source reveals the stratigraphy of the Smooth Ridge in unprecedented detail. In conjunction with previously collected widely-spaced multichannnel seismic data, observations and samples obtained using remotely-operated vehicle (ROV) dives, and piston cores, this new survey reveals the erosional and depositional history of Smooth Ridge. The continuity of seismic reflections indicates nearly undisturbed deposition occurred until at least the mid-Miocene. Since that time, and especially since the upper Pliocene, the record is marked by unconformities and infill due to shifting channels, large slumps and landslides, and sediment waves. Several crossing seismic lines provide a quasi-three-dimensional view of a distinct slump scar's structure, and reveal a history of multiple headwall failures. Other subsurface structures, including a much larger, and older, slump feature, have no bathymetric expression at all. 14C dated piston cores, and ROV observations and sampling reveal that sediments have not been accumulating in the Holocene. Exposure of Plio-Pleistocene strata on the surface of Smooth Ridge in water depths of less than 1 km indicates that this is an area of active seafloor erosion. Measurements of sulfate gradients in piston cores indicate sulfate depletion occurs between 3 to 5 m below the seafloor, which is unusually shallow for continental margin sediments and suggests enhanced biogeochemical/microbiological activity occurs in the subsurface under Smooth Ridge.