HYDROLOGIC FLUCTUATIONS AT PYRAMID , , AND THE , DURING THE MEDIEVAL CLIMATE ANOMALY

KENNETH D. ADAMS Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512 [email protected]

Lake levels in the western have fluctuated throughout the Holocene in response to changes in the hydrologic balance of their watersheds. The magnitudes of lake-level fluctuations are not only based on changes in climate but are also controlled by the hypsometries of individual basins, the presence and elevations of surrounding sills, and in the case of Walker Lake, through river diversions. This presentation focuses on the lake-level histories of Walker Lake, the Carson Sink, and through the Medieval Climate Anomaly (MCA; A.D. 900-1350), a time period characterized by severe and sustained droughts as well as periods wetter than modern. Although not as temporally precise as tree-ring studies, lake-level histories help discern the severity of droughts as well as the magnitude of wet periods. Despite differences in hydrology, hypsometry, and the effects of sills, there are commonalities in the three records. Walker Lake was low at A.D. 950 (<1,205 m), A.D. 1150 (<1,224 m), and at A.D. 1650 (<1,215 m). The first and last of these low periods, however, are associated with evidence for diversion of the into the Carson Sink. Walker Lake also reached relative highstands at about A.D. 1030 (~1,245m) and A.D. 1290 (~1,255 m), the latter level being several meters above the historic highstand (A.D. 1868; ~1,252 m). A large lake in the normally dry Carson Sink formed around A.D. 1100, reaching an elevation of ~1,204 m and surface area of ~3,000 km2. The timing of this lake was coincident with the possible addition of the Walker River, but this diversion by itself is not enough to account for the large Medieval lake. At Pyramid Lake, levels were below 1,174 m around A.D. 950 and again at A.D. 1300, but reached near the historic highstand level (~1,181 m; A.D. 1868) in the intervening time around A.D. 1100. The relatively low amplitude of lake-level fluctuations at Pyramid Lake through the MCA may be explained by a low sill (~1,177 m) that exports water to . Lake-level fluctuations in the western Great Basin are correlative with hydrologic records interpreted from tree rings and pollen and show regional and dramatic responses to short-lived climate changes during the MCA, both drier and wetter than present.

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EXAMINING GULF OF ALASKA MARINE PALEOCLIMATE AT SEASONAL TO DECADAL TIMESCALES

JASON A. ADDISON (1), BRUCE P. FINNEY (2), AND JOSEPH S. STONER (3) (1) U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 [email protected] (2) Department of Biological Sciences, Idaho State University, Pocatello, ID 83209-8007 [email protected] (3) College of Ocean and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331-8563 [email protected]

The Gulf of Alaska, located in the subarctic northeast Pacific Ocean, experiences dramatic climate variability over seasonal, annual, and decadal timescales. Environmental forcing mechanisms that affect physical parameters (e.g., precipitation and SST) can be expressed through indicators of marine ecosystem productivity due to a coupled positive feedback mechanism between the oceanic Alaska Gyre upwelling center and the atmospheric Aleutian Low pressure cell. This system is sensitive to low-latitude phenomena (ENSO), and due to the Pacific-North American teleconnection pathway, conditions in the Gulf of Alaska can influence distant regions throughout the Northern Hemisphere. However, it differs from most eastern boundary current settings (e.g., California) in that it is dominated by downwelling of surface waters throughout most of the year. Using these modern observations as a template for describing past fluctuations in paleoceanographic proxies, we present data from two marine sediment cores collected in temperate ice-free fjords along the Gulf of Alaska margin. These cores preserve evidence of past environmental variability at decadal to annual temporal resolutions for the past 4,000 (EW408- 44JC) to 8,000 (EW408-33JC) years. Computerized tomography scans show complex internal structures in these cores, including millimeter-scale laminations as well as high-density turbidite layers likely formed by past seismic or flood activity. Isotopic and geochemical analysis of the laminations indicate they are composed of cyclical couplets, consisting of a black, high-density terrigenous organic matter (OM)-rich band and a green, low-density marine OM-rich band. Based on a linear age-depth model interpolated between two well-preserved AMS 14C macrofossil samples, we find that preliminary lamination thickness measurements of the marine OM-rich bands between 3,900 to 3,300 cal yr B.P. indicate variability in the range of ENSO periodicities. These results suggest a linkage between tropical forcing and extratropical sedimentation that predates anthropogenic climate change.

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MULTI-PROXY EVIDENCE FOR MIDDLE AND LATE HOLOCENE FLUCTUATIONS IN CLIMATE REGIME IN THE NORTH-CENTRAL GREAT BASIN

LYSANNA ANDERSON, DAVE WAHL, SCOTT STARRATT, AND ELMIRA WAN U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 [email protected], [email protected], [email protected], [email protected]

The north-central Great Basin lies within the transition zone between the winter-dominated precipitation regime of the Pacific coastal states and the monsoon-driven summer precipitation regime of the Southwest. Paleoclimatic reconstruction of fluctuations in the dominance of these regimes across the region has proven difficult due to a paucity of paleoclimate records. Here we present a high-resolution middle and late Holocene charcoal record to augment existing pollen and diatom data from Favre Lake in the Ruby Mountains, Nevada (40° 26‘ 39.80‖ N, 115° 20‘ 49.5‖ W, 2,899 m a.s.l.). High concentrations of charcoal corresponding to diatom and pollen data indicate rising lake level are interpreted as reflective of sustained summer precipitation and a strengthened southwestern monsoon at around 5,400 cal yr B.P. These conditions may have supported an increase in fire intensity and frequency as a result of increased fuel buildup and frequent lightning. Lower and more variable charcoal concentrations after approximately 4,000 cal yr B.P., concurrent with relatively quiescent pollen and diatom assemblages, suggests the influence of a strengthening and increasingly variable ENSO, resulting in a shift to a more variable, lower intensity fire regime.

THE IMPACT OF LITTLE ICE AGE COOLING ON MOUNTAIN HEMLOCK (Tsuga mertensiana) DISTRIBUTION IN SOUTHCENTRAL, ALASKA

R. SCOTT ANDERSON (1), DARRELL S. KAUFMAN (1), CALEB SCHIFF (1), TOM DAIGLE (2), AND EDWARD BERG (3) (1) School of Earth Sciences and Environmental Sustainability, Northern Arizona University, Flagstaff, AZ 86011 [email protected], [email protected], [email protected] (2) GEI Consultants, 4601 DTC Boulevard, Suite 900, Denver, CO 80237 [email protected] (3) U.S. Fish and Wildlife Service, Kenai National Wildlife Refuge, P.O. Box 2139, Soldotna, AK 99669 (retired) [email protected]

The natural distribution of mountain hemlock (Tsuga mertensiana) in the northeast Pacific is in regions of cool to cold maritime climate, with cool winters and short summers. Presently, the species reaches its northern distribution in southcentral Alaska. We investigated the Holocene history of vegetation and climate change for two sites in and near the Kenai Mountains, south of Anchorage. Mica Lake is located at 100 m elevation on an island in Prince William Sound, near the northern limits of the tree, whereas Goat Lake is located at 550 m elevation, in the Kenai

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Mountains, at the upper local limit of mountain hemlock. From pollen analysis of these lake sediments, mountain hemlock became established at Mica Lake by at least 6,000 cal yr B.P. The tree became established at the higher elevation Goat Lake sometime after 3,000 years ago. Expansion at both sites was abruptly curtailed during the colder climate of the Little Ice Age, commencing at Goat Lake in the mid-17th century. The decline was more extensive at the Goat Lake site, where climatic conditions may have been severe enough to reduce or eliminate the mountain hemlock forest there. This is consistent with tree-ring evidence of major glacial advance (Wiles and Calkin 1993; 1994; Daigle and Kaufman, 2008; Wiles et al. 2009) at this time in the Kenai Mountains. Warmer conditions during the 20th century have reversed that trend.

Wiles, G.C. and Calkin, P.E., 1993, Neoglacial fluctuations and sedimentation of an iceberg-calving glacier resolved with tree rings (Kenai Fjords National Park, Alaska): Quaternary International, v. 18, p. 35–42. Wiles, G.C., and Calkin, P.E., 1994, Late Holocene, high-resolution glacial chronologies and climate, Kenai Mountains, Alaska: Geological Society of America Bulletin, v. 106, p. 281-303. Wiles, G.C., Barclay, D.J., Calkin, P.E., and Lowell, T.V., 2008, Century to Millennial-Scale Temperature Variations for the Last Two Thousand Years Inferred from Glacial Geologic Records of Southern Alaska: Global and Planetary Change, v. 57, doi:10.1016/j.gloplacha.2006.07.036 Daigle, T. A. and Kaufman, D. S., 2009, Holocene Climate inferred from glacier extent, lake sediment and tree rings at Goat Lake, Kenai Mountains, Alaska, USA: Journal of Quaternary Science, v. 24, p. 33–45.

RESPONSE OF DIATOM AND SILICOFLAGELLATE ASSEMBLAGES TO CLIMATE CHANGE IN THE SANTA BARBARA BASIN DURING THE PAST 178 YEARS AND THE RISE OF THE TOXIC DIATOM PSEUDO-NITZSCHIA AUSTRALIS

JOHN A. BARRON (1), DAVID BUKRY (1), AND DAVID B. FIELD (2) (1) Volcano Science Center, MS 910, U.S. Geological Survey, Menlo Park, CA 94025 [email protected], [email protected] (2) Department of Natural Sciences, Hawaii Pacific University, Kaneohe, HI 96744 [email protected]

Diatoms and silicoflagellate assemblages studied in two year-increments of varved samples in Santa Barbara Basin (SBB) box core 0806 spanning 1830 to 2007 suggest that unprecedented warming of surface waters began at about 1940, which is in agreement with CalCOFI SST data and changes in planktonic foraminferal assemblages. These earlier studies argued that increased stratification and deepening of the thermocline occurred during the latter half of the 20th Century within 50–100 km of the southern California coast in response to anthropogenically-forced global warming. Diatoms (Thalassionema nitzschioides = TN) and silicoflagellates (Distephanus speculum s.l. = DS) indicative of cooler waters and a shallow thermocline declined markedly in relative numbers in the SBB beginning at about 1940. Prior to that time, TN constituted on average ~30% of the Chaetoceros-free diatom sediment assemblage and DS on average ~36% of the silicoflagellate assemblage. Between 1940 and 1996 these relative abundances drop to ~20% (TN) and ~8% (DS). Cooling of surface waters coincident with the onset of negative PDO conditions in the North Pacific in 1998 brought about a return to pre-1940 values of these cool

4 water taxa (TN ~31%, DS ~25%). However, this recent regional cooling appears to have been accompanied by profound changes to surface water productivity events in the SBB. Pseudo- nitzschia australis, a diatom associated with domoic acid, a neurotoxin that causes shellfish poisoning and marine mammal deaths, appeared suddenly in the SBB sediment record in 1999 and increased significantly in numbers as a bloom-forming taxon (relatively to Chaetoceros spores) in 2003. Prior to 2003 diatom blooms represented in the SBB sediment record consisted predominantly of Chaetoceros spores and less commonly of Rhizosolenia spp. (Neocalyptrella robusta and R. setigera). Fecal pellets dominated by valves of P. australis, however, are abundant in both the 2003 and 2006 samples, coincident with recorded incidents of domoic acid increase and widespread shellfish poisoning in the SBB. According to published studies the first recorded large-scale toxigenic P. australis bloom in the SBB occurred in June 1998 as part of more widespread blooms and shellfish poisoning along the central California coast. Although high numbers (or blooms) of P. australis were reported in plankton studies off the Scripps Pier in La Jolla during the 1930‘s, 1967, and 1983, blooms of P. australis associated with toxic domoic acid levels were first reported in 1991 in Monterey Bay. Biologists have shown that Pseudo-nitzschia blooms correspond to lowered surface temperatures and increased that are typical of coastal upwelling events, but they have debated whether increased nutrients levels from river runoff have been a factor in the recent increase of these blooms. Laboratory studies have demonstrated that toxin production in some species of Pseudo-nitzschia may increase under silicic acid or phosphorous limitation. Whatever the cause, our 177 year-long diatom sediment record suggests that the recent increase of Pseudo- nitzschia blooms in the SBB has occurred at the expense of Chaetoceros and Rhizosolenia, the natural bloom-forming diatoms in the SBB.

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EXTENDING THE RECORD OF ABRUPT AND MILLENNIAL-SCALE CLIMATE AND OCEAN CHANGE THROUGH THE MID-PLEISTOCENE TRANSITION IN SANTA BARBARA BASIN, CALIFORNIA

RICHARD J. BEHL (1), SARA AFSHAR (1), JAMES P. KENNETT (2), CRAIG NICHOLSON (3), CHRISTOPHER C. SORLIEN (2), COURTNEY J. MARSHALL (1), TESSA M. HILL (3), SARAH M. WHITE (3), WALTER E. DEAN (4), AND JOHN A. BARRON (5) (1) Department of Geological Sciences, California State University, Long Beach, CA 90840 [email protected], [email protected], [email protected] (2) Department of Earth Science, University of California, Santa Barbara, CA 93106 [email protected], [email protected], [email protected] (3) Department of Geology, University of California, Davis, CA 95616 [email protected], [email protected] (4) U.S. Geological Survey, Federal Center, P.O. Box 25046, Denver, CO 80225 [email protected] (5) U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 [email protected]

Quaternary strata in the Santa Barbara basin, California, hold the potential to extend subdecadal- resolution paleoclimate records back through the Mid-Pleistocene Transition (>1 Ma). In support of proposed continuous coring by IODP, we conducted an integrated seismic acquisition and piston coring campaign in 2005 and 2008 where we acquired >40 2-11 m piston cores that provide ~2,000-9,000 year windows into past climate behavior. We identified and mapped distinctive seismic stratigraphic horizons across the basin to seafloor outcrop in pre-existing multichannel seismic (MCS) reflection data and in high-resolution MCS and towed chirp data acquired during our research cruises. Horizons and cores are dated by interpolation between ODP Site 893, a previously published 1-Ma horizon, and recovered tephra, biostratigraphic, and climatic datums. Sedimentation rates are high enough (70-130 cm/1,000 yr) to generate ultra- high-resolution data on the rate and character of climate and ocean change on human time scales. High-frequency climatic oscillations are recorded in many of these cores by variations in massive to laminated sedimentary fabric, oxygen and carbon isotopes, % total organic carbon, % carbonate, % biogenic silica, abundance of redox- and productivity-sensitive elements, or planktonic foraminiferal assemblages. In general, warm interstadials are represented by laminated, organic-rich sediment deposited under highly productive surface waters. Rapid, multi- decadal-scale climatic and oceanographic transitions occur during different climatic states, such as: MIS 3-like intermediate conditions, deglacial transitions, and glacial episodes, but not during otherwise fully interglacial conditions. These results indicate that the California margin has been sensitive to climatic forcing and experienced rapid climatic fluctuations since at least the Mid- Pleistocene Transition when predominance of 41,000 year climate cycles shifted to a 100,000 year climate cycle regime.

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SUBSTRATE AND CLIMATE INFLUENCES ON HOLOCENE FOREST DEVELOPMENT

CHRISTY E. BRILES (1,2), CATHY WHITLOCK (3), CARL N. SKINNER (4), AND JERRY MOHR (5) (1) School of Geography and Environmental Science, Monash University, Australia, VIC 3800 [email protected] (2) Palynology Laboratory, Texas A&M University, College Station, TX, 77803-4352 (3) Department of Earth Sciences, Montana State University, Bozeman, MT 59717 (4) U.S. Forest Service, Pacific Southwest Research Station, Redding, CA 96002 (5) College of Forestry, Oregon State University, Corvallis, OR 97331

The role of substrates in facilitating plant adjustments to climate change and influencing fire regimes in the past has received little attention. The Klamath Mountains of northern California consist of a mélange of rock types, including ultramafic types with high levels of toxic minerals and low levels of nutrients for plants that result in unique and diverse plant communities. To better understand the development of these diverse forests, pollen and macroscopic charcoal preserved in the sediments of eight cirque in different geological settings, were analyzed. The records were compared with independent climate records from the Klamath Mountain region to determine the relative role of geology and climate in shaping forests and fire regimes since the last glacial period (~15,000 yr B.P.). Comparison of sites suggests that ultramafic and non- ultramafic substrates supported distinctly different plant communities through the period. Plants on ultramafic substrates were less responsive to climate change than forests on non-ultramafic substrates, with the only major compositional change occurring at the glacial/interglacial transition (~11,500 yr B.P.). Plants on non-ultramafic substrates were more responsive to climate changes, and tracked climate by moving along elevational gradients. Fire regimes were similar until 4,000 yr B.P. on both substrate types. After 4,000 yr B.P., understory fuels on ultramafic substrates became sparse and fire activity decreased, while on non-ultramafic substrates forests became increasingly denser and fire activity increased. The combination of long-term persistence of plant communities on ultramafic sites and individualistic range adjustments of forest dominants on non-ultramafic sites help to explain the high levels of plant diversity and endemism in the Klamath Mountain region.

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PRELIMINARY RESULTS FROM A NEW HIGH-RESOLUTION ICE CORE FROM COMBATANT COL, MOUNT WADDINGTON, BRITISH COLUMBIA, CANADA

DOUGLAS H. CLARK (1), NICOLE BOWERMAN (1) ERIC J., STEIG (2), PETER NEFF (2), ERIN PETTIT (3), JOSEPH MCCONNELL (4), BELLA BERGERON (5), AND BRIAN MENOUNOS (6) (1) Geology Department, Western Washington University, Bellingham, WA 98225 [email protected] (2) Earth and Space Sciences, University of Washington, Seattle, WA 98025 (3) Department of Geology and Geophysics, University of Alaska, Fairbanks, AK 99775 (4) Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512 (5) ICDS, Madison, WI 53706 (6) University of Northern British Columbia, Prince George, BC, V2N 4Z9, Canada

In July, 2010, we recovered a 140 m ice core from Combatant Col, elevation 3,200 m, on the shoulder of Mount Waddington, British Columbia Coast Range, Canada, as part of a larger Canadian effort (WC2N) to investigate glacier-climate linkages across western Canada. The geographic setting and depth of ice (200+ m) at the site make it one of the more promising locations for collecting a relatively long ice-core record in North America outside of Alaska, and should help improve our understanding of long-term variability in the pattern and strength of precipitation across the region. Analysis of gridded GPS stakes during the summer provide constraints on glacier flow across the Col and will be used to develop a flow model to evaluate thinning and flow of ice at the core site. We also collected continuous weather data and shallow snow samples in the Col during the spring and summer in order to assess the evolution of snow over the course of the summer. Preliminary analyses of melt-layers, stable water isotope ratios, soot, and elemental concentrations in our cores show unambiguous seasonal stratigraphy in the ice, which will eventually provide a detailed age-depth model. The ice accumulation rate recorded in the ice core averages 2,500-3,500 kg/m3yr. Ice temperature and instrumental records indicate that mean annual temperature at the Col is -5°C. Summer surface melt produces local melt horizons that are consistent with the identification of summertime snow in the isotope, soot, and dust stratigraphy. Infrequent melt horizons also occur within the winter stratigraphy, but there is no evidence for significant migration of water across annual layers. Detailed analyses of the full core are in-process…more details at the meeting!

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PROJECTED 21ST CENTURY TRENDS IN HYDROCLIMATOLOGY OF THE TAHOE BASIN

ROBERT COATS (1), MARIZA COSTA-CABRAL (2), MICHAEL DETTINGER (3), JOHN RIVERSON (4), JOHN REUTER (1), GOLOKA SAHOO (1), GEOFFREY SCHLADOW (1), AND BRENT WOLFE (5) (1) University of California Tahoe Environmental Research Center, Davis, CA 95616 [email protected] (2) Hydrology Futures, Seattle, WA 98107 [email protected] (3) U.S. Geological Survey, Scirpps Institution of Oceanography, La Jolla, CA 92093 [email protected] (4) Tetra Tech Inc., Fairfax, VA 22201 [email protected] (5) Northwest Hydraulic Consultants, Inc., West Sacramento, CA 95691 [email protected]

Using historic lake temperature, air temperature and hydrologic data, we previously showed that 1) the average temperature and thermal stability of have increased since 1970, 2) basin air temperatures have increased since 1910, 3) date of snowmelt peak runoff is shifting, and 4) the snowfall:rainfall ratio is decreasing. Here we report on the results of efforts to model impacts of 21st century climate change on basin hydroclimatology and on Lake Tahoe itself. Meteorological data from the GFDL model for two emission scenarios were downscaled to a 12 km grid, bias-corrected, and used to drive a distributed hydrologic model. Output from this watershed model, along with the meteorological data, was then used as input to a 1-d hydrodynamic and water quality model of the lake (DLM-WQ, developed at U.C. Davis), and to calculate stream-flow statistics for the Upper (UTR) and trends in the Palmer Drought Severity Index (PDSI) for two sites representing wet and dry zones in the basin. The results indicate that 1) recent trends in basin climate and hydrology will continue, with a possible 5 oC increase in average annual air temperature by 2100, 2) precipitation will continue to shift from snow to rain, and annual amounts are projected to decline in the latter half of this century, 3) the timing of snowmelt and the hydrograph centroid are likely to shift toward earlier dates, 4) the magnitude of the estimated 100-year flood of the UTR is likely to vary greatly over the course of this century but eventually decline in response to warming and drying, 5) summer low-flow is projected to decline, 6) drought, as measured by the PDSI, is projected to increase, especially in the latter third of this century, and most strongly on the eastern (drier) side of the basin, 7) the lake may be expected to continue warming, and the resulting increasing thermal stability will likely limit deep mixing and deep ventilation, with impacts on dissolved oxygen, internal nutrient loading and water quality, and 8) the annual frequency of episodes of no-lake-outflow is likely to increase, especially toward the end of this century.

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POST-GLACIAL PLANT MIGRATIONS ARE SIMILAR TO HISTORIC AND ONGOING DISPERSAL AND SUCCESSION

KENNETH L. COLE (1, 2), KIRSTEN IRONSIDE (2), AND NEIL COBB (2) (1) Southwest Biological Science Center, Colorado Plateau Research Station, U.S. Geological Survey, P.O. Box 5614, Northern Arizona University, Flagstaff, AZ 86011 [email protected] (2) Merriam-Powell Center for Environmental Research, P.O. Box 4071, Northern Arizona University, Flagstaff, AZ 86011 [email protected], [email protected]

Modeling the effects of warming climates on plant species requires estimates of their future dispersal and proliferation into new areas. Estimates of likely spread into new areas of potential climate can be informed by: 1) paleo-migration and succession rates averaged over millennia following past sharp increases in temperature or past disturbances, 2) observations of historic shifts in response to 20th century warming climates and disturbances, and 3) recent vegetative dynamics observed through permanent plots or autecological studies. While good data for a single species rarely exists for all three time periods, information from two or more sources is usually in agreement. Because dispersal and proliferation for many species requires a chance sequence of favorable years, migration rates are best projected as averages over 50 years or more. Species vary greatly in their rates of potential migration. Early successional, disturbance-adapted herbs, grasses, and shrubs that are widely spread by wind or animals (ie. Encelia farinose, Erodium cicutarium), have averaged as much as 1000 m/yr in historic and recent data. Late successional trees of humid forests (ie. Picea mariana, Fagus grandifolia) seem to have migrated at rates as fast as 500 m/yr in the early postglacial despite requiring a century or more to succeed to dominance of historic old fields. This pattern suggests expansion outward from undetected satellite populations. But even at 500 m/yr, these species will only spread about 45 km by the time the atmosphere reaches a doubling of pre-industrial carbon dioxide. Late successional trees in semi-arid regions (ie. Pinus edulis, Juniperus monosperma) have migrated at 40 to 100 m/yr in postglacial and historic records. But the slowest rates of past and recent dispersal and proliferation belong to many late successional desert shrubs and succulents (ie. Coleogyne ramosissima, Larrea tridentata, Yucca brevifolia) which have, and are, only spreading at 10 m/yr or less.

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GEOCHEMICAL EVIDENCE FOR CHANGES IN SURFACE-WATER PRODUCTIVITY AND BOTTOM-WATER REDOX CONDITIONS DURING GLACIAL-INTERGLACIAL TRANSITIONS IN THE SANTA BARBARA BASIN

WALTER E. DEAN Geology and Climate Change Science Center, MS 980, U.S. Geological Survey, Federal Center, Denver CO 80225 [email protected]

Geochemical investigations of the transition between the last glacial interval (LGI) and the Holocene, and between stadial and interstadial intervals in Oxygen Isotope Stage 3 (OIS 3) in sediment cores from the Gulf of Alaska, the Alta and Baja California margins, and the Cariaco Basin show distinct differences. In general, interstadial and interglacial intervals are characterized by high surface-water productivity, oxygen-deficient bottom waters, and laminated sediments. Glacial and stadial intervals are characterized by low surface-water productivity, well-oxygenated bottom waters, and bioturbated sediments. Surface-water productivity is tracked by concentrations of organic carbon (OC) and cadmium (Cd). Bottom-water oxygen conditions are tracked by laminated vs. bioturbated sediments and concentrations of redox-sensitive trace elements, notably molybdenum (Mo), vanadium (V), nickel (Ni), uranium (U), and zinc (Zn). Results show that interglacial and interstadial intervals, such as the Bölling-Alleröd (B-A) warm interval, the Holocene, and interstadials within OIS 3, are characterized by laminated sediments and high concentrations of OC, Cd, and Mo. Glacial and stadial intervals, such as the LGI, the Younger Dryas (YD) cold interval, and stadials within OIS 3, are characterized by bioturbated sediments and low concentrations of OC, Cd, and Mo. Recent results from overlapping piston cores that collected sediments in the Santa Barbara Basin with largely undated ages going back to older glacial-interglacial transitions show similar sedimentological and geochemical characteristics as younger transitions, such as the B-A/YD, namely, laminated sediments containing high concentrations of OC, Cd, and Mo in interglacials and bioturbated sediments containing low concentrations of OC, Cd, and Mo in glacials. The best dated of these transitions is between OIS 16 and OIS 15, which contains the Lava Creek B ash dated at 639,000 years old. Oxygen isotope data on these cores obtained by Jim Kennett show that the transition from cold to warm can occur within decades. The interglacial intervals have millennial-scale interstadial- stadial cycles like those in OIS 3 on the California margin, and some of the stadials were as abrupt and as cold as the YD.

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EVALUATION OF VEGETATION DYNAMICS AND CLIMATIC OSCILLATIONS IN THE SACRAMENTO-SAN JOAQUIN DELTA OF CALIFORNIA DURING THE HOLOCENE

IRINA DELUSINA Department of Geology University of California, Davis, CA 95616 [email protected]

Pollen analysis of three cores of peat, deposited in the Sacramento-San Joaquin Delta of California and situated in different locations: Webb Tract levee, Browns Island, and Franks Tract wetland, was used to reconstruct the vegetation dynamics and climatic trends during the Holocene. A salinity index, calculated from pollen criteria, was also used. The pollen data indicate that between about 6,500 and 5,250 yr B.P., when peat first started to form, the area was undergoing a relatively cool period and that fresh or low salinity water existed in the delta area. This interval was followed by a recognizable shift in forest vegetation which indicates a warming trend that reached its peak at 5,000 yr B.P. The salinity of the water at this point was the highest for the studied time interval. A new, cooler interval occurred between 4,000 and 2,050 yr B.P., with low salinity. However, in the middle of this interval at about 2,900 years BP, there is a peak in salinity, which probably indicates a drought. After 2,050 yr B.P., cool and wet conditions, with moderate to high salinity, are established. After 1,250 yr B.P., conditions move toward wet and warm, and the salinity becomes high again. The study demonstrates how the process of peat formation and local environmental and hydrological conditions are influenced by general climatic trends. This study was conducted within the framework of Project REPEAT (2007-2009).

PROJECTED CLIMATE CHANGES AND FLOOD RISKS IN CALIFORNIA

MICHAEL D. DETTINGER (1), TAPASH DAS (2), DANIEL R. CAYAN (1), AND THERESA CARPENTER (2,3) (1) U.S. Geological Survey, Scripps Institution of Oceanography, La Jolla, CA 92093 [email protected] Scripps Institution of Oceanography, La Jolla, CA92093 (2) Hydrologic Research Center, 12780 High Bluff Drive, Suite 250 San Diego, CA 92130 Current projections of climate change are unanimous in calling for warming temperatures over the western States. Beyond this, they more-or-less unanimously yield trends towards less precipitation over the extreme southwest and more over the extreme northwest, but are indeterminate (as a whole) over the rest of the western States. These precipitation uncertainties reflect tradeoffs between two fairly simple and reliable global-scale heat-transfer processes that are energized directly by increasing greenhouse-gas concentrations in all climate models and thus are unlikely to be resolved any time soon. Despite uncertainties about overall, long-term

12 precipitation amounts over the western States, the direct influences of warming, together with projections of increased storm intensities that most climate models share, current projections of flood risk around the and in flash-flood zones of southern California suggest that risks may increase substantially in most California settings during the 21st century. Results from a) storm-typing analyses of multi-model ensembles of current climate-change projections, b) snow-fed hydrology simulations forced with multi-model ensembles of downscaled climate- change projections, and c) flash-flood frequencies simulated by geomorphically constrained runoff–generation models forced by downscaled, orographically enhanced precipitation projections, taken together suggest that—regardless of whether average precipitation in California increases or decreases—floods may be enhanced under the 21st century climate.

SIMULATING MOUNTAIN CLIMATES: CHALLENGES AND APPROACHES

PHILIP B. DUFFY Climate Central, Inc. Palo Alto, CA 94028 and Woods Institute on the Environment, Stanford University, Stanford, CA 94305 [email protected]

The mountainous regions near the Pacific are among the most vulnerable to climate change. And impacts of climate change in these regions can have widespread effects, for example increased water scarcity. At the same time, our ability to simulate past climate and project future climate is generally worse in mountainous regions than elsewhere. I will discuss challenges inherent in understanding and simulating climate in mountainous regions, as well as approaches commonly used to address them. The talk should be useful to those not specifically interested in mountain climates because, as I will point out, difficulties simulating mountain climates are generally more extreme versions of those encountered when working elsewhere.

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COMPARISON OF VARVE CHRONOLOGY AND 14C DATES AT HIGH RESOLUTION: REEVALUATING THE AGE OF THE SANTA BARBARA BASIN LATE HOLOCENE PALEOCLIMATE SEQUENCE

LARIANNA DUNN (1), INGRID L. HENDY (1), AND ARNDT SCHIMMELMANN (2) (1) Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109 [email protected], [email protected] (1) Department of Geological Sciences, Indiana University, Bloomington, IN 47405 [email protected]

One of the most significant recent shifts in climate was the transition between the Medieval Warm Period (MWP) and the Little Ice Age. This transition occurred in Santa Barbara Basin (SBB) around A.D. 1200 based on radiocarbon (14C) dating, while the varve-count chronology suggests A.D. 1400. This 200 year difference is extremely important for accurately comparing the SBB paleoclimate record to records both in the southwest region and globally. There are three possible factors that may contribute to the discrepancy between SBB varve-count and 14C chronologies: 1) erosion of varves below turbidites (i.e. ‗missing varves‘), 2) Changes in surface water 14C reservoir ages (e.g., due to changes in upwelling), and 3) varve counting errors when sedimentation failed to express distinct seasonal differences (undercounting of varves), or when very strong seasonal changes in sedimentation were interpreted as annual varves (overcounting of varves). Previous studies lacked sufficient temporal resolution to determine the cause of the discrepancy between these independent dating techniques. Laminated sediments from SBB have previously been dated using consecutive varve-counting covering the past ~ 2,000 years. Here we provide the first high-resolution 14C study in the SBB. Kasten core SPR0901-06-KC (34°16.914N, 120°02.419W) was sampled at ~5 cm intervals over the upper 2.6 meters, and 53 14C ages for mixed planktonic foraminfera (particularly Globigerina bulloides and Neogloboquadrina pachyderma) were generated at Lawrence Livermore National Laboratory‘s Center for Accelerator Mass Spectrometry. After removing a local 14C reservoir effect of 633 years (presumed to have been constant), 14C dates were then calibrated with IntCal09 using the calibration program CALIB v. 6.0. Comparison of the calibrated 14C datum to the varve chronology reveals an increasing offset from the varve chronology back to A.D. 440, with the loss of ~15 years in every 100 varves counted. The results demonstrated a linear difference in age with an r2 of 0.78, indicating a consistent net undercounting in varve years relative to 14C years.

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INITIAL RESULTS FROM A NEW LAKE ELSINORE SEDIMENT CORE REVEAL EVIDENCE FOR HYDROLOGIC CHANGE DURING THE LATE GLACIAL-HOLOCENE TRANSITION

JOANNA M. FANTOZZI (1), MATTHEW E. KIRBY (1), STEVEN P. LUND (2), AND CHRISTINE A. HINER (1) (1) Department of Geological Sciences, California State University, Fullerton, CA 92834 [email protected] (2) Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089 [email protected]

While there are several well-developed records of marine climate from Southern California that span the late Glacial-Holocene transition, there are currently no high-resolution terrestrial counterparts. In June 2010, a 20 meter sediment core covering 10-30 meters below the sediment- water interface was extracted from the depocenter of Lake Elsinore, California – the largest natural, permanent lake in the region. Here, we present the initial results of a multi-proxy study on the section of this sediment core that spans the late Glacial-Holocene transition (18.5-10 m below the sediment-water line [bswl]). Initial results reveal three distinct sediment units. Unit I (15-10 m bswl) is composed of a homogeneous, often mottled (bioturbated?), gray mud with high and moderately variable magnetic susceptibility values (avg = 1.20 ± 0.29 x 10-7 m3/kg), low organic matter content (6.50 ± 0.83%), and highly variable carbonate content (12.21 ± 4.89%). Unit II (17-15m bswl) is a transitional unit that begins as a gray mud similar to that of Unit I and transitions into a massive to laminated brown mud with low and variable magnetic susceptibility values (0.88 ± 0.38 x 10-7 m3/kg), increasing organic matter content (11.52 ± 2.19%), and highly variable carbonate content (10.84 ± 4.75%). Unit III (18-17.5m bswl) is characterized by a massive to laminated brown mud with very low and stable magnetic susceptibility values (0.87 ± 0.19 x 10-7 m3/kg), declining organic matter content (11.21 ± 2.02%), and low to negligible carbonate content (5.0 ± 0.87%). Together, these data indicate a significant change in Lake Elsinore‘s depositional environment that is likely related to hydrologic change (i.e. average lake level) during the late Glacial-Holocene transition – a change that has not previously been documented in southern California.

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A HISTORICAL RECONSTRUCTION OF AN ALEXANDRIUM CATENELLA CYST RECORD FROM SEQUIM BAY, WASHINGTON AND ITS RELATION TO CLIMATE VARIABILITY

KIRSTEN FEIFEL AND RITA HORNER Department of Oceanography, University of Washington, Seattle, WA 98195 [email protected]

Detection of paralytic shellfish toxins (PSTs) due to blooms of the harmful alga Alexandrium catenella has increased in Puget Sound, Washington since the 1970s. This increase has been linked to large-scale climate variability such as the Pacific Decadal Oscillation (PDO), and local variables such as air temperature, stream flow, and sea surface temperature. However, existing records of A. catenella bloom dynamics, based on toxins in shellfish, are relatively short, dating only to 1957, and therefore it is difficult to statistically assess the influence of short-term, stochastic environmental variability versus long-term, multi-decadal, trends in relation to climatology. Hence, we examined the relationship between historical climate variability and profiles of A. catenella cysts in a sediment core from Sequim Bay, Washington, in order to better determine the influence of climate on A. catenella populations. The cyst record allowed us to extend the A. catenella history in Sequim Bay to 1878 and to statistically evaluate the historical relationship between the cyst record and available environmental parameters. There is no statistically significant relationship between the cyst record and PDO or stream flow, but there is a positive, significant relationship between local air temperature and sea surface temperature. The disconnect between historical, large-scale North Pacific sea surface variability, as measured by the PDO index, may highlight the importance of local climate variability and the possible influence of recent warming in the Puget Sound due to anthropogenic climate change as driving factors of the A. catenella population increase in the 1970s.

MULTIPLE MODES OF VARIABILITY IN THE NORTHEAST PACIFIC: A HISTORICAL PERSPECTIVE

DAVID B. FIELD Hawaii Pacific University, Kaneohe, HI 96744-5297 [email protected]

Recent flooding in southern California has been occurring in the La Niña winter of 2010-2011, which is an atypical pattern of La Niña conditions; high rainfall is more typically associated with El Niño conditions or a positive phase of the Pacific Decadal Oscillation (PDO). Much attention has been given to the PDO as a dominant source of decadal-scale variability in North Pacific SST patterns, which, in turn, are associated with variations in precipitation off western North America. However, the PDO has the trend in SSTs removed. Moreover, paleo-records indicate that the PDO may not have been as predominant a form of variability prior to the 20th century, and thus may not be a dominant mode in the future either. I present records of planktonic

16 foraminifera from two-year intervals obtained from annually laminated sediments of the Santa Barbara Basin to illustrate the importance of both the warming trend in the 20th century as well as multiple modes of variability prior to the 20th century. The 20th century warming in the eastern Pacific is characterized by two distinct pulses, which match the global temperature anomalies: one from 1925 and another around 1977. Prior to the 20th century, foraminifera assemblages indicate anomalously cool or warm periods could be accompanied by a shallow or deep thermocline. These different oceanographic conditions arise not just from expansions and contractions of the Aleutian Low pressure system (as seen in association with the PDO) but from shifts in the position of high and low pressure cells, as modified by the jet stream.

HYDROLOGIC RESPONSE TO CLIMATE CHANGE AND HABITAT RESILIENCY ILLUSTRATED USING FINE-SCALE WATERSHED MODELING

ALAN L. FLINT (1), LORRAINE E. FLINT (1), ELISABETH MICHELI (2), STUART B. WEISS (3), AND MORGAN KENNEDY (2) (1) U.S. Geological Survey, Placer Hall, 6000 J Street, Sacramento, CA 95819 [email protected] (2) Pepperwood Preserve, Santa Rosa, CA 95404 (3) Creekside Center for Earth Observation, 27 Bishop Lane, Menlo Park, CA 94025

In the face of rapid climate change predictions of landscape change are of great interest to land and resource managers that endeavor to develop long term plans with the goal of maintaining biodiversity and ecosystem services, and adapting to extreme changes in the landscape. Climate models, primarily exhibited as increases in air temperature, often support habitat modeling that predicts large scale migrations, either northward or up in elevation, or extinctions of sensitive species. Current studies rely most dominantly on large spatial scale projections (> 10 km) of changes in precipitation and air temperature that neglect the subtleties of topographic shading, geomorphic features of the landscape and fine-scale differences in soil properties. Fine-scale modeling has been tested using climate parameters with improved correlations of vegetation distribution with temperature. For this study, future climate projections were downscaled to 270- m and applied to a hydrologic model to calculate future changes in recharge, runoff, and climatic water deficit for basins draining into the northern San Francisco Bay. We generated future watershed hydrology scenarios using a coupled climate-hydrology Basin Characterization Model (BCM) that predicts water cycle fractions of runoff, recharge, evapotranspiration, and streamflow. Primary BCM inputs consist of topography, soil composition and depth, parent geology, and spatially-distributed values (measured or estimated) for air temperature and precipitation. Model calibration is achieved by using historic precipitation and temperature as BCM inputs and comparing model estimates of discharge with streamflow measured at gages. Using estimates of future precipitation and air temperature derived from Global Circulation Models (GCMs) (two models, GFDL and PCM, for two

17 emissions scenarios, A2 and B1) as model input, we describe observed variability over the last century and estimate watershed-scale hydrologic response to potential climate change scenarios for approximately the next century. Results indicate large hydrologic variability among scenarios, increased water deficits, and local scale resiliency of habitats to climate change.

HIGH RESOLUTION CLIMATE PROJECTIONS AND THEIR USE IN IMPACTS AND ADAPTATION ASSESSMENTS IN CALIFORNIA

GUIDO FRANCO California Energy Commission, 1516 Ninth Street, Sacramento, CA 95814 [email protected]

In 2003 the California Energy Commission‘s Public Interest Energy Research (PIER) Program adopted a strategy to produce climate projections for California at adequate spatial and temporal resolutions for both research and long-term planning. The long-term strategy also included the goal of generating ―probabilistic‖ climate projections for California (Franco et al., 2003). Since then, all the steps included in that strategy have been implemented such as: 1) development of climate scenarios for two California Assessments, 2) development and testing of a new statistical downscaling technique designed to simulate daily events, 3) development of a technique to translate multiple projections into ―probabilistic‖ distributions, 4) enhancement of three dynamic regional climate models and simulations of historical conditions, 5) development of a protocol to inter-compare dynamic and statistical downscaling techniques, 6) inter-comparison of dynamic and statistical regional climate models for California, and, 7) estimation of the probability of future global climate forcing using expert elicitation techniques. This presentation will briefly discuss the lessons learned from scientific and resource management perspectives and will present preliminary ―probabilistic‖ climate projections for California.

Franco, G., Wilkinson, R., Sanstad, A., Wilson, M., and Vine, E., 2003, PIEREA Climate Change Research, Development and Demonstration Plan. California Energy Commission. Publication Number: 500-03- 025FS.

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ABOVE-TREELINE LINANTHUS PUNGENS SHRUB-CHRONOLOGIES ON THE EASTERN SIERRA NEVADA CREST, MONO COUNTY, CALIFORNIA CONTAIN RECORDS OF PRECIPITATION AND TEMPERATURE

REBECCA S. FRANKLIN (1), MALCOLM K. HUGHES (1) AND CONSTANCE I. MILLAR (2) (1) Laboratory of Tree-Ring Research, University of Arizona, AZ 85721 [email protected] (2) U.S. Forest Service, Pacific Southwest Research Station, Albany, CA 94710-0011 [email protected]

Herb- or shrub-chronology, a technique adapted from dendrochronology, is the study of the annual growth rings in roots of certain perennial dicotyledonous plants. The presence of annual growth increments in high-elevation plants is significant as it highlights the importance of herbchronology for climatic, ecological, and geomorphologic applications in alpine and extra- arboreal regions. For an above-treeline site on the eastern crest of the Sierra Nevada range at the Barney Lake rock glacier (BLRG) (37.56466N, 118.96554W), I will discuss the dendrochronological potential of several species colonizing this rock glacier with a focus on the ring-width chronology and climate response of the species Linanthus pungens (Torr.) J.M. Porter & L.A. Johnson. Commonly known as Granite Gilia, this species is a low-branching shrub (10- 20 cm high) native to California and is found throughout the arid mountainous western U.S. and British Columbia at elevations ranging from 1,500–3,700 m. The BLRG chronology is 112 years in length with signal strength of EPS > 0.85 from 1952 through 2008. In an exploration of the BLRG chronology, I will present an analysis of correlations with PRISM climate data, SNOTEL April snow water equivalent, Palmer Drought Severity Index, Multivariate ENSO Index , Pacific Decadal Oscillation and local climate station temperature and precipitation records and the potential for climate reconstructions using L. pungens.

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THE PALEOCLIMATE POTENTIAL AND ENIGMA OF LAGUNA MINUCUA, OAXACA, MEXICO

MICHELLE GOMAN (1), CHARLOTTE PEARSON (2), WILLIAM GUERRA (1), ARTHUR JOYCE (3), AND DARREN DALE (4) (1) Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, NY 14853 [email protected] (2) Cornell Tree Ring Laboratory, Cornell University, Ithaca, NY 14853 [email protected] (3) Department of Anthropology, University of Colorado at Boulder, CO 80309 [email protected] (4) Cornell High Energy Synchrotron Source, Cornell University, Ithaca, NY 14853 [email protected]

Despite over 50 years of paleoecological and paleoclimatological research the climate history of much of Mexico remains poorly understood. To some extent this is caused by the difficulty of deconvolving the long history of human impacts to the natural environment from natural climate- driven forcings. Further, research has tended to focus on two key regions within Mexico (central Mexico and the southern Maya lowland region) in part driven by the availability of suitable sedimentary archives but also because of these regions well known and popular cultural history (i.e. the Aztecs and Maya, respectively). However, this focus has resulted in an incomplete understanding of paleoclimate changes, particularly in tropical western Mexico, the purported location of Zea mays domestication. In order to address this data gap we undertook an extensive field research campaign in the summer of 2008 in the lowlands and highlands of Oaxaca and Guerrero, Mexico with the aim of locating suitable archives for paleoenvironmental reconstructions. The field season was highly successful with nine lacustrine and wetland sites cored and two locations sampled for dendrochronological analysis. We present preliminary data from Laguna Minucua, located within the Sierra Madre del Sur at an elevation of ~2,500 m. Laguna Minucua is a small (~0.25 ha), shallow (< 30 cm deep at time of coring) pond with no apparent inlets or outlets; it appears to have formed from a carbonate sink hole but this is not verified. The site is surrounded on the northwest side by a calcareous ridge, which has stands of Pinus oaxacana and Quercus spp. growing on the slope. We retrieved two sediment cores from the site (3.5 m and 5.6 m long). Surprisingly, given the shallow water depth, the cores are well- laminated and possibly varved. Here we present a preliminary analysis of the observed laminae using a combination of high resolution synchrotron and scanning XRF data, magnetic susceptibility data, and micro- morphological characterization from thin sections. We discuss the possible implications of this for the chronology for the site.

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MONSOON PRECIPITATION RECONSTRUCTED FROM TREE RINGS IN THE SOUTHWESTERN

DANIEL GRIFFIN (1,2), CONNIE A. WOODHOUSE (1,2), DAVID M. MEKO (1), RAMZI TOUCHAN (1), STEVEN W. LEAVITT (1), CHRISTOPHER L. CASTRO (3), CARLOS M. CARILLO (3), AND BRITTANY CIANCARELLI (3) (1) Laboratory of Tree-Ring Research, University of Arizona, Tucson, AZ 85721 [email protected] (2) School of Geography and Development, University of Arizona, Tucson, AZ 85721 (3) Department of Atmospheric Sciences, University of Arizona, Tucson, AZ 85721

The North American monsoon system, emanating northward from Mexico during the warm season, delivers up to 60% of the annual precipitation to the southwestern United States (SWUS). The SWUS, however, is predominately on the fringe of monsoon influence, and warm- season precipitation across the region is highly variable on annual to decadal time scales. Interannual monsoon moisture variability, a key factor influencing summer water demand and ecosystems in the SWUS, has been the focus of extensive research in recent decades. While tree rings have revealed much about the long-term hydroclimatic history of this region‘s westerly- driven winter climate regime, no dendroclimatic studies have systematically targeted the monsoon across the SWUS. Our group is developing the region‘s first network of monsoon- sensitive chronologies, focusing on variability in the latewood (summer growth) of precisely dated tree rings from some 50 sites. This study describes the relationship between warm-season precipitation and tree-growth from sites across the SWUS and presents the first tree-ring reconstruction of monsoon (July-August) precipitation for southeastern Arizona and southwestern New Mexico. The 350-year reconstruction, which explains over 55% of the variance in the instrumental record, reveals severe and persistent monsoon droughts, including several that coincided with sustained dryness in the cool season. None of the sustained cool season droughts of this period appear to have been offset by persistently wet monsoons, and the widely discussed tendency for cool season dry (wet) extrema to be followed by wet (dry) monsoons seems to have been most consistent during the late 20th century. http://monsoon.ltrr.arizona.edu

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THE TIMING OF MULTI-DECADAL DROUGHT SIGNALS RECORDED IN THE ELEMENTAL COMPOSITION OF SANTA BARBARA BASIN SEDIMENTS

INGRID L. HENDY (1), LARIANNA DUNN (1), AND ARNDT SCHIMMELMANN (2) (1) Department of Geological Sciences, University of Michigan, MI 48109 [email protected] (2) Department of Geological Sciences, Indiana University, Bloomington, IN 47405 [email protected]

Santa Barbara Basin (SBB) is renowned for high quality paleoclimate records due to an extremely high sedimentation rate, high biological productivity, and suboxic bottom waters that preserve annually laminated, anoxic sequences. Here we extend an annually resolved high- resolution paleoclimate record back 1,800 years. XRF analysis of Si, S, Ti, and Ca at 200 µm intervals on the upper 65 cm of box core SPR0901-4BC and overlapping sections of kasten core SPR0901-03KC (275 cm) were conducted using an ITRAX core scanner, equipped with a Cr- tube. Core sections were spliced together between instantaneous sedimentation events (turbidites and flood deposits) to provide a continuous sedimentary record with a resolution of four to eight counts per year. High resolution 14C dating on planktonic foraminifera was completed on SPR0901-06KC (255 cm) at 5 cm intervals. Two preliminary age models were generated by removing instantaneous sedimentation events from the sequence and generating ages using a linear interpolation between (1) sedimentary events dated by previous varve chronology studies, and (2) the same events dated by the newly calibrated 14C datum. Ti counts relate to the relative contribution of lithogenic to biogenic components in SBB sediments. Low Ti counts indicate little riverine detrital input during drought conditions, while high counts suggest increased river discharge with high associated lithogenic components. During the 20th century high Ti count years correlate with El Niño and positive PDO years. Multi-decadal low Ti count intervals exist between A.D. 1110-1180, 1290-1320, 1530-1550, and 1740-1760 based on varve chronology suggest earlier drought conditions far more severe that occurring during California‘s written history. The multi-decadal droughts may have been widespread as these intervals correlate with droughts suggested by the Cariaco Basin, Venezuela runoff record. Yet based on the 14C derived chronology, these mega droughts shift to A.D. 790-810, 990-1080, 1195-1230, 1470-1505, and 1700-1720 and subsequently occur during wet intervals recorded in Cariaco Basin. Resolution of dating issues is vital if we are to understand the climate mechanisms, which produced these multi-decadal droughts.

22

LINKS BETWEEN SOUTHERN CALIFORNIA CURRENT VARIABILITY AND NORTHERN HEMISPHERE TEMPERATURES: THE PAST MILLENNIUM

JUAN CARLOS HERGUERA (1), P. GRAHAM MORTYN, (2,3), AND MIQUEL ÀNGEL MARTÍNEZ-BOTÍ (2) (1) División de Oceanología, Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE), México [email protected] (2) Institute of Environmental Science and Technology (ICTA), Universitat Autonoma de Barcelona, Spain (3) Geography Department, Universitat Autonoma de Barcelona, Spain

Instrumental sea surface temperature (SST) variability of the California Current System (CCS) for the last century is thought to be modulated by interannual to interdecadal oscillations superimposed on a background warming trend. However, our understanding of the amplitude of multidecadal SST changes over the last millennium, its persistence through time, and drivers before the instrumental record are still not well characterized. Here we present an absolutely- dated and decadally-resolved planktonic foraminiferal Mg/Ca reconstruction of summer SSTs in the southern dynamic boundary of the CCS for the past millennium to explore the links between this eastern boundary current, Northern Hemisphere (NH) temperatures end equatorial ocean dynamics. Summer SST variability is inversely linked with continental NH temperatures on multidecadal timescales and directly linked with the Equatorial Pacific ocean dynamics until the 19th-20th century, when continental NH temperatures become the dominant driver. This inverse pattern is best explained by the seasonal ocean-land temperature contrast during the spring to early summer warming process that enhances the ocean-continent pressure gradient and drives the persistent alongshore winds, and upwelling processes on multidecadal timescales. However, this pattern seems to reverse during the last third of the 20th century with a trend towards warmer SSTs, probably associated with a cloud cover reduction over the northeast Pacific, that leads to increased SSTs, a weaker subtropical high and a lessening of the trade winds as a positive feedback for further warming in response to increased atmospheric greenhouse gases.

23

OCCURRENCE OF SEVERE DROUGHT CONDITIONS IN COASTAL SOUTHERN CALIFORNIA DURING THE MEDIEVAL CLIMATE ANOMALY INFERRED FROM POLLEN DEPOSITED IN THE SANTA BARBARA BASIN SINCE ~ A.D. 800

HEUSSER, LINDA (1), BARRON, JOHN (2), AND HENDY, INGRID (3) (1) Lamont Doherty Earth Observatory, Palisades, NY 10964 [email protected] (2) U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 (3) Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109

Pollen analyses of the upper 3.95 m from ODP Site 893B from the Santa Barbara Basin (SBB) provide proxy evidence for major climate-driven changes in the vegetation onshore between ~ A.D. 800 and A.D. 1800. Dominance of plant communities adapted to drought conditions of hot, dry southern California summers (chamise chaparral and coastal sage scrub) corresponds with increases in the duration and severity of western U.S. drought identified by Stine (1994) and Cook et al. (2004) and with MacDonald and Case's (2005) interpretation of more negative Pacific Decadal Oscillation variability during the Medieval Climate Anomaly. Extreme drought conditions occur during a period of multi-decadal drought recorded by the high resolution-Ti record between A.D. 1000-1100 (14C corrected) (Hendy et al., 2011). The shift toward wetter, cooler conditions at ~ A.D. 1400 (an increase in more mesic oak and pine communities such as scrub oak and pine woodland chaparral, or more open grass woodland) coincides with temperature changes in the waters offshore. Correlative diatom and planktonic foraminifera deposited in the SBB during the Little Ice Age suggest increased seasonal sea surface temperature changes with cooler winters and warmer springs, respectively (Barron et al., 2010; Fisler and Hendy, 2008). The distinctive signature of the 19th and 20th century pollen assemblages reflects agricultural and residential impact on the natural vegetation of southern coastal California following European settlement.

Barron, J., Bukry, D., and D. Field, 2010, Santa Barbara Basin diatom and silicoflagellate response to global climate anomalies during the past 2200 years: Quaternary International, v. 215, p 34-44. Cook, E., Woodhouse, C., Eakin, M., Meko, D.M., Stahle, D.W., 2004, Long-term aridity changes in the western United States Science v. 306 n. 5698, p. 1015-1018. Fisler, J. and Hendy, I., 2008, California Current System response to late Holocene climate cooling in southern California: Geophysical Research Letters, v. 35, L09702. Hendy, I.L., Dunn, L., and Schimmelmann, A., 2011, The timing of multi-decadal drought signals recorded in the elemental composition of Santa Barbara Basin sediments: Abstracts of the 25th Pacific Climate Workshop, Asilomar, California, March 6-9, 2011. MacDonald, G. M. and Case, R.A., 2005, Variations in the Pacific Decadal Oscillation over the past millennium: Geophysical Research Letters, v. 32, n. 8, L08703. Stine, S., 1994, Extreme and persistent drought in California and Patagonia during mediaeval time: Nature, v. 369, n. 6481, p. 546-549.

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TWENTY-FIVE YEARS OF CO-EVOLUTION OF DENDROCLIMATOLOGY AND PACLIM

MALCOLM K. HUGHES Laboratory of Tree-Ring Research, University of Arizona, Tucson, AZ 85721 [email protected]

Referring to the late 1970s, Hughes et al. (2011) recently wrote that ―From today’s viewpoint, it is difficult to imagine how little was known about interannual- to century-scale variability in the climate system at that time, with published sketches of the spectrum of climate variability exhibiting little or no power between bidecadal and millennial frequencies‖. The first of what became the PACLIM multidisciplinary workshops was held at Asilomar just a few years later in 1984. The scientific programs of these workshops track a rapid evolution of understanding of the climate system on time-scales of relevance to society, the landscape, the oceans and ecological systems. The pioneering dendroclimatological work of Harold Fritts, dealt with geographic and time domains of interest to PACLIM. In the past 25 years, Fritts‘ contributions have been built upon by his students and colleagues. Not only has this approach been expanded to cover much of the globe, and enhanced to provide more process-based understanding of climate and its impacts, but it has provided an example of the multidisciplinary approach so characteristic of PACLIM. Drought, streamflow, fire climatology, circulation indices, and extreme climatic events have all figured in the contributions dendroclimatology has made to understanding of the climate system and its interactions with society, the biosphere, and the geosphere over the Pacific-Western Americas domain.

Hughes, M.K., Swetnam, T.S., and Diaz, H.F., editors, 2011, Dendroclimatology: Progress and Prospects: Springer, Dordrecht, xii + 365 pp.

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ENVIRONMENTAL AND BIOTIC CHANGE AT THE NANODIAMOND DATUM: THE YOUNGER DRYAS BOUNDARY IMPACT HYPOTHESIS

JAMES KENNETT (1), ALLEN WEST (2), DOUGLAS KENNETT (3), CHARLES KINZIE (4), AND WENDY WOLBACH (5) (1) Department of Earth Science, University of California Santa Barbara, Santa Barbara, CA 93106 [email protected] (2) Geosciences Consulting, Dewey, AZ 86327 [email protected] (3) Department of Anthropology, University of Oregon, Eugene, OR 97403 [email protected] (4) Department of Chemistry, De Paul University, Chicago, IL 60614 [email protected] (5) Department of Chemistry, De Paul University, Chicago, IL 60614 [email protected]

The onset of the Younger Dryas (YD) cool episode is marked by a diverse assemblage of abundant nanodiamonds at the YD boundary layer (YDB) that forms a widely correlated datum across North America and Western Europe. This evidence is consistent with a high-temperature cosmic impact event at 12,900 +/- 100 cal yr B.P. The YDB is marked by a complex and broad array of abrupt and potentially linked changes in atmospheric and oceanic circulation, ice sheets, North American continental hydrosphere, the biosphere including extinctions, and human adaptations, and possible population reductions and reorganization. The cause of the YD is controversial and currently debated, yet any causal hypothesis needs to account for these changes. We will review and challenge recent contributions that have questioned evidence for an impact event at the YD onset. Younger Dryas cooling is enigmatic in its timing, magnitude and abruptness at near-peak insolation. Such cooling episodes with YD characteristics and timing in earlier terminations appear more affiliated with terminal glacial episodes. Younger Dryas onset is also outstanding because of close collective association with major, abrupt continental-scale ecological reorganization, megafaunal extinction, and human adaptive and population change. Climate change at the YD onset was remarkably abrupt (~one year) suggesting atmospheric climate response preceded oceanic change. A major North American hydrographic reorganization, apparently associated with destabilization of ice sheet margins, was marked by abrupt switch in flow from the south to northern oceans. This outburst flooding may have coincided with major drainage of Lake Agassiz. Associated outburst floods affected widely separated areas of the Arctic. The most pronounced oceanic effect was change in meridional overturning. Major responses recorded in temperate environments include widespread evidence of biomass burning, changes in sediment deposition including a layer with diverse exotic materials interpreted to be of cosmic impact origin, broad continental vegetation disruption, abrupt megafaunal extinction, and genetic bottlenecks reflecting population declines and/or animal migrations. The North American human record suggests abrupt disappearance of the Clovis

26 culture, a human genetic bottleneck, and a widespread archeological gap during the early centuries of the YD cooling episode.

EFFECTS OF BASELINE CONDITIONS ON THE SIMULATED HYDROLOGIC RESPONSE TO PROJECTED CLIMATE CHANGE: A CASE STUDY OF THE ALMANOR CATCHMENT, NORTH FORK OF THE FEATHER RIVER BASIN, CALIFORNIA

KATHRYN M. KOCZOT (1), STEVEN L. MARKSTROM (2), AND LAUREN E. HAY (2) (1) U.S. Geological Survey CAWSC, 4165 Spruance Road, Suite 200, San Diego, CA 92101 [email protected] (2) U.S. Geological Survey, Box 25046, Federal Center Mail Stop 412, Denver, CO 80225 [email protected], [email protected]

The hydrologic response to changes in 21st century climate was evaluated for the Almanor Catchment in the North Fork of the Feather River basin, California. Changes in temperature and precipitation projected from five general circulation models using one late 20th century and three 21st century emission scenarios were downscaled to three different baseline conditions. Baseline conditions are periods of measured temperature and precipitation selected from 20th century data, and used to represent historical climate. The three baseline conditions were selected to represent a drier-than-average climate cycle, an average-to-wetter climate cycle, and a wetter-than-average climate cycle. The hydrologic effects of the climate projections are simulated by using the Precipitation Runoff Modeling System (PRMS), which is a watershed hydrology model. Hydrologic components (i.e. snowpack formation and melt, evapotranspiration, and streamflow) from the PRMS simulations are compared. Results indicate that, when the study area displays climate with highly variable cycles, the selection of a specific period used to represent baseline conditions has a substantial effect on the simulation of some, but not all, hydrologic variables. This effect seems to be amplified in hydrologic variables that accumulate over time, such as soil-moisture content. Furthermore, the uncertainty associated with baseline conditions should be evaluated by using a range of different baseline conditions representative of the climate of the basin of interest. This is particularly important for studies in basins with highly variable climate, such as the Almanor Catchment.

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FIRE HISTORY IN THE EASTERN UINTA MOUNTAINS, UTAH, USA

REBECCA KOLL (1,2) AND MITCHELL J. POWER (1,2) (1) Department of Geography, University of Utah, Salt Lake City, UT, 84112 (2) Utah Museum of Natural History, University of Utah, Salt Lake City, UT 84112 [email protected]

A 2.1-meter-long sediment core from the eastern Uinta Mountains provides a 10,600-year-long record of vegetation change and fire history. Few studies have explored the long-term vegetation and disturbance history from the Uinta Mountains. As a result, significant gaps remain in understanding historical processes affecting biodiversity from this region. The charcoal-based fire history reconstruction from Reader Fen (3,205m a.s.l.) suggests fires occurred on average every 400 years during the last 10,600 years. A previously published pollen-based vegetation history (Carrara et al., 1985) near Reader Fen suggests subalpine forest species (e.g. Picea engelmannii and Pinus contorta) arrived in the Uinta Mountains soon after glaciers retreated (7,500 cal yr B.P.). From ~5,500 to 2,500 cal yr B.P., arboreal species increased in high- elevation forests and fires occurred. During the last 500 years, and particularly during the last century, fire frequency has increased. This long-term perspective suggests fire activity has increased in high-elevation forests during the historical period (Agee and Skinner, 2005; Long, 2003). Understanding the frequency and magnitude of past disturbances is necessary for understanding the catalyst of vegetation change and for making informed management decisions on present and future ecological change in the Uinta Mountains.

Agee, J.K. and Skinner, C.N., 2005, Basic principles of forest fuel reduction treatments: Forest Ecology and Management, v. 211, p. 83–96. Carrara, P.E., Short, S.K., and Shroba, R.R., 1985, A pollen study of Holocene peat and lake sediments, Leidy Peak area, Uinta Mountains, Utah: Brigham Young University Geology Studies, v. 32, n. 1, p. 1-7. Long, J.N., 2003, Diversity, complexity and interactions: an overview of Rocky Mountain forest ecosystems: Tree Physiology, v. 23, p. 1091–1099.

EL NIÑO IN THE HOLOCENE AND LAST GLACIAL MAXIMUM

ATHANASIOS KOUTAVAS Department of Engineering Science and Physics, College of Staten Island, City University of New York, Staten Island, NY 10314 [email protected]

The El Niño-Southern Oscillation (ENSO) is a major influence in the global climate and a source of uncertainty in future regional climate responses including prominently those over western North America. To better understand ENSO sensitivity, modes of variability, and the strength and stability of its teleconnections, it is important to reconstruct past ENSO activity at its source region – the equatorial Pacific. Efforts toward paleo-ENSO reconstructions have had limited success because they have relied mostly on fossil corals which are short-lived and discontinuous,

28 or land archives (tree-rings and lake sediments) which assume stable atmospheric teleconnections. In this work I have taken an alternative approach, which utilizes individual planktonic foraminifera from marine sediments accumulating in the Galapagos region, a hotspot of ENSO activity. The oxygen isotope composition of foraminiferal calcite records the anomalous warming and freshening that occurs during El Niño (opposite for La Niña). Because each foraminifer lives for only a few weeks to a month, its chemistry provides a short snapshot of sea surface conditions that resolves the ENSO timescale despite the slower accumulation rate of the sediment within which it is embedded. Analysis of multiple co-occurring individuals can reveal the total variance within a sample, reflecting the seasonal and interannual ENSO variability. We have conducted over 2,000 individual analyses in the Holocene and LGM sections of a core from the Galapagos and resolved highly significant changes in variance. Minimum variance is observed in the middle Holocene approximately 6,500-4,000 years ago, while maximum variance occurred in the LGM. While these variance estimates incorporate both ENSO and seasonal effects, additional constraints suggest they are primarily driven by ENSO modulation. The middle Holocene ENSO suppression evident in these data matches the timing of western U.S. droughts inferred from lake records, suggesting ENSO has had a profound influence on North American climate over the Holocene.

HAWAIIAN FOREST BIRDS: THE PAST, PRESENT AND FUTURE STATUS OF AN ENDANGERED AVIFAUNA

DENNIS A. LAPOINTE (1), CARTER T. ATKINSON (1), PAUL C. BANKO (1), RICHARD J. CAMP (2), P. MARCOS GORRESEN (2) , JAMES D. JACOBI (1), THANE K. PRATT (1), AND MICHAEL D. SAMUEL (3) (1) U.S. Geological Survey, Pacific Island Ecosystems Research Center, Kilauea Field Station, Hawai’i Volcanoes National Park, HI 96718 [email protected] (2) Hawai‘i Cooperative Studies Unit, Pacific Aquaculture and Coastal Resources Center, University of Hawai‘i at Hilo, HI 96720 [email protected] (3) U.S. Geological Survey, Wisconsin Cooperative Wildlife Research Unit, University of Wisconsin, Madison, WI 53706 [email protected]

The Hawaiian forest birds are among the most endangered avifauna of the world. Entire bird groups have disappeared from the Hawaiian Islands, and of the more than fifty, historically- known species of Hawaiian honeycreeper, only 17 remain. Due to the extreme geographical isolation, few birds colonized the Hawaiian Islands but, released from direct competition, predation, and disease, these founders flourished and evolved amid the heterogeneous geography of the archipelago. This process of colonization and speciation is best characterized by the honeycreepers; the largest radiation of endemic forest birds in the Hawaiian Islands, or for that matter, birds on any oceanic archipelago. But this remarkable avifauna has suffered great loses

29 since the arrival of humankind. Extinctions and population declines began with the inadvertent introduction of predatory rats, overharvesting of flightless species and destruction of lowland forest by Polynesians. Habitat destruction and degradation and predation accelerated with the arrival of Westerners and their domestic animals and pests, leading to more extinction and increasing rates of population decline. The introduction of mosquito vectors, avian disease pathogens, and vertebrate and invertebrate competitors led to the displacement of many native bird species from lowland forests. Today, on protected lands, there are apparently stable populations of only a handful of the remaining species. However, habitat degradation, predation, disease and food web disruption by invasive hymenoptera continue to impact critical populations. Additionally, climate change will likely increase habitat degradation, disease, and food web disruption further restricting remaining populations to smaller and more dispersed refuges. Although the fate of Hawaiian forest birds appears bleak, there are reasons for hope. Some populations of Hawaii amakihi have evolved tolerance to avian malaria and are burgeoning in the once quieted lowland forests. Captive breeding and release programs have prevented the extinction of at least two species and consortiums of managed conservation lands increase the extent and suitability of remaining forest bird habitat.

SEVERITY AND FORCING OF DROUGHT IN THE NORTHWESTERN GREAT PLAINS SINCE 1365

SUZAN L. LAPP, JESSICA R. VANSTONE, JEANNINE-MARIE ST. JACQUES, AND DAVID J. SAUCHYN Prairie Adaptation Research Collaborative (PARC), University of Regina, Regina, SK, S4S 7H9, Canada [email protected], [email protected], [email protected], [email protected]

The 20th century hydroclimatology of the Pacific Northwest has been linked to natural recurring large-scale climate patterns such as the Pacific Decadal Oscillation (PDO) and the El Niño- Southern Oscillation (ENSO). Tree-ring proxy data analyses carried out in western North America have proven valuable to quantify natural climate variation over centuries to millennia. A reconstruction of PDSI over the western Canadian Prairie region provides a record of drought for the past 800 years. We are able to mine these long reconstructions for much more information about the frequency/duration of positive (wet) and negative (dry) moisture anomalies during difference phases of PDO and ENSO, as reconstructed from tree-ring datasets. As well, by comparing these moisture reconstructions to temperature reconstructions of the region we are able to identify warm/cool drought periods. These reconstructions reflect the seasonal changes in moisture relative to both the instrumental and future time periods. The large- scale climate patterns will also be derived from multiple GCMs, for the 21st century, as tools to better understand projections of future moisture variability. Decision makers responsible for

30 adaptation to climate variability and change may use our forecasts of persistent departures from mean hydroclimate to plan for future climate conditions.

THE LAST 2,000 YEARS OF CALIFORNIA CLIMATE VARIABILITY: COMPARISON OF SEDIMENT RECORDS OF LATE HOLOCENE PALEOCLIMATE FROM THE WESTERN UNITED STATES STEVE LUND (1), LARRY BENSON (2), MATTHEW KIRBY (3), WILL BERELSON (1), SARAH FEAKINS (1), AND FRANK CORSETTI (1) (1) Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089 [email protected] (2) Department of Anthropology, University of Colorado, Boulder, CO 80309 (3) Department of Geology, California State University, Fullerton, CA 92834

We have recovered late Holocene paleoclimate records from eight sediment sequences in the California region, which form a transect from northwestern Nevada to Baja California: Pyramid Lake (Nevada), Walker Lake (Nevada), (California), Owens Lake (California), Santa Cruz coast (California), Zaca Lake (California), Lake Elsinore (California), Pescadero Basin (Mexico). The cores are all 14C dated and correlated with paleomagnetic field secular variation. Work is just beginning in some records, while other records are fully published. In this study, our goal is to compare evidence for multi-decadal to millennial-scale climate/environmental variability among the records and look for regional patterns of variability. Different records have different degrees of resolution or response, so distinctive patterns in some records are not expected to be visible in all records. We see clear evidence for centennial- to millennial-scale variability in these records, but it is not yet clear that we can assign a specific regional pattern to that variability. Similarly, we see evidence for ENSO to multi-decadal variability in several of the records, but it is not clear that the same multi-decadal pattern can be correlated across the region.

31

A SEASON SPECIFIC PALEOCLIMATE RECORD FROM A NORTHERN WASATCH MOUNTAINS SPELEOTHEM AND LINKAGES TO THE PACIFIC

ZACHARY LUNDEEN (1), ANDREA BRUNELLE (1), STEPHEN J. BURNS (2), YEMANE ASMEROM (3), AND VICTOR POLYAK (3) (1) Department of Geography, University of Utah, Salt Lake City, UT 84112 [email protected] (2) Department of Geosciences, University of Massachusetts Amherst, Amherst, MA, 01003 (3) Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM, 87131

Pacific Ocean influences on spatiotemporal precipitation variability in the American West are well documented, especially with respect to El-Niño-Southern Oscillation and the Pacific Decadal Oscillation. However, the effects of these large-scale teleconnection patterns on precipitation distribution are most pronounced in the winter, with less noticeable effects the rest of the year. Linking terrestrial paleoclimate records to past ENSO or PDO variability in the Pacific Ocean is hampered by the lack of season-specific paleoclimate proxies. Rather than being able to isolate winter season precipitation amounts, most paleoclimate records are instead more representative of mean annual effective moisture conditions. We present an isotope-based paleoclimate record from a speleothem in the Bear River Range, the northernmost extension of the Wasatch Mountains. Due to the location‘s characteristics, we interpret the speleothem stable isotope data as a record of winter precipitation amount and temperature variability. The record shows a generalized pattern of wet early Holocene conditions, a dry middle Holocene, and a wet neoglacial period. Significant droughts occurred from ~6,200-7,200 cal yr B.P., and at ~4,200 cal yr B.P. Temperatures were generally cool in the early Holocene and show a consistent warming trend through the middle Holocene. Anthropogenic warming is evident in the record, with modern oxygen isotope delta values more than two standard deviations above the Holocene mean.

DECICPHERING THE ROLE OF CLIMATE- VERSUS HUMAN-CAUSED DISTURBANCE DURING THE 19TH AND 20TH CENTURY: A COMPARISON OF ISOTOPIC, STOICHOIMETRIC, POLLEN, AND PLANT MACROFOSSILS FROM TWO LAKES IN THE WESTERN U.S.

ANTHONY N. MACHARIA AND (1), AND MITCHELL J. POWER (1,2) (1) Department of Geography, University of Utah, Salt Lake City, UT 84112 [email protected] (2) Utah Museum of Natural History, University of Utah, Salt Lake City, UT 84112

Historical paleoenvironmental interpretations of biotic and abiotic processes in lake sediment records are complicated by recent anthropogenic activities. To disentangle the role of climate versus people in 19th and 20th century lake sediment records we use sedimentary elemental and

32 stable isotopes, plant macrofossils, charcoal and pollen records. Ecological effects of climatic- versus anthropogenic disturbances are compared for two lakes in the Western U.S. (Utah Lake (48 10‘N, 114 21‘W) and Foy Lake (40° 13.82'N, 111° 47.12'W). Trends in bulk sediment δ15N values were most effective in distinguishing the relative role of climate versus anthropogenic activity as the dominant mechanism of ecosystem disturbance. In the organic-rich Foy Lake sediments, influxes of allochthonous materials generated significant shifts in δ13C, and C:N ratios while the δ15N values and charcoal records show the most dramatic shifts in Utah Lake. The disturbance from late 19th century sawmill operations and widespread forest fires were responsible for the observed shifts in Foy Lake, while agricultural activities, urban development, and 20th century variations in Utah Lake hydrology help explain trends in Utah lake sediments. Changes in pollen and macrofossil composition in Utah Lake reinforce these interpretations. Observed differences in sedimentary δ18O at both lakes reflect the contrasting climatological and hydrological settings of the two basins. These results demonstrate that the influx of nutrients and particulate organic matter from natural and anthropogenic sources produce dramatic changes in sedimentary geochemistry. Using multiple tools for interpreting past environmental change in lake systems can help decipher natural versus anthropogenic drivers.

PACIFIC OCEAN SEA SURFACE TEMPERATURE INFLUENCE ON SOUTHWESTERN UNITED STATES CLIMATE DURING THE PAST MILLENNIUM: NEW EVIDENCE FROM A WELL-CALIBRATED, HIGH-RESOLUTION STALAGMITE δ18O RECORD FROM THE SIERRA NEVADA, CALIFORNIA

STARYL E. MCCABE-GLYNN (1), KATHLEEN R. JOHNSON(1), MAX B. BERKELHAMMER (2), ASHISH SINHA (3), H. CHENG (4,5), AND LARRY EDWARDS (5) (1) Department of Earth System Science, University of California, Irvine, CA 92696 [email protected] (2) Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309 (3) Earth Sciences Department, California State University, Dominguez Hills, Carson, CA 90747 (4) Institute of Global Environmental Change, Xi’an Jiaotong Univ., Xi’an, Shaanxi, China (5) Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455

Proxy data from tree-rings and lake sediments indicate that past droughts in the southwestern U.S. were of greater magnitude and longer duration than the 20th century droughts. To determine the natural range and mechanisms of past hydrologic variability in the southwestern U.S., we are using speleothems from Crystal Cave in Sequoia National Park, California, on the southwestern flank of the Sierra Nevada (36.58°N; 118.56°W; 1,540 m), to develop a well-dated, high resolution (near-annually resolved) oxygen isotope record of past climate. We have conducted an instrumental calibration study using a 10.5 cm stalagmite, CRC-3, that formed over the past 1,000 years until it was collected in 2008. Initial results suggest that speleothem, and hence

33 rainfall, δ18O at this site is not correlated to temperature or precipitation amount, but is strongly influenced by the moisture source and rainout history of landfalling storms, in agreement with a recent isotope-enabled GCM study (isoGSM). A comparison between the instrumental portion of the CRC-3 timeseries reveals a strong inverse relationship with the PDO index, indicating that speleothem δ18O at this site is highly sensitive to Pacific Ocean SST patterns. The CRC-3 timeseries (A.D. 957 to 2008) exhibits a prominent decadal to multidecadal scale variability which we infer to reflect the influence of changing SST's on the precipitation patterns in the southwestern U.S. Here we present a comparison of this record with existing proxy records of SST, drought, and precipitation variability over the last millennium.

LATEST QUATERNARY PALEOCEANOGRAPHIC CHANGES ON THE FARALLON ESCARPMENT OFF CENTRAL CALIFORNIA

MARY MCGANN U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 [email protected]

A suite of climate proxy data (benthic and planktic foraminiferal assemblage census counts, Benthic Foraminiferal Oxygen Index (BFOI) values, and total carbon, organic carbon, and calcium carbonate analyses of sediments) coupled with previously published data (stable isotopes and Ca/Cd) from off central California on the Farallon Escarpment (1,605 m; 37°13.4'N,

123°14.6'W; core F-8-90-G21) are used to investigate paleoceanographic changes from the last glacial maximum to the late Holocene. A Q-mode cluster analysis divided the planktic fauna into Pleistocene and Holocene clusters whereas the benthic fauna was separated into three clusters, one Pleistocene and two Holocene. Stable oxygen isotope values show an increase in water temperature of ~1°C from the late glacial to late Holocene, which is supported by a change in faunal composition of the planktic assemblage suggesting warmer surface waters. A general trend of decreasing dissolved oxygen concentration from the Pleistocene (well oxygenated; 3.0-

6.0+ ml/L O2) to the Holocene (poorly oxygenated; 1.5-3.0 ml/L O2), reflecting decreased ventilation, is evident in the BFOI data and agrees with the Cd/Ca data except for an increase between ~13,000-11,000 cal yr B.P. when ventilation briefly improved. Middle Holocene cooling, suggested in other central and northern California margin studies, is not evident in F-8- 90-G21, which compares more favorably with studies from southern California and British Columbia. Total carbon and organic carbon values are highest in the Bølling-Allerød, early Holocene, and late Holocene. Similarly, calcium carbonate values are high in the Bølling- Allerød and peak in the early Holocene, but decrease significantly in the latest middle and late Holocene which coincides with a depauparate planktic fauna in the upper 60 cm (~7,000-0 cal yr B.P.) of the core and poor preservation of the benthic fauna at and above 40 cm (~3,000-0 cal yr B.P.). The depauparate faunas are thought to be biologically, not taphonomically, controlled because the abundance of planktic foraminifera remains low today in waters off central California. Decoupling of the planktic and benthic faunal response to changing climatic

34 conditions is evident, with the surface-dwelling assemblage often leading the bottom-dwelling assemblage by several millenia.

A 9,700-YEAR MULTI-PROXY RECONSTRUCTION OF HYDROLOGIC AND VEGETATION HISTORY FROM A LOW-ELEVATION SPRING-FED MEADOW, EAST CENRAL NEVADA

SCOTT MENSING (1) AND SAXON E. SHARPE (2) Department of Geography, University of Nevada, Reno, NV 89503 [email protected] Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512 [email protected]

A ~9,700-year-old 7-m-long sediment core obtained from Stonehouse spring in the Spring Valley in east-central Nevada (White Pine County) contains a unique record because 1) springs are not commonly cored for paleoenvironmental data so this project shows that springs can produce viable long-term hydrologic histories, 2) little is known about past biologic and hydrologic variability in the Spring Valley area so these cores provide the first paleoenvironmental record at this locality, 3) sediments date to the early Holocene, a relatively long and high resolution record, 4) springs are often biodiversity hot spots and the sole habitat for many spring-dwelling species, and 5) springs are closely associated with physiochemical characteristics of groundwater systems which are usually fed by climate. Thus, spring sediments can provide long-term biologic, hydrologic, and climatic information. This project uses pollen, mollusks, diatoms, and chironomids from the core (elevation 1,914 m) to evaluate past hydrology and climate. Evaluating the hydrologic and climate history of this area is important because 40,000 to 60,000 acre-feet of groundwater are planned to be pumped from Spring Valley by the Southern Nevada Water Authority, the owner of Stonehouse spring. Preliminary results from pollen show low pollen accumulation rates, supporting the suggestion of high sedimentation rates associated with generally high meadow productivity. Preliminary results from mollusks recovered from the core show time intervals with no mollusks, intervals with mixed aquatic and terrestrial mollusks, and intervals with spring-obligate mollusks. Periods with mollusks are associated with clay rich sediments and low percent organics, suggesting standing water. Future work includes additional radiocarbon dates, analysis of ostracodes and diatoms, and the integration of these paleohydrologic and paleoclimatic proxy data with other records to determine both the long-term hydrologic variability of Stonehouse and how well hydrology and climate are linked at this location.

35

THERMAL AND HYDROLOGIC ATTRIBUTES OF ROCK GLACIERS AND RELATED LANDFORMS IN THE SIERRA NEVADA, CALIFORNIA: FIVE YEARS OF iBUTTON RECORDS

CONSTANCE I. MILLAR, ROBERT D. WESTFALL, AND DIANE L. DELANY Pacific Southwest Research Station, U.S. Forest Service, Albany, CA 94710 [email protected], [email protected], [email protected]

Over the past five years we have deployed iButton thermochrons in and around environments of rock glaciers and related landforms (boulder streams and talus) of the eastern Sierra Nevada. Our goal has been to explore thermal regimes and hydrologic capacity of these little-known features. Whereas we have reported individual results at previous PACLIM Workshops, and while we await results from an ongoing intensive study, we take this opportunity to synthesize consistent trends that have emerged from the iButton records. We propose ―active‖ Sierran features to have attributes that include:1) persistent water in outlet streams through the year (frozen in winter), 2) mean outlet stream temperatures < 0°C (annual) and < 2°C (summer), 3) mean annual temperature of air in the rock matrix 1 m below the surface -1°C, 4) matrix summer temperatures highly attenuated relative to surface temperatures, 5) lapse rates mostly negative in summer within the matrix environments, and no obvious trend in winter when features are snow-covered, and 6) floristically diverse wetland communities or persistent water bodies at the forefront. From these trends, we hypothesize active landforms to contain embedded ice that is the source of persistent and cold outlet streams, and that supports adjacent wetlands or lakes. Karst ponds that develop on some rock glaciers reveal stratified ice (to ~10 m depth), suggesting sedimentary (glaciogenic) origin. Whether all ice in active features forms this way or whether some features, especially active boulder streams and taluses, develop ice lenses from permafrost origin is unknown. We propose ―inactive‖ features to have attributes that include: 1) outlet streams often missing or dry by late summer or fall, especially in drought years, 2) mean outlet stream temperatures 1-3°C (annual) and 4-8°C (summer), 3) mean annual temperature of air in the rock matrix 5-7°C, 4) attenuated matrix summer temperatures relative to surface, 5) strongly positive summer lapse rates within features in the matrix, and negative lapse rates in winter, the latter appearing more correlated with persistent snowpack at the base than elevation within the feature, and 6) forefields of drier meadow communities and shrublands and lakes rarely present. Internal thermal conditions of inactive and active rock matrices have complex seasonal patterns relative to surface temperatures. For instance during early spring, temperature profiles suggest that melting snow refreezes in the matrix, coating rocks below the surface with layers of ice, a situation we have observed in the field to persist even after surface snowpack has melted. Although inactive features do not appear to contain persistent ice, they remain reliable sources of groundwater and support unique vegetation communities and important wildlife habitat even during droughts. Active versus inactive landforms are not readily distinguished by systematic differences in environmental context (e.g. aspect), elevation (although active features tend to be higher), form and appearance (active and inactive features can both have oversteepened fronts), or capacity to support soil and vegetation. Intensive study of groundwater and/or permafrost

36 processes of these landforms will be important for understanding their hydrologic contributions as temperatures increase in the future and other water sources disappear.

A NEW LOOK AT THE CHRONOLOGY FOR A CLASSIC PLEISTOCENE LAKE: LAKE BONNEVILLE’S PROVO SHORELINE

DAVID M. MILLER (1), CHARLES G. OVIATT (2), AND JOHN P. MCGEEHIN (3) (1) U.S. Geological Survey, 345 Middlefield Road, MS 973, Menlo Park, CA 94025 [email protected] (2) Department of Geology, 108 Thompson Hall, Kansas State University, Manhattan, KS 66506 [email protected] (3) U.S. Geological Survey, 12201 Sunrise Valley Drive, MS 926A, Reston, VA 20192 [email protected]

Lake Bonneville is one of the most studied and best dated Pleistocene lakes in the world and its radiocarbon chronology serves as a benchmark for new chronometric methods. However, many uncertainties remain, including issues with the dated materials, their relation to lacustrine deposits, and interpreting stratigraphy and geomorphology of the deposits. The Provo shoreline, generally considered to have been occupied during a period of overflow following the 17,500 cal yr B.P. Bonneville flood until ~15,000 cal yr B.P., is the biggest geomorphic feature of Lake Bonneville; its size has been attributed by many workers to stability of the overflow threshold. During the course of studying the Provo shoreline to better determine the hydrologic maximum for Lake Bonneville, we discovered that the relative ages of widely preserved beaches separated vertically by ~3 m are the opposite of what has been widely assumed. The highest beach is the youngest based on stratigraphy and geomorphology, and the Provo beach gravels thus represent beach sedimentation during several lake-level rises. These relations could be explained by rises in the overflow threshold by alluvial fan or landslide deposition. New radiocarbon dates from gastropods collected within the beach gravels young upward and are among the oldest obtained for the Provo deposits. The ages suggest that all or most of the beach deposits we studied (three locations, three sets of deposits) formed early in the Provo time period, ~18,000 to 17,000 cal yr B.P. In contrast, most previous ages were obtained from shells in offshore sand deposits, and are 17 to 15,000 cal yr B.P. The new data raise questions about the timing of the Bonneville flood, the duration of Provo overflow, whether beach deposition shifted to offshore sand deposition after 17,000 cal yr B.P., and whether Lake Bonneville radiocarbon ages on gastropods are reliable. We conclude that significant uncertainties exist in the gastropod-dated chronology for Lake Bonneville, and urge caution in interpreting radiocarbon ages at their reported uncertainties, as well as in interpreting origins of landforms.

37

HOLOCENE VEGETATION AND DISTURBANCE RECONSTRUCTIONS FROM THE TRANSITION REGION OF THE GREAT BASIN AND COLORADO PLATEAU IN UTAH, USA

JESSE L. MORRIS (1), ANDREA R. BRUNELLE (1) AND MITCHELL J. POWER (1,2) (1) Department of Geography, University of Utah, Salt Lake City, UT 84112 [email protected], [email protected] (2) Utah Museum of Natural History, University of Utah, Salt Lake City, UT 84112 [email protected]

Wildfire and bark beetles are important disturbance agents in western North America. This research provides new insights into the ecology of these disturbances in the subalpine spruce/fir forests of central and southern Utah. Two lacustrine records retrieved from the Wasatch and Aquarius Plateaus suggest that epidemic spruce beetle (Dendroctonus rufipennis) disturbances have pronounced impacts on vegetation composition and thusly pollen accumulation, and recur at least at multicentennial intervals. The mean return interval (MRI) for stand-replacing fire events is similarly long, ranging between 300-500 years. We report that wildfire does not follow spruce beetle outbreaks, which supports dendroecological data conducted elsewhere in the western U.S. Our records also demonstrate that forest composition is important in disturbance ecology, particularly when considered over longer timescales. As the subalpine landscape transitioned from the relatively cool late Pleistocene to the relatively warm middle Holocene, these ecosystems shifted from spruce parkland to closed-canopy spruce/fir forests. Coincident with greater stand density and fuel/host continuity, wildfire and spruce beetle disturbance events became more frequent. The 20th century portion of these records reflect a general absence of fire and the most significant spruce beetle outbreaks observed over the Holocene. The intensity of these recent outbreaks are likely associated with anthropogenic modifications to the landscape during the historic period, including logging, grazing, and fire suppression.

NORTHEAST PACIFIC AND WESTERN NORTH AMERICAN CLIMATE VARIATIONS DURING 2009-2011

TOM MURPHREE Department of Meteorology, Naval Postgraduate School, Monterey, CA 93943 [email protected]

The northeast Pacific Ocean and western North America region experienced several major intraseasonal to interannual climate variations during 2009-2011, including El Niño, La Niña, Madden-Julian Oscillation, and Arctic Oscillation events and/or their associated impacts. These variations had significant impacts on atmospheric and oceanic temperatures and circulations, and precipitation in the region. These impacts appear to have been, in part, a result of constructive interference between the different variations. There is also some preliminary evidence that

38 global warming may have affected the magnitude of these impacts. The basic patterns and processes associated with these variations and their impacts on the northeast Pacific Ocean and western North American region will be reviewed, with a focus on extreme temperature and precipitation events in western North America during 2009-2011.

VERTICAL MOVEMENT OF LOW-OXYGEN WATERS IN SANTA BARBARA BASIN FOR THE PAST 15,000 YEARS

SARAH MYHRE (1), TESSA M. HILL (1), JAMES P. KENNETT (2), KENICHI OHKUSHI (3), AND RICHARD BEHL (4) (1) Bodega Marine Laboratory, P.O. Box 247, Bodega Bay, CA 94923 [email protected] (2) Department of Earth Science, 1006 Webb Hall – MC 9630, University of California, Santa Barbara, CA 93106-9630 (3) Ibaraki University 2-1-1, Bunkyo, Mito, 310-8512, Japan (4) Department of Geological Sciences, California State University Long Beach, 1250 Bellflower Boulevard, 1250 Long Beach, CA 90840-3902

Here we constrain the upper vertical boundary of the California Margin Oxygen Minimum Zone (OMZ) through the past 15,000 years. The depth and intensity of the California Margin OMZ is responsive to events of rapid warming, however the spatial extent and underlying mechanism for the synchrony is not clear. We construct a depth transect within Santa Barbara Basin (34 15‘N, 119 45‘W) using a core from 418 m water depth (MV0811-15JC), and previously investigated cores from 481 m (MD02-2503) and 570 m (MD02-2504a) water depths. The transect spans 152 vertical meters and ends 32 m above basin‘s western sill depth. Isotope stratigraphy and radiocarbon dating (planktonic foraminiferal calcite) were used to generate an age model. Foraminiferal and invertebrate assemblages and sediment laminations reconstruct bottom water oxygenation. Oxygen isotopic values at all three sites record similar surface water 18O shifts over the deglaciation (1.5‰ magnitude; based upon planktonic foraminifera Globigerina bulloides) and a smaller but analogous 18O shift is seen in benthic records (0.5‰ magnitude; based on benthic foraminifera Uvigernia peregrina). The Bølling-Allerød lamination record indicates strong hypoxia below 480 m; however laminations are not preserved at 418 m. In contrast, benthic foraminiferal assemblages show similar responses (albeit more muted in the shallowest site) to low-oxygen concentrations during the Bølling-Allerød, with species Nonionella stella, Bolivina tumida, and Bulimina tenuata dominating at all three sites. Invertebrate fauna diversity and abundance exhibit taxa-specific synchronicity with respect to climate transition intervals, indicating cross-community responses to fluctuating oxygen concentrations. At core MV0811-15JC, 32 m above the western basin sill, the proxies in the Bølling-Allerød indicate marginally low oxygen conditions; strong enough to affect foraminiferal and invertebrate assemblages, yet not strong enough to preserve annual laminations

39 like those seen in the deeper sites. These results indicate that OMZ waters ephemerally and intermittently shoaled above 418 m during the Bølling-Allerød.

URANIUM ISOTOPIC VARIATIONS IN MODERN SOILS AND DATED SOIL MINERALS: CALIBRATING A POTENTIAL PALEO-RAINFALL PROXY

JESSICA OSTER, KATHARINE MAHER, AND DANIEL IBARRA Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305 [email protected], [email protected], [email protected]

Dated secondary minerals, such as pedogenic carbonate and opal and speleothem, display substantial secular variations in initial (234U/238U) that may be related to environmental variability. (234U/238U) of secondary minerals should record the U isotopic value of the soil water or drip water from which they precipitate. Variation in soil water (234U/238U) may reflect changes in eolian inputs, infiltration rates, or weathering rates. Given this wide array of potential influences, distinguishing which processes led to initial (234U/238U) variability in the past can be challenging. Here we present preliminary results from a combined study of modern soil water chemistry from three soil sequences in Nevada and pedogenic mineral uranium isotopic variability from Fish Lake Valley, Nevada. Modern soil waters from Diamond Valley, Newark Valley, and Fish Lake Valley show significant initial (234U/238U) variability between sites, but are consistent along soil profiles. Soil water initial (234U/238U) values appear to be set in the Av layer and reflect soil parent material and grain size, and the degree of silicate versus carbonate weathering in the soil profile. Initial (234U/238U) values vary significantly along an elevation transect in Fish Lake Valley, with lower elevation soil waters displaying higher (234U/238U) values, possibly reflecting slower water infiltration rates due to less precipitation at lower elevations. The results of this modern soil water chemistry study were used to parameterize two -recoil loss factor, and infiltration rate on soil water initial (234U/238U) values. Fish Lake Valley pedogenic opal displays substantial initial (234U/238U) variability (1.0-1.8) over the past 140,000 years, with generally lower values during past glacial periods, and higher values during interglacials. This variability could reflect generally wetter conditions during glacial periods, and drier conditions during interglacials.

40

PLEISTOCENE PRECIPITATION VARIABILITY IN THE CENTRAL SIERRA NEVADA: STALAGMITE RESULTS AND FUTURE DIRECTIONS

JESSICA OSTER (1), ISABEL MONTAÑEZ (2), AND JERRY POTTER (2) (1) Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305 [email protected] (2) Department of Geology, University of California, Davis, CA 95616 [email protected], [email protected]

U-series-calibrated paleoclimate records for stalagmites from two central Sierra Nevada foothills caves document precipitation changes that are approximately coeval with Greenland temperature changes during the last glacial period and deglaciation. The Moaning Cave isotopic and trace element stalagmite proxies record variations in precipitation between 16,500 and 8,700 years ago that suggest drier and possibly warmer conditions during Northern Hemisphere warm periods and wetter and possibly colder conditions during high-latitude cool periods during the last deglaciation (Oster et al., 2009). New paleoclimate proxy records for a stalagmite from McLean‘s Cave, document changes in precipitation that are approximately coeval with interstadials and stadials associated with Dansgaard-Oeschger cycles between 68,000 and 56,000 years ago, during Marine Isotope Stages 4 and 3. The McLean‘s Cave stalagmite documents drier conditions in central California during Greenland interstadial events, signified by elevated 18O, 13C, grayscale, [Sr], and [Ba], and less radiogenic 87Sr/86Sr. Conversely, wetter conditions in California during Greenland stadials are signified by more negative 18O, 13C, lower grayscale, [Sr], and [Ba], and more radiogenic 87Sr/86Sr. The precipitation changes indicated by the Moaning and McLean‘s Cave records for the western Sierra Nevada are consistent with a broad picture of precipitation variability throughout the Northern Hemisphere in response to climate changes in the high northern latitudes, with the polar jet stream and Intertropical Convergence Zone shifting southward during Northern Hemisphere cold periods and northward during warm periods. Our new observations further support other paleoclimate records and models that link reduced precipitation in central California with changes in Arctic sea-ice extent and thermohaline circulation in the North Atlantic coincident with Arctic warming. We are further investigating these relationships by expanding our cave monitoring research and speleothem paleoclimate reconstructions to include other central and northern Sierra Nevada caves. We are also in the process of testing the linkage between high latitude climate conditions and California precipitation using the NCAR Community Climate System Model 3.

Oster, J.L., Montañez, I.P., Sharp, W.D., and Cooper, K.M., 2009, Late Pleistocene California droughts during deglaciation and Arctic warming: Earth and Planetary Science Letters, DOI: 10.1016/j.epsl.2009.10.003

41

FORAMINIFERAL SHELL THINNING OVER THE LAST 100 YEARS IN VARVED SEDIMENT FROM THE SANTA BARBARA BASIN, CALIFORNIA

DOROTHY PAK (1), LILY CLAYMAN (1), JAMES WEAVER (2), ARNDT SCHIMMELMANN (3), AND INGRID HENDY (4) (1) Marine Science Institute, University of California, Santa Barbara, CA 93106 [email protected] (2) Wyss Institute, Harvard University, Cambridge, MA 02138 (3) Department of Geological Sciences, Indiana University, Bloomington, IN 47405 [email protected] (4) Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109 [email protected]

Foraminiferal shell weights have been used as a proxy for calcite dissolution in marine sediments and to infer periods of past ocean acidification, assuming that lower shell weights are due to shell thinning in response to lower ocean water pH. Previous laboratory studies have shown that calcification rates of some species of planktonic foraminifera decrease in response to lower carbonate ion concentrations, however, it is difficult to distinguish between post- depositional dissolution and reduced biogenic calcification. A 2009 box core collected from the center of Santa Barbara Basin (586 m water depth, 34° 16.847‘ N, 120° 02.268‘ W) has provided a high-resolution record of varved sediment since A.D. 1780. We present a record of size- normalized shell weights of the near-surface dwelling planktonic foraminifera Globigerina bulloides spanning the last 250 years. Results indicate that foraminiferal shell weights in Santa Barbara Basin were highest between 1900 and 1920 and decreased significantly in the mid-1970s coincident with northeast Pacific Ocean warming as the Pacific Decadal Oscillation shifted from cool to warm phase. Scanning electron microscopy of the foraminiferal shells indicates that the decrease in shell weight was accompanied by a distinctive change in morphology. High shell weight G. bulloides have numerous, closely spaced spine bases and large pores while low shell weight G. bulloides have a smooth shell texture and small pores. The smooth-shell surface morphology is replicated in laboratory dissolution experiments, consistent with removal of an outer layer of calcite during shell thinning and partial dissolution of G. bulloides. Downcore thin- shelled G. bulloides may be the result of either reduced calcification or subsequent partial dissolution as the northeast Pacific Ocean warmed in the 1970s.

42

LONG-TERM SNOWPACK VARIABILITY AND CHANGE IN THE NORTH AMERICAN CORDILLERA

GREGORY T. PEDERSON (1), STEPHEN T. GRAY (2), CONNIE A. WOODHOUSE (3), JULIO L. BETANCOURT (4), DANIEL B. FAGRE (1), JEREMY S. LITTELL (5), EMMA WATSON (6), BRIAN H. LUCKMAN (7), AND LISA J. GRAUMLICH (8) (1) U.S. Geological Survey, Northern Rocky Mountain Science Center, Bozeman, MT 59715 [email protected], [email protected] (2) Civil and Architectural Engineering, University of Wyoming, Laramie, WY 82071 [email protected] (3) Geography and Development, University of Arizona, Tucson, Arizona 85721 [email protected] (4) U.S. Geological Survey, National Research Program, Tucson, AZ 85719 [email protected] (5) Climate Impacts Group, University of Washington, Seattle, WA 98195 [email protected] (6) Environment Canada, Ontario, Canada [email protected] (7) Department of Geography, University of Western Ontario, London Ontario N6A 5C2, Canada [email protected] (8) College of the Environment, University of Washington, Seattle, WA 98195 [email protected]

In the mountains of western North America, snowpack controls the amount and timing of runoff, while also influencing myriad ecosystem processes. Within the Columbia, Missouri, and Colorado River drainages, 60-80% of streamflow originates as snowpack, and snow serves as the primary water source for >70 million people. In much of this region, observational records show diminished snowpack since the 1950s, with further declines projected for the 21st century. However, questions remain as to whether observed declines might result from natural variability, as well as to how the magnitude and spatial extent of recent events fits into the context of the Medieval Climate Anomaly, Little Ice Age, and other key climatic periods of the past 1,000+ years. In the first study of its kind, we use tree rings to produce millennial-length reconstructions of snowpack at multiple spatial scales for key runoff generating areas in the North American Cordillera. Results confirm that snowpack has declined significantly across the Northern Rocky Mountains during the 20th century, and over the entire cordillera since the 1980s. Such coherent and persistent snowpack declines are rare in the reconstructions; before the 1950s the region exhibits substantial inter-basin variability with northern areas tending toward wetness when the south was dry, and vice-versa (i.e. the north-south moisture dipole). Cordillera-wide periods of low snowpack shown for the 1350s, 1400s, and post-1980s era correspond with times of anomalous warmth at regional and hemispheric scales. This implies Pacific Basin forcing of winter precipitation, and the resulting north-south dipole, have been defining features of snowpack variability for at least the last millennium, but temperature also has the potential to synchronize snowpack anomalies across the entire cordillera. When combined with the high

43 likelihood of future warming, these results may herald a fundamental shift in regional snowpack and water supplies.

FOSSIL WETLANDS IN THE DESERTS OF THE AMERICAN SOUTHWEST

JEFFREY S. PIGATI U.S. Geological Survey, Denver Federal Center, Box 25046, MS-980, Denver, CO 80225 [email protected]

Today, wetlands constitute ~0.3% of the total land cover in the deserts of the American Southwest, and encompass a variety of hydrologic settings, including seeps, springs, marshes, and wet meadows. These systems form in areas where water tables approach or breach the ground surface, most often near the distal toes of alluvial fans or where shallow faults or bedrock force groundwater to the surface. When active, desert wetlands serve as important watering holes for local fauna, support vegetation that depends on access to ground water for survival, and act as catchments for eolian and alluvial sediments. The interaction between hydrologic systems (emergent ground water and surface water), biologic systems (plants and animals), and geologic systems (eolian and alluvial sediments) in wetlands creates unique and complex depositional environments that are preserved in the geologic record as ground-water discharge (or GWD) deposits. Here I present the results of ongoing investigations of GWD deposits along an east- west transect across the Mojave Desert and southern Great Basin, and compare the results to GWD deposits elsewhere in the American Southwest in an attempt to better understand what drove changes in hydrologic conditions in this region during the Pleistocene. I will also discuss innovative methods of dating GWD deposits that we have developed, which have implications for dating other types of Quaternary deposits in arid environments.

CHIRONOMID PALEOCLIMATOLOGY: THE VIEW FROM THE GREAT BASIN

DAVID F. PORINCHU Department of Geography, The Ohio State University, Columbus, OH 43201 [email protected]

Much progress has been made in using sub-fossil midges to reconstruct Holocene climate change in the Great Basin of the United States and address outstanding questions relating to recent and long-term climate change in this region. High-resolution (sub-decadal) chironomid stratigraphies spanning the 20th century, developed for a number of lakes in the Great Basin, reveal dramatic shifts in midge community composition have occurred in recent decades and that variations in midge community composition are tracking observed changes in July temperature. These studies demonstrate that sub-fossil chironomid analysis can provide detailed records of local and regional climatechanges at sub-decadal timescales. Application of a midge-based inference

44 model to late Holocene sediment has also provided insight into regional climate and environmental conditions by providing a quantitative reconstruction of the thermal conditions that existed during the last 2,000 years. A sediment core representing the past 2,000 years was recovered from Stella Lake in the Snake Range of the central Great Basin in Nevada. The core was analyzed for sub-fossil chironomids and sediment organic content. The midge-based temperature reconstruction suggests that the interval between A.D. 600 and 1300 was characterized by fluctuating temperature: a depression of approximately 1.2oC temperature occurred between ~ A.D. 700 and 850 corresponding to the Carolingian cold phase and was followed by an increase in MJAT of approximately 1.8 C between A.D. 900 and 1300 corresponding to the classical Medieval Climate Anomaly (MCA). Comparison of the Stella Lake temperature reconstruction to previously published paleoclimatic records from this region indicates that the Carolingian period was characterized by both decreased temperature and increased effective moisture. The prolonged interval of elevated temperatures that characterized the central Great Basin between A.D. 900 and 1300 correspond to regional records of widespread aridity and are concurrent with hemispheric temperature trends associated with the MCA. This record increases our understanding of temperature variability and temperature-drought relations in the arid Southwest.

BIOMASS BURNING IN THE AMERICAS AFTER A.D. 1500: EUROPEAN CONTACT OR CLIMATE?

MITCHELL JAMES POWER (1), FRANCIS MAYLE (2), PATRICK J BARTLEIN (3) (1) Utah Museum of Natural History and Department of Geography, University of Utah, Salt Lake City, UT 84112 [email protected] (2) School of Geosciences, University of Edinburgh, Edinburgh, EH8 9AD United Kingdom (3) Department of Geography, University of Oregon, Eugene, OR 97403

The degree to which indigenous population collapse, caused by European contact, led to a decline in biomass burning across the Americas, is a topic of considerable debate. Here, we investigate this issue by synthesizing charcoal records from the Americas, as a proxy for biomass burning over the past 2,000 years. We find a clear, widespread signal that the Americas experienced a post-1492 decrease in biomass burning, with a nadir centered ca. A.D. 1600-1800, although inter-regional comparisons show that the amplitude of this downturn varied considerably. However, charcoal records from outside of the Americas show a similar decrease. This observation, with regional paleoclimate records and pre-Columbian population estimates suggests that Little Ice Age cooling played a greater role than indigenous population collapse in driving the decline in biomass burning.

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THE PACLIM YEAR: WESTERN CLIMATE 2010-2011 IN PERSPECTIVE

KELLY T. REDMOND Western Regional Climate Center, Desert Research Institute, 2215 Raggio Parkway, Reno NV, 89512 [email protected]

For the third year in a row the western states remained in a relatively cool pattern compared with the last one to two decades, though parts of the region have remained somewhat warm. Spring 2011 and especially May showed very cool temperatures. The monsoon season was generally wetter and warmer than average. Markedly cool temperatures were noted all summer along the immediate California coastline, close to the coolest on record. The 2010 fire season was much less active than during the previous decade. La Niña developed during the summer, and became one of the strongest in the last six decades, persisting into spring. The spatial pattern of precipitation anomalies differed in important respects from the expected canonical pattern. Of special note was the extremely wet start to Water Year 2010-2011, well south along the California coast, and in a swath extending northeastward from there into Colorado. Despite the lengthy presence of La Niña, calendar year 2010 ended as globally the warmest year on record (within uncertainty), from both surface and satellite observations. A six-week lull in snow accumulation commenced at the start of 2011 along the West Coast, followed by a period that more closely resembled the typical La Niña climate pattern in western North America. The winter so far has shown a significant number of vigorous storms and noteworthy temperature and hydrologic extremes in the western states, nationwide, and over North America. Both La Niña and the negative phase of the Arctic Oscillation have appeared to be significant factors in the winter so far. The Arctic and Greenland, by contrast, have experienced yet another very mild winter, and Arctic ice thus far this winter is the lowest extent on record. Long-term drought has diminished this winter over much of the West, but has expanded in eastern parts of the Southwest. The Colorado River may experience near to above average snowmelt stream flow. Globally, 2011 has started out cool to near average in temperature.

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EVIDENCE FOR LATE HOLOCENE HYDROLOGIC CHANGE AT BIG SODA LAKE, A MAAR LAKE IN NORTHWEST NEVADA

LIAM REIDY (1), ROGER BYRNE (1), LYNN INGRAM (2), MICHAEL ROSEN (3), AND MARITH REHEIS (4) (1) Department of Geography, University of California, Berkeley, CA 94720 [email protected], [email protected] (2) Department of Earth and Planetary Sciences, University of California, Berkeley, CA 94720 [email protected] (3) U.S. Geological Survey, 2730 North Deer Run Road, Carson City, NV 89701 [email protected] (4) U.S. Geological Survey, P.O. Box 25046, Lakewood, CO 80225 [email protected]

During the past 130 years paleolimnological research in the Great Basin has produced a rich record of late Quaternary environmental change. Most of this research has focused on the evidence of lake level changes and their implications for our understanding of climate change in the region. However, despite the progress that has been made relatively few of these studies have focused on high resolution i.e. sub-decadal scale records. Here we present the preliminary results of δ18 O and x-ray fluorescence (XRF) analyses on the upper 2-meters of a laminated sediment core recovered from Big Soda Lake, a maar lake near Fallon, Nevada. Core chronology is provided by 210Pb, the first appearance of non-native pollen types, radiocarbon, and two dated tephra. The data provide a 1,500 year record of regional climate change in the Carson Sink area. High resolution δ18 O and XRF data indicate sub-decadal changes in lake levels during the late Holocene and more recent changes associated with disturbance alongside the lake during the late 19th and early 20th centuries. Oscillations in the oxygen isotope record during the pre- historic period indicate significant changes in lake water levels. As the lake is only fed by precipitation and groundwater inflow these changes in lake level must be related to regional climate shifts. The abrupt change to lower oxygen isotope values near the top of the record marks the introduction of fresh groundwater to the lake. Construction of an project in the early 1900s caused increases in nearby groundwater levels which, in turn, caused lake levels to rise by 18 m between 1907 and 1930. Longer cores (8.80 m and 9.30 m) recovered in November 2010 are presently being analyzed to extend the record to the middle Holocene.

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WATER YEAR 2011: THE RAINS HAVE COME BACK

MAURICE ROOS California Department of , Sacramento, CA 95821 [email protected]

This will be a report on how the current water year is shaping up with a hydrologic review and some perspective on the past several years including the 2007-2009 California drought. This water year started off well in October with an abundance of rain eventually producing about 250% of average by the end of the month. Nearly ¾ the monthly total was produced by an atmospheric river from the semitropical western Pacific Ocean during the fourth week of the month. The wet streak continued in November with northern Sierra Nevada eight station average precipitation 127% of average followed by a very wet December nearly twice normal. The three month total for the northern Sierra on January 1 was 1.8 times average. Statewide precipitation was even better at almost twice average for the three month period. The Sierra snowpack was a robust 210 percent of average and 75% of an average April 1 pack in terms of water content. In contrast to patterns expected in a La Niña year, the southern Sierra was 270% compared to 180% in the north. Southern California suffered from floods during Christmas week. In January, the tide shifted with the buildup of a high pressure system just offshore. As of this writing in late January we have had three weeks of mostly dry weather. The snowpack has remained at about ¾ of the April 1 average, hopefully to be available later in the season as enough usable snowmelt to produce at least a near normal water supply. Now to review the recent past, including the 2007-2009 three year drought and how it compares with past droughts. After a very wet water year in 2006, which had statewide runoff slightly over 170% of average, we had three consecutive years of much below average runoff. This drought was not quite as severe as the six year 1987-1992 drought. For the Sacramento four river runoff, the average annual amount in 2007-2009 was 11.1 million acre-feet (maf), compared to 10.1 maf during 1987-1992 and a two year average of only 6.7 maf in 1976-1977. The 50 year average is 18.6 maf for the Sacramento four rivers. When one looks at the runoff deficits, the recent three year drought seemed to have greater consequences than previous. One factor is continuing urban growth and therefore higher water demand with basically the same supply infrastructure. Another is higher environmental demands. Since previous droughts environmental factors have now reduced available water supplies for agricultural and urban users. What has happened is a substantial increase in environmental water demands with no significant change in supply facilities. It would be nice to distinguish between drought and water shortage. The former is a hydrologic deficiency; the later would be due to demands exceeding the assured supply or lack of facilities to meet water requirements even in normal years.

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EVIDENCE OF HYDROLOGICAL CHANGES CAUSED BY HUMAN DISTURBANCE RECORDED IN NITROGEN AND CARBON ISOTOPES FROM BIG SODA AND PYRAMID LAKES, NEVADA

MICHAEL R. ROSEN (1), LIAM REIDY (2), SIMON POULSON (3), CAROL KENDALL (4), ROGER BYRNE (2), AND MARITH REHEIS (5) (1) U.S. Geological Survey, 2730 North Deer Run Road Carson City, NV 89701 [email protected] (2) Department of Geography, University of California, Berkeley, CA 94720 [email protected] (3) Department Geological Sciences and Engineering, University Nevada, Reno, NV 89557 [email protected] (4) U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 [email protected] (5) U.S. Geological Survey, P.O. Box 25046, Lakewood, CO 80225 [email protected]

Nitrogen isotopes of lake sediment organic matter have been used to determine changes in lake productivity, eutrophication, and hydrology. However, isotopic shifts caused by human-induced changes to the hydrology of lakes have rarely been documented in lake sediments. Nitrogen isotope data collected from Big Soda Lake, a volcanic maar lake near Fallon, Nevada, and Pyramid Lake, a large terminal lake located about 40 km northeast of Reno, Nevada, show distinct opposite shifts in the early 1900‘s to the present that are likely caused by the construction of the Newlands Irrigation Project, which diverted water away from the Truckee River and Pyramid Lake down the Truckee Canal to Lahontan Reservoir. This water was used to irrigate farmland near Big Soda Lake, which caused its lake level to rise 18 m by 1930. At the same time Big Soda Lake was rising, Pyramid Lake level was falling and stopped overflowing to nearby Lake Winnemucca in the early 1930‘s. This caused Lake Winnemucca to become a dry lake in the late 1930‘s. The differing hydrologic history of the two lakes is evident in the approximately 10‰ negative isotopic shift in δ15N at Big Soda Lake in the upper 15 cm of sediment. This change occurred around A.D. 1900 based on 210Pb sedimentation rates. The negative shift is likely caused by build-up of high ammonium concentrations (NH3 is approximately 45 mg/L in the monimolimnion) due to meromixis, which began after the lake level rose. This build-up led to a large isotopic fractionation that is associated with ammonium assimilation. This in turn caused a decrease in the δ15N values of the deposited organic matter. In Pyramid Lake, a 2‰ increase in δ15N occurred over approximately the same time period as the decrease in Big Soda Lake. As 14N is preferentially incorporated into phytoplankton, phytoplankton N can have δ15N values several ‰ lower than that of the dissolved inorganic nitrogen (DIN), so the δ15N value of the remaining DIN will increase in the deposited sediment. These data possibly indicate an increase in primary productivity of Pyramid Lake during this time. Stable δ13C isotope data from both lakes show similar opposite trends over the same time periods. Pyramid Lake δ13C values became more negative after 1930 and Big Soda Lake became more positive. Even though climate during this time was the same for both lakes, the hydrologic

49 changes to both basins have caused opposite trends in δ15N values of deposited organic matter in these lakes. Determining the changes in nitrogen isotope composition during these known changes in recent hydrologic conditions can allow a better understanding of possible changes observed in these lakes during the Holocene.

EROSION OF TOPMOST VARVES BY TURBIDITE DEPOSITION LIMITS VARVE COUNT ACCURACY IN SANTA BARBARA BASIN, CALIFORNIA

ARNDT SCHIMMELMANN (1), INGRID HENDY (2), DOROTHY PAK (3), AND AARON ZAYIN (1) (1) Department of Geological Sciences, Indiana University, Bloomington, IN 47405 [email protected] (2) Department of Geological Sciences, University of Michigan, MI 48109 [email protected] (3) Marine Science Institute, University of California, Santa Barbara, CA 93106 [email protected]

The annually laminated (i.e. varved) sediment in the central Santa Barbara Basin (SBB) off California has been dated independently by consecutive varve-counting of the last 2,000 varves and by radiometric methods (e.g., radiocarbon ages of foraminifera). Age differences among dating methods are in part caused by errors in varve counting that cumulatively reduce dating accuracy down core. For example, some varves can be missing in the sedimentary record if the topmost, youngest, and least consolidated sediment is eroded by occasional strong bottom currents. The silled nature of the SBB usually precludes strong bottom currents, but the shear of fast-flowing and dense turbidite currents from up-slope may erode and suspend topmost bacterial mat and underlying soft sediment. A 2009 SBB box core from 585.8 m water depth (34° 16.847‘ N, 120° 02.268‘ W) featured continuously varved sediment from A.D. 1931 to 2009. However, below the 1931 varve, a 6 cm thick turbidite was found resting on the 1923 varve, as determined by cross-correlation of the pre-1924 varve pattern with records from other box cores featuring continuous varves across the 20th century. The turbidite was likely triggered seismically on 5 August 1930 when a strong earthquake shook Santa Barbara. The local 1930 turbidite eroded annual varves from 1924 to 1930. Sectioning of a cylindrical sub-core from the same box core showed 1-cm large rip-up clasts of varved sediment with various angles of lamination embedded in the lower portion of the 1930 turbidite. The presence of occasional thick turbidites in SBB sediments, especially prior to A.D. 1850, likely causes undercounting of varves.

50

RAINFALL, RUNOFF, AND POST-WILDFIRE GEOMORPHIC TRANSPORT PROCESSES

KEVIN M. SCHMIDT (1), MAIANA N. HANSHAW (1), JAMES F. HOWLE (2), AND JONATHAN D. STOCK (1) (1) U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 [email protected], [email protected], [email protected] (2) U.S. Geological Survey, 5229 North Lake Boulevard, Carnelian Bay, CA 96140 [email protected]

Moderate rainfall rates that are insufficient to erode unburned landscapes can trigger accelerated sediment transport rates in landscapes denuded of vegetation by wildfire. To quantify how rapidly burned steeplands in southern California erode during rainfall, we monitored rainfall/runoff relationships and generated time-series of high-resolution topography by surveying steep, low-order drainage basins using repeat terrestrial laser scanning (TLS), lidar. Our goals were to map geomorphic process signatures with respect to rainfall rates and understand the mechanisms of sediment transport processes characteristic of post-wildfire erosion including debris-flows. Through repeat TLS, generation of bare-earth model DEMs, and field mapping, we documented how patterns of exhumed bedrock, sediment redistribution/volume changes on hillslopes, and sediment infilling of low-order valleys rapidly altered both the variable source area for overland runoff and the sediment available for transport by post-fire debris flows. We derived ten distinct map units representing geomorphic processes through field observations of topographic character, sedimentary structures, and depositional or erosional relationships. Map unit boundaries varied over time in response to changing rainfall/runoff relationships, storm magnitudes, and local conversion to sediment supply limited conditions where the underlying bedrock or competent soil horizons were exhumed. In response to precipitation intensities exceeding 20 mm/hr in four separate events, steep hillslopes underlain by cohesive sediments in the western Transverse Range, California, experienced overland-flow erosion over 70% of the area, but triggered no debris flows. In contrast, steep hillslopes underlain by non-cohesive plutonic rocks in the San Gabriel Mountains, California experienced widespread erosion along the valley axis exceeding 1.5 m depth, in addition to numerous debris flows in response to four storms with rainfall rates ranging from 7 to 28 mm/hr; with the highest averaged hourly rainfall intensities occurring during a localized convective storm. If climatic forecasts of more frequent wildfire and greater precipitation variability are realized, accelerated sediment transport rates may enhance conversion from soil-mantled, shrub-dominated chaparral hillslopes to bedrock-dominated, grassland ecosystems.

51

MODELED PLEISTOCENE DISTRIBUTIONS OF THREE CLIMATICALLY SENSITIVE TREE TAXA IN CENTRAL AND NORTHWESTERN MEXICO

DYUTI SENGUPTA AND ROGER BYRNE Department of Geography, University of California, Berkeley, CA 94720 [email protected], [email protected]

Paleoecological reconstructions that include the Last Glacial Maximum (LGM; 21,000 cal yr B.P.) from central and northwestern and Mexico are scarce. Only a handful of pollen records and glacial evidence are commonly cited to describe conditions in central Mexico during the LGM. For northwestern Mexico the story is similar, although the combination of high resolution packrat middens, oceanic cores and terrestrial sediment cores lend more support to reconstruction scenarios. In addition to traditional methods of proxy data analysis and interpretation, phylogenetic analysis and paleoecological modeling serve as another means of visualizing past environments. Recent improvements in climate modeling techniques and species distribution (SDM) modeling software, coupled with increased data availability has greatly benefited the process of visualizing past environments. However, the results are not always in agreement with well-accepted paleoproxy interpretations. Here we consider three important cool climate taxa that appear in both central and northwestern Mexico (Abies, Picea, Artemisia), to test the usefulness of two models in a paleoclimatic context. On comparing the model results to proxy data and phylogenetic interpretations, we find agreement in some regions of Mexico for all three taxa. These results make clear that careful selection of relevant taxa and ecological variables and an understanding of both the modeling technique and the climate data is crucial to generating plausible results. We also suggest the possibility that the LGM climate projection may be inaccurate in certain regions of Mexico, thereby affecting the model results.

CMIP3 PROJECTIONS FOR THE PACIFIC DECADAL OSCILLATION FOR 2000- 2050 UNDER THE B1, A1B, AND A2 SRES EMISSION SCENARIOS

JEANNINE-MARIE ST. JACQUES, SUZAN LAPP, ELAINE BARROW, AND DAVID SAUCHYN Prairie Adaptation Research Collaborative (P.A.R.C.), Room 120, 2 Research Drive, University of Regina, Regina, SA, S4S 7H9, Canada [email protected]

The climatology and hydrology of western North America display strong periodic cycles which are correlated with the low-frequency Pacific Decadal Oscillation (PDO). The PDO‘s signature is seen throughout the entire North Pacific Ocean, with related significant associations to hydrology and ecology in western North America and northeastern Asia. Therefore, the status of the PDO in a warmer world caused by anthropogenic climate change is of great interest. We developed early 21st century projections of the PDO, using data from archived runs of the most recent high-resolution global climate models from the IPCC Fourth Assessment Report (AR4)

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(Phase 3 of the Coupled Model Intercomparison Project - CMIP3). These PDO projections for 2000-2050 showed a weak multi-model mean shift towards more occurrences of the negative phase PDO for the B1, A1B and A2 emissions scenarios. If present-day teleconnection correlation patterns hold, this suggests future declines in American Southwest and northern Mexican surface water availability, and thereby negative impacts on agriculture and hydroelectric power generation. It also suggests an increase in future winter precipitation for the Pacific Northwest of North America. However, not all the models showed a consistent shift to negative PDO conditions.

PROJECTED NORTHERN ROCKY MOUNTAIN ANNUAL STREAMFLOW FOR 2000-2099 UNDER THE B1, A1B AND A2 SRES EMISSIONS SCENARIOS

JEANNINE-MARIE ST. JACQUES (1), SUZAN LAPP (1), YANG ZHAO (2), ELAINE BARROW (1) AND DAVID SAUCHYN (1) (1) Prairie Adaptation Research Collaborative (P.A.R.C.), Room 120, 2 Research Drive, University of Regina, Regina, SA, S4S 7H9, Canada [email protected] (2) Department of Mathematics and Statistics, University of Regina, Regina, SA, S4S 0A2, Canada

The 20th century hydroclimatology of the northern Rocky Mountains is heavily influenced by recurring large-scale climate patterns: the Pacific Decadal Oscillation (PDO), the El Niño- Southern Oscillation (ENSO), and the Arctic Oscillation/North Atlantic Oscillation (AO/NAO). Hence, northern Rocky Mountain river discharge variability can be successfully modeled by regression techniques using these climate indices as predictors. Generalized least squares (GLS) regression addresses residual autocorrelation and allows reliable significance testing of any predictor coefficients, and hence, is highly suitable for hydrological modeling. We developed GLS regression equations which captured a major portion of streamflow variability for ten centennial-length northern Rocky Mountain annual discharge records. Both unregulated and paired regulated and naturalized flows were examined. Using archived global climate model runs from the Coupled Model Intercomparison Project Phase 3 (CMIP3), we projected the PDO, ENSO and NAO for the 21st century for the B1, A1B and A2 SRES emission scenarios. These projected climate indices were used as inputs into the GLS equations, giving projected northern Rocky Mountain river discharges for the 21st century. These projections showed generally declining trends in surface water availability for 2001-2100. Researchers have projected increases in summer warmth and typically decreasing summer precipitation, and increases in winter precipitation and temperature for this region under greenhouse forcing. Our results suggest that in the competition between these two opposing effects on surface water availability, the former will dominate.

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AN EMPIRICAL METHOD TO FORECAST THE EFFECT OF STORM INTENSITY ON SHALLOW LANDSLIDE ABUNDANCE

JONATHAN D. STOCK (1) AND DINO BELLUGI (2), (1) U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 [email protected] (2) Department of Earth and Planetary Sciences, University of California, Berkeley, CA 94720 [email protected]

Intense rainfalls from historic storms have triggered widespread shallow landslides in the coastal mountains of California. Varved sediments in the Santa Barbara Basin may contain the geologic record of such storms over the past millennium. These deposits are substantially thicker than those associated with storms of January 1969, the most recent historic events to generate widespread landslides in southern California. If layer thickness scales with storm intensity, these layers imply that southern California has experienced storms that are massive compared to our recent historical experience. Unlike seismic hazard maps, we cannot begin to quantify the magnitude of landslide hazards that will accompany such a storm. Put simply, we cannot answer the question of how many shallow landslides California's largest storms would trigger. We hypothesize that shallow landslide abundance in a landscape increases with rainfall intensity, duration and the number of unstable model cells for a given shallow landslide susceptibility model. We use digital maps of historic shallow landslides in northern and southern California, and nearby rainfall records to construct a relation between rainfall intensity and the fraction of unstable model cells that actually fail in historic storms. We find that this fraction increases as a power law with the 6-hour rainfall intensity for sites in southern California. We use this relation to forecast shallow landslide abundance for a dynamic numerical simulation storm for California (Arkstorm), representing the most extreme historic storms known to have impacted the state.

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PROJECTED SEA-LEVEL RISE IMPACTS ON THE SALT MARSH LANDSCAPES OF SAN FRANCISCO BAY, CALIFORNIA AND ITS RESIDENT SALT MARSH WILDLIFE SPECIES

JOHN TAKEKAWA (1), KAREN THORNE (1), KYLE SPRAGENS (1), MICHAEL CASAZZA (2), CORY OVERTON (2), JUDITH DREXLER (3), DAVE SCHOELLHAMMER (3), AND KATHLEEN SWANSON (3) (1) Western Ecological Research Center, San Francisco Bay Estuary Field Station, U.S. Geological Survey, 505 Azuar Drive, Vallejo, CA 94592 [email protected] (2) Western Ecological Research Center, Dixon Field Station, U.S. Geological Survey, 6924 Tremont Road, Dixon, CA 95620 [email protected] (3) California Water Science Center, U.S. Geological Survey, Placer Hall, 6000 J Street, Sacramento, CA 95819 [email protected]

Coastal salt marshes and estuaries are projected to be disproportionately impacted by climate change and sea-level rise, according to the Intergovernmental Panel on Climate Change. Over 80% of wetlands in San Francisco Bay estuary have been lost to urban development and landscape modification. The San Francisco Bay estuary, though severely fragmented and modified, represents one of the largest tidal salt marsh complexes in the western United States and contains important remaining habitat for federal- and state-listed species. Maintenance and expansion of habitat is crucial to the successful recovery of endangered species, but it remains unknown how much of a detrimental effect sea-level rise may impact the amount and quality of habitat for these species. The focus of this interdisciplinary study is to evaluate sea-level rise impacts to salt marsh habitats and wildlife by synthesizing field data, modeling, and using ArcGIS tools to develop impact models. Work was done at 13 salt marsh sites around the San Francisco Bay area. Our work illustrates the risk to wildlife species and identifies critical sea- level rise thresholds for species. In addition sediment modeling and downscaling of tidal cycles are being used to better understand impacts. Habitat impact models and ongoing research objectives will be presented.

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DIAGNOSING AND PROJECTING CLIMATE CHANGE IN THE HAWAIIAN ISLANDS

OLIVER ELISON TIMM (1), THOMAS W. GIAMBELLUCA (1), AND HENRY F. DIAZ (2) (1) University of Hawaii at Manoa, Honolulu, HI 96822 (2) NOAA-CIRES Climate Diagnostics Center, Boulder, CO 80305 [email protected]

Hawai‗i has experienced a gradual warming in the last 100 years and especially since the mid- 1970s. Likewise, the statewide rainfall experienced decadal changes and an overall drying trend, particularly during the wetter winter months. The warming trend is largest in higher elevated regions on the islands, and this is consistent with other studies that support a general amplification of anthropogenic warming with elevation. In Hawai‗i, the upper mountain slopes harbor most of the remaining intact native ecosystems and a continuous warming is likely to have severe impacts. For example, endangered Hawaiian honeycreepers currently find refuge in high-elevation forests, where low temperatures limit the activity of disease-carrying mosquitoes. Changes in temperatures and precipitation can force endemic species to abandon their old natural habitat zones, migrate to more agreeable areas, or in worst case the habitat zones could vanish entirely. Another unique feature of the climate of the Hawaiian Islands is that in most areas, the highest intensity rainfalls contribute disproportionately to the annual means. We have been focusing on diagnosing changes in the upper rainfall quantiles in the context of natural and anthropogenic forcing.

PALEOFIRE REGIMES IN MEDITERRANEAN CLIMATE REGIONS

SHIRA TRACY (1), MITCHELL POWER (1), R. SCOTT ANDERSON (2), AND THE GPWG COMMUNITY (1) Utah Museum of Natural History, Department of Geography, University of Utah, Salt Lake City, UT 84112 [email protected] (2) School of Earth Sciences & Environmental Sustainability, Northern Arizona University, Flagstaff, AZ 86011

Biological hotspots support high concentrations of endemic species and serve as an effective conservation tool by delineating geographic boundaries. Here we explore the role of fire as a potential mechanism of diversity across similar Mediterranean type climates. Fire and climate linkages during the last 15,000 years were examined from five Mediterranean ecosystems, including; coastal California, Mediterranean basin, central Chile, southwestern Australia, and Southern Africa. These regions support Mediterranean climates with winter wet and summer dry precipitation, associated ocean upwelling, and the absence of glaciated terrains. Sites from the Global Charcoal Database were compared to pollen studies from localities in Mediterranean

56 hotspots. We hypothesize fire maintains mosaic landscapes by short fire return intervals, contributing to the high levels of endemicity. Global analysis of Mediterranean fire activity suggests a rapid rise in fires between14,000 and 13,000 cal yr B.P., followed by a decline from 13,000 to 12,000 cal yr B.P. After 9,000 cal yr B.P., fire activity increased in all Mediterranean regions until the middle Holocene. Analysis of five isolated Mediterranean regions reveals a coherent pattern in fire activity across all locations beginning by 9,500 cal yr B.P. As Mediterranean-type vegetation developed between 5,000 and 2,000 cal B.P., increased climate variability associated with ocean upwelling, produced increased variability in fire regimes and a potential mechanism for the development of Mediterranean diversity. Identifying the long-term interrelationship between fire and the presence and abundance of endemic species will provide a better understanding of the role fire plays in the development and long-term stability in Mediterranean hotspots. With increasing anthropogenic pressure, and high levels of fire suppression in Mediterranean hotspots, more research is necessary to aid future conservation and fire management strategies in these unique regions.

GUIDING CLIMATE CHANGE PLANNING FOR SAN FRANCISCO BAY TIDAL MARSHES

SAM VELOZ (1), NADAV NUR(1), LEO SALAS(1), JULIAN WOOD(1), DIANA STRALBERG (1,2), GRANT BALLARD (1), AND DENNIS JONGSOMJIT (1) (1) PRBO Conservation Science, Petaluma, CA 94954 [email protected] (2) Department of Biological Sciences, University of Alberta, Edmonton, AB, T6G 2R3, Canada

Climate change will affect wetlands in San Francisco Bay through sea-level rise changes in seasonal salinity and changes in tidal-inundation regimes. These changes are likely to convert tidal freshwater and brackish wetlands into more saline systems and result in greater inundation of tidal marshes, thereby changing plant species composition and structure for birds and other wildlife and threatening the long-term sustainability of vegetated marsh habitats and the ecosystem services they provide. Using several different scenarios of suspended sediment supply and rates of sea-level rise we projected potential changes in tidal marsh habitats at twenty year intervals from 2010-2100. In areas with low sediment availability (25-50 mg/L) such as southern Marin, sedimentation models predict marsh drowning within 20-100 years, depending on the rate of sea level rise. In areas with very high sediment availability (300 mg/L) such as the Petaluma River and south San Francisco Bay, models predict marsh resilience even under high rates of sea level rise (up to 165 cm over the next century). In areas with intermediate sediment availability, however, marsh sustainability will depend on the rate of sea-level rise. Under high rates of sea level rise, only low marsh can be maintained. We present results of future tidal marsh simulations that project future distributions and abundance patterns of principal plant species and key tidal-marsh dependent birds in relation to physical variables (elevation, salinity, channel

57 density, etc.). Summer salinity and tidal marsh elevation were consistently important variables for predicting the distribution of tidal marsh vegetation. The distribution and abundance models are being used to assess the vulnerability of tidal marsh bird species of conservation concern, including the Federally-endangered Clapper Rail and the State-threatened Black Rail to climate change. Our findings and recommendations can inform decisions that will shape efforts to conserve and restore San Francisco Bay wetlands and vertebrate populations that depend on tidal wetlands, as well as guide decision making by government agencies at the local, regional, and state levels.

LATE HOLOCENE ENSO VARIABILITY IN THE CENTRAL PACIFIC: PRELIMINARY DATA FROM PALMYRA ATOLL

DAVID WAHL (1), ALEXIS VISCAINO (2), ROB DUNBAR (2), AND LYSANNA ANDERSON (1) U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 [email protected]; [email protected] Environmental Earth System Science, Stanford University, CA 94305 [email protected]; [email protected]

Variations in present day tropical Pacific precipitation are tied to patterns of SST anomalies primarily driven by shifting modes of ENSO. Instrumental records from the low latitude central Pacific region exhibit a strong response to ENSO dynamics, suggesting paleoclimate reconstructions from this region would hold great potential for more fully understanding the relationship between ENSO variability and synoptic climate patterns. However, due to its remoteness and lack of viable research sites, a paucity of high-resolution late Holocene climate reconstructions from the central Pacific currently exists. Palmyra Atoll, a remote uninhabited series of islets in the central Pacific, represents one of these rare viable sites. Using multiple proxies to reconstruct past sea surface conditions, we seek to understand the relationship between ENSO variability and known late Holocene climate events (ie. the Medieval Climate Anomaly and Little Ice Age). We report preliminary data from a 3.2 m sediment core retrieved from the west lagoon on Palmyra Atoll (5º 53' 05.25" N; 162º 05' 21.63" W; water depth 51 m). Radiocarbon determinations on pteropods from the basal sediment of the core indicate the record extends to ~ 640 cal yr B.P. (A.D. 1310). Evidence for construction on the atoll during WWII includes a discreet horizon of coarse-grained carbonate, providing a chronologic marker at 8 cal yr B.P. (A.D. 1942). Oxygen isotopic composition of authigenic carbonates, high-resolution scanning XRF, 14C, and 210Pb data are currently being collected, and together will be used to construct a model of changing sea surface conditions for the region.

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ELKHORN SLOUGH TIDAL WETLANDS: PAST, PRESENT AND FUTURE

ELIZABETH BURKE WATSON (1,2), ERIC VAN DYKE (2), AND KERSTIN WASSON (2,3) (1) Department of Land, Air and Water Resources, University of California, Davis, CA 95616 [email protected] (2) Elkhorn Slough National Estuarine Research Reserve, Watsonville, CA 95076 (3) Ecology and Evolutionary Biology, University of California, Santa Cruz, CA 95064

Tectonic uplift, a narrow continental shelf, and heavy surf place strong natural limits on the areal extent of tidal wetland habitat along the California coast. Concurrently, human activities and associated landscape changes have led to the large-scale destruction of much of the region‘s tidal wetlands. Tidal wetlands at Elkhorn Slough, central Monterey Bay, are thus a regionally important resource: this area supports among the largest remaining extents of tidal wetlands in California. Unfortunately, these wetlands are in deteriorated condition: a large portion were diked off from tidal exchange (these areas exist today as shallow eutrophic ponds), and in fully tidal locations, hydrologic modifications to the estuary have resulted in plant mortality and marsh loss. At Elkhorn Slough National Estuarine Research Reserve, we are conducting a study utilizing stratigraphic assessments and habitat modeling in order to address key questions about the historical extent, current trajectory, and future distribution of estuarine wetlands at Elkhorn Slough, with an emphasis on understanding the impacts of climate variability and climate change on this coastal resource. For the purposes of habitat reconstruction, sediment stratigraphies with chronologic control established using radiocarbon dating, have revealed dramatic variability in marsh extent at Elkhorn Slough, revealing clear episodes of past marsh deterioration. Studies of contemporary sediment accumulation undertaken using sediment-erosion tables, sediment tiles, marker beds, and recent radiometric dating (e.g. 137Cs/210Pb) reflect a submerging marsh plain and escalating accumulation rates in both vegetated and deteriorated tidal marsh. Implementation of a habitat model (Sea level affecting marshes – SLAMM) has identified low suspended sediment concentrations as an obstacle to marsh sustainability under even the most moderate sea level rise/climate scenarios, but has identified potential future marsh migration pathways. These data will be used to help set well-informed targets for marsh acreage in the estuary and to understand what geographical areas are likely sites for marsh migration.

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A LATE-HOLOCENE RECORD OF DISTURBANCE FROM THE NORTHERN ROCKY MOUNTAINS, USA

JENNIFER H. WATT (1), ANDREA BRUNELLE (1), AND KURT KIPFMUELLER Department of Geography, RED Lab, University of Utah, Salt Lake City, UT 84112 [email protected] Department of Geography, Center for Dendrochronology, University of Minnesota, Minneapolis, MN 55455

Mountain pine beetle (MPB) outbreaks have impacted or are currently affecting many pine communities in the western U.S. It is not clear if these large-scale outbreaks are unprecedented or if they have previously occurred at this magnitude. Reconstructing high-resolution disturbance regimes (fire and MPB) from sedimentary records for the Holocene (the last 10,000 years) will provide insight on disturbance ecology in subalpine forests. The records presented here use charcoal to identify past fire disturbance and a new pollen method to identify past MPB outbreaks. The new pollen method was developed from recent studies in spruce-fir forests where changes in pollen composition were used to identify past spruce beetle outbreaks. Initially, it was unclear if this would work in pine-dominated systems where there is not the same trade-off between dominant tree taxa. Two late Holocene records from Fishstick Lake, Idaho and Lake of the Woods, Montana demonstrate that pollen ratios can be used to identify past bark beetle outbreaks in pine-dominated forests.

FROM ATMOSPHERIC CIRCULATION TO GRAPE TEMPERATURES: MACRO-, MESO-, TOPO-, AND MICROCLIMATE IN VINEYARDS (AND YOUR GLASS)

STUART B. WEISS Viticision/Creekside Center for Earth Observation 27 Bishop Lane,Menlo Park, CA 94025 [email protected]

Few agricultural crops are as sensitive to weather and climate as wine grapes. Small fluctuations in temperature and phenology can make the difference between high quality and poor quality crops. Climate change will challenge continued production of quality wine grapes in the Pacific States. In order to effectively consider climate change in vineyard design and management, a multi-scale approach to climate is required, descending scales from macroclimate through mesoclimate, topoclimate, and microclimate. In this presentation, I describe applications of this hierarchy to vineyards. Station data, and interpolated surfaces such as PRISM account for macroclimatic and mesoclimatic gradients down to a scale of 800 m. Ripening dates, both past and projected, of grape varieties can be estimated from monthly data at these scales. Topoclimatic gradients are derived from digital elevation models (DEMs) using solar radiation models, topographic position, and slope, and have profound effects on minimum and maximum temperatures. At the finest scale, microclimate

60 encompasses the effects of vegetation canopies on solar radiation, humidity, and temperature, such as the effects of trellis design on berry temperature on either side of the trellis. Hemispherical photography quantifies trellises from a ―grapes‘ eye view,‖ allowing estimation of solar radiation on grape clusters at half hourly intervals for each month. By combining all of these methods with inexpensive temperature sensors, the temperatures of grape clusters can be tracked through growing seasons using local weather station data, with numerous key insights into vineyard design and management in a variable and changing climate.

MILLENNIAL-SCALE CLIMATE OSCILLATIONS OVER THE PAST 735,000 YEARS AS RECORDED IN HIGH-RESOLUTION MARINE SEDIMENT RECORDS FROM SANTA BARBARA BASIN, CALIFORNIA

SARAH M. WHITE (1), TESSA M. HILL (1), JAMES P. KENNETT (2), AND RICHARD BEHL (3) (1) Department of Geology, University of California, Davis, CA 95616 [email protected], [email protected] (2) Department of Earth Science, University of California, Santa Barbara, CA 93106 [email protected] (3) Department of Geological Sciences, California State University, Long Beach, CA 90840 [email protected]

A lack of high-resolution climate records beyond the last glacial period has limited understanding of causes, effects, and temporal development of Quaternary abrupt climate shifts. Santa Barbara Basin (SBB), with a sedimentation rate of 100 cm/1,000 yr, provides uniquely well-preserved sediments spanning the past ~700,000. Five piston cores from SBB, each spanning ~5,000, were dated to ~735,000, 460,000, and 290,000 years ago. These cores allow us to see whether millennial-scale climate shifts have changed in amplitude, shape, and/or timing since the Mid-Pleistocene Transition, and how they are expressed in the Pacific in terms of ocean circulation, productivity, and oxygenation. We use stable isotopes of planktonic (Globigerina bulloides, Neogloboquadrina pachyderma), and benthic foraminifera (Uvigerina peregrina) and planktonic foraminiferal assemblage analyses including % N. pachyderma (d), and sediment lamination data. δ18O data of G. bulloides and N. pachyderma show shifts of up to 1.4‰ in as briefly as ~80 years and 2.5‰ over ~1,000 years during warming. Water column stratification (shown by the difference between G. bulloides and N. pachyderma δ18O) increases during interstadials. The % N. pachyderma (d) often varies in tandem with planktonic δ18O, but exhibits threshold behavior instead of smooth change, and is generally higher during interstadials and/or moderate water column stratification. δ13C values broadly correlate with shifts in δ18O, and reflect changing ocean circulation, carbon cycling, and/or methane release. Preserved sediment laminations coincide with intervals of warm, stratified upper waters. A comparison of our data to SBB records from the past 60,000 years (Behl and Kennett, 1996; Hendy and Kennett, 1999, 2000; Hill et al., 2006) shows that typical stadial-interstadial shifts in planktonic δ18O (~1.5‰)

61 are similar to those recorded during the past 60,000 years, although changes in % N. pachyderma (d) are smaller, and planktonic assemblages are slightly different, with fewer G. bulloides, Globigerina quinqueloba, and Globorotalia scitula, and more N. pachyderma (s).

Behl, R.J., and Kennett, J.P., 1996, Brief interstadial events in the Santa Barbara Basin, NE Pacific, during the last 60 kyr: Nature, v. 376, p. 243-246. Hendy, I.L. and Kennett, J.P., 1999, Latest Quaternary North Pacific surface water responses imply atmospherically- driven climate instability: Geology, v. 27, n. 4, p. 291-294. Hendy, I.L. and Kennett, J.P., 2000, Stable isotope stratigraphy and paleoceanography of the last 170 ka: ODP Site 1014, Tanner Basin, California: Ocean Drilling Program Scientific Reports, v. 167, p. 129-140. Hill, T.M., Kennett, J.P., Pak, D.K., Behl, R.J., Robert, C., and Beaufort, L., 2006, Pre-Bølling warming in Santa Barbara Basin, California: Surface and intermediate water records of early deglacial warmth: Quaternary Science Reviews, v. 25, n. 21-22, p. 2835-2845.

CLIMATE DRIVERS OF STREAMFLOW SYNCHRONICITY IN WESTERN U.S. RIVERS OVER MULTIPLE CENTURIES

ERIKA K. WISE Department of Geography, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599 [email protected]

Twentieth century high- and low-streamflow events in the western U.S. have been linked to Pacific and Atlantic Ocean influences, including those described by the El Niño–Southern Oscillation (ENSO), the Pacific Decadal Oscillation, and the Atlantic Multidecadal Oscillation. Extended streamflow records, reconstructed using tree rings, have identified drought and pluvial periods in the past that were more extreme than those recorded during in the instrumental record. This study compares a new tree-ring based reconstruction of Snake River streamflow with streamflow reconstructions of the Colorado, Sacramento, and Verde rivers. Results suggest that changes in the predominance of zonal versus meridional atmospheric flow may have influenced patterns of synchronous and asynchronous streamflow in the four rivers. Spatial drought patterns indicate a zonal flow pattern during two of the most severe droughts in the Snake River record (the 1630s and the 1930s), which were much less severe in the Verde River record. The Snake River‘s low-flow period in the early 1700s, which was less severe in magnitude, is replicated in the flow of all four rivers and may be indicative of persistent meridional flow. These drought patterns appear to correspond to shifts in Pacific Ocean conditions; however, direct comparisons between these periods and reconstructed indices such as ENSO are hindered by inconsistencies between existing reconstructions of paleo-teleconnections.

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VARIATION IN FORAMINIFERAL DISTRIBUTIONS ACROSS THE PLEISTOCENE- HOLOCENE TRANSITION OFF THE KAYAK SLOPE, NORTHERN GULF OF ALASKA

SARAH D. ZELLERS, KATHRYN MUELLER, AND DIANA D. HILL Department of Biology and Earth Science, University of Central Missouri, Warrensburg, MO 64093 [email protected]

The Integrated Ocean Drilling Program is considering drilling in the Gulf of Alaska (GOA), where the interplay among climate, tectonics, and deposition can be examined. A slope site off Kayak Island, sampled by jumbo piston core (EW040885JC), is providing insight into paleoceanographic, depositional, geochemical, and climatic changes across the Pleistocene- Holocene transition, including the Bølling–Alleröd (Bø–Al) warm interval and the Younger Dryas (YD) cold interval. These intervals were determined by geochemical analyses, siliceous microfossil distributions, and isotopic analyses by various researchers. Foraminiferal biofacies also track the Bø–Al and YD intervals. Core EW040885JC contains four intervals with distinct faunal assemblages. From 1124 to 680cm core depth, samples consist of a sandy diamicton with a mixture of outer shelf taxa (Epistominella pacifica , Uvigerina, Cassidulina, Islandiella, and Cibicides), and common Elphidium clavatum, indicating transport into deep water by ice rafting and/or currents. Planktonic foraminifera are abundant and consist mainly of Neogloboquadrina pachyderma (sinistral and some dextral) and Globigerina bulloides. Two samples from a short interval (680 to 640 cm), corresponding to the Bø–Al, consist of brown, laminated calcareous ooze dominated by benthic taxa (Bolivina and Bulimina) indicative of low oxygen and a few planktonic foraminifera. Above this zone (640 to 410 cm) are bioturbated, silty muds with low abundances of Gyroidina, Bolivina, and the shelf taxa listed above, along with abundant planktic foraminifera (N. pachyderma and G. bulloides), corresponding, in part, to the YD. From 410 to the top of the core (0 cm), foraminifera are not common, with muds dominated by abundant radiolarians, diatoms, and sponge spicules. Assemblages show a change from glacially-influenced deposition, to low oxygen bottom waters, to climatic conditions favoring silica production at the top.

DEVELOPING ROBUST AGE MODELS FOR LAKE RECORDS: CASE STUDIES FROM CALIFORNIA

SUSAN R.H. ZIMMERMAN, TOM GUILDERSON, AND TOM BROWN Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, CA 94550 [email protected]

In recent years, it has become apparent that Earth‘s climate system is variable on many scales of time and space, and includes abrupt changes that have global effects. When attempting to

63 understand the relationships of decadal- to centennial-scale variability between sites and depositional environments, a ―coarse‖ age model with a handful of ages does not suffice. To better describe patterns of past drought in California, we are establishing robust, high-resolution 14C chronologies for regional lakes ranging from 34º to 42º latitude, 540 to 2,100 m elevation, and in a variety of vegetational, hydrological, geochemical, and biological settings. Almost 300 radiocarbon dates have been measured on terrestrial and aquatic macrofossils, as well as bulk sediment – macrofossil pairs. The latter have yielded no single answer to the meaning of bulk- sediment dates; in a few instances, a constant off-set is implied, but in most cases there is no pattern, reinforcing the unreliability of bulk sediment dates. As a complement to the radiocarbon measurements, some sediment sequences have also had 210Pb, 137Cs, and paleomagnetic secular variation (PSV) measurements, providing independent information to refine the age model. Construction of a robust age model from any set of measured ages requires honest recognition of uncertainties due to the reliability of individual ages and methods, differences in calendar-year calibration datasets, interpolation between discretely-dated horizons, and sources of geological variability. Calibration of radiocarbon dates to calendar years requires an internationally-accepted calibration data-set (e.g, INTCAL-09), and is relatively simple to do with programs like Calib and OxCal, but requires a rigorous propagation of errors which in reality should yield an age envelope and probability distribution. Several calibration programs contain the ability to include Bayesian statistics (priors) of the calibration curve and construct an age-model with simulated calendar uncertainties. We present examples of various methods for construction of robust, high-precision age models, and a picture of past droughts in California emerging from our lacustrine records.

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