DOCSLIB.ORG

Is Ocean Thermohaline Circulation Linked to Abrupt Stadial/Interstadial Transitions? Edward A

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Is Ocean Thermohaline Circulation Linked to Abrupt Stadial/Interstadial Transitions? Edward A Quaternary Science Reviews 19 (2000) 255}272 Is ocean thermohaline circulation linked to abrupt stadial/interstadial transitions? Edward A. Boyle Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA Abstract Are the abrupt stadial/interstadial (S/IS) climate transitions observed in the Greenland ice cores also seen in marine climate records? Literature which shows that the S/IS events have a large footprint in ocean surface marine properties encompassing the entire Northern Hemisphere has been reviewed. Whether this in#uence extends to the deepcirculation is more equivocal on most recent evidence. Several of the `Heinricha ice rafting debris events are clearly associated with elimination of North Atlantic source waters from the deepAtlantic. But most cores studied do not resolve the other S/IS events, exceptfor one new record from the Bermuda Rise which shows all of the major S/IS cycles in benthic foraminiferal. Deep-sea corals can tell us how rapid these events are in the deepsea. 1999 Elsevier Science Ltd. All rights reserved. 1. Introduction precipitation, and water vapor transport. Stommel (1961) used a simple box model to demonstrate that a convec- Paleoclimate studies of ice cores and other archives tive seawater system could have multiple stable solutions. reveal dramatic decadal}century climate transitions, Subsequent studies have employed models with a wide which raise signi"cant concerns about the predictability range of complexity and sophistication to draw the same of climate. Central Greenland ice cores show rapid re- conclusion (e.g. Marotzke, 1994; Marotzke and Willeb- gional temperature shifts of as much as a third of the full rand, 1991; Weaver and Hughes, 1994). Although it is glacial/interglacial amplitude (Grootes et al., 1993; more di$cult to prove that the real ocean has multiple Grootes and Stuiver, 1997). Several mechanisms have stable states than it is to illustrate such behavior in model been proposed to account for these rapid climate transi- systems, no one has conversely proven that these mul- tions, known as stadial/interstadial (S/IS) transitions. tiple states cannot exist in the real ocean. A large and One class of theories invokes instabilities in large conti- growing volume of theoretical work supports the notion nental ice sheets (MacAyeal, 1993a,b; Saltzman and Ver- that ocean thermohaline instabilities may have caused bitsky, 1994,1996). Another class of explanations cites the past abrupt climate changes. inherent instability of the ocean thermohaline circulation Although it is common to discuss changes in the ther- (Broecker et al., 1990; Broecker et al., 1985). Thermoha- mohaline circulation as if deep-water sources can only be line circulation instabilities may raise more concern for `ona or `o!a, the real situation is likely to be complex, predicting future climate than do ice sheet instabilities with evolutions between some range of continuum states (Broecker, 1997). Certainly, there is evidence for signi"- occurring gradually as well as through abrupt changes. cant climate change within the last 10,000 yr, a time of For example, there is paleoceanographic data indicating low ice volume (e.g. Keigwin, 1996). that Glacial North Atlantic Deep-water (DADW) did not A well-established literature has explored the mecha- vanish entirely but became a shallow water mass with net nisms responsible for ocean thermohaline circulation export from the Atlantic (Boyle and Keigwin, 1987; Du- instabilities. The fundamental reason for this instability is plessy et al., 1988; Oppo and Lehman, 1993; Yu et al., that the density of polar waters is governed strongly both 1996). Models show more complex behavior as well by temperature and salinity. Although there is a strong (Manabe and Stou!er, 1995,1997; Weaver et al., 1991; feedback between the atmospheric temperature and sea Rahmsdorf, 1995). The deep-water response may be de- surface temperature, there is essentially no feedback pendent on the character of the forcing * meltwater between the saltiness of seawater and evaporation, discharge may elicit a di!erent oceanic response than 0277-3791/99/$- see front matter 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 2 7 7 - 3 7 9 1 ( 9 9 ) 0 0 0 6 5 - 7 256 E.A. Boyle / Quaternary Science Reviews 19 (2000) 255}272 iceberg discharge. There is already evidence from modern be a relationshipbetween deep-waterand the S/IS oceanography that deep convection can change on inter- events. This evidence begins to speak to this question nannual and decadal time scales, and that spreading of amplitudes and phase relationships, but more de- velocities of pulses of deepwater formation can be sur- tailed work will be required to answer this question. This prisingly rapid (e.g., Sy et al., 1997). Although the dis- paper will conclude on a "rmly agnostic note concerning cussion below may seem to be dominated by `ona or the "nal question } do thermohaline circulation instabili- `o!a thinking, this usage is just a shorthand for what ties cause S/IS transitions or is it vice versa? This ques- clearly is a much more subtle matter, including interan- tion may well take a decade or more of research to nual and decadal changes, wave propagation within the answer. ocean (e.g. DoK scher et al., 1994), and changes to the property "elds. For the purposes of this paper, I will consider the circulation `changeda when it has persisted 3. Evidence for a link between abrupt climate change in long enough to a!ect the steady-state tracer "eld (T, S, Greenland and the sea surface chemistry), since this is the type of evidence we most commonly use in the paleoceanographic record. Numerous studies have established that there is a tight Given this strong theoretical support, it may be sur- link between events in central Greenland and character- prising that there is little observational evidence in the istics of the surface ocean. literature showing a strong link between the ocean ther- Following upon studies by Ruddiman et al. (1980) and mohaline circulation and abrupt climate transitions such Heinrich (1988), Bond et al. (1993) presented evidence as those seen in the Greenland ice cores. As it turns out, it for a one-to-one correspondence between S/IS cycles is surprisingly di$cult to "nd paleoclimatic archives in and northern North Atlantic surface temperatures at the deepsea that can establish whether or not deep-water a site near Ireland (as re#ected in the relative abund- properties are closely linked to abrupt climate transitions ance of the polar foraminifera left-coiling N. pachyderma) on decadal-to-century time scales. The major impedi- (Fig. 1). Furthermore, they called attention to the `super- ment is biological stirring of the upper few centimeters of groupa of smaller cycles that end with major episodes deep-sea sediments, which constitutes a low-pass "lter of ice rafting of glacial debris observed by Heinrich removing evidence for short-term events (given typical (1988). The identi"cation of the marine events and oceanic sedimentation rates of a few centimeters per the ice core events relies to some extent on pattern thousand years). As will be seen, the only solutions to this matching. The marine chronology } based on a few problem are: (1) to work at sites where the accumulation relatively uncertain radiocarbon ages (from the low- rate of detritus on the sea#oor is much higher than radiocarbon tail), and oxygen isotope stratigraphy based normal, (2) to work with sediments deposited under upon tuning to Milankovitch cycles } is simply too anoxic (nonbioturbated) conditions, or (3) to seek out inaccurate to show that the ice core and marine cycles are new high-resolution archives, such as deep-sea corals. precisely coeval. Furthermore, some of the cycles are This paper will review the evidence for the link between indistinct in the marine record because they occur at the the S!IS transitions seen in Greenland and the deep-sea limits of temporal resolution allowed for by the sedi- record of climate change. mentation rate and bioturbation. Nonetheless, few mar- ine paleoceanographers would doubt the Bond et al. premise that the S/IS events are re#ected in the marine 2. Some questions temperature record. Improving the accuracy and pre- cision of the chronology is a challenge for all work in this E Is there any evidence for a relationshipbetween (S/IS) "eld. transitions and the thermohaline circulation? The link between North Atlantic SST and the Green- E If so, do the amplitudes of the S/IS transitions and the land S/IS events is likely to be closer than could be thermohaline signals correspond? demonstrated in the core studied by Bond et al. Lehman E What is the detailed phase relationship between ther- and Keigwin (1992) showed that a more detailed corre- mohaline circulation and other manifestations of S/IS spondence between climate events could be seen in transitions in the earth's climate system? a higher sedimentation rate core o! Norway covering the E Who is the chicken, and what is the egg? past glacial to present. More recently, Kroon et al. (1997) have presented faunal paleotemperature evidence from I will show that there is evidence in the literature for a core on the continental margin o! Scotland (56/-10/36, links between interstadials and thermohaline circulation, 56343N, 9319W, 1320 m) for the period extending from but that this evidence is far from su$cient to establish the last glacial maximum through to the end of deglaci- a cause-and-e!ect relationship. New evidence from ation (Fig. 2). This high accumulation rate core shows Bermuda Rise sediment cores begins to "ll this gap, a strong pattern matching the submillennial details and the reader may come to believe that there may in fact of deglaciation as recorded by the Greenland isotope E.A.
Load more

Recommended publications
  • Modeling the Paleocirculation of the Mediterranean
    PALEOCEANOGRAPHY, VOL. 13, NO. 6, PAGES 586-606, DECEMBER 1998 Modeling the palcocirculation of the Mediterranean- The last glacial maximum and the Holocene with emphasis on the formation of sapropel $1 Paul G. Myers and Keith Haines Departmentof Meteorology,University of Edinburgh,Edinburgh, Scotland, United Kingdom Eelco J. Rohling Departmentof Oceanography,Southampton University, Southampton, England, United Kingdom Abstract. An ocean generalcirculation model is used to simulatethe thermohalinecirculation in the Mediter- ranean sea during the last glacial maximum and the Holocene,when the sapropel$• was deposited.The model is forced by prescribedsurface temperatures and salinities,where present-dayvalues lead to very realistic sur- face buoyancyfluxes. Differentpaleoreconstructions for the surfacesalinity and temperaturedistributions during these periods are tested. In both periods, under all reconstructions,antiestuarine flow is maintained at Gibraltar and Sicily. The Holocenecirculation has fresh intermediatewater producedin the Adriatic and an upward salt flux from the old waters below help maintain its outflow at Sicily. The depth of ventilation around the basin is broadly consistentwith the shallowestsapropel layers observed. Shoaling of the easternpycnocline occurs in all experimentsin both periods,possibly indicating enhancedproductivity, although the reasonsfor this are different in each case. 1. Introduction 1.1. The Last Glacial Maximum At the southern boundary of Europe the Mediter- The most recent Pleistoceneglaciation reached its ranean region is today generally warm, with a semi maximumat •020,000years B.P. Duringthis last glacial arid climate. The present-dayMediterranean (Figure maximum (LGM) extensiveice sheets,up to several 1) circulationis lagoonalor antiestuarine(both as a kilometersthick, coveredthe northernparts of North wholeand for eachof its main subbasins),with surface Americaand Eurasia[CrowIcy, 1988].
    [Show full text]
  • New Oceanic Proxies for Paleoclimate
    Earth and Planetary Science Letters 203 (2002) 1^13 www.elsevier.com/locate/epsl Frontiers New oceanic proxies for paleoclimate Gideon M. Henderson à Department of Earth Sciences, Oxford University, South Parks Road, Oxford OX1 3PR, UK Received 11 March 2002; received in revised form 24 June 2002; accepted 28 June 2002 Abstract Environmental variables such as temperature and salinity cannot be directly measured for the past. Such variables do, however, influence the chemistry and biology of the marine sedimentary record in a measurable way. Reconstructing the past environment is therefore possible by ‘proxy’. Such proxy reconstruction uses chemical and biological observations to assess two aspects of Earth’s climate system ^ the physics of ocean^atmosphere circulation, and the chemistry of the carbon cycle. Early proxies made use of faunal assemblages, stable isotope fractionation of oxygen and carbon, and the degree of saturation of biogenically produced organic molecules. These well-established tools have been complemented by many new proxies. For reconstruction of the physical environment, these include proxies for ocean temperature (Mg/Ca, Sr/Ca, N44Ca) and ocean circulation (Cd/Ca, radiogenic isotopes, 14C, sortable silt). For reconstruction of the carbon cycle, they include proxies for ocean productivity (231Pa/230Th, U concentration); nutrient utilization (Cd/Ca, N15N, N30Si); alkalinity (Ba/Ca); pH (N11B); carbonate ion concentration 11 13 (foraminiferal weight, Zn/Ca); and atmospheric CO2 (N B, N C). These proxies provide a better understanding of past climate, and allow climate^model sensitivity to be tested, thereby improving our ability to predict future climate change. Proxy research still faces challenges, however, as some environmental variables cannot be reconstructed and as the underlying chemistry and biology of most proxies is not well understood.
    [Show full text]
  • Climate and Deep Water Formation Regions
    Cenozoic High Latitude Paleoceanography: New Perspectives from the Arctic and Subantarctic Pacific by Lindsey M. Waddell A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Oceanography: Marine Geology and Geochemistry) in The University of Michigan 2009 Doctoral Committee: Assistant Professor Ingrid L. Hendy, Chair Professor Mary Anne Carroll Professor Lynn M. Walter Associate Professor Christopher J. Poulsen Table of Contents List of Figures................................................................................................................... iii List of Tables ......................................................................................................................v List of Appendices............................................................................................................ vi Abstract............................................................................................................................ vii Chapter 1. Introduction....................................................................................................................1 2. Ventilation of the Abyssal Southern Ocean During the Late Neogene: A New Perspective from the Subantarctic Pacific ......................................................21 3. Global Overturning Circulation During the Late Neogene: New Insights from Hiatuses in the Subantarctic Pacific ...........................................55 4. Salinity of the Eocene Arctic Ocean from Oxygen Isotope
    [Show full text]
  • Meteorology and Oceanography of the Middle East
    LIBRARY AND INFORMATION SERVICES DIVISION Current References (91-3) METEOROLOGY AND OCEANOGRAPHY OF THE MIDDLE EAST U. S. DEPARTMENT OF COMMERCE Nationa~ Oceanic and Atmospheric Administration Nationa~ Environmenta~ Sate~~ite, Data, and Information Service Nationa~ Oceanographic Data Center MARCH 1991 METEOROLOGY AND OCEANOGRAPHY OF THE MIDDLE EAST March 1991 With the outbreak of hostilities in the Arabian Gulf, there has been heightened interest in atmospheric and oceanographic data and information about the Middle East. This bibliography has been prepared to answer a wide range of questions related to this area. The bibliography is divided into five sections: I. Atmospheric Circulation page 1 II. Desalination page 7 Ill. Oceanic Circulation page 45 IV. Oil and Marine Pollution page 69 v. Data Distribution Plots page 171 The majority of the information provided in the first four parts is the result of searching the following databases: Chemical Abstracts Search Aquatic Sciences and Fisheries Abstracts Oceanic Abstracts Pollution Abstracts National Technical Information Service GeoRef Waternet Biosis Enviroline Environmental Bibliography Pascal Magazine Index New Search Newswire DOE Energy Water Resources Abstracts The citations go back as far as 1967 so as to provide a good overview of the literature and data available. Recent news ·articles have been included on the massive oil spills due to Operation Desert Storm. Data sets with information pertinent to the various subject areas (ie. Atmospheric Circulation) have been retrieved from the National Oceanographic Data Center's NEDRES database and incorporated. Questions about materials cited in the first four sections may be addressed to: NOAA Central Library Reference Desk, E/OC4 6009 Executive Boulevard Rockville, Maryland, 20852 Phone enquiries may be made to (301) 443-8330.
    [Show full text]
  • Reconstruction of Past Changes in Ocean Salinity – a Compound Specific Stable Hydrogen Isotope Approach
    Reconstruction of past changes in ocean salinity – a compound specific stable hydrogen isotope approach Sebastian Kasper ISBN 978-94-6203-839-4 Printed by Wöhrmann Print Service, Zutphen. cover image: Ocean surface salinity map from Ocean Atlas 2009 generated in Ocean Data View Reconstruction of past changes in ocean salinity – a compound specific stable hydrogen isotope approach Reconstructie van saliniteitsveranderingen van de Oceaan in het verleden – een component specifieke stabiele waterstof isotopen benadering (met een samenvatting in het Nederlands) Rekonstruktion der Salinitätveränderungen vergangener Ozeane – ein komponentenspezifischer stabiler Wasserstoff Isotopen Ansatz (mit einer Zusammenfassung in deutscher Sprache) Proefschrift ter verkrijging van de graad van doctor aan de Universiteit Utrecht op gezag van de rector magnificus, prof.dr. G.J. van der Zwaan, ingevolge het besluit van het college voor promoties in het openbaar te verdedigen op dinsdag 23 juni 2015 des avonds te 6.00 uur door Sebastian Kasper geboren op 25 september 1983 te Heinsberg, Duitsland Promotoren: Prof. dr. ir. S. Schouten Prof. dr. ir. J.S. Sinninghe Damsté Copromotor: Dr. M.T.J. van der Meer For my brothers. Table of contents Chapter 1 Introduction and general outline 7 PART I Chapter 2 Salinity changes in the Agulhas leakage area recorded by stable 19 Hydrogen isotopes of C37 alkenones during Termination I and II Chapter 3 Salinity changes in the southern Agulhas Current since the Last 35 Glacial Maximum Chapter 4 Past salinity changes in the eastern
    [Show full text]
  • Constraints on Surface Seawater Oxygen Isotope Change Between the Last Glacial Maximum and the Late Holocene
    UC Davis UC Davis Previously Published Works Title Constraints on surface seawater oxygen isotope change between the Last Glacial Maximum and the Late Holocene Permalink https://escholarship.org/uc/item/4p44s1x9 Authors Waelbroeck, C Kiefer, T Dokken, T et al. Publication Date 2014-12-01 DOI 10.1016/j.quascirev.2014.09.020 Peer reviewed eScholarship.org Powered by the California Digital Library University of California Quaternary Science Reviews 105 (2014) 102e111 Contents lists available at ScienceDirect Quaternary Science Reviews journal homepage: www.elsevier.com/locate/quascirev Constraints on surface seawater oxygen isotope change between the Last Glacial Maximum and the Late Holocene * C. Waelbroeck a, , T. Kiefer b, T. Dokken c, M.-T. Chen d, H.J. Spero e, S. Jung f, M. Weinelt g, M. Kucera h, A. Paul h, on behalf of MARGO Project Members a LSCE/IPSL, Laboratoire CNRS-CEA-UVSQ, 91198 Gif-sur-Yvette, France b PAGES International Project Office, 3012 Bern, Switzerland c Uni Research Climate and Bjerknes Centre for Climate Research, Allegaten 55, 5007 Bergen, Norway d Institute of Applied Geosciences, National Taiwan Ocean University, Keelung 20224, Taiwan e Department Earth and Planetary Sciences, University of California Davis, Davis, CA 95616, USA f Grant Institute, University of Edinburgh, Edinburgh EH9 3JW, UK g Institute for Geosciences, University of Kiel, 24098 Kiel, Germany h MARUM e Center for Marine Environmental Sciences and Department of Geosciences, University Bremen, 28334 Bremen, Germany article info abstract 18 18 Article history: Estimates of the change in surface seawater d O(d Osw) between the Last Glacial Maximum (LGM) and Received 23 May 2014 Late Holocene (LH) are derived from homogenous data sets with rigorous age control, namely MARGO Received in revised form sea surface temperature (SST) estimates and oxygen isotopic ratios (d18O) of planktonic foraminifers.
    [Show full text]
  • International Ocean Discovery Program Expedition 369 Preliminary Report
    International Ocean Discovery Program Expedition 369 Preliminary Report Australia Cretaceous Climate and Tectonics Tectonic, paleoclimate, and paleoceanographic history of high-latitude southern margins of Australia during the Cretaceous 26 September–26 November 2017 B.T. Huber, R.W. Hobbs, K.A. Bogus, and the Expedition 369 Scientists Publisher’s notes Core samples and the wider set of data from the science program covered in this report are under moratorium and accessible only to Science Party members until 25 May 2019. This publication was prepared by the JOIDES Resolution Science Operator (JRSO) at Texas A&M University (TAMU) as an account of work performed under the International Ocean Discovery Program (IODP). Funding for IODP is provided by the following international partners: National Science Foundation (NSF), United States Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan European Consortium for Ocean Research Drilling (ECORD) Ministry of Science and Technology (MOST), People’s Republic of China Korea Institute of Geoscience and Mineral Resources (KIGAM) Australia-New Zealand IODP Consortium (ANZIC) Ministry of Earth Sciences (MoES), India Coordination for Improvement of Higher Education Personnel (CAPES), Brazil Portions of this work may have been published in whole or in part in other IODP documents or publications. Disclaimer Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the participating agencies, TAMU, or Texas A&M Research Foundation. Copyright Except where otherwise noted, this work is licensed under the Creative Commons Attribution 4.0 International (CC BY 4.0) license (https://creativecommons.org/ licenses/by/4.0/).
    [Show full text]
  • VARIATIONSUS CLIVAR VARIATIONS CUS CLIVAR Lim Ity a Bil Te V Cta Ariability & Predi
    VARIATIONSUS CLIVAR VARIATIONS CUS CLIVAR lim ity a bil te V cta ariability & Predi Summer 2016 • Vol. 14, No. 3 Probing the Past for Recent natural variability of the Iceland Keys to the Future Scotland Overflows on decadal to Guest Editor: millennial timescales: Clues from the ooze K. Halimeda Kilbourne U. Maryland Center for 1 2 Environmental Science Ulysses S. Ninnemann and David J. R. Thornalley 1 The Atlantic Meridional Overturning University of Bergen and Bjerknes Centre for Climate Research, Norway Circulation (AMOC) has a profound 2University College London, United Kingdom impact on the climate system. But how AMOC has behaved in the past and how it will evolve in the future could be better addressed with longer observational records. For example multidecadal variability in Atlantic climate may be linked ow variable is the Atlantic Ocean’s Meridional Overturning Circulation (AMOC)? to AMOC intensity, but the observational record of AMOC and HThis question has become increasingly important in recent years due to the theoretically linked variables, such ocean’s influence on climate and potential impacts on future climate development. as the Inter-Tropical Convergence The northward flow of warm near-surface waters and southward flow of cooler Zone position or SST, are not long enough to establish the connection deep water comprising the AMOC redistributes a significant amount of heat within in the system. Evidence of these the Atlantic basin (Johns et al. 2011). This influences regional temperature and variables from natural archives of rainfall patterns (Enfield et al. 2001; Knight et al. 2006), including those on adjacent Earth’s past may provide a way forward without having to wait continents, and helps to ameliorate the human impacts of fossil fuel burning multiple decades or centuries for by absorbing CO2 from the atmosphere and transporting it into the deep ocean the observational record to become (Sabine et al.
    [Show full text]
  • High-Resolution Sea Surface Reconstructions Off Cape Hatteras Over the Last 10 Ka C
    High-resolution sea surface reconstructions off Cape Hatteras over the last 10 ka C. Cléroux, Maxime Debret, Elsa Cortijo, J.C. Duplessy, F. Dewilde, J. Reijmer, Nicolas Massei To cite this version: C. Cléroux, Maxime Debret, Elsa Cortijo, J.C. Duplessy, F. Dewilde, et al.. High-resolution sea surface reconstructions off Cape Hatteras over the last 10 ka. Paleoceanography, American Geophysical Union, 2012, 27 (1), pp.PA1205. 10.1029/2011PA002184. hal-00737002 HAL Id: hal-00737002 https://hal.archives-ouvertes.fr/hal-00737002 Submitted on 17 Sep 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. PALEOCEANOGRAPHY, VOL. 27, PA1205, doi:10.1029/2011PA002184, 2012 High-resolution sea surface reconstructions off Cape Hatteras over the last 10 ka Caroline Cléroux,1,2 Maxime Debret,3 Elsa Cortijo,1 Jean-Claude Duplessy,1 Fabien Dewilde,1 John Reijmer,4 and Nicolas Massei3 Received 8 June 2011; revised 6 December 2011; accepted 6 December 2011; published 9 February 2012. [1] This study presents high-resolution foraminiferal-based sea surface temperature, sea surface salinity and upper water column stratification reconstructions off Cape Hatteras, a region sensitive to atmospheric and thermohaline circulation changes associated with the Gulf Stream.
    [Show full text]
  • Paleosalinity: Confidence Limits and Future Applications
    Marine Geology 163Ž. 2000 1±11 www.elsevier.nlrlocatermargeo Letter Section Paleosalinity: confidence limits and future applications Eelco J. Rohling ) School of Ocean and Earth Science, Southampton UniÕersity, Southampton Oceanography Centre, Southampton SO14 3ZH, UK Received 7 May 1999; accepted 18 August 1999 Abstract Error propagation is investigated through the only commonly applied technique for reconstruction of paleosalinity, based on oxygen isotope residuals. Although this technique is known to be fairly inaccurate, there remained a need for thorough assessment of confidence limits in a variety of global settings. Here, it is found that a theoretical minimum error bar of between "0.3½ and 0.7½ applies to paleosalinity estimates, and that real-life practical limits are rarely better than "0.6½. Best results are expected in the latitudinal ranges )508N and )708S, taking care to avoid the sea±ice margin. Confidence intervals at low and mid-latitudesŽ. including marginal seas are very wide, at least "1.8½ for the Mediterranean and "2.2½ for the equatorial Atlantic. It appears that oxygen isotope distributions are best used in their own right to investigate circulation and advective processes in coupled ocean±atmosphere±cryosphere models, instead of calibrating them to paleosalinity to define restoring boundary conditions. However, isotope residual-based paleosalinity maps from large numbers ofŽ. regionally averaged studies in the above-mentioned latitudinal bands may help in defining initial conditions and first-order validation arguments for models. q 2000 Elsevier Science B.V. All rights reserved. Keywords: paleoceanography; stable oxygen isotopes; paleosalinity; confidence limits 1. Introduction Paleosalinity is one of the major unsolved variables in paleoceanographic studies.
    [Show full text]
  • Chapter 4, Potential for Abrupt Change in the Atlantic Meridional Overturning Circulation, Final Report, Abrupt Climate Change
    SAP 3.4: Abrupt Climate Change Chapter 4. The Potential for Abrupt Change in the Atlantic Meridional Overturning Circulation Lead Author: Thomas L. Delworth,* NOAA Geophysical Fluid Dynamics Laboratory, Princeton, NJ Contributing Authors: Peter U. Clark,* Department of Geosciences, Oregon State University, Corvallis, OR Marika Holland, NCAR, Boulder, CO William E. Johns, Rosenstiel School of Marine and Atmospheric Science, University of Miami, FL Till Kuhlbrodt, Department of Meteorology, NCAS-Climate, University of Reading, United Kingdom Jean Lynch-Stieglitz, School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA Carrie Morrill,* CIRES, University of Colorado/NOAA, Boulder, CO Richard Seager,* Columbia University, Palisades, NY Andrew J. Weaver,* School of Earth and Ocean Sciences, University of Victoria, BC, Canada Rong Zhang, NOAA Geophysical Fluid Dynamics Laboratory, Princeton, NJ * SAP 3.4 Federal Advisory Committee Member Key Findings The Atlantic Meridional Overturning Circulation (AMOC) is an important component of the Earth’s climate system, characterized by a northward flow of warm, salty water in the upper layers of the Atlantic, and a southward flow of colder water in the deep Atlantic. This ocean circulation system transports a substantial amount of heat from the Tropics and Southern Hemisphere toward the North Atlantic, where the heat is transferred to the atmosphere. Changes in this circulation have a profound impact on the global climate system, as indicated by paleoclimate records. These include, for example, changes in African and Indian monsoon rainfall, atmospheric circulation of relevance to hurricanes, and climate over North America and Western Europe. In this chapter, we have assessed 258 SAP 3.4: Abrupt Climate Change what we know about the AMOC and the likelihood of future changes in the AMOC in response to increasing greenhouse gases, including the possibility of abrupt change.
    [Show full text]
  • Eastern Pacific Warm Pool Paleosalinity and Climate Variability: 0-30 Ky
    Eastern Pacific Warm Pool paleosalinity and climate variability: 0-30 ky H. M. Benway1, A.C. Mix1, B. A. Haley2, G. P. Klinkhammer1 1. College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331 USA 2. Leibniz-Institute of Marine Sciences, IFM-GEOMAR, East Shore Campus, Kiel, GERMANY 1 Abstract Multi-proxy geologic records of δ18O and Mg/Ca in fossil foraminifera from sediments under the Eastern Pacific Warm Pool (EPWP) region west of Central America document variations in upper ocean temperature, pycnocline strength, and salinity (i.e., net precipitation) over the past 30 ky. Although evident in the paleotemperature record, there is no glacial-interglacial difference in paleosalinity, suggesting that tropical hydrologic changes do not respond passively to high-latitude ice sheets and oceans. Millennial variations in paleosalinity with amplitudes as high as ~4 PSU occur with a dominant period of ~3-5 ky during the glacial/deglacial interval and ~1.0-1.5 ky during the Holocene. The amplitude of the EPWP paleosalinity changes greatly exceeds that of published Caribbean and western tropical Pacific paleosalinity records. EPWP paleosalinity changes correspond to millennial-scale climate changes in the surface and deep Atlantic and the high northern latitudes, with generally higher (lower) paleosalinity during cold (warm) events. In addition to Intertropical Convergence Zone (ITCZ) dynamics, which play an important role in tropical hydrologic variability, changes in Atlantic-Pacific moisture transport, which is closely linked to ITCZ dynamics, may also contribute to hydrologic variations in the EPWP. Calculations of interbasin salinity average and interbasin salinity contrast between the EPWP and the Caribbean help differentiate long-term changes in mean ITCZ position and Atlantic-Pacific moisture transport, respectively.
    [Show full text]