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  • American Geophysical Union  (26)
  • Nature Publishing Group  (2)
  • Geological Society of America (GSA)  (1)
  • 1
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 422 (2003), S. 277-277 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The conversion of surface water to deep water in the North Atlantic results in the release of heat from the ocean to the atmosphere, which may have amplified millennial-scale climate variability during glacial times and could even have contributed to the past 11,700 years of relatively mild ...
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2012-07-01
    Description: Paleoclimate evidence from South America and Asia has been interpreted to indicate that tropical rainfall migrated southward during the Northern Hemisphere cooling associated with Heinrich stadial 1 (HS1), an event of massive iceberg discharge to the North Atlantic ca. 18–15 ka. Although arid conditions associated with such a shift are well documented in southern Asia, as far south as Borneo, debate still exists regarding the precipitation response in southern Indonesia and Australia during HS1. This study utilizes concentrations of the long-lived nuclide 232Th as a proxy for detrital riverine input and 230Th normalization to estimate the history of preserved fluxes reaching the seafloor in the Flores Sea, located between southern Sulawesi and the Lesser Sunda Islands, Indonesia. Because the only source of 232Th to the ocean is continental minerals, this proxy is a robust indicator of continental weathering. The 230Th normalized burial fluxes of lithogenic and biogenic matter demonstrate that both detrital and biogenic fluxes in the Flores Sea were higher during HS1 than any other period in the past 22 k.y. High detrital fluxes indicate enhanced precipitation runoff from surrounding landmasses during a period of maximum southward shift of the Intertropical Convergence Zone. This study further constrains the northern limit of enhanced rainfall associated with a southward shift of Australian monsoon-related rainfall at the time of HS1 and highlights the value of 232Th as a proxy of continental input to deep-sea sediment records.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
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  • 3
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 27 (2012): PA3231, doi:10.1029/2012PA002313.
    Description: Accurate low-latitude sea surface temperature (SST) records that predate the instrumental era are needed to put recent warming in the context of natural climate variability and to evaluate the persistence of lower frequency climate variability prior to the instrumental era and the possible influence of anthropogenic climate change on this variability. Here we present a 235-year-long SST reconstruction based on annual growth rates (linear extension) of three colonies of the Atlantic coral Siderastrea siderea sampled at two sites on the northeastern Yucatan Peninsula, Mexico, located within the Atlantic Warm Pool (AWP). AWP SSTs vary in concert the Atlantic Multidecadal Oscillation (AMO), a basin-wide, quasiperiodic (∼60–80 years) oscillation of North Atlantic SSTs. We demonstrate that the annual linear growth rates of all three coral colonies are significantly inversely correlated with SST. We calibrate annual linear growth rates to SST between 1900 and 1960 AD. The linear correlation coefficient over the calibration period is r = −0.77 and −0.66 over the instrumental record (1860–2008 AD). We apply our calibration to annual linear growth rates to extend the SST record to 1775 AD and show that multidecadal SST variability has been a persistent feature of the AWP, and likely, of the North Atlantic over this time period. Our results imply that tropical Atlantic SSTs remained within 1°C of modern values during the past 225 years, consistent with a previous reconstruction based on coral growth rates and with most estimates based on the Mg/Ca of planktonic foraminifera from marine sediments.
    Description: Funding was provided by a scholarship to L.F.V.B. from ‘Consejo Nacional de Ciencia y Tecnología’ (CONACyT-Mexico), by CONACyT projects 104358 and 23749 to P.B., and by NSF OCE-0926986 to A.L.C. and D.W.O.
    Description: 2013-03-29
    Keywords: Atlantic Warm Pool ; Atlantic multidecadal variability ; Little Ice Age ; Sr/Ca ; Coral ; Sea surface temperature
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 4
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 21 (2006): PA1014, doi:10.1029/2005PA001162.
    Description: Sea surface temperature (SST) and seawater δ18O (δ18Ow) were reconstructed in a suite of sediment cores from throughout the Arabian Sea for four distinct time intervals (0 ka, 8 ka, 15 ka, and 20 ka) with the aim of understanding the history of the Indian Monsoon and the climate of the Arabian Sea region. This was accomplished through the use of paired Mg/Ca and δ18O measurements of the planktonic foraminifer Globigerinoides ruber. By analyzing basin-wide changes and changes in cross-basinal gradients, we assess both monsoonal and regional-scale climate changes. SST was colder than present for the majority of sites within all three paleotime slices. Furthermore, both the Indian Monsoon and the regional Arabian Sea mean climate have varied substantially over the past 20 kyr. The 20 ka and 15 ka time slices exhibit average negative temperature anomalies of 2.5°–3.5°C attributable, in part, to the influences of glacial atmospheric CO2 concentrations and large continental ice sheets. The elimination of the cross-basinal SST gradient during these two time slices likely reflects a decrease in summer monsoon and an increase in winter monsoon strength. Changes in δ18Ow that are smaller than the δ18O signal due to global ice volume reflect decreased evaporation and increased winter monsoon mixing. SSTs throughout the Arabian Sea were still cooler than present by an average of 1.4°C in the 8 ka time slice. These cool SSTs, along with lower δ18Ow throughout the basin, are attributed to stronger than modern summer and winter monsoons and increased runoff and precipitation. The results of this study underscore the importance of taking a spatial approach to the reconstruction of processes such as monsoon upwelling.
    Description: Analyses were funded by a SGER grant from the NSF (OCE03–34598). Funding was also provided by a Schlanger Ocean Drilling Program Fellowship (to K.A.D.) and NSF Grant OCE02–20776 (to D.W.O.). 16
    Keywords: Arabian Sea ; Mg/Ca ; Indian monsoon
    Repository Name: Woods Hole Open Access Server
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  • 5
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 7 (2006): Q10N03, doi:10.1029/2005GC001226.
    Description: The geostrophic shear associated with the meridional overturning circulation is reflected in the difference in density between the eastern and western margins of the ocean basin. Here we examine how the density difference across 30°S in the upper 2 km of the Atlantic Ocean (and thus the magnitude of the shear associated with the overturning circulation) has changed between the last glacial maximum and the present. We use oxygen isotope measurements on benthic foraminifera to reconstruct density. Today, the density in upper and intermediate waters along the eastern margin in the South Atlantic is greater than along the western margin, reflecting the vertical shear associated with the northward flow of surface and intermediate waters and the southward flowing North Atlantic Deep Waters below. The greater density along the eastern margin is reflected in the higher δ 18O values for surface sediment benthic foraminifera than those found on the western margin for the upper 2 km. For the last glacial maximum the available data indicate that the eastern margin foraminifera had similar δ 18O to those on the western margin between 1 and 2 km and that the gradient was reversed relative to today with the higher δ 18O values in the western margin benthic foraminifera above 1 km. If this reversal in benthic foraminifera δ 18O gradient reflects a reversal in seawater density gradient, these data are not consistent with a vigorous but shallower overturning cell in which surface waters entering the Atlantic basin are balanced by the southward export of Glacial North Atlantic Intermediate Water.
    Description: This work was supported by NSF award OCE-9984989/OCE-0428803 to J.L.-S., NSF award OCE-9986748 to D.W.O. and W.B.C., NSF OCE-0222111 to C.D.C., and SEGRF fellowship at LLNL to J.M.
    Keywords: Last Glacial Maximum ; South Atlantic ; Meridional overturning circulation ; Oxygen isotopes ; Benthic foraminifera
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: 994101 bytes
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  • 6
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 36 (2009): L11703, doi:10.1029/2009GL038677.
    Description: Proxy reconstructions and model simulations suggest that steeper interhemispheric sea surface temperature (SST) gradients lead to southerly Intertropical Convergence Zone (ITCZ) migrations during periods of North Atlantic cooling, the most recent of which was the Little Ice Age (LIA; ∼100–450 yBP). Evidence suggesting low-latitude Atlantic cooling during the LIA was relatively small (〈1°C) raises the possibility that the ITCZ may have responded to a hemispheric SST gradient originating in the extratropics. We use an atmospheric general circulation model (AGCM) to investigate the relative influence of low-latitude and extratropical SSTs on the meridional position of the ITCZ. Our results suggest that the ITCZ responds primarily to local, low-latitude SST anomalies and that small cool anomalies (〈0.5°C) can reproduce the LIA precipitation pattern suggested by paleoclimate proxies. Conversely, even large extratropical cooling does not significantly impact low-latitude hydrology in the absence of ocean-atmosphere interaction.
    Description: This work was supported by NSF grants OCE 0623364 and ATM 033746 as well as the student research fund of MIT’s Department of Earth, Atmospheric and Planetary Science.
    Keywords: Climate ; ITCZ ; Little Ice Age
    Repository Name: Woods Hole Open Access Server
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  • 7
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 20 (2005): PA3009, doi:10.1029/2004PA001091.
    Description: Similar orbital geometry and greenhouse gas concentrations during marine isotope stage 11 (MIS 11) and the Holocene make stage 11 perhaps the best geological analogue period for the natural development of the present interglacial climate. Results of a detailed study of core MD01-2443 from the Iberian margin suggest that sea surface conditions during stage 11 were not significantly different from those observed during the elapsed portion of the Holocene. Peak interglacial conditions during stage 11 lasted nearly 18 kyr, indicating a Holocene unperturbed by human activity might last an additional 6–7 kyr. A comparison of sea surface temperatures (SST) derived from planktonic foraminifera for all interglacial intervals of the last million years reveals that warm temperatures during peak interglacials MIS 1, 5e, and 11 were higher on the Iberian margin than during substage 7e and most of 9e. The SST results are supported by heavier δ18O values, particularly during 7e, indicating colder SSTs and a larger residual ice volume. Benthic δ13C results provide evidence of a strong influence of North Atlantic Deep Water at greater depths than present during MIS 11. The progressive ocean climate deterioration into the following glaciation is associated with an increase in local upwelling intensity, interspersed by periodic cold episodes due to ice-rafting events occurring in the North Atlantic.
    Description: This work was partially undertaken in association with the ‘‘POP Project,’’ EC grant EVK2-2000-00089. Funding for L.A. was provided by the Portuguese Foundation for Science and Technology under the fellowship contract SFRH/BPD/1588/2000 and by the Calouste Gulbenkian Foundation, through a visiting fellowship to Woods Hole Oceanographic Institution.
    Keywords: Stage 11 ; Interglacials ; Planktonic foraminifera ; Stable isotopes ; Western Iberian margin ; Eastern North Atlantic
    Repository Name: Woods Hole Open Access Server
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  • 8
    Publication Date: 2022-05-25
    Description: © Macmillan Publishers Limited, 2011. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nature Communications 2 (2011): 293, doi:10.1038/ncomms1297.
    Description: The relative importance of north–south migrations of the intertropical convergence zone (ITCZ) versus El Niño-Southern Oscillation and its associated Pacific Walker Circulation (PWC) variability for past hydrological change in the western tropical Pacific is unclear. Here we show that north–south ITCZ migration was not the only mechanism of tropical Pacific hydrologic variability during the last millennium, and that PWC variability profoundly influenced tropical Pacific hydrology. We present hydrological reconstructions from Cattle Pond, Dongdao Island of the South China Sea, where multi-decadal rainfall and downcore grain size variations are correlated to the Southern Oscillation Index during the instrumental era. Our downcore grain size reconstructions indicate that this site received less precipitation during relatively warm periods, AD 1000–1400 and AD 1850–2000, compared with the cool period (AD 1400–1850). Including our new reconstructions in a synthesis of tropical Pacific records results in a spatial pattern of hydrologic variability that implicates the PWC.
    Description: This work was supported by the Natural Science Foundation of China (NSFC) (40730107) and the Major State Basic Research Development Program of China (973 Program) (No.2010CB428902). DWO acknowledges support from the US NSF.
    Repository Name: Woods Hole Open Access Server
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  • 9
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 27 (2012): PA2207, doi:10.1029/2011PA002244.
    Description: At the peak of the previous interglacial period, North Atlantic and subpolar climate shared many features in common with projections of our future climate, including warmer-than-present conditions and a diminished Greenland Ice Sheet (GIS). Here we portray changes in North Atlantic hydrography linked with Greenland climate during Marine Isotope Stage (MIS) 5e using (sub)centennially sampled records of planktonic foraminiferal isotopes and assemblage counts and ice-rafted debris counts, as well as modern analog technique and Mg/Ca-based paleothermometry. We use the core MD03-2664 recovered from a high accumulation rate site (∼34 cm/kyr) on the Eirik sediment drift (57°26.34′N, 48°36.35′W). The results indicate that surface waters off southern Greenland were ∼3–5°C warmer than today during early MIS 5e. These anomalously warm sea surface temperatures (SSTs) prevailed until the isotopic peak of MIS 5e when they were interrupted by a cooling event beginning at ∼126 kyr BP. This interglacial cooling event is followed by a gradual warming with SSTs subsequently plateauing just below early MIS 5e values. A planktonic δ18O minimum during the cooling event indicates that marked freshening of the surface waters accompanied the cooling. We suggest that switches in the subpolar gyre hydrography occurred during a warmer climate, involving regional changes in freshwater fluxes/balance and East Greenland Current influence in the study area. The nature of these hydrographic transitions suggests that they are most likely related to large-scale circulation dynamics, potentially amplified by GIS meltwater influences.
    Description: This work is a contribution of the European Science Foundation EuroMARC program, through the AMOCINT project, funded through grants from the Research Council of Norway (RCN) and contributes to EU-FP7 IP Past4Future. N. Irvalı was additionally funded by an ESF EUROCORES Short-term Visit grant and a RCN Leiv Eiriksson mobility grant to support research stays at the University of Edinburgh, UK, and Woods Hole Oceanographic Institution, USA, respectively, during which parts of the data for this paper were acquired. U. Ninnemann was funded by a University of Bergen Meltzer research grant.
    Description: 2012-11-12
    Keywords: Eirik Drift ; MIS 5e ; North Atlantic ; Last interglacial ; Multiproxy
    Repository Name: Woods Hole Open Access Server
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  • 10
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 20 (2005): PA4005, doi:10.1029/2004PA001061.
    Description: Detailed deglacial and Holocene records of planktonic δ18O and Mg/Ca–based sea surface temperature (SST) from the Okinawa Trough suggest that at ∼18 to 17 thousand years before present (kyr B.P.), late spring/early summer SSTs were approximately 3°C cooler than today, while surface waters were up to 1 practical salinity unit saltier. These conditions are consistent with a weaker influence of the summer East Asian Monsoon (EAM) than today. The timing of suborbital SST oscillations suggests a close link with abrupt changes in the EAM and North Atlantic climate. A tropical influence, however, may have resulted in subtle decoupling between the North Atlantic and the Okinawa Trough/EAM during the deglaciation. Okinawa Trough surface water trends in the Holocene are consistent with model simulations of an inland shift of intense EAM precipitation during the middle Holocene. Millennial-scale alternations between relatively warm, salty conditions and relatively cold, fresh conditions suggest varying influence of the Kuroshio during the Holocene.
    Description: Funding for this research was provided by NSFC (grants 40106006 and 40206007), SKLLQG (grant LLQG0204), and the NSF (OCE-020776 to DWO). Y.S.'s visit to WHOI was supported via a NSF START Fellowship.
    Keywords: Okinawa Trough ; Deglaciation ; Holocene ; Kuroshio Current ; East Asian monsoon ; Mg/Ca ; Oxygen isotopes ; Foraminifera
    Repository Name: Woods Hole Open Access Server
    Type: Article
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