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  • Artikel  (14)
  • Mg/Ca  (4)
  • Cd/Ca  (3)
  • Coral  (3)
  • North Atlantic  (3)
  • AAIW  (1)
  • American Geophysical Union  (14)
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  • Artikel  (14)
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  • 1
    Publikationsdatum: 2022-05-25
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 2013-03-29
    Schlagwort(e): Atlantic Warm Pool ; Atlantic multidecadal variability ; Little Ice Age ; Sr/Ca ; Coral ; Sea surface temperature
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
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  • 2
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    American Geophysical Union
    Publikationsdatum: 2022-05-25
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 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
    Schlagwort(e): Arabian Sea ; Mg/Ca ; Indian monsoon
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  • 3
    Publikationsdatum: 2022-05-25
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 2012-11-12
    Schlagwort(e): Eirik Drift ; MIS 5e ; North Atlantic ; Last interglacial ; Multiproxy
    Repository-Name: Woods Hole Open Access Server
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  • 4
    Publikationsdatum: 2022-05-25
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 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.
    Schlagwort(e): Okinawa Trough ; Deglaciation ; Holocene ; Kuroshio Current ; East Asian monsoon ; Mg/Ca ; Oxygen isotopes ; Foraminifera
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  • 5
    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 23 (2008): PA1217, doi:10.1029/2007PA001450.
    Beschreibung: Benthic foraminiferal Cd/Ca from a Florida Current sediment core documents the history of the northward penetration of southern source waters within the surface return flow of the Atlantic meridional overturning circulation (AMOC). Cd seawater estimates (CdW) indicate that intermediate-depth southern source waters crossed the equator and contributed to the Florida Current during the Bølling-Allerød warm period of the last deglaciation, consistent with evidence of only a modest AMOC reduction compared to today. The CdW estimates also provide the first paleoceanographic evidence of a reduction in the influence of intermediate-depth southern source waters within the Florida Current during the Younger Dryas, a deglacial cold event characterized by a weak North Atlantic AMOC. Our results reveal a close correspondence between the northward penetration of intermediate-depth southern source waters and the influence of North Atlantic Deep Water, suggesting a possible link between intermediate-depth southern source waters and the strength of the Atlantic AMOC.
    Beschreibung: This work was funded by the NSF and the WHOI Ocean and Climate Change Institute.
    Schlagwort(e): Meridional overturning ; Cd/Ca ; Younger Dryas
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  • 6
    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 23 (2008): PA3102, doi:10.1029/2007PA001572.
    Beschreibung: We analyzed strontium/calcium ratios (Sr/Ca) in four colonies of the Atlantic coral genus Montastrea with growth rates ranging from 2.3 to 12.6 mm a−1. Derived Sr/Ca–sea surface temperature (SST) calibrations exhibit significant differences among the four colonies that cannot be explained by variations in SST or seawater Sr/Ca. For a single coral Sr/Ca ratio of 8.8 mmol mol−1, the four calibrations predict SSTs ranging from 24.0° to 30.9°C. We find that differences in the Sr/Ca–SST relationships are correlated systematically with the average annual extension rate (ext) of each colony such that Sr/Ca (mmol mol−1) = 11.82 (±0.13) – 0.058 (±0.004) × ext (mm a−1) – 0.092 (±0.005) × SST (°C). This observation is consistent with previous reports of a link between coral Sr/Ca and growth rate. Verification of our growth-dependent Sr/Ca–SST calibration using a coral excluded from the calibration reconstructs the mean and seasonal amplitude of the actual recorded SST to within 0.3°C. Applying a traditional, nongrowth-dependent Sr/Ca–SST calibration derived from a modern Montastrea to the Sr/Ca ratios of a conspecific coral that grew during the early Little Ice Age (LIA) (400 years B.P.) suggests that Caribbean SSTs were 〉5°C cooler than today. Conversely, application of our growth-dependent Sr/Ca–SST calibration to Sr/Ca ratios derived from the LIA coral indicates that SSTs during the 5-year period analyzed were within error (±1.4°C) of modern values.
    Beschreibung: This work was funded by National Science Foundation (NSF) grant OCE- 0402728, the WHOI Ocean and Climate Change Institute, and an NSF Graduate Student Fellowship.
    Schlagwort(e): Coral ; Strontium/calcium ; Growth rate
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  • 7
    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 26 (2011): PA2206, doi:10.1029/2010PA002038.
    Beschreibung: Western subtropical North Atlantic oceanic and atmospheric circulations connect tropical and subpolar climates. Variations in these circulations can generate regional climate anomalies that are not reflected in Northern Hemisphere averages. Assessing the significance of anthropogenic climate change at regional scales requires proxy records that allow recent trends to be interpreted in the context of long-term regional variability. We present reconstructions of Gulf Stream sea surface temperature (SST) and hydrographic variability during the past two millennia based on the magnesium/calcium ratio and oxygen isotopic composition of planktic foraminifera preserved in two western subtropical North Atlantic sediment cores. Reconstructed SST suggests low-frequency variability of ∼1°C during an interval that includes the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). A warm interval near 1250 A.D. is distinct from regional and hemispheric temperature, possibly reflecting regional variations in ocean-atmosphere heat flux associated with changes in atmospheric circulation (e.g., the North Atlantic Oscillation) or the Atlantic Meridional Overturning Circulation. Seawater δ 18O, which is marked by a fresher MCA and a more saline LIA, covaries with meridional migrations of the Atlantic Intertropical Convergence Zone. The northward advection of tropical salinity anomalies by mean surface currents provides a plausible mechanism linking Carolina Slope and tropical Atlantic hydrology.
    Beschreibung: This study was supported by the Woods Hole Oceanographic Institution’s Ocean and Climate Change Institute (OCCI) and by the National Science Foundation.
    Schlagwort(e): North Atlantic ; Regional paleoclimate ; LIA ; MCA ; NAO
    Repository-Name: Woods Hole Open Access Server
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  • 8
    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Geophysical Union, 2003. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 18 (2003): 1086, doi:10.1029/2003PA000888.
    Beschreibung: Benthic foraminiferal Cd/Ca from an intermediate depth, western South Atlantic core documents the history of southward penetration of North Atlantic Intermediate Water (NAIW). Cd seawater estimates (CdW) for the last glacial are consistent with the production of NAIW and its export into the South Atlantic. At ∼14.5 ka concurrently with the onset of the Bølling-Allerød to Younger Dryas cooling, the NAIW contribution to the South Atlantic began to decrease, marking the transition from a glacial circulation pattern to a Younger Dryas circulation. High CdW in both the deep North Atlantic and the intermediate South Atlantic imply reduced export of deep and intermediate water during the Younger Dryas and a significant decrease in northward oceanic heat transport. A modern circulation was achieved at ∼9 ka, concurrently with the establishment of Holocene warmth in the North Atlantic region, further supporting a close linkage between deepwater variability and North Atlantic climate.
    Beschreibung: This work was supported by an MIT John Lyons Fellowship, a WHOI Ocean and Climate Change Institute Fellowship, and NSF grant OCE96-33499.
    Schlagwort(e): Cd/Ca ; δ13C ; Younger Dryas ; Intermediate water ; Foraminifera
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  • 9
    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 26 (2011): PA3219, doi:10.1029/2011PA002132.
    Beschreibung: Shell chemistry of planktic foraminifera and the alkenone unsaturation index in 69 surface sediment samples in the tropical eastern Indian Ocean off West and South Indonesia were studied. Results were compared to modern hydrographic data in order to assess how modern environmental conditions are preserved in sedimentary record, and to determine the best possible proxies to reconstruct seasonality, thermal gradient and upper water column characteristics in this part of the world ocean. Our results imply that alkenone-derived temperatures record annual mean temperatures in the study area. However, this finding might be an artifact due to the temperature limitation of this proxy above 28°C. Combined study of shell stable oxygen isotope and Mg/Ca ratio of planktic foraminifera suggests that Globigerinoides ruber sensu stricto (s.s.), G. ruber sensu lato (s.l.), and G. sacculifer calcify within the mixed-layer between 20 m and 50 m, whereas Globigerina bulloides records mixed-layer conditions at ∼50 m depth during boreal summer. Mean calcifications of Pulleniatina obliquiloculata, Neogloboquadrina dutertrei, and Globorotalia tumida occur at the top of the thermocline during boreal summer, at ∼75 m, 75–100 m, and 100 m, respectively. Shell Mg/Ca ratios of all species show a significant correlation with temperature at their apparent calcification depths and validate the application of previously published temperature calibrations, except for G. tumida that requires a regional Mg/Ca-temperature calibration (Mg/Ca = 0.41 exp (0.068*T)). We show that the difference in Mg/Ca-temperatures of the mixed-layer species and the thermocline species, particularly between G. ruber s.s. (or s.l.) and P. obliquiloculata, can be applied to track changes in the upper water column stratification. Our results provide critical tools for reconstructing past changes in the hydrography of the study area and their relation to monsoon, El Niño-Southern Oscillation, and the Indian Ocean Dipole Mode.
    Beschreibung: This project was funded by the German Ministry of Education and Research (BMBF project PABESIA) and the “Deutsche Forschungsgemeinschaft” (DFG project HE 3412/15–1).
    Schlagwort(e): Indian Ocean ; Mg/Ca ; Alkenone ; Oxygen isotopes ; Planktic foraminifera ; Thermal structure
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
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  • 10
    Publikationsdatum: 2022-10-26
    Beschreibung: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Spooner, P. T., Thornalley, D. J. R., Oppo, D. W., Fox, A. D., Radionovskaya, S., Rose, N. L., Mallett, R., Cooper, E., & Roberts, J. M. Exceptional 20th century ocean circulation in the Northeast Atlantic. Geophysical Research Letters, 47(10), (2020): e2020GL087577, doi:10.1029/2020GL087577.
    Beschreibung: The North Atlantic subpolar gyre (SPG) connects tropical and high‐latitude waters, playing a leading role in deep‐water formation, propagation of Atlantic water into the Arctic, and as habitat for many ecosystems. Instrumental records spanning recent decades document significant decadal variability in SPG circulation, with associated hydrographic and ecological changes. Emerging longer‐term records provide circumstantial evidence that the North Atlantic also experienced centennial trends during the 20th century. Here, we use marine sediment records to show that there has been a long‐term change in SPG circulation during the industrial era, largely during the 20th century. Moreover, we show that the shift and late 20th century SPG configuration were unprecedented in the last 10,000 years. Recent SPG dynamics resulted in an expansion of subtropical ecosystems into new habitats and likely also altered the transport of heat to high latitudes.
    Beschreibung: We thank Janet Hope and UCL laboratory staff, colleagues who sailed on EN539, Kathryn Pietro‐Rose, Sean O'Keefe and Henry Abrams, Sara Chipperton, Tanya Monica, Laura Thrower and Kitty Green for sediment processing, Miles Irving for artwork assistance, James Rolfe for nitrogen isotope measurement, Maryline Vautravers and Michael Kucera for guidance, Arne Biastoch and Christian Mohn for discussion of VIKING20, and Chris Brierley, Meric Srokosz, and Jon Robson for comments. Funding was provided by National Science Foundation (NSF) grant OCE‐1304291 to D.W.O. and D.J.R.T., the Leverhulme Trust, National Environment Research Council (NERC) grant NE/S009736/1, and the ATLAS project to D.J.R.T. This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement 678760 (ATLAS). This paper reflects only the authors views and the European Union cannot be held responsible for any use that may be made of the information contained herein.
    Schlagwort(e): Foraminifera ; Subpolar gyre ; North Atlantic ; Ocean circulation ; Industrial era
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
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