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  • 11
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    Muted change in Atlantic overturning circulation over some glacial-aged Heinrich events (2014)
    Details
    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature Geoscience 7 (2014):144–150, doi:10.1038/ngeo2045.
    Beschreibung: Heinrich events - surges of icebergs into the North Atlantic Ocean - punctuated the last glacial period. The events are associated with millennial-scale cooling in the Northern Hemisphere. Freshwater from the melting icebergs is thought to have interrupted the Atlantic meridional overturning circulation, thus minimizing heat transport into the northern North Atlantic. The northward flow of warm water passes through the Florida Straits and is reflected in the distribution of seawater properties in this region. Here we investigate the northward flow through this region over the past 40,000 years using oxygen isotope measurements of benthic foraminifera from two cores on either side of the Florida Straits, which allow us to estimate water density, which is related to flow via the thermal wind relation. We infer a substantial reduction of flow during Heinrich Event 1 and the Heinrich-like Younger Dryas cooling, but little change during Heinrich Events 2 and 3, which occurred during an especially cold phase of the last glacial period. We speculate that because glacial circulation was already weakened before the onset of Heinrich Events 2 and 3, freshwater forcing had little additional effect. However, low-latitude climate perturbations were observed during all events. We therefore suggest these perturbations may not have been directly caused by changes in heat transport associated with Atlantic overturning circulation as commonly assumed.
    Beschreibung: The authors acknowledge the US National Science Foundation (OCE-0096472, OCE-0648258 and OCE-1102743), a grant from the Comer Science and Education Foundation and a Rutt Bridges Undergraduate Research Fellowship to L.G.H. for funding this work. PC acknowledges the supports from the Natural Science Foundation of China (40921004 and 40930844). S.M. was funded through the DFG Research Center/Cluster of Excellence “The Ocean in the Earth System”.
    Beschreibung: 2014-07-12
    Repository-Name: Woods Hole Open Access Server
    Materialart: Preprint
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  • 12
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    Consistently dated Atlantic sediment cores over the last 40 thousand years (2019)
    In:  EPIC3Scientific Data, 6(165), ISSN: 2052-4463
    Details
    Publikationsdatum: 2020-02-13
    Beschreibung: Rapid changes in ocean circulation and climate have been observed in marine-sediment and ice cores over the last glacial period and deglaciation, highlighting the non-linear character of the climate system and underlining the possibility of rapid climate shifts in response to anthropogenic greenhouse gas forcing. To date, these rapid changes in climate and ocean circulation are still not fully explained. One obstacle hindering progress in our understanding of the interactions between past ocean circulation and climate changes is the difficulty of accurately dating marine cores. Here, we present a set of 92 marine sediment cores from the Atlantic Ocean for which we have established age-depth models that are consistent with the Greenland GICC05 ice core chronology, and computed the associated dating uncertainties, using a new deposition modeling technique. This is the first set of consistently dated marine sediment cores enabling paleoclimate scientists to evaluate leads/lags between circulation and climate changes over vast regions of the Atlantic Ocean. Moreover, this data set is of direct use in paleoclimate modeling studies.
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , isiRev
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  • 13
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    Evidence from the Florida Straits for Younger Dryas ocean circulation changes (2011)
    American Geophysical Union
    Details
    Publikationsdatum: 2022-05-26
    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): PA1205, doi:10.1029/2010PA002032.
    Beschreibung: The waters passing through the Florida Straits today reflect both the western portion of the wind-driven subtropical gyre and the northward flow of the upper waters which cross the equator, compensating North Atlantic Deep Water export as part of the large-scale Atlantic meridional overturning circulation. It has been postulated from various lines of evidence that the overturning circulation was weaker during the Younger Dryas cold event of the last deglaciation. We show here that the contrast in the oxygen isotopic composition of benthic foraminiferal tests across the Florida Current is reduced during the Younger Dryas. This most likely reflects a decrease in the density gradient across the channel and a decrease in the vertical shear of the Florida Current. This reduced shear is consistent with the postulated reduction in the Atlantic meridional overturning circulation. We find that the onset of this change in density structure and flow at the start of the Younger Dryas is very abrupt, occurring in less than 70 years.
    Beschreibung: We thank the National Science Foundation (grants OCE‐0648258 and OCE‐0096472) and the Comer Science and Education Foundation for supporting this research. MWS was supported by a NOAA Global Change Postdoctoral Fellowship.
    Schlagwort(e): Florida Straits ; Younger Dryas ; Florida Current
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
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  • 14
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    Consistently dated Atlantic sediment cores over the last 40 thousand years (2019)
    Nature Research
    Details
    Publikationsdatum: 2022-05-26
    Beschreibung: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Waelbroeck, C., Lougheed, B. C., Riveiros, N. V., Missiaen, L., Pedro, J., Dokken, T., Hajdas, I., Wacker, L., Abbott, P., Dumoulin, J., Thil, F., Eynaud, F., Rossignol, L., Fersi, W., Albuquerque, A. L., Arz, H., Austin, W. E. N., Came, R., Carlson, A. E., Collins, J. A., Dennielou, B., Desprat, S., Dickson, A., Elliot, M., Farmer, C., Giraudeau, J., Gottschalk, J., Henderiks, J., Hughen, K., Jung, S., Knutz, P., Lebreiro, S., Lund, D. C., Lynch-Stieglitz, J., Malaize, B., Marchitto, T., Martinez-Mendez, G., Mollenhauer, G., Naughton, F., Nave, S., Nuernberg, D., Oppo, D., Peck, V., Peeters, F. J. C., Penaud, A., Portilho-Ramos, R. d. C., Repschlaeger, J., Roberts, J., Ruehlemann, C., Salgueiro, E., Goni, M. F. S., Schonfeld, J., Scussolini, P., Skinner, L. C., Skonieczny, C., Thornalley, D., Toucanne, S., Van Rooij, D., Vidal, L., Voelker, A. H. L., Wary, M., Weldeab, S., & Ziegler, M. Consistently dated Atlantic sediment cores over the last 40 thousand years. Scientific Data, 6, (2019): 165, doi:10.1038/s41597-019-0173-8.
    Beschreibung: Rapid changes in ocean circulation and climate have been observed in marine-sediment and ice cores over the last glacial period and deglaciation, highlighting the non-linear character of the climate system and underlining the possibility of rapid climate shifts in response to anthropogenic greenhouse gas forcing. To date, these rapid changes in climate and ocean circulation are still not fully explained. One obstacle hindering progress in our understanding of the interactions between past ocean circulation and climate changes is the difficulty of accurately dating marine cores. Here, we present a set of 92 marine sediment cores from the Atlantic Ocean for which we have established age-depth models that are consistent with the Greenland GICC05 ice core chronology, and computed the associated dating uncertainties, using a new deposition modeling technique. This is the first set of consistently dated marine sediment cores enabling paleoclimate scientists to evaluate leads/lags between circulation and climate changes over vast regions of the Atlantic Ocean. Moreover, this data set is of direct use in paleoclimate modeling studies.
    Beschreibung: The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Program (FP7/2007-2013 Grant agreement n° 339108). New 14C dates for cores EW9209-1JPC and V29-202 were funded by NSF OCE grants to DWO. FN, ES and AV acknowledge FCT funding support through project UID/Multi/04326/2019. We thank T. Garlan and P. Guyomard for having given us access to cores from the Service Hydrographique et Océanographique de la Marine. We acknowledge N. Smialkowski for help with formatting the data into text files, and L. Mauclair, L. Leroy and G. Isguder for the picking of numerous foraminifer samples for radiocarbon dating. We are grateful to S. Obrochta, E. Cortijo, E. Michel, F. Bassinot, J.C. Duplessy, and L. Labeyrie for advice and fruitful discussions. This paper is LSCE contribution 6572.
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
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  • 15
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    Remineralization dominating the δ13 C decrease in the mid-depth Atlantic during the last deglaciation (2021)
    Elsevier
    Details
    Publikationsdatum: 2022-10-26
    Beschreibung: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Gu, S., Liu, Z., Oppo, D. W., Lynch-Stieglitz, J., Jahn, A., Zhang, J., Lindsay, K., & Wu, L. Remineralization dominating the δ13 C decrease in the mid-depth Atlantic during the last deglaciation. Earth and Planetary Science Letters, 571, (2021): 117106, https://doi.org/10.1016/j.epsl.2021.117106.
    Beschreibung: δ 13 C records from the mid-depth Atlantic show a pronounced decrease during the Heinrich Stadial 1 (HS1), a deglacial episode of dramatically weakened Atlantic Meridional Ocean Circulation (AMOC). Proposed explanations for this mid-depth decrease include a greater fraction of δ 13 C -depleted southern sourced water (SSW), a δ 13 C decrease in the North Atlantic Deep Water (NADW) end-member, and accumulation of the respired organic carbon. However, the relative importance of these proposed mechanisms cannot be quantitatively constrained from current available observations alone. Here we diagnose the individual contributions to the deglacial Atlantic mid-depth δ 13 C change from these mechanisms using a transient simulation with carbon isotopes and idealized tracers. We find that although the fraction of the low- δ 13 C SSW increases in response to a weaker AMOC during HS1, the water mass mixture change only plays a minor role in the mid-depth Atlantic δ 13 C decrease. Instead, increased remineralization due to the AMOC-induced mid-depth ocean ventilation decrease is the dominant cause. In this study, we differentiate between the deep end-members, which are assigned to deep water regions used in previous paleoceanography studies, and the surface end-members, which are from the near-surface water defined from the physical origin of deep water masses. We find that the deep NADW end-member includes additional remineralized material accumulated when sinking from the surface (surface NADW end-member). Therefore, the surface end-members should be used in diagnosing mechanisms of changes. Furthermore, our results suggest that remineralization in the surface end-member is more critical than the remineralization along the transport pathway from the near-surface formation region to the deep ocean, especially during the early deglaciation.
    Beschreibung: This work is supported by US National Science Foundation (NSF) P2C2 projects (1401778, 1401802, and 1566432), and the National Science Foundation of China No. 41630527. S.G. is supported by Shanghai Pujiang program.
    Schlagwort(e): δ13 C ; Water mass composition ; Remineralization ; End-member ; HS1
    Repository-Name: Woods Hole Open Access Server
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  • 16
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    Seawater cadmium in the Florida Straits over the Holocene and implications for Upper AMOC variability (2022)
    American Geophysical Union
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    Publikationsdatum: 2022-08-19
    Beschreibung: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography and Paleoclimatology 37, (2022): e2021PA004379, https://doi.org/10.1029/2021pa004379.
    Beschreibung: Atlantic Meridional Overturning Circulation (AMOC) plays a central role in the global redistribution of heat and precipitation during both abrupt and longer-term climate shifts. Over the next century, AMOC is projected to weaken due to greenhouse gas warming, though projecting its future behavior is dependent on a better understanding of how AMOC changes are forced. Seeking to resolve an apparent contradiction of AMOC trends from paleorecords of the more recent past, we reconstruct seawater cadmium, a nutrient-like tracer, in the Florida Straits over the last ∼8,000 years, with emphasis on the last millennium. The gradual reduction in seawater Cd over the last 8,000 years could be due to a reduction in AMOC, consistent with cooling Northern Hemisphere temperatures and a southward shift of the Intertropical Convergence Zone. However, it is difficult to reconcile this finding with evidence for an increase in geostrophic flow through the Florida Straits over the same time period. We combine data from intermediate water depth sediment cores to extend this record into the Common Era at sufficient resolution to address the broad scale changes of this time period. There is a small decline in the Cd concentration in the Late Little Ice Age relative to the Medieval Climate Anomaly, but this change was much smaller than the changes observed over the Holocene and on the deglaciation. This suggests that any trend in the strength of AMOC over the last millennium must have been very subtle.
    Beschreibung: This work was funded by the NSF Graduate Research Fellowship DGE-1148903 (SV) and NSF grant OCE-1459563 and OCE-1851900 (JLS).
    Schlagwort(e): AMOC ; seawater cadmium ; Florida Straits ; Holocene ; Little Ice Age
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  • 17
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    World Atlas of late Quaternary Foraminiferal Oxygen and Carbon Isotope Ratios (2022)
    Copernicus GmbH
    In:  EPIC3Earth System Science Data, Copernicus GmbH, 14(6), pp. 2553-2611, ISSN: 1866-3508
    Details
    Publikationsdatum: 2022-11-02
    Beschreibung: 〈jats:p〉Abstract. We present a global atlas of downcore foraminiferal oxygen and carbon isotope ratios available at https://doi.org/10.1594/PANGAEA.936747 (Mulitza et al., 2021a). The database contains 2106 published and previously unpublished stable isotope downcore records with 361 949 stable isotope values of various planktic and benthic species of Foraminifera from 1265 sediment cores. Age constraints are provided by 6153 uncalibrated radiocarbon ages from 598 (47 %) of the cores. Each stable isotope and radiocarbon series is provided in a separate netCDF file containing fundamental metadata as attributes. The data set can be managed and explored with the free software tool PaleoDataView. The atlas will provide important data for paleoceanographic analyses and compilations, site surveys, or for teaching marine stratigraphy. The database can be updated with new records as they are generated, providing a live ongoing resource into the future. 〈/jats:p〉
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , NonPeerReviewed
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  • 18
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    Assessing the potential capability of reconstructing glacial Atlantic water masses and AMOC using multiple proxies in CESM (2020)
    Elsevier
    Details
    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 Gu, S., Liu, Z., Oppo, D. W., Lynch-Stieglitz, J., Jahn, A., Zhang, J., & Wu, L. Assessing the potential capability of reconstructing glacial Atlantic water masses and AMOC using multiple proxies in CESM. Earth and Planetary Science Letters, 541, (2020): 11629, doi:10.1016/j.epsl.2020.116294.
    Beschreibung: Reconstructing the Atlantic Meridional Overturning Circulation (AMOC) during the Last Glacial Maximum (LGM) is essential for understanding glacial-interglacial climate change and the carbon cycle. However, despite many previous studies, uncertainties remain regarding the glacial water mass distributions in the Atlantic and the AMOC intensity. Here we use an isotope enabled ocean model with multiple geotracers (δ 13 C,E Νd,231 Pa/ 230Th,δ 18 Ο and Δ 14 C) and idealized water tracers to study the potential constraints on LGM ocean circulation from multiple proxies. Our model suggests that the glacial Atlantic water mass distribution can be accurately constrained by the air-sea gas exchange signature of water masses (δ13 C AS), but E Nd might overestimate the North Atlantic Deep Water (NADW) percentage in the deep Atlantic probably because of the boundary source of Nd. A sensitivity experiment with an AMOC of similar geometry but much weaker strength suggests that the correct AMOC geometry is more important than the AMOC strength for simulating the observed glacial δ13 C AS and E Nd and distributions. The kinematic tracer 231Pa/230Th is sensitive to AMOC intensity, but the interpretation might be complicated by the AMOC geometry and AABW transport changes during the LGM. δ 18 Ο in the benthic foraminifera (δ 18 Οc) from the Florida Straits provides a consistent measure of the upper ocean boundary current in the model, which potentially provides an unambiguous method to reconstruct glacial AMOC intensity. Finally, we propose that the moderate difference between AMOC intensity at LGM and PD, if any, is caused by the competition of the responses to CO2 forcing and continental ice sheet forcing.
    Beschreibung: We thank two anonymous reviewers for their useful and constructive comments. We also thank Editor Dr Laura F. Robinson for handling the manuscript. This work is supported by National Science Foundation of China No. 41630527, US National Science Foundation (NSF) P2C2 projects (1401778, 1401802, and 1566432). We would like to acknowledge the high-performance computing support from Yellowstone (ark:/85065/d7wd3xhc) and Cheyenne (doi:10.5065/D6RX99HX) provided by NCAR's Computational and Information Systems Laboratory, sponsored by the National Science Foundation and from Center for High Performance Computing and System Simulation, Pilot National Laboratory for Marine Science and Technology (Qingdao). Data used to produce the results in this study can be obtained from HPSS at CISL: /home/sgu28/CTRACE_decadal or by contacting the authors.
    Schlagwort(e): Last Glacial Maximum ; AMOC ; Water mass ; Multi-proxy
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
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