Deglacial Heat Uptake by the Southern Ocean and Rapid Northward Redistribution Via Antarctic Intermediate Water

Poggemann, David Willem; Nürnberg, Dirk; Hathorne, Ed C; Rath, Willi; Reißig, Stefan; Bahr, André

doi:10.1029/2017pa003284

Cited by 18 publications

(31 citation statements)

References 87 publications

(273 reference statements)

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“…However, during last deglaciation, colder water masses at 17-15.2 and 12.6-11.9 cal kyr BP in the North Indian Ocean seem to be inconsistent with previous studies suggesting a warming of AAIW during Heinrich Stadial 1 and Younger Dryas (Poggemann et al, 2018). This appearing discrepancy may relate to a smaller range of IWT variations in the northern Indian Ocean compared to other areas and/or to differences associated to local effects on the two areas that are very different. ]…”

Section: 1029/2019pa003801contrasting

confidence: 85%

North Indian Ocean Circulation Since the Last Deglaciation as Inferred From New Elemental Ratio Records for Benthic Foraminifera Hoeglundina elegans

Sépulcre

Bassinot

et al. 2020

Paleoceanog and Paleoclimatol

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The evolution of intermediate circulation in the northern Indian Ocean since the last deglaciation has been reconstructed from two marine cores located at intermediate depths off the southern tip of India (MD77-191) and in the northern Bay of Bengal (BoB) (MD77-176). Benthic foraminiferal δ 13 C, seawater carbonate ion concentration ([CO 3 2− ]) estimated from the Sr/Ca, and paleotemperature reconstructed on the basis of the Mg/Li of aragonite benthic species Hoeglundina elegans were used to trace the evolution of past intermediate-deepwater masses and to constrain ocean-atmosphere exchanges during the two-stage increase in atmospheric CO 2 across the last deglaciation. The intermediate water [CO 3 2− ] was mainly affected by changes in the ocean alkalinity inventory, associated with the modulation of atmospheric CO 2 on glacial-interglacial timescales. Higher benthic foraminiferal δ 13 C, depleted [CO 3 2− ], and decreased benthic-planktonic 14 C age offsets at intermediate water depths suggest a release of deep-sea CO 2 to the atmosphere through the Antarctic Intermediate Water (AAIW) in the Southern Ocean during the 17-15.2 and 12.6-10.5 cal kyr BP time intervals. In addition, the decreased H. elegans Mg/Li record seems to reflect an increased contribution of cold water mass during the 17-15.2 and 12.6-11.9 cal kyr BP intervals and throughout the Holocene. In contrast, two warm events occurred in the 15-13.3 and 11-10.3 cal kyr BP time intervals. During the late Holocene, a decrease in the intermediate water [CO 3 2−] indicates a contribution to atmospheric CO 2 rise since 8 cal kyr BP, due to the depleted global ocean alkalinity and/or the variations in surface productivity (at least for MD77-191). 2−]) is a particularly important one as it determines the seawater carbonate saturation state with respect to the calcium carbonates in the water column as well as at the seafloor. Variations in seawater [CO 3 2− ], by driving changes in the ©2020. American Geophysical Union. All Rights Reserved.

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Section: 1029/2019pa003801contrasting

confidence: 85%

North Indian Ocean Circulation Since the Last Deglaciation as Inferred From New Elemental Ratio Records for Benthic Foraminifera Hoeglundina elegans

Sépulcre

Bassinot

et al. 2020

Paleoceanog and Paleoclimatol

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“…Synchronously, the Southern Hemisphere increased the heat fluxes and reduced sea ice cover in the Southern Ocean. Thus, strong winds enhanced the upwelling and increased the northward penetration of the northward flow of AAIW/SAMW, which could increase northward transport of nutrient and heat at intermediate waters depth (Anderson et al, ; Poggemann et al, , ; Skinner et al, ). The role of AAIW is still controversial during the last deglaciation in the Atlantic Ocean, several studies suggesting a reduced northward flux of AAIW into the tropical Atlantic (e.g., Came et al, ; Gu et al, ; Howe et al, ; Xie et al, ).…”

Section: Discussionmentioning

confidence: 99%

“…The role of AAIW is still controversial during the last deglaciation in the Atlantic Ocean, several studies suggesting a reduced northward flux of AAIW into the tropical Atlantic (e.g., Came et al, 2008;Gu et al, 2017;Howe et al, 2016;Xie et al, 2012). However, other studies indicate an increased penetration of AAIW in the Atlantic Ocean (e.g., Dubois-Dauphin et al, 2016;Pahnke et al, 2008;Poggemann et al, 2017Poggemann et al, , 2018. This is also strongly supported by the intermediate records of benthic carbon isotope, ɛ Nd , and B-P age offsets from the North Indian (Bryan et al, 2010;Jung et al, 2009;Yu et al, 2018), and Pacific Ocean (e.g., Bostock et al, 2010;Mix et al, 1991;Pahnke & Zahn, 2005).…”

Section: 1029/2018gc008179mentioning

confidence: 99%

Changes in Intermediate Circulation in the Bay of Bengal Since the Last Glacial Maximum as Inferred From Benthic Foraminifera Assemblages and Geochemical Proxies

Sépulcre

Licari

et al. 2019

Geochem Geophys Geosyst

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Benthic foraminiferal assemblages and geochemical tracers (δ18O, δ13C and 14C) have been analyzed on benthic and planktonic foraminifera from core MD77‐176, located in the northern Bay of Bengal, in order to reconstruct the evolution of intermediate circulation in the northern Indian Ocean since the last glaciation. Results indicate that during the Last Glacial Maximum (LGM), Southern Sourced Water masses were dominant at the core site. A high relative abundance of intermediate and deep infaunal species during the LGM reflects low oxygen concentration and/or mesotropic to eutrophic deep water conditions, associated with depleted benthic δ13C values. During the Holocene, benthic foraminiferal assemblages indicate an oligotropic to mesotrophic environment with well‐ventilated bottom water conditions compared with LGM. Higher values for benthic foraminifera δ13C and B‐P 14C age offsets suggest an increased contribution of North Atlantic Deep Water to the northern Bay of Bengal during the Late Holocene compared to the LGM. Millennial‐scale events punctuated the last deglaciation, with a shift in the δ13C and the ɛNd values coincident with low B‐P 14C age offsets, providing strong evidence for an increased contribution of Antarctic Intermediate Water at the studied site. This was associated with enhanced upwelling in the Southern Ocean, reflecting a strong sea‐atmospheric CO2 exchange through Southern Ocean ventilation during the last deglaciation.

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“…Previous studies suggest that HS1 warming occurred in the intermediate depth (1.2–1.4 km; Marcott et al, ; Weldeab et al, ; Thiagarajan et al, ) and middepth (1.8–2.6 km; Roberts et al, ) of the North Atlantic, as well as the intermediate depth (0.6–0.85 km; Poggemann et al, ; Roberts et al, ) and deep South Atlantic (3.8 km; Roberts et al, ). However, aside from a single deep‐sea coral clumped isotope record (Thiagarajan et al, ), intermediate and deep water temperatures in these previous studies were estimated using the magnesium/calcium ratios (Mg/Ca) of benthic foraminifera.…”

Section: Introductionmentioning

confidence: 94%

Atlantic Circulation and Ice Sheet Influences on Upper South Atlantic Temperatures During the Last Deglaciation

Umling

Oppo

Chen

et al. 2019

Paleoceanog and Paleoclimatol

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Atlantic Meridional Overturning Circulation (AMOC) disruption during the last deglaciation is hypothesized to have caused large subsurface ocean temperature anomalies, but records from key regions are not available to test this hypothesis, and other possible drivers of warming have not been fully considered. Here, we present the first reliable evidence for subsurface warming in the South Atlantic during Heinrich Stadial 1, confirming the link between large-scale heat redistribution and AMOC. Warming extends across the Bølling-Allerød despite predicted cooling at this time, thus spanning intervals of both weak and strong AMOC indicating another forcing mechanism that may have been previously overlooked. Transient model simulations and quasi-conservative water mass tracers suggest that reduced northward upper ocean heat transport was responsible for the early deglacial (Heinrich Stadial 1) accumulation of heat at our shallower (~1,100 m) site. In contrast, the results suggest that warming at our deeper site (~1,900 m) site was dominated by southward advection of North Atlantic middepth heat anomalies. During the Bølling-Allerød, the demise of ice sheets resulted in oceanographic changes in the North Atlantic that reduced convective heat loss to the atmosphere, causing subsurface warming that overwhelmed the cooling expected from an AMOC reinvigoration. The data and simulations suggest that rising atmospheric CO 2 did not contribute significantly to deglacial subsurface warming at our sites.

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Deglacial Heat Uptake by the Southern Ocean and Rapid Northward Redistribution Via Antarctic Intermediate Water

Cited by 18 publications

References 87 publications

North Indian Ocean Circulation Since the Last Deglaciation as Inferred From New Elemental Ratio Records for Benthic Foraminifera Hoeglundina elegans

North Indian Ocean Circulation Since the Last Deglaciation as Inferred From New Elemental Ratio Records for Benthic Foraminifera Hoeglundina elegans

Changes in Intermediate Circulation in the Bay of Bengal Since the Last Glacial Maximum as Inferred From Benthic Foraminifera Assemblages and Geochemical Proxies

Atlantic Circulation and Ice Sheet Influences on Upper South Atlantic Temperatures During the Last Deglaciation

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