Climate, CO2 and Ice Sheets - A Southern Ocean Perspective


Contact
Thomas.Ronge [ at ] awi.de

Abstract

A prominent two-step rise in atmospheric CO2 marked the end of the last glacial. The steps coincided with climatic intervals Heinrich Stadial 1 (HS1) and the Younger Dryas (YD). Records of 231Pa/230Th on sediment cores bathed by NADW, revealed a rapid reduction of the Atlantic Meridional Overturning Circulation (AMOC), during these intervals. It was argued that a weakened AMOC would have significantly reduced the efficiency of the biological pump and thus might have contributed to the rise in atmospheric CO2. Despite playing an important role, this process fails to account for the enigmatic drop in atmospheric Δ14C and δ13C during HS1 that marks the first step of the CO2-rise. Increasing CO2-concentrations with a simultaneous drop in their Δ14C, call for the ventilation of an old and 14C-depleted carbon reservoir. In this respect, several studies point to the presence of very old, 14C-depleted deep- waters in the glacial Southern Ocean, which rejuvenated during the last deglaciation. However, the accumulation of 14C-depleted, carbon-rich waters in the deep Southern Ocean requires circulation patterns that significantly differ from todays. Here we present a set of multi-proxy records to understand the evolution of the Southern Indian and the Southwest Pacific Oceans over the last 35,000 years. Our reconstructions are based on transects of four sediment cores from the South Indian and five sediment cores from the Southwest Pacific, covering the AAIW as well as the UCDW and LCDW. Our data show that throughout the last glacial the deep-water circulation of both Southern Ocean sectors weakened. This reduction favored the observed accumulation of 14C-depleted CO2 in Circumpolar Deep Waters (CDW) and allowed for the expansion of Antarctic ice sheets up to the continental shelf edge. Parallel to the HS1 increase of atmospheric CO2, the deep circulation picked up its pace and recovered toward the Holocene. This trend is in remarkable agreement with atmospheric changes in CO2, Δ14C and δ13C as well as the deglacial collapse of ice sheets. Hence, we are confident that the Southern Ocean played the dominant role in the first rise in atmospheric CO2. In addition the observed deglacial SPOC strengthening may have supported the transport of warm CDW onto the shelf areas since the timing of retreating Antarctic ice sheets is in good agreement with our recent reconstructions.



Item Type
Conference (Talk)
Authors
Divisions
Primary Division
Programs
Primary Topic
Peer revision
Not peer-reviewed
Publication Status
Published
Event Details
27'th International Polar Conference, 25 Mar 2018 - 29 Mar 2018, Rostock.
Eprint ID
46883
Cite as
Ronge, T. , Geibert, W. , Lippold, J. , Lamy, F. , Schnetger, B. , Prange, M. and Tiedemann, R. (2018): Climate, CO2 and Ice Sheets - A Southern Ocean Perspective , 27'th International Polar Conference, Rostock, 25 March 2018 - 29 March 2018 .


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