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High resolution reconstruction of Southwest Atlantic sea-ice and its role in the climate changes of Marine Isotope Stages 3 and 2

Collins, Lewis G., Pike, Jennifer, Allen, Claire S. and Hodgson, Dominic A. 2012. High resolution reconstruction of Southwest Atlantic sea-ice and its role in the climate changes of Marine Isotope Stages 3 and 2. Paleoceanography 27 (3) , pp. 1-17. 10.1029/2011PA002264

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Abstract

[1] Recent modeling suggests that changes in Southern Ocean sea-ice extent potentially regulated the exchange of CO2release between the ocean and atmosphere during glacials. Unfortunately, a lack of high-resolution sea-ice records from the Southern Ocean has prevented detailed testing of these model-based hypotheses with field data. Here we present high-resolution records of Southern Ocean sea-ice, for the period 35–15 cal ka BP, derived from diatom assemblages measured in three glacial sediment cores forming an ∼8° transect across the Scotia Sea, southwest Atlantic. Chronological control was achieved through a novel combination of diatom abundance stratigraphy, relative geomagnetic paleointensity data, and down-core magnetic susceptibility and ice core dust correlation. Results showed that the winter sea-ice edge reached its maximum northward extent of ∼53°S, at least 3° north of its modern limit, between ∼25 and ∼23.5 cal ka BP, predating the Last Glacial Maximum (LGM). Maximum northward expansion of the summer sea-ice edge also pre-dated the LGM, advancing to at least 61°S, and possibly as far north as 55°S between ∼31 and ∼23.5 cal ka BP, a ∼12° advance from its modern position. A clear shift in the seasonal sea-ice zone is evident following summer sea-ice edge retreat at ∼23.5 cal ka BP, potentially related to austral insolation forcing. This resulted in an expanded seasonal sea-ice zone between ∼22.5 cal ka BP and deglaciation. Our field data confirm that Southern Ocean sea-ice had the physical potential to influence the carbon cycle both as a physical barrier and more importantly through the suppression of vertical mixing and cycling of pre-formed nutrients. Our data indicates that Southern Ocean sea-ice was most effective as a physical barrier between ∼31 and ∼23.5 cal ka BP and as a mechanism capable of reducing vertical mixing between ∼22.5 cal ka BP and deglaciation. However, poor correlations with atmospheric CO2 variability recorded in ice cores, particularly the lack of a CO2response during a rapid sea-ice meltback event, recorded at our study sites at the same time as Antarctic Isotopic Maximum 2, suggest that Southern Ocean sea-ice in the Scotia Sea did not play a controlling role in atmospheric CO2 variation during the glacial.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Ocean Sciences
Subjects: Q Science > QE Geology
Additional Information: Pdf uploaded in accordance with publisher's policy at http://www.sherpa.ac.uk/romeo/issn/1944-9186/ (accessed 20/02/2014).
Publisher: American Geophysical Union
ISSN: 0883-8305
Funders: NERC
Date of First Compliant Deposit: 30 March 2016
Last Modified: 04 Jun 2017 04:46
URI: http://orca.cf.ac.uk/id/eprint/44376

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