High resolution reconstruction of Southwest Atlantic sea-ice and its role in the carbon cycle during marine isotope stages 3 and 2
Recent modeling suggests that changes in Southern Ocean sea-ice extent potentially regulated the exchange of CO2 release 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-ba...
| Published in: | Paleoceanography |
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| Main Authors: | , , , |
| Format: | Article in Journal/Newspaper |
| Language: | unknown |
| Published: |
American Geophysical Union
2012
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| Subjects: | |
| Online Access: | http://nora.nerc.ac.uk/id/eprint/16544/ http://www.agu.org/journals/pa/pa1203/2011PA002264/2011PA002264.pdf |
| Summary: | Recent modeling suggests that changes in Southern Ocean sea-ice extent potentially regulated the exchange of CO2 release 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 CO2 response during a rapid ... |
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