SOUTHERN OCEAN DEGLACIAL AND HOLOCENE CLIMATE INFERRED FROM DIATOMS

The site TN057-17 (50°S 6°E) from the Atlantic sector of the Southern Ocean is today located on the Antarctic Polar Front (APF), and therefore is in an ideal position for reconstructing past APF changes. By combining the sedimentary records of a trigger and a piston core from TN057-17, we reconstructed a high-resolution record of changes in summer sea surface temperature (SSST) and sea ice cover since the Last Glacial Maximum, based on diatom transfer functions. With 13 14C-AMS and 1 U/Th dates from both TN057-17 cores, the resulting record is capable of resolving the high-frequency deglacial and Holocene climate variability.

The record displays reduction in yearly sea ice presence from an LGM at 21.5 cal. kyr. BP. This was interrupted by a reversal between 14.5-12.5 cal. kyr. BP. Reduction commenced again into the Early Holocene. From 11 cal. kyr. BP, sea ice cover reappeared, increasing gradually to a maximum at 4.3 cal. kyr. BP. In the Late Holocene, sea ice presence has been fluctuating, but generally decreasing. Our deglaciation record correlates well with that of Vostok and Byrd ice cores, and that of core TN057-13PC4 (53°S, 5°E).

The SSST record shows a 6000-year cyclicity, with fast warming occuring at 18.5, 12.5 and 4 cal. kyr. BP. The first two warmings followed by slow (3-6 ka) cooling. A cold reversal between 13.6-12.5 cal. kyr. BP seems offset from the sea-ice record, closer to the Indian Ocean Cold Reversal. The coldest interval of the Holocene is centered at 4.3 cal. kyr. BP, a millenia later than the Neoglacial around Antarctica. Apparently, this part of the record shows more affinity to a North Atlantic record of SSST and Greenland ice core records.

The record gives evidence for an oceanic climate controlled mainly by the influence of insolation on the atmospheric circulation. This is overlain by prominent, possibly solar-driven, cycles with multicentennial- and millennial-scale periods. The hemispherical polarity of the SSST changed hemisphere to hemisphere from northern to southern hemisphere summer insolation at least 3 times since the Last Glacial Maximum, perhaps indicating a fluctuating influence of the termohaline circulation on the climate of the Southern Ocean.