Late Quaternary environmental changes and latitudinal shifts of the Antarctic Circumpolar Current as recorded by dinoflagellate cysts from offshore Chile (41°S)

The late Quaternary organic-walled dinoflagellate cyst record of Site 1233 (41 degrees S, offshore Chile) was studied with a similar to 200 year resolution spanning the last 25,000 years The study provides the first continuous record of sub-recent and recent dinoflagellate cysts in the Southeast (SE) Pacific. Major changes in the composition of the cyst association, cyst concentration and morphology of Operculodinium centrocatpum reflect changes in sea surface temperature (SST), sea surface salinity (SSS), palaeoproductivity and upwelling intensity. These changes can be associated with latitudinal shifts of the circumpolar frontal systems. The high cyst concentration, high Brigantedinium spp abundances, low species diversity and the occurrence of certain cold water species are supportive for a 7-10 degrees equatorward shift of the Antarctic Circumpolar Current (ACC) during the coldest phase of the List Glacial Maximum (LGM) between 25 and 211 cal ka BP Deglacial warming initiated at similar to 18.6 cal ka BP Termination 1(18 6-11.1 cal ka BP) is interrupted by an unstable period of extreme seasonality, rather than a cooling event, between 14.4 and 13 2 cal ka BP, synchronous with the Antarctic Cold Reversal (ACR). The Holocene Maximum is observed between 11 6 and 98 cal ka BP and is typified by the most southward position of the northern margin of the ACC A cooling phase occurred during the early Holocene (until similar to 7 cal ka BP) and during the last similar to 0 8 ka. Our data indicates that the SE Pacific (41 degrees S) climate has been influenced over the whole record by changes in the Southern Hemisphere (SH) high-latitudes, while during the mid to late Holocene, also a tropical forcing mechanism was involved, including the El Nino Southern Oscillation and the variable Hadley cell intensity Furthermore, this study showed a relationship between the variable morphology of the spines/processes of O. centrocarpum and the combined variation of sea surface salinity and temperature (SSS/SST-ratio). (C) 2010 Elsevier Ltd All rights reserved