Latitudinal shifts in the Polar Front in Indian sector of the Southern Ocean: evidences from silicoflagellate assemblage

摘要

We used silicoflagellate assemblage records to describe the polar frontal variability over the last 48kyr in the Indian sector of the Southern Ocean. The studied core was collected onboard ORV Sagar Nidhi from within the Polar frontal zone (PFZ) during the 4th Indian Scientific Expedition to Southern Ocean. The Polar front is dominated by silica-rich sediments (diatoms and silicoflagellates). Silicoflagellates were dominated by Distephanus speculum and Dictyocha fibula species. The biostratigraphic record of these silicoflagellates was used qualitatively to examine past changes in polar frontal variability in the Southern Ocean. Warming is indicated by an increase (decrease) in Dictyocha sp. (Distephanus sp.) from the LGM to the Holocene. Dictyocha sp. abundance indicates warmer temperatures during 43-45 kyr and is nearly synchronous with the warming event recorded in an Antarctic ice core. Dictyocha/ Distephanus ratio also suggests a northern and southern shift in the polar front during LGM and 43-45 kyr respectively. The southward displacement of the frontal system is linked to an increase in sea surface temperature as evidenced from the δ~(18)O Byrd Antarctic ice core data and solar insolation data. The low dust flux, higher δ18O and absence of an upwelling indicator diatom, Thallasionema nitzchoides during the Antarctic warming event also suggest stronger thermal stratification during the Antarctic warming event as compared to LGM. The present study would improve our understanding of the frontal variability under future warming scenarios.