Sea ice extent and seasonality for the Early Pliocene northern Weddell Sea

Growth increment analysis coupled with stable isotopic data (δ18O/δ13C) from Early Pliocene (ca 4.7 Ma)
Austrochlamys anderssoni from shallow marine sediments of the Cockburn Island Formation, northern
Antarctic Peninsula, suggest these bivalves grew through much of the year, even during the coldest parts of
winter recorded in the shells. The high frequency fluctuation in growth increment width of A. anderssoni
appears to reflect periodic, but year-round, agitation of the water column enhancing benthic food supply
from organic detritus. This suggests that Austrochlamys favoured waters that were largely sea ice free. Our
data support interpretation of the Cockburn Island Formation as an interglacial marine deposit and the
previous hypothesis that Austrochlamys retreated from the Antarctic as sea ice extent expanded, this
transition occurring during climate cooling in the Late Pliocene.