Some Palaeoecological Remarks on the Ross Sea Shelf, Antarctica

Three gravity cores collected during the austral summer 1990\u201391 in different areas of the Ross Sea continental shelf have been studied. Sedimentological, micropalaeontological and chronological data show evidence for the different evolution of the Drygalski Basin, the Joides Basin and the Cape Adare area, during the late Quaternary. The advance of glaciers during LGM is well documented in the Drygalski Basin, where a basal till testifies the presence of an ice sheet anchored on the seafloor. In contrast, a glacial marine diamicton with calcareous foraminifers in the basal part of the core collected in the Joides Basin indicates that the West Antarctic Ice Sheet was not completely grounded on the seafloor during LGM. The successive deglacial phase is more or less synchronous in both basins (about 17ka B.P.) and is documented in the overlaying units by the occurrence of well-sorted sands and foraminifer colonization. A very different sediment accumulation rate between the Drygalski and the Joides Basins is probably related to higher bioproductivity and mud accumulation in the latter during the Holocene. The Cape Adare area is a different example of environmental evolution, as shown by the presence of biogenic calcareous deposits. These deposits occur throughout the entire core, but they decrease in phase with increasing terrigenous inputs, probably during interglacial times. Within this evolution, foraminiferal and ostracod assemblages are sensitive to glacial/interglacial conditions. Their higher diversity is mainly recorded during glacial time