DEFICIENCIES IN THE DIATOM EVIDENCE FOR A PLIOCENE REDUCTION OF THE EAST ANTARCTIC ICE-SHEET

Evidence for Pliocene reduction of the East Antarctic Ice Sheet (EAIS) has been inferred from the presence of Pliocene planktic marine diato ms in tills of the Sirius Group now exposed along the slopes of the Tr ansantarctic Mountains. We highlight deficiencies in this diatom evide nce for a Pliocene reduction of the EAIS. First, we examine what diato m habitats are left behind by a retreating ice sheet, in this case the Fennoscandian Ice Sheet (FIS), and find that diatoms should occur in planktic and benthic marine, brackish water, freshwater, and terrestri al habitats. We expect that during former reexpansions, these diverse diatom assemblages were picked up by the advancing FIS and deposited i n tills. This is shown to be the case, and diatoms found in tills from Sweden and Finland reflect the many habitats over which the FIS passe d. If there was a reduction of the EAIS during the Pliocene followed b y renewed glaciation, diatoms from many different habitats should be f ound in the resulting tills of the Sirius Group. This is not the case. Only marine planktic diatoms and a few freshwater forms are reported. Similarly, vertical (downsection) distribution of diatoms in Sirius G roup and Fennoscandian tills differ. While in the Sirius Group, diatom s appear restricted to surface and near-surface sediments, in Fennosca ndia they are found throughout the tills. Such data do not support a P liocene reduction model for the EAIS.