From marine evidence, it is possible to deduce that significant ice-sheet growth in West Antarctica commenced during the Middle Miocene around ca. 14 Ma. In the Ross Sea and Weddell Sea regions, WAIS reached its fully glacial configuration, comparable with today, during the Late Miocene. The APIS established its present size during the later part of the Late Miocene. In the western Bellingshausen and Amundsen seas, the WAIS may not have grown to its full size until the Early Pliocene. Throughout the Late Miocene and Pliocene, WAIS and APIS repeatedly advanced across the adjacent shelves, and during the Early Pliocene, WAIS and APIS may have been more dynamic (Barker, 1995; Bart, 2001; Hepp et al., 2006). Seismic profiles from the West Antarctic continental margin suggest there was no prolonged deglaciation during the late Neogene, but these records cannot be used to determine whether or not the WAIS and APIS decreased drastically in size during short-term interglacial periods. Investigations on sedimentary records drilled at the ODP Leg 178 sites do not corroborate a significant ice volume reduction (Barker et al., 2002; Hillenbrand and Ehrmann, 2005).
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