Southern Ocean warming and Wilkes Land ice sheet retreat during the mid-Miocene

Observations and model experiments highlight the importance of ocean heat in forcing ice sheet retreat during the present and geological past, but past ocean temperature data are virtually missing in ice sheet proximal locations. Here we document paleoceanographic conditions and the (in)stability of the Wilkes Land subglacial basin (East Antarctica) during the mid-Miocene (~17-13.4 million years ago) by studying sediment cores from offshore Adélie Coast. Inland retreat of the ice sheet, temperate vegetation, and warm oligotrophic waters characterise the mid-Miocene Climatic Optimum (MCO; 17-14.8 Ma). After the MCO, expansion of a marine-based ice sheet occurs, but remains sensitive to melting upon episodic warm water incursions. Our results suggest that the mid-Miocene latitudinal temperature gradient across the Southern Ocean never resembled that of the present day. We demonstrate that a strong coupling of oceanic climate and Antarctic continental conditions existed and that the East Antarctic subglacial basins were highly sensitive to ocean warming.This research used samples and data from the Integrated Ocean Drilling Program (now International Ocean Discovery Program; IODP). F.S. and H.B. thank NWO (Netherlands Organisation for Scientific Research) for funding research grant NNPP 866.10.110. P.K.B. was supported through NWO-VENI project number 863.13.002. F.S. thanks the ANDRILL SMS co-chiefs Fabio Florindo and David Harwood. S.P. was supported through the U.S. Science Support Program and the National Science Foundation (OCE 1060080). U.S. acknowledges funding received from the Natural Environment Research Council (NERC Grant NE/H000984/1). R.M. acknowledges support through the Rutherford Discovery Fellowship (RDF-13- VUW-003). The work of S.S. was carried out under the program of the Netherlands Earth System Science Centre (NESSC), which is supported financially by the Ministry of Education, Culture and Science (OCW). J.P. acknowledges support through the IODP priority program of the German Research Foundation (DFG). C.E. thanks the Spanish MINECO for scientific research grant CTM2014-60451-C2-1-P co-funded by the European Union through FEDER funds. Joe Prebble is thanked for providing dinoflagellate cyst counts from surface sediment samples of the Southern Ocean