Middle Miocene grounding events on the Ross Sea outer continental shelf, Antarctica

Abstract

The middle Miocene δ18O enrichments from deep-sea data and eustatic sea level falls are traditionally attributed to expansion of the East Antarctic Ice Sheet. Interpretations of such data have led many to conclude that the West Antarctic Ice Sheet (WAIS) was not well-developed until the late Miocene. In such a scenario, middle Miocene glaciation on the Ross Sea shelf would have had to be minimal, perhaps in the form of ice caps, to be consistent with proxy data. New seismic-stratigraphic analysis of the Ross Sea outer continental shelf suggests that at least five grounding events (ice sheet advances into the marine environment, in contact with the sea floor) occurred in the middle Miocene. Because West Antarctica constitutes a major part of the drainage basin for the Ross Sea, these results do not support the long-standing assumption that West Antarctica was substantially ice-free, although the number of WAIS grounding events generally matches the number of extreme δ18O enrichments and eustatic lowstands. Rather, the seismic-stratigraphic evidence from the Ross Sea shelf documents waxing and waning of a well-developed WAIS in the marine environment at least on the Pacific sector of the West Antarctic continental shelf, and suggests a WAIS that was more robust in the middle Miocene than has previously been deduced from proxy data.