Onset of Cenozoic Antarctic glaciation

Abstract

This paper considers the wide range of evidence, both direct and indirect, for the onset of Cenozoic Antarctic glaciation. It distinguishes two useful phases of Antarctic glacial onset: an initial phase of mountain glaciation, from which ice streams occasionally and in isolated locations reached sea level, and a subsequent phase of “full” glaciation, with an ice sheet as large as today's, extending everywhere to sea level. According to direct evidence, generally proximal, from the continent itself or surrounding Southern Ocean, the first of these occurred probably during the late Eocene, while the second developed at the Eocene–Oligocene boundary. Indirect evidence, mainly involving proxy measurements from DSDP and ODP sites remote from the Southern Ocean, suggests that middle and late Eocene glaciations may have been full also (ice sheets possibly even larger than today's) but short-lived, and that the E/O boundary onset differed from these mainly in producing a stable ice sheet. In pursuing the notion of glacial onset, we examined the direct record separately for East Antarctica, West Antarctica, and the Antarctic Peninsula, the different sub-ice topography and geographic positions of which suggest that their glacial histories could have been different. The direct record for an initial, middle or late Eocene phase is very sparse: only the rare occurrence of IRD at Southern Ocean DSDP and ODP sites suggests the possibility of early ice, and all three regions include mountains that could have hosted such ice. Although the indirect record and climate modelling in combination suggest that “full” glaciation of each region was probably synchronous, we find differences in the available direct evidence. There is abundant evidence that East Antarctica became fully glaciated in the earliest Oligocene, but certain evidence of glaciation of a similar age extending to sea level is sparse for the Antarctic Peninsula, and is not found until the late Oligocene for West Antarctica. High-resolution direct evidence is required to resolve uncertainties in glacial history.