SUBGLACIAL DIATOMS REVEAL MIOCENE TO PLEISTOCENE HISTORY OF THE WEST ANTARCTIC ICE SHEET

Much is now known of the Miocene to Recent climatic development around Antarctica, including repeated marine ice sheet advance and retreat cycles, from ocean drilling in the Southern Ocean and along the Antarctic continental margin (notably the ANDRILL project). However, very few direct observations of West Antarctic submarine interior basins are available. Each West Antarctic Ice Sheet (WAIS) retreat results in marine productivity events characterized by deposition of diatomaceous sediments into the basins. These sediments contain a mixed and incomplete record of multiple marine events in the West Antarctic interior spanning the Cenozoic, including unequivocal evidence of Pleistocene WAIS collapse, which highlights the sensitivity of the system to past, thus future warming.

Recently, the WISSARD (Whillans Ice Stream Subglacial Access Research Drilling) science team recovered tills from two locations on the Whillans Ice Stream at Subglacial Lake Whillans (SLW) and the Whillans Grounding Zone (WGZ) along the Gould Coast of West Antarctica. These are the first sediments recovered from the West Antarctic interior since drilling by Caltech scientists in previous decades.

We report new analyses of fossil diatoms in both new and archived subglacial sediments. These analyses show that the West Antarctic interior was dominantly marine through much of the Miocene, and that episodic deposition events, representing WAIS collapse, occurred through the Pliocene and Pleistocene.

The best evidence to date for Late Pleistocene (potentially MIS-5e) collapse of the WAIS includes silt sized aggregates of Pleistocene aged marine diatoms in cores from the WGZ. In particular, the occurrence of a radiolarian that encases an assemblage of diatoms that is indistinguishable from the modern pelagic assemblages of the Southern Ocean Ooze Belt (dominated by F. kerguelensis and Thalassiothrix sp.) provides compelling evidence that these aggregates reflect primary deposition under open ocean conditions, and are not the result of sub ice-shelf water column advection.

Such evidence of a history of dynamic behavior of the WAIS highlights concerns regarding future and potentially ongoing collapse in a warming world.