MODELLING THE EAST ANTARCTIC CRYOSPHERE DURING THE PLIOCENE

The mid-Pliocene (~3Ma) is important for palaeoclimate reconstruction, as it was the last time in Earth history when global temperatures were significantly warmer than modern, over a period longer than any Quaternary interglacial. It is unique in that continental configurations were relatively unchanged from the modern, and geological proxies are superior to preceding warm periods, due to improved geographic distribution, biota-environment correlations and stratigraphy. Therefore, the period may represent the best available analogue for future climate change. Global Climate Models (GCMs) have been successfully run, using the USGS PRISM2 (Pliocene Research, Interpretation and Synoptic Mapping) reconstruction. The most advanced GCMs include fully coupled atmosphere, ocean, sea ice and vegetation models, however the ice sheet extent must still be prescribed.

There has been great controversy over the extent of the East Antarctic Ice Sheet (EAIS) during the Pliocene. One group of researchers claim that the Pliocene saw huge changes in East Antarctic ice volume, while the conventional view of a stable EAIS since the Miocene is upheld by others. The geological record on Antarctica is sparse, but data apparently supporting and refuting both viewpoints has been obtained, making the EAIS potentially the largest uncertainty in Pliocene palaeoclimate modelling. Thus, it is important that the extent of the EAIS during the Pliocene is tested through modelling, particularly when it has been shown that reduction in terrestrial ice sheet coverage may be the major contributing factor to the increased temperatures.

PRISM2 specifies a 33% reduction in East Antarctic ice volumes, however this is based on evidence from Pliocene palaeo-shorelines and marine benthic oxygen isotope records, both of which have large uncertainties. Outputs from fixed ice sheet GCM modelling experiments can be used to drive a three dimensional, thermomechanical ice sheet model (ISM). This will allow the validity of this supposition and other prescribed Antarctic ice sheets to be tested. Presented here are the initial results of our ice sheet modelling studies using the British Antarctic Survey ISM and the Hadley Centre GCM to simulate the equilibrium response of the Antarctic Ice Sheet to the modelled Pliocene climate, based on the PRISM2 data set.