Pliocene Ice Sheets

Huybrechts (1993) provided the first detailed modelling investigation into Pliocene Antarctic Ice Sheets. He tackled the problem of whether the East Antarctic Ice Sheet was stable at this time, or susceptible to significant changes (both hypotheses have been developed from the geological record; see Miller and Mabin, 1998). Running a standard ice-sheet model, using the shallow-ice approximation under a selection of climate forcing parameters, Huybrechts showed that the East Antarctic Ice Sheet could withstand a mean annual temperature rise of around 10°C and that several degrees in excess of this amount of warming was required to significantly alter the ice-sheet configuration (Fig. 6.4). When the ice sheet was forced to change, it first did so predominantly across the Dome C region, where topography is lowest in East Antarctica. While the model was not used to understand the form and

Figure 6.4: Numerical modelling results of the Antarctic Ice Sheet under a variety of climate warming scenarios. Taken from Huybrechts (1993) with permission from The University of Edinburgh.

flow of the Pliocene ice sheet, it did demonstrate that even with substantial climate warming, a large semi-continental-scale ice mass was predicted. Air temperatures needed to rise by around 15°C of modern values in order to reduce the ice sheet to a series of small isolated ice caps. As such warming is unlikely for the Pliocene, Huybrechts (1993) concluded that the idea of widespread decay of ice at this time is not supported by ice-sheet modelling.

Huybrechts' results are relatively easy to replicate within a simple ice-sheet model. Siegert et al. (2005b) ran a basic shallow-ice approximation EISMINT model with a simplistic climate control. By raising the equilibrium line altitude (ELA) to 400 m above sea level (i.e. a climate warming scenario of over 15°C), the East Antarctic Ice Sheet reduced in size across the Dome C region. Further increases in the ELA resulted in the complete decay of ice at Dome C, but retention of a large ice sheet on the higher ground focused at Dome A and Ridge B.

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