According to recent observations the Antarctic and Greenland Ice Sheets are changing rapidly. Many qualitative ice sheet models predict that climate change will lead to collapse of the West Antarctic Ice Sheet. The effects of this may be felt worldwide by a rapid sea level rise. Two sessions, CR13 "Modelling Ice Sheets and Glaciers" and NP2.05/CR15 "Nonlinear cryospheric dynamics" discuss new quantitative insights into the behaviour of marine ice sheets. Several presentations in these sessions question these models by zooming in on processes near the grounding lines of glaciers and the effect of lubrication at their base. It seems that ice sheet theories are a step further to becoming "real".

Recent observations of enhanced change in the Antarctic and Greenland ice sheets have led to reexamination of theories of marine ice-sheet dynamics. These are important because the grounding lines (the margins of the ice-sheets where grounded ice detaches from the sea-bed to form floating ice shelves) can show advance or retreat, which has a direct and potentially significant effect upon sea-level.

Thus far, many qualitative theories have suggested instability — the large scale retreat of marine-based ice-sheets in the face of climate change — leading to an enhanced increase in sea-level. This is particularly true of the West Antarctic Ice Sheet, where some workers have suggested rapid collapse leading to a 6 m sea-level rise. However, mathematical analysis of the problem exposes extreme difficulties, which has led to a lack of quantitative sophistication in model predictions.

In session CR13 presentations by Schoof and by Hindmarsh focus on mathematical descriptions of the flow fields near the grounding line. They emphasize the acceleration produced by the large lateral forces near the grounding line. Both agree that this zone of acceleration profoundly affects the overall stability of marine ice sheets, but differ significantly on the quantitative effects.Both these authors consider simplified models of marine ice-sheets, ignoring certain contributions of forces and other aspects of ice physics. In NP2.05/CR15 presentations are made by Nowicki and Wingham and by Pattyn. Nowicki and Wingham consider all the forces, while Pattyn considers other aspects of ice-sheet physics, in particular lubrication mechanisms, dicussing their impact on marine ice-sheet stability.

Richard Hindmarsh (British Antarctic Survey):
"These represent 'real' theories of marine ice-sheet dynamics rather than at best, unbenchmarked model runs or at worst qualitative statements such as "if you get rid of an ice-shelf, the marine ice-sheet will retreat". Now we can answer more specific questions. Being theories they can predict what behaviour models should show, without the assumptions that go into models."

Participants:

Richard Hindmarsh rcah@bas.ac.uk
Christian Schoof cschoof@eos.ubc.ca
Frank Pattyn fpattyn@ulb.ac.be

Session: CR13 Modelling ice sheets and glaciers | >>programme
Session: NP2.05/CR15 Nonlinear cryospheric dynamics | >>programme