BREAKUP AND CONDITIONS FOR STABILITY OF THE NORTHERN LARSEN ICE SHELF, ANTARCTICA

The breakup of ice shelves has been widely regarded as an indicator of climate change(1), with observations around the Antarctic Peninsula h aving shown a pattern of gradual retreat, associated with regional atm ospheric warming-and increased summer melt and fracturing processes(2- 9). The rapid collapse of the northernmost section of tile Larsen Ice Shelf (Larsen A), over a few days in January 1995, indicated that, aft er retreat beyond a critical limit, ice shelves may disintegrate rapid ly. Here we use a finite-element numerical model that treats ice as a continuum without fracture(10) to examine the breakup history(2) betwe en 1986 and 1997 of the two northern sections of Larsen Ice Shelf (Lar sen A and Larsen B), from which we establish stability criteria for ic e shelves. Analysis of various ice-shelf configurations reveals charac teristic patterns in the strain rates near the ice front which we use to describe the stability of the ice shelf. On Larsen A, only the init ial and final ice-front configurations show a stable pattern. Larsen B at present exhibits a stable pattern, hut if the ice front were to re treat by a further Few kilometres, it too is Likely to enter an irreve rsible retreat phase.