Antarctic ice shelf collapse explained (2/8/2008)

When the Larsen B Ice Shelf in Antarctica collapsed in 2002, the event appeared to be a sudden response to climate change, and this long, fringing ice shelf in the north west part of the Weddell Sea was assumed to be the latest in a long line of victims of Antarctic summer heat waves linked to Global Warming.

However in a paper published in the Journal of Glaciology, Prof. Neil Glasser of Aberystwyth University, working as a Fulbright Scholar in the US, and Dr Ted Scambos of University of Colorado's National Snow and Ice Data Centre now say that the shelf was already teetering on collapse before the final summer.

"Ice shelf collapse is not as simple as we first thought," said Professor Glasser, lead author of the paper. "Because large amounts of meltwater appeared on the ice shelf just before it collapsed, we had always assumed that air temperature increases were to blame. But our new study shows that ice-shelf break up is not controlled simply by climate. A number of other atmospheric, oceanic and glaciological factors are involved. For example, the location and spacing of fractures on the ice shelf such as crevasses and rifts are very important too because they determine how strong or weak the ice shelf is".

The study is important because ice shelf collapse contributes to global sea level rise, albeit indirectly. "Ice shelves themselves do not contribute directly to sea level rise because they are floating on the ocean and they already displace the same volume of water. But when the ice shelves collapse the glaciers that feed them speed up and get thinner, so they supply more ice to the oceans," Prof. Glasser explained.

Professor Glasser acknowledges that global warming had a major part to play in the collapse, but emphasises that it is only one in a number of contributory factors, and despite the dramatic nature of the break-up in 2002, both observations by glaciologists and numerical modeling by other scientists at NASA and CPOM (Centre of Polar Observation and Modeling) had pointed to an ice shelf in distress for decades previously. "It's likely that melting from higher ocean temperatures, or even a gradual decline in the ice mass of the Peninsula over the centuries, was pushing the Larsen to the brink", said co-author Ted Scambos of University of Colorado's National Snow and Ice Data Centre.

The focus of further study is now moving to the Larsen C shelf, a much thicker and apparently more stable area, and while there are at present no signs that this shelf is likely to collapse, Professor Glasser's paper will play an important role in informing future study. The keen interest expressed in the paper has also been a boost to Professor Glasser's hopes of raising funds to travel to Antarctica this year to conduct some of his research in the field.

The Journal of Glaciology is one of the most influential journals in the field, and as a sign of its esteem for the research conducted by Professor Glasser and the team, the journal decided to 'fast-track' the paper through the publication process and give it prominence as lead article in the first edition in 2008.

Note: This story has been adapted from a news release issued by Aberystwyth University

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