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Melting of Larsen Ice Shelf, Antarctic Peninsula

location mapIn October 2003, a team of scientists from the UK announced in Science the results of their study of melting of the Larsen Ice Shelf, which fringes the east coast of the Antarctic Peninsula. The team are from the University of Cambridge, University College London and University of Bristol - working together with the Instituto Antártico Argentino. Episodes of ice shelf disintegration have been the subject of much scientific debate, but until 2003, neither the mechanism of ice shelf collapse nor the source of the climate warming in the area had been explained. The team's study revealed that the Larsen Ice Shelf thinned by as much as 18 m from 1992 to 2001 and that much of this was due to enhanced ocean melting.

See the press releases from: University of Cambridge and University of Bristol
which followed publication by
Andrew Shepherd, Duncan Wingham, Tony Payne and Pedro Skvarca in
Science, 2003, (31 October), Vol. 302, 856-859

and
Geophysical Research Abstracts, Vol. 5, 04113, 2003c

These papers followed presentations by the authors to the
Tenth Annual WAIS Workshop, 17-20 September 2003, Sterling VA, USA
and American Geophysical Union, Fall Meeting 2002, (abstract #C51A-0918).

From radar measurements using European Space Agency satellites, accurate to within 20 cm, the team mapped the height of the Larsen Ice Shelf surface since 1992. After accounting for the movement caused by ocean tides, the data revealed a clear pattern of surface lowering across the majority of the Larsen Ice Shelf. After eliminating other potential causes - such as increased summer melt water production - the team attributed the signal to enhanced melting at the base of the Larsen Ice Shelf.

This melting is releasing very large quantities of very cold water into the oceans and may create a disturbance affecting patterns of global ocean circulation. The team predict that in less than a hundred years the remaining Larsen Ice Shelf will thin and further sections will disintegrate and collapse.

Dr Andrew Shepherd at the Scott Polar Research Institute (SPRI), University of Cambridge, said:
"We have shown that the Larsen Ice Shelf has progressively thinned due to the combined effects of surface and basal ice melting. This previously undetected imbalance may provide a simple link between the regional climate warming and the successive disintegration of Larsen Ice Shelf sections, and suggests that fluctuations in the surrounding ocean should be considered in any future assessment of the region's climate change."

Further photos and animated movies of the Larsen Ice Shelf are available on the SPRI website.
See also earlier research by Andy Shepherd - ESA website, Frascati

Press reports

Tim Radford in The Guardian (London)
Jocelyn Kaiser in Science


COMMENT

1. Christine Hulbe, a professor at Portland State University, said the paper provides a "great measurement" of changes under way. However, she disagreed with the conclusion that ice thinning is related to the fracturing and collapse of the shelves, saying thinning could reduce the stress on the ice. The section that disintegrated in 2002 was an area where there were ponds of meltwater on the surface, Hulbe said. Areas equally thin, but without meltwater ponds didn't collapse.

She was part of an earlier team of scientists — Ted Scambos and Jennifer Bohlander of the National Snow and Ice Data Center (NSIDC) at the University of Colorado, and Mark Fahnestock of the University of Maryland which focused on the Larsen Ice Shelf following its major retreats in 1995 and 1998. Using satellite images of melt water on the ice surface and a computer simulation of the motions and forces within an ice shelf, her team demonstrated that added pressure from surface water which filled crevasses can crack through the ice entirely. See Melt-Pond Theory.

See
Journal of Glaciology, 2003, Vol. 49, No. 164, pp. 22.36
MacAyeal, D.R., Scambos, T.A., Hulbe, C.L. and Fahnestock, M.A.
Catastrophic ice-shelf break-up by an ice-shelf-fragment-capsize mechanism

and from 2001, Press Releases from NASA News, and University of Colorado;

Journal of Glaciology, 2001, Vol. 46, No. 154, pp. 516-530
Scambos, T.A., Hulbe, C., Fahnestock, M., and Bohlander, J.
The link between climate warming and break-up of ice shelves in the Antarctic Peninsula.

Scientists at NSIDC found that glaciers flowing into the Larsen B Ice Shelf accelerated immediately after a section of it collapsed early in 2002 - and they are still speeding up. See their press release.

2. Dr David Vaughan and Chris Doake of the British Antarctic Survey have reported extensively on the climate warming in the area, and have modelled shelf stresses and possible causes of breakup. They too collaborated with Skvarca, and with Austrian and German scientists, Dr. Helmut Rott and Dr. Wolfgang Rack, and conducted detailed satellite radar image studies and field studies in the area. The radar study showed ice flow increase in the years leading to break-up and an increased velocity of the glaciers as the shelves disappeared. Their radar images have provided very detalied views of the events leading up to past ice shelf collapses.

[Further comment from David Vaughan to follow.]

See:
Vaughan, D.G. and C.S.M. Doake
Recent atmospheric warming and retreat of ice shelves on the Antarctic Peninsula.
Nature, 1996, 379: 328-331.


LINKS

Recently updated information from NSIDC
View latest images of the Antarctic Ice Shelves
State of the Cryosphere: Ice Shelves


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