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The air content of Larsen Ice Shelf

Ice sheets contain air that is trapped when fallen snow is buried and compacts into ice. The amount of air retained is determined by the rate of snowfall, the temperature of the ice, and any summertime melting that occurs. The air content of ice sheets has previously only been measurable using relatively labour-intensive ground-based techniques.

The air content of Larsen Ice Shelf, calculated from airborne radar data gathered in the 1997-98 season. The southwestern edge of the ice shelf contains up to 20 m of air in the ice column, while northeast portions of Larsen C Ice Shelf and all of Larsen B contain almost no air. The lack of air is attributed to high surface melting. Increased surface melting caused Larsen B to collapse in 2002, and the northern part of Larsen C is observed to be lowering.
The air content of Larsen Ice Shelf, calculated from airborne radar data gathered in the 1997-98 season. The southwestern edge of the ice shelf contains up to 20 m of air in the ice column, while northeast portions of Larsen C Ice Shelf and all of Larsen B contain almost no air. The lack of air is attributed to high surface melting. Increased surface melting caused Larsen B to collapse in 2002, and the northern part of Larsen C is observed to be lowering.

This paper presents a new method for deriving the air content of floating ice shelves from radio-echo sounding, allowing the use of airborne radar surveys to determine detailed maps of air content over large areas. The method is applied to data from a 1997-98 BAS-Argentine airborne survey of Larsen Ice Shelf, revealing large gradients in air content that are consistent with sparse existing ground-based measurements.

The amount of air in Larsen Ice Shelf decreases sharply from south to north, which can be explained by satellite evidence that summertime surface melting is greater in the north. Melting and refreezing of the ice surface in the north converts porous snow into solid ice, reducing the amount of air trapped in the ice shelf.

These results are of great importance because over recent decades Larsen Ice Shelf has been affected by the atmospheric warming of the Antarctic Peninsula. Larsen B Ice Shelf collapsed in 2002, and satellite observations show that the surface of Larsen C is lowering. Larsen C contained enough air in 1997-98 that increased surface melting could have caused air loss that would explain the lowering. A modern repeat of the survey could therefore determine whether Larsen C is being eroded by a warming atmosphere.

Link to the full paper in the NERC Open Research Archive


Authors

Holland, P.R., Corr, H.F.J., Pritchard, H.D., Vaughan, D.G., Arthern, R.J., Jenkins, A., Tedesco, M. 2011

Publication

Geophysical Research Letters, 38, No. 10, L10503, 6p