Measuring the air content of the Larsen Ice Shelf



[1] The surface elevation of the Larsen Ice Shelf in the Antarctic Peninsula has decreased by about 0.1 meter per year since 1992. This could be caused either by an increase in the density of firn (compacted snow) at the surface of the ice shelf or by an increase in melting of ice at the base of the shelf. Attributing the observed decrease to one of these causes would help researchers to know whether atmospheric or ocean warming is affecting the ice shelf. To do this, it is necessary to know the density or air content of the firn. However, firn air content has been measurable only with labor-intensive ground-based techniques. To overcome those challenges, Holland et al. developed a new method that uses radar sounding measurements to estimate air content. Using this approach, they observed spatial variations in the air content of the shelf. Overall, they found that the air content suggested that loss of air (increased firn density) could account for the observed lowering of the surface of the ice shelf, though the result does not rule out a contribution from melting at the base of the ice shelf. (Geophysical Research Letters, doi:10.1029/2011GL047245, 2011)