Significant Glacier Thinning in the Larsen B Embayment, Antarctica, 2002-2006

Altimetry data derived from nine ICESat operational periods and two long-range aircraft ATM missions acquired between November 2002 and June 2006 quantify significant elevation changes for several glaciers flowing into the now-collapsed section of the Larsen B Ice Shelf. The combined elevation time series from ICESat and ATM indicates the surface height of the lower Crane Glacier where it was crossed by ICESat Track 0018, about 24 km inland from the March 17, 2002 ice edge, lowered >125 m between November 26, 2002 and October 28, 2005. Between late 2002 and late 2003, the elevation loss here was about 15 m and was about 40 m by late 2004 at this location. At the location of Track 0129, about 12 km from the March 17, 2002 ice edge, little to no elevation change occurred between November 26, 2002 and October 30, 2003 despite an adjacent about 11 km retreat in the ice edge location; this is apparently due to inland ice moving downstream rapidly to maintain the floating glacier terminus. However, between Oct. 30, 2003 and March 2, 2004, >70 m of elevation loss occurred at this point, what was a about 5 km wide glacier became a fjord, and the ice front moved a further 8 km inland. The Crane ice front has held a position near a bedrock high at about this point since late 2004 or early 2005 (Hulbe et al., GRL in review). Available ICESat Track 0137 altimetry from the adjacent Hektoria/Green/Evans glacier system, shows 40 to 50 m elevation losses over the same time period indicating that losses initially observed for the Hektoria (Scambos et al., GRL 2004) are continuing further inland. In contrast, little to no elevation change is observed for the Flask and Leppard Glaciers that are still buttressed by a shrinking remnant of the Larsen B Ice Shelf over the same time period as well as a series of smaller glaciers that likely do not flow in deep troughs. The available data is currently insufficient to resolve seasonal or dynamic variations in elevation change but these results indicate the role that ice shelf removal and associated changes in the stress field play in glacier dynamics.