Rapid dynamic thinning events during 1985-2010 on Upernavik Isstrøm, West Greenland:C21C-04

Many glaciers along the southeast and northwest coast of Greenland have accelerated, increasing the ice sheet's contribution to global sea-level rise. Here, we map elevation changes on Upernavik Isstrøm (UI), West Greenland, during 2003-2009 using high-resolution Ice, Cloud and land Elevation Satellite (ICESat) laser altimeter data supplemented with altimeter surveys from NASA's Airborne Topographic Mapper (ATM) during 2002-2010. To assess thinning prior to 2002, we analyze aerial photographs from 1985. We document at least two distinct ice loss events characterized by rapid dynamic thinning, increased ice speed, and a retreat of the calving front. The most recent event coincides with the speedup of several glaciers along the northwest coast of Greenland in 2005, and with changes in the rate of mass loss observed using data from the Gravity Recovery and Climate Experiment (GRACE) satellite gravity mission. The first event of increased ice loss could have also taken place along the extended northwest coast. The total dynamic induced ice volume loss on the frontal portion of UI caused by the two events is 45.5 +/- 5.4 km3 (during 1985-2010), while the total melt induced ice volume loss during this same period is 7.4 +/- 1.3 km3.