Accelerated Elevation Change of Greenland´s Jakobshavn Glacier Observed by ICESat and IceBridge

The recent accelerated ice mass loss of the Greenland ice sheet and its outlet glaciers has been widely documented. The Jakobshavn isbrae/glacier is one of the fastest melting glaciers in Greenland. To determine its elevation change rate, recent observations from the laser altimetry mission Ice, Cloud, and land Elevation Satellite (ICESat) (2003-2009) and the airborne campaign IceBridge (2009-2011) were used. The results confirm previously determined elevation loss rates of several decimeters per year. Specifically, the outlet glacier declines up to several meters per year, while the high-elevation areas of the ice sheet exhibit loss of a few decimeters or even elevation gain for some years. Specifically, the three study areas show the following ranges of elevation change rates and standard deviation between 2003 and 2011: (1) - 0.64 to -2.56 ±0.43m/yr for areas below 1500-m elevation; (2) +0.17 to -0.55 ±0.16m/yr for areas above 1500 m; and (3) -2.31 to -5.18 ±0.55 m/yr for outlet glacier. Elevation change accelerates at -0.09 to -0.27 m/yr² between 2004 and 2011. The uncertainty is better than 0.55 m/yr which demonstrates that both ICESat and IceBridge observations allow for the accurate estimation of rates at the observed magnitudes. Part of the uncertainty can be attributed to the slope correction used to project two footprints at different epochs onto a common location. The slope correction was applied based on the ICESat 1-km digital elevation model and the IceBridge Airborne Topographic Mapper slope data sets. An improved understanding of annual and seasonal variability of elevation change will result in better quantification of its mass balance and its contribution to sea level change.