Volume change of Jakobshavn Isbrae, West Greenland: 1985-1997-2007

Following three decades of relative stability, lakobshavn Isbrae, West Greenland, underwent dramatic thinning, retreat and speed-up starting in 1998. To assess the amount of ice loss, we analyzed 1985 aerial photos and derived a 40 m grid digital elevation model (DEM). We also obtained a 2007 40 m grid SPOT DEM covering the same region. Comparison of the two DEMs over an area of similar to 4000 km(2) revealed a total ice loss of 160 +/- 4 km(3), with 107 +/- 0.2 km(3) in grounded regions (0.27 mm eustatic sea-level rise) and 53 4 km(3) from the disintegration of the floating tongue. Comparison of the DEMs with 1997 NASA Airborne Topographic Mapper data indicates that this ice loss essentially occurred after 1997, with +0.7 +/- 5.6 km(3) between 1985 and 1997 and -160 +/- 7 km(3) between 1997 and 2007. The latter is equivalent to an average specific mass balance of -3.7 +/- 0.2 m a(-1) over the study area. Previously reported thickening of the main glacier during the early 1990s was accompanied by similar-magnitude thinning outside the areas of fast flow, indicating that the land-based ice continued reacting to longer-term climate forcing.