摘要：Following three decades of relative stability, Jakobshavn Isbræ, 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 ∼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.
