<p>Jakobshavn Isbræ, West Greenland, which holds a 0.6-m sea level volume equivalent, has been speeding up and retreating since the late 1990s. Interpretation of its retreat has been hindered by difficulties in measuring its ice thickness with airborne radar depth sounders. Here, we employ high-resolution, helicopter-borne gravity data from 2012 to reconstruct its bed elevation within 50 km of the ocean margin using a three-dimensional inversion constrained by fjord bathymetry data offshore and a mass conservation algorithm inland. We find the glacier trough to be asymmetric and several 100 m deeper than estimated previously in the lower part. From 1996-2016, the grounding line migrated at 0.6 km/yr from 700 m to 1,100 m depth. Upstream, the bed drops to 1,600 m over 10 km then slowly climbs to 1,200 m depth in 40 km. Jakobshavn Isbræ will continue to retreat along a retrograde slope for decades to come.
An L., E. Rignot, S.H.P. Elieff, M. Morlighem, R. Millan, J. Mouginot, D.M. Holland, D. Holland, and J. Paden (2017), Bed elevation of Jakobshavn Isbræ, West Greenland, from high-resolution airborne gravity and other data, Geophys. Res. Lett., 44, doi:10.1002/2017GL073245.
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