Significant thinning of the south Greenland ice sheet margin

The repeated laser altimetry by NASA between 1993 and 1999 documented that the southern ice sheet margin north of Qaqortoq to has been thinning significantly. In order to gain insight to the thinning a ground monitoring program was established. It became clear that thinning rates were nearly an order of magnitude higher than first observed by NASA i.e. 8 m/yr from 1985 to 2000. And, the calving front has been retreating in total 5 km since 1890 at increasing rate where 4 km of the retreat has been over the last 30 years. Modelling results show that the front has reached the flotation point and became instable as a result of mass balance adjustment to warmer climate after the little ice age ending around 1890. The disintegration of the front has resulted in reduction in backpressure and backward migration of the thinning up on the land-based part of the margin all the way to the equilibrium line. In addition to dynamically driven thinning (some 45%) increased melting has also provided a contribution to thinning which is the remaining 55%.