The Greenland ice sheet continues to lose mass and thus contributes at about 0.7 millimeters per year to the currently observed sea level change of about 3 mm per year. This trend increases each year by a further 0.07 millimeters per year. The pattern and temporal nature of loss is complex. The mass loss is largest in southwest and northwest Greenland; the respective contributions of melting, iceberg calving and fluctuations in snow accumulation differing considerably. This result has been published by an international research group led by the GFZ German Research Centre for Geosciences in the latest issue of Earth and Planetary Science Letters, 1 June 2012. The result was made possible by a new comparison of three different types of satellite observations: measurements of the change in gravity by changes in ice mass with the satellite pair GRACE, height variation with the laser altimeter on the NASA satellite ICESat and determination of the difference between the accumulation of regional atmospheric models and the glacier discharge, as measured by satellite radar data.
For the first time and for each region, the researchers could determine with unprecedented precision which percentage melting, iceberg calving and fluctuations in rainfall have on the current mass loss. “Such an increase in mass loss in the northwest after 2005 is partly due to heavy snowfall in the years before”, says GFZ scientist Ingo Sasgen, head of the study. “The previous mass gain was reduced in subsequent years. Similarly in eastern Greenland: In the years 2008 and 2009 there was even a mass increase”. As the researchers were able to show, this was not due to decreased glacier velocities, but because of two winters with very heavy snowfall. Meanwhile, the loss of ice mass continues here. For all studied regions the melting and calving periods between 2002 and 2011 are extraordinarily high compared to those of the last five decades.
The work was created in the framework of the Helmholtz Climate Initiative REKLIMof the Helmholtz Association and the EU project ice2sea. Due to the study, the researchers can get a little closer to understanding the current developments of the Greenland ice sheet. Ingo Sasgen: “We now know very well how calving glaciers and melting contribute to the current mass balance, and when regional trends are largely caused by rainfall variations. And we also know where our measurements must be improved.” One such area is north-western Greenland, where the comparison of data indicates an abrupt increase in the calving rate, which was detected by the radar data inadequately. The REKLIM/ice2sea scientists want to find out what causes this increase and if it has a continuous or episodic character. A necessary prerequisite is a sufficiently long time series of measurements that is to be created by the continued precise gravity measurements in the context of the new satellite mission GRACE-FO (Gravity Recovery And Climate Experiment – Follow On).