The Greenland ice sheet is melting from below, caused by a high heat flow from the mantle into the lithosphere, according to a study by the international research initiative IceGeoHeat led by the GFZ German Research Centre for Geosciences and published in the journal Nature Geoscience.
This influence is very variable spatially and has its origin in an exceptionally thin lithosphere. Consequently, there is an increased heat flow from the mantle and a complex interplay between this geothermal heating and the Greenland ice sheet. This effect cannot be neglected when modeling the ice sheet as part of a climate study, the researchers suggested.
The continental ice sheets play a central role in climate; interactions and feedback processes between ice and temperature rise are complex and still a current research topic. The Greenland ice sheet loses about 227 gigatonnes of ice per year and contributes about 0.7 millimeters to the currently observed mean sea level change of about 3 mm per year.
Existing model calculations, however, were based on a consideration of the ice cap and considered the effect of the lithosphere, i.e. the earth’s crust and upper mantle, too simplistic and primarily mechanical: the ice presses the crust down due to its weight.
GFZ scientists Alexey Petrunin and Irina Rogozhina have now coupled an ice/climate model with a thermo-mechanical model for the Greenland lithosphere.
We have run the model over a simulated period of three million years, and taken into account measurements from ice cores and independent magnetic and seismic data. Our model calculations are in good agreement with the measurements. Both the thickness of the ice sheet as well as the temperature at its base are depicted very accurately.—Alexey Petrunin
The model can even explain the difference in temperature measured at two adjacent drill holes: the thickness of the Greenland lithosphere and thus the geothermal heat flow varies greatly in narrow confines.
The temperature at the base of the ice, and therefore the current dynamics of the Greenland ice sheet, is the result of the interaction between the heat flow from the earth’s interior and the temperature changes associated with glacial cycles. We found areas where the ice melts at the base next to other areas where the base is extremely cold.—Irina Rogozhina (GFZ), corresponding author and initiator of IceGeoHeat
Petrunin, A. G., Rogozhina, I., Vaughan, A. P. M., Kukkonen, I. T., Kaban, M. K., Koulakov, I. & Thomas, M. (2013) Heat flux variations beneath central Greenland's ice due to anomalously thin lithosphere. Nature Geoscience doi: 10.1038/ngeo1898