Study says basal melting should be factored into climate modelsBy Summit VoiceFRISCO — While all eyes have been on the surface of he Greenland ice sheet and its outlet glaciers in recent years, it turns out the ice is also melting at the bottom, heated by a high heat
flow from the mantle into the lithosphere (essentially the crust and the upper mantle). An international research team led by the GFZ German Research Centre for Geosciences concluded that the thinness of the Earth’s crust beneath Greenland enables an increase flow of heat from the mantle, but the effects on the Greenland ice sheet are highly variable.Using special instruments, the researchers found areas where the ice melts at the base next to other areas where the base of the ice sheet is extremely cold. The study is published online in the current issue of Nature Geoscience.The scientists said the impacts of the bottom-up ice melt need to be included when scientists model ice sheet projections in the context of climate studies.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.
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”, said Petrunin. “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. “
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 over small distances.
“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,” said corresponding author Irina Rogozhina, who initiated IceGeoHeat project.
The current climate is influenced by processes that go far back into the history of Earth. The Greenland lithosphere is 2.8 to 1.7 billion years old and is only about 70 to 80 kilometers thick under Central Greenland. It’s not clear with the Earth’s crust is so thin in this region, but it turns out that the coupling of models of ice dynamics with thermo-mechanical models of the solid earth allows a more accurate view of the processes that are melting the Greenland ice.