August 12, 2013
Underground Heat Flow Contributing To Greenland Ice Sheet Melting
redOrbit Staff & Wire Reports - Your Universe Online
High heat flow from the mantle into the lithosphere is causing the Greenland ice sheet to melt from below, according to new research published in Sunday’s online edition of the journal Nature Geoscience.
This phenomenon, the researchers explain, is very variable spatially and originates in an exceptionally thin lithosphere (the Earth’s crust and upper mantle). As a result, they report there is an increase in the heat flow from the mantle and a complex interaction between this geothermal heating and the ice sheet itself.
This effect cannot be ignored when creating models of the ice sheet as part of climate-related research, members of the GFZ German Research Centre for Geosciences-led IceGeoHeat initiative explained in a statement. IceGeoHeat is a multinational effort to reconstruct geothermal heat flow distribution in regions covered by large-scale ice masses.
Each year, the Greenland ice sheet loses approximately 227 gigatons of ice, contributing roughly 0.7 millimeters to the currently observed mean sea level change of about three millimeters annually. However, the IceGeoHeat team reports most existing climate model calculations are based on the ice cap alone, as they considered the lithosphere too simplistic and primarily mechanical in that the ice pushes the crust down due to its weight.
“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,” Dr. Petrunin said in a statement. “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.”
Furthermore, the authors report their new model can also explain the difference in temperature measured at two adjacent drilling locations. The cause, they say, is the thickness of the Greenland lithosphere, which causes the geothermal heat flow to vary wildly – even in regions that are close together.
“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,” Rogozhina said. “We found areas where the ice melts at the base next to other areas where the base is extremely cold.”
According to the researchers, the Greenland lithosphere is 2.8 to 1.7 billion years old and is only about 70 to 80 kilometers thick under the central part of the country. Scientists have not yet been able to determine exactly why it is so thin. However, by pairing ice dynamics models with thermo-mechanical models, the researchers believe they will allow experts to more accurately discern the processes which are melting the Greenland ice sheet.