The latest bad news for the earth’s northern polar region from Ohio State University:
The same hotspot in Earth’s mantle that feeds Iceland’s active volcanoes has been playing a trick on the scientists who are trying to measure how much ice is melting on nearby Greenland.
According to a new study [open access] in the journal Science Advances, the hotspot softened the mantle rock beneath Greenland in a way that ultimately distorted their calculations for ice loss in the Greenland ice sheet. This caused them to underestimate the melting by about 20 gigatons (20 billion metric tons) per year.
That means Greenland did not lose about 2,500 gigatons of ice from 2003-2013 as scientists previously thought, but nearly 2,700 gigatons instead —a 7.6 percent difference, said study co-author Michael Bevis of The Ohio State University.
“It’s a fairly modest correction,” said Bevis, the Ohio Eminent Scholar in Geodynamics, professor of earth sciences at Ohio State and leader of GNET, the Greenland GPS Network.
“It doesn’t change our estimates of the total mass loss all over Greenland by that much, but it brings a more significant change to our understanding of where within the ice sheet that loss has happened, and where it is happening now.”
The Earth’s crust in that part of the world is slowly moving northwest, he explained, and 40 million years ago, parts of Greenland passed over an especially hot column of partially molten rock that now lies beneath Iceland. The hotspot softened the rock in its wake, lowering the viscosity of the mantle rocks along a path running deep below the surface of Greenland’s east coast.
During the last ice age, Greenland’s ice sheet was much larger than now, and its enormous weight caused Greenland’s crust to slowly sink into the softened mantle rock below. When large parts of the ice sheet melted at the end of the ice age, the weight of the ice sheet decreased, and the crust began to rebound. It is still rising, as mantle rock continues to flow inwards and upwards beneath Greenland.
The existence of mantle flow beneath Greenland is not a surprise in itself, Bevis said. When the Gravity Recovery and Climate Experiment (GRACE) satellites began measuring gravity signals around the world in 2002, scientists knew they would have to separate mass flow beneath the earth’s crust from changes in the mass of the overlying ice sheet.