Greenland lost nearly 2,700 gigatons of ice from 2003-2013, not about 2,500 gigatons as scientists previously thought — a 7.6 percent difference, a study says.
“It’s a fairly modest correction,” said study co-author Michael Bevis of The Ohio State University in the US.
“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,” Bevis, who is also the leader of GNET, the Greenland GPS Network, said.
The researchers found that the same hotspot in the 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 the new study published 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.
The new results revealed that the pattern of modern ice loss is similar to that which has prevailed since the end of the last Ice Age.
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.
“This result is a detail, but it is an important detail,” Bevis said.
“By refining the spatial pattern of mass loss in the world’s second largest — and most unstable — ice sheet, and learning how that pattern has evolved, we are steadily increasing our understanding of ice loss processes, which will lead to better informed projections of sea level rise,” Bevis noted.
The team used GPS to measure uplift in the crust all along Greenland’s coast.
That is when they discovered that two neighbouring stations on the east coast were uplifting far more rapidly than standard models had predicted.
“We did not expect to see the anomalous uplift rates at the two stations that sit on the ‘track’ of the Iceland hot spot,” Bevis said.
“We were shocked when we first saw them. Only afterwards did we make the connection,” Bevis pointed out.
He added that the discovery holds big implications for measuring ice loss elsewhere in the world.