21 November 2018
An immense, ancient impact crater (click here) has been discovered under the dense arctic ice covering Greenland. Over 300 metres deep and more than 30 kilometres wide, the crater is one of the 25 largest ever found on Earth. It’s also the first one to be found under a continental ice sheet.
The researchers behind the discovery say that the huge, bowl-shaped indentation was formed when an iron meteorite almost a kilometre wide smashed into the Earth as recently as 12,000 years ago. The impact zone in northwestern Greenland is now covered by the Hiawatha Glacier.
“The crater is exceptionally well-preserved, and that is surprising, because glacier ice is an incredibly efficient erosive agent that would have quickly removed traces of the impact. But that means the crater must be rather young from a geological perspective,” Professor Kurt H. Kjær, the leader of the team that worked on the discovery, said in a statement. "So far, it has not been possible to date the crater directly, but its condition strongly suggests that it formed after ice began to cover Greenland, so younger than 3 million years old and possibly as recently as 12,000 years ago – toward the end of the last ice age.”
In 2015, scientists first developed theories that there was a crater in the area. The team has since worked to survey the region using satellite imagery and radar systems capable of penetrating continental ice sheets....
"Has Arctic Sea Ice Loss Contributed to Increased Surface Melting of the Greenland Ice Sheet?"
Jiping Liu, Zhigiang Chen, Jennifer Francis, Mirong Song, Thomas Mote and Yongyun Hu
In recent decades, (click here) the Greenland ice sheet has experienced increased surface melt. However, the underlying cause of this increased surface melting and how it relates to cryospheric changes across the Arctic remain unclear. Here it is shown that an important contributing factor is the decreasing Arctic sea ice. Reduced summer sea ice favors stronger and more frequent occurrences of blocking-high pressure events over Greenland. Blocking highs enhance the transport of warm, moist air over Greenland, which increases downwelling infrared radiation, contributes to increased extreme heat events, and accounts for the majority of the observed warming trends. These findings are supported by analyses of observations and reanalysis data, as well as by independent atmospheric model simulations using a state-of-the-art atmospheric model that is forced by varying only the sea ice conditions. Reduced sea ice conditions in the model favor more extensive Greenland surface melting. The authors find a positive feedback between the variability in the extent of summer Arctic sea ice and melt area of the summer Greenland ice sheet, which affects the Greenland ice sheet mass balance. This linkage may improve the projections of changes in the global sea level and thermohaline circulation.
