Greenland鈥檚 more than 860,000 square miles are largely covered with ice and glaciers, and its melting fuels as much as one-third of the sea level rise in 51在线. That鈥檚 why a team of 51在线 geoscientists鈥� new discovery of one of the mechanisms that allows Greenland鈥檚 glaciers to collapse into the sea has special significance for the Sunshine State.
In , a group of scientists led by , uncovered a process that can control the 鈥渃alving鈥� of glaciers 鈥� when large chunks of glacier ice collapse into the sea, forming icebergs like the one that sank the Titanic. The discovery by the team that included USF PhD student Surui Xie; David Holland, PhD, and Irena Va艌kov谩, PhD, at New York University (NYU) and NYU-Abu Dhabi Research Institute; and Denis Voytenko, PhD, formerly at NYU and now at Nielson Communications, will help the scientific community better model future Greenland ice loss and sea level rise.
Glacier calving is one of the more dramatic aspects of climate change. Depending on the height of the glacier, calving can be akin to an ice structure the size of a tall skyscraper falling into the sea. Dixon鈥檚 team caught one such calving on video.
鈥淚ceberg calving has been challenging to model,鈥� Dixon said. 鈥淥ne of the big unknowns in future sea level rise is how fast Greenland falls apart, and iceberg calving is one of the least understood mechanisms.鈥�
The team ventured to Greenland in the summer of 2016 to install a new radar system to better understand the process. In particular, they wanted to monitor formations known as pro-glacial 鈥渕茅lange鈥� (from the French word for mixture), a combination of sea ice and icebergs in front of the glacier. The m茅lange can be tightly packed in the long, narrow fjords that front many of Greenland鈥檚 glaciers that meet the sea.
Scientists have long known that m茅lange can impede glaciers as they move toward the sea, but they haven鈥檛 had the data to fully understand the phenomenon.
Dixon鈥檚 team developed a new radar-based approach to precisely measure elevations of the m茅lange in front of Jakobshavn Glacier , a major outlet glacier on Greenland鈥檚 west side. Using analytical techniques developed by Xie, the scientists measured the height of the m茅lange. The scientists found a thick m茅lange wedge pressed up against the glacier in late spring and early summer.
During this period, no icebergs calved, the scientists observed. Once the wedge thinned and melted by mid-summer, calving began in earnest.
鈥淥n the surface, this m茅lange is a subtle thing 鈥� it appears almost flat鈥� but underwater, there are huge variations,鈥� Dixon said. 鈥淚t鈥檚 really the underwater part that is pinning the glacier back and preventing it from calving. By precisely measuring the surface elevations, we were able to get a handle on the much bigger sub-surface variations, which define m茅lange thickness.鈥�
Earlier this spring, Jakobshavn Glacier, which has been Greenland's fastest -thinning glacier for the last 20 years, was slowing in its movement toward the ocean in what appears to be a cyclical pattern of warming and cooling. But because Jakobshavn is still giving up more ice than it accumulates each year, its sheer size makes it an important factor in sea level rise, the NASA scientists maintain.
鈥淥ur study helps understand the calving process,鈥� Dixon said. 鈥淲e are the first to discover that m茅lange isn鈥檛 just some random pile of icebergs in front of the glacier. A m茅lange wedge can occasionally 鈥榟old the door鈥� and keep the glacier from calving.鈥�