According to a Penn State-led team of scientists, dark patches of open sea that develop in the ice-choked seas around Helheim Glacier may give fresh information about how a fast changing Greenland glacier loses ice.
“Greenland is losing a lot of ice, and it flows from the heart of the ice sheet to the ocean through outlet glaciers like Helheim,” said Sierra Melton, a Penn State doctorate candidate in geosciences. “It’s critical to understand what’s going on at these glaciers.”
During warm seasons, enough meltwater flows from under Helheim, causing plumes of buoyant fresh water to rise to the surface of the sea in front of the glacier and be seen as patches of open water, according to the scientists.
Using satellite and time-lapse photographs to track these plumes, the scientists discovered that while the plumes were visible on the surface, massive icebergs stopped breaking away, or calving, from the glacier near the plumes.
“We’d observe a lot of calving, and then it’d stop while the plume was visible, and then it’d start again when the plume dissipated,” Melton said. “When calving did occur, it was far from the plume. They were constantly divided by time and place.”
Calving at Helheim entails enormous pieces of ice breaking off from behind the rock at the glacier’s front, which may reach 300 feet in some places. Helheim used to end in a floating extension known as an ice shelf or ice tongue, similar to bigger Antarctic glaciers, but that ice has since broken off and evaporated, revealing the cliff. According to the scientists, calving accounts for almost half of the ice loss from the Greenland Ice Sheet and is a substantial contributor to sea level rise.
“Sierra’s work, including this paper, is an important contribution to the larger effort to understand how iceberg calving really works and what controls its speed, so we can do a better job of projecting what will happen in Greenland and Antarctica, and what that means for sea-level rise and coastal people,” said Richard Alley, Evan Pugh University Professor of Geosciences at Penn State, Melton’s adviser and a co-author on the paper.
While the association between plumes and calving has been detected earlier at Helheim, direct observations are difficult due to inaccessible terrain on the glacier and ice in the sea. From 2011 to 2019, the scientists undertook a more extensive research utilizing high-resolution satellite imagery and hundreds of time-lapse photographs from cameras stationed around the glacier.
The results, published in the Journal of Glaciology, imply that the link between meltwater outflow and calving is caused by changes in hydrology and pressure underneath the glacier.
During the melt season, water pools in crevasses and creates lakes on the glacier’s surface. According to the experts, some meltwater flows to the glacier bed, where it starts to fill up holes and establish a network between them.
“A subglacial drainage system evolved in such a manner that if there isn’t much water beneath the glacier, there is minimal water pressure,” Melton said. “As the water level rises under the glacier, so does the pressure.”
According to the experts, as more water flows to the bottom and water pressure builds, the glacier’s march toward the sea accelerates and fissures emerge in the ice, making it more prone to calving.
However, if enough water is present at the glacier bed, the water may carve channels in the bottom of the ice that send meltwater towards the sea, functioning as a form of relief valve that lessens the water pressure under the glacier ice, according to the scientists. These conduits may discharge enough fresh water to cause plumes to appear on the sea’s surface.
“We believe the lower pressure design prevents major calving because cracks in the bottom of the ice cannot occur,” Melton said. “In essence, the mechanism that sustains the plume’s existence should reduce calving.”
Sridhar Anandakrishnan, professor of geosciences and Melton’s co-adviser, and Byron Parizek, professor of mathematics and geosciences, both contributed from Penn State.
Leigh Stearns, associate professor, and Michael Shahin, doctoral candidate, from the University of Kansas, as well as Adam LeWinter, physical scientist, and David Finnegan, director of remote sensing, from the Cold Regions Research and Engineering Laboratory, contributed.
This study was funded by the National Science Foundation, the Natural Environment Research Council of the United Kingdom, and the Heising-Simons Foundation.
