Velocity of Outlet Glaciers Plays Pivotal Role in Ice Loss from Greenland Ice Sheet

Journal of Glaciology, August 3

The velocity of outlet (or peripheral) glaciers greatly influences the rate of ice loss from the Greenland Ice Sheet. During late spring, the onset of surface melt prompts most glaciers in the colder, northern regions of Greenland to speed up for several weeks, before abruptly slowing to previous speeds as melt slows in late summer. However, glaciers in the warmer southern and central regions commonly show only a small acceleration before slowing throughout the summer, even reaching slower speeds than prior to melt. The reduced speed of these southern glaciers suggests that there is less meltwater stored at their base on which the glacier flows. Instead, it allows water to flow through the glaciers and drain more quickly into the surrounding area. In this way, increasing amounts of meltwater flowing through glaciers during the summer does not necessarily correspond to an acceleration of the glacier. The Greenland Ice Sheet has been losing mass at an accelerating rate since the 1990s due to both increases in calving (or iceberg loss) from accelerating glaciers, and surface meltwater runoff. The number of slower glaciers with high-efficiency meltwater loss has been increasing across Greenland since 2019 due to rapidly increasing temperatures, and may be accelerating Greenland’s ice loss, even as glacier speed and iceberg discharge slows.