Influence of Ocean Waters in Retreat Episodes of a West Greenland Tidewater Outlet Glacier

Abstract

The behavior of tidewater outlet glaciers is critical for understanding the dynamics of the Greenland Ice Sheet. The retreat of these glaciers has far-reaching implications, with impacts ranging from altering local fjord ecosystems to affecting global sea levels. Here, we integrated hydrographic with glaciological parameters to investigate the rapid retreat of Narsap Sermia (NS)—a West Greenland tidewater outlet glacier located near Greenland's largest city, Nuuk. In just 20 years, from 2003 to 2023, NS retreated by 6.7 km with ice discharge volume increasing by 35%–52%, which was more than double the average increase in glacier discharge observed for Greenland Ice Sheet outlet glaciers during the same period. This retreat occurred in three big episodes: 2004–2005, 2010–2012, and 2019–2021. Three main phases were identified during these retreats: a trigger, a cascade, and a stabilization. Each retreat episode was triggered by a surge in subglacial discharge caused by increased meltwater over the Ice Sheet or drainage of ice-dammed lakes. Importantly, warm ocean conditions were necessary to allow these initial retreats to cascade. Stabilization could occur when the terminus eventually settled on more favorable bed topography or if the glacier was in contact with colder oceanic inflows. Based on the pattern established by these past retreats, NS might retreat further for 30 km in a few decades if there is no topographic stabilization. NS thus highlights the role changing ocean temperatures can play in regulating tidewater outlet glacier processes and, consequently, its impacts on local fjord glacial ice cover, eco-hydrology and nearby communities.