The importance of Atlantic Water pathways for understanding glacier discharge in Northwest Greenland

Abstract

It is well known that warming of deep Atlantic Water in recent decades resulted in extensive retreat of marine terminating glaciers in Northwest Greenland and increased their discharge, which contributed significantly to sea level rise. Here we use data and model resources over a wide range of space and timescales to determine how the pathways of deep Atlantic Water, through the complex bathymetry of Melville Bay, increased the vulnerability of glaciers over the observed ocean warming period. New observations of salinity and temperature of the ocean water and bathymetry from NASA’s Ocean Melting Greenland mission as well as Mankoff’s discharge estimates are combined with FESOM and HYCOM ocean model results. We have shown that these pathways of Atlantic Water are crucial for understanding the increase in discharge of certain glaciers over the ocean warming period. More specifically, the vulnerability of a marine terminating glacier in Northwest Greenland to Atlantic Water depends on its latitudinal position, the location of the fjordal channel entrance along the Southern or Northern canyon head and whether the fjordal channel is deep enough to be a pathway for Baffin Bay Intermediate Water. The Upernavik N and C glaciers, which are in the most vulnerable position, contributed 10% to the total discharge change of Northwest Greenland. In addition, the glaciers that exhibited the largest normalised discharge change showed correspondence between their discharge estimates and the observed changes in fjord geometry during the retreat of the glacier calving front. Warming of deep Atlantic Water impacted the normalised discharge estimates, but the sensitivity of the fjord geometry also controlled large parts of the observed trends. With this study, new insights in the vulnerability of marine terminating glaciers were obtained, which showed that the pathways of Atlantic Water should not be overlooked when developing climate models.