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Abstract

Warming of deep Atlantic Water in recent decades has resulted in extensive retreat of marine terminating glaciers in Northwest Greenland, increasing their discharge, contributing significantly to sea level rise. We use data and numerical models to consider whether the pathways of deep Atlantic Water, through the complex system of canyons 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 ocean model results. We find that the 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 to the fjord geometry also controlled large parts of the observed trends.