The processes controlling advance and retreat of outlet glaciers in fjords draining the Greenland Ice Sheet remain poorly known, undermining assessments of their dynamics and associated sea-level rise in a warming climate. Mass loss of the Greenland Ice Sheet has increased six-fold over the last four decades, with discharge and melt from outlet glaciers comprising key components of this loss. Here we acquired oceanographic data and multi-beam bathymetry in the previously uncharted Sherard Osborn Fjord in northwest Greenland where Ryder Glacier drains into the Arctic Ocean. Our data show that warmer subsurface water of Atlantic origin enters the fjord, but Ryder Glacier's floating tongue at its present location is partly protected from the inflow by a bathymetric sill located in the innermost fjord. This reduces under-ice melting of the glacier, providing insight into Ryder Glacier's dynamics and its vulnerability to inflow of Atlantic warmer water.

Martin Jakobsson, Larry A. Mayer, Johan Nilsson, Christian Stranne, Brian Calder, Matthew O'Regan, John W. Farrell, Thomas M. Cronin, Volker Brüchert, Julek Chawarski, Björn Eriksson, Jonas Fredriksson, Laura Gemery, Anna Glueder, Felicity A. Holmes, Kevin Jerram, Nina Kirchner, Alan Mix, Julia Muchowski, Abhay Prakash, Brendan Reilly, Brett Thornton, Adam Ulfsbo, Elizabeth Weidner, Henning Åkesson, Tamara Handl, Emelie Ståhl, Lee-Gray Boze, Sam Reed, Gabriel West, June Padman