Abstract

Ocean currents are important drivers of mass loss from ice sheets, both around Antarctica and in the glacier fjords of Greenland. Below ice shelves, the ocean causes basal melting, which reduces ice sheet stability and increases ice discharge, contributing to sea level rise. We want to understand currents under ice shelves better and improve their representation in climate models. Our modelling study focuses on Greenland’s largest floating ice tongue, the 79° North Glacier, which is similar to Antarctic ice shelves, so our findings can be generalised to both polar regions. Although our 2D-vertical model of the 79°N fjord is idealised, the results agree well with observations of melt rate and overturning strength. This is the first application of adaptive vertical coordinates to an ice cavity, achieving a vertical resolution finer than 1 m in the entrainment layer of the subglacial plume and thus allowing an accurate representation of the plume development. The subglacial plume is the current at the ice–ocean interface and the primary cause of basal melting. We show that the plume development is dominated by entrainment only initially. In the stratified upper part of the glacier cavity, the subglacial plume is subject to continuous detrainment. In a sensitivity study, we analyse the impact of ambient stratification and subglacial runoff on the melt rate and on the depth of plume detachment from the ice tongue. As an outlook, we explore how the situation changes in a more realistic setting with cross-fjord resolution and three-dimensional circulation.