Abstract

The Greenland Ice Sheet loses roughly half of its mass by ice discharge at marine terminating glaciers. Some of the largest and fastest flowing glaciers around Greenland calve kilometre-scale icebergs into long, narrow and deep fjords. These enormous icebergs typically capsize, or “flip” into more gravitationally stable orientations, and in doing so are thought to vigorously mix the stratified ocean within a small region in front of the glacier front. We investigate the effect of sudden ocean mixing events on flow within an idealised, linearly-stratified model fjord using the Oceananigans.jl nonhydrostatic model. A large fraction of the available potential energy is rapidly converted to kinetic energy and radiates away as internal waves. These internal waves produce pulses of elevated melt rate across the entire glacier front, with magnitudes comparable to melt rates due to subglacial discharge plumes. On longer timescales, the qualitative character of the response depends on the ratio of fjord width, W, to first baroclinic Rossby deformation radius, R. Typical Greenland fjords have W/R between 0.5 and 2.0. Within this range of W/R, our model predicts the appearance of a long-lived nearly geostrophic anticyclonic eddy spanning the entire width of the fjord, constrained to mid-depths, in front of the glacier terminus. This eddy drives a sustained melt anomaly at mid-depths for many days, which may promote undercutting. We also investigate sensitivity to the horizontal extent of the region over which the fluid is mixed, and find that increasing the mixed volume beyond some critical value destabilises the abovementioned eddy, leading to its break up and consequently reducing the predicted glacier melt rate.