Wintertime Fjord-Shelf Interaction and Ice Sheet Melting in Southeast Greenland

A realistic numerical model was constructed to simulate the oceanic conditions and circulation in a large southeast Greenland fjord (Kangerdlugssuaq) and the adjacent shelf sea region during winter 2007-2008. The major outlet glaciers in this region recently destabilized, contributing to sea level rise and ocean freshening, with increased oceanic heating a probable trigger. It is not apparent a priori whether the fjord dynamics will be influenced by rotational effects, as the fjord width is comparable to the internal Rossby radius. The modeled currents, however, describe a highly three-dimensional system, where rotational effects are of order-one importance. Along-shelf wind events drive a rapid baroclinic exchange, mediated by coastally trapped waves, which propagate from the shelf to the glacier terminus along the right-hand boundary of the fjord. The terminus was regularly exposed to around 0.5TW of heating over the winter season. Wave energy dissipation provoked vertical mixing, generating a buoyancy flux which strengthened overturning. The coastally trapped waves also acted to strengthen the cyclonic mean flow via Stokes' drift. Although the outgoing wave was less energetic and located at the opposite sidewall, the fjord did exhibit a resonant response, suggesting that fjords of this scale can also exhibit two-dimensional dynamics. Long periods of moderate wind stress greatly enhanced the cross-shelf delivery of heat toward the fjord, in comparison to stronger events over short intervals. This suggests that the timescale over which the shelf wind field varies is a key parameter in dictating wintertime heat delivery from the ocean to the ice sheet. Plain Language Summary A computer simulation of the ocean around Greenland was used to study the movement of water in and out of a large fjord. This is important because warm water that gets into the fjord may come into contact with the Greenland Ice Sheet and cause it to melt. The simulation indicates that a significant amount of warm water comes into contact with the ice during the winter. This was previously difficult to measure because of the difficulties in taking direct measurements of the water during the Greenland winter.