Physical oceanographic conditions and a sensitivity study on meltwater runoff in a West Greenland fjord: Kangerlussuaq

Summary In this paper, we discuss the first setup of a hydrodynamic model for the fjord-type estuary Kangerlussuaq, located in West Greenland. Having such a high-fidelity numerical model is important because it allows us to fill in the temporal and spatial gaps left by in situ data and it allows us to examine the response of the fjord to changes in ice sheet runoff. The numerical model is calibrated against in situ data, and a one-year simulation was performed to study the seasonal variability in the physical oceanographic environment and the fjord's response to changing meltwater runoff. The fjord consists of two distinct parts: a deep inner part that is 80 km long with weak currents and a shallow part that covers the outer 100 km of the fjord connected to the ocean. The outer part has very fast currents, which we suggest prevents winter sea ice formation. The dominant currents in the fjord are oriented parallel to the long axis of the fjord and are driven by tides and (during summer) freshwater inflow from meltwater-fed rivers. Furthermore, mixing processes are characterized by strong tidal mixing and bathymetric restrictions, and the deep-lying water mass is subject to renewal primarily in wintertime and is almost dynamically decoupled from the open ocean during summertime. Finally, a sensitivity study on the changing meltwater runoff was performed, showing that increasing freshwater runoff considerably strengthens stratification in the upper 100 m of the water column in the inner part of the fjord.