Interannual summer mixing processes in the Ilulissat Icefjord, Greenland

Abstract

In the stratified water column inside the Ilulissat ice fjord, oceanic mixing processes can promote an upward transport of heat and salt from the subsurface to the surface mixed layer. Our objective was to map the temporal variation of vertical mixing inside the fjord by estimating the diapycnal mixing rates derived from oceanographic data collected during summer research cruises between 2009 and 2017. We applied the Thorpe scale method based on local density inversions. We found enhanced mixing in the deep water at 400 m sill depth inside the fjord, with diapycnal diffusivity reaching a maximum value of 1× 10 –3.5 m 2 s −1 . The strongest mixing rates in 2013, and the weakest during 2016, were mainly due to the Glacier's melting conditions and melange. The highest values of diapycnal diffusivity values occurred during years when low melange concentrations inside the ice fjord increased ventilation, which favored the intrusion of Polar and Irminger waters that perturbed the water structure. These years were also associated with a decrease in diffusive convection processes. Our results give insight into how the intrusion of waters from Disko Bay to the Ilulissat ice fjord may affect the stability of the Jakobshavn Isbræ Glacier. • · Water mixing interaction in the Ilulissat Ice Fjord, increase diapycnal diffusivities by more than one order of magnitude. • We used the Thorpe method to estimate mixing rates in the IIF system. • A warm water intrusion in 2013 lifted the isopycnals reducing the ice melange leading to the retreat of the glacier front.