Reconstructing Fjord Circulation Near a Greenland Tidewater Glacier with Physical Modeling and in Situ Mooring Data

Abstract:

The rapid speedup of Greenland tidewater glaciers over the last decade, and subsequent mass loss, has been attributed to an increase in air temperature and a synchronous increase in ocean temperatures. The warming subtropical waters previously thought to only exist offshore of Greenland, have been observed throughout most Greenland fjords, and have been suggested to play a large role in submarine melting of the floating glacier terminus and subsequent calving. Warm subtropical water can become entrained by subglacial meltwater as it exits from beneath the glacier. As the buoyant subglacial meltwater moves along the glacier terminus to the surface, the entrained subtropical water contributes to terminus melting and subsequent iceberg melting. However, the impact of a meltwater plume on fjord stratification has been difficult to study due to the limited accessibility of the proglacial environment. We collected a mooring record of salinity and temperature from 2010-2013 at 14 m depth in Sermilik fjord, East Greenland (~25-30 km from the terminus of Helheim Glacier). This record shows a temperature deviation from a sinusoidal seasonal trend between June and October each year; temperatures steadily decrease between June and August and warm again over the subsequent two months. We hypothesize there are three factors driving temperature and salinity changes in the surface waters: (1) subglacial meltwater release, (2) glacier calving, and (3) proglacial circulation. In this study we construct a physical model of the proglacial fjord environment. We modify the quantity, duration and depth of subglacial meltwater release to reconstruct the mooring temperature and salinity records. Results of this study illuminate the influence of subglacial discharge and iceberg melt on proglacial fjord dynamics, an important component in understanding ice sheet- ocean interactions in a warming climate.