Only skin deep? Linking sea surface temperatures with glacier discharge and deep fjord temperature change

The Greenland ice sheet (GIS) contributes one-quarter of the globe's total sea level rise each year and one-third of its mass loss occurs at outlet glaciers. One mechanism for this loss is through melting at the ice-ocean boundary through interactions with relatively warm ocean water. In situ ocean measurements serve as the predominant method for studying these harsh and remote fjord environments, but have often only been acquired within the last decade in most Greenland fjords. Since many outlet glaciers began to accelerate and retreat before that period, the lack of earlier measurements requires us to rely on an understanding of contemporary fjord processes and inference of past conditions to evaluate the ocean's role in observed glacier change. Satellite-derived sea surface temperature (SST) have been widely unused in studies of glacial fjords and may hold clues to fjord heat content and ice-ocean interactions spanning before rapid change began at the turn of the century. However, the utility of this method has not been thoroughly explored.

In this study, we produce Landsat and MODIS SST time series in order to determine changes in fjord water masses and the timing and magnitude of meltwater influx into Sermilik Fjord from 2000 to present. SSTs were derived from Landsat 7 and 8 and MODIS thermal infrared imagery to produce a time series of the fjord and neighboring continental shelf ocean surface. Comparing the SSTs to in situ ocean temperature measurements taken from 2009 to present at the Sermilik Fjord, we find that SSTs reflect different environmental variables depending on where the SSTs are acquired within the fjord-shelf system: air temperature, surface Polar Water temperature, deeper Atlantic Water temperature, and glacial meltwater influx into the fjord. The SST record over the last 18 years thus provides insight into changes in the magnitude and timing of subglacial discharge, ocean heat content, and subglacial melting within the Sermilik Fjord.