Leveraging sustained monitoring of a southeast Greenland glacial fjord to understand ice-ocean and biogeochemical interactions

Greenland’s glacial fjords are the sites of climatically important exchanges of heat, freshwater, and nutrients between the North Atlantic Ocean and the Greenland ice sheet, as well as hosting productive ecosystems integral to local communities. Though both glacial inputs and ocean exchanges are modulated by seasonal and interannual variability, observational studies of the complex interactions that take place in these fjords often necessarily rely on data from a single field campaign, amounting to a summer snapshot of fjord conditions.

We have sustained a long-term monitoring program in Sermilik Fjord, a major glacial fjord in southeast Greenland, since 2008, collecting ocean temperature and salinity profiles almost annually, supplemented by ongoing mooring records that cover the full period from 2008-2023. This exceptional data set, at times augmented by the collection of complementary data such as velocity measurements and noble gas, nutrient, and dissolved oxygen concentrations, has given us a more robust understanding of the fjord circulation and water mass transformations. This in turn can be leveraged to help us address a range of questions within this complex system.

We apply this foundational knowledge of Sermilik Fjord to interpret the cycling of mercury in the fjord from full water column measurements of mercury concentrations from summer 2021. We use a water mass analysis to show that the exported glacially-modified waters are depleted in inorganic mercury (HgII) relative to ambient ocean waters. We propose that sediments initially suspended in glacier meltwaters scavenge particle-reactive HgII and are subsequently buried, making the fjord a net sink of oceanic mercury.