The impact of shelf, local wind, and glacial forcings on the circulation in a Greenlandic fjord

Fjords form a key link in the climate system by connecting glaciers of the Greenland Ice Sheet to the ocean. They are the gateways for importing oceanic heat to melt ice and for exporting meltwater into the ocean. Yet, it is unclear how much the various potential drivers of fjord circulation – including buoyancy, tidal, local wind, and shelf forcings – contribute to these heat and meltwater fluxes. Building on observations from Sermilik Fjord at the terminus of Helheim Glacier, we use two models (ROMS and an analytical model) to explore the competition between shelf and local forcing in a fjord. Moored records from Sermilik Fjord show two seasonal regimes: the non-summer months are dominated by shelf-forcing with occasional bouts of strong local wind forcing, while the summer is characterized by both shelf-forced flows and a buoyancy-driven exchange. With ROMS numerical simulations and an analytical model, we explore the dynamics of the shelf-driven flows and their competition with local forcing within the fjord. These modeling results are used to elucidate the different regimes found in Sermilik and to explore the relative importance of shelf versus local forcing across the parameter space of Greenland’s fjords.