Unsteady Circulation in a Glacial Fjord: A Multiyear Modeling Study of Milne Fiord

Abstract

The exchange of heat and freshwater between glaciers and the ocean is dictated by the circulation in glacial fjords and ice shelf cavities. Therefore, our ability to estimate and predict these fluxes depends on our understanding of the circulation mechanisms inside these polar estuaries. Here, we use an exceptionally long observational data set (8+ years) to develop and validate a high‐resolution realistic numerical model of Milne Fiord (Nunavut, Canada), a glacial fjord with an ice shelf at its mouth. Model results show the circulation inside Milne Fiord from 2011 to 2019 is highly three‐dimensional and unsteady. Three distinct circulation modes are identified (eddy, front, barotropic). The shifts between circulation modes are driven by density variations in the offshore coastal current, which restrict vertical stretching, allowing (or not) the coastal current to develop sufficient relative vorticity to enter the fjord. The unsteadiness of the system results in an overturning estuarine circulation with mean velocities ∼50 times smaller than the instantaneous field. Moreover, analysis of the model outputs suggest that at least 2 years of simulation are needed to yield reliable average heat flux estimates in this environment. This work highlights the value of combining long term (>1 year) observations with numerical modeling. This allowed us to uncover the spatial and temporal variability of the system, which impacts how heat and freshwater fluxes can be reliably estimated.