Efficient simulation of glacial fjord dynamics using a new reduced physics model (FjordRPM)

Interactions between ice masses and the ocean are key couplings in the global climate system. In many cases these interactions occur through glacial fjords, which are long, deep, and narrow troughs connecting the open ocean to marine-terminating glaciers. By controlling the fluxes of ocean heat towards the ice sheet and ice sheet freshwater towards the ocean, glacial fjords play an important role in modulating ice sheet mass loss and the impacts of freshwater on ocean circulation. Yet, these dynamics occur at small scales that are challenging to resolve in earth system models and so are they often ignored, represented in an ad-hoc manner, or studied using expensive high-resolution models that are limited in scope.Here, we propose a means of capturing glacial fjord dynamics at negligible computational expense in the form of a new "reduced physics" model (FjordRPM) that resembles a "1.5-dimensional" or box model. We describe the make-up of the model and show that it accurately captures glacial fjord circulation when compared with simulations in a full general circulation model (MITgcm). We conclude by considering applications for the model, including furthering the understanding of fjord circulation, the production of ocean temperature boundary conditions for ice sheet models and freshwater boundary conditions for ocean models, and the potential to act as a bridge between ice sheet and ocean in earth system models.