Accelerated oceanic forcing in coupled ice sheet-ocean modelling

Coupled ice sheet - ocean models are increasingly being developed and applied to important questions pertaining to processes at the Greenland and Antarctic Ice Sheet margins, and the wider implications of such processes. In particular, ice sheet - ocean interactions have a strong control on ice sheet stability and sea level contribution. One of the challenges of such coupled modelling activities is the timescale discrepancy between ice and ocean dynamics, which, combined with the high cost of ocean models, can limit the timeframe that can be modelled. Here we present an "accelerated oceanic forcing'' approach to the ocean side of the coupling, in which the rates of change passed from ice model to ocean model components are increased by a constant factor and the period for which the  ocean model is run is correspondingly decreased. The ice sheet change over a coupling interval is thus compressed into  a shorter period over which the ocean model is run, based on the assumption that the ocean response time frame is shorter than  the compressed run period. We demonstrate the viability of this approach in an idealised setup based on the Marine Ice Sheet-Ocean Model Intercomparison Project, using the open-source Framework for Ice Sheet-Ocean Coupling (FISOC) combining two different ocean models (FVCOM and ROMS) and the ice-sheet model Elmer/Ice. We also demonstrate that the mean cavity residence time computed from the stand-alone ocean simulations can guide the selection of a suitable enhanced forcing factor for the coupled simulations.