Calibration of a coupled ice sheet-ocean model using observations of ice dynamics and basal melt in West Antarctica

Abstract. Coupled ice sheet-ocean models are increasingly used to investigate the complex interactions between ice dynamics and ocean forcing in West Antarctica, yet uncertainties in model parameters limit confidence in long-term sea-level projections. Among these parameters, ocean-model melt rates are typically calibrated using only basal melt observations for static ice-shelf geometries, neglecting feedbacks associated with evolving ice geometry, particularly in the Amundsen Sea sector.

Here, we calibrate a fully coupled ice sheet-ocean model using an ensemble of simulations constrained by spatial observations of basal melt rates and changes in ice speed and thickness over a historical period. This represents the first calibration to jointly incorporate oceanic and glaciological observations for optimizing melt-rate parameters. To match the historical observations of ice dynamical changes, the transient-coupled calibration favours parameter values that enhance basal melt near deep grounding lines, highlighting the sensitivity of ice dynamics to localized ocean forcing.

Using the historically-calibrated model, we provide century-scale projections of sea-level contribution under two scenarios: present-day control and warm RCP8.5 forcing. In the warm case, the transient-coupled calibration increases projected 2100 sea-level rise by 14 mm relative to a melt-only calibration. This exceeds the 7 mm difference simulated between the two climate scenarios. These findings underscore the critical importance of jointly validating against oceanic and glaciological observations in model calibration.