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

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 tuning melt-rate parameters. To match the historical observations of ice dynamical changes, the transient-coupled calibration requires enhanced melt near the grounding line, 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 climate scenarios. In a warm RCP8.5 scenario, the transient-coupled calibration increases projected 2100 sea-level rise by 10 mm relative to a melt-only calibration, exceeding the 7 mm difference due to a change in climate forcing alone. These findings underscore the critical importance of jointly constraining oceanic and glaciological observations in model calibration. Further improvements will include extending the hindcast period, testing additional forcing scenarios, and calibrating ice-sheet model parameters.