The Impact of GIA Corrections on Gravimetric Basin-Scale Ocean Mass Budgets

En-Chi Lee , Christopher Harig

Closing the sea-level budget is crucial for validating our understanding of climate change and sea-level rise. Satellite gravimetry (Gravity Recovery and Climate Experiment, GRACE) and altimetry are primary tools for measuring the ocean mass. Still, both datasets must be corrected for glacial isostatic adjustment (GIA), the ongoing viscoelastic response of the Earth to past deglaciation. Disagreements amongst GIA models, from ice histories to Earth rheological structures, create uncertainties not captured by many previous studies, especially at ocean basin scales. Using an ensemble of 32 GIA models, we show that whilst the global ocean mass budget closes (at 2.25±0.48 mm/yr from GRACE and 2.28±0.16 mm/yr from altimetry-steric), the choice of GIA model is the dominant driver of non-closure at basin scales. These discrepancies are strongest in the long-wavelength coefficients that can arise directly from the GIA rotational response and indirectly through the GIA-corrected geocentric motion estimates. They manifest differently in gravimetric, altimetric, and sea-level fingerprint (SLF) estimates. No single GIA model can simultaneously close the mass budget in all basins, demonstrating that closing the basin-scale ocean mass budget provides a powerful new and independent constraint for GIA model development. Our results suggest that reconciling basin-scale sea level observations favours a GIA model with a stronger response in the Northern Hemisphere, potentially from a larger or later-deglaciating Fennoscandian Ice Sheet. Such findings provide a path to resolving GIA model ambiguity and improving regional sea level change projections.