A 3D glacial isostatic adjustment model reconciles conflicting geographic trends in North American Marine Isotope Stage 5a sea level observations
Reconstructions of peak global mean sea level (GMSL) during past warm intervals serve to calibrate ice sheet sensitivity to past climate and contextualize future change. One method to estimate GMSL is to fit sea level predictions from numerical glacial isostatic adjustment (GIA) models to compilations of geological and geomorphological relative sea level indicator elevations corrected for tectonics.
Glacial isostatic adjustment simulations using earth models that vary viscoelastic structure with depth alone cannot simultaneously fit geographic trends in the elevation of marine isotope stage (MIS) 5a relative sea level indicators across continental North America and the Caribbean and yield conflicting estimates of global mean sea level. We present simulations with a GIA model that incorporates three-dimensional (3-D) variation in North American viscoelastic earth structure constructed by combining high-resolution seismic tomographic imaging with a new method for mapping this imaging into lateral variations in lithospheric thickness and mantle viscosity. We pair this earth model with a global ice history based on updated constraints on ice volume and geometry. The GIA prediction provides the first simultaneous reconciliation of MIS 5a North American and Caribbean RSL high stands and strengthens arguments that MIS 5a peak GMSL reached values close to that of the Last Interglacial. This result highlights the necessity of incorporating realistic 3-D earth structure into GIA predictions with continent-scale RSL data sets. (Thompson et al., Geology, 2023)