3D Glacial Isostatic Adjustment along the deglacial forebulge of the Atlantic coasts of North America and Europe

The deglacial forebulge along the Atlantic coasts of North America and Europe has been a key area for glacial isostatic adjustment (GIA) studies. Relative sea level (RSL) changes in this region are highly sensitive to the 3D Earth structure, and the area hosts abundant RSL data that can help constrain the 3D Earth structure. However, many previous studies either relied primarily on 1D Earth models or adopted 3D structures without systematically exploring the magnitude of lateral heterogeneity or the uncertainty associated with deglacial ice histories.

 

Here, we use the latest standardized deglacial RSL databases from the Atlantic coasts of North America and Europe for comparison with 3D GIA models coupled with two widely used ice models, ICE-6G_C and ANU-ICE. Our 3D Earth model consists of a 1D background viscosity model (η_o) and lateral viscosity variations; the latter are derived from shear velocity anomalies in a seismic tomography model and scaled by a factor (β) denoting the magnitude of lateral heterogeneity. We explore a range of η_o and β to assess the sensitivity of RSL predictions to both the background viscosity and the magnitude of lateral heterogeneity. The RSL databases include sea-level index points and limiting data, which we further classify by depositional setting (base of basal, basal, intercalated). We compare the RSL data to the GIA model predictions using a weighted misfit approach that reflects data type and interpretive uncertainty.

 

We find that 3D Earth structure has significant influence on RSL predictions, and the optimal 3D models substantially improve the fit to RSL data compared with 1D GIA models (e.g., ICE-6G_C VM5a). The Atlantic coast RSL datasets from North America and Europe favor different combinations of η_o and β, although the former provides stronger constraints owing to its higher spatial coverage and lower data uncertainty. Notably, despite differences in ice history, ICE-6G_C and ANU-ICE prefer similar 3D Earth structures. Ongoing work will quantify the uncertainty of the 3D model resolved by the available RSL data.