Barbados-based estimate of ice volume at Last Glacial Maximum affected by subducted plate

The record of sea-level change at Barbados derived from the dating of fossil corals(1-3) has been used to argue that globally averaged, or eustatic, sea level during the Last Glacial Maximum was approximately 120 m below present(3). This estimate is roughly 10 m lower than inferences based on sea-level data from other far-field sites(4) and, if correct, would suggest that the Barbados record is a largely uncontaminated measure of eustasy(3). However, these previous analyses(1-4) were based on numerical corrections for glacial isostatic adjustment that adopted one-dimensional viscoelastic Earth models. Here we assess the impact of three-dimensional mantle viscoelastic structure on predictions of post-glacial sea-level change at Barbados. Our simulations indicate that the predictions are strongly perturbed by the presence of a high-viscosity slab associated with subduction of the South American Plate beneath the Caribbean Plate. The slab suppresses local deformation and reduces the sea-level rise predicted during the deglaciation phase. To accommodate this reduction while maintaining a fit to the Barbados sea-level record requires an excess ice volume at the Last Glacial Maximum equivalent to about 130 m of eustatic sea-level rise. Given a downward revision in estimates of the Antarctic ice sheet contribution(5) to this excess ice volume, we conclude that a significant amount of Northern Hemisphere ice at the Last Glacial Maximum remains unaccounted for in sea-level-based ice sheet reconstructions.