Vertical Displacements and Sea-Level Changes in Eastern North America Driven by Glacial Isostatic Adjustment: an Ensemble Modeling Approach

Abstract

Glacial isostatic adjustment (GIA) describes the response of the solid Earth, oceans, and gravitational field to the spatio-temporal evolution of ice sheets during a glacial cycle. Present-day vertical displacements and sea-level changes vary throughout eastern North America in response to the melting of the Laurentide Ice Sheet following the Last Glacial Maximum. We use the open-source software SELEN4.0 (a SealEveL EquatioN solver) to investigate the influence of GIA on vertical land motions and sea-level changes in eastern North America. Further, we evaluate the uncertainties associated with the lithospheric thickness and viscosity structure using an ensemble modeling approach (129,956 total simulations). We identify the best-fitting rheological profiles by comparing modeled vertical displacements to vertical velocity rates derived from Global Positioning System (GPS). We find a general pattern of subsidence (causing accelerated relative sea-level rise) in the eastern United States region and uplift (causing relative sea-level fall) in the eastern Canada region consistent with previous studies for two tested ice sheet models (ICE-6G(VM5a) and ICE-7G(VM7)). Overall, we find lower rates of modeled vertical displacement using ICE-6G(VM5a) compared with ICE-7G(VM7), which produces lower residuals when compared with the GPS-derived vertical velocity rates. Our ensemble analysis identifies adjustments to the nominal VM5a and VM7 viscosity models that improve fits to the GPS-imaged vertical velocity rates throughout eastern North America and on the North American Atlantic Coast. The differences in our best-fitting models for inland versus coastal regions highlight the importance of exploring lateral viscosity variations for GIA modeling throughout North America and elsewhere.