AN ENSEMBLE MODELING APPROACH TO ESTIMATE VERTICAL DISPLACEMENTS AND SEA-LEVEL CHANGES IN EASTERN NORTH AMERICA DRIVEN BY GLACIAL ISOSTATIC ADJUSTMENT

Glacial isostatic adjustment (GIA) describes the response of the solid Earth, oceans, and gravitational field to the growth and decay of global ice sheets during a glacial cycle. Since the Last Glacial Maximum, vertical displacements and sea-level changes have varied significantly throughout eastern North America in response to the melting of the Laurentide Ice Sheet. Using the open source software SELEN4.0 (a SealEveL EquatioN solver) we investigate vertical land motions and sea-level changes in eastern North America due to the influence of GIA using ice sheet models ICE6G and ICE7G paired with the nominal viscosity profiles VM5a and VM7, respectively. Further, we evaluate uncertainties in lithospheric thickness as well as viscosity variations of the asthenosphere, transition zone, and shallow lower mantle using an ensemble modeling approach for the recent ice sheet model ICE7G assuming five different ensemble set-ups (43,714 total simulations). By comparing modeled vertical displacements to the GPS imaged vertical velocity solution from Hammond et al. (2021), we identify the best-fitting models in eastern North America and along the East Coast of the United States. Both ICE6G(VM5a) and ICE7G(VM7) show general patterns of subsidence consistent with previous studies. However, we find lower rates of modeled vertical displacements using ICE6G(VM5a) compared with ICE7G(VM7) suggesting results from ICE6G(VM5a) better fit the Hammond et al. (2021) vertical velocity solution. Our ensemble results indicate the VM7 viscosity profile may require adjustments for eastern North America, and we provide a new viscosity model. Further, the structural differences in our best-fitting models for eastern North America and the US East Coast substantiate the need to explore lateral variations in viscosity for GIA modeling throughout North America.