PAST AND PRESENT SEA-LEVEL CHANGES AND THEIR UNCERTAINTIES IN NORTH AMERICA FROM 3D GLACIAL ISOSTATIC ADJUSTMENT MODELLING

North America, whose northern part was covered by the Laurentide Ice Sheet during the Last Glacial Maximum (LGM) with a sea-level equivalent of ~85 m (Peltier et al., 2015, JGR), has been a key area for Glacial Isostatic Adjustment (GIA) studies. Previous GIA studies have applied 1D models of Earth’s internal structure in such analyses, however, seismic tomography, field geology and more recent studies reveal the potential importance of 3D models of this structure. Here, we use (1) quality-controlled deglacial sea level database from the Atlantic (Engelhart and Horton, 2012, QSR; Vacchi et al., 2018, QSR) and Pacific coasts of North America (Engelhart et al. 2015, QSR); (2) Global Navigation Satellite System (GNSS) data and (3) Gravity Recovery And Climate Experiment (GRACE) data in North America to investigate the effects of lateral variations of elastic lithospheric thickness, mantle viscosities, and sub-lithosphere and asthenosphere properties on relative sea-level (RSL) predictions in North America. We fix the glaciation/deglaciation model with the ICE-6G_C ice model (Peltier et al., 2015, JGR).

We compute gravitationally self-consistent RSL histories for the 3D Earth models with time dependent coastlines and rotational feedback using the Coupled Laplace-Finite Element Method.Spatially, the size of the deglacial RSL uncertainties varies across North America with the largest from Hudson Bay (~30 m at 15 ka BP) and near previous ice margins along the northern Atlantic (e.g. ~25 m at 15 ka BP) and Pacific coasts (e.g. 20 m at 15 ka BP). Temporally, RSL uncertainties decrease from the LGM to present except for west of Hudson Bay and northeastern Pacific coast, where uncertainties increase from 30 to 45 m between 15 and 11 ka BP. Present-day rates of vertical land motion and gravity change uncertainties are largest in southwestern Hudson Bay with magnitude of 2.4 mm/year and 0.4 microGal/year, mainly due to the 3D viscosity structure in the lower mantle. To study the GIA component in present sea level change, we also compare the predicted present rate of sea-level change with uncertainty, with tide gauge data from Permanent Service for Mean Sea level.