Glacial isostatic adjustment along the Pacific coast of central North America

We infer the GIA signal and its uncertainty along the central Pacific coast of North America using 680 sea-level index points and over 20,000 model runs sampling >700 (1-D) Earth viscosity models and 29 ice sheet reconstructions. Due to the large spatial extent and different tectonic settings of the study area, we divided it into three sub-regions (northern, central and southern) for which model parameters were inferred separately. Also, given that this region is tectonically active, the influence of this process (as well as sediment isostatic adjustment) was accounted for where possible by removing it from the data using published estimates. Our results indicate that it is not possible to produce an acceptable to for all of the RSL data with a single set of model parameters, suggesting significant lateral variability in viscous structure. Specifically, low viscosities (1019–1020 Pas) are inferred in the upper mantle within the northern region (southwestern British Columbia and northwest Washington) compared to those inferred (2–5 × 1020 Pas) for the central and southern regions (extending from southern Washington to southern California). High quality model fits were obtained for all data except those from the northern region where no single parameter set was able to capture both the rapid and large RSL fall during the late glacial and the monotonic rise during the mid-to-late Holocene at all localities. This suggests the need for an Earth model that incorporates departures from a linear Maxwell rheology (as applied here) and/or lateral variations in viscosity structure. Using our optimal model parameter sets, we show that GIA is a significant contributor to both contemporary vertical land motion and relative sea level change in our study region and so should be considered when interpreting observations of these signals and for making future relative sea level projections. Model output of present-day vertical land motion at 483 GPS stations and sea-level change at 56 tide gauge stations is provided (with estimated uncertainty) so that these data can be used to study non-GIA processes more accurately.