The thickness history of the northern sector of the Laurentide Ice Sheet: an assessment of glacial isostatic adjustment models, sea-level measurements, and vertical land motion rates

Abstract:

The fit of glacial isostatic adjustment (GIA) model predictions to 24 relative sea-level histories and an additional 18 present-day GPS-measured vertical land motion rates constrains the thickness and volume history of the central and northern Laurentide Ice Sheet. The predictions of the best-fit GIA model indicate respective peak ice thicknesses west and east of Hudson Bay of 3.4-3.6 km and approximately 4 km. These values represent, respectively, a large decrease, and a moderate increase, to the load thickness compared to ICE-5G. This result is generally consistent with other GIA studies focussing on space-geodetic constraints. The large reduction to the ice load west of Hudson Bay also reduces the vertical mantle response along the margins of the load centre, which improves the fit to relative sea-level data from the southern Canadian Arctic Archipelago. The fit of GIA model predictions to relative sea-level data from the Baffin Sector of the Laurentide Ice Sheet indicate peak ice thicknesses there of 1.2-1.3 km, a modest reduction compared to ICE-5G. On Baffin Island, the modelled elastic crustal response of the Earth to present-day ice mass changes is large. Accounting for this effect improves the agreement between GPS measurements of vertical crustal motion and the GIA model predictions. However, work is needed to incorporate more detailed observations and modelling of present-day changes to glaciers and ice caps. Overall, the fit to the data is most strongly improved in the region west of Hudson Bay (the χ² RSL misfit is reduced by a factor of ~4) although the entire revised reconstruction for the central and northern Laurentide Ice Sheet provides an improved fit to both the regional RSL data (the cumulative χ² misfit is reduced by a factor of >2) and the GPS data (the RMS misfit is reduced by a factor of 9).