The influence of decadal- to millennial-scale ice mass changes on present-day vertical land motion in Greenland: implications for the interpretation of GPS observations

We show predictions of present-day vertical land motion in Greenland using a recently developed glacial isostatic adjustment (GIA) model, calibrated using both relative sea level (RSL) observations and geomorphological constraints on ice extent. Predictions from our GIA model are in agreement with the relatively small number of GPS measurements of absolute vertical motion from south and southwest Greenland. This suggests that our model of ice sheet evolution over the Holocene period is reasonably accurate. The uplift predictions are highly sensitive to variations of upper mantle viscosity. Thus, depending on the Earth model adopted, different periods of ice loading change dominate the present-day response in particular regions of Greenland. We also consider the possible influence of more recent changes in the ice sheet by applying a second ice model; specifically, a surface mass balance (SMB) model, which covers the period 1866 to 2005. Predictions from this model suggest that decadal-scale SMB changes over the past ∼140 years play only a small role in determining the present-day viscous response (at the sub-mm/yr level in most locations for a range of Earth model parameters). High rates of peripheral thinning from 1995 to 2005 predicted using the SMB model produce large elastic uplift rates (∼6 mm/yr) in west and southwest Greenland. This suggests that in some areas close to the ice margin, modern surface mass balance changes have a dominant control on present-day vertical land motion.