Impacts of climate change on secular and seasonal ground motion in Iceland as measured by CGPS

Abstract:

Rapid melting of ice in Iceland results in uplift rates exceeding 25 mm/yr in central Iceland and uplift accelerations of nearly 2 mm/yr², but the relative contributions of the lithosphere’s elastic and viscoelastic responses to uplift acceleration is currently not well understood. We analyzed data from 62 continuous GPS (CGPS) stations throughout Iceland to investigate the uplift signal and its relationship to ice melting. We find that sites in central and southern Iceland, closest to the major ice caps, which measure the largest velocities and accelerations, also display the largest annual vertical variations. Velocity and acceleration estimates are positively correlated with the amplitude of annual site motion with calculated correlation coefficients of 0.8027 and 0.4664 respectively (r₉₅ = 0.2489, n = 62). Since seasonal snow load on the Icelandic glaciers account for a significant proportion of the annual signal measured by GPS, these observations suggest that variability of snow and ice mass loads result in a similar spatial pattern of crustal motion on both annual and decadal time scales, presumably controlled by the current locations of the ice caps and driven by weather and climate, respectively. Simple admittance analysis indicates that annual differences in ice cap mass balance translate to contemporaneous vertical position differences, with model results within 10 mm of observations. We are also able to reproduce observed velocities and accelerations by calculating the response to unloading over a viscous half-space. Both models, however, require an accelerating ice melt rate. We aim to include variations in the seasonal component of CPGS site motion in Iceland as a way to improve our models. We build upon previous work (Grapenthin et al., 2006) and take into account the changing global climate and a documented lengthening of the Arctic melt season in an attempt to better constrain the elastic contribution to observed uplift.