Crustal uplift due to ice mass variability on Upernavik Isstrّm, west Greenland

We estimate the mass loss rate of Upernavik Isstrøm (UI) using surface elevation changes between a SPOT 5 Digital Elevation Model (DEM) from 2008 and NASAʹs Airborne Topographic Mapper (ATM) data from 2010. To assess the validity of our mass loss estimate, we analyze GPS data between 2007 and 2011 from two continuous receivers, UPVK and SRMP which are established on bedrock and located ∼ 65 and ∼ 2 km from the front of UI, respectively. We construct along-track elevation changes on UI for several time intervals during 2005–2011, based on ATM, SPOT 5 and Ice, Cloud, and land Elevation Satellite (ICESat) data to assess temporal changes of UI. We estimate a mass loss rate of −6.7±4.2 Gt/yr, over an area of ∼ 1600 km 2 . The ice mass loss occurs primarily over the northern glacier of UI. This pattern is also observed ∼ 40 km upstream, where we observe glacier thinning at a rate of −1.6±0.3 m/yr across the northern portion of UI and −0.5±0.1 m/yr across the southern portion. GPS measurements suggest bedrock uplift rates of 7.6±0.6 mm/yr (UPVK) and 16.2±0.6 mm/yr (SRMP). The modeled ice mass loss of UI causes bedrock uplift rates of 1.3±0.6 mm/yr (UPVK) and 8.3±4.2 mm/yr (SRMP). Including additional contributions from ice mass changes outside UI and from Glacial Isostatic Adjustment (GIA), we obtain total modeled uplift rates of 4.7±0.6 mm/yr (UPVK) and 13.8±4.2 mm/yr (SRMP). The modeled uplift rates from our UI ice mass loss are substantially lower, indicating that additional mass loss is taking place outside of UI. We obtain a difference of 0.6 mm/yr between the modeled and observed relative uplift rates (SRMP relative to UPVK), suggesting that the mass loss of UI is well captured in the model. We observe elevation changes from −15 to −40 m/yr near the front during the period 2005–2011, indicating that UI undergoes large variations in thinning pattern over short time spans.