Annual Variations in GPS-measured Loading Deformation near Upernavik Isstrøms, Greenland

Abstract:

Most of observational studies on the Greenland Ice Sheet mass balance focus on detecting linear trends of mass loss at multi-decadal or longer periods. Yet short-term, non-secular mass variations are poorly observed, especially at individual outlet glaciers that are largely responsible for recent dramatic changes happening on Greenland. In this study we examined the annual variations in the crustal uplift measured at two continuous Global Positioning System (GPS) stations near Upernavik Isstrøms in western Greenland. Both GPS time series show pronounced annual cycles, resulted from strong annual changes in all surface mass combined. To detect and interpret glaciological signature in the GPS uplift measurements, we modeled and removed surface mass loading from non-ice sources, including atmospheric, ocean, and continental water mass changes. Of these components, the atmospheric mass loading is the largest contributor, accounting for about 47–70% of the annual variability. We also compared the residual GPS uplift with the modeled surface mass balance (SMB) loading based on a climate simulation model RACMO2/GR and found that the latter overestimates the annual variability. This discrepancy makes it difficult to assess contributions from glacial dynamics to the glacial mass balance at annual periods and requires an improved modeling effort. Our study underlines the importance of quantifying loading from various sources and their uncertainties for better understanding short-term glacial variability from GPS measurements.