Annual variations in GPS‐measured vertical displacements near Upernavik Isstrøm (Greenland) and contributions from surface mass loading

Abstract

In response to present‐day ice mass loss on and near the Greenland Ice Sheet, steady crustal uplifts have been observed from the network of Global Positioning System (GPS) stations mounted on bedrock. In addition to the secular uplift trends, the GPS time series also show prominent annual variability. Here we examine the annual changes of the vertical displacements measured at two GPS stations (SRMP and UPVK) near Upernavik Isstrøm in western Greenland. We model elastic loading displacements due to various surface mass loading including three nonice components: atmospheric pressure, ocean bottom pressure, continental water storage, and one ice component, i.e., surface mass balance (SMB). We find that the contribution from atmospheric pressure changes can explain 46% and 78% of the annual amplitude observed in the GPS verticals at SRMP and UPVK, respectively. We also show that removing the predicted loading displacements due to SMB adversely increases the annual variance of the GPS residuals. However, using the GPS data alone, we cannot identify the exact cause(s) of this discrepancy because the annual loading displacements are sensitive to the SMB changes from over 85% of the ice sheet area. Alternatively, by differencing vertical displacements between the two stations, we find a good agreement between the modeled differential SMB loading displacements and the GPS residuals after removing nonice components. Our study highlights the necessity of correcting for nonice loading contributions in the GPS measurements of crustal deformation to infer ice mass changes in Greenland at annual periods.

Characterizing the Seasonal Crustal Motion in Tianshan Area Using GPS, GRACE and Surface Loading Models

“…The linear trends caused by tectonic process were removed from the time series [8,11,18]. To further analyze the correlation between the three time series, the mean, trend, annual and semiannual signals were simultaneously fitted using Equation (2) [39].…”

“…SLMs can not only remove the corresponding seasonal effect of surface loadings in the GPS results, but also provide smaller scale change information that cannot be resolved by GRACE [12][13][14]. The combination of GRACE and SLMs is used to remove the effect of non-tectonic seasonal signals in the GPS data, which is helpful for obtaining accurate tectonic deformation field information and other geophysical phenomena we are interested in within the target area [15][16][17][18][19].…”

Transient Variations in Glacial Mass Near Upernavik Isstrøm (West Greenland) Detected by the Combined Use of GPS and GRACE Data

“…SRMP (54.3937°W, 72.9107°N) is located only 1.5 km west of the UI‐2's frontal position in 2011, whereas UPVK (56.1280°W, 72.7883°N) is on an island located 65 km farther west of the glaciers. To obtain daily positions, we process the GPS data from 2007 to 2016 using the GIPSY‐OASIS v6.4 software package and using conventional methods detailed in Khan, Liu, et al () and Liu et al (). We estimate the position uncertainties using the flicker plus white noise model (Khan, Liu, et al (); Williams et al, ).…”

“…Liu et al () gave a detailed description of modeling ATML, TWS, and NTOL at the two Upernavik GPS sites. Here we only provide a summary.…”

“…The transient change starting in mid-2011 was mainly due to ablation. Specifically, the ice melted more in 2012 and less in 2013 with little contribution from anomalies in accumulation.In the past decade the Greenland GPS network (GNET), deployed on bedrock around the coast of Greenland, has been continuously operating and monitoring the crustal displacement caused by the solid Earth's elastic/viscoelastic response to present/historical ice mass changes (Adhikari et al, 2017;Bevis et al, 2012;Khan et al, 2014;Khan, Liu, et al, 2010;Khan et al, 2016;Liu et al, 2017). Most of the previous studies have been focusing on the linear and seasonal changes in crustal loading/unloading, whereas only a few investigated short-term changes.…”