ALBERT

Description: The continuously operating Global Positioning System (GPS) sites mounted on bedrock around the coast of Greenland provide important geodetic datasets to quantify the solid Earth's response to historical and present-day ice mass variations. The presence of colored noise and changeable seasonal signals makes it difficult to detect transient changes in GPS time series. Here we apply the Multichannel Singular Spectral Analysis to the combination of GPS data and Gravity Recovery and Climate Experiment (GRACE) data so that we can identify and fully utilize the spatial correlations from these two independent datasets. Using the GPS and GRACE data near Upernavik Isstrøm in West Greenland as an example, we demonstrate that this method successfully detects two transient signals in ice mass variations during 2008 and 2014. Our forward modeling of loading displacements due to changes in surface mass balance (SMB) and ice dynamics suggests that the transient change starting in mid-2008 was due to the combined contributions from dynamically-induced mass loss and SMB. 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. This dataset includes: (1) Vertical displacements inferred from GPS and GRACE with atmospheric loading, non-tidal ocean loading, and terrestrial water storage loading removed. Gaps are filled and linear trends are also removed. This data are used for multi-channel singular spectral analysis (M-SSA) in the paper. (2) Transient and seasonal signals extracted from GPS and GRACE data by M-SSA. (3) Transient and seasonal signals extracted from surface mass balance data by M-SSA. (4) Transient signals inferred from glacial dynamics.