Reconstruction of Greenland Ice Sheet Mass Balance Using Laser Altimetry Measurements

Recent reconstructions show the imbalance of the Greenland Ice Sheet in the last few decades. It is also projected to continue losing mass in the 21st century under all scenarios of climate change. To better understand the processes of ice mass loss and improve projections, reconstruction of the ice sheet's mass balance with a high spatiotemporal resolution is of great importance. Altimetry measurements capture the detailed surface elevation change with high vertical and horizontal accuracy, which can be converted to mass change using the density of ice. Fusing laser altimetry measurements from NASA's Operation IceBridge, ICESat, and ICESat-2, the Surface Elevation Reconstruction And Change Detection method (SERAC) obtained tens of thousands of time series of surface elevation changes across the ice sheet since the early 1990s. First, we examine these irregularly sampled time series for outliers. Next, the total ice thickness change is calculated by removing elevation changes due to vertical crustal deformation. Finally, dynamic ice thickness change is obtained by removing the elevation changes due to firn compaction and Surface Mass Balance estimated by the IMAU and GSFC FDM (Firn Densification Model). We found that most dynamic ice thickness change time series can be approximated using a third-order polynomial model. However, recent higher resolution data from ICESat-2 reveals the seasonality of dynamic ice thickness change in some tidewater glaciers. We will examine these time series to model the seasonality. The obtained continuous approximation of dynamic ice thickness change at >60,000 locations, combined with the FDMs and SMB anomalies from RACMO2.3p2 and MERRA-2 allows the reconstruction of GrIS ice thickness and mass balance change with unprecedented details. We will present gridded products of mass balance and ice thickness change partitioned to surface processes and ice dynamics, together with the time series, and provide tools to process them.