Continuous Monthly Observations of Greenland Ice Sheet Discharge via Improved Multi-Decadal Flux Reconstructions of all Major Outlet Glaciers

As part of the Greenland Ice Mapping Project (GIMP), we have derived an improved time series of monthly discharge estimates of the Greenland Ice Sheet (GrIS) from high-resolution flow speed measurements of all major (> 1 km wide) Greenland outlet glaciers. Dense time series are produced by first combining repeat-path and cross-path combinations of ASTER, Landsat 7 and Landsat 8 optical imagery, with orthorectification errors corrected using the GIMP digital elevation model. Flow speed estimates calculated over both short and long temporal intervals are augmented with observations from previously documented TerraSAR-X and RADARSAT-1 and -2 radar measurements. Seasonal variability in glacier flow is estimated by combining annual mean observations of flow speeds with available wintertime speed observations from radar sources. Annual flow speed models are constrained by available short-baseline observations from both optical and radar sources, to produce continuous time series of glacier flow speeds that capture long term dynamical changes and variability in the timing and magnitude of seasonal acceleration. In conjunction with observations of glacier flow speeds, variability in ice thickness derived from ASTER, SPOT-5 and Arctic DEM's are integrated to produce high-resolution time series of glacier discharge. Monte Carlo-based methods are implemented on glacier time series to derive discharge uncertainty estimates. Taken together, these individual glacier discharge time series are used to calculate continuous monthly observations of net ice discharge from the GrIS. Here we discuss distinct features in the time series of GrIS discharge and variability of the net seasonal flux signal over the 2000-2016 period. As a NASA MEaSUREs Project, all GIMP products are openly available at the National Snow and Ice Data Center.