Decade Long Time Series (2015 - 2024) of Ice Slab Expansion in Greenland using Sentinel-1 SAR

Ice slabs are multi-meter thick layers of refrozen meltwater that form in the Greenland Ice Sheet (GrIS) percolation zone and play a crucial role in modulating surface runoff. The limited permeability of ice slabs restricts the vertical percolation of meltwater into underlying firn, thus accelerating runoff. Improving understanding of ice slab growth and evolution is crucial to improving understanding of GrIS supraglacial hydrology, reducing uncertainty in projections of GrIS surface runoff rates, and improving global sea level rise estimates. Existing maps of ice slab extent have been developed using NASA’s Operation Ice Bridge Accumulation Radar data collected between 2011-2014 and 2017-2018 as well as Soil Moisture Active Passive (SMAP) L-band radar data averaged over 2015-2019, however both of these datasets have some combination of limited spatial resolution, poor spatial coverage, or inconsistent temporal coverage, making it difficult to capture high resolution rates of inland expansion.

Here, we present the first annual time series of ice slab extent from 2015 through 2024, derived from polarimetric Sentinel-1 backscatter measurements. This work yields maps of the full spatial extent and continuity of ice slabs at 500 m² resolution and establishes a comprehensive decade-long record of ice slab behavior in a warming climate. To assess atmospheric drivers of ice slab growth over this time, we compare our observations of inland expansion to hindcasts from two regional climate models: MAR and RACMO. We also compare our time series to the existing MacFerrin and Brils models of ice slab expansion to evaluate whether computationally expensive firn models are needed to predict ice slab expansion. Our work ensures continuous monitoring of ice slab expansion into the 2030s with the arrival of each new year of Sentinel-1 data and provides a basis for improving model predictions of surface mass balance in Greenland’s wet snow zone.