Abstract
Mass loss across the Greenland Ice Sheet (GrIS) margin is increasing, with dynamic ice flux into the oceans and negative surface mass balance (SMB) being the two main mechanisms of mass loss. In this study, we focus on the SMB component, particularly negative SMB changes in the marginal ablation zone. Currently, SMB models struggle to represent spatial and temporal ablation variations near the GrIS margin, and recent studies have recommended using in-situ measurements and new remote sensing datasets to improve model skill along the ice sheet boundary. We detail and demonstrate a new satellite-based mass budget approach for estimating ablation rates throughout the Upernavik Isstrøm (UI) and Kangiata Nunaata Sermia (KNS) outlet regions. From 2019-2021, we report 396 total ablation rates and uncertainties over nine seasonal, temperate periods, with average measurements of -2.13±3.59 cm/d at UI and -2.50±3.25 cm/d at KNS. Validation efforts using nearby Automatic Weather Station (AWS) observations from the Programme for Monitoring of the Greenland Ice Sheet (PROMICE) network are encouraging, as the ablation rates are within or closely reflect spatially bounded ablation observations. Our mass budget method also shows an ability to reproduce observed ablation rates ranging from ~0 to -6 cm/d. While the average uncertainty at UI and KNS is about ±3.4 cm/d, uncertainty analysis reveals ablation rates at slow-flowing areas, with low longitudinal and transverse stresses, can be estimated within ±2 cm/d. Further validation and uncertainty analyses may improve spatial confidence to where our method can be scaled across a considerable extent of the GrIS margin, without an AWS.