Supraglacial lakes (SGLs) and slush are prevalent features of Antarctic ice shelf surface hydrology and efficiently transfer energy to the ice by melt-albedo feedbacks (Dell et al., 2020; Moussavi et al., 2020). There have been few efforts to quantify the energy exchanges between supraglacial meltwater, atmosphere, and ice (Jakobs et al., 2019), despite suggestions that low albedo surface features are melt hotspots (Miles et al., 2016). This study aims to quantify the extra energy absorbed by SGLs and slush on Nivlisen Ice Shelf (NIS), East Antarctica, over the austral summers of 2017-2020.

First, a new method is developed for defining SGL, slush, and ice extent using a Principal Components Analysis (PCA) on spectral data derived from Sentinel-2 and Landsat 8 imagery. A surface energy balance (SEB) model is developed, following Buzzard et al. (2018) and Law et al. (2020), and applied across the extracted supraglacial feature extents using Global Forecast System meteorological data.

The SEB model calculates the mean daily energy absorbed by lake and slush areas as ~ 8.7 MJ/m2 and ~ 0.54 MJ/m2 for the austral summers of 2017-2020. Modelled energy balance at lake and slush regions is most sensitive to incident shortwave radiation, although local ice shelf processes affect spatial variability of sensible and latent heat fluxes. The results of the SEB model are validated by comparing modelled cumulative energy absorption at SGLs with inferred energy transfer derived from SGL volume. The Nash-Sutcliffe Efficiency value of 0.922 implies that the modelled energy absorption matches the inferred dataset well. Furthermore, high agreement (62 %) between the supraglacial feature masks, produced using different satellite data, supports further use of the PCA in Antarctic hydrological research.

Overall, despite the low spatial coverage of SGLs at ~ 1.6 % of the total area, water coverage on NIS represents a substantial means of energy absorption. A significant finding of this study is that exclusion of slush in previous energy balance calculations is likely to have underestimated the net transfer of energy to Antarctic ice shelves. Total extra energy absorbed across the slush region in 2019 is equivalent to that absorbed by SGLs, suggesting that slush extent can be a significant control on energy absorption.

The confirmed significance of slush and SGLs for energy absorption, and the validity of the SEB model, support the application of methods developed in this study at pan-Antarctic scales. Quantification of the ice sheet-scale energy absorption by SGLs and slush would provide a baseline to gauge meltwater and sea level rise contribution under different atmospheric forcing projections.