Quantification of the Impact of Supraglacial Lakes and Slush on Surface Energy Balance of Ice Shelves: Nivlisen Ice Shelf, East Antarctica

• Main Author: Lefroy, Naomi
• Format: Master Thesis
• Language: English
• Published: Scott Polar Research Institute 2020
• Subjects: Supraglacial lakes; Slush; Antarctic ice shelves; Surface hydrology; Nivlisen Ice Shelf; East Antarctica; Antarctic; Austral; Nash; Nivlisen; Sutcliffe; Antarc*; Antarctica; Ice Shelf; Ice Shelves
• Online Access: https://doi.org/10.17863/CAM.70559; https://www.repository.cam.ac.uk/handle/1810/323107

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 ...