Abstract
Abstract. Surface meltwater is widespread around the Antarctic Ice Sheet margin and has the potential to influence ice shelf stability, ice flow and ice–albedo feedbacks. Our understanding of the seasonal and multi-year evolution of Antarctic surface meltwater is limited. Attempts to generate robust meltwater cover time series have largely been constrained by computational expense or limited ice surface visibility associated with mapping from optical satellite imagery. Here, we add a novel method for calculating visibility metrics to an existing meltwater detection method within Google Earth Engine. This enables us to quantify uncertainty induced by cloud cover and variable image data coverage, allowing time series of surface meltwater area to be automatically generated over large spatial and temporal scales. We demonstrate our method on the Amery Ice Shelf region of East Antarctica, analysing 4164 Landsat 7 and 8 optical images between 2005 and 2020. Results show high interannual variability in surface meltwater cover, with mapped cumulative lake area totals ranging from 384 to 3898 km2 per melt season. By incorporating image visibility assessments, however, we estimate that cumulative total lake areas are on average 42 % higher than minimum mapped values. We show that modelled melt predictions from a regional climate model provide a good indication of lake cover in the Amery region and that annual lake coverage is typically highest in years with a negative austral summer SAM index. Our results demonstrate that our method could be scaled up to generate a multi-year time series record of surface water extent from optical imagery at a continent-wide scale.
Highlights
Surface meltwater has been known to exist in Antarctica since the early 20th century, when explorers noted the presence of thaw-water streams on the Nansen Ice Shelf (Priestly and David, 1912)
As shown by Moussavi et al (2020), we find that the application of a band-thresholding technique within Google Earth Engine (GEE) is highly successful at rapidly identifying surface meltwater features over large areas and time periods
False negative results were rare and mainly occurred where surface water was much darker in colour, presumably either due to sediment suspended within the water column or where lakes appeared to be very deep
Summary
Surface meltwater has been known to exist in Antarctica since the early 20th century, when explorers noted the presence of thaw-water streams on the Nansen Ice Shelf (Priestly and David, 1912). The majority of surface melting occurs at lower latitudes and elevations of the ice sheet periphery (Kingslake et al, 2017), with ponding of surface meltwater abundant on relatively flat ice shelf surfaces (Alley et al, 2018; Stokes et al, 2019). Surface snow scouring by katabatic winds can amplify albedo effects associated with blue-ice areas or exposed nunataks, which can promote surface melting at a localised scale (Kingslake et al, 2017; Arthur et al, 2020a; Jakobs et al, 2021).
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