Abstract
AbstractSurface meltwater is becoming increasingly widespread on Antarctic ice shelves. It is stored within surface ponds and streams, or within firn pore spaces, which may saturate to form slush. Slush can reduce firn air content, increasing an ice-shelf's vulnerability to break-up. To date, no study has mapped the changing extent of slush across ice shelves. Here, we use Google Earth Engine and Landsat 8 images from six ice shelves to generate training classes using a k-means clustering algorithm, which are used to train a random forest classifier to identify both slush and ponded water. Validation using expert elicitation gives accuracies of 84% and 82% for the ponded water and slush classes, respectively. Errors result from subjectivity in identifying the ponded water/slush boundary, and from inclusion of cloud and shadows. We apply our classifier to the Roi Baudouin Ice Shelf for the entire 2013–20 Landsat 8 record. On average, 64% of all surface meltwater is classified as slush and 36% as ponded water. Total meltwater areal extent is greatest between late January and mid-February. This highlights the importance of mapping slush when studying surface meltwater on ice shelves. Future research will apply the classifier across all Antarctic ice shelves.
Highlights
Surface meltwater is present on the majority of Antarctica’s ice shelves (e.g. Langley and others, 2016; Kingslake and others, 2017; Macdonald and others, 2019; Stokes and others, 2019; Arthur and others, 2020a; Dell and others, 2020; Banwell and others, 2021)
As with the ponded water class, these discrepancies tend to cancel out between experts giving an overall mean spread across all ice shelves of just 5%
The relative importance of each band within our supervised classifier was determined within Google Earth Engine (GEE) using the ‘.explain()’ function, and the results show that all bands contribute towards the classification of slush and ponded water (Table 6)
Summary
Surface meltwater is present on the majority of Antarctica’s ice shelves (e.g. Langley and others, 2016; Kingslake and others, 2017; Macdonald and others, 2019; Stokes and others, 2019; Arthur and others, 2020a; Dell and others, 2020; Banwell and others, 2021) It can act as a key control on ice-shelf stability (Lai and others, 2020) and the contribution of Antarctica’s grounded ice to global sea level rise (Rignot and others, 2004; Berthier and others, 2012; Furst and others, 2016). Despite the potential role of water as slush in driving hydrofracture, there has been very little research investigating the changing extent of slush on ice shelves This means that previous research will have underestimated total surface meltwater areas on Antarctic ice shelves, and underestimated their potential vulnerability to hydrofracture and collapse
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