Abstract

Quantifying the extent and distribution of supraglacial hydrology, i.e. lakes and streams, is important for understanding the mass balance of the Antarctic ice sheet, and its consequent contribution to global sea level rise. The existence of meltwater on the ice surface has the potential to affect ice shelf stability and grounded ice flow, through hydrofracturing and the associated delivery of meltwater to the bed. In this study, we systematically map all observable supraglacial lakes and streams in West Antarctica, by applying a semi-automated Dual-NDWI (Normalised Difference Water Index) approach to > 2000 images acquired by the Sentinel-2 and Landsat-8 satellites during January 2017. We use a K-Means clustering method to partition water into lakes and streams, which is important for understanding the dynamics and inter-connectivity of the hydrological system. When compared to a manually-delineated reference dataset on three Antarctic test sites, our approach achieves average values for sensitivity (85.3 % and 77.6 %), specificity (99.1 % and 99.7 %) and accuracy (98.7 % and 98.3 %) for Sentinel-2 and Landsat-8 acquisitions, respectively. In total, we identified 10,478 supraglacial features (10,223 lakes and 255 channels) on the West Antarctic Ice Sheet (WAIS) and Antarctic Peninsula (AP), with a combined area of 119.4 km2 (114.7 km2 lakes, 4.7 km2 channels). 27.3 % of feature area was found on grounded ice, 17.8 % of feature area comprised lakes which crossed the grounding line, while 54.9 % of feature area was found on floating ice shelves. New continental-scale inventories such as these, the first produced for WAIS and AP, are made possible by the recent expansion in satellite data provision. The inventories provide a baseline for future studies and a benchmark to monitor the development of Antarctica’s surface hydrology in a warming world, and thus enhance our capability to predict the collapse of ice shelves in the future. The dataset is available at https://doi.org/10.5281/zenodo.5109856 (Corr et al., 2021).

Highlights

  • 20 The supraglacial hydrological network describes the complex, interconnected system of water movement over the surface of glaciers and ice sheets

  • We identified 10,478 supraglacial features (10,223 lakes and 255 channels) on the West Antarctic Ice Sheet (WAIS) and Antarctic Peninsula (AP), with a combined area of 119.4 km2 (114.7 km2 lakes, 4.7 km2 channels). 27.3% of feature area was found on grounded ice, 17.8% of feature area comprised lakes which crossed the grounding line, while 54.9% of feature area was found on floating ice shelves

  • Supraglacial lakes (SGLs) are found in expected regions, on and around the grounding zone of the Antarctic peninsula ice shelves including Larsen C (∼130 lakes), Larsen D (∼250), George VI (∼5,550), Wilkins (∼1450) and Bach (∼950)

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Summary

Introduction

20 The supraglacial hydrological network describes the complex, interconnected system of water movement over the surface of glaciers and ice sheets. Knowing the location and characteristics of supraglacial hydrological networks are important on ice sheets because they can alter the location, volume, timing and rate of meltwater drainage (Bell et al, 2018) As such, they provide a possible mechanism through which climate warming and associated increases in surface melt might affect the dynamic stability of Earth’s polar ice sheets (Bell et al, 2018; Lenaerts et al, 2016; Trusel et al, 2015). It is possible that supraglacial hydrology may exert a larger effect on Antarctica’s future evolution, for example the limit on rise in global temperatures of 1.5◦C (UN Paris Agreement’s goal is to limit global warming to well below 2◦C, preferably to 1.5◦C, compared to pre-industrial levels: https://unfccc.int/sites/default/files/english_paris_ agreement.pdf) will likely cause the Antarctic Peninsula to experience irreversible, dramatic change to glacial, terrestrial and 65 ocean systems (Siegert et al, 2019) Under this degree of warming (1.5◦C), ice shelves will experience continued increase in meltwater production and meltwater will become more extensive (Siegert et al, 2019). The impact of increased meltwater upon ice shelf stability and ice dynamics is not well understood, and mapping the distribution and evolution of the hydrological system from Earth observation has become a key priority of research

Data and methods
Satellite imagery
Normalised Difference Water Index (NDWI) thresholding
Cloud, rock masking and elimination of slush, blue-ice and shaded pixels
Post-processing
Lake vs channel classification
Accuracy assessment
Distribution of supraglacial lakes and streams in West Antarctica
Comparison to supraglacial features in East Antarctica
Data usage
Conclusions
Code and data availability

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