Seasonal evolution of supraglacial lakes and rivers on the southwest Greenland Ice Sheet

Kang Yang,Xin Lu,Laurence C Smith,Lincoln H Pitcher,Yao Lu,Dirk Van As,Matthew G Cooper,Manchun Li

doi:10.1017/jog.2021.10

Kang Yang, Xin Lu + Show 6 more

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https://doi.org/10.1017/jog.2021.10

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Abstract

AbstractSupraglacial lakes and rivers dominate the storage and transport of meltwater on the southwest Greenland Ice Sheet (GrIS) surface. Despite functioning as interconnected hydrologic networks, supraglacial lakes and rivers are commonly studied as independent features, resulting in an incomplete understanding of their collective impact on meltwater storage and routing. We use Landsat 8 satellite imagery to assess the seasonal evolution of supraglacial lakes and rivers on the southwest GrIS during the 2015 melt season. Remotely sensed meltwater areas and volumes are compared with surface runoff simulations from three climate models (MERRA-2, MAR 3.6 and RACMO 2.3), and with in situ observations of proglacial discharge in the Watson River. We find: (1) at elevations >1600 m, 21% of supraglacial lakes and 28% of supraglacial rivers drain into moulins, signifying the presence of high-elevation surface-to-bed meltwater connections even during a colder-than-average melt season; (2) while supraglacial lakes dominate instantaneous surface meltwater storage, supraglacial rivers dominate total surface meltwater area and discharge; (3) the combined surface area of supraglacial lakes and rivers is strongly correlated with modeled surface runoff; and (4) of the three models examined here, MERRA-2 runoff yields the highest overall correlation with observed proglacial discharge in the Watson River.

Highlights

Extensive fluvial supraglacial hydrologic networks are observed across the southwest Greenland Ice Sheet (GrIS) ablation zone (Smith and others, 2015, 2017; Yang and Smith, 2016; Pitcher and Smith, 2019)
The present study firmly asserts the presence of high-elevation (>1600 m) moulins on the southwest GrIS, with 21% of high-elevation supraglacial lakes and 28% of rivers draining into them (Figs 3f, 5c)
We find 2.5–14.4% of surface runoff is stored in supraglacial lakes and rivers, a finding consistent with: (1) a model study for Paakitsoq, which reports values of 5–10% of runoff stored in supraglacial lakes in 2001, 2002 and 2005 (Arnold and others, 2014); (2) a value of 12% modeled for the entire southwest sector of the GrIS in 2003 (Leeson and others, 2012); and (3) remotely sensed values of 7–13% for the Watson river basin in 2010 and 2012 (Fitzpatrick and others, 2014)

Summary

Introduction

Extensive fluvial supraglacial hydrologic networks are observed across the southwest Greenland Ice Sheet (GrIS) ablation zone (Smith and others, 2015, 2017; Yang and Smith, 2016; Pitcher and Smith, 2019). Supraglacial lakes are located in surface topographic depressions (Liang and others, 2012) and are estimated to impound 5–13% of instantaneous surface meltwater during the melt season (Leeson and others, 2012; Arnold and others, 2014; Fitzpatrick and others, 2014) While most of these lakes drain laterally into supraglacial rivers over timescales of weeks to months (Tedesco and others, 2013; Smith and others, 2015), some drain vertically via hydrofracture and moulin formation over hours to days (Das and others, 2008), and others retain meltwater overwinter (Koenig and others, 2015; Lampkin and others, 2020). Both rivers and lakes inject meltwater into the ice sheet via moulins and crevasses, modulating basal water pressure and evolution of the subglacial hydrologic system (Hoffman and others, 2011; Andrews and others, 2014)

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