Abstract
ABSTRACTThe controls on rapid surface lake drainage on the Greenland ice sheet (GrIS) remain uncertain, making it challenging to incorporate lake drainage into models of GrIS hydrology, and so to determine the ice-dynamic impact of meltwater reaching the ice-sheet bed. Here, we first use a lake area and volume tracking algorithm to identify rapidly draining lakes within West Greenland during summer 2014. Second, we derive hydrological, morphological, glaciological and surface-mass-balance data for various factors that may influence rapid lake drainage. Third, these factors are used within Exploratory Data Analysis to examine existing hypotheses for rapid lake drainage. This involves testing for statistical differences between the rapidly and non-rapidly draining lake types, as well as examining associations between lake size and the potential controlling factors. This study shows that the two lake types are statistically indistinguishable for almost all factors investigated, except lake area. Thus, we are unable to recommend an empirically supported, deterministic alternative to the fracture area threshold parameter for modelling rapid lake drainage within existing surface-hydrology models of the GrIS. However, if improved remotely sensed datasets (e.g. ice-velocity maps, climate model outputs) were included in future research, it may be possible to detect the causes of rapid drainage.
Highlights
AND AIMSMany supraglacial lakes that form annually within the ablation zone of the Greenland ice sheet (GrIS) drain in the mid- to late season, while others freeze in the autumn (Selmes and others, 2013; Tedesco and others, 2013; Miles and others, 2017)
Previous studies have suggested that rapid lake drainage is a key contributor to the GrIS’s negative mass balance and may become more widespread in the future as lakes continue to advance inland
This means that we cannot recommend an empirically supported alternative to the fracture area threshold parameter in use within current surface-hydrology models of the GrIS (Banwell and others, 2013, 2016; Arnold and others, 2014; Clason and others, 2015; Koziol and others, 2017), but nor can we provide evidence to support the use of a fracture area threshold parameter in future surface-hydrology models if the aim is to predict the precise magnitude and timing of individual rapid lake-drainage events
Summary
AND AIMSMany supraglacial lakes (hereafter ‘lakes’) that form annually within the ablation zone of the Greenland ice sheet (GrIS) drain in the mid- to late season, while others freeze in the autumn (Selmes and others, 2013; Tedesco and others, 2013; Miles and others, 2017). Draining lakes, and those draining rapidly, are of additional interest because they affect ice velocities via the delivery of large meltwater volumes to the ice-sheet bed (e.g. Zwally and others, 2002; van de Wal and others, 2008; Schoof, 2010; Colgan and others, 2011a; Cowton and others, 2013; Fitzpatrick and others, 2013; Bougamont and others, 2014 Dow and others, 2014) These meltwater pulses can overwhelm the capacity of the subglacial drainage system, lower subglacial effective pressure, enhance basal sliding and increase surface ice velocity by >200% of background winter levels over short (hourly–daily) timescales (Shepherd and others, 2009; Schoof, 2010; Hoffman and others, 2011; Bartholomew and others, 2011a,b, 2012; Banwell and others, 2013; Tedesco and others, 2013; Andrews and others, 2014; Bougamont and others, 2014; Kulessa and others, 2017). This moulin opening is important because cold-based ice at central depths of the GrIS acts as a thermal barrier to water penetration, likely meaning that water can reach the ice bed only through such fractures (Irvine-Fynn and others, 2011; Lüthi and others, 2015; Greenwood and others, 2016; Poinar and others, 2017)
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