A decade (2002–2012) of supraglacial lake volume estimates across Russell Glacier, West Greenland

Abstract

Abstract. Supraglacial lakes represent an ephemeral storage buffer for meltwater runoff and lead to significant, yet shortlived, episodes of ice-flow acceleration by decanting large meltwater and energy fluxes into the ice sheet's hydrological system. Here, a methodology for calculating lake volume is used to quantify storage and drainage across Russell Glacier, West Greenland, between 2002 and 2012. Using 502 MODIS scenes, water volume at ∼ 200 seasonally occurring lakes was derived using a depth-reflectance relationship, which was independently calibrated and field validated against lake bathymetry. The inland expansion of lakes is strongly correlated with air temperature: during the record melt years of 2010 and 2012, lakes formed and drained earlier, attaining their maximum volume 38 and 20 days earlier than the 11 yr mean, as well as occupying a greater area and forming at higher elevations (> 1800 m) than previously. Despite occupying under 2 % of the study area, lakes delay the transmission of up to 7-13 % of the bulk meltwater discharged. Although the results are subject to an observational bias caused by periods of cloud cover, we estimate that across Russell Glacier, 28 % of supraglacial lakes drain rapidly (< 4 days). Clustering of such events in space and time suggests a synoptic trigger mechanism. Further, we find no evidence to support a unifying critical size or depth-dependent drainage threshold.

Sensitive response of the Greenland Ice Sheet to surface melt drainage over a soft bed

“…10) cannot be instantaneously accommodated by expansion of a channelized basal drainage system 51 . Rather, the accelerated flow observed in late summer, when an efficient drainage system had already developed 12,28,51 , points to subglacial evacuation of water in a high-pressure system 5,30 .…”

“…Surface melt and storage in SGLs occurred at higher elevations during recent warm summers, and are expected to expand inland as climate warms [9][10][11] , but it remains unclear how this will affect ice flow. Interpretation of field observations is complex, with some studies suggesting that more melt will increase annual flow [12][13][14] while others suggest the opposite [15][16][17][18] .…”

Recent Advances in Our Understanding of the Role of Meltwater in the Greenland Ice Sheet System

“…In order for surface lakes to drain, an appropriate stress regime in the ice is required with existing crevasses, which can then be exploited and expanded by ponded surface waters draining englacially via hydrofracture [46][47][48]. There is as yet no evidence however to support the idea of a unifying critical lake volume or depthdependent drainage threshold [38].…”

“…The lakes can either drain rapidly by hydrofracture [9,41,42] or more slowly by overtopping their topographic lip and draining supraglacially downstream [43][44][45]; a 5-year study of 2000 Greenland-wide supraglacial lakes estimated that 13% of the lakes were 'fast-draining' (< 2 days) [35], while a 10-year catchment-based study of~200 lakes estimated that 28% of the lakes drained 'rapidly' (< 4 days) [38]. Rapid lake drainage results in large volumes of water entering the subglacial drainage system in a few hours with rates of 8700 and 3300 m 3 s −1 recorded [9,41].…”

“…During the course of each melt season, the lakes first form at lower elevations, and the majority subsequently drain, with these processes extending to higher elevations as air temperatures rise and the melt season progresses [38][39][40]. The lakes can either drain rapidly by hydrofracture [9,41,42] or more slowly by overtopping their topographic lip and draining supraglacially downstream [43][44][45]; a 5-year study of 2000 Greenland-wide supraglacial lakes estimated that 13% of the lakes were 'fast-draining' (< 2 days) [35], while a 10-year catchment-based study of~200 lakes estimated that 28% of the lakes drained 'rapidly' (< 4 days) [38].…”