Linking surface hydrology to flow regimes and patterns of velocity variability on Devon Ice Cap, Nunavut

Abstract

ABSTRACT. Supraglacial meltwater reaching a glacier bed can increase ice surface velocities via hydraulic jacking and enhanced basal sliding. However, the relationships between the structure of supraglacial drainage systems, sink-point distributions, glacier flow processes and the magnitude of interannual velocity variability are poorly understood. To explore the hypothesis that spatial variations in the rate and mechanisms of glacier flow are linked to variations in supraglacial drainage system structure and sink-point distribution across an ice cap, we mapped supraglacial drainage systems on Devon Ice Cap from Landsat-7 ETM+ imagery. Spatial patterns of surface velocity and interannual velocity variability were determined using gradient correlation applied to Landsat-7 ETM+ images. Velocity variability is greater in areas close to sink-point locations, presumably because hydrologically forced basal sliding and/or bed deformation are enhanced in such areas. The distribution and characteristics of supraglacial drainage systems may play an important role in determining the distribution of regions of basal sliding, highlighting the need for knowledge of the supraglacial drainage system structure and sink-point distribution to inform efforts to model the dynamic response of Arctic ice caps to future climate warming.

Supraglacial rivers on the northwest Greenland Ice Sheet, Devon Ice Cap, and Barnes Ice Cap mapped using Sentinel-2 imagery

“…Extensive, complex supraglacial river networks have been observed in the ablation zone of the southwest Greenland Ice Sheet (GrIS) (Thomsen et al, 1989;McGrath et al, 2011;Yang and Smith, 2013;Lampkin and VanderBerg, 2014;Poinar et al, 2015;Smith et al, 2015;Yang and Smith, 2016a;Koziol et al, 2017;Smith et al, 2017), the Antarctic Ice Sheet (Bell et al, 2017;Kingslake et al, 2017), some large ice caps/fields (e.g., Devon Ice Cap (Dowdeswell et al, 2004;Boon et al, 2010), and Juneau Ice Field (Marston, 1983;Karlstrom et al, 2014)) as well as smaller stream systems on many mountain glaciers (Stenborg, 1968;Hambrey, 1977;Knighton, 1985;Brykała, 1998;Rippin et al, 2015;Decaux et al, 2018). These surface drainage features impact the efficacy and speed of meltwater routing to the englacial, subglacial, and proglacial portions of glaciers and ice sheets (Stenborg, 1968;Marston, 1983;Smith et al, 2017;Decaux et al, 2018) and thus coupling processes of surface melt with subglacial hydrology and ice flow (Zwally et al, 2002;Bartholomew et al, 2011;Andrews et al, 2014;Poinar et al, 2015;Smith et al, 2015;Wyatt and Sharp, 2015;Karlstrom and Yang, 2016;Yang and Smith, 2016a;Smith et al, 2017). Where meltwater accumulates on ice shelves, hydrofracture of surface crevasses can trigger their rapid collapse, causing debuttressing and acceleration of upstream glaciers (Scambos et al, 2000;…”

Flow Routing for Delineating Supraglacial Meltwater Channel Networks

“…Manual digitizing nonetheless reveals a well-developed and extensive supraglacial channel network. Previously, there has been limited automated delineation of supraglacial channels over heavily crevassed ice surfaces (e.g., [2,10]), in spite of the fact that the coincidence of crevasses and supraglacial meltwater channels have been linked to high ice flow velocity and variability [3,13,68]. [6] noted that multispectral methods often fail to fully map supraglacial river networks at low elevations (below 1200 m) on the GrIS, although their methods were limited by the 15-m resolution of Landsat data.…”

“…Supraglacial meltwater channels are ubiquitous fluvial features in the ablation zones of glaciers and ice sheets (e.g., [1][2][3][4]). They are of intrinsic interest to researchers as unique fluvial systems as well as for the important roles they play in glacial hydrology.…”

“…Manual delineation of meltwater channels and lakes has been widely used with imagery from various satellites. Landsat ETM+ has been used to assist with meltwater channel digitization on the Devon Ice Cap [3] and the Greenland Ice Sheet (GrIS) [6,29,30]. Optical imagery from WorldView-1 has been used to delineate channels on the GrIS [13,31,32].…”

“…As fluvial systems, researchers have been interested in their morphometrics and controlling processes (e.g., [1,[5][6][7][8][9]), and in how their form may encode landscape processes [10]. Hydrologically, supraglacial meltwater channels influence the spatial and temporal distribution of surface water inputs to en-and sub-glacial hydrological systems [3,[11][12][13], which in turn have been shown to influence glacier and ice sheet dynamics (e.g., [3,14,15]). This recent and growing interest has been concurrent with a growing availability of high-resolution remotely sensed imagery and topographic data of ice surfaces [16][17][18][19][20].…”