Role of discrete recharge from the supraglacial drainage system for modelling of subglacial conduits pattern of Svalbard polythermal glaciers

Abstract

Abstract. Being a determinant factor of the glacier's dynamic, subglacial water behavior needs a special attention. Water flowing from the glacier's surface is the principal source supplying the subglacial drainage system. Therefore, insight into the state and evolution of the supraglacial drainage system is crucial for recognition of recharge pattern of the englacial and subglacial drainage pathways. Climate warming causes increased ablation generating higher amount of meltwater and thinning of glacier.Decadal timescale evolution of the supraglacial drainage leads to some modifications of the system in opposition to its nearly 5 stable state on an annual timescale. For two studied glaciers Hansbreen and Werenskioldbreen in southern Svalbard surface meltwater is the main runoff component. During the ablation season 2015, 72.5 % of the total amount was provided by meltwater and 27.5 % by precipitations. Supraglacial catchments were determined on the high resolution digital elevation model using standard watershed modelling tool in ArcGIS, for each water-input area (WIA). Spatialized water runoff calculations for all the main WIAs have been done. Having data on the water sources from catchments delimited on glacier's surface, mod-10 elling of a theoretical pattern of subglacial conduits was done considering discrete water recharge via moulins, shear fractures or crevasses. Classical modelling with an assumption of homogeneous water supply was done for comparison. Several water pressure conditions have been taken into account as well. Results show that models of subglacial drainage system with homogeneous water recharge are more realistic for tidewater glaciers with rather broad permeable firn areas and creased frontal zones, while discrete water recharge models are better for land-terminating glaciers with almost continuous impermeable su-15 perficial cold ice layer. Subglacial channel models are assumed to be valid for a minimum period of two decades taking into account evolution of supraglacial drainage system and ice thickness changes of Svalbard polythermal glaciers.

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

“…Small supraglacial streams are ubiquitous on the southwest GrIS yet are largely undetected in 30 m resolution Landsat 8 images (Yang and Smith, 2016; Yang and others, 2019b). Although small streams enhance surface meltwater routing (Decaux and others, 2018; Yang and others, 2018), coarser images of large supraglacial rivers capture the overall drainage pattern of supraglacial hydrologic networks effectively (see Table S1 and Fig. S2).…”

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

“…However, the spatial resolution of the Sentinel-2 images is three times higher than that of the Landsat-8 images and thus supraglacial drainage patterns are much better resolved in the Sentinel-derived map products (see close-up images, Figures 7 -9). Sentinel-mapped supraglacial river networks are also more continuous, which is crucial for investigating surface meltwater routing (King et al, 2016;Yang and Smith, 2016a;Smith et al, 2017;Decaux et al, 2018;Yang et al, 2018). On all three ice masses, supraglacial rivers generally flow from high-elevation slushy zones to low-elevation bare ice ablation zones.…”

“…The supraglacial drainage patterns mapped in this study have important implications for surface meltwater routing. Supraglacial river networks and their corresponding ice surface catchments determine the timing and magnitude of peak supraglacial river discharge and corresponding inputs to englacial and subglacial drainage systems through moulins (Smith et al, 2017;Decaux et al, 2018;Yang et al, 2018).…”

“…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;…”

The Role of Winter Rain in the Glacial System on Svalbard

“…For spatial analysis of air temperature and precipitation distributions, we used a digital elevation model (DEM) with a resolution of 100 m horizontally and ±5 m vertically, both estimated from Very High Resolution Satellite VHRS images from WorldView-2 (2015) [42].…”