The Possible Transition From Glacial Surge to Ice Stream on Vavilov Ice Cap

Abstract

Surge-type glaciers typically undergo cyclical flow instability due to mass accumulation; however, some recent glacier surges have caused irreversible ice loss in a short period. At Vavilov Ice Cap, Russia, surge-like behavior initiated in 2013 and by spring 2019 the ice cap had lost 9.5 Gt of ice (11% mass of the entire basin). Using time series of surface elevation and glacier velocity derived from satellite optical and synthetic-aperture radar imagery, we identify a shift of flow pattern starting in 2017 when shear margins formed within the grounded marine piedmont fan. Multiple summer speedups correlate with warmer summers during 2015-2019 and suggest that surface melt may access the subglacial environment. Force balance analysis and examination of the Péclet number show that glacier thinning propagated upstream in 2016-2017, and diffusion became a significant dynamic response to thinning perturbations. Our results suggest that the glacier has entered a new ice stream-like regime. Plain Language SummaryA glacier surge is a sudden speedup of glacier flow coinciding with a large advance of the ice front. Some glaciers surge periodically every 10-100 years, and so surge mechanism is thought to be independent of climate change. However, some recent surges have evacuated so much ice that another surge is unlikely to occur in the same place again. A glacier surge at the Vavilov Ice Cap, Russia, is one of these cases. Since 2013, the glacier has drained more than 11% of the ice basin (9.5 Gt) into the ocean. After the initial surge in 2013, the glacier still retains fast flow at around 1.8 km/year, an unusually high and long-lasting speed for a glacier surge. To understand the future of the surge, we use satellite images to calculate surface elevations and ice speeds, and analyze their change over time for the glacier. The results reveal that the glacier now physically behaves more like an "ice stream," a stream of fast-flowing ice within an ice sheet, which can probably flow at high speed for a long time and drain ice efficiently. This is the first documented case of an ice stream-like feature ever being formed.

Glacier Image Velocimetry: an open-source toolbox for easy and rapid calculation of high-resolution glacier-velocity fields

“…This mean difference is ≤1% the total velocity across the majority of the glacier surface (Fig 9(b)). In this region of the glacier surface, the annual variability in ice-surface velocities is on the order of several hundred metres per year (Fig 8(d) and (e)), and this difference between our results using GIV and those of Zheng et al (2019b) could plausibly result from the slightly different dates covered or differing image resolutions (10 m for Sentinel-2 compared to 15 or 30 m for Landsat). The high-magnitude difference bands on either side of the fast-moving central region may also result in whole or part from georeferencing errors in GIV, in CARST, or in our work to georeference these two velocity maps to one another.…”

“…The third is the Vavilov ice cap, located on October Revolution Island, in the Arctic Ocean off the mainland Russian coast, whose western outlet glacier is now surging into the ocean. We validate PIV against published results (Zheng et al, 2019b) using another image-based ice-velocity tool, CARST (Zheng et al, 2019a).…”

“…CC BY 4.0 License. et al, 2018; Zheng et al, 2019b). This sudden shift in ice behaviour was not accompanied by any dramatic climatic shift, and the exact triggers are a matter of active debate (Willis et al, 2018, and references therein).…”

“…(2019b) using CARST (Zheng et al, 2019a). Zheng et al (2019b)'s velocities were generated based on a single Landsat 8 pair dated 2017/05/06 and 2017/05/22. We compared the ice-surface velocity magnitude calculated from this pair to the May 2017 average velocity map generated from Sentinel-2 imagery using GIV through the approach described above.…”

“…We use GIV to derive a 100-m resolution ice-velocity map of a 365-km 2 area of the Western flank of the ice cap using the entire Sentinel-2 archive (beginning in 2016). newly formed western frontal lobe extruded beyond the prior grounding line, flow has concentrated into a single branch with well-developed shear margins separating a central region with rapid ice flow from slow-moving lateral portions (Zheng et al, 2019b).…”