Subglacial permafrost dynamics and erosion inside subglacial channels driven by surface events in Svalbard

Abstract

Abstract. Cold glacier beds, i.e. where the ice is frozen to its base, are widespread in polar regions. Common theories state that stable permafrost should exist under glacier beds on shorter time scales, varying from years to decades. Presently, only a few direct measurements of both subglacial permafrost and the processes influencing its thermal regime exist. Here, we present subglacial permafrost and active layer measurements obtained from within the basal drainage systems of two cold-based glaciers on Svalbard during the summer melt season. Temperature observations were obtained from subglacial sediment that was accessed through the drainage systems of the two glaciers in the winters before. The temperature records cover the periods from spring to autumn in 2016 and 2019, at the glaciers Larsbreen and Tellbreen in central Svalbard, respectively. The ground temperature below Larsbreen indicates colder ground conditions, whereas the temperatures of the Tellbreen drainage system show considerably warmer conditions, close to the freezing point. We suggest the latter is due to the presence of liquid water all year round inside the Tellbreen drainage system. Both drainage systems investigated show an increase in subglacial sediment temperatures after the disappearance of snow bridges and the subsequent connection to surface meltwater supply at the start of the summer melt season. Temperature records show influence of sudden summer water supply events, when heavy melt and rain left their signatures on the thermal regime and the erosion of the glacier bed. Observed vertical erosion can reach up to 0.9 m per day at the base of basal drainage channels during summer. We also show that the thermal regime under the subglacial drainage systems is not stable during summer, but experiences several freeze-thaw cycles driven by weather events. Our results show the direct importance of heavy melt events and rain on the thermal regime of subglacial permafrost and the erosion of the glacier bed in the vicinity of subglacial drainage channels. Increased precipitation and surface melt, as expected for future climate, will therefore likely lead to increased degradation of subglacial permafrost, as well as higher subglacial erosion around the preferential hydrological paths. This in turn might have significant impacts on proglacial and fjord ecosystems due to increased sediment and nutrient input.

Subsurface Flow Path Modeling From Inertial Measurement Unit Sensor Data Using Infinite Hidden Markov Models

“…Similarly to the previous examples, the supraglacial channel path reconstruction error was calculated using the equation (7), taking the GNSS path as the ground truth. As we only have a partial GNSS path, the accuracy estimation is based of the regions where the ground truth data exists.…”

“…The problem with inaccessibility can be tackled by using the Lagrangian sensors; they are small devices that passively follow the water flow [6], [7]. These sensing drifters move with the changing environment, thus allowing collection of a wide range of observational data (e.g., pressure, temperature).…”

Subglacial permafrost dynamics and erosion inside subglacial channels driven by surface events in Svalbard

“…Data availability. All data can be found under https://doi.org/10.5281/zenodo.4116255 (Alexander et al, 2020).…”

Sustained high winter glacier velocities from brief warm events

“…Forecasted surface variables (e.g., 2 m temperature, 2 m humidity) are interpolated over the grid based on optimal interpolation (Giard & Bazile, 2000). Alexander et al (2020) Here we used hourly model data to calculate average daily temperature and net precipitation. Because we present daily average results, it is possible to have liquid rain on a day when the daily average temperature is below zero.…”