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Department of Geography

 

 

Investigating basal conditions and flow dynamics on Vestfonna Ice Cap, Svalbard

The body of scientific evidence for significant anthropogenic impacts on the global climate is growing and public concern underscores a need for better assessments of contemporary environmental changes in regions such as the Arctic. Although the vast majority of ice on Earth is stored in Greenland and Antarctica, it is important to keep in mind that 70% of the cryospheric contribution to 20th century sea-level rise was attributed to the retreat of mountain glaciers and small ice caps. Arctic ice caps are an important component of global change, especially as Arctic temperatures are increasing at almost twice the global average.

This project focuses on Vestfonna Ice Cap, located in northeast Svalbard. This Arctic ice cap is of particular interest because its northern ice margin terminates on land while the southern margin contains a series of tidewater outlet glaciers, comparable to those draining the Greenland Ice Sheet (Figure 1). Airborne radio-echo sounding data collected in 1983 and 1986 by Scott Polar Research Institute showed that the volume of Vestfonna Ice Cap was about 500 km3. Aerial photographs and satellite imagery subsequently showed that flow speeds on the southern tidewater glaciers were several hundred metres per year. This was an order of magnitude faster than the surrounding ice and more than double the calculated balance velocities. It was suggested that this negative state of mass balance was a result of short-lived glacier surges. However, the interior ice plateau on Vestfonna Ice Cap is today experiencing widespread and progressive thinning, either as a result of changing regional climate dynamics or enhanced discharge from tidewater outlet glaciers.

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Figure 1. InSAR-derived velocity map of Vestfonna Ice Cap. Black line illustrates approximate location of a radar transect and red dots show location of study areas where GPS receivers were installed in 2008. White dashed line represents the ice divide. FB and K mark the locations of Frazerbreen and Kinnvika field station. Inset shows location of Vestifonnna Ice Cap in Svalbard.

Arctic ice caps and the Greenland Ice Sheet rest on bedrock above or close to sea level. Glaciologists have for years assumed that such position would be stable and that demise of these ice masses would require thousands of years, even under global warming scenarios, because processes controlling the rate of ice flow take place in subglacial environments covered by thick polar ice. This assumption has now been discarded, as it was shown recently that surface meltwater can penetrate to the base of Arctic ice caps, possibly even the Greenland Ice Sheet, and cause ice-flow speed-up due to enhanced basal sliding. This mechanism is potentially dangerous because accelerated ice flow leads to thinning, which in turn leads to an increase in surface melt, as a larger part of the ice sheet moves into lower and warmer elevations.

If positive feedbacks between surface hydrology and ice motion are widespread, they may trigger a much faster demise of polar ice masses compared to the existing estimates, which provide the basis for projections by the Intergovernmental Panel on Climate Change. The widespread thinning of Arctic ice caps and the Greenland Ice Sheet indicates that ice-mass loss from enhanced flow dynamics has increased over the last decade. However, ocean currents may also take part in the observed changes along the Greenland coast, as warm and saline Atlantic water in the Arctic gyre may reach the front of tidewater glaciers and result in glacier retreat (Figure 2). The need of a better understanding of ice-climate and ice-ocean dynamics firmly embeds glaciological processes in Earth system models.

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Figure 2. Photograph of tidewater glacier in northeast Svalbard

In this project, we are conducting glaciological investigations on Vestfonna Ice Cap with the aim to determine how ice flow responds to atmospheric forcing and changes in the position of calving ice margins. The project includes the collection of radio-echo sounding data in a traverse across the ice cap and in two designated study areas, one on the land-terminating northern ice margin and one on a southern tidewater glacier (Figure 1). The radar data provide a means to measure ice thickness and examine the nature of the bed, e.g. the distribution of melting and freezing and the presence of water, which serves as a lubricant. In 2008, we installed five GPSs on Frazerbreen, a fast-flowing tidewater glacier, and two GPSs on the land terminating northern ice margin (Figure 3). In 2009, we will compare GPS data with output from automatic weather stations and digital imagery from time-lapse cameras recording changes in the position of Frazerbreen’s calving ice-front. The fieldwork is co-ordinated through the Kinnvika International Polar Year Consortium.

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Figure 3. Installing GPS receiver on Frazerbreen

The data acquired through this project will result in a better quantitative understanding of glacier dynamics in a warming Arctic. Project outcomes will elucidate ice-climate as well as ice-ocean dynamics. A clear understanding of both of these forcing components is a crucial part of producing accurate estimates of sea level rise in the 21st century and beyond.

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Figure 4. The Kinnvika station near Vestfonna Ice Cap.

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Figure 5. Sea ice and open water near the coast of Nordaustlandet, Svalbard