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Tracers study reveals rivers beneath the Greenland Ice Sheet

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Posted March 15, 2013
Moulins deliver surface meltwater through 1km of ice to the bed of the ice sheet. Image by Dr Dave Chandler

Moulins deliver surface meltwater through 1km of ice to the bed of the ice sheet. Image by Dr Dave Chandler

Meltwater flow beneath the Greenland Ice Sheet has been traced up to 60km from the ice margin by a team of scientists from the Universities of Bristol, Edinburgh, Aberdeen and Aberystwyth. Their work, which represents the first successful attempt to trace meltwater flow through thick ice and over distances of some tens of kilometres on an ice sheet, is published in Nature Geoscience this month.

The project, funded by the Natural Environment Research Council UK, employed artificial tracer methods whereby the team injected small amounts of gas and liquid tracers into holes (moulins) in the ice sheet surface at Leverett Glacier (SW Greenland), then monitored their appearance in the rivers draining the ice sheet at its margins.

The group, led by Professor Jemma Wadham of the Bristol Glaciology Centre, (University of Bristol), showed that by the peak melt season, meltwater flows rapidly at the ice sheet bed through channels over large areas of the melt zone.  Only further inland (60km), where ice is thicker, do channels fail to develop and slow-inefficient drainage pathways dominate.

Dr Dave Chandler, Research Assistant in Bristol’s School of Geographical Sciences and lead author on the paper, said: “Our results confirm what people suspected from satellite and velocity studies on the ice sheet surface.  They show that the hydrological system beneath the ice sheet evolves from a slow-inefficient drainage system to a fast-efficient network of channels as the melt season progresses.”

“It was a challenging project to deliver,” said Professor Wadham.  “The volumes of meltwater flowing into the ice sheet are vast.  This causes many tracers injected to the ice surface to be diluted to below detection by the time you try to measure them in rivers at the ice margin.  To overcome this, we injected highly sensitive gas tracers which have been used in oceanography to trace currents over entire ocean basins.”

The team adapted oceanographic tracer techniques, injecting gas tracers at 100sm depth in moulins on the ice sheet in order to prevent loss of the gas before it entered the basal drainage system.  In order to do this, they required several kilometres of ruggedized garden hose (supplied by Hozelock UK).  At the ice sheet margin, teams of up to ten people worked around the clock to measure tracer concentrations in the river draining the glacier.

The team’s results highlight that large volumes of meltwater may be routed by channels beneath the Greenland Ice Sheet during summer.  This acts to minimize the area of meltwater lubrication of the ice sheet bed, with implications for ice sheet dynamics.

Source: University of Bristol

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