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Matt Covington, associate professor of geosciences at the University of Arkansas, flies a drone over the Greenland ice cap. Credit: Jason Gulley
The researchers climbed into mills, which drain meltwater from the ice sheet, to better understand how volume relates to the movement of ice.
The holes that carry surface meltwater to the base of the Greenland ice sheet, called mills, are much larger than previously thought, according to a new study based on observation and first-hand exploration by a team including a geologist from the University of Arkansas.
The additional volume could influence the stability of the Greenland ice sheet and how quickly it slides out to sea.
Researchers inside a mill on the Greenland ice cap. Credit: Jason Gulley
The team studied the relationship between the size of the mills and the daily variation in water depth during the summer melt season. Scientists believe that increasing the depth of the water, and therefore the pressure, inside the mills lubricates the base of the ice sheet and increases the speed of its movement towards the sea, like an icicle slides easily. on a thin film of water. But so far, little was known about the actual size of the mills and how much water they can hold.
“We compared our models with field observations of water levels and it looked like we would need really huge volumes inside the mills to produce the relatively smaller water variations that we were seeing,” he said. said Matt Covington, associate professor of geosciences and first author of the study published in the journal Geophysical research letters. “Then when we went back the next year and explored a mill, it was giant. This is a case where the model made the prediction, and we went into the field and it turned out to be right.
University of Arkansas associate professor of geosciences Matt Covington climbs a mill on the Greenland ice cap. Credit: Jason Gulley
The team made two trips to the Greenland Ice Cap in October 2018 and October 2019. During each trip, they used ropes and other climbing equipment to abseil 100 meters to two separate mills. , almost reaching the water level.
“It’s intimidating,” said Covington, an experienced cave explorer. “You come back over the edge and you just see bluish ice coming down as far as you can see, then it’s blackness and there’s also occasional noises of ice crashing down, which is pretty disconcerting.
Scientists have long observed that the Greenland ice sheet is moving, and have speculated that warmer summer melt seasons due to climate change could accelerate this movement. But researchers have little data to help them understand the interaction between meltwater and the base of the ice sheet. The team’s findings add to the knowledge of how water interacts with the base of the ice cap.
University of Arkansas Associate Professor of Geoscience Matt Covington is investigating a mill on the Greenland ice cap. Credit: Jason Gulley
“We are trying to understand how the meltwater interacts with the movement of the ice, and the main thing we found is that the water pressure in these mills is not as variable as what has. been observed previously, and that this appears to be the result of really large volumes in the mills, ”Covington said.
Reference: “Moulin Volumes Regulate Subglacial Water Pressure on the Greenland Ice Sheet” by MD Covington, JD Gulley, C. Trunz, J. Mejia and W. Gadd, October 9, 2020, Geophysical research letters.
DOI: 10.1029 / 2020GL088901
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