The researchers climbed into mules that drain the melted water from the ice sheet to better understand how volume is related to the movement of ice.
The holes that carry surface melting water to the base of Greenland̵
The extra volume can affect the stability of Greenland’s ice sheet and how fast it slides into the sea.
The team investigated the relationship between the size of the mules and the daily change in water depth in them during the summer melting season. Scientists believe that the increased depth of the water and therefore the pressure inside the mules lubricates the base of the ice sheet and increases the speed of its movement to the sea, in a way that the ice cube easily slides on a thin water film. But so far little was known about the actual size of the mule and how much water they could hold.
“We compared our models to on-site water level observations, and it looked like we would need really huge amounts inside the mule to produce the relatively smaller variations in water we observe,” said Matt Covington, an associate professor of geology and first author of the study published in the journal Geophysical research letters. “Then, when we came back the following year and studied mule, it was gigantic. This was the case when the model made the prediction and we went out into the field and it turned out to be true. “
The team made two trips to the Greenland ice sheet in October 2018 and October 2019. During each trip, they used ropes and other climbing equipment to slide 100 meters into two separate mules, almost reaching the water level. .
“It’s scary,” said Covington, an experienced cave explorer. “Go back over the edge and you just see bluish ice coming down as far as you can see, and then it’s dark and you also sometimes hear the sound of ice crashing, which is pretty disturbing.”
Scientists have long noticed that Greenland’s ice sheet is moving and suggest that warmer summer melting seasons due to climate change may accelerate that movement. But researchers have little data to help them understand the interaction between the melt water and the base of the ice sheet. The team’s findings contribute to the knowledge of how water interacts with the base of the ice sheet.
“We’re trying to understand how molten water interacts with the movement of ice, and the main thing we’ve found is that the water pressure in these mules isn’t as variable as we’ve seen before, and that it seems to be the result of really big volumes in the mules, ‘said Covington.
Reference: “Moulin volumes regulate the 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