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UNIVERSITY OF HOKKAIDO
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IMAGE: THE SUGGESTED VALLEY AND THE POSSIBLE RIVER THAT FLOWS FROM THE DEEP INNER OF GREENLAND TO THE DEEP PETERMANN FJORD BELOW THE ICE SHEET OF GREENLAND (500 METERS BELOW SEA LEVEL). (CHRISTOPHER CHAMBERS ET AL,… view more CREDIT: CHRISTOPHER CHAMBERS ET AL, THE CRYOSPHERE, 12 NOVEMBER 2020.
Computational models suggest that meltwater originating from the deep interior of Greenland could flow the full length of a subglacial valley and exit at Petermann Fjord along the island’s north coast. Updating ice sheet models with this open valley could provide further information for future predictions on climate change.
Radar surveys have previously mapped the bedrock of Greenland buried under two to three thousand meters of ice. Mathematical models were used to fill gaps in the survey data and infer bedrock depths. Investigations revealed the long valley, but suggested it was segmented, preventing water from flowing freely through it. However, the peaks that divide the valley into segments only appear in areas where mathematical modeling was used to fill in the missing data, so they might not be real.
Christopher Chambers and Ralf Greve, scientists at the University of Hokkaido’s Institute of Low Temperature Science, wanted to explore what could happen if the valley were open and melt increased into an area deep inland from Greenland known for melting. Collaborating with researchers from the University of Oslo, they ran numerous simulations to compare water dynamics in northern Greenland with and without valley segmentation.
The results, recently published in The Cryosphere, show a drastic change in the way the water that melts at the base of the ice sheet would flow if the valley were truly open. A distinct subglacial stream runs from the melting point to the Petermann Fjord, which is more than 1,000 kilometers away on the north coast of Greenland. The stream appears only when the segmentation of the valley is removed; there are no other major changes in the landscape or in the dynamics of the water.
“The results are consistent with a long subglacial river,” says Chambers, “but considerable uncertainty remains. For example, we don’t know how much water, if any, is available to flow down the valley, and whether it actually flows out at the Petermann Fjord or it is refrozen, or comes out of the valley, along the way “.
If the water is flowing, the model suggests that it could cross the entire length of the valley because the valley is relatively flat, similar to a river bed. This suggests that no part of the ice sheet forms a physical block. The simulations also suggested that there was more water flow towards the fjord with a flat valley base 500 meters below sea level than when it was 100 meters below. Furthermore, when melting is only increased in the deep interior in a known region of basal melting, the simulated discharge is increased along the entire length of the valley only when the valley is unblocked. This suggests that a fairly finely tuned relationship between the valley shape and the overlying ice may allow for the development of a very long downstream water path.
“Further radar investigations are needed to confirm the accuracy of the simulations,” says Greve, who developed the model used in the study, called the Simulation Code for Polythermal Ice Sheets (SICOPOLIS). “This could introduce a fundamentally different hydrological system for the Greenland ice sheet. Correct simulation of such a long subglacial hydrological system could be important for future accurate simulations of the ice sheet in a changing climate. “
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From EurekAlert!
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