Huge quantities of meltwater falling from the surface to the base causes high rates of melting at the bottom of the ice sheet. When the meltwater falls, energy is converted into heat in a process similar to hydroelectric power.
An international team of scientists, led by the University of Cambridge, found that the largest source of heat beneath the world's second largest city is caused by meltwater descending from the ice sheet to the bed.
The lubricating effect of meltwater has a strong effect on the movement of glaciers and the quantity of ice discharged into the ocean, but directly measuring conditions beneath a kilometer of ice is a challenge.
It is difficult to understand the behavior of the ice sheet because of the lack of direct measurement. The Greenland Ice Sheet is the single largest contributor to sea level rise due to both melting and discharge.
In a study published in the Proceedings of the National Academy of Sciences, the Cambridge-led team has found that when meltwater is transferred to the base through large cracks in the ice, it becomes heat.
Thousands of meltwater lakes and streams form on the surface of the Greenland Ice Sheet as temperatures rise and daily sunlight increases. Many of the lakes fall through the cracks in the ice sheet when they drain to the bottom. Connection between surface and bed are often open with a continued supply of water.
As part of the EU-funded RESPONDER project, Professor Christoffersen has been studying meltwater lakes, how and why they drain so quickly, and the effect that they have on the overall behavior of the ice sheet as global.
The current work is the culmination of a seven-year study on Store Glacier, one of the largest outlets from the Greenland Ice Sheet.
When studying the melting of ice sheets and glaciers, we look at sources of heat like friction, geothermal energy, and heat losses into the ice above. When the water falls, there is a lot of energy stored on the surface and it has to go somewhere.
The researchers used phase-sensitive radio-echo sounding to measure melt rates.
The radar system on Store Glacier was installed by Tun Jan Young as part of his PhD at Cambridge.
The melt rates measured on the surface with a weather station were often higher than the melt rates observed with radar, but the surface received energy from the sun while the base did not. The Cambridge researchers collaborated with scientists from the University of California Santa Cruz and the Geological Survey ofDenmark and Greenland to explain the results.
During the summer of 2014, meltwater was transferred to the bed of Store Glacier every day. The power produced by the falling water during peak melt periods was comparable to the power produced by the Three Gorges Dam in China. With a melt area that expands to nearly a million square kilometers at the height of summer, the Greenland Ice Sheet produces more hydropower than the world's ten largest hydroelectric power stations combined.
Given what we are seeing at the high latitudes in terms of climate change, this form of hydropower could easily double or triple.
To verify the high melt rates recorded by the radar system, the team integrated independent temperature measurements from the nearby borehole. The melting point of the ice sheet base is -0.40 degrees, which is unexpectedly warm for an ice sheet base with a water temperature of +0.88 degrees.
Christoffersen said that the meltwater heats up when it hits the bed because the drainage system is less efficient. The water is heated by the reduced drainage efficiency. The melt rate estimates were a full two orders of magnitude out when we took this heat source out of our calculations. The melt rate we are reporting is completely unprecedented because of the heat generated by the falling water.
The first concrete evidence of an ice-sheet mass-loss mechanism is presented in the study. While the high melt rates are specific to heat produced in subglacial drainage paths carrying surface water, the volume of surface water produced in Greenland is huge and growing.
More information: Rapid basal melting of the Greenland Ice Sheet from surface meltwater drainage, Proceedings of the National Academy of Sciences (2022). DOI: 10.1073/pnas.2116036119. Journal information: Proceedings of the National Academy of Sciences Citation: Accelerating melt rate makes Greenland Ice Sheet world's largest 'dam' (2022, February 21) retrieved 21 February 2022 from https://phys.org/news/2022-02-greenland-ice-sheet-world-largest.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
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