Research: The subglacial water system under firn aquifers

How do firn aqufiers change the water drainage system under a glacier? If firn aquifers drain irregularly in time, or continuously in time, or even if they drain in sync with the melt season, we’re finding that they have a substantial effect on the subglacial hydrologic system downstream.

Model domain for GlaDS under an idealized Greenland outlet glacier (panel c) downstream of a firn aquifer (green). From Poinar, Dow, and Andrews, 2019. “Long‐Term Support of an Active Subglacial Hydrologic System in Southeast Greenland by Firn Aquifers.” Geophysical Research Letters, 10.1029/2019GL082786

The flow of ice and meltwater from the Greenland Ice Sheet into the ocean affects sea levels. Ice flow is sensitive to meltwater that travels underneath the glacier. Where and when that water reaches the glacier bed shapes the water channel network under the glacier. We use a computer model to analyze how firn aquifers, newly discovered meltwater pockets that sit dozens of meters below the ice sheet surface in east Greenland, change the water channel network under local glaciers. We find that the firn‐aquifer water supply can maintain a water channel network under the glacier that changes less over each season, compared to areas without firn‐aquifer water. This subglacial channelization could explain observations of steadier glacier flow in locations with firn aquifers.

(see Plain Language Summary at

Helheim Glacier, in Southeast Greenland. Photo by Jeremy Harbeck (NASA Goddard Space Flight Center) on board NASA Operation IceBridge flight, September 2016.
When water from the firn aquifer drains to the bed of the glacier, where does it go and how long does it take to reach the ocean?
The answer depends on how much water drains, how fast it drains, and when (what season) it drains.
Video available at

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