Permafrost Springs on Earth and Mars|
by Chris McKay
One part of the solution to this puzzle may be found on Earth in the Canadian Arctic. There are two sets of perennial springs located on Axel Heiberg Island that flow through 600 m of permafrost and these springs are not associated with any volcanic heat sources. Located at nearly 80N these are the most poleward springs known, and to our knowledge the only example of cold springs in thick permafrost.
Axel Heiberg Island is mostly bare ground, with less than 35% covered by glaciers or ice caps. The average air temperature at the springs sites is approximately -17C. The two springs both discharge a brine with measured discharge temperatures that range from -2 to +6.5 C and remain constant throughout the year despite air temperatures that fall well below -40C. Flow rates are also constant with little variation.
We think that the springs are the results of a subsurface salt aquifer. Water enters and leaves this salt reservoir by way of the salt domes which reach the surface. The water flows down into the salt dome from a large lake - Phantom Lake - that sits on top of one of the surface salt deposits at high elevation. After flowing through the salt to deep underground, the current seeps back up through the salt to the surface, forming a spring.
The Arctic springs demonstrate that liquid water is capable of reaching the surface in regions of thick, continuous permafrost without strong volcanic heating sources. This could have happened on Mars. However the question of the source of the water on Mars remains unclear. In the Arctic the source of the water is essentially summer glacial meltwater conveniently stored in a large lake that happens to sit on a salt structure at high elevation. So in the Arctic there is a constant supply of water and a hydrostatic pressure to drive the flow. For Mars this is obviously not the case. The water must be a remnant of an early period or recently melted ice or both. Where did the water come from and why did it flow recently? We donít know. Mysteries remain and until we can get to Mars studies of water flow and springs in the Arctic may provide us with our best clues.
This work is done by a team lead by Wayne Pollard of McGill University and this year the field team included Dale Andersen, Chris McKay, Jen Heldmann, and Margarita Marinova.