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Lakes Under Ice?

How can there be a lake under an ice sheet?   While it might seem impossible that there could be pooled collections of water under a million year old ice sheet that is close to 2 miles thick, in fact scientists have located more than to 200 subglacial lakes in Antarctica.  How do these lakes form?  One way that liquid can form under ice is from energy radiating up from in the interior of the Earth.  The center of the Earth is hot and radiates heat, called geothermal heat.  This heat can be enough to warm and melt the bottom of the ice sheets.  Where there are topographic depressions this water will pool and collect into lakes.  Lakes can also form by the pressure of these several kilometers of  glacial ice pressing down.  This pressure can create heat causing melting at the base of the glacier, which pools into lakes.   

Just how big is a subglacial lake?   Lake Vostok, imaged here, is the largest Antarctic subglacial lake we are currently aware of. Vostok (Russian for 'East') rests on the East side of the Gamburtsev Mountains lying under 4000 meters of ice. It measures 250 km long, 50 km across at its widest, and 800 meters deep and at its deepest. The total size is close to that of Lake Ontario making it the sixth largest lake in the world  However, there are also many small lakes. 

Why are these lakes important?  As recently as 1998 scientists thought that these subglacial lakes were isolated pockets of water that had been protected from any outside influences for perhaps millions of years, like liquid museums.  Was there life in these lakes that had survived from before the last ice age?  The lakes do have the potential to be filled with life, but not in the form of fish or mollusks, but in a very small form such as microbes and bacteria.  These minute life forms are expected to have made their way down from the surface snow over the course of thousands of years.  Their isolation could mean that they have unusual mutations or adaptations to this extreme environment, which is highly pressurized, without light, and extremely cold.   However, we have learned in the last 20 year that these lakes are not completely isolated!

This image (created by Zina Deretsky/NSF) is a rendering of the complex network of ice streams and lakes that scientists have found exist under the ice sheet in Antarctica. The movement of water through this under-ice network affects the overlying ice sheet and the dynamics of the many ice streams that carry ice from the center of the continent towards the surrounding ocean. There is still much that is unknown about this process. Understanding the linkages between ice sheets and underlying subglacial environments is a key piece of this research as well as other research being conducted as part of the current IPY.

Although scientists have not yet sampled in any of the lakes they have collected enough data from radar, gravity and other remote methods to learn that water moves in and out of these lakes, connecting under the ice in a rather elaborate plumbing system.  While we don’t fully understand this system , we know this plumbing system has important consequences for the overlying glacier. Subglacial lakes that connect and drain into ice streams that flow under the ice sheet, can significantly increase the movement of the overlying ice.  Ice movement in the interior of Antarctica has been measured at about 2 meters a year. Water flowing out of the subglacial lakes can cause a ‘greasing’ underneath the ice sheet that actually floats the ice sheet off the bedding underneath causing it to slide along like a sled on a slick base.  This acceleration of movement from the underlying water can escalate glacier movement from 2 meters to 2 kms a year!  This means that slow moving ice in the interior of Antarctica could be accelerated so that it moves more quickly towards the exterior edges of the continent where it can be warmed by ocean currents causing ice sheet melting.  While scientists don’t yet know if subglacial lakes actually cause the onset of ice stream movement, it is something we hope to learn more about through this IPY project.

Ho do subglacial lakes speed the ice flow? Using satellite measurements, Bell et al. (Nature 445 904–907 (2007).) found four subglacial lakes right at the onset of fast ice flow at the Recovery Glacier ice stream in Dronning Maud Land, Antarctica. They propose that the freezing of lake water to the base of the ice sheet (pink area), together with water spilling over from the lake and scouring the bedrock, could reduce friction and help speed up ice flow towards the sea.

How do satellite measurements work? The relative strength of reflection of ground-based radar distinguishes between bedrock and water at the base of an ice sheet, and the characteristic flat area in the ice surface above a subglacial lake can be detected by satellite-based surface observations.

Image and caption by permission from Macmillan Publishers Ltd: Nature, Kohler, J., Glaciology: Lubricating lakes, 445, 830-831(22 February 2007)

This project funded through NSF Antarctic Research Grants #ANT 0632292; ANT 0619457 | contact us | web master
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