Ice from a Dry Valley

Some of the weirdest places on what is arguably the world’s weirdest continent are located just across McMurdo Sound from Ross Island.



A USGS map of the Dry Valleys in relation to Ross Island, highlighting two of the largest and best-studied valleys. Click for larger version.

These are the Dry Valleys, so called because they are some of the few places on the continent that are free of ice and snow. Almost no snow or rain falls here, and what does fall is blown away or evaporated by the constant strong winds. The valleys are so dry and cold that NASA used them as a testing ground for the Viking Mars lander.

The winds that blow through the Dry Valleys are called katabatic winds. Katabatic winds arise from air simply flowing downhill off of a continent. The center of Antarctica is at high altitude due to the kilometers of ice that have built up there, and is also very cold. Cold air is denser than warm air, so the cold air from the middle of the continent naturally wants to flow downhill toward the edges. Places like the Dry Valleys act as bottlenecks, where the winds are forced through a narrow place and therefore have to blow even faster.

The wind is the main source of erosion in the Dry Valleys. It picks up tiny grains of sand that carve the rocks into strange forms called ventifacts:



Ventifact image courtesy the Exploratorium's website.

But the Dry Valleys aren’t entirely dry. They’re home to a number of lakes and streams, some of which are fresh and some of which are extremely salty. Some are frozen right to the bottom, others are liquid below their covering of ice. Some have distinct horizontal layers of water of different salinities.

We are interested in one lake in particular, in Garwood Valley. This lake is one of the high-salinity ones, and we’re hoping to use it to get an idea of how a particular type of ice on Snowball Earth might look.

So far, you may recall, we’ve been looking at what happens when crystals of hydrohalite form within sea ice. Here on modern Earth, those crystals don’t last long; the sea ice warms up, dissolving them. On Snowball Earth, though, the temperatures would be around -30C even in the tropics. The hydrohalite would remain crystallized indefinitely.

In the tropics of the Snowball, where evaporation would exceed precipitation, the ice around the hydrohalite would gradually sublime (that is, transition from solid ice to water vapor without going through a liquid phase in between.) With the ice sublimed away, the hydrohalite would be left behind on the surface. Like table salt, it would reflect a lot of light, and it might have a quite significant effect on the albedo.

We can’t observe this effect on modern sea ice, of course, because it doesn’t stay cold enough for long enough. We can try the next best thing, though: salty lakes in the Dry Valleys. We know of one lake in particular that develops a crust, not of hydrohalite, but of another low-temperature salt called mirabilite that we hope might have similar qualities.

Our first helicopter flight to the Dry Valleys leaves on the 10th of October; then we get a day to crunch data collected on that flight before we go out again. I may not get much time to write in between, but I’ll try to post lots of pictures. In between now and then I’ll see if I can get in a post about other weird things in the Dry Valleys, including Blood Falls, cryptobiotic soils, and ancient mummified seals.

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One Response to “Ice from a Dry Valley”

  1. Whys and Wherefores « Squid on the Ice Says:

    […] found anywhere else on Earth: sea ice so cold that the salts trapped within it can crystallize, and ice whose surface has sublimated away to leave behind a crust of the salt mirabilite. This year we’re once again seeking ice that exists nowhere else. In this case, we’re […]

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