We’re on weather hold at McMurdo, waiting for some snow to
clear, which is the perfect time to write a quick post.
What’s the Cold Dirt team up to this year? We’re here in the
McMurdo Dry Valleys again trying to learn more about shallow groundwater.
Because it’s so cold in Antarctic (-18˚C is the average temperature in this
part of the world), most of the ground is frozen all the time. This frozen
ground is called permafrost. But in the summer, temperatures climb up to
freezing, or even a little bit above. When that happens, the warm surface of
the soil starts to thaw. The ground thaws and ice in it melts down to a depth
of 30-60 cm (about 1-2 feet). This is called the “active layer” among
permafrost geologists because it is where freeze-thaw activity occurs.
When the active layer forms, the near-surface hydrological
system starts to spin up. Water melted from ground ice, snow banks, and even
sucked into the soil from thirsty salts starts to flow downhill. The water fills up the space between the ground surface
and the frozen soil down below (called the ice table), making streaks of wet,
muddy soil we call “water tracks.” Water tracks are like underground streams
that connect the tops of the valleys to the ponds and lakes at the bottom of
the valleys.
Water tracks in lower Taylor Valley. Snow melts and water flows downhill. Even in Antarctica.
This mud isn’t just fun for making mud pies, it’s actually
very important for understanding how the ecosystem here functions and how it
fits in to the bigger global climate system. Water tracks carry water and
nutrients (like carbon and nitrogen) to microbes, algal mats, and invertebrates
in the soils. These organisms may be far from streams and lakes and would be
cut off from food and water without the underground plumbing system provided by
water tracks. As a result, there’s actually quite a bit of soil carbon (living
and dead microorganisms and nematode worms) that builds up in water tracks.
Water tracks provide an organizing principle to the soil biological community
here in the Dry Valleys, marking of places that are wet enough,
food-rich-enough, but not too salty to live in.
Water tracks also give us an idea of what Antarctica might
have been like 15-30 million years ago, when large parts of it were not coveredin ice sheets. If Antarctica was cold, but not quite so cold as today, large ice-free areas
may have been crisscrossed by networks of water tracks. This shallow groundwater
system might have been enough to support large communities of plants, microbes,
and some organisms like insects and small invertebrates. If so, Antarctica may
have looked much like the high Arctic today. Carbon preserved from this
comparably warm portion of Antarctic history may be stored beneath the ice
sheets today.
