Climate change puts spotlight back on Antarctic soils
March 26, 2014
If the name Ernest Shackleton rings a bell, it’s probably because of his Endurance expedition to Antarctica in 1914–1916. After the destruction of their ship in the pack ice stranded Shackleton and his crew in Antarctica for 20 harrowing months, the British explorer managed to bring back every one of his men alive. Many soil scientists, though, remember Shackleton best for what he brought back from an earlier Antarctic voyage in 1907–1909: the first documented samples of the continent’s “soil.”
“Soil” is just what the scientist H.I. Jensen tentatively called the loose, sandy, and grayish material when he analyzed it in 1916, and it would take soil scientists 60 to 70 more years to decide that it truly was soil and delete those quotation marks for good. Why did Antarctica’s soils prove so puzzling? It comes down to how unusual they are.
To start, Antarctic soils are frozen like their counterparts in the Arctic and high mountain regions. But they’re also extremely dry like soils in the world’s hottest deserts. They tend to be poorly developed by the standards of temperate areas, yet they are often several million years old. They also don’t support much familiar plant life, nor do they seem to contain any organic matter or microorganisms—at least at first glance.
So different are they from other soils, in fact, that a new soil order—the Gelisols—was added to the U.S. classification system in 1997 to accommodate them. (In Canada and Europe, these same soils are called “Cryosols,” and in Russia, “Cryozems.”) What’s more, as scientists around the world argued about this addition, they ended up revisiting and refining the very definition of soil itself.
Now, questions about Antarctic soils have shifted from how they fit with other soils to where they factor in a contemporary conundrum: climate change. Historically, less than 0.5% of Antarctica has been ice free—and, hence, potentially soil covered—with the McMurdo Dry Valleys in Victoria Land making up 15% of the total ice-free area. But as temperatures warm and Antarctica’s glaciers retreat, more land is being exposed, especially on the wet and relatively warm Antarctic Peninsula, says University of Wisconsin soil scientist Jim Bockheim.
Exactly what this will mean for Antarctica—or the planet, for that matter—is hard to predict right now. What is clear is that change is happening quickly, Bockheim says, and he’s in one of the very best positions to know. Beginning in 1969, Bockheim spent 12 field seasons in Antarctica to become one of the world’s foremost experts on its unique soils. He then studied Arctic soils for two decades before returning to Antarctica in 2004 for seven more seasons.
In the vast history of Antarctic soil development, it was a blip of time to be away. Still, it was enough. “The beauty of [my hiatus] was that suddenly I could see major differences as a consequence of warming, not only on the peninsula but also in the Dry Valleys,” Bockheim says. “I was seeing things I had never seen before.”
Deep Cold and Extreme Dryness
What distinguishes Antarctica’s soils? They are cold, of course; like other “permafrost-affected” soils around the globe, they are constantly frozen within one meter of the surface. And “cryoturbation”—the mixing and churning of the soil’s layers from repeated freezing and thawing—is the main soil-forming process.
But the word “frozen” implies the presence of hard ice, when all that really defines permafrost is a soil temperature below 0°C (32°F) for two or more years in a row. In other words, while ice is a critical player in Antarctic soils, permafrost can exist without ice in Antarctica. In fact, this “dry-frozen” permafrost is a common occurrence because of the continent’s extreme aridity, Bockheim says.
This produces a phenomenon that even soil scientists sometimes struggle to grasp, unless they’ve seen it firsthand. “In Antarctica, you can easily dig a soil in certain areas, and then you stick a thermometer in, and lo-and-behold, the soil is at minus 30 degrees,” Bockheim says. “But it’s also loose. You can take a handful of it, and you might find the odd grain of ice. But it’s so dry that the soil isn’t cohesive.”
Another effect of the desert dryness is that Antarctic soils can accumulate salts to very high concentrations. In temperate areas, water from rainfall or melting snow will periodically flush salts into deeper soil layers. Likewise, salts move downward in Antarctic soils when the top layer of soil thaws in summer.
But when a thick region of dry-frozen permafrost has developed beneath the seasonal thaw zone, salts won’t migrate any further due to the lack of water, accumulating instead in a layer. “So eventually after several million years a salt pan can develop—a hard pan,” Bockheim says. “It takes a pick to get down through it.”
Yet another oddity of Antarctic soils lies in their layering: Rather than running parallel to the surface as usual, the different strata—or “horizons”—in Antarctic soils are broken and contorted from cryoturbation. But the biggest obstacle to Antarctic soils being recognized as such was their dearth of plant life (see sidebar).
It seems an ironic objection considering what’s been happening on the continent lately.
A Changing Climate, a Changing Ecosystem
Jutting for miles into the Southern Ocean, the Antarctic Peninsula has always been wetter and warmer than most other regions of the continent—and today it’s warmer still. The peninsula is in fact experiencing the most pronounced warming of anywhere on earth, Bockheim says: Up 3.5 degrees on average over the past 50 years, and as much as 6 degrees during the austral winter of June, July, and August. Its glaciers are retreating as a result, exposing new soil and allowing plants to take root where they never have before.
One flowering plant is doing especially well. During the last half century, Antarctic hair grass has expanded tremendously in the maritime regions of the continent, giving them an oddly verdant look today in summer. But looks aren’t all. The plants are removing carbon dioxide from the air, fixing it into biomass, and adding organic matter to the soil in places formerly blanketed only by ice and snow. What this shift may mean for the global carbon cycle scientists are only starting to examine.
Plants aren’t only present on the coasts, either. Mosses, lichens, and algae thrive even in the desiccated, Mars-like environment of the Dry Valleys, and like plants everywhere, they feed the rest of the ecosystem, says Ed Gregorich, a soil scientist with Agriculture and Agri-Food Canada who has taken three trips to Antarctica. In typical Antarctic fashion, though, these plants do it in a unique way.
Take the Garwood Valley, for example, where Gregorich worked as part of an international research team in the mid-2000s. Like all the Dry Valleys, Garwood is exceedingly arid. But during the austral summer, parts of the nearby Garwood Glacier melt, feeding streams that empty into a small lake, called Lake Colleen. Water and warmer temperatures in turn fuel the growth of mosses, lichens, and algae, both along the stream banks and the lakeshore.
Then when the weather cools again, the seasonal halt in glacial melt causes the streams to dry, the lake to shrink, and the organic debris from plant growth to freeze-dry in place. It doesn’t stay put, though. Intense, katabatic winds blow the material all over the valley floor, where it’s decomposed slowly by microorganisms and contributes to soil organic matter.
“So in a way,” Gregorich says, “the system functions in the opposite way to ecosystems in our temperate environment.” That is, lakes in temperate areas are the downstream collection points for nutrients and organic matter that flow off the land. But in Antarctic lakes like Colleen, the reverse is true: Organic matter forms in the lake and then disperses away from the water and across the landscape.
The other important point is that although the Dry Valley ecosystem is simple, it is an ecosystem—complete with primary producers and decomposers poised to respond to increased temperature and moisture. Thus, if the Dry Valleys warm and their glaciers melt further, “these lower plant forms will grow and the microbial activity will pick up,” Gregorich says. “So, climate change will have implications here.”
Where Are the Snow Patches?
Whether the Dry Valleys are indeed heating up is the subject of debate, however. Some scientists have found no evidence of warming. Others believe the valleys are actually cooling. But when Bockheim returned to the Dry Valleys in 2004 after two decades away, for him there was little doubt.
Before GPS, for instance, he and other scientists found their research sites again each year by identifying them in relation to “semi-permanent” patches of snow of distinctive sizes and shapes. They’d find the right patches on an aerial photograph, stick a pin through them, and then consult a topographic map of these locations to get the actual coordinates for the study sites.
“So they were very important markers. Then I go back 20 years later and I say, ‘Where are the snow patches?’” Bockheim says. “They’re gone!” All that’s left are hollows in the ground—niches where soil eroded for decades underneath the now-melted snow. Evidence of melting is also apparent in places where accumulated salts have washed downhill with water. In other spots, soil formation is clearly revving up due to more frequent cycles of freezing and thawing.
What this all suggests is that more study is needed, and as someone who has appreciated Antarctic soils from the beginning, Bockheim is gratified to see the new attention being paid to these peculiar soils. At the same time, he harbors no illusions about what’s truly powering the scientific buzz.
True, Antarctic soil itself grabbed the spotlight when the Gelisols were under debate. “But the real interest,” Bockheim says, “came with the warming.”
This story first appeared in the March-April 2014 issue of Soil Horizons.