Published March 13, 2014
Features
Spotlight Back on Antarctica's Peculiar Soils as Scientists
Study Climate Change Effects
Madeline Fisher
I
f 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.
M. Fisher, science communications manager, Soil Science Society of America, Madison, WI
doi:10.2136/sh2014-55-2-f
Open access.
Published in Soil Horizons (2014).
© Soil Science Society of America
5585 Guilford Rd., Madison, WI 53711 USA.
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Soil Horizons
p. 1 of 4
Team members install rings to collect gas
samples to measure soil respiration in Dry
Valley soils.
Close up photography documents soil
conditions at the time of sampling.
One of the few areas of Antarctica not
covered by thousands of meters of ice,
the McMurdo Dry Valleys stand out in
this satellite image. For a few weeks each
summer, temperatures are warm enough
to melt glacial ice, creating streams that
feed freshwater lakes that lie at the
bottom of the valleys. Image by Robert
Simmon and courtesy of NASA.
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.”
What Makes Antarctic Soils
So Different?
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.
A highly cryoturbated Gelisol profile.
Courtesy of Dr. C.L. Ping.
Soil Horizons
p. 2 of 4
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.”
Salt pan. Courtesy of Jim Bockheim.
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.
Antarctic hair
Flickr/¡WOUW!
grass.
Courtesy
of
What Makes Soil, Soil?
From the time of his first trip to Antarctica in 1969, Jim Bockheim says he always
considered the “weathered, surficial
deposits” on the continent to be soils. But
when the University of Wisconsin professor submitted one of his first papers on
Antarctica’s soils to the journal Geoderma
in 1982, the editor Roy Simonson warned
Bockheim that others might not agree.
“He was a very wise man,” Bockheim
says, “and he wrote to me that I needed
to give a working definition of soil in
my paper because a lot of people weren’t
going to be convinced that they really
were soils.”
So after consulting the literature, the soil
scientist put together his thoughts. Soil,
he wrote, was any surface material composed of solids, liquids, and gases that
showed visible signs of weathering and
was organized into layers or “horizons.”
In the end, the new description wasn’t
much different from older definitions
except in one significant way: Bockheim
removed the requirement that soil support higher plants.
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 AgriFood 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
Soil Horizons
p. 3 of 4
Less developed than other soils, Antarctic
soils can be loose, soft, and sandy or
frozen, hard, and rocky.
Soil taxonomy is a practical system, Bockheim explains, focused on the potential
uses of soil. For example, soils are
described and classified to help assess
whether the ground can support a building or road, house a septic system, or
produce crops or forests. That’s why
some scientists objected to calling Antarctica’s surface deposits “soil.” All
they seemed capable of growing were
microbes, mosses, and a few other lowly
life forms.
Still, Bockheim’s definition was accepted
and published by Geoderma, and then in
1992, his work caught the attention of the
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.
Collecting soil gas samples next to a lake
in the Dry Valleys.
Soil Conservation Service (now, the Natural Resources Conservation Service).
Having recently grown interested in
soils of the polar regions, the agency was
intrigued by his ideas on revising the
U.S. soil classification system to better
accommodate them—especially those in
Antarctica. In 1994, Bockheim was asked
to lead the International Committee on
Permafrost-Affected Soils. Three years of
intense debate later the committee established a 12th soil order specifically for
permanently frozen soils: the Gelisols.
What’s more, when the agency revised
its formal definition of soil in 1999, it
adopted Bockheim’s definition from 1982.
No longer would any soil have to support
higher plants to be worthy of the name.
Bockheim is glad Antarctica’s soils are
“official” now, and he’s proud of his role
in getting the Gelisols recognized. He
also thinks it was all pretty inevitable.
“The point is that there are soils in Antarctica, which are 11 or 12 million years
old and are very strongly altered,” he
says. “So if we didn’t call them soils,
what would we call them?”
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?
Evidence of melting is evident when
comparing snow patches in the Peleus
drift east of Lake Vanda in 1977 (left)
compared with 2005 (right). Courtesy of
Jim Bockheim.
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 nowmelted 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.
Soil Horizons
p. 4 of 4
Evidence of melting is also apparent in
places where accumulated salts have
washed downhill with water. Courtesy of
Jim Bockheim.
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.”