These wet patches in Antarctica’s McMurdo Dry Valleys are created by the salty soils sucking water out of the atmosphere. Photo courtesy of Joseph Levy, Oregon State University |
The
frigid McMurdo Dry Valleys in Antarctica are a cold, polar desert, yet
the sandy soils there are frequently dotted with moist patches in the
spring despite a lack of snowmelt and no possibility of rain.
A
new study, led by an Oregon State University geologist, has found that
that the salty soils in the region actually suck moisture out of the
atmosphere, raising the possibility that such a process could take place
on Mars or on other planets.
The
study, which was supported by the National Science Foundation, has been
published online this week in the journal Geophysical Research Letters,
and will appear in a forthcoming printed edition.
Joseph
Levy, a post-doctoral researcher in OSU’s College of Earth, Ocean, and
Atmospheric Sciences, said it takes a combination of the right kinds of
salts and sufficient humidity to make the process work. But those
ingredients are present on Mars and, in fact, in many desert areas on
Earth, he pointed out.
“The
soils in the area have a fair amount of salt from sea spray and from
ancient fjords that flooded the region,” said Levy, who earned his
doctorate at Brown University. “Salts from snowflakes also settle into
the valleys and can form areas of very salty soil. With the right kinds
of salts, and enough humidity, those salty soils suck the water right
out of the air.”
“If
you have sodium chloride, or table salt, you may need a day with 75%
humidity to make it work,” he added. “But if you have calcium chloride,
even on a frigid day, you only need a humidity level above 35 percent to
trigger the response.”
Once
a brine forms by sucking water vapor out of the air, Levy said, the
brine will keep collecting water vapor until it equalizes with the
atmosphere.
“It’s kind of like a siphon made from salt.”
Levy
and his colleagues, from Portland State University and Ohio State
University, found that the wet soils created by this phenomenon were 3-5
times more water-rich than surrounding soils—and they were also full of
organic matter, including microbes, enhancing the potential for life on
Mars. The elevated salt content also depresses the freezing temperature
of the groundwater, which continues to draw moisture out of the air
when other wet areas in the valleys begin to freeze in the winter.
Though
Mars, in general, has lower humidity than most places on Earth, studies
have shown that it is sufficient to reach the thresholds that Levy and
his colleagues have documented. The salty soils also are present on the
Red Planet, which makes the upcoming landing of the Mars Science
Laboratory this summer even more tantalizing.
Levy
said the science team discovered the process as part of “walking around
geology”—a result of observing the mysterious patches of wet soil in
Antarctica, and then exploring their causes. Through soil excavations
and other studies, they eliminated the possibility of groundwater, snow
melt, and glacial runoff. Then they began investigating the salty
properties of the soil, and discovered that the McMurdo Dry Valleys
weather stations had reported several days of high humidity earlier in
the spring, leading them to their discovery of the vapor transfer.
“It
seems kind of odd, but it really works,” Levy said. “Before one of our
trips, I put a bowl of the dried, salty soil and a jar of water into a
sealed Tupperware container and left it on my shelf. When I came back,
the water had transferred from the jar to the salt and created brine.
“I knew it would work,” he added with a laugh, “but somehow it still surprised me that it did.”
Evidence
of the salty nature of the McMurdo Dry Valleys is everywhere, Levy
said. Salts are found in the soils, along seasonal streams, and even
under glaciers. Don Juan Pond, the saltiest body of water on Earth, is
found in Wright Valley, the valley adjacent to the wet patch study area.
“The
conditions for creating this new water source into the permafrost are
perfect,” Levy said, “but this isn’t the only place where this could or
does happen. It takes an arid region to create the salty soils, and
enough humidity to make the transference work, but the rest of it is
just physics and chemistry.”
Other
authors on the study include Andrew Fountain, Portland State
University, and Kathy Welch and W. Berry Lyons, Ohio State University.
About
the OSU College of Earth, Ocean, and Atmospheric Sciences: CEOAS is
internationally recognized for its faculty, research and facilities,
including state-of-the-art computing infrastructure to support real-time
ocean/atmosphere observation and prediction. The college is a leader in
the study of the Earth as an integrated system, providing scientific
understanding to address complex environmental challenges
