February 7, 2013
Antarctica’s Salty Don Juan Pond Offers Watery Hope For Mars
Lawrence LeBlond for redOrbit.com - Your Universe Online
Several bodies of water around the world are known for their salty content. Among the most well-known are the Great Salt Lake in Utah and the Dead Sea. But these bodies of water pale in comparison to Don Juan Pond in Antarctica, known as the saltiest body of water on Earth. The pond, situated in the McMurdo Dry Valleys of the harsh, icy continent, keeps from freezing because of its salt-rich composition.
But why this landlocked pond, unattached from the Southern Ocean, remains so salty is something that researchers from Brown University wanted to get to the bottom of.
To figure out the conundrum, the geologists used time lapse photography and other data to monitor the body of water and its surroundings. What they found is that water sucked out of the atmosphere by parched, salty soil is the key ingredient in keeping the pond so brackish and in a liquid state.
The Brown team, upon answering the long-puzzling riddle, now believe the similarities between the Dry Valleys of Antarctica and the frozen desert of Mars, will offer important implications for water flow on the Red Planet both in the past and, more importantly, in the present.
The study was conducted by James Dickson and James Head of Brown University, Joseph Levy of Oregon State, and David Marchant of Boston University. The findings are published in the journal Scientific Reports.
"It was a simple idea," Dickson said of the team's approach. "Let's take 16,000 pictures of this pond over the course of two months and then see which way the water's flowing. So we took the pictures, correlated them to the other measurements we were taking, and the story told itself."
The pictures revealed that water levels in the pond increase in pulses that coincide with daily temperature peaks, which suggests the water comes partly from snow melt from the midday sun. Of course, this does not explain the pond´s high salt content, which is eight times saltier than the Dead Sea. So the team had to look at a second source of liquid documented in their photos in which they discovered the channel of loose sediment to the west of the pond.
Previous research had found this sediment to be high in calcium chloride salt. To see if this was the source of the pond´s sodium intake, the team set up a second time-lapse camera to monitor the channel. They then synchronized the pictures with data collected from nearby weather stations.
The pictures taken showed dark streaks of moisture called water tracks forming in the soil whenever the relative humidity spiked. They found similar water tracks on to the north of the pond as well. They determined that these water tracks were formed by the salt content in the soil that absorbs any available moisture in the air, a process known as deliquescence. The salt then trickles down through the soil until it reaches the permafrost layer below. This is where it sits until the occasional flow of snow melt washes the salt down the channel into the pond.
The new findings refute the earlier theory that the pond´s salty nature derived from salts deep underground being pushed upward. This was the leading theory since the pond was discovered in 1961. The new findings show no evidence whatsoever that this underground process contributes to the pond's brackish nature.
Dickson and Head said the Don Juan Pond study is a good model for searching for water on other planets, such as the cold, dry desert of Mars.
They noted that the water tracks at Don Juan Pond look eerily familiar to features recently imaged on Mars called recurring slope lineae. These features appear as dark streaks that flow downward off cliff faces. These lineae often recur in the same places at the same times of year, which lead scientists to hypothesize that there may be flowing water on present-day Mars.
Frost has been observed on Mars, which suggests that the atmosphere contains at least some water vapor. Also, chloride-bearing salts have been detected, which would be capable of the same kind of deliquescence as seen in Antarctica.
"Broadly speaking, all the ingredients are there for a Don Juan Pond-type hydrology on Mars," Dickson said in a statement. It's not likely that there's enough water currently on Mars for the water to form ponds, but stronger flows in Mars's past might have formed plenty of Don Juan Ponds.
"Don Juan Pond is a closed basin pond and we just documented a couple hundred closed basins on Mars," Head added. "So what we found in Antarctica may be a key to how lakes worked on early Mars and also how moisture may flow on the surface today."