World’s saltiest pond suggests water on Mars

A team of geologists led by Brown University have discovered the secrets of a pond in Antarctica with the world’s highest salt content. Their findings, published in Scientific Reports, suggest that such ponds could be possible on Mars.

Don Juan Pond is situated in the McMurdo Dry Valleys in Antarctica. Amazingly, the pond is able to remain fluid in one of the coldest and driest places on Earth thanks to its high salt content – eight times higher than that of the Dead Sea. The team used time-lapse photography to show that water sucked out of the atmosphere by dry, salty soil is the source of the saltwater brine that keeps the pond from freezing.

“It was a simple idea,” James Dickson, who led the study, 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 peaks in temperature. This suggested that the water comes partly from snow warmed just enough by the midday sun to melt, however, this data did not explain the pond’s high salt content.

The team had to look for another water source and eventually discovered a channel of loose sediment located to the west of the pond. The pictures showed dark streaks of moisture forming in the soil whenever the relative humidity in the air spiked. The effect was due to salt in the soil absorbing any available moisture in the air, a process called deliquescence. The water-laden salts then trickled down through loose soil until they reach the permafrost layer beneath where the flow of snowmelt washes them down the channel and into the pond.

The images of the water tracks at Don Juan are similar to features recently imaged on Mars called recurring slope lineae. Some researchers believe these streaks indicate some kind of flowing brine suggesting that there might be flowing water on the Red Planet.

“Broadly speaking, all the ingredients are there for a Don Juan Pond-type hydrology on Mars,” Dickson said. “It’s not likely that there’s enough water currently on Mars for the water to form ponds, but stronger flows in Mars’ past might have formed plenty of Don Juan Ponds.”

Paper: Don Juan Pond, Antarctica: Near-surface CaCl2-brine feeding Earth's most saline lake and implications for Mars

http://www.nature.com/srep/2013/130130/srep01166/full/srep01166.html