Salty Antarctic pond could help scientists understand history of water on Mars

Extensive groundwater system could be the source of the salt on Earth but not on Mars.
By Laurel Kornfeld | Nov 24, 2017
A shallow, extremely salty pond in Antarctica, one of the closest Earth analogues to features on Mars, could help scientists better understand the history of water flow on the ancient Red Planet.

Discovered in 1961 during a science expedition, the Antarctic pond is just several inches deep but salty enough to keep water in liquid form in temperatures as low as minus 58 degrees Fahrenheit (minus 40 degrees Celsius).

Unlike common salt used in food, the Antarctic salt has a composition that is 95 percent calcium chloride, which lowers the freezing point of water enough to keep it liquid during Antarctic winters.

Jonathan Toner, co-author of a new study on the pond published in the journal Earth and Planetary Science Letters, acknowledged that finding a solution of such pure, heavy salt--which makes water more dense and viscous than usual--is a rare occurrence.

While uncertain as to the process that resulted in the pond's unusual salt content, scientists have generally attributed it to feeding via deep groundwater.

A high evaporation rate in the very dry environment nearby and calcium chloride's ability to form much higher concentrations of salt than sodium chloride (common table salt) does are likely the reasons the pond has a composition as high as 40 percent salt.

The recent study used computer models of the pond's chemistry along with a 2013 paper that claimed the salt's origin to be a more shallow source.

In the 2013 study, scientists argued that calcium chloride in soil surrounding the pond sucked water from the atmosphere and that seasonal snow melts washed the salts into the pond.

Dark streaks on slopes close to the pond were attributed to the presence of water.

According to Toner and his research team, the scientists who conducted that study did not give sufficient consideration to the possibility the site having a deep source of groundwater.

They outlined two possible sources for the salt--either deep groundwater or atmospheric evaporation--and emphasized the computer model precisely matched conditions produced by deep groundwater.

In a slow process that takes thousands to tens of thousands of years, salty water is filtered through frozen soils, where it interacts with nearby minerals to produce pure calcium chloride, the researchers state.

Calcium chloride has been detected by scientists who drilled into the Antarctic soil.

A sizable groundwater system that feeds a nearby lake located in a region rich in calcium chloride may regularly flush out the pond, Toner added.

Although a better understanding of surface streaks could provide scientists with new insights into similar streaks on Mars, the Red Planet is too cold to have a groundwater system, meaning dark streaks on the Martian surface formed differently from those in Antarctica, Toner said.






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