Monday, February 18, 2013

EARTH’S SALTIEST POND AND IMPLICATIONS FOR WATER FLOW ON MARS



Antarctica’s Don Juan Pond, the most saline natural body of water on Earth, is found in the McMurdo Dry Valleys and its high salinity keeps it from freezing. Using time-lapse photography and other data, a team of researchers from Brown, Oregon State, and Boston University have been able to show that water sucked out of the atmosphere by the salty soil is the source of the saltwater brine. This brine, combined with fresh water that flows in from melting snow, enables the pond to remain fluid. Because there are a number of similarities between the Dry Valleys and the Martian desert, these findings could have implications for past and possibly present water flow on the Red Planet.

This new research represents some of the most detailed observations ever made of Don Juan Pond. The team analysed 16,000 pictures taken of the pond over the course of two months to see which way the water was flowing. The analysis from the images was then correlated with other measurements.

The images showed that water levels in the pond increased in pulses that timed with daily peaks in temperature. This suggested that some of the water came from snow that was melted by the midday sun. The influx of freshwater did not however explain the high salinity content of the pond; eight times higher than the Dead Sea. The researchers therefore sought a second source of liquid.

The second source of water was identified as coming from a channel of loose sediment located to the west of the pond; previous research had found this sediment was high in calcium chloride salt. To verify that this sediment was the source of the pond’s salt, the researchers set up a second time-lapse to observe the channel and then synchronised the pictures with data collected from weather stations nearby.

The images showed water tracks (dark streaks of moisture) forming in the soil whenever there was a spike in the relative humidity in the air. Similar water tracks were also noted forming on a cliff face north of the pond. A process known as deliquescence is responsible for forming these tracks, whereby the salt in the soil absorbs all available moisture in the air. These water-laden salts trickle down through the loose soil until they reach the permafrost layer, where they sit until the odd flow of snowmelt washes the salts down the channel and into the pond. The team was able to conclude that the tracks were the result of deliquescence when they saw how closely the appearance of water tracks correlated to their humidity readings. This process was the key to keeping the pond’s salinity so high. These findings refute the dominant interpretation: that Don Juan Pond’s briny waters must be supplied from groundwater.

NASA’s Mars Global Surveyor probe has already identified alluvial fan-shaped salt formations and recurring slope lineae on the surface of Mars, which could be an indication of some kind of flowing brine (http://on.fb.me/11qtXLN). The images of the water tracks at Don Juan Pond look similar to these features, and the research into the pond adds weight to the idea that the lineae seen on Mars are formed by flowing brine. Frost has been observed on Mars which suggests the atmosphere contains some water vapour. Chloride-bearing salts have been detected on Mars; they would be capable of the same kind deliquescence seen at Don Juan Pond. The processes at the pond do not require groundwater and groundwater is not thought to exist on Mars. The research at Don Juan Pond may provide insights into early lake formation on Mars and also about any present-day water flow on the Martian surface.


Microbial life found in Lake Vida’s frozen brine in Antarctica: http://on.fb.me/Y9DpOz
The Dry Valleys: http://on.fb.me/Y6CgFK
Bacteria living within saline deposits in Rio Tinto:http://on.fb.me/X24PIe

http://news.brown.edu/pressreleases/2013/02/antarctica
James L. Dickson, James W. Head, Joseph S. Levy, David R. Marchant. Don Juan Pond, Antarctica: Near-surface CaCl2-brine feeding Earth's most saline lake and implications for Mars. Scientific Reports, 2013; 3 DOI: 10.1038/srep01166

Image credit: Geological Sciences/Brown University



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