Salt pond in Antarctica, among the saltiest waters on Earth, is fed from beneath

Posted: November 19, 2017 by oldbrew in research

Don Juan Pond, Antarctica [image credit: NASA]

Researchers plan to camp near this shallow pond for six weeks starting in December, to get detailed measurements of its liquid and explore the local area.

At the base of the Transantarctic Mountains lies a geological oddity, reports Hannah Hickey at UW News.

Don Juan Pond is one of the saltiest bodies of water on the planet, filled with a dense, syrupy brine rich in calcium chloride that can remain liquid to minus 50 degrees Celsius, far below the freezing point of water.

But the source of water and salt to this unusual pond remains a mystery — even as hints emerge that water in a similar form could exist on Mars.

A new University of Washington study uses the pond’s bizarre chemistry to pinpoint the water’s source.

The recent paper, published Sept. 15 in Earth and Planetary Science Letters, reports that it is fed by a regional deep groundwater system and not, as previously suggested, from moisture seeping down from local valley slopes.

“Don Juan Pond is probably one of the most interesting ponds on Earth,” said lead author Jonathan Toner, a UW research assistant professor in Earth and space sciences. “After 60 years of extensive study, we still don’t really know exactly where it’s coming from, what drives the fact that it’s visible on the surface, and how it’s changing.”

The perennial pond measures about 100 by 300 meters, the size of a few football fields, and is about 10 centimeters (4 inches) deep on average. It was first visited in 1961 and named after the expedition’s helicopter pilots, Donald Roe and John Hickey, earning it the name Don Juan Pond. The unique salts in the pond lower the freezing point, which is why this saline pond can exist in a place where the temperature ranges from minus 50 to plus 10 degrees Celsius (-58 to +50 F).

The pond was long believed to be fed by deep groundwater. But then a high-profile 2013 paper suggested that near-surface moisture seeps, similar to recurring slope lineae features recently observed on Mars, were transporting salts downhill to create the salt pond.

Toner is a geochemist specializing in the formation and properties of water in extreme environments on Earth, Mars and beyond. For the new study, Toner created a model to compute how salty water changes during evaporation, freezing, and with different water and salt inputs and outputs. In Antarctica’s appropriately named McMurdo Dry Valleys, water evaporation concentrates salts in the pond, which forces some salts to crystallize. These processes, along with inputs and outputs, cause the pond’s water to change over time.

Toner ran his model for two situations: one where the water was gurgling up from beneath, and another where it was trickling down from near-surface seeps. Results show that the observed chemical makeup could only be produced from underneath.

“You couldn’t get Don Juan Pond from these shallow groundwaters,” Toner said. “It’s definitely coming from the deep groundwater.”

Continued here.

  1. Real science and no mention of climate.

    Well done.

  2. JB says:

    “It’s definitely coming from the deep groundwater.” So says Toner about his computer model.

    Has the result of computer modeling been verified by observation?

    “the source of water and salt to this unusual pond remains a mystery”

  3. ivan says:

    JB, I don’t think there are many models pertaining to earth science that have been verified and tested against real world data. This is in contrast to engineering where models have to be verified before they are used for anything.

  4. oldbrew says:

    ‘in a place where the temperature ranges from minus 50 to plus 10 degrees Celsius’

    Probably not a lot of evaporation going on?

  5. p.g.sharrow says:

    this “salt”pond appears to me to be the result of sublimation and freezeout of the H2O. Take a bucket of “salty” water and freeze dry it and the CaCl will wind up on the surface like an oily scum. This little shallow pond is like a playa lake bed out in the desert of drying out glacier…pg

  6. JB says:

    @Ivan I agree with that observation–especially with astro-science. Until a model has been tested and verified, the most essential part of science is left undone, and calling what they do (speculating and modeling) as “science” is closer to fakery and a house of cards. Mathematics doesn’t care about the validity of a premise. It will allow you to be confident in a wrong solution even though the result appears rational. Karl Popper did not consider modeling to be science at all. From my own limited forays into modeling I found that at best it only helped me discern some errors in my own presuppositions. While that was useful at times, testing at the bench was far more productive.

    Stuffing a number of traceable salt isotopes into the water table would lead to some useful information.

  7. p.g I think you have the formula wrong. Calcium Chloride is CaCl2 which is very soluble in water and even sublimes taking moisture from the atmosphere. It is strange that it exists in large quantities. It could result from the reaction of HCL on limestone. Most seawater is low in calcium because CaCO3 is very insoluble. If CaCl2 is present with the absorption of CO2 from the atmosphere CaCO3 is precipitated out and lowering the pH. It is known that some volcanoes emit Chlorine Cl2 which can react with water at high temperature to form HCl. Maybe somewhere below the surface magma is decomposing salt NaCl in seawater to form HCL which then is reacting with a local deposit of limestone (CaCO3)

  8. p.g.sharrow says:

    @cement you are right about my shorten formula. I used to use CaCl2 dissolved in water to add lots of weight to tractor tires. I think you are correct that this source is geological. Likely a magmic warm spring traveling through limestone or marl shale further up under the glacier. I was pointing out the surface observation of this shallow small brine pond at the foot of a glacial moraine…pg

  9. oldbrew says:

    For saltwater that’s as saturated as it can possibly get (i.e. there’s no way to dissolve any more salt in it no matter how hard you tried), the freezing point is -21.1 degrees Celsius. This is when the saltwater is 23.3% salt (by weight).

    Air temps can go down to -50C where the pond is, but it doesn’t freeze. Is that where pg’s warm spring comes in?

  10. p.g.sharrow says:

    @oldbrew, I would think that the Calcium Chloride enrichment in the pond is a factor of the extreme cold and dryness that has fractioned the salts to yield the concentrated CaCl2 brine in the shallow pond. I would expect to see NaCl deposits precipitated below…pg

  11. oldbrew says:

    Calcium chloride from OxyChem is refined from natural brines found in sandstone formations beneath the earth.

    During the Cambrian period, Gondwana had a mild climate. West Antarctica was partially in the northern hemisphere, and during this period large amounts of sandstones, limestones and shales were deposited.
    . . .
    As a result of continued warming, the polar ice caps melted and much of Gondwana became a desert. In East Antarctica the seed fern became established, and large amounts of sandstone and shale were laid down at this time.

  12. Oldbrew in the Chemical Engineering Handbook it has that CaCl2 is deliquescent and its solubility in cold (0C) water is 50.5 parts to 100 parts of water , In hot water (200C) the solubility is 347 parts per 100 parts of water. So if there is very hot sea water (under pressure and high temperature ) being forced through a limestone bed the conditions are there to form CaCl2 in high concentration solution.

  13. oldbrew says:

    c/f – the pond is in Wright Valley so nowhere near any seawater, unless it’s going a long way underground. There are a number of these ponds there but DJ is the most saline.

    Possibly the Ross Sea retreated leaving lakes behind.