Thanks for the link Barry. I had also argued that the "swiss" cheese formations at the south pole suggests water beneath the CO2 covering. See the sci.astro post copied below.
But I disagree with one of their conclusions. They argue that none of this could be liquid water. My argument
for water is that the swiss-cheese formations are analogues of Marangoni convection on Mars. See the examples of Marangoni convection in the links in the post.
Marangoni convection would require water in liquid form. I argue that the over-pressure of the CO2 ice plus possibly salt content would allow the water to remain liquid. This occurs with the ice-covered lakes of Antarctica which remain liquid beneath an ice cover despite below freezing average temperatures above the ice:

APOD: 2003 January 28 - The Lost World of Lake Vida
http://antwrp.gsfc.nasa.gov/apod/ap030128.html

Lake Hoare
http://www.everettak.org/~toby/antarctica/LakeHoare.html

Bob Clark

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From: Robert Clark (rgclark@my-deja.com)
Subject: Marangoni convection on Mars?
Newsgroups: sci.astro, alt.sci.planetary, sci.geo.geology, sci.physics
Date: 2001-08-22 21:59:25 PST

Convection has been argued to occur on Mars to produce some of the
landforms seen on Mars:

"Convection in a catastrophic flood deposit as the mechanism for the
giant polygons on Mars"
Jour. Geophys. Res., v. 105, E7, July 25, 2000, pp.17617-17628,
http://ethel.la.asu.edu/asu_tes/TES_Editor/PERSONNEL/LANE/polygonabstr.html
[abstract]

Also in my opinion MGS images indicate recent convection driven
processes to create some of the features seen:

From: Robert Clark (rgclark@my-deja.com)
Subject: Indications of recent liquid water on Mars.
Newsgroups: sci.astro, sci.astro.seti, sci.geo.geology,
alt.sci.planetary
Date: 2001-03-13 18:44:04 PST
http://groups.google.com/groups?th=1cc4be53b681caa8

Marangoni convection is a type of convection driven by differences in
surface tension. Since surface tension is dependent on temperature it
can occur under temperature variations in a liquid, and under
evaporation. It can also occur within mixtures of two different
liquids.

Some examples of Marangoni convection:

MARANGONI CONVECTION
http://nimbus.colorado.edu/hart/pages/Demonstrations/Marangoni/marangoni_convection.htm

Marangoni-Bénard-Convection-Cells
http://www.physiology.rwth-aachen.de/user/jaeger/diplom/index_e.html

Rayleigh-Bénard and Bénard-Marangoni convection
http://mobydick.physics.utoronto.ca/thermal.html

An image of unusual formations at the south pole of Mars reminded me
of the cells created at the surface of liquids in Marangoni
convection:

Martian Swiss Cheese
New pictures from NASA's Mars Global Surveyor spacecraft show exotic
terrain made of dry ice near the Red Planet's south pole.
http://spacescience.com/headlines/y2000/ast09mar_1.htm

If they are due to convection then that would require liquid for
their formation. Since these are formed close to the surface it would
appear to be liquid water rather than liquid CO2 which requires high
pressure to be in liquid form. Water could remain in liquid form much
closer to the surface with the overpressure of an ice covering. And
recent research suggests that likely the south pole consists largely
of water ice below a CO2 covering.

Two possibilities for the Marangoni convection firstly would be a
temperature difference due to a warmer temperature beneath the CO2 ice
allowing the water to remain liquid and colder temperatures at the
level of the CO2 ice. Another would be due to temperature variations
as water evaporated or boiled off as the CO2 ice covering partially
sublimated during southern summer.

Bob Clark

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