If it is the case that all the CO2 over the south pole would disappear over times of a few hundred years it doesn't seem reasonable that it would just stop there. I'm positing that this would also continue to sublimation and perhaps melting of the underlying water ice as well.
Both Pathfinder and Viking observed whitish rocks at the surface and close to the surface that most scientists interpret to be duricrust. On Earth duricrust forms most commonly as evaporite deposits requiring liquid water.
The most most common form of duricrust on Earth is formed of calcium carbonate. Another common form is formed from sulfate in the form of indurated gypsum.
Pathfinder scientists concluded that the duricrust is widespread at the Pathfinder site just centimeters below the surface:

Pathfinder found red, white and blue rocks on Mars.
"A University of Arizona scientist told the American Astronomical
Society that Pathfinder pictures taken with different filters show a
faint bluish tint on one side of exposed rocks, while the other side
of the rocks is a typical Martian red. Some partially buried rocks
are a whitish color and may actually be layers of a hard material
called caliche, a calcium carbonate rock material common in Arizona."
http://www.spacetoday.org/SolSys/Mars/MarsPathfinder.html

MARS PATHFINDER LANDING SITE:
GEOLOGY OF MARS
"During its traverse to Yogi the rover stirred the soil and exposed material from several cm in depth. During one of the turns to deploy the APXS (inset and white arrow), the wheels dug particularly deeply and exposed white material. Spectra of this white material show it is virtually identical to Scooby Doo, and
such white material may underly much of the site."
http://www.nd.edu/~cneal/eg.101/geology.1.html

Pathfinder's Finds
"Britt classifies Scooby Doo and its kin as a third kind of rock that he calls "caliche-like," after a cemented mineral common in the Tucson area.
When it rains in the desert, calcium-rich salts leach out of the upper soil and begin to percolate downward. But before they've penetrated more than a foot or so, the water evaporates in the
scorching heat, concentrating them into a layer—caliche—that has many of the properties of con-crete.
Says Britt, "There's a big debate about
whether the caliche-like stuff should be classified as soil or rock. The people from moist climates who have never tried digging in it call it soil.
Those of us from arid regions call it rock. And since I'm the chair of the mineralogy and geo-chemistry science group, it's rock."
p. 9,
http://pr.caltech.edu/periodicals/EandS/articles/Pathfinder%20Feature.pdf

The carbonate form of duricrust, caliche, is in general harder than the sulfate form. This perhaps is what led Pathfinder scientist Dan Britt to conclude that the duricrust was composed of the carbonate form since Sojourner's wheels were unable to scratch the material. It might be possible to distinguish between the two by comparing how Sojourner rover wheels can scratch either material in experiments on Earth.
In any case, there just aren't that many minerals that would be at the surface or close to the surface, that would be white and that would be hard. And either of the carbonate and sulfate possibilities would require liquid water at the surface.
Here are some sites that describe the carbon cycle on Earth. They show CO2 can be removed from the atmosphere and then ultimately returned to the atmosphere in a process involving the atmosphere, rock and water:

CO2 Cycle
"Just as H2O circulates between the atmosphere, the ground, and ocean waters in the water cycle, CO2 also circulates between these three reservoirs, solidifing as rock, dissolving out of rock into the water, baked out of rock into the air, or being absorbed directly into the waters at the Earth's surface. The transfer of CO2 between the air, water, and the ground is called the carbon cycle."
http://www.windows.ucar.edu/tour/link=/earth/Water/co2_cycle.html

The Carbon Cycle and Earth's Climate.
"Carbonate Rocks

1. Carbon dioxide is removed from the atmosphere by dissolving in water and forming carbonic acid

CO2 + H2O -> H2CO3 (carbonic acid)

2. Carbonic acid is used to weather rocks, yielding bicarbonate ions, other ions, and clays

H2CO3 + H2O + silicate minerals -> HCO3- + cations (Ca++, Fe++, Na+, etc.) + clays

3. Calcium carbonate is precipitated from calcium and bicarbonate ions in seawater by marine organisms like coral

Ca++ + 2HCO3- -> CaCO3 + CO2 + H2O
the carbon is now stored on the seafloor in layers of limestone"
http://www.columbia.edu/~vjd1/carbon.htm

Bob Clark