Bob Clark wrote:-

The current understanding is that the water is in frozen form beneath the CO2 ice cover in the south polar cap. However, it has been speculated that there could be pools or lakes of liquid water beneath the ice at both the north and south poles, in analogy with the perennially ice covered lakes in Antarctica. The temperatures above these lakes in Antarctica can be below -80°C. In fact it is not known for certain how these lakes remain liquid in Antarctica.

Au contraire, mon brave, it is indeed well understood how the lakes remain liquid. Most are extremely strong brines. The local air temperature at any moment is not the deciding factor, it's the year-round average temperature, plus a bit of energy from geothermal warming, and from sunlight penetrating the ice.

Some suggestions are that it's due to the pressure of the ice cover or due to geothermal heating. Note also that the temperatures above the ice covering the likely ocean on Europa are even lower than those at the south pole on Mars. Interestingly recent research suggests the thickness of the Europan ice instead if being 10 to 20 km thick may be comparable to the thickness over Lake Vostok in Antarctica.

And other recent research suggests that the Europan ocean is mythical, and the measurements are easily satisfied by a small fraction of brine between a solid icy crystal mush.

Also if you check the animated graph on the TES web page at:
http://wwwflag.wr.usgs.gov/USGSFlag/Space/MGS_TES/spole99.html, you'll see that during southern Summer the temperature can be as high as -40°C as far as south as 80°S latitude.

Oh wow, as if I didn't know that. :-)

Unfortunately, the winter temperature is -130 C and the annual mean temperature around -100 C.

To be fair however, and constructive, I should add that during my recent trip to the States I had some discussions with Jeff Kargel that have convinced me that basal melting of the polecaps of Mars are, in fact, possible.

However, this possibility is only allowed IF the polecaps contain 30% CO2 AND all the water is frozen as CO2 clathrate. AND, this raises the amusing possibility (nay, probability) that any excess CO2 will form dry ice layers in the polecap and these will melt to produce liquid CO2 at half the depth that the clathrate melts to produce water. (CO2 liquid will form at ~1800m and liquid water at ~3.5 km. Further amounts of liquid CO2 will also form when the clathrate melts).

Mars is an amusing and paradoxical planet.