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. 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.
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.

Bob Clark