More on the briny water of Lake Vida that remains liquid under an ice cover. This shows you can have a relatively thin ice cover even with an average temperature of -30 C:

Researchers Uncover Extreme Lake
Washington - Dec 18, 2002
http://www.spacedaily.com/news/life-02zzf.html

Resurrection After 2,800 Years
WASHINGTON, Dec. 17, 2002
"Mars, thought to be one of the most likely places for life elsewhere in the solar system, is a place of deep cold, said Christopher P. McKay, a planetary researcher at NASA's Ames Research Center in Moffett Field, Cal.
"For this reason, studies of how liquid water can persist in cold environments is relevant to the search for life," said McKay in an e-mail. "Vida shows us a new way in which ice, salt and water can combine to allow liquid water habitats ... suitable for life to persist."
"Doran said water flows into Lake Vida during some Antarctica summers, but the new water stays on top of the ice, sealing the lake.
"In warm summers, you get a lake on top of a lake - a one meter of water sitting on top of 19 meters of ice," he said. "That freezes over the winter and you get a buildup year after year."
"Salt is expelled as the water turns to ice and is concentrated below, said Doran. Over many thousands of years, the salt concentrates in the water, making the water increasingly difficult to freeze. He estimated that water just below the ice may have a freezing point of minus 10 degrees."
http://www.cbsnews.com/stories/2002/12/17/tech/main533277.shtml

Bob Clark