Nice article here:
How The World's Saltiest Pond Gets Its Salt; Implications For Water On Mars.
by Staff Writers
Providence RI (SPX) Feb 11, 2013
It discusses the famous Don Juan Pond in Antarctica that manages to remain liquid all year round despite subfreezing temperatures.
In addition to snow melt, the researchers observations suggest nearby areas of high salt content suck water vapor out of the air during peaks of high humidity. Because of the freezing point depression characteristic of salts this water vapor can then condense to liquid even in subfreezing temperatures.
The researchers observed water tracks in these high salt regions and expect that this seeps underground and flows underground into Don Juan Pond.
Because of the high amount of salts on Mars this process could also happen there. Then we would want to look for such tracks during peaks of high humidity on Mars. MSL Curiosity does have humidity sensors but it's unclear whether they have reported reliable readings yet.
The author of this blog discusses the problems with the MSL humidity sensors:
SANITY CHECK FOR RELATIVE HUMIDITY AT MSL CURIOSITY.
The author of the blog seems to have a particular point of view (for instance he believes the pressures on Mars are much higher than expected) still he discusses in depth the readings reported by NASA from the various Mars spacecraft.