The freezing temperature of water can be lowered by dissolved salts. What about for dissolved CO2? How would this lower the freezing point depending on the percentage of CO2?
Water on Mars would be expected to have some amount of dissolved CO2 from the atmosphere. However, I imagine the percentage amount would be rather small because of the low atmospheric pressure.
But in the case of water under CO2 ice you would expect some of the ice to sublimate and would be under higher pressure. In that case a higher percentage of CO2 could dissolve in the water. I'm wondering how the freezing point could be lowered in this scenario.

Actually I'm also wondering about the case of the boiling point increased by dissolved CO2 under (very) high pressures. ( Perhaps you could guess why? (;-) )
What might be expected to be the amount of dissolved of CO2 in water with the CO2 at high pressure and how would this effect the boiling point of water?

Bob Clark