There are no known extremophiles that can exist at a temperature lower than the freezing temperature of water. It is believed that liquid water is a crucial ingredient to the chemistry that leads to the origin of life. To change water-ice to liquid water requires energy.
First, you need energy to raise the ice from wherever temperature it is, to Celsius. This is called the Specific Heat and is kiloJoules/kilogram C Then you need enough energy added to the ice near 40$ C to actually melt the ice by increasing the kinetic energy of the water molecules so that their hydrogen bonds weaken, and the water stops acting like a solid.