Winter's Child( Savage Species, p. 40)
You are adapted to a cold environment.
As an arctic dweller, you are more hardy. The DC of your Fortitude save to avoid subdual damage from cold is reduced to 10 (see Cold Dangers in Chapter 3 of the DUNGEONMASTER's Guide). In addition, you can make a saving throw each minute (DC 10, +1 for each previous check) to resist the effects of hypothermia in very cold water.