Alteration 7, Water 6, 80 gems.
Sea of Ice freezes all the water on the map. This means that rivers are passable even in heat dominions, and that units cannot enter nor leave underwater provinces except through magickal means such as teleport and the like. Furthermore, sailing does not work and is rendered useless. Sea of Ice works with Vengeful Waters, and turns all of the water elementals spawned by it into Ice Elementals, regardless of the temperature scales.