I was wondering if someone could explain how ice crystals are being formed in the tank/pipeline BP is trying to use to stem the flood of oil pumping into the ocean. A friend and me were discussing it and a few questions came to mind about it, not just related to this issue. He suggested that the higher pressures deep in the ocean lower the freezing point of water enough so that it does not freeze, which seemed plausible to me. But after looking it up, it sounds as though pressure has a very small effect on the freezing temperature - something like 135atms of pressure being necessary to lower the freezing temp by 1C. But ice always seems to form at the surface of a body of water and never in the deep. Is this because the ground at the bottom of the sea floor is always warmer than freezing temperature and the temperatures at the surface?