If staying put on Antarctic sea ice is fraught with peril, traveling across it is even more so. For not only are your chances of suffering frostbite or getting lost in a whiteout or dying from hypothermia even greater, but you also have to cope with extremely treacherous ice conditions. As the Shackleton expedition's forays over the Weddell Sea ice showed, traveling over pressure ridges - places where colliding floes have tossed up massive slabs of sea ice - is challenging if not impossible. In addition, cracks can appear without warning, weak bridges of ice can form over unseen leads, and sea ice begins to break apart when the seawater temperature rises above 28.5°F or even in strong wind or swells.
Seawater immediately beneath sea ice is roughly the same temperature as the ice, or about 28.5°F. If you fall in, at the least you may have your breath knocked out of you, or you may involuntarily lurch into a spastic fetal position and lose control of your muscles. If unprotected by survival gear, you would be able to swim at most a mile before the coldness utterly incapacitated you. If you stayed put where you fell in, you'd lose consciousness in five to seven minutes and, if you didn't drown right away, you'd freeze to death in ten to 30 minutes.