Alaskan painter Toni Onley once described an Arctic shoreline as “great blocks of ice thrown up in confusion—like a Cubist’s dream.” Similarly, standing on the Beaufort Sea’s shore, writer Annie Dillard (in Teaching a Stone to Talk) contemplated a “mess of ice . . . standing ﬂoes, ice sheets upright, tilted, frozen together and jammed—which extended out to the horizon.” This chaos occurs at the ﬂoe or ﬂaw edge where pack ice, driven by wind and current, rips and shreds the seaward edge of an otherwise stable, ﬂat, often gently nubbled, sometimes vast sheet of sea ice anchored to the land. In Shadow of the Hunter, Richard Nelson writes: “Finally the pack pressed in against the fast ice, and huge ridges began grinding together. The sight was awesome, even for men who had seen it many times before. Colossal boulders of ice turned and fell, sending shivers through the ﬂoes. Low rumblings gave voice to the incredible power before them, as the faces of ice mountains met in slow, pulverizing collisions.” Fast ice forms anew each year, with wind and ocean depth playing the most important roles in determining its extent. Iñupiaq people call this motionless expanse tuwak. Fast ice may or may not be separated from pack ice (the perpetually moving ﬂoes of annual and multi-year polar ice) by stretches of open water, called ﬂaw leads. Eskimo hunters regularly traverse fast ice to hunt at the ﬂaw lead, where sea mammals associated with pack ice—seals, bowhead whales, belugas, and narwhals—congregate to breathe. Here, too, is where polar bears, drawn to the ﬂoe edge by the concentration of prey, often come ashore across the reach of fast ice. From miles away hunters on tuwak may spy steam rising from a ﬂaw lead or see a patch of dark cloud, both revealing open water. Other names: landfast ﬂoe, tuaq (Yup’ik), ﬂaw ice. Global warming, by delaying the seasonal formation of fast ice, is threatening the ice-dependent universe of polar bear, bowhead whale, Eskimo.