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IPY Science - Sea Ice

Sea ice, the thin layer of ice that covers most of the Arctic Ocean and surrounds most of the Antarctic continent, represents a distinctive feature of our planet. Sea ice spreads and retreats seasonally. It drifts and packs under the influence of wind and currents. It isolates the atmosphere from the ocean and produces the coldest saltiest ocean waters. It restricts the movement of ships but supports the traverses of bears. Sea ice contains unique organisms that sustain under-ice ecosystems. Poised where slight warming converts ice to water, sea ice has an exquisite sensitivity to climate. Its disappearance from any region, at any season, will represent a profound planetary change. Understanding sea ice and predicting its future represents a crucial challenge for IPY.

Sea Ice Formation
A clear 3-cm layer of ice on a lake will support a person. The same person could push a finger through 3 cm of sea ice. The formation of sea ice draws pure water into ice crystals, leaving behind a saltier brine. The brine accumulates in pockets and channels, which prevent the formation of continuous ice crystals. Air temperatures, wind, tides, currents, remnant ice, river flows, and the presence of surface debris or oceanic microorganisms all influence freezing and the structure of new ice. English words - nilas ice, frazzle ice, grease ice, pancake ice - demonstrate the complexity of the freezing process. Inuit languages convey a deep understanding of sea ice and of its suitability for travel and hunting. Sea ice often survives for several years, and the surfaces of multi-year ice record a complicated history of temperature, compression, fracture, melting, snowfall, dust collection, and wind erosion. Out of sight to most observers, the underside of sea ice presents an equally complex and fascinating appearance.

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Sea Ice and Climate
Above sea ice, air masses cut off from direct contact with the relatively warm ocean lose substantial heat to space, especially during winter darkness. This cooling process, which can produce surface air as cold as -30C, represents an important