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When the sea around Antarctica drops to minus 1.9 degrees centigrade, it begins to freeze. A slight swell on the surface produces pancake ice - vaguely circular or square slabs of ice with raised edges. In the frigid air, the ice above the waterline grows into crystals. The early explorers called these fantastic shapes ice flowers. As it gets colder, the ice thickens and at the coast it freezes fast to the margins of the land. Farther out the pack ice consolidates into vast plains of sea ice.