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Ethereal swirls of grease ice appear turquoise against the midnight blue of the northern Baltic Sea in this false-color satellite image taken over the Aland Islands (red) between Finland and Sweden. The second stage of sea ice formation, grease ice consists of a viscous mix of tiny ice crystals and resembles an oil slick on the ocean's surface. Wind and currents constantly shape and reshape grease ice into surreal, ghostly patterns. Image courtesy of USGS.