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This image shows eddies in the Gulf of Alaska as measured by the TOPEX/Poseidon and ERS-2 satellites. Each eddy is indicated by the year
and location where it formed.
Eddies are roatating masses of water in the ocean that typically form along the boundaries of ocean currents. In the Gulf of Alaska eddies of warm water, filled with nutrients from shallow coastal water, mix with the cold water off the continental shelf. The mixing fertilizes the nutrient-poor water of the gulf, resulting in blooms of phytoplankton (microscopic ocean plants.)
Satellites monitor movement and evolution of eddies continuously. Using radar that sees through clouds, the TOPEX/Posedion mission and the European Remote-Sensing Satellite-2 (ERS-2) produce maps of sea surface height. Since eddies that are warmer than the surrounding water are
higher than the usual sea surface height they appear on these maps. This image shows the difference from normal sea surface height for the Gulf of Alaska. Warm core eddies appear as red circles.
Located in eastern Canada, the Gulf of St. Lawrence owes many of its unique characteristics to its geography. Sea water flows into and out of the gulf through only two channels. Currents and tides sweep cold, Arctic seawater through the narrow Strait of Belle Isle in the north. In the south, the wider Cabot Strait admits warmer water from the Atlantic Gulf Stream. With no other outlet to the Atlantic, the Gulf of St. Lawrence is relatively isolated.
Submerged in the Atlantic Ocean off the coast of Spain and Portugal are giant, salty whirlpools of warm water. These deep-water whirlpools are part of the ocean’s circulatory system, and they help drive the ocean currents that moderate Earth’s climate. Warm water ordinarily sits at the ocean’s surface, but the warm water flowing out of the Mediterranean Sea is so salty (and therefore dense) that when it enters the Atlantic Ocean at the Strait of Gibraltar, it sinks to depths of more than 1,000 meters (one-half mile) along the continental shelf. This underwater river then separates into clockwise-flowing eddies that may continue to spin westward for more than two years, often coalescing with other eddies to form giant, salty whirlpools that may stretch for hundreds of miles. Because the eddies originate from the Mediterranean Sea, scientists call them “Meddies.”