Mediterranean Whirlpools

Deep in the Atlantic Ocean off the coast of Spain and Portugal are giant, salty whirlpools of warm water. These whirlpools are part of the ocean's circulatory system, and they help drive the ocean currents that moderate Earth's climate.

Warm water usually sits near the ocean's surface, but the warm water flowing out of the Mediterranean Sea is so salty and dense that when it enters the Atlantic Ocean at the Strait of Gibraltar, it sinks to depths of more than half a mile (1,000 meters) along the continental shelf.

This underwater river then splits into clockwise-flowing eddies that may continue to spin westward for more than two years. These often coalesce with other eddies to form giant, salty whirlpools that stretch for hundreds of miles. Because they originate from the Mediterranean Sea, scientists call them "Meddies."

Although Meddies are submerged beneath hundreds of feet of water, scientists recently developed a technique to detect them from space by measuring changes in sea surface height. The warm water of the Meddies causes the ocean around them to expand, raising the height of the sea surface above. This image shows where the Meddies (deep red areas) bumped up the sea surface height in 2005, as compared to the average annual conditions from 1993-2005.

The Meddies produced anomalies more than 2 inches above average heights, spreading across the Atlantic to the west of the Strait of Gibraltar. While some Meddies appear isolated, others seem to be merging. Areas for which there were no data are colored white.

--LiveScience Staff