Origin of Meddies

 
Eddies form when warm, salty Mediterranean water flows out of the Strait of Gibraltar beneath cooler incoming water and descends along the continental slope. At a depth of around 1000 metres, the salty and warm tongue of Mediterranean water reaches neutral buoyancy with the surrounding ocean water and separates from the continental slope. Pieces of this water pinch off and drift southwestward in the Atlantic Ocean as clockwise-rotating (=anticyclonic) lenses of salty, warm water that are called Meddies.

Blue lines in the figure are contours of constant salinity (in practical salinity units, a measure based on conductivity), and the arrows indicate general water flow.

Subsurface water in the Mediterranean is around 12 degrees Celsius and comparatively salty, at 3.8 percent. Typical Meddies are around 800 metres thick and 100 kilometers in diameter. They contain about 0.08 percent more salt than the surrounding ocean water, which corresponds to around 2 billion tons of salt per Meddy. The number of

Meddies are living quite long because rotate rapidly and translate slowly through the calm waters of the Canary Basin: they are quite stable. The number of Meddies in the Canary Basin is unknown but may be around 25 at a time.

The above text is adapted from:

P.L. Richardson: "Tracking Ocean Eddies", American Scientist 81, 261--271, 1993.

The above figure (JPEG; 22kb) is Fig. 10 in that paper.

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last modified: 29 March 2006