Eddies

When two currents collide, they create eddies, like these cloud formations photographed from a satellite above the Canary Islands in the North Atlantic.

Canary_A2002186_1155_250m

Eddies are also seen where the Oyashio Current collides with the Kuroshio Current near Hokkaido.

220px-Japan's_ocean_currents   220px-Spring_Bloom_Colors_the_Pacific_Near_Hokkaido

They show up because of phytoplankton growing in the surface waters. These become concentrated along the boundaries of the eddies, tracing out the motions of the water.

Eddy_currents_due_to_magnet.svg

Eddies can also be induced (red I) on a conductive metal plate (C) as it moves under a magnet (N). The magnetic field (green B) is directed down through the plate.