Upwelling
Cold, nutrient-rich water rising from the deep to the surface, feeding plankton and some of the world's biggest fisheries.
Also: coastal upwelling
When winds push surface water away from a coast, cold water from below rises to replace it, carrying nutrients that feed plankton. The largest upwelling zones lie off Peru and Chile, south-west Africa, north-west Africa and California, and they support huge catches of anchovies, sardines and mackerel. The Peruvian anchoveta fishery, in most years the largest single-species fishery in the world, depends on it. When El Nino weakens the upwelling, the anchoveta can crash. The south-west monsoon drives upwelling along India's west coast that feeds the oil sardine and mackerel.