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WonderOcean productivity fact

Along some coasts, winds push surface water out to sea and cold, nutrient-rich water rises from the depths to take its place. This upwelling feeds plankton and, through them, some of the richest fishing grounds on Earth.

Upwelling

OceanClimateBiologyScience

The story behind the card

Five coastal upwelling zones stand out: the Humboldt Current off Peru and Chile, the California Current, the Canary Current off north-west Africa, the Benguela Current off south-western Africa and the Somali Current off Somalia and Oman. Together they cover only about 5 per cent of the ocean, yet they yield roughly a quarter of the world's marine fish catch, much of it small fish such as anchovies and sardines. Off Peru, the anchoveta supports one of the largest single-species fisheries in the world. That richness is fragile. During an El Niño, warm water spreads along the South American coast and weakens the upwelling, so fewer nutrients reach the surface and anchovy numbers crash, along with the seabirds and sea lions that feed on them. The El Niño of 1972 to 1973, on top of heavy fishing, helped bring Peru's anchovy fishery to collapse.

Türkçe oku
Bazı kıyılarda rüzgâr yüzeydeki suyu açığa doğru iter ve boşalan yeri derinlerden gelen soğuk, besin dolu su doldurur. Dipten yükselen bu su planktonu besler; dünyanın en bereketli balık avlaklarından bazıları bu sayede var olur.

Rüzgârın kıyıdan açığa sürdüğü suyun yerine dipten soğuk suyun geldiği beş büyük bölge öne çıkar: Peru ve Şili açıklarındaki Humboldt Akıntısı, Kaliforniya Akıntısı, Kuzeybatı Afrika açıklarındaki Kanarya Akıntısı, Afrika'nın güneybatısındaki Benguela Akıntısı ve Somali ile Umman açıklarındaki Somali Akıntısı. Bu bölgeler okyanusun yalnızca yüzde 5'i kadarını kaplar, ama dünyadaki deniz balığı avının aşağı yukarı dörtte biri buradan çıkar; bunun büyük kısmı hamsi ve sardalya gibi küçük balıklardır. Peru açıklarındaki hamsi avı, tek bir türe dayanan dünyanın en büyük balıkçılıklarından biridir. Ama bu bolluk kırılgandır. El Niño yıllarında Güney Amerika kıyısı boyunca ılık su yayılır ve dipten gelen soğuk su zayıflar. Yüzeye daha az besin ulaşır, hamsi sayısı çöker; hamsiyle beslenen deniz kuşları ve deniz aslanları da aç kalır. 1972-1973 El Niño'su, aşırı avlanmayla birleşince Peru'nun hamsi avcılığını çökertti.

Sources and further reading

Background reading: Upwelling
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