Creeping dead zones

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Greenpeace action to block the outflow pipes of paper-pulp manufacturers Peterson & Son, Moss, Norway. The discharge has a heavy oxygen-depleting effect on the seawater into which it flows, killing fish and vegetation.

Creeping dead zones are areas where the water at the sea-floor isanoxic - meaning that it has very low (or completely zero)concentrations of dissolved oxygen. This situation is the result ofcoastal waters algae blooms due to nutrient pollution from sewagedischarges and agriculture. As the algae die and rot, they consumeoxygen, and the oxygen dissolved in the water falls to levels unable tosustain marine life. CDZ are especially dangerous to fisheries becausethey afflict coastal waters where many fish spawn and spend most oftheir lives before moving to deeper waters.

These dead zones are occurring in many areas along the coasts of majorcontinents, and they are spreading over larger areas of the sea floor.Well known CDZs have long afflicted the Baltic Sea and are an annualfeature in the Gulf of Mexico where the Mississippi River brings downhuge quantities of fertilisers from the agricultural heartlands of theUnited States. Many of the areas where increasing deoxygenisation hasrecently been observed are near the mouths of major river systems, andthey're now spreading to other bodies of water, such as the Black Sea,Adriatic Sea, Gulf of Thailand and Yellow Sea. They're also appearingoff South America, Japan, Australia and New Zealand.

The phenomenon is getting noticeablyworse. According to the UN Environmental Programme (UNEP), the numberof known oxygen-starved areas has doubled since 1990 to nearly 150,with some stretching 70,000 square kilometres, about the size ofIreland.