Global warming is creating a 'dead zone' in the Sea of Japan. Rising temperatures are bringing to halt a circulation process that is crucial to marine life, say researchers in Japan. In winter, oxygen-rich surface water in the Sea of Japan becomes colder than the water below and sinks, taking oxygen with it. The oxygen encourages the growth of bacteria. The bacteria breaks down organic matter falling to the seabed. At the same time, the sea current brings inorganic matter up from the depths on which the plant plankton feed. The effect of the convection current can be felt more than 2,500 metre below the surface. But the convection current is now so weak that it doesn't reach down beyond a few hundred metre. This can choke off life at the bottom of the food chain and extinguish species higher up. Yoon believes the culprit is global warming with the average temperature around the northern Sea of Japan having increased by between 1.5-3C in the past 50 years (New Scientist, Vol 168, No 2273).
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