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Famine threat to tropical seas as warming quickens

James Randerson

Study shows phytoplankton respond by scaling down productivity.

GLOBAL WARMING is creating an ocean famine in swaths of tropical and sub-tropical seas, according to research using nearly a decade of satellite data.

The finding, which has long been predicted by computer models, suggests that as warming continues, fish stocks in tropical and sub-tropical regions will drop significantly. The study showed that in some ocean regions microscopic plants in the plankton, known as phytoplankton, respond to rising temperatures by scaling down their productivity by 30 per cent or more. With less production at the bottom of the food chain, fish and other large ocean creatures have less to eat.

Commenting on the study in the journal Nature, Scott Doney of Woods Hole Oceanographic Institution in Massachusetts said that if the trends observed in the satellite observations continued "the future suggests that marine biological productivity in the tropics and mid-latitudes will decline substantially."

The changes occur because warmer surface temperatures lead to changes in the flow of ocean currents that deliver nutrient-rich water from the cooler depths to the surface.

About half of the production generated by the world's living organisms is done by phytoplankton, microscopic green plants which operate in the top 100 to 200 metres of the ocean where light levels are high enough for photosynthesis.

Each day they pull in more than 100 million tonnes of CO2. "Almost the whole food chain of the open ocean depends on these plants,"' said Duncan Purdie, a plankton expert at the British National Oceanography centre in Southampton, U.K. —

© Guardian Newspapers Limited 2006

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