As Climate Warms, Underwater Deserts Grow in Tropical Oceans (5/11/2008)

Researchers collect oxygen samples off the Cape Verde Islands. - Photograph Courtesy:K laus Scheurich

Oxygen-poor waters are expanding in tropical regions of the Atlantic and Pacific oceans, according to new research published in the latest issue of Science. Oxygen-starved oceans, which have been predicted by climate change models, could have far-reaching impacts on ecosystems because macroorganisms cannot survive in such hypoxic waters.

Using data spanning from 1960 to 2007, lead author Lothar Stramma and his coauthors examined the concentration of oxygen at intermediate depths ranging 300 to 900 meters below the ocean's surface.

The research team discovered particularly low oxygen regions in the eastern tropical Atlantic and the equatorial Pacific. The time series suggests that as the global ocean has warmed over the past 50 years, oxygen levels in some areas of the ocean have declined and produced large underwater deserts.

Climate change models have predicted decreased oxygen in oceans because oxygen cannot dissolve in warmer water as well as it does in cooler water.

Not all the ocean regions analyzed in the 2 May Science report showed the same expansion and intensification of oxygen-poor waters. Oxygen levels in the northern Indian Ocean and in deep, oxygen-rich waters of the Labrador Sea had no apparent oxygen changes from 1960 to 2007.

The constancy of some waters compared to the decrease in oxygen observed in the Atlantic and Pacific oceans demonstrates the validity of the changes as opposed to results arising from differences in measurement techniques or observational biases.

The geological records show that oxygen levels have varied widely in oceans' past. In the Cretaceous period (144 to 65 million years ago), for example, the records indicate "altered biogeochemical cycles and dramatic consequences for ecosystems associated with reductions of ocean oxygen," wrote Stramma, an oceanographer at Universität Kiel in Kiel, Germany. Similarly, the trends observed in the Science report "affect carbon and nitrogen cycles, with fundamental implications for marine ecosystems and thereby fisheries resource management issues."

Note: This story has been adapted from a news release issued by the American Association for the Advancement of Science

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