Low oxygen areas in oceans threatening survival of fish


Washington : Unchecked global warming is causing dead zones or low-oxygen areas in oceans, threatening the very survival of fish, crabs and clams, according to a Danish study.

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In shallow coastal regions, these zones can be caused by runoff of excess fertilisers from farming. Curbing their flow into such zones could help them recover, but expanding dead zones caused by global warming will stay for thousands of years.

Gary Shaffer, professor, Niels Bohr Institute, University of Copenhagen, who headed the research team at the Danish Centre for Earth System Science (DCESS), explained that “such expansion would lead to increased frequency and severity of fish and shellfish mortality events, for example off the west coasts of the continents like off Oregon and Chile”.

Together with Steffen Olsen, oceanographer at Danish Meteorological Institute and Jens Olaf Pepke Pedersen, physicist at National Space Institute, Technical University of Denmark, Shaffer has performed projections with the newly-developed DCESS Earth System Model.

“If, as in many climate model simulations, the overturning circulation of the ocean would greatly weaken in response to global warming, these oxygen minimum zones would expand much more and invade the deep ocean,” said Shaffer.

Extreme events of ocean oxygen depletion leading to anoxia are thought to be prime candidates for explaining some of the large extinction events in Earth’s history including the largest such event at the end of the Permian 250 million years ago, said a University of Copenhagen release.

Shaffer warned that reduced fossil fuel emissions are needed over the next few generations to limit ongoing ocean oxygen depletion and acidification and their long-term adverse effects.

The findings were published on-line in Nature Geoscience.