Global Warming to Create "Permanent" Ocean Dead Zones?

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Warmer water can hold less oxygen compared with cooler waters. "As the ocean is heated by a warmer atmosphere, oxygen concentrations decrease, Shaffer said.

Furthermore, as Earth's icy poles gradually transform into open oceans, new organisms, from plankton to shellfish, will move in.

This biological boom further decreases the available oxygen in the ocean interior because when organisms die, their bodies drift to the sea floor and are broken down by bacteria which require oxygen to survive.

If biological production in the ocean increases, so too does the population of oxygen-consuming bacteria, said Shaffer, whose research is detailed in the current issue of the journal Nature Geoscience.

Doomsday Scenario

Francis Chen is a marine ecologist at Oregon State University who was not involved in the study.

By modeling how the ocean system will respond to and in turn, influence climate change, Shaffer and his colleagues have provided a means of systematically looking at how multiple factors will play out, Chen said.

"Such studies are an important tool for examining what the future may hold for the world's oceans," he said.

Paul Wignall, a professor of paleoenvironments at the University of Leeds in the United Kingdom, called the new predictions "the doomsday scenario for the oceans."

Wignall, who was not involved in the current research, has studied the Permian extinction 250 million years ago.

Also known as the "Great Dying," the event is considered the worst mass extinction in Earth's history, affecting 95 percent of all marine species. Growing evidence suggests global warming and oxygen-poor oceans—possibly stemming from volcanic eruptions—were major factors.

(Related: "Did Million-Year-Long Eruptions Cause Mass Extinction?" [May 2, 2006].)

"The proposed mechanism for these ancient crises is exactly the same as modeled in this paper," Wignall said.

In the case of the Permian period, up to 80 percent of the Earth's oceans were not just oxygen poor, but actually anoxic, or completely lacking in oxygen. Scientists think the oceans remained in this lifeless state for about 20 million years.

"We do not predict ocean anoxia," Shaffer said, "but a worst-case scenario could possibly lead to ocean anoxia."

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