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Conservation Science for a Healthy Planet

Low oxygen levels, coral bleaching getting worse in oceans

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Global warming is making the world’s oceans sicker, depleting them of oxygen and harming delicate coral reefs more often, two studies show.

The lower oxygen levels are making marine life far more vulnerable, the researchers said. Oxygen is crucial for nearly all life in the oceans, except for a few microbes.

“If you can’t breathe, nothing else matters. That pretty much describes it,” said study lead author Denise Breitburg, a marine ecologist at the Smithsonian Environmental Research Center. “As seas are losing oxygen, those areas are no longer habitable by many organisms.”

She was on a team of scientists, convened by the United Nations, who reported that the drop in oxygen levels is getting worse, choking large areas, and is more of a complex problem than previously thought. A second study finds that severe bleaching caused by warmer waters is hitting once-colorful coral reefs four times more often than it used to a few decades ago. Both studies are in Thursday’s edition of the journal Science.

When put all together, there are more than 12 million square miles (32 million square kilometers) of ocean with low oxygen levels at a depth of several hundred feet (200 meters), according to the scientists with the Global Ocean Oxygen Network. That amounts to an area bigger than the continents of Africa or North America, an increase of about 16 percent since 1950….

Denise Breitburg et al. Declining oxygen in the global ocean and coastal waters. Science, 2018 DOI: 10.1126/science.aam7240Map of the world, with low oxygen zones in ocean (blue) and coasts (red)

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