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Decreasing ocean oxygen levels could be catastrophic, scientists say

A new study by researchers at the National Center for Atmospheric Research finds that ocean oxygen levels are decreasing due to climate change, and that the effects will only get worse as the ocean warms. 

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Peter Gash, owner and manager of the Lady Elliot Island Eco Resort in the Great Barrier Reef area, snorkels during an inspection of the reef's condition in an area called the 'Coral Gardens' located at Lady Elliot Island, Australia, in 2015.

Whales and swimming humans must surface in order to breathe, but most marine life depends on dissolved oxygen – and now, climate change is decreasing oxygen levels in Earth's oceans.

According to a new study in Global Biogeochemical Cycles, fish, clams, shrimp, octopuses, and more may soon be gasping for air.

"Loss of oxygen in the ocean is one of the serious side effects of a warming atmosphere, and a major threat to marine life," lead author Dr. Matthew Long, a researcher at the National Center for Atmospheric Research says in a press release from the Center (NCAR). 

How does a warming climate affect the ocean's oxygen levels?

The entire ocean gets oxygen from the water surface, where oxygen is absorbed from the atmosphere, or from phytoplankton that release oxygen into the water through photosynthesis.

When the planet warms, as it is happening now, less oxygen enters the top layers of the ocean. Even less oxygen filters down to the deeper, colder, reaches of the sea: warm water is more buoyant than cold water, so the warm surface waters are unlikely to reach the ocean's depths.

This means that a warming earth has grave consequences for sea life that relies on oxygen, including such familiar creatures as crabs, squids, and many kinds of fish. 

"Many forms of marine life depend on oxygen, they require oxygen to survive," Dr. Long tells The Christian Science Monitor in a phone interview. "As oxygen levels decline, the increasing stresses on ocean systems, as well as implications for our ability to extract the services of these marine resources."

Why are scientists just discussing this problem now?

Researchers have known for years that decreasing oxygen levels in the ocean would impact marine life. But the unique contribution of this study, according to Long, is its use of an atmospheric supercomputer to provide earth system simulations that can tell scientists about the future of the oceans.

For a long time, he says, scientists had a difficult time separating natural variations in oxygen concentration at the ocean's surface from the effects of climate change.

"What we've done is apply a novel technique to separate the components of variability," he explains.

Using NCAR's supercomputer, this study found the point at which natural variations in ocean oxygen levels are overwhelmed by climate change stimulated changes – and it's less than 15 years away. Deoxygenation is already happening, but its spread will likely increase over the next twenty years. 

"The bottom line," he adds, "is that without addressing climate warming, there is not much we can do to address deoxygenation."

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