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A large research synthesis, published in one of the world's most influential scientific journals, has detected a decline in the amount of dissolved oxygen in oceans around the world — a long-predicted result of climate change that could have severe consequences for marine organisms if it continues.

The paper, published Wednesday in the journal Nature by oceanographer Sunke Schmidtko and two colleagues from the GEOMAR Helmholtz Centre for Ocean Research in Kiel, Germany, found a decline of more than 2 percent in ocean oxygen content worldwide between 1960 and 2010.

The loss of ocean oxygen "has been assumed from models, and there have been lots of regional analysis that have shown local decline, but it has never been shown on the global scale, and never for the deep ocean," said Schmidtko, who conducted the research with Lothar Stramma and Martin Visbeck, also of GEOMAR.

Because oxygen in the global ocean is not evenly distributed, the 2 percent overall decline means there is a much larger decline in some areas of the ocean than others.

Moreover, the ocean already contains so-called oxygen minimum zones, generally found in the middle depths. The great fear is that their expansion upward, into habitats where fish and other organism thrive, will reduce the available habitat for marine organisms.

In shallower waters, meanwhile, the development of ocean "hypoxic" areas, or so-called "dead zones," may also be influenced in part by declining oxygen content overall.

On top of all of that, declining ocean oxygen can also worsen global warming in a feedback loop. In or near low oxygen areas of the oceans, microorganisms tend to produce nitrous oxide, a greenhouse gas. Thus the new study "implies that production rates and efflux to the atmosphere of nitrous oxide ... will probably have increased."

https://www.washingtonpost.com/news/energy-environment/wp/2017/02/15/its-official-the-oceans-are-losing-oxygen-posing-growing-threats-to-marine-life/

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