Oxygen Levels in Oceans have dropped 2% in 50 years

[_MeDotOrg]

We may not have any coral reefs in 50 years.

Climate change is extending far beyond the threat of melting polar ice caps -- it's putting a dangerous stranglehold on life in oceans, too.

A new study published in the science journal Nature Wednesday found that the ocean's worldwide oxygen content declined by more than 2% between 1960 and 2010.

Scientists have long warned about the potentially deadly consequences of the ocean's declining oxygen levels on marine life, and its resulting impact on humans.

The study came from the GEOMAR Helmholtz Centre for Ocean Research in Kiel, Germany, where the three co-authors -- Sunke Schmidtko, Lothar Stramma and Martin Visbeck -- pulled data dating back to 1960.
Using information on oxygen, temperature and other factors relating to the world's oceans, they mapped it around the globe and estimated the overall oxygen loss.

"We were able to document the oxygen distribution and its changes for the entire ocean for the first time. These numbers are an essential prerequisite for improving forecasts for the ocean of the future," wrote Schmidtko.

While 2% may sound like only a small change, it doesn't take much of a drop to threaten the state of oceans. The only organism in the ocean that thrives with little-to-no oxygen is bacteria.

"Just a little loss of oxygen in coastal waters can lead to a complete change in ecosystems -- a small decrease in oxygen like this can transform from something desirable to very undesirable," said David Baker, Assistant Professor at the University of Hong Kong's Swire Institute of Marine Sciences.

Oxygen in the world's oceans is not evenly distributed, and the 2% drop represents just an average of all the globe's oceans together.

In some parts of the world, there has been a much steeper decline of oxygen levels over the past five decades -- for example, in the North Pacific, where the largest volume of oxygen was lost. The largest percentage was lost in the Arctic Ocean.

"The oxygen losses in the ocean can have far-reaching consequences because of the uneven distribution. For fisheries and coastal economies this process may have detrimental consequences," wrote Stramma.