A new study found that oxygen levels in the ocean have fallen by 2 percent over 50 years, threatening fish stocks and other marine life. The study was conducted by the Geomar Helmholtz Centre for Ocean Research in Germany, and was the most comprehensive examination of this subject yet.

Few marine organisms are able to adapt to low oxygen levels, if the drop in oxygen levels continues at this pace, it could mean losses of 7 percent by 2100. The falling oxygen levels are thought to be related to climate change, and rising temperatures specifically.

The research examined data from between 1960 and 2010, and is the first study to show shifts in distribution of oxygen in the entirety of the world’s oceans. According to lead author of the study Dr Sunke Schmidtko:

“Since large fish in particular avoid or do not survive in areas with low oxygen content, these changes can have far-reaching biological consequences.”

Some areas have been affected by this drop more than others – the greatest volume of total oxygen loss was in the Pacific, whereas the arctic has lost the highest percentage of its oxygen.

“While the slight decrease of oxygen in the atmosphere is currently considered non-critical, the oxygen losses in the ocean can have far-reaching consequences because of the uneven distribution,” said Lothar Stramma, one of the other authors of the report.

Oceans absorb over 30 percent of carbon emissions from land, and consequently have seen some of the most damaging effects of climate change, including rising sea levels and damage to coral reefs. When PH levels fall as carbon is absorbed, more acidic oceans make it difficult for organisms to construct shells and other calcium-based structures. Higher temperatures cause reproductive problems for many fish, who have begun migrating to cooler areas.

Marine conservation biologist Callum Roberts, from the University of York, explained:

“What we’re seeing is fallout from global warming. It’s straightforward physics and chemistry playing out in front of our eyes, entirely in keeping with what we’d expect and yet another nail in coffin of climate change denial.”

“As the world warms up, the thickness and temperature of the surface layers are increasing. This acts like a stronger lid on the world’s oceans, so there’s less oxygen transported down below. Unless we address greenhouse gas emissions urgently we’ll see more and more of this,” according to Roberts.

“Life will become harder for creatures that live in the sea and for those that depend on them – ie us.”

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