Ocean water with zero oxygen quadrupled in volume in past 50 years

'The decline in ocean oxygen ranks among the most serious effects of human activities on the Earth's environment'

Josh Gabbatiss
Science Correspondent
Thursday 04 January 2018 20:03
Comments
There has been a ten-fold increase in low oxygen zones around coastal regions in the past 50 years
There has been a ten-fold increase in low oxygen zones around coastal regions in the past 50 years

The volume of water in the world’s oceans that is totally devoid of oxygen has more than quadrupled over the past 50 years, according to a new study.

Over the past half century, the open ocean has lost around 2 per cent of its dissolved oxygen, vital for sustaining fish and other marine life.

There has also been a ten-fold increase in low oxygen sites, known as “dead zones”, in coastal regions during this period.

Oxygen saturation is a major limiting factor that affects ocean productivity, as well as the diversity of creatures living in it and its natural geochemical cycling.

The new study, published in the journal Science, represents the most comprehensive view yet of ocean oxygen depletion.

Pollution and climate change both play significant roles in depleting the ocean’s oxygen levels and the authors emphasise the role humans must play in addressing these issues.

“Oxygen is fundamental to life in the oceans,” said lead author Dr Denise Breitburg, a marine ecologist with the Smithsonian Environmental Research Centre. “The decline in ocean oxygen ranks among the most serious effects of human activities on the Earth’s environment.”

The work was published by scientists from GO2NE – Global Ocean Oxygen Network – a United Nations working group set up to investigate the impact of oxygen loss from the oceans.

“Combined effects of nutrient loading and climate change are greatly increasing the number and size of ‘dead zones’ in the open ocean and coastal waters, where oxygen is too low to support most marine life,” said Dr Vladimir Ryabinin, executive secretary of the International Oceanographic Commission, which formed GO2NE.

Nutrient loading refers to pollution from sewage and fertiliser run-off that contains nutrients that stimulate the growth of algae in the water. Blooms of algae form and when they die the bacteria that degrades them consumes the oxygen present in the water.

Warming surface waters resulting from climate change also make it more difficult for oxygen to penetrate into the ocean’s depths.

As the entire ocean gets warmer, this effect means less oxygen can be held inside it.

In dead zones oxygen levels tend to be so low that any animals living there suffocate and die. As a result, marine creatures avoid these areas, resulting in their habitats shrinking.

Even in areas where oxygen depletion is less severe, smaller decreases in oxygen levels can impact animals in various non-lethal ways such as stunting their growth and hindering reproduction.

The researchers warned that the effects of oxygen depletion in the oceans are extensive and ecological impacts go hand in hand with direct effects on the humans that rely on the sea for their livelihoods.

“It’s a tremendous loss to all the support services that rely on recreation and tourism, hotels and restaurants and taxi drivers and everything else,” said Dr Lisa Levin, a biological oceanographer at Scripps Institution of Oceanography, one of the study’s co-authors.

“The reverberations of unhealthy ecosystems in the ocean can be extensive.”

Lyndsey Dodds, head of UK marine policy at WWF, added: “This just shows even more pressures on our oceans. We hear a lot about plastics now, and unsustainable fishing, but this is certainly an issue that seems to have less attention, despite the potentially catastrophic impact.”

However, the authors of the new study state that despite the dramatic figures, the problem of oxygen depletion can be dealt with.

They highlight efforts to provide better sewage treatment in Chesapeake Bay in the eastern US, which have resulted in substantial increases in water oxygen levels.

“This is a problem we can solve,” said Dr Breitburg. “Halting climate change requires a global effort, but even local actions can help with nutrient-driven oxygen decline.”

Register for free to continue reading

Registration is a free and easy way to support our truly independent journalism

By registering, you will also enjoy limited access to Premium articles, exclusive newsletters, commenting, and virtual events with our leading journalists

Please enter a valid email
Please enter a valid email
Must be at least 6 characters, include an upper and lower case character and a number
Must be at least 6 characters, include an upper and lower case character and a number
Must be at least 6 characters, include an upper and lower case character and a number
Please enter your first name
Special characters aren’t allowed
Please enter a name between 1 and 40 characters
Please enter your last name
Special characters aren’t allowed
Please enter a name between 1 and 40 characters
You must be over 18 years old to register
You must be over 18 years old to register
Opt-out-policy
You can opt-out at any time by signing in to your account to manage your preferences. Each email has a link to unsubscribe.

By clicking ‘Create my account’ you confirm that your data has been entered correctly and you have read and agree to our Terms of use, Cookie policy and Privacy notice.

This site is protected by reCAPTCHA and the Google Privacy policy and Terms of service apply.

Already have an account? sign in

By clicking ‘Register’ you confirm that your data has been entered correctly and you have read and agree to our Terms of use, Cookie policy and Privacy notice.

This site is protected by reCAPTCHA and the Google Privacy policy and Terms of service apply.

Register for free to continue reading

Registration is a free and easy way to support our truly independent journalism

By registering, you will also enjoy limited access to Premium articles, exclusive newsletters, commenting, and virtual events with our leading journalists

Already have an account? sign in

By clicking ‘Register’ you confirm that your data has been entered correctly and you have read and agree to our Terms of use, Cookie policy and Privacy notice.

This site is protected by reCAPTCHA and the Google Privacy policy and Terms of service apply.

Join our new commenting forum

Join thought-provoking conversations, follow other Independent readers and see their replies

Comments

Thank you for registering

Please refresh the page or navigate to another page on the site to be automatically logged inPlease refresh your browser to be logged in