New Delhi: As Earth is warming up, the ocean is losing its breath and can cause serious damage to marine life, affect livelihoods of millions of people and trigger the release of dangerous greenhouse gases like nitrous oxide, said a latest study published on Thursday in noted international journal Science.

The study said that in the past 50 years, the amount of water in the open ocean with zero oxygen has gone up more than fourfold and in coastal water bodies, including estuaries and seas, low-oxygen sites have increased more than 10-fold since 1950.

Scientists expect oxygen to continue dropping even outside these zones as Earth warms up. The study said in order to halt the decline, the world needs to rein in both climate change and nutrient pollution.

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

“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. The reverberations of unhealthy ecosystems in the ocean can be extensive," said Lisa Levin, a biological oceanographer at Scripps Institution of Oceanography at the University of California San Diego, US.

The study was done by a team of scientists from GO2NE (Global Ocean Oxygen Network), a new working group created in 2016 by the United Nation’s Intergovernmental Oceanographic Commission.

It is a first such study that takes a sweeping look at the causes, consequences and solutions to low oxygen worldwide, in both open ocean and coastal waters. It highlighted the biggest dangers to the ocean and society, and what it will take to keep Earth’s waters healthy and productive.

Explaining the importance of oxygen in oceans, Vladimir Ryabinin, executive secretary of the International Oceanographic Commission, which formed the GO2NE group, said, “Approximately half of the oxygen on Earth comes from the ocean."

“However, 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," Ryabinin added.

The authors point out that in areas traditionally called “dead zones", like those in Chesapeake Bay (in the US) and the Gulf of Mexico, oxygen plummets to levels so low many animals suffocate and die. As fish avoid these zones, their habitats shrink and they become more vulnerable to predators or fishing. But the problem goes far beyond dead zones, the authors explained in an official statement.

The danger due to low oxygen in oceans is manifold. For instance, as per the study, even small oxygen declines can stunt growth in animals, hinder reproduction and lead to disease or even death.

“It also can trigger the release of dangerous chemicals such as nitrous oxide, a greenhouse gas up to 300 times more powerful than carbon dioxide, and toxic hydrogen sulfide. While some animals can thrive in dead zones, overall biodiversity falls," the study warns.

To keep low oxygen in check, the scientists said the world needs to take on the issue from three angles—address the causes, nutrient pollution and climate change. “This is a problem we can solve. Halting climate change requires a global effort, but even local actions can help with nutrient-driven oxygen decline," said Breitburg.

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