World's oceans lost 2% of oxygen over last 50 years, warn scientists

New Delhi: Scientists have warned that oxygen content in the world's oceans has decreased by more than two per cent since 1960, putting marine life at high risk of devastating consequences.

They said oxygen, which is an essential necessity of life on land and in the ocean, is threatened by global warming.

The authors said they needed to conduct more research to determine how much of the oxygen loss was due to global warming and how much was related to natural climate cycles.

In those five and a half decades, parts of the oceans devoid of oxygen, called anoxic waters, have quadrupled, said a new study, while adding that the production and flow of nitrous oxide, a powerful greenhouse gas, "will probably have increased.

Oceans cover nearly three-quarters of the Earth's surface, provide about half of the oxygen we breathe and feed billions of people every year.

“A two per cent decrease of ocean oxygen content may not sound like much", research scientist Denis Gilbert of Fisheries and Oceans Canada wrote in a comment on the study.

But, he warned, "the implications of this for marine ecosystems could be severe in parts of the ocean where oxygen is already low".

The report found that the largest decrease happened near areas where oxygen was already low, in so-called "dead zones", where oxygen levels declined by 4 per cent every decade.

Most oxygen was lost in the Equatorial and North Pacific Ocean, the Southern Ocean, and the South Atlantic Ocean.

"Oxygen data in the Arctic, Equatorial and North Pacific ... and Southern Ocean show a continuous decrease, and together are responsible for 60 per cent of the global oceanic oxygen loss," the study reported.

The study also reiterated an older warning that the loss of oxygen would accelerate - with predictions of a 1-7 per cent decline by 2100.

The findings "should ring yet more alarm bells about the consequences of global warming," Gilbert said.

The study has been published in the science journal Nature.

(With AFP inputs)