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The seas have less oxygen now than they used to. Why, and what does this mean?

In many parts of the world, including along the western coast of the United States, fish have been dying en masse — a clear illustration of the ways in which deoxygenation is choking the oceans.

By: Explained Desk | New Delhi | Updated: December 9, 2019 6:54:49 am
ocean pollution, IUCN report on ocean pollution, decreasing oxygen in oceans, un Climate Change Conference madrid, climate change, indian express explained The deoxygenation of the oceans occurred due to climate change and other human activities (such as the nutrient runoff from farm fertilizers into waterways), the report said.

The world’s oceans have less oxygen today than they did up to, say, 1950 or 1960, according to a new study.

Who has carried out this study, and what does it say?

The report is the work of 67 scientists from 17 countries around the world. The International Union for Conservation of Nature (IUCN), the global authority on the status of the natural world and the measures needed to safeguard it, released the study on Saturday (December 7) at the United Nations Climate Change Conference currently underway in Madrid.

According to the findings of the study, the levels of oxygen in oceans fell by around 2 per cent from 1960 to 2010. The deoxygenation of the oceans occurred due to climate change and other human activities (such as the nutrient runoff from farm fertilizers into waterways), the report said.

So, how dangerous is that?

According to Dan Laffoley, the principal adviser in IUCN’s global marine and polar programme and an editor of the report, who was quoted by ‘The New York Times’, the decline in oxygen levels might not seem significant because, “we’re sort of sitting surrounded by plenty of oxygen and we don’t think small losses of oxygen affect us”.

However, Laffoley cautioned, “If we were to try and go up Mount Everest without oxygen, there would come a point where a 2 per cent loss of oxygen in our surroundings would become very significant.”

The comparison with Mount Everest is relevant because the oxygen content of the world’s oceans is not uniform. ‘The NYT’ report noted that a study published in the journal ‘Science’ had established that the water in some parts of the tropics had experienced a 40 per cent to 50 per cent reduction in oxygen.

And what can deoxygenation do to oceans?

In many parts of the world, including along the western coast of the United States, fish have been dying en masse — a clear illustration of the ways in which deoxygenation is choking the oceans.

Also, the loss of oxygen in the oceans can affect the planetary cycling of elements such as nitrogen and phosphorous which are essential for life on Earth, Dr Laffoley said in ‘The NYT’ report.

As oceans lose oxygen, they become more acidic, a phenomenon that has resulted in some places in shellfish having their shells degraded or dissolved — the so called “osteoporosis of the sea”.

Apart from their declining oxygen content, oceans have, since the middle of the 20th century, absorbed 93 per cent of the heat associated with human-caused greenhouse gas emissions, leading to mass bleaching of coral reefs.

Also, since warmer water occupies more space than cooler water, NASA estimates that this is the reason for roughly a third of the rise in sea levels.

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