We’re dissolving the ocean floor

The ocean floor is dissolving, and it will get worse because of humans.

Normally, the bottom of the ocean is a chalky white, thanks to dead creatures piling up over millions of years. Most of these are the shells and skeletons of corals and planktons, which are made up of the mineral calcite. These dissolve over time and in so doing help to neutralise the acidity of the oceans. Over thousands of years, the levels of acid fluctuate, but this process keeps that acid in check.

Now, the bottom of the ocean, often a few kilometres deep and still largely unexplored, is turning a murky brown. This is because so much carbon dioxide (CO2) is going into the ocean that it’s dissolving the shells and skeletons on the ocean floor.

The natural cycle is no longer working.

Unable to test every single ocean, researchers from McGill University in Canada tested their thesis in their laboratory. It is the first research to look into acidity on the ocean floor.

Current CaCO3 Dissolution at the Seafloor Caused by Anthropogenic CO2 was published in the peer-reviewed journal Proceedings of the National Academy of Sciences of the United States of America.

CaCO3 is calcium carbonate.

Worryingly, the researchers point out that the acidity that’s reacting with the ocean floor now is from a long time ago. “Because it takes decades or even centuries for carbon dioxide to drop down to the bottom of the ocean, almost all the carbon dioxide created through human activity is still at the surface.”

At the moment, more carbon is being pumped into the atmosphere than at any time since the dinosaurs went extinct. This means the current dissolution of the ocean floor will accelerate, according to the researchers.

The only way to arrest this is to decrease the carbon going into the atmosphere and oceans. World governments agreed to work towards this goal in Paris in 2015, but analysis done by the United Nation shows that, at best, they’re doing only half of what is required to keep these emissions below dangerous levels.

In other research about oceans, scientists from the universities of Toronto and California have looked at what happened to the oceans 50-million years ago, when there was a sudden increase of carbon dioxide in the atmosphere. The world became hotter during an event known as the Paleocene-Eocene thermal maximum.

A hotter world meant (and means) less oxygen in the ocean. That creates circumstances for sulfate-eating bacteria to thrive. These create hydrogen sulfide, which is toxic, even in small concentrations. This is ingested by smaller creatures and fish, which are eaten by bigger fish. This means the top-level predators, such as tuna and whales, take in the highest concentration of toxins.

The researchers at the universities said: “Increased atmospheric carbon dioxide concentrations go hand in hand with oxygen loss in the ocean, and this is the first demonstration that the carbon dioxide released from human activity could be large enough to turn parts of the ocean into a toxic brew.”

This research, Large-scale Ocean Deoxygenation during the Paleocene-Eocene Thermal Maximum, was published in the peer-reviewed journal Science earlier this month.

  • The Mail & Guardian reported last month that an industrial lubricant (polychlorinated biphenyl), which has been banned for 30 years, is killing tuna, whales and other large ocean predators in a similar fashion. It is eaten by smaller fish in small quantities, which then get eaten by bigger fish. This means the predators at the top take in life-threatening amounts of the lubricant.

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Sipho Kings
Sipho is the Mail & Guardian's News Editor. He also does investigative environment journalism.
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