Huge volcanic eruptions caused a deep-sea mass extinction 55m years ago, study finds

Huge volcanic eruptions may have caused a deep-sea mass extinction more than 55 million years ago by warming up sea temperatures, scientists have said.

But they warn that this natural event does not come close to matching the damage human activity is causing today.

In a study published in the journal Proceedings of the National Academy of Sciences, researchers suggest eruptions centred around what is now Iceland sent huge amounts of carbon dioxide into the atmosphere.

It was then absorbed by the oceans over thousands of years and drove temperatures up by between 5C and 8C.

The event, known as the Paleocene-Eocene Thermal Maximum (PETM), occurred around 55.6 million years ago.

And researchers say it triggered chemical reactions that caused waters to become highly acidic, killing and impairing many marine species.

But they warn current human-led emissions are releasing carbon into the oceans up to eight times faster than the volcanoes did.

Study co-author Dr Barbel Honisch, a geochemist at Lamont-Doherty Earth Observatory at Columbia University in the US, said: "If you add carbon slowly, living things can adapt. If you do it very fast, that's a really big problem."

She added: "The past saw some really dire consequences, and that does not bode well for the future.”

While scientists have known about the PETM carbon surge for decades, the reason behind it has been unclear.

To find out more, the researchers mimicked highly acidic ocean conditions in the lab, where they cultured tiny shelled marine organisms called foraminifera.

They compared the geochemical information gathered from the lab-grown organisms with the data from fossilised foraminifera from the PETM time period.

This method allowed the researchers to calculate the amount of carbon added to the ocean during the PETM, which, they say, was as much as 14.9 quadrillion metric tons over about 5,000 years.

They say carbon would have come from carbon dioxide emitted directly by the volcanic eruptions, the combustion of surrounding sedimentary rocks, and some methane welling up from the depths.

However, the researchers warn humans are now introducing carbon into the oceans three to eight times faster than these ancient volcanoes, or possibly even more.

Atmospheric levels have shot up from about 280 parts per million in the 1700s to about 415 today and are on a path to keep rising rapidly, they said.

And as oceans continue to absorb carbon dioxide, rapid acidification is starting to stress marine life.