Acidic oceans triggered mass extinction over 250 million years ago

Edinburgh study finds evidence that ocean acidification was to blame for the Permian-Triassic Boundary extinction 252 million years ago (Photo: Shutterstock)

In order to better understand how climate change will unfold over the coming decades, some scientists are looking to the remote past and specific climatic catastrophes to help shed light the so-called Anthropocene and its consequences for life on Earth. Recently, researchers at the University of Utah looked into the so-called Paleocene-Eocene thermal maximum for clues. Now, a study by the University of Edinburgh highlights evidence that the rapid acidification of oceans 252 million years ago caused the greatest extinction of all time.

Known as the Permian-Triassic Boundary extinction, more than 90 percent of marine life and two thirds of land animals were wiped out as the Earth’s oceans absorbed huge amounts of carbon dioxide from volcanic eruptions known as Siberian Traps.

The Edinburgh study provides some evidence of the missing connection between acidification and mass extinction through analysis of high-resolution seawater pH records across the period when massive amounts of carbon were being pumped into the atmosphere. The researchers used boron isotope data combined with a quantitative modeling approach.

The team analyzed rocks collected in the United Arab Emirates region in the Middle East, which would have been on the ocean floor at the time. The rocks preserve a detailed record of changing oceanic conditions of the period and enabled researchers to develop a climate model to work out what drove the extinction.

Then and now

This is the first time that the high acidity levels of the oceans have been shown to be directly linked to this mass extinction and could help scientists better understand how ocean acidification taking place now due to emissions caused by human activity could threaten marine life.

One of the parallels between then and now is the speed at which carbon was released. Although the scientists say that the volcanic explosions of 252 million years ago probably added more carbon to the atmosphere than current fossil fuel reserves, the rate at which the carbon was released, which played a key role in driving ocean acidification, is similar to today.

The mass extinction of both marine and land-based animals shows that extreme change took place in all of the Earth’s ecosystems. The extinction took place over a 60,000 year period, while the acidification of the oceans spanned around 10,000 years.

The first phase of extinction coincided with a slow flow of carbon into the atmosphere. During this phase, ocean pH remained stable. But during the second extinction pulse, carbon emissions intensified and led to an abrupt acidification event that caused the loss of mainly heavily calcified marine biota such as corals.

"Scientists have long suspected that an ocean acidification event occurred during the greatest mass extinction of all time, but direct evidence has been lacking until now,” said Dr Matthew Clarkson, of the School of GeoSciences. "This is a worrying finding, considering that we can already see an increase in ocean acidity today that is the result of human carbon emissions."

The study, which was carried out in collaboration with the University of Bremen in Germany and the UK Universities of Exeter, Leeds and Cambridge, has been published in the journal Science.

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