Scientists suggest causes behind one of the biggest climate disasters

A team of researchers from the University of Exeter has shed new light on the causes of Oceanic Anoxic Event 2, which saw the Earth severely warm and the oceans acidify about 94 million years ago. The research was published in Nature communication.

The episode, called ‘Oceanic Anoxic Event 2’, marked one of the most significant climate disasters in geological history, causing extinctions in the oceans and on land.

Anoxic events are prolonged periods during which large portions of Earth’s oceans run out of dissolved oxygen, creating toxic water and leading to mass extinctions and habitat loss.

The cause of this anoxic event – ​​which lasted more than 500,000 years – is a source of debate among experts.

However, the team of researchers has shown that massive volcanism was likely the cause, by tracing the source to a vast oceanic plateau beneath the remote Kerguelen Islands.

For the new study, the researchers analyzed geochemical and micropaleontological data collected from ocean sediment cores in the Mentelle Basin, located off the coast of Western Australia, collected by the International Ocean Discovery Program.

They found that the sediment cores showed clear evidence of sedimentary mercury – indicating a series of significant “pulses” of intense massive volcanism leading up to and during the main phase of the anoxic event.

Furthermore, radiogenic isotopes of neodymium and strontium show that the Kerguelen Plateau, which was much closer to the Mentelle Basin in the Cretaceous, was uplifted as part of the volcanic activity.

The research team suggests that severe volcanic events would have led to an explosion of carbon dioxide being released – which would play a major role in warming the climate and causing ocean acidification.

They believe this phenomenon is the main reason for the anoxic event, and what pushed Earth to a tipping point at the time and moving into a ‘greenhouse world’.

Chloe Walker-Trivett, who led the research during her Ph.D. studies at the Camborne School of Mines at the University of Exeter’s Penryn Campus said: “Despite OAE 2 being really well studied, most research to date has focused on the Northern Hemisphere, leading to a rather one-sided picture of the event.

“Our Southern Hemisphere research site off the coast of southwestern Australia was located at a high southern latitude (~60 degrees south latitude) during the mid-Cretaceous period, when OAE 2 occurred, and has given us a completely new vantage point and the Kerguelen volcanism as the likely trigger.” .”

Sev Kender, from the University of Exeter and co-author of the study, added: ‘Detecting the timing of massive volcanism in the geological past is challenging, but crucial if we are to use past rapid warming events as a possible analogy for future climate. change.

“Our key innovation was combining the new mercury proxy for volcanic eruptions, with radiogenic neodymium and strontium isotopes that determine the sources of eroded rocks in the ocean basin.

“The increasing amount of eroded material from a volcanic source showed that the nearby large igneous province of Kerguelen was uplifted at the time of active volcanism, rather than a series of other volcanic provinces previously considered to be the cause.”