Scientists indicate the causes of one of the most significant 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 severe global warming and acidification of oceans around Earth around 94 million years ago. The study is published in The nature of communication.

Dubbed “Oceanic Anoxic Event 2”, this episode marked one of the most significant climate catastrophes in the geological record, causing extinctions in the oceans and on land.

Anoxic events are extended periods when large areas of Earth’s oceans are depleted of dissolved oxygen, creating toxic waters and leading to mass extinctions and habitat loss.

The cause of this anoxic event—which lasted >500,000 years—has been a source of debate among experts.

However, a team of researchers showed that the likely trigger was massive volcanism that imprinted a source on a vast oceanic plateau beneath the remote Kerguelen Islands.

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

They found that the sediment cores showed clear evidence of sedimentary mercury—marking a series of significant “pulses” of intense mass volcanism during and during the main phase of the anoxic event.

Radiogenic isotopes of neodymium and strontium further indicate that the Kerguelen Plateau, which was much closer to the Mentelle Basin during the Cretaceous, was uplifted by volcanic activity.

The research team suggests that severe volcanic events would lead to an explosion of carbon dioxide release, which would help warm the climate and cause ocean acidification.

They believe this phenomenon is the main reason for the anoxic event and what pushed the Earth to the tipping point where it moved into a “greenhouse world” at that time.

Chloe Walker-Trivett, who led the research while undertaking her Ph.D. studies at the Camborne School of Mines at the University of Exeter’s Penryn Campus said: “Although OAE 2 has been really well studied, until now most research has focused on the Northern Hemisphere, leading to a rather one-sided view of the event.

“Our Southern Hemisphere research site on the southwest coast of Australia was at a high southern latitude (~60 degrees south) during the mid-Cretaceous when OAE 2 occurred, giving us a completely new perspective and identifying Kerguelen volcanism as the likely trigger. .”

Sev Kender from the University of Exeter and co-author of the study added: “Detecting the timing of mass volcanism in the geological past is challenging but essential if we are to use past rapid global warming events as a possible analogue for future climate. change.

“Our key innovation was to combine a new mercury proxy for volcanic eruptions with radiogenic isotopes of neodymium and strontium that determine the sources of eroded rocks into the ocean basin.

“Increasing amounts of eroded material from a volcanic source have shown that the nearby large Kerguelen igneous province was uplifted during the period of active volcanism rather than a number of other volcanic provinces previously thought to be the cause.”