The University of Exeter has shed new light on the causes of second oceanic anoxic eventwhich caused severe global warming and acidification of the oceans 94 million years ago.
The study, which attributes this event to a succession of pulses of massive volcanismhas been published in Nature Communications.
The episode, called the “second oceanic anoxic event” (OAE 2), was one of the major climate disasters of the geological record, causing extinctions in the oceans and on land.
The anoxic events are prolonged periods in which large swaths of Earth’s oceans run out of dissolved oxygen, creating toxic waters and leading to mass extinctions and habitat loss.
The cause of this anoxic event, which lasted more than 500,000 yearshas been the subject of debate among experts.
However, the team of researchers has shown that massive volcanism was the probable triggerpointing to a vast oceanic plateau beneath the remote Kerguelen Islands as the source.
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.
Pulses of massive volcanism
They discovered that the sediment cores showed clear evidence of sedimentary mercurywhich meant a series of significant “pulses” of intense massive volcanism in the period before and during the main phase of the anoxic event.
Furthermore, radiogenic isotopes of neodymium and strontium show that Kerguelen plateauwhich was much closer to the Mentelle basin in the Cretaceous period, was uplifted as part of volcanic activity.
The research team suggests that severe volcanic events would have caused a carbon dioxide release explosionwhich would be essential to warm the climate and cause ocean acidification.
They believe that this phenomenon is the key reason for the anoxic event and what forced the Earth to reach a tipping point to become a “greenhouse world” at that moment.
Chloe Walker-Trivettwho led the research while undertaking his PhD studies at Camborne School of Mines at the University of Exeter’s Penryn Campus, said: “Although OAE 2 has been very well studied, most research so far “They have focused on the northern hemisphere, which has led to a rather one-sided view of the event.”
“Our southern hemisphere study site, off the southwestern coast of Australia, was at a high southern latitude (about 60 degrees south) during the mid-Cretaceous, when OAE 2 occurred, and has given us a completely new, and has pointed out Kerguelen volcanism as the probable trigger.
Sev Kenderfrom 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 want to use past rapid global warming events as a possible analogue for future climate change.” ».
“Our key innovation was to combine the new mercury indicator for volcanic eruptions with radiogenic isotopes of neodymium and strontium that determine the sources of eroded rocks in the ocean basin. The increasing amount of material eroded from a volcanic source showed that the nearby Great “Kerguelen Igneous Province was rising at the time of active volcanism, rather than a number of other volcanic provinces that had previously been considered the cause.”
