Earth has undergone multiple mass extinctions during its existence; for example, the Toarcian Oceanic Anoxic Event (T-OAE) has decimated the planet’s marine ecosystems. But according to a new study by international researchers from Caltech, George Mason University, the University of Naples and elsewhere, the destructive effects of the T-OAE over a period of 300,000 to 500,00 years could pale in comparison to what humanity would do in a short time. can reach. fraction of the time.
About 183 million years ago, cataclysmic volcanic activity in modern-day South Africa spewed about 20,500 gigatons of carbon dioxide into the atmosphere, raising sea levels, water temperatures and acidification. The resulting deoxygenation (called anexia) caused a mass extinction of marine life that would take up to half a million years to recover. Although researchers have long known about the T-OAE, they have not yet fully understood its true scope. This is especially a problem when it comes to predicting the consequences of future anoxic ocean scenarios for the planet.
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“Despite the recognition of the T-OAE as a potential analogue for future ocean deoxygenation, current knowledge about the severity of global ocean anoxia is largely limited to investigations of the trace element and isotopic composition of black shale, which are often influenced by local processes. the team explained in the abstract of their paper published on June 24 Proceedings of the National Academy of Sciences. To better understand the dynamics of the T-OAE, researchers therefore turned to uranium isotopes for help.
As an accompanying announcement from Caltech explains, the amount of uranium isotopes in the ocean is directly related to the lack of oxygen. If you can measure the isotopic composition of uranium samples, you can estimate the oxygen level of seawater (or lack thereof). Although it is impossible to sample water directly from the T-OAE, rocks such as limestone provide data from that era thanks to their uranium content. Uranium generally remains soluble in water when the oceans are oxygen-rich, but precipitates and settles in the ocean floor during periods of oxygen deficiency. By examining how much uranium is in ocean sediment dating back to the T-OAE, experts can estimate how bad the situation really got during the extinction.
After collecting 30 sections of stratified limestone from the Mercato San Severino region of southern Italy, researchers analyzed them for both the amount of uranium and their isotopic variations. Using a model developed by Michael Kipp, former Caltech postdoctoral researcher and current Duke University faculty, the team then determined the anoxic levels from the period.
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“Using this model, we found that oxygen deficiency was 28 to 38 times that of the modern ocean,” Francois Tissot, professor of geochemistry at Caltech and co-author of the study, said in a statement. “Today, only about 0.2 percent of the ocean floor is covered by anoxic sediments, similar to those in the Black Sea. At the time of the T-OAE, 183 million years ago, 6 to 8 percent of the ocean floor was covered by anoxic sediment.”
By better understanding how much greenhouse gas is needed to cause such dramatic levels of ocean oxygen, the team can extrapolate that to humanity’s effects on the environment. And as unfortunate as it is, modern society gives T-OAE a run for its money. Based on researchers’ calculations, human emissions since the Industrial Revolution already represent 12 percent of all CO2 generated during the entire T-OAE – in less than 0.1 percent of the time.
“If we do not reduce CO2 emissions and continue on the rising CO2 trajectory, we can clearly see that there will be serious negative consequences for the ocean ecosystem,” Tissot said on Monday.
The disturbing figures illustrate the importance of quickly curbing society’s disastrous pollution output in favor of truly sustainable practices. If we don’t do that, it’s clear that the T-OAE could look mild compared to our impact.