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This decline may have contributed to the mass extinction, in which up to 90% of species in the oceans perished, and indicates that more organic carbon was buried in the extinction event than previously expected. The work is published in AGU Advances.
“This research tells us more about what was going on with molybdenum during this extinction event, but we also took it a step further,” Jeremy Owens, assistant professor in the Department of Earth and Ocean Sciences, said in a statement. Atmosphere and co-author of the article. “Our findings help us understand how much carbon is circulating through the system, which is much larger than previously thought, potentially on the scale of recent increases in the atmosphere and oceans due to human activities.”
Previous research had shown a decline in molybdenum during the main phase of the ancient mass extinction, but it was not clear how widespread this decline was, when it began, or how long it lasted.
To answer these questions, the researchers analyzed rocks from three sites in Alberta, Canada, that were part of a massive ocean surrounding the ancient continent of Pangea. Because the site is linked to this global ocean, the researchers were able to infer conditions across the globe, rather than in a single basin.
They found new estimates for the onset and duration of molybdenum reduction and the initial deoxygenation phase. Their research showed that the decline preceded the start of the extinction by about a million years and lasted about two million years in all, much longer than scientists previously thought.
The decrease in molybdenum also indicates a massive increase in the burial of organic carbon in the ocean which may be many times greater than previously estimated. These calculations were based on estimates of carbon dioxide released from volcanic activity, which means that the release of carbon dioxide from volcanoes was actually much higher than what would be needed to balance global carbon stocks.
Just like 183 million years ago, today more and more carbon dioxide is being added to the Earth system, potentially depleting marine trace minerals like molybdenum that many organisms rely on to survive as the oceans lose oxygen and bury more organic carbon. After the ancient extinction event, global conditions gradually became more suitable for life, but this process took hundreds of thousands of years.
“The uniqueness of the study sites allowed us to take an in-depth look at how the chemistry of the global ocean has changed over millions of years, reconciling much of the current scientific debate focused on local versus global aspects of this ocean.” Timeframe Theodore Thiem, a former postdoctoral fellow at Florida State and now an assistant professor at the College of Charleston, said in a statement.
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