Ancient mass extinction was preceded by a drop in a crucial trace element.
According to a recent study from Florida State University, a major extinction event around 183 million years ago was preceded by a fall in the element molybdenum across Earth’s oceans.
The decline shows that significantly more organic carbon was buried in the extinction event than had been previously believed, and it may have contributed to the mass extinction, which resulted in the loss of up to 90% of species in the oceans. The findings were recently published in the journal AGU Advances.
“This research tells us more about what was happening with molybdenum during this extinction event, but we also take it a step further,” said Jeremy Owens, an associate professor in FSU’s Department of Earth, Ocean and Atmospheric Science and a paper co-author. “Our findings help us understand how much carbon was cycling through the system, and it’s much larger than previously thought — potentially on the scale of modern atmospheric and oceanic increases due to human activities.”
Previous research has shown that molybdenum levels fell throughout the main phase of the ancient mass extinction, but it was not clear how widespread the drop was, when it began, or how long it lasted.
In order to answer those questions, the scientists examined rocks from three locations in Alberta, Canada, which had formerly been a part of a large ocean that encircled the ancient continent of Pangea. Because the site was linked to the global ocean, the researchers could infer conditions across the entire globe instead of only a particular basin.
They discovered new estimates for the start and duration of molybdenum decline, as well as the first phase of deoxygenation. Their study revealed that the decline began around one million years before the extinction and lasted almost two million years in total, which is far longer than experts had previously estimated.
The decrease in molybdenum also implies a massive increase in organic carbon burial in the ocean that may have been several times larger than previous calculations. Those calculations were based on estimations of carbon dioxide released from volcanic activity, implying that carbon dioxide release from volcanoes was actually much higher, which would be necessary to balance global carbon reservoirs.
Just like 183 million years ago, more and more carbon dioxide is being added to the Earth system today, which could reduce marine trace metals such as molybdenum that many organisms rely on for survival as the oceans lose oxygen and bury more organic carbon. After the ancient extinction event, global conditions gradually became more hospitable to life, but that process took hundreds of thousands of years.
“The uniqueness of the study sites has allowed us to take a deep look into how the chemistry of the global ocean changed across millions of years, which reconciles much of the current scientific debates that are focused on the local versus global aspects of this time interval,” said Theodore Them, a former postdoctoral fellow at FSU who is now an assistant professor at the College of Charleston.
Reference: “Reduced Marine Molybdenum Inventory Related to Enhanced Organic Carbon Burial and an Expansion of Reducing Environments in the Toarcian (Early Jurassic) Oceans” by T. R. Them II, J. D. Owens, S. M. Marroquín, A. H. Caruthers, J. P. Trabucho Alexandre and B. C. Gill, 22 November 2022, AGU Advances.
The study was funded by the National Science Foundation, NASA, and the Sloan Foundation.