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Researchers find decrease in crucial trace element preceded ancient mass extinction

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AGU Advances (2022). DOI: 10.1029/2022AV000671″ width=”800″ height=”403″/>

Idealized Molybdenum (Mo) and Mo/Total Organic Carbon (TOC) Systems in the Marine Domain. The bottom panel (solid line) represents local Mo concentrations and Mo/TOC values ​​measured from fine-grained, siliceous-dominant sediments. The top panel (dashed line) represents the global oceanic Mo reservoir. Pie charts represent the relative contribution of the aerobic and reducing environments to the burial of Mo within the global ocean. (a) In this non-ocean anaerobic event (OAE) scenario, anoxic and organic-rich sediments are sandwiched between oxygenated organic-poor sediments. Locally, sedimentary Mo values ​​increase during anaerobic sedimentation, but there is little or no change in marine Mo reservoirs due to widespread anoxic and organic carbon (OC) burial. (b) In this OAE scenario, anoxic and organic-rich sediments are deposited between oxygenated organic-poor sediments. Locally, there is only a modest increase in sedimentary Mo values ​​during anaerobic sedimentation, with widespread anaerobic and OC burial resulting in a synchronous decrease in the size of global marine Mo reservoirs. (c) In this OAE scenario, anoxic and organic-rich sediments are deposited in open ocean (Cariaco-like) basins over the entire study period. Increasing Mo and OC burial before the classical OAE interval reduces local sedimentary Mo values. After the OAE interval, the global Mo reservoir begins to recover as local sedimentary Mo values ​​begin to increase and widespread deposition under anaerobic conditions decreases. *Note that these idealized TM records are derived from fine-grained, siliceous-dominant sediments, as the proxies are not adjusted for limestone. Furthermore, in these idealized recordings, low TOC intervals are associated with oxygenated settings and high TOC intervals are associated with anaerobic settings. In fact, both low-TOC and high-TOC sediments could deposit in either redox region, generating an auxiliary local redox proxy (e.g., iron speciation) to distinguish them. is needed. It is also important to note that Mo chemostratigraphy from highly restricted sedimentary environments (such as the T-OAE Yorkshire record) may resemble Scenario C. credit: Progress of AGU (2022). DOI: 10.1029/2022AV000671

A new study from Florida State University found that the element molybdenum decreased throughout the planet’s oceans prior to a significant extinction event about 183 million years ago.

This may have contributed to the decrease. mass extinctionsuggesting that up to 90% of marine species died and more organic carbon was buried in the ocean. extinction Events than previously estimated.works are published in Progress of AGU.

“This study tells us more about what was happening with molybdenum during this extinction event, but it goes a step further,” said an associate professor in the Department of Earth, Ocean and Atmospheric Sciences at FSU in a paper. said co-author Jeremy Owens. “Our findings help us understand how much carbon was circulating in the system, which is much larger than previously thought, and is much larger in the modern atmosphere and ocean due to human activity. It could be the size of the increase.”

Previous studies have shown that molybdenum declined during key stages of the ancient mass extinction, but it is unclear how widespread the decline was, how early it started, and how long it lasted. did.

To answer these questions, researchers analyzed rocks from three locations in Alberta, Canada. These places were part of a huge ocean that surrounded the ancient continent of Pangea. Because the site was connected to that global ocean, researchers were able to infer the situation across the globe, not just in a single basin.

They found new estimates for the onset and duration of molybdenum drawdown and the initial stages of deoxygenation. Their study showed that the decline preceded the onset of extinction by about 1 million years and lasted about 2 million years in total.

A decrease in molybdenum also implies a significant increase in organic carbon burial in the ocean that could have been several times larger than previous calculations. These calculations were based on estimates of carbon dioxide released from volcanic activitywhich means carbon dioxide emissions Emissions from volcanoes are actually much higher and are necessary to balance global carbon reservoirs.

More and more like 183 million years ago carbon dioxide As the ocean loses oxygen and buries more, it could deplete marine trace metals such as molybdenum, which many organisms rely on for survival. organic carbon. after antiquity extinction incidentthe world conditions gradually became more livable, but the process took hundreds of thousands of years.

“The uniqueness of the research site allowed us to delve deeply into how Earth’s chemistry works. sea ​​of ​​the world This reconciles much of the current scientific debate that focuses on the local and global aspects of this time interval,” said Theodore, a former FSU postdoctoral fellow and now assistant professor at the University of Charleston. Them said. .

For more information:
TR Them et al. Decrease in marine molybdenum stocks associated with enhanced organic carbon burial and expansion of reducing environments in Toarcian (lower Jurassic) oceans. Progress of AGU (2022). DOI: 10.1029/2022AV000671

Quote: Researchers Discover Decrease of Important Trace Element Preceding Ancient Mass Extinction (November 22, 2022) https://phys.org/news/2022-11-decrease-crucial-element-ancient Retrieved 11/23/2022 from -mass.html

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