Home North pole ice Researchers find low oxygen and sulphide levels in oceans played a bigger role in ancient mass extinction

Researchers find low oxygen and sulphide levels in oceans played a bigger role in ancient mass extinction

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Seth Young’s research group collects and describes limestone samples from a field site in the Roberts Mountains, Nevada. Credit: Anders Lindskog / Florida State University

Researchers at Florida State University have new insight into the complicated puzzle of environmental conditions that characterized the Late Ordovician (LOME) mass extinction, which killed about 85% of species in the ocean.

Their work on the 445 million year old mass extinction has been published online in the journal AGU advances Monday.

“We found that the reducing conditions – with little or no oxygen and little or no levels of hydrogen sulfide – probably play a much bigger role than we previously thought,” said lead author Nevin. Kozik, PhD student in the Department of Earth, Ocean and Atmospheric Scientist and researcher at the National High Magnetic Field Laboratory, headquartered at FSU. “If you imagine a pie chart of the causes of this extinction, we are increasing this wedge which signifies oxygen deficiency, which occurs in concert with a cooling climate and widespread habitat loss due to sea level change. . “

The research is the first study to use measurements from multiple elements from multiple sites to examine the conditions that led to LOME, the second largest extinction event in Earth’s history and the only mass extinction to occur during what are called ice house conditions, when Earth’s climate is cold enough at the poles to support ice caps year round.

To measure oxygen and sulphide concentrations from millions of years ago, scientists use geochemical proxies that correspond to ancient marine conditions. The iodine concentrations and sulfur isotopes from three sites provided information on oxygen and sulphide levels in the ancient ocean.

The extinction occurred in two separate pulses. Using these geochemical measurements as environmental indicators, the researchers found that oxygen levels decreased before the first pulse and remained low. Levels of hydrogen sulfide in the oceans initially declined, causing the first pulse of the extinction event, but these levels then increased, coinciding with the second and final pulse of the extinction.

At the same time as Earth’s climate cooled, glaciers were expanding at the former South Pole (now North Africa), resulting in a drop in sea level and loss of habitat. for marine organisms in the shallow sea lanes of the tropics.

“Geological records indicate that there were many environmental factors at play to lead to this extinction event,” Kozik said. “The processes that we relate here are like several life-killing punches during this time.”

Even though conditions became inhospitable for many organisms around the planet, the environment in some places remained rich in oxygen and able to support a diversity of life. Researchers found evidence of higher oxygen levels at a site near present-day Quebec that housed a shallow reef on the continental shelf 445 million years ago.

“We know that life had to survive and persist after this mass extinction, and now we have an indication that at least this place had enough oxygen to support life,” said co-author Seth Young, associate professor at the Land, Ocean Department. and atmospheric scientist and researcher at the National High Magnetic Field Laboratory, headquartered at FSU. “It’s consistent with what you find in the rock and fossil record that the reefs persist during this extinction event. The fossils suggest that at least there life was OK.”

The extinction event is an ancient analogue of what is happening on Earth today. The Earth today, as in the Upper Ordovician, is in a period of ice age and is experiencing a significant loss of biodiversity, global warming and a decrease in ocean oxygen.

“All of these things are really important and provide a modern perspective on this mass extinction event,” Young said. “It is important not only to understand what caused this extinction event, but also how the earth system came out of it and continued. Period of survival as and what led to the re-emergence and re- diversification of life. “

Researchers from the Virginia Polytechnic Institute and the State University and University of California at Riverside contributed to this study.


Researchers find oxygen surge coincided with ancient global extinction


More information:
Nevin P. Kozik et al, Geochemical records reveal a prolonged and differential marine redox change associated with the late Ordovician climate and massive extinctions, AGU advances (2022). DOI: 10.1029 / 2021AV000563

Provided by Florida State University

Quote: Researchers Discover Low Oxygen and Sulfide Levels in Oceans Played Larger Role in Ancient Mass Extinction (2022, Jan 10) Retrieved Jan 10, 2022 from https://phys.org / news / 2022-01-oxygen-sulfide-oceans-greater- role.html

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