The ocean floor is vast and diverse, accounting for more than 70% of the earth’s surface. Scientists have long used information in the sediments (rocks and microbial feces) at the bottom of the ocean to reconstruct past ocean conditions.
These reconstructions are very important to understand how and when oxygen is available in the Earth’s atmosphere, and eventually increase to a level that supports life as we know it today.
Geoscientists such as David Fike of the School of Arts and Sciences at Washington University in St. Louis said that, however, reconstruction that relies on sedimentary rock signals ignores the influence of the local sedimentation process and assumes the consequences.
Their new research was published on February 26 in Scientific progress Based on the pair called pyrite (FeS2 pcs) Is formed in the presence of bacteria. With chemically reduced iron (Fe) and sulfur (S), pyrite buried in marine sediments is one of the key controls to control the oxygen content in the earth̵
The researchers compared pyrite in sediments collected in boreholes drilled on the offshore shelf of New Zealand’s east coast with sediments drilled from the same basin but hundreds of kilometers into the Pacific Ocean.
Feck, Professor of Earth and Planetary Sciences at the University of Washington and Director of Environmental Studies, said: “We can obtain gradients from shallow to deep sediments and compare the differences in the isotopic composition of pyrite between these parts.”
Fick said: “We proved that for this basin located in the open ocean, you will receive very different signals between shallow water and deep water. This is prima facie evidence that these signals are not a global fingerprint of oxygen in the atmosphere. ,” He also serves as the head of the International Center for Energy, Environment and Sustainable Development (InCEES) at the University of Washington.
Fick said that instead of pointing directly at oxygen, the same signals from pyrite can be reinterpreted because they are related to other important factors, such as sea level changes and plate tectonics.
Fike and the first author Virgil Pasquier, a postdoctoral researcher at the Weizmann Institute of Science in Israel, first questioned the use of pyrite in a 2017 PNAS publication using Mediterranean sediments Is used as an agent in the research. In post-doctoral research, Pasquale has been collaborating with Professor Itay Halevy of the Weizmann Institute to understand various methods of controlling the isotopic composition of pyrite. Their results raise concerns that pyrite sulfur isotopes are commonly used to reconstruct the earth’s evolving oxidation state.
Pasquale said: “Strictly speaking, we are studying the coupled cycle of carbon, oxygen and sulfur, and the control of the oxidation state of the atmosphere.”
He said: “For a paper, it is more sexy to reconstruct past ocean chemistry changes than to focus on burying rocks or what happened during burial.” “But I found this part more interesting. Because of the life of most microorganisms. -Especially when oxygen initially accumulates in the atmosphere-it occurs in sediments. And if our ultimate goal is to understand the oxygenation of the ocean, then we must understand this.”
In this study, the research team performed 185 sulfur isotope analyses of pyrite in two boreholes. They determined that the changes in the signals in the pyrite in offshore boreholes are more controlled by local sedimentary changes driven by sea level than by any other factors.
Conversely, sediments in deeper boreholes are not affected by sea level changes. Instead, they recorded signals related to the long-term reorganization of ocean currents.
“This is a water depth threshold,” said co-author, Dr. Roger Bryant. Graduated from the Fike laboratory at the University of Washington and is now a postdoc at the University of Chicago. “Once it falls below the water depth, the sulfur isotopes are obviously insensitive to the climate and environmental conditions in the surface environment.”
Fick added: “Earth is a complex place and we need to remember that when we try to reconstruct the changes in the past. There are many different processes that affect the types of signals preserved. To better understand the long-term evolution of the earth , We need to have a more detailed understanding of how to extract information from these signals.”
Faster than we thought-the vulcanization of organic materials
Strong local rather than global control over the sulfur isotopes of marine pyrite, Scientific progress February 26, 2021: Volume 7, No. 9, eabb7403. DOI: 10.1126/sciadv.abb7403
Courtesy of Washington University in St. Louis
Citation: When using pyrite to understand the Earth’s oceans and atmosphere: Think local rather than global (February 26, 2021) is February 28, 2021 from https://phys.org/news/2021-02-pyrite -earth-ocean-atmosphere-local.html retrieved
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