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New ideas about how carbonates record the global carbon cycle



New ideas about how carbonates record the global carbon cycle

Geyman dives for a sediment sample in the Bahamas. Analyzing the examples helps to recreate the complex chemistry of Earth's past. Credits: Emily Geyman

When scientists want to study the ancient geological past of the Earth – typically more than 100 million years ago – they turn into rocks often called carbonates.


Calcium carbonates, which are ubiquitous carbonate forms, are minerals that precipitate from seawater and form layered sedimentary deposits on the seabed. It is commonly known as limestone. For more than 3.5 billion years the Earth's history has become chronic in carbonate rocks. Many scientists use it to reconstruct histories of change in climate and the past global carbon cycle; that is, the process in which carbon passes between oceans, atmosphere, biosphere and solid rock.

S You can learn a lot from carbonates, dedi he said. 2019 Emily Geyman, a graduate of geology at Princeton, is the author of an article published on November 8th. National Academy of Sciences Proceedings (PNAS). The report was the result of a senior thesis study in which Geyman explored the chemical composition of carbonates and how these carbonates record the carbon cycle.

“What makes carbonates particularly useful against something like sandstone, G Geyman said. “The deposition of carbonate directly from sea water, so the idea is that the chemistry of carbonates can measure, Tell us something about the old ocean. "

However, not all carbonates are preserved in geological records. For example, deep sea carbonates typically sublimate; therefore, scientists often turn into carbonates that accumulate on shallow continental shelves. The problem, however, is that scientists still do not know enough about how to translate properties such as ocean chemistry, ocean temperature, wave energy and water depth into the shallow carbonate registry.

But now researchers at Princeton are working to address this question.

"Today, no one has looked at the equivalent of these old limestones and does not understand the translation," said Adam Maloof, a geology professor who collaborated on paper with Geyman. Gibi It's like trying to translate old texts without Rosetta Stone. We needed our Rosetta Stone. ”

Researchers not only find Rosetta Stones in the form of an innovative hypothesis, but the findings also challenge the traditional logic of using carbonates to rebuild the global carbon cycle.

"One of the most common measurements we have made of old carbonates is the carbon isotope composition," Geyman said. “And we associate the carbon isotope composition with the global deterioration of the carbon cycle.”

Studying old isotopes – different forms of the same element – is a key to understanding how much and why the Earth's global carbon cycle has changed in the past. Maloof is very important because the carbon cycle acts as a thermostat to regulate the temperature of the Earth. Understanding how this thermostat works will help us predict future climate change.

His research led them to Andros Island in the Bahamas, an almost completely deserted island in the Great Bahama Bank.

The Bahamas is a great place to study Earth's ancient geological past. "In much of the history of the world," Geyman said, "Many of the Earth's surface today resembled the Bahamas. "Said.

The aim was to understand how water chemistry controls the chemistry of the rock – basically how carbon isotopes are recorded in contemporary environments and what it can say about the past carbon cycle.

Anız If you want to find out what old sea levels and seawater chemistry look like from old carbonates, ”Geyman said, gidip go to the modern analogue and see how good modern carbonates are formed right now. Should you ask current ocean chemistry and current sea level? ""

What they found and previous studies showed was that there was something strange about the Bahamian sediment. The limestone formed there had carbon-13, which seemed very high compared to single-cell plank floating all over the open ocean.

A large percentage of old carbonates also indicate that this is abnormally high carbon-13. If you assume that this reflects the global ocean conditions, Maloof says, "You make hard inferences about the major changes in the carbon cycle."

Instead, Geyman and Maloof developed a hypothesis that they called the günlük daily carbon cycle engine ". As the name implies, the transaction involves a 24-hour cycle. When the sun shines during the day, aquatic plants extract carbon – 12 from water from the photosynthesis process and use it to make plant material. Since plants preferably take carbon-12, the carbon remaining in the water is enriched with carbon-13.

The main component in this process is that the limestone forms the fastest during the peak period of photosynthesis, since photosynthesis makes water more saturated with calcium carbonate. At night photosynthesis opens the aerobic airway and the carbon held in the plant tissue returns to water. However, limestone formation hardly keeps track of the night, Maloof said, because there is little rainfall. If rainfall occurs evenly overnight, the average carbon-13 level will be normal because the carbon-12 will be returned to the system.

This process, proposed by researchers, can only take place if the water is shallow enough and protected on shelves and platforms on continental shelf, such as the Bahamas. The same daily process occurs in the open ocean, but the movement of the waves constantly mixes and brings new water, so that carbon-13 is never raised to these extremes.

Bahamian sediments absorb calcium carbonates from seawater, making it difficult to use ancient limestones to record a global carbon cycle. Maloof cannot be assumed to have a single and a single carbon conversion process that characterizes the past.

Uz We use a modern analogue to study the past, G Geyman added, geçmiş and the past is key to understanding the future in many ways. G

Geyman is currently doing a master's degree focusing on glalogy at the University of Tromsø in Arctic Norway as part of the Sachs Global Scholarship from Princeton.

Bahamas carried out his work as part of his young and senior independent work at Princeton. A successful young scientist has already received numerous awards and awards. Peter W. Stroh's Environmental Thesis Award, the Calvin Dodd MacCracken Prize from Princeton School of Engineering and Applied Sciences, and the Edward Sampson 1914 Award for outstanding work in environmental geology.

Maloof received great praise for Geyman. Abilir He can do anything, ”he said. “Really good observers do fieldwork… and they're not computer scientists who can do amazing analysis. It's him. ”

The article "An everyday carbon engine explains 13C enriched carbonates without increasing global oxygen production" was published online by Emily Geyman and Adam Maloof on November 8th. National Academy of Sciences Proceedings


Mankind did not live until 1965 with a high carbon dioxide atmosphere


More information:
Emily C. Geyman et al. A daily carbon engine discloses 13C-enriched carbonates without increasing spherical oxygen production. National Academy of Sciences Proceedings (2019). DOI: 10.1073 / pnas.1908783116

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Princeton University

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New thoughts on how carbonates record the global carbon cycle (2019, 11 November)
Retrieved on November 11, 2019
From https://phys.org/news/2019-11-thoughts-carbonates-global-carbon.html

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