The dig site in Oman.
Photo Credit: Keele University
Scientific Frontline: Extended "At a Glance" Summary: Natural Carbon Sequestration in Mantle Rocks
The Core Concept: Carbon dioxide (\(CO_2\)) can be permanently sequestered for millions of years when carbon-rich fluids react with subterranean rocks to form stable, solid carbonate minerals.
Key Distinction/Mechanism: Instead of being transported deep into the Earth's core or released back into the atmosphere via volcanic eruptions, ocean sediments carrying \(CO_2\) are dragged into subduction zones. The \(CO_2\) is channeled along tectonic plate boundary faults into the shallow mantle, where it undergoes chemical reactions with the surrounding rock to lock the carbon away in solid form.
Major Frameworks/Components:
- Subduction Zones: Tectonic intersections where one plate sinks beneath another, acting as a primary driver for the global carbon cycle.
- Ophiolites: Uplifted sections of oceanic crust and upper mantle that allow scientists to study deep-Earth geological processes at the surface.
- Halogen Fingerprinting: The chemical analysis of trace elements (chlorine, bromine, and iodine) within microscopic mineral grains to identify the specific fluid reactions and sources of the trapped carbon.
Branch of Science: Isotope Geochemistry, Geology, and Earth Sciences.
Future Application: Understanding how the Earth naturally moves and permanently stores carbon provides critical insights for developing and optimizing human-engineered carbon capture and storage (CCS) technologies to combat global climate warming.
Why It Matters: The research indicates that carbon sinks in subduction zones are a massive and vital component of Earth's long-term climate regulation. Calculations reveal that over 90% of the \(CO_2\) within a sinking tectonic plate can be locked away in the shallow mantle, with the Oman site alone estimated to have naturally sequestered over one billion tons of \(CO_2\).
Researchers have shed new light on how a unusual rock formation in Oman was created, which could reveal new details about the Earth’s ability to store carbon dioxide (\(CO_2\)) for millions of years.
The study, led by Keele University, in collaboration with The University of Manchester and University of Ottawa, looked at geological evidence from Oman to better understand processes that occur in subduction zones - where one of the Earth’s tectonic plates sinks beneath another due to the plates colliding together. Such zones are active around much of the Pacific “Ring of Fire” today.
Subduction zones are key to the global carbon cycle because ocean sediments carried by the sinking plate contain large amounts of \(CO_2\). Scientists have long debated what happens to this carbon after it sinks - some are transported deep into the Earth, while some return to the atmosphere via volcanic eruptions.
Another possibility is that \(CO_2\) becomes trapped in rocks when carbon-rich fluids react with them, forming minerals known as carbonates, which lock the carbon away for millions of years. These reactions happen tens of kilometers underground, so they are difficult to observe and study.
“In some parts of the world, sections of oceanic crust and upper mantle - known as ophiolites - have been pushed to the surface, allowing us to study them in detail. One of the best-preserved examples is the Semail Ophiolite in Oman, which is estimated to have naturally sequestered over one billion tons of \(CO_2\). Scientists have long debated exactly how these rocks formed, and more recently attention has turned toward their role as a long‑term natural reservoir for carbon.”Co-author Ray Burgess, Professor of Isotope Geochemistry at The University of Manchester
To resolve this, the team analyzed halogens - chlorine, bromine, and iodine - which were present within individual mineral grains. These elements can leave a fingerprint of the fluid reactions and sources of carbon which formed the carbonate minerals.
Their results, published in Nature Communications, indicated that there were at least two separate events where \(CO_2\) reacted with the rocks. It was found that most of the carbonate minerals formed from fluids that match those usually found in subduction zones.
They also calculated that over 90% of the \(CO_2\) in the sinking plate could have been channeled along the plate boundary fault into the shallow mantle and locked away, indicating that carbon sinks in subduction zones are not only real, but could play a significant role in the Earth’s carbon cycle, by offering a way to store huge amounts of \(CO_2\) for millions of years.
Lead author, Dr Elliot Carter, from the School of Life Sciences at Keel University said: “As our climate warms there’s been increasing attention on these strange and enigmatic rocks and what they can tell us about how the Earth moves carbon around and how humans could store it in the future”
“Zooming into chemical differences between different microscopic crystals really gave us the key to unlock the story of these rocks”
“We can now tell that rocks such as those in Oman likely form an important part of Earth’s long-term carbon cycle.”
Published in journal: Nature Communications
Title: Carbonated mantle peridotites represent a hidden sink for subducted \(CO_2\)
Authors: Elliot J. Carter, Brian O’Driscoll, Ray Burgess, Patricia L. Clay, Hélène Balcone-Boissard, Pierre Bürckel, and the Oman Drilling Project Science Team
Source/Credit: University of Manchester
Reference Number: es031026_01
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