More Carbon Could Be Stored Deep in the Earth

Cambridge University and NTU Singapore have found that slow-motion collisions of tectonic plates drag more carbon into Earth’s interior than previously thought. Only about a third of the carbon recycled beneath volcanic chains returns to the surface via recycling, in contrast to previous theories that what goes down mostly comes back up.

Carbon rich materials could be placed where tectontic plates are going into the earth and almost two-thirds of the carbon will remain trapped for billions of years. Subduction is the process that destroys old lithosphere. An oceanic plate can descend beneath another oceanic plate – Japan, Indonesia, and the Aleutian Islands are examples of this type of subduction.

There are a number of ways for carbon to be released back to the atmosphere (as CO2) but there is only one path in which it can return to the Earth’s interior: via plate subduction. Here, surface carbon, for instance in the form of seashells and micro-organisms which have locked atmospheric CO2 into their shells, is channelled into Earth’s interior. Scientists had thought that much of this carbon was then returned to the atmosphere as CO2 via emissions from volcanoes. But the new study reveals that chemical reactions taking place in rocks swallowed up at subduction zones trap carbon and send it deeper into Earth’s interior – stopping some of it coming back to Earth’s surface.

The team conducted a series of experiments at the European Synchrotron Radiation Facility, “The ESRF has world-leading facilities and the expertise that we needed to get our results,” said co-author Simon Redfern, Dean of the College of Science at NTU Singapore, “The facility can measure very low concentrations of these metals at the high pressure and temperature conditions of interest to us.” To replicate the high pressures and temperatures of subductions zones, they used a heated ‘diamond anvil’, in which extreme pressures are achieved by pressing two tiny diamond anvils against the sample.

The work supports growing evidence that carbonate rocks, which have the same chemical makeup as chalk, become less calcium-rich and more magnesium-rich when channelled deeper into the mantle. This chemical transformation makes carbonate less soluble – meaning it doesn’t get drawn into the fluids that supply volcanoes. Instead, the majority of the carbonate sinks deeper into the mantle where it may eventually become diamond.

White headed black arrows indicate carbonate flux and blue arrows water flux. Blue shaded areas indicate water-rich regions. The melting of carbonated igneous oceanic crust is not shown as it starts at depths of 300 km22. The image is to scale, apart from the thickness of oceanic sediments that has been exaggerated.

Nature – Deep carbon cycle constrained by carbonate solubility

Earth’s deep carbon cycle affects atmospheric CO2, climate, and habitability. Owing to the extreme solubility of CaCO3, aqueous fluids released from the subducting slab could extract all carbon from the slab. However, recycling efficiency is estimated at only around 40%. Data from carbonate inclusions, petrology, and Mg isotope systematics indicate Ca2+ in carbonates is replaced by Mg2+ and other cations during subduction. Here we determined the solubility of dolomite [CaMg(CO3)2] and rhodochrosite (MnCO3), and put an upper limit on that of magnesite (MgCO3) under subduction zone conditions. Solubility decreases at least two orders of magnitude as carbonates become Mg-rich. This decreased solubility, coupled with heterogeneity of carbon and water subduction, may explain discrepancies in carbon recycling estimates. Over a range of slab settings, we find aqueous dissolution responsible for mobilizing 10 to 92% of slab carbon. Globally, aqueous fluids mobilize 35+20−17% (27+16−13 Mt/yr) of subducted carbon from subducting slabs.

SOURCES- Nature Communications, University of Cambridge
Written By Brian Wang,

11 thoughts on “More Carbon Could Be Stored Deep in the Earth”

  1. Vitrified nuclear waste could be carried to the inner earth placed correctly at these locations disposed permanently on human time scales.

  2. Even if the Earth's average temperature goes up 6 degrees C, arctic Siberia and Canada won't get any more sunshine in winter than they do now – and most of our fertile alluvial soils will be under salt water. Have you seen a map of China after the ice caps melt ? Ditto India, Pakistan, Germany, California, most of the Sunbelt States – plenty of opportunities for fish, not much for people. If there's any way we can slow or stop warming, it's obviously a far better outcome than adaptation. The dinosaurs 'adapted' to meteor-induced climate change by going belly up ( apart from the little ones you see flying around.) We think we're so much smarter, but we've induced our own climate apocalypse, and haven't even got the wit to stop making it worse.

  3. But that's OK, because this article has found a system that will get rid of carbon over 10s of millions of years. So that… is completely irrelevant to any human issue.

    To be fair, the article itself doesn't make any claims that this would be useful.

  4. quite a developed science – most typical ecosystems have been fully inventoried and assessed for complexity… seems that ecosystem engineers would be an easy next step…

  5. Yeah and a timeline of 50 – 150 years…
    Industries, country borders, and entire political systems rise and fall many times in that sort of schedule…

  6. of course. And who has actually identified the 'ideal world' that we should be aspiring to rather than this constant conflict of sentimental conservation and ruthless exploitation.
    easy: natural eco-system complexity metrics. The notion of looking at an ecosystem for a hugely diverse spectrum of various complementary and mutually-beneficial adversarial players. Nature can be so much more than it is — when we establish 'great' nature we can start to determine a great world.
    The Perfect Metric: organism and ecosystem complexity – the Great Overcoming of Entropy (in the Big Sense) – one place, culture, planet at a time.

  7. Agreed. It's all about addressing the multi-decade effects of all things man-made – land use, noise, air quality, water use, C02, etc. All resources easily managed and mitigated. Civilization is merely the use of and modification of the existing resources in conjunction with all else. Nature is not some friendly and cutesy disney character – it is ruthless survival and conflict and prosperity and adapatation. I have great confidence that society will be greater for having modernized and adapted to the current conditions while still supporting a rich complexity of life that would not have otherwise occurred without the knowledge and perseverence of our previous generations.

  8. Lost Cause.
    When the permafrost melts and releases 'some of the' trillions of tons C, as compared to the 'not even a trillion' currently in the atmosphere, what will it matter?
    I am glad that we have gone through the multi-generational exercise of establishing various threats, risks, and inconveniences that increased atmospheric C can have.
    Now this will all serve the grand purpose of Adaptation. Time to 'man up' and deal with the likely extreme situations (which are easily dealt with my modern economies) and go forward. Prosperity is the Daughter of Austerity and Challenge (not the Son of the Millenial/ Gen-z snowflake B-H-L woke-activist).
    At the worst, massive change to ecosystems will be opportunities to re-establish a positive balance with modern lifestyles – nothing in the worst predictions are insurmountable or existential.
    At best, much of the growing, warming, wetting, and increased agricultural lands realized (hello, yes, I am looking at you northern Canada, Russia, and China) will be a transitional experience into a lush and intense late 21st century.
    Yo. Yo. Whiny b**ches – time to meet the opportunities presented and flourish.

  9. Exactly. I loved this line "Carbon rich materials could be placed where tectontic plates are going into the earth and almost two-thirds of the carbon will remain trapped for BillionS of years" The warming sun shuts down the Carbon cycle in 1 billion years so nothing like swinging for the fences I guess. I am sure as carbon based life forms we can come up with something else. Would any of you artificial Silicon beings like to be called human we ran out of carbon for the old humans?

  10. That's brilliant. Mankind comes along and saves C3 plant life from a massive extinction event by rescuing carbon millions of years of plants had buried in coal deposits.

    And now we're going to recreate that risk by putting the carbon beyond our reach?

    Maybe we should be less concerned about establishing whether we're increasing atmospheric carbon dioxide levels, and more concerned about establishing whether doing so was bad?

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