Clay minerals call the shots with carbon

The path of clay minerals and organic matter bound to them from the land surface to marine sediment. Credit Graphic: ETH Zurich after Blattmann et al., Science 2019

The path of clay minerals and organic matter bound to them from the land surface to marine sediment. Credit Graphic: ETH Zurich after Blattmann et al., Science 2019

Rivers discharge a constant supply of sediment into the world’s oceans. This sediment is largely composed of various clay minerals – the products of rock weathering – and organic compounds of plant origin that have decomposed in soils. These two components end up in rivers as a result of erosion.

On its way to the oceans, organic matter in sediments binds with clay minerals to form clay-?humus complexes. Once they reach the sea, these complexes sink to the seabed, where they are buried by other sediments. This captures the carbon contained in these complexes, removing it over geological timescales from the atmosphere and from the pools of carbon standing in rapid exchange with Earth’s surface.

This is why clay minerals, also known as phyllosilicates, are extremely important for the global carbon cycle: some 90 percent of the organic carbon sequestered in the seabed around the continents is related to reactions between organic material and various minerals. A variety of phyllosilicates are responsible for a particularly large share because their small size and their geometry mean they have a particularly high specific surface area and can bind large quantities of carbon.

It all depends on the variety

However, not all clay minerals form stable complexes with organic substances. In a recent article in the journal Science, a team of researchers from ETH Zurich and Tongji University in Shanghai shows that different kinds of clay minerals interact with organic matter to varying degrees, in a process that determines the cycling of organic carbon. This also affects the extent to which each clay mineral acts as an agent for carbon sequestration, since the binding of carbon with a particular phyllosilicates depends on its mineralogical structure and characteristics. The greater the specific surface area and the stronger its reactivity, the greater the quantity of organic matter that can bound to it and the higher the volume of carbon sequestered in the sediment.

The researchers studied these processes in the South China Sea, where the clay mineral smectite from Luzon (the main island of the Philippines), kaolinite from the Chinese mainland, and mica and chlorite from the mountains of Taiwan all meet. Thomas Blattmann, a former ETH doctoral student and the study’s lead author, says that this sea offers the best conditions in the world for studying the interactions between phyllosilicates and organic matter. Other oceans feature a “chaotic mixture” of phyllosilicates in which the processes that the researchers are interested in overlap. “That makes it harder to determine the effects of individual kinds of clay minerals. In contrast, in the South China Sea it’s clear from which land mass each clay mineral is sourced – and that’s unique.”

Clay minerals trap carbon

Smectite is formed when volcanic bedrock is chemically weathered; in freshwater, it binds with organic material from fertile, humus-?rich soils. Once these complexes reach saltwater, however, the smectites swap their organic loadings. They take up carbon compounds dissolved in the seawater and release the organic matter that originated from land to the ocean. What happens to this organic matter next is unclear. Blattmann thinks it likely that organic substances from Luzon either oxidise, are consumed by microorganisms, or remain freely dissolved for thousands of years in seawater. Phyllosilicates from the mountains of Taiwan behave differently. They bind very tightly with continental carbon from Taiwan, carrying the organic matter quickly and efficiently into the sea.

“How carbon originating from land masses is transferred to the world’s oceans and stored there ultimately depends on the kind of clay mineral. These minerals affect the large-?scale transfer of organic carbon from continents to their sink on the ocean floor,” Blattmann explains.

New findings raise new questions

“Phyllosilicates play a more important role in the global carbon cycle than we previously assumed,” says Tim Eglinton, a professor at the Geological Institute at ETH Zurich. The greater their specific surface area, the greater the quantity of organic matter they can take up and, consequently, the higher the volume of carbon they can sequester on the ocean floor. “However, this isn’t something we can quantify, because we are only just beginning to understand the specific behaviour of these various clay minerals. It will take a great deal of additional research for us to arrive at any conclusions regarding the vast expanses of the world’s oceans.”

###

Reference

Blattmann TM, Liu Z, Zhang Y, Zhao Y, Haghipour N, Montluçon DB, Plötze M, Eglinton TI. Mineralogical control on the fate of continentally-?derived organic matter in the ocean. Science 03 Oct 2019: eaax5345, DOI: 10.1126/science.aax5345

From EurekAlert!

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42 thoughts on “Clay minerals call the shots with carbon

  1. It will take a great deal of additional research for us to arrive at any conclusions …

    A research to get more money.

    When they talk about carbon, do they mean carbon or carbon-dioxide?

    Blattmann thinks it likely that organic substances from Luzon either oxidise, are consumed by microorganisms, or remain freely dissolved for thousands of years in seawater.

    and ends up one day as carbon-dioxide, giving up full cycle.

    It sounds like a draft to a study, to apply for funding.
    Why don’t they apply for money to study why a worm is longer than it is round?

      • It is caused by resistentialism (look it up) – the harrassment of the animate by the inanimate e.g:

        Your shoes laces are more likely to be undone if you are in a hurry. Or

        The more expensive the carpet the more often the toast lands butter side down. Did those clowns in Manchester consider the price of the carpet?

    • So you think it is stupid and silly to improve our understanding of how possibly the largest single factor in regulating the carbon cycle performs?

      I dunno … seems like this is an extremely good topic to investigate. That is, if one cares to fight pseudo science global warming BS with actual, you know, science.

      One of the most obvious tenets of the pursuing the science of how our planet performs with respect to climate change is that what we DON’T know about it vastly exceeds the tiny little bit we DO know today.

      • I thought that the single largest carbon sink was the ocean. There are huge mountain ranges of limestone and dolomite.

        • Exactly.

          ‘some 90 percent of the organic carbon sequestered in the seabed around the continents’

          ‘Around the continents’ is limiting. Not obvious to many readers.

        • The total mass of carbon in the earth is estimated at 1.8 times ten to the 21st kg, most of which is in the crust and upper mantle where it exchanges via vulcanism and plate techtonics with the atmosphere, oceans, and biosphere. The total mass of carbon sequestered in the oceans is 3.9 times ten to the 13th kg (39,000 Gigatonnes). Therefore the carbon sequestered in rocks is approximately 5 times ten to the 7th times that in the oceans.

      • The problem is that this little backwater of geology (climatology) which probably got no more than a few million in NSF funding per year 30 years ago is now one of the biggest gravy trains in federally funded science. Even if the research is legit, do we really need to be spending billions a year to understand every detail of the carbon cycle? I am reminded of the superconducting supercollider, during my time in grad school. I agreed with the politicians who killed it – it just wasn’t worth the money. Or to put it better – there were many worthier projects to fund with our limited resources. The other problem is that everyone on that gravy train will fight to keep the choo choo running, and it will be very difficult to convince anyone in this field that their research isn’t vital to mankind.

    • What’s old is new again. Here is a paper from 1957 discussing stable organic/clay complexes which are very important for soil but maybe not so much so for climate (https://www.nature.com/articles/180048b0). Reproduction of results is, of course, important but this phenomenon has been well studied over the decades. An insidious part of the CAGW scam has been the taking of old findings, add a CAGW spin and presto chango you have a new round of publications which ignore the original work.

    • Research about carbon compounds, from methane and methanol to partially broken down DNA, proteins, and carbohydrates.

      The chemistry is unbelievably complex.

  2. So is there any mechanism which would cause the carbon to b e released into the Worlds atmosphere , or what might happen to it long term.

    Excuse me being a bit cynical, but “”More research needed” sounds like please send more money.

    MJE VK5ELL

      • Not to mention the concordant decomposition of these materials in tectonic subduction zones. That volcanic carbon dioxide comes from somewhere.

        • Yes, that’s my understanding. Dying zooplankton sink to the bottom of the oceans, taking their calcium carbonate structures with them.

          Maybe two billion years later, when they are subducted under another tectonic plate, the heat will decompose their structure and their carbon will be put back in the cycle.

          It is a cycle. A very long one.

  3. The perfect circle… Clay minerals trap carbon… Clay minerals become shale… Trapped carbon becomes oil… Drill, frac, repeat…

  4. As presented this is a flawed study. The author seems to ignore/dismiss the steady settling of pelagic organisms, such as plankton, that die and rain down on the forming seabed. Where this process is sufficiently rapid a crude oil deposit might be formed/trapped in the accumulating sediment. The author also utilizes clay nomenclature that tends to reflect x-ray diffraction instead of the more modern, and more useful to geologists, Short Wave Infrared Reflection. The author does get a break, of sorts, because he included a lot of question marks. Funding????? There, I included some question marks of my own.

  5. “However, this isn’t something we can quantify, because we are only just beginning to understand the specific behaviour of these various clay minerals.” The paper is behind a paywall, can’t seem to get the abstract, but would be curious as to their homework. I suspect that it is true that there is importance and not enough work, but this has a long history of interest, some way back when I was in college. When freshwater and its contents hit even highly diluted sea water, unusual chemical things happen. Even an acid pH sometimes.

    Geologists, as above, and even some of us biologists, know about this, here is a sample–
    Whitehouse, U. G., L. M. Jeffrey and J. D. Debbrecht. 1958. Differential settling tendencies of clay minerals in saline waters. Proceedings National Conference Clays Clay Minerals. 7:1-79.

    Whitehouse, U. G. and R. S. McCarter. 1958. Diagenetic modification of clay mineral types in artificial sea water. Proceedings National Conference Clays Clay Minerals. 5:81-119.

    Hyne, N. J., L. W. Laidig, and W. A. Cooper. 1979. Prodelta sedimentation on a lacustrine delta by clay mineral flocculation. Journal of Sedimentary Petrology. 49(4):1209-1216.

    Gibbs, R. J. 1983. Coagulation rates of clay minerals and natural sediments. Journal of Sedimentary Petrology. 53(4):1193-1203.

  6. As a matter of fact very little organic material gets sequestrated in sea-bottom sediments at the present time. Almost all gets eaten by various organisms, there is almost no organics-rich sediments being deposited:

    http://ksuweb.kennesaw.edu/~jdirnber/oceanography/LecuturesOceanogr/LecGeology/0510.jpg

    About the only exception is the Black Sea (and minor areas on continental shelves) where the bottom is anoxic. And this has been so for the last c. 35 million years with an icehouse climate and well-oxygenated abyssal waters.

    Earlier during hothouse climates major areas of the deep sea periodically became anoxic and large amounts of organics-rich shales were deposited. They are the source-rocks for most oil and NG.

    This research has some intrinsic interest but is completely irrelevant to the “climate crisis” despite the authors’ waffling about carbon. But of course it might fool some ignorant activist with influence on funding.

    • I was about to ask weather all these hydroelectric reservoirs around the globe used nowdays, are withdrawing clay from the oceans that used to go there just a few decades ago. And that this could contribute to raising CO2 levels in the air. I trust that scientists are checking what goes in to the ocean floor but couldn´t it be so that clay contributes to the deep ocean vater carbon content? So that withdrawing clay amount to the ocean can make a significant difference anyhow?

      • Short answer “Yes”.

        The effect of e. g. the Assuan dam is very obvious in the Nile Delta and the eastern Mediterranean as the sediment is now being trapped in the reservoir.

        It is however a temporary problem. In a few centuries the reservoir will be full.

  7. This probably means that dredging rivers will be banned for fear of releasing the locked-in carbon. Expect more flooding in marshy areas.

  8. This is actually an important part of mankind’s impact on the environment.

    Most major rivers have been canalised to allow for smoother, quicker flowing water – and fewer floods.
    That means less clay is washed out to sea.
    The impact of this on atmospheric CO2 trends should be considered.

    And this is why asking for more research is an appropriate thing for a paper to do. Science is never finished, settled, complete.

    • This would have been true if large amounts of organics were being deposited on the ocean bottom. However this is not so. Essentially all organics get eaten and converted to CO2.

      • Apart from the bits of the eating things (plankton) that sink to the bottom.
        And the CO2 that is dissolved in the water that downwells before reaching the surface.
        And the organics tied to clay that sinks below the well-lit levels very quickly.

        More research is required.

      • Most definitely NOT “apart from the bits of the eating things (plankton) that sink to the bottom”.

        Remember that there is no primary production below the photic zone. Everything that lives in the deep ocean is dependent on the drizzle of dead organisms from above, and it is all consumed. What isn’t eaten on the way down is eaten by bottom-living and bottom-burrowing organisms. The deep sea is a very nutrient-poor environment.

        It is this rain of dead organisms that accumulate on anoxic (oxygen-free) bottoms, but not elsewhere, since nothing except a few anaerobic bacteria can live there.

        P.S. It is not quite true that there is no primary production in the deep sea, “smokers”, hydrothermal vents do support local communities based on bacteria that can use chemicals in the hydrothermal fluids as an energy source. However the larger organisms in these “oases” are also dependent on oxygen in the water.

        And the reason there is much CO2 and little O2 in upwelling deep water is that the deep sea organisms have been consuming the O2 and turning it into CO2 during the 1,000 years or so a particular dollop of water takes to transit through the deeps and return to the surface.

    • Why is impact on atmospheric CO₂ so important? As long as we do not get a trend that is negative, there should not be anything to be concerned about.
      A study in economic and practical purification and maintenance of the rivers ought to be much more valuable. Studies cost money, thus it is in the public’s interest that the studies directly or indirectly have the possibility to lead to something that will benefit the society.
      Studies in basic physics may just be an exception, where free hands are needed in order to discover the unknown.

  9. Related question for the experts:

    How does sedimentation of the ocean bottoms by particulate from rivers, settling organisms (plankton, etc), and airborne dust (the Sahara Desert, etc.) affect changes in sea level? Is it significant??

  10. It is not clear what effect the phyllosilicates would have on the CO2 content of the atmosphere, although the article states that some of the organic matter could dissociate from the clays in the ocean. If this free organic matter was consumed by small sea organisms aerobically, this could release CO2 into the ocean, while anaerobic digestion would release methane.

    Since this is an entirely natural process without man-made intervention, it probably continues regardless of what people do, and there are many natural processes occurring all the time that are not well understood. This is another demonstration of the futility of attributing all “climate change” to anthropogenic CO2 emissions, while many natural processes could have a much greater effect on the climate.

    • Some of the C that has been sequestrated in the ground does get recirculated back into the atmosphere by volcanic action (even the coal in diamonds is partly organic). Whether this is enough to maintain sufficient CO2 in the atmosphere in the long run is uncertain.

      • You’re quite right tty.
        The carbon from the (formerly CO2 rich) atmosphere has been (and is being) taken up by sea creatures (molluscs, crustaceans and plankton) and sequestered as calcium carbonate in rocks’ limestone, chalk, marble etc. as part of the long term carbon cycle. It’s estimated there is 10 to 20 thousand times more carbon now locked up in the earths crust than all the fossil fuels. Unfortunately the L. T. C. cycle is dysfunctional; a more stable earths crust means fewer volcanoes and the consequent inability to recycle the earths carbon. Just as well we came along!

  11. I’m not saying the authors aren’t seeking more funding when they saying ‘more study needed.’ Maybe they are. But when I was a geology undergrad I figured out that a convenient way to end any major paper was with an ‘Areas for Further Study’ section. It’s a handy way to wrap things up: admitting the incompleteness of your work without actually admitting it, and anticipating those ‘Why didn’t you talk about this? kind of questions. It served me well.

  12. Old rumours have it that some of the first large organic molecules that led to even lager self assembling organic molecules first self assembled on a phyllosilicate substrate.

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