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.”
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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
A research to get more money.
When they talk about carbon, do they mean carbon or carbon-dioxide?
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?
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
The perfect circle… Clay minerals trap carbon… Clay minerals become shale… Trapped carbon becomes oil… Drill, frac, repeat…
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.
“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.
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.
This probably means that dredging rivers will be banned for fear of releasing the locked-in carbon. Expect more flooding in marshy areas.
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.
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??
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.
And as this process continues eventually all life on earth will die from insufficient CO2.
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.
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.