Global Cooling Unearthed by MIT: Tectonic Clay Efficiently Traps Organic Carbon

Global Cooling Unearthed Tectonic Clay

MIT researchers have discovered that smectite, a clay mineral formed from plate tectonics, can sequester carbon effectively, influencing global climate over millennia. Their findings suggest that smectite has been instrumental in triggering past ice ages and offers potential for future climate change mitigation. Credit:

An accordion-textured clay called smectite efficiently traps organic carbon and could help buffer global warming over millions of years.

MIT geologists have found that a clay mineral on the seafloor, called smectite, has a surprisingly powerful ability to sequester carbon over millions of years.

Under a microscope, a single grain of the clay resembles the folds of an accordion. These folds are known to be effective traps for organic carbon.

Tectonic Origins of Carbon-Trapping Clays

Now, the MIT team has shown that the carbon-trapping clays are a product of plate tectonics: When oceanic crust crushes against a continental plate, it can bring rocks to the surface that, over time, can weather into minerals including smectite. Eventually, the clay sediment settles back in the ocean, where the minerals trap bits of dead organisms in their microscopic folds. This keeps the organic carbon from being consumed by microbes and expelled back into the atmosphere as carbon dioxide.

Over millions of years, smectite can have a global effect, helping to cool the entire planet. Through a series of analyses, the researchers showed that smectite was likely produced after several major tectonic events over the last 500 million years. During each tectonic event, the clays trapped enough carbon to cool the Earth and induce the subsequent ice age.

The findings are the first to show that plate tectonics can trigger ice ages through the production of carbon-trapping smectite.

Smectite Clay Traps Carbon

MIT geologists have found that tectonic activity gives rise to smectite, a type of clay that can sequester a surprising amount of organic carbon within its microscopic folds (shown here), over millions of years. Credit: Photo courtesy of Anthony Priestas, Boston University

Present and Future Potential of Smectite

These clays can be found in certain tectonically active regions today, and the scientists believe that smectite continues to sequester carbon, providing a natural, albeit slow-acting, buffer against humans’ climate-warming activities.

“The influence of these unassuming clay minerals has wide-ranging implications for the habitability of planets,” says Joshua Murray, a graduate student in MIT’s Department of Earth, Atmospheric, and Planetary Sciences. “There may even be a modern application for these clays in offsetting some of the carbon that humanity has placed into the atmosphere.”

Murray and Oliver Jagoutz, professor of geology at MIT, published their findings on November 30 in the journal Nature Geoscience.

Link Between Tectonics and Climate Change

The new study follows up on the team’s previous work, which showed that each of the Earth’s major ice ages was likely triggered by a tectonic event in the tropics. The researchers found that each of these tectonic events exposed ocean rocks called ophiolites to the atmosphere. They put forth the idea that, when a tectonic collision occurs in a tropical region, ophiolites can undergo certain weathering effects, such as exposure to wind, rain, and chemical interactions, that transform the rocks into various minerals, including clays.

“Those clay minerals, depending on the kinds you create, influence the climate in different ways,” Murray explains.

At the time, it was unclear which minerals could come out of this weathering effect, and whether and how these minerals could directly contribute to cooling the planet. So, while it appeared there was a link between plate tectonics and ice ages, the exact mechanism by which one could trigger the other was still in question.

With the new study, the team looked to see whether their proposed tectonic tropical weathering process would produce carbon-trapping minerals, and in quantities that would be sufficient to trigger a global ice age.

Simulation Studies

The team first looked through the geologic literature and compiled data on the ways in which major magmatic minerals weather over time, and on the types of clay minerals this weathering can produce. They then worked these measurements into a weathering simulation of different rock types that are known to be exposed in tectonic collisions.

“Then we look at what happens to these rock types when they break down due to weathering and the influence of a tropical environment, and what minerals form as a result,” Jagoutz says.

Next, they plugged each weathered, “end-product” mineral into a simulation of the Earth’s carbon cycle to see what effect a given mineral might have, either in interacting with organic carbon, such as bits of dead organisms, or with inorganic, in the form of carbon dioxide in the atmosphere.

From these analyses, one mineral had a clear presence and effect: smectite. Not only was the clay a naturally weathered product of tropical tectonics, it was also highly effective at trapping organic carbon. In theory, smectite seemed like a solid connection between tectonics and ice ages.

Tracing Ancient Clays

But were enough of the clays actually present to trigger the previous four ice ages? Ideally, researchers should confirm this by finding smectite in ancient rock layers dating back to each global cooling period.

“Unfortunately, as clays are buried by other sediments, they get cooked a bit, so we can’t measure them directly,” Murray says. “But we can look for their fingerprints.”

The team reasoned that, as smectites are a product of ophiolites, these ocean rocks also bear characteristic elements such as nickel and chromium, which would be preserved in ancient sediments. If smectites were present in the past, nickel and chromium should be as well.

To test this idea, the team looked through a database containing thousands of oceanic sedimentary rocks that were deposited over the last 500 million years. Over this time period, the Earth experienced four separate ice ages. Looking at rocks around each of these periods, the researchers observed large spikes of nickel and chromium, and inferred from this that smectite must also have been present.

The Significant, Long-term Effects of Smectite

By their estimates, the clay mineral could have increased the preservation of organic carbon by less than one-tenth of a percent. In absolute terms, this is a minuscule amount. But over millions of years, they calculated that the clay’s accumulated, sequestered carbon was enough to trigger each of the four major ice ages.

“We found that you really don’t need much of this material to have a huge effect on the climate,” Jagoutz says.

“These clays also have probably contributed some of the Earth’s cooling in the last 3 to 5 million years, before humans got involved,” Murray adds. “In the absence of humans, these clays are probably making a difference to the climate. It’s just such a slow process.”

“Jagoutz and Murray’s work is a nice demonstration of how important it is to consider all biotic and physical components of the global carbon cycle,” says Lee Kump, a professor of geosciences at Penn State University, who was not involved with the study. “Feedbacks among all these components control atmospheric greenhouse gas concentrations on all time scales, from the annual rise and fall of atmospheric carbon dioxide levels to the swings from icehouse to greenhouse over millions of years.”

Potential Applications and Future Research

Could smectites be harnessed intentionally to further bring down the world’s carbon emissions? Murray sees some potential, for instance, to shore up carbon reservoirs such as regions of permafrost. Warming temperatures are predicted to melt permafrost and expose long-buried organic carbon. If smectites could be applied to these regions, the clays could prevent this exposed carbon from escaping into and further warming the atmosphere.

“If you want to understand how nature works, you have to understand it on the mineral and grain scale,” Jagoutz says. “And this is also the way forward for us to find solutions for this climatic catastrophe. If you study these natural processes, there’s a good chance you will stumble on something that will be actually useful.”

Reference: “Palaeozoic cooling modulated by ophiolite weathering through organic carbon preservation” by Joshua Murray, and Oliver Jagoutz, 30 November 2023, Nature Geoscience.
DOI: 10.1038/s41561-023-01342-9

This research was funded, in part, by the National Science Foundation.

4 Comments on "Global Cooling Unearthed by MIT: Tectonic Clay Efficiently Traps Organic Carbon"

  1. Interesting work. It may shed some light on the origin of black shales. However, with respect to the role of tectonically-produced smectite in causing global glaciation, I see a major problem. The periodic nature and duration of Pleistocene glaciation is explained adequately by Milankovitch Cycles. On the other hand, while subduction of tectonic plates is episodic, there is no evidence that it is periodic. It is generally believed that chemical weathering is easiest in magmatic rocks composed of minerals that precipitate early in the Bowen’s Reaction Series. That would be mafic and ultramafic rocks such as are found in oceanic crust. However, Large Igneous Province eruption events can also produce huge outpourings of mafic basalts unrelated to oceanic basalt subduction, which is pretty much going on all the time. I think that there are a lot of loose ends in their conclusions, and that they are too anxious to tie their findings to Anthropogenic Global Warming.

    What “climate catastrophe?” It has been much warmer in the past, such as during the Eocene, and it was a time of rapid evolution of mammals, and deep chemical weathering even outside the tropics.

  2. Curious that so much effort here tries, once again, to link CO2 to climate change. As the plates move they change the ocean circulation patterns, thus causing the distribution of energy carried by ocean waters to change. Could it be that the church of climate change is preparing the parishioners for the coming cooling period?

  3. Nothing renders scientific findings more irrelevant and faulty, unreliable and less scientific than government funding.

  4. The Great flood was NOT caused by US yuppies driving Ford Explorers in the 80’s and 90’s….

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