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an image of earth that includes the ocean bathymetry Earth’s ocean floors play a larger role in our planet’s carbon cycle than previously understood (PHOTO CREDIT: NASA)

The Carbon Cycle and Solid Earth Connection Redefined

UCLA researchers’ work upends our understanding of the connections between the solid Earth dynamics and the long-term carbon cycle, with implications for the search for life in outer space.

A new study from researchers at UCLA and Penn State, published yesterday in PNAS, sheds light on the last 80 million years of variation in the depth at which carbon is sequestered (CCD) in the ocean. So much light, in fact, that it explains up to 50 percent of the measured changes in the CCD , previously attributed to other causes, potentially changing  the way we understand that process as a whole.  

The carbon cycle, the movement of carbon between the atmosphere, oceans, and continents, is a fundamental process that regulates Earth’s climate. Some things, like volcanic eruptions or human activity, emit carbon dioxide into the atmosphere. Others, such as forests and oceans, absorb that CO2. In a well-regulated system, the right amount of CO2 is being emitted and absorbed to maintain a healthy climate. 

The long-term cycle has a lot of moving parts, all functioning on different time scales. One of those parts, which the researchers were specifically focused on, is seafloor bathymetry – the mean depth and shape of the ocean floor. This is, in turn, controlled by the relative positions of the continent and the oceans, sea level, as well as the flow within Earth’s mantle.  “We were able to show, for the first time, a new major role the shape and depth of our ocean floor plays in the long term carbon cycle,” said Matthew Bogumil, lead author on the paper and PhD student in UCLA’s Department of Earth, Planetary, and Space Sciences. 

“We were able to show, for the first time, a new major role the shape and depth of our ocean floor plays in the long term carbon cycle.”

Matthew Bogumil

We have long known that the ocean is the largest absorber of carbon on our planet and thus also directly controls the amount of atmospheric carbon dioxide. But until now, exactly how changes in seafloor bathymetry over Earth’s history affected the ocean’s ability to sequester carbon in carbonates was not well understood. “Typically, carbon cycle models over Earth’s history consider the seafloor bathymetry as either fixed or a secondary factor. ,” said Tushar Mittal, professor of geosciences at Penn State and one of the paper’s authors. “However, our research shows that both the mean seafloor depth as well as the bathymetric distribution within different ocean basins strongly affect how much carbon is absorbed by oceans and where it is deposited on the seafloor.”

This new understanding of the carbon cycle – that the shape and depth of ocean floors is perhaps the greatest influencer of carbon sequestration – actually has great implications for the search for habitable planets in our universe. 

“When looking at far away planets, we currently have a limited set of tools to give us a hint about their potential for habitability,” said Carolina Lithgow-Bertelloni, one of the paper’s authors and chair of UCLA’s Department of Earth, Planetary, and Space Sciences department. “Now that we understand the important role bathymetry plays in the carbon cycle, we can directly connect the planet’s interior evolution to its surface environment  when making inferences from JWST observations and understanding planetary habitability in general.” 

But this breakthrough represents only the beginning of the researchers’ work in this area. “Now that we know how important bathymetry is in general, we plan to use new simulations and models to better understand how differently shaped ocean floors will specifically affect the carbon cycle and how this has changed over Earth history, especially the Early Earth when most of the land was underwater,” said Bogumil.