The shape and depth of the seabed profoundly influence how carbon is stored there, study finds

The movement of carbon between the atmosphere, oceans and continents – the carbon cycle – is a fundamental process that regulates Earth’s climate. Certain factors, such as volcanic eruptions or human activity, emit carbon dioxide into the atmosphere. Others, like forests and oceans, absorb this CO₂. In a well-regulated system, the right amount of CO₂ is emitted and absorbed to maintain a healthy climate. Carbon sequestration is one of the tactics in the current fight against climate change.

A new study finds that the shape and depth of the ocean floor explains up to 50% of the changes in the depth at which carbon has been sequestered in the ocean over the past 80 million years. Previously, these changes were attributed to other causes. Scientists have long known that the ocean, the largest carbon absorber on Earth, directly controls the amount of atmospheric carbon dioxide. But until now, it was not understood exactly how seafloor topographic changes over Earth’s history affected the oceans’ ability to sequester carbon.

The work is published in the journal Proceedings of the National Academy of Sciences.

“We were able to show, for the first time, that the shape and depth of the ocean floor play a major role in the long-term carbon cycle,” said Matthew Bogumil, lead author of the paper and a doctoral student at the UCLA on Earth, planets. and space sciences.

The long-term carbon cycle has many moving parts, all operating on different timescales. One of these is seafloor bathymetry, which is the average depth and shape of the ocean floor. This is, in turn, controlled by the relative positions of the continent and oceans, sea level, as well as flow within the Earth’s mantle. Carbon cycle models calibrated with paleoclimate data sets provide the basis for scientists’ understanding of the global marine carbon cycle and how it responds to natural disturbances.

“In general, carbon cycle models of Earth history view seafloor bathymetry as a fixed or secondary factor,” said Tushar Mittal, co-author of the paper and professor of geosciences at Pennsylvania. State University.

The new research reconstructed bathymetry over the past 80 million years and connected the data to a computer model that measures marine carbon sequestration. The results showed that ocean alkalinity, calcite saturation state, and carbonate clearing depth strongly depended on changes in the shallow parts of the ocean floor (about 600 meters or less) and the distribution of regions deeper seas (greater than 1,000 meters). These three measurements are essential to understanding how carbon is stored in the seabed.

The researchers also found that for the current geological era, the Cenozoic, bathymetry alone accounted for 33-50% of the observed variation in carbon sequestration and concluded that by ignoring bathymetric changes, the researchers attribute attributing changes in carbon sequestration to other, less certain factors. , like atmospheric CO₂the temperature of the water column and the silicates and carbonates released into the ocean by rivers.

“Understanding important long-term carbon cycle processes can better inform scientists working today on marine carbon dioxide removal technologies to combat climate change,” Bogumil said. “By studying what nature has done in the past, we can learn more about the possible outcomes and practicality of marine sequestration to mitigate climate change.”

This new understanding that the shape and depth of the ocean floor is perhaps the greatest influence on carbon sequestration may also make it easier to find habitable planets in our universe.

“When we observe distant planets, we currently have a limited set of tools to give us an idea of ​​their habitability potential,” said co-author Carolina Lithgow-Bertelloni, a UCLA professor and director from the Department of Earth, Planetary and Space Sciences. “Now that we understand the important role bathymetry plays in the carbon cycle, we can directly relate the planet’s interior evolution to its surface environment by making inferences from JWST observations and understanding habitability planetary in general.”

This major advance represents only the beginning of the researchers’ work.

“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 time. of Earth’s history, especially early Earth when most of the earth was underwater,” Bogumil said.