The shape and depth of the ocean floor profoundly affect how carbon is stored there, the study shows

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

A new study finds that the shape and depth of the ocean floor explain 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, Earth’s largest carbon sink, directly controls the amount of atmospheric carbon dioxide. But until now, it was not well understood how changes in seafloor topography over Earth’s history affect the ocean’s ability to sequester carbon.

The work was 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 plays a major role in the long-term carbon cycle,” said Matthew Bogumil, lead author of the paper and a UCLA doctoral student on Earth , planetary. and space sciences.

The long-term carbon cycle has many moving parts, all operating on different time scales. One of those parts is sea bathymetry – the average depth and shape of the ocean floor. This, in turn, is controlled by the relative positions of the continent and oceans, sea level, and the flow within the Earth’s mantle. Carbon cycle models calibrated with paleoclimate datasets form the basis for scientists’ understanding of the global marine carbon cycle and how it responds to natural perturbations.

“Typically, models of the carbon cycle throughout Earth’s history consider seafloor bathometry as a fixed or secondary factor,” said Tushar Mittal, co-author of the paper and a professor of geosciences at Pennsylvania State University.

The new research reconstructed bathymetry over the past 80 million years and fed the data into a computer model that measures marine carbon sequestration. The results showed that ocean alkalinity, the state of calcite saturation, and the depth of carbonate compensation depended strongly on changes in the shallow parts of the ocean floor (about 600 meters or less) and how the deeper marine regions are distributed ( more than 1000 meters). These three measures are critical to understanding how carbon is stored on the ocean floor.

The researchers also found that for the current geologic era, Cenozoic bathymetry alone accounted for 33%–50% of the observed variation in carbon sequestration, and concluded that by ignoring bathymetric changes, researchers mistakenly attribute changes in carbon sequestration to other less important factors. certain. , such as atmospheric CO₂water column temperature and silicates and carbonates washed into the ocean by rivers.

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

This new understanding that the shape and depth of ocean floors is perhaps the biggest influencer of carbon sequestration may also help the search for habitable planets in our universe.

“When we look at distant planets, we currently have a limited set of tools to give us a hint of their potential for habitability,” said co-author Carolina Lithgow-Bertelloni, a UCLA professor and chair of the department of Earth, planetary sciences. and spatial. “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 when inferring from JWST observations and understanding planetary habitability in general.”

The discovery represents just 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 how this has changed during the history of the Earth, especially the early Earth, when most of the land was under water,” said Bogumil.