West LA Times

The movement of carbon between the atmosphere, oceans, and continents — known as the carbon cycle — is a fundamental process that regulates Earth’s climate. A new study has found that the shape and depth of the ocean floor explain up to 50% of the changes in depth at which carbon has been sequestered over the past 80 million years. This finding could inform ongoing efforts to combat climate change through marine carbon sequestration.

The study highlights that while some factors, such as volcanic eruptions or human activity, emit carbon dioxide into the atmosphere, others like forests and oceans absorb it. In a well-regulated system, the right amount of CO2 is emitted and absorbed to maintain a healthy climate. Carbon sequestration is one tactic in the current battle against climate change.

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

Seafloor bathymetry — the mean depth and shape of the ocean floor — is controlled by factors such as continental positions, sea level, and mantle flow within Earth. Carbon cycle models calibrated with paleoclimate datasets form the basis for understanding how global marine carbon cycles respond to natural perturbations.

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

Published in Proceedings of the National Academy of Sciences, this research reconstructed bathymetry over 80 million years and used computer models to measure marine carbon sequestration. The results indicated that ocean alkalinity, calcite saturation state, and carbonate compensation depth depended significantly on changes to shallow parts of the ocean floor (about 600 meters or less) and on how deeper marine regions (greater than 1,000 meters) are distributed. These measures are critical for understanding how carbon is stored in ocean floors.

For the current geologic era (the Cenozoic), bathymetry alone accounted for 33%–50% of observed variations in carbon sequestration. Researchers concluded that ignoring bathymetric changes leads to mistakenly attributing changes in carbon sequestration to other factors like atmospheric CO2 levels or water column temperature.

“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 stated. “By studying what nature has done in the past, we can learn more about possible outcomes and practicality of marine sequestration.”

This new understanding also aids in searching for habitable planets beyond our solar system. “When looking at faraway planets...we currently have a limited set of tools to give us a hint about their potential for habitability,” said co-author Carolina Lithgow-Bertelloni from UCLA. “Now that we understand [bathymetry's] role...we can directly connect [a planet’s] interior evolution to its surface environment.”

The researchers plan further studies using new simulations and models to better understand how differently shaped ocean floors will specifically affect historical changes in Earth's carbon cycle.