A recent study reveals that the shape and depth of the ocean floor account for up to 50% of the changes in oceanic carbon sequestration depth over the past 80 million years. Previous explanations for these changes were attributed to other factors. It has been established that the ocean, the largest carbon absorber on Earth, controls atmospheric carbon dioxide levels. However, the impact of seafloor topography on the ocean's carbon sequestration ability had been unclear.
"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, the paper's lead author and a UCLA doctoral student of earth, planetary, and space sciences.
The long-term carbon cycle operates with various elements over different timescales. One significant element is seafloor bathymetry, which includes the mean depth and shape of the ocean floor. This factor is influenced by the positions of continents and oceans, sea levels, and mantle flow. Carbon cycle models, using paleoclimate datasets, form the basis of our understanding of the global marine carbon cycle and its response to natural disturbances.
"Typically, carbon cycle models over Earth's history consider seafloor bathymetry as either a fixed or a secondary factor," said Tushar Mittal, the paper's co-author and a professor of geosciences at Pennsylvania State University.
Published in Proceedings of the National Academy of Sciences, the study reconstructed bathymetry over the last 80 million years and used a computer model to measure marine carbon sequestration. Results showed that ocean alkalinity, calcite saturation state, and carbonate compensation depth were strongly affected by changes in shallow ocean areas (about 600 meters or less) and the distribution of deeper regions (greater than 1,000 meters). These factors are crucial in understanding how carbon is stored in the ocean floor.
The researchers found that, for the current geologic era, the Cenozoic, bathymetry alone explained 33%-50% of the variation in carbon sequestration. Ignoring bathymetric changes has led researchers to incorrectly attribute changes in carbon sequestration to other factors, such as atmospheric CO2, water column temperature, and silicates and carbonates from 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 possible outcomes and practicality of marine sequestration to mitigate climate change."
This new insight into the influence of ocean floor shape and depth on carbon sequestration also has implications for the search for habitable planets.
"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, a UCLA professor and department chair of earth, planetary and space sciences. "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."
The researchers' work is far from over.
"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's history, especially the early Earth, when most of the land was underwater," Bogumil said.
Research Report:The effects of bathymetry on the long-term carbon cycle and CCD
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