The long-term surface carbon cycle is a balance of carbon fluxes between sources (e.g., volcanoes) and sinks (primarily carbon burial by carbonate-bearing minerals following surface weathering, which are then recycled via subduction). This process has helped to regulate climate throughout Earth’s history and ensured continued surface habitability. Where, when, and how carbon is sequestered from the atmosphere into seafloor carbonate sediments is critical for understanding climate evolution and how it responds to perturbations (e.g., anthropogenic and large volcanic eruptions). Since the carbonates are deposited on the seafloor, the spatial distribution of the seafloor depths (i.e., the seafloor bathymetry) directly determines when and how much carbonates are sequestered, hence the net C removal. Seafloor bathymetry, controlled by Earth’s interior processes significantly evolves over 10s of millions of years. The effects on Earth’s carbon cycle have not been carefully explored before.
EPSS Grad student Matthew Bogumil, Prof. Carolina Lithgow-Bertelloni, and Penn State’s Prof. Tushar Mittal have shown that bathymetry, both the mean seafloor depths and the full depth distribution, exert significant control on ocean chemistry (e.g., ocean acidity and alkalinity). This is important because it demonstrates that seafloor bathymetry directly affects the global carbon cycle and atmospheric CO2 since the oceans are the biggest surface carbon reservoir. Considering the plausible range of bathymetric configurations over the last 80 Myr of Earth’s history, as much as 50% of the observed changes in the carbonate sequestration depth can be explained by changes in bathymetry alone rather than changes in volcanic sources and/or terrestrial weathering. Our results highlight that the evolving solid Earth provides not only a boundary condition for surface processes but can also control physical-chemical feedbacks. These findings are not limited to our home planet and are relevant for understanding the planetary habitability of terrestrial-like planets.
Read more on the UCLA Division of Physical Sciences website, or the PNAS publication.