Diverse Carbonates in Exoplanet Oceans Promote the Carbon Cycle

This is a Preprint and has not been peer reviewed. The published version of this Preprint is available: https://doi.org/10.3847/2041-8213/aca90c. This is version 1 of this Preprint.

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Authors

Kaustubh Hakim, Meng Tian , Dan James Bower , Kevin Heng 

Abstract

Carbonate precipitation in oceans is essential for the carbonate-silicate cycle (inorganic carbon cycle) to maintain temperate climates. By considering the thermodynamics of carbonate chemistry, we demonstrate that the ocean pH decreases by approximately 0.5 for a factor of 10 increase in the atmospheric carbon dioxide content. The upper and lower limits of ocean pH are within 1-4 of each other, where the upper limit is buffered by carbonate precipitation and defines the ocean pH when the carbon cycle operates. If the carbonate compensation depth (CCD) resides above the ocean floor, then carbonate precipitation and the carbon cycle cease to operate. The CCD is deep (>40 km) for high ocean temperature and high atmospheric carbon dioxide content. Key divalent carbonates of magnesium, calcium and iron produce an increasingly wider parameter space of deep CCDs, suggesting that chemical diversity promotes the carbon cycle. The search for life from exoplanets will benefit by including chemically more diverse targets than Earth twins.

DOI

https://doi.org/10.31223/X59M4X

Subjects

Astrophysics and Astronomy, Planetary Geochemistry, Planetary Sciences

Keywords

Extrasolar rocky planets, carbon dioxide, Habitable zone, Ocean-Atmosphere interactions, Geological processes

Dates

Published: 2023-12-22 21:51

Last Updated: 2023-12-23 05:51

License

CC BY Attribution 4.0 International