Hakim, Kaustubh ; Tian, Meng ; Bower, Dan J. ; Heng, Kevin

published in Astrophysical Journal Letters, 942 issue L20 (2023)

Abstract: The American Astronomical Society, find out more. The Institute of Physics, find out more. THE FOLLOWING ARTICLE ISOPEN ACCESS Diverse Carbonates in Exoplanet Oceans Promote the Carbon Cycle Kaustubh Hakim1, Meng Tian1, Dan J. Bower1, and Kevin Heng2,3,4 Published 2023 January 5 • © 2023. The Author(s). Published by the American Astronomical Society. The Astrophysical Journal Letters, Volume 942, Number 1 Citation Kaustubh Hakim et al 2023 ApJL 942 L20 DOI 10.3847/2041-8213/aca90c DownloadArticle PDF DownloadArticle ePub Figures Tables References Article metrics 981 Total downloads 11 citation on Dimensions. MathJax Turn off MathJax Share this article Share this content via email Share on Facebook (opens new window) Share on Twitter (opens new window) Share on Mendeley (opens new window) Article and author information 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: 10.3847/2041-8213/aca90c
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