In coccolithophores, stable isotopes recorded in both the calcite exoskeleton (coccoliths), and organic carbon (Corg), can reflect their physiological response to environment, and thereby have a wide usage in paleoclimate and biogeochemistry studies. Recently, Liu et al.1 reported that coccolithophore Ochrosphaera neapolitana has much more positive carbon isotope fractionations relative to dissolved inorganic carbon (DIC) in both coccolith and Corg compared with those published previously for other species2,3,4 and attributed such unexpected positive carbon isotope fractionations to a unique carbon pathway in this species. However, we find that these extreme isotopic fractionations should be attributed to the poor constraints in DIC carbon isotope ratios instead of the coccolithophores’ physiological response to pCO2. More careful measurements of DIC carbon isotope would benefit data interpretations and comparisons in future laboratory culture works focusing on phytoplankton’s response to ocean acidification.
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ARISING FROM Y.-W. Liu et al. Nature Communications https://doi.org/10.1038/s41467-018-04463-7 (2018)
Zhang H., Torres-Romero I. & Stoll H. M., 2022. Re-examining extreme carbon isotope fractionation in the coccolithophore Ochrosphaera neapolitana. Nature Communications 13: 7606. doi: 10.1038/s41467-022-35109-4. Article.
