Temperature is a better predictor of stable carbon isotopic compositions in marine particulates than dissolved CO2 concentration

What is it about?

The stable carbon isotopic composition of marine particulate organic matter (δ13C_POM) varies with source and environmental conditions. Dissolved carbon dioxide (CO2) concentration is thought to influence δ13C_POM more than temperature, but this relationship is poorly constrained in marginal seas. Here we present δ13C_POM, hydrographic and carbonate system variables at the deep chlorophyll maxima of the southern Yellow Sea in late summer 2017. We find δ13C_POM values varied between stable and cyclonic gyre regions, but indicated autochthonous organic matter production and were more strongly correlated with temperature than dissolved CO2 concentration throughout. We find that the relationship between temperature and δ13C_POM was independent of CO2 concentration, whereas the relationship between δ13C_POM and CO2 concentration was dependent on temperature also being correlated with CO2 concentration. We suggest that temperature is the primary determinant of marine δ13C_POM due to temperature-dependent metabolism in phytoplankton, irrespective of inorganic carbon acquisition mode.

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Why is it important?

Although dissolved carbon dioxide concentration was thought to influence δ13C_POM more than temperature, we suggest that temperature is the primary determinant of marine δ13C_POM, irrespective of inorganic carbon acquisition mode.