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

Abstract

The stable carbon isotopic composition of marine particulate organic matter (δ13CPOM) varies with source and environmental conditions. Dissolved carbon dioxide (CO2) concentration is thought to influence δ13CPOM more than temperature, but this relationship is poorly constrained in marginal seas. Here we present δ13CPOM, hydrographic and carbonate system variables at the deep chlorophyll maxima of the southern Yellow Sea in late summer 2017. We find δ13CPOM 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 δ13CPOM was independent of CO2 concentration, whereas the relationship between δ13CPOM and CO2 concentration was dependent on temperature also being correlated with CO2 concentration. We suggest that temperature is the primary determinant of marine δ13CPOM due to temperature-dependent metabolism in phytoplankton, irrespective of inorganic carbon acquisition mode.