Relationship between aqueous CO2 concentrations and stable carbon isotope discrimination in the diatoms Chaetoceros calcitrans and Ditylum brightwellii

Abstract

Recent work has focused on a possible relationship between marine organic δ13C and the concentration of carbon dioxide dissolved in seawater [CO2(aq)]. This relationship is based on the general assumption that diffusive CO2 uptake is the main pathway of photosynthetic carbon acquisition by phytoplankton. This study found an inverse linear relationship between [CO2(aq)] and organic δ13C in the marine diatoms Chaetoceros calcitrans and Ditylum brightwellii. However, the relationship was not a function of diffusive CO2 use by these diatoms, which have previously been shown to be HCO3- users. Our findings underline the importance of understanding the mechanisms of phytoplankton carbon acquisition in interpreting carbon isotope data.