ABSTRACT: Recent work has focused on a possible relationship between marine organic d¹³C 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 d¹³C 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.

KEY WORDS: Organic d¹³C · Carbon dioxide · Bicarbonate · Chaetoceros calcitrans · Ditylum brightwellii

Published in MEPS Vol. 171 (1998) on October 1
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1998