MEPS 182:295-298 (1999)  -  doi:10.3354/meps182295

ABSTRACT: The carbon isotopic fractionation of phytoplankton photosynthesis (ε _p) has been interpreted by previous authors as inconsistent with active bicarbonate uptake. This interpretation contradicts the results of numerous physiological studies demonstrating significant active bicarbonate uptake in phytoplankton. Using a simple model of cellular regulation of carbon acquisition we show that an upward curvature of ε _p as a function of the ratio of growth rate to carbon dioxide concentration does not exclude active bicarbonate uptake. Our model describes adequately published carbon isotope data for cyanobacteria, diatoms, and coccolithophores consistent with active bicarbonate uptake.

KEY WORDS: Phytoplankton · Carbon isotopic fractionation · Model · Active carbon uptake · Bicarbonate · Carbon dioxide