Stable carbon isotope fractionation by marine phytoplankton during photosynthesis

In the marine environment, the range of values of carbon isotope fractionation between particulate tissue of phytoplankton and inorganic carbon can be more than 20‰ (− 35‰ < δ 13 C < − 14‰). This review considers the influence of seawater temperature, lipid content of phytoplanktonic cells, kinetic fractionation, and carbon pathway on δ 13 C values observed at sea. In order to study the contribution of carboxylases (RUBISCO and the β‐carboxylases phosphoenolpyruvate carboxylase, phosphoenoplpyruvate carboxykinase and pyruvate carboxylase) to variations of particulate δ 13 C values at sea, we present results obtained simultenously on carboxylase activities and δ 13 C in various environmental conditions. The lowest δ 13 C values are clearly associated with predominance of ribulose‐1.5‐bisphosphate carboxylase activity, but it was more difficult to explain the high δ 13 C values. Different hypotheses are discussed.