ABSTRACT: The ¹³C/¹²C distributions in plants record the integrated pattern of photosynthetic carbon acquisition. Most planktonic marine algae are small, relatively rare and hard to separate from background particles, so that very few investigations have used delta¹³C to study algal photosynthesis in the sea. Diatoms are perhaps the best studied group among the marine microalgae, and this review summarizes current knowledge of effects of temperature, salinity, pH, growth rate and CO₂ concentrations on diatom delta¹³C. External CO₂ concentrations have the strongest effect demonstrated thus far on ¹³C/¹²C distributions and isotope fractionation, with the largest isotopic discriminations found in high CO₂ conditions. Both models and culture studies suggest that delta¹³C values record the balance between algal growth demand versus supply of inorganic carbon in seawater, and that carbon isotope studies can be used to probe the diversity of algal carbon acquisition strategies in the sea.

KEY WORDS: Diatoms . ¹³C/¹²C . Isotope fractionation . CO₂(aq) . Biomarkers

Published in MEPS Vol. 134 (1996) on April 25
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1996