ABSTRACT
The stable carbon isotopic composition of surface water particulate organic matter has been shown to correlate with the concentration of dissolved carbon dioxide. The potential of this proxy has been exploited mainly by palae-oceanographers for the reconstruction of past variations in the ocean and atmospheric CO2, derived from the analysis of the carbon isotopic composition of organic matter in marine sediments. This chapter discusses the observations on the variation of particulate organic matter in the oceans by open ocean studies, as well as the assimilation and carboxylation of inorganic carbon in marine and freshwater algae through laboratory studies. In laboratory studies there is a need for more careful studies on the relationship between CO2 and the level of discrimination against both carbon and oxygen for a wider range of species. Detailed measurements of the isotopic and chemical equilibria of the inorganic carbon system are also necessary if inter-laboratory comparisons of cultured algae are to be realised.
