Carbon isotope ratio monitoring-gas chromatography mass spectrometric measurements in the marine environment: biomarker sources and paleoclimate applications

Some applications in the use of compound-specific isotopic analyses (CSIA) for biomarker source elucidation in the marine environment and its potential applications to paleoclimatology are evaluated in the present study. The potential use of the carbon isotope ratios of marine biomarkers as recorders of CO2 levels has been considered. A significant correlation between delta(13)C cholesterol of suspended particulates and seawater CO2 concentrations from the south Indian Ocean has been found. delta(13)C composition in biomarkers of different functionalities from three photosynthetic organisms has been examined. Small variations within and between biosynthetically related compound classes have been observed in cyanobacteria. In algae, e.g. diatoms and dinoflagellates, significant differences between the average delta(13)C composition of fatty acids and sterols were observed (7.5 parts per thousand and 2 parts per thousand, respectively). These differences can be attributed to diverse isotope effects associated with different biosynthetic reactions. Isotopic variations among homologues of the same lipid class have also been observed. In diatoms, variations were up to 5 parts per thousand within each class of fatty acids and sterols and in the dinoflagellate species, these variations were lower than 3 parts per thousand. These differences, and particularly the intra-specific shifts in delta(13)C lipid composition, must be considered for the correct interpretation of changes in delta(13)C molecular signatures in the marine environment. (C) 1999 Elsevier Science B.V. All rights reserved.