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 potentia l applications to paleoclimatology are evaluated in the present study. The potential use of the carbon isotope ratios of marine biomarkers as recorder s of CO2 levels has been considered. A significant correlation between delt a(13)C cholesterol of suspended particulates and seawater CO2 concentration s from the south Indian Ocean has been found. delta(13)C composition in bio markers of different functionalities from three photosynthetic organisms ha s been examined. Small variations within and between biosynthetically relat ed compound classes have been observed in cyanobacteria. In algae, e.g. dia toms and dinoflagellates, significant differences between the average delta (13)C composition of fatty acids and sterols were observed (7.5 parts per t housand and 2 parts per thousand, respectively). These differences can be a ttributed to diverse isotope effects associated with different biosynthetic reactions. Isotopic variations among homologues of the same lipid class ha ve also been observed. In diatoms, variations were up to 5 parts per thousa nd within each class of fatty acids and sterols and in the dinoflagellate s pecies, these variations were lower than 3 parts per thousand. These differ ences, and particularly the intra-specific shifts in delta(13)C lipid compo sition, must be considered for the correct interpretation of changes in del ta(13)C molecular signatures in the marine environment. (C) 1999 Elsevier S cience B.V. All rights reserved.