| Compound-specific carbon isotopic analyses can be used to follow the production and reworking of marine organic matter. Molecular indicators of sources of organic carbon, or lipid biomarkers, have been used to reconstruct biological communities in settings ranging from modern oceans and terrestrial environments to those from the Precambrian. The isotopic compositions of these biomarkers can reflect paleoceanographic conditions, sources of organic carbon, and biogeochemical processes.;The abundances and isotopic compositions of lipids, in particular algal sterols, reflect the primary producer community and environment, notably concentrations of CO2 and nutrients. Some lipid biomarkers are produced mainly by heterotrophic or consumer organisms. The delta13C values of such biomarkers reflect both the food source and fractionations associated with metabolism. Such processes are studied here using isotopic compositions of dietary algae and animal tissues in samples from Botany Bay, Sydney, Australia. These data help to constrain the fractionation of carbon isotopes during consumption of primary products and its effects on the sedimentary lipid record.;The isotopic compositions of major sterol biomarkers from the sediments of the Ross Sea, Antarctica, yield information about phytoplanktonic communities and environments. The relationships between delta13C values of the sterols indicate similarities or differences in sources of the compounds, aiding in reconstruction of average phytoplankton bloom assemblages throughout the Ross Sea, Antarctica, over the last 1000-10,000 yrs. Carbon isotopic patterns observed in total organic carbon are mirrored by variations in primary products, showing that these patterns are the result of changes in autochthonous organic carbon rather than variations in inputs of allochthonous material. |
