Predictive isotopic biogeochemistry: Hydrocarbons from anoxic marine basins

• Published in: Organic geochemistry 1994, Vol.21 (6), p.629-644
• Main Authors: Freeman, Katherine H., Wakeham, Stuart G., Hayes, J.M.
• Format: Article
• Language: English
• Subjects: anoxic sediments; Applied sciences; Bacteria; Biomass; Black Sea; Carbon - analysis; Carbon - chemistry; Carbon Dioxide; Carbon Isotopes; Cariaco Trench; Constitution and properties of crude oils, shale oils, natural gas and bitumens. Analysis and characteristics; Crude oil, natural gas and petroleum products; diploptene; dissolved inorganic carbon; Earth sciences; Earth, ocean, space; Energy; Environmental Microbiology; Europe; Exact sciences and technology; Fuels; Gas Chromatography-Mass Spectrometry; Geologic Sediments - analysis; Geologic Sediments - chemistry; Geologic Sediments - microbiology; Hydrocarbons; Hydrocarbons - analysis; Hydrocarbons - chemistry; Hydrocarbons - metabolism; Isotope geochemistry; Isotope geochemistry. Geochronology; lycopane; Marine Biology; methanogens; Oceans and Seas; particulate organic carbon; pentamethyleicosane; Phytoplankton; Sedimentary rocks; Space life sciences; squalene
• ISSN: 0146-6380; 1873-5290
• DOI: 10.1016/0146-6380(94)90009-4

Carbon isotopic compositions were determined for individual hydrocarbons in water column and sediment samples from the Cariaco Trench and Black Sea. In order to identify hydrocarbons derived from phytoplankton, the isotopic compositions expected for biomass of autotrophic organisms living in surface waters of both localities were calculated based on the concentrations of CO 2(aq) and the isotopic compositions of dissolved inorganic carbon. These calculated values are compared to measured δ values for particulate organic carbon and for individual hydrocarbon compounds. Specifically, we find that lycopane is probably derived from phytoplankton and that diploptene is derived from the lipids of chemoautotrophs living above the oxic/anoxic boundary. Three acyclic isoprenoids that have been considered markers for methanogens, pentamethyleicosane and two hydrogenated squalenes, have different δ values and apparently do not derive from a common source. Based on the concentration profiles and isotopic compositions, the C 31 and C 33 n-alkanes and n-alkenes have a similar source, and both may have a planktonic origin. If so, previously assigned terrestrial origins of organic matter in some Black Sea sediments may be erroneous.