Isotopic biomarker carbon isotopes

Biomarker Carbon-Isotope Analyses. While a forest/non-forest carbon-isotope signature is readily identifiable in terrestrial environments, it is very difiScult to obtain complete, well dated fluvial sequences. Complete sedimentary sequences are readily available fi-om the submarine fan deposits which lie off the mouth of the Amazon River 82 but the analysis of bulk sediments fi om the marine environment is not appropriate because terrestrially-derived riverbome carbon in the sample rapidly becomes mbced with marine-derived carbon offshore fi om the river mouth. 

Sass E, Kolodny Y (1972) Stable isotopes, chemistry and petrology of carbonate concretions (Mishash formation, Israel). Chem Geol 10 261-286 Sauer PE, EgUnton Tl, Hayes JM, Schimmelmann A, Sessions AL (2001) Compound-specific D/H ratios of hpid biomarkers from sediments as a proxy for environmental and climatic conditions. Geochim Cosmochim Acta 65 213-222... 

Newer instrumental methods of potential utility in organic analysis of environmental and geological biomarkers are compound specific isotope analysis (CSIA) and carbon-14 dating with accelerator mass spectrometry (AMS). CSIA provides the carbon isotope composition of individual... 

Boschker, H.T.S., de Brower, I.F.C., and Cappenberg, T.E. (1999) The contribution of macrophyte-derived organic matter to microbial biomass in salt-marsh sediments Stable carbon isotope analysis of microbial biomarkers. Limnol. Oceanogr. 44, 309-319. 

Schouten, S., Klien, W.C.M., Breteler, K., Blokker, P., Schogt, N., Irene, W., Rupstra, I.C., Grice, K., Bass, M., and Damste J.S.S. (1998) Biosynthetic effects on the stable carbon isotopic compositions of algal lipids Implications for deciphering the carbon isotopic biomarker record. Geochim. Cosmochim. Acta 62, 1397-1406. 

Summons, R.E., Jahnke, L.L., and Roksandic, Z. (1994) Carbon isotopic fractionation in lipids from methanotrophic bacteria relevance for interpretation of the geochemical record of biomarkers. Geochim. Cosmochim. Acta 58, 2853-2863. 

Marine DOC has stable carbon isotope values between —21%o and —22%o (Dmtfel et al., 1992) consistent with a largely marine source. While these data seem to exclude a significant contribution from C3 terrestrial plants, there is increasing evidence for an important contribution from C4 plants to persistent POM in marine sediments on the continental shelf and slope (see below). Desorption of C4 plant carbon and incorporation into oceanic DOC would be difficult to detect by isotopic or molecular biomarker analyses. 

Prahl et al. (1994) also concluded that terrestrial OC contributes significantly to Washington Margin sediments. These authors determined bulk elemental and stable carbon isotopic compositions and concentrations of a range of vascular plant biomarkers (epicuticular wax-derived n-alkanes, lignin-derived phenols and cutin-derived hydroxy-alkanoic acids) for sediments from the Columbia... 

By virtue of where, when, and how the various organic matter inputs were formed and transported to the underlying sediments, it is possible to exploit specific chemical and isotopic characteristics to make inferences about the sources and composition of sedimentary organic matter. Much of this information is inaccessible at the bulk level. For example, bulk elemental compositions and stable carbon isotopic compositions are often insufficiently unique to distinguish and quantify sedimentary inputs. Abundances and distributions of source-specific organic compounds ( biomarkers ) can help to identify specific inputs. However, this molecular marker approach suffers from the fact that the source diagnostic marker compounds are... 

The diversity in stable carbon isotopic compositions evident at the molecular level became apparent with the advent of gas chromatography coupled to isotope ratio mass spectrometry (IRM-GC-MS e.g., Hayes et al., 1990). More recently, age variations among different biomarkers have been investigated (e.g., Eglinton et al., 1997 Pearson et al., 2001). Substantial variability has been observed where inputs from diverse sources are encountered, even within depth horizons representing short periods of sediment accumulation. For example, surficial sediments from the Bermuda Rise in the northern Sargasso Sea deposited over a time span of less than 300 yr... 

Carbon isotopic composition of individual biomarkers in gilsonites (Utah). In Compound-specific Analysis in Biogeochemistry and Petroleum Research (eds. M.Schoell and J. M. Hayes). Org. Geochem. 21, 673-683. 

Jahnke L. L., Summons R. E., Hope J. M., and Des Marais D. J. (1999) Carbon isotopic fractionation in lipids from metha-notrophic bacteria II. The effects of physiology and environmental parameters on the biosynthesis and isotopic signatures of biomarkers. Geochim. Cosmochim. Acta 63, 79-93. 

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