Biomarkers isotopic composition

The haptophyte microalga Emiliania huxleyi produces biomarkers in the form of long-chain (C37, C38, and C39) alkenones (Brassell, 1993). Alkenones are well preserved in marine sediments and their molecular distributions and isotopic composition have been used to infer paleo-temperatures (Brassell, 1993) and pC022 values (Jasper et ak, 1994), respectively. Unsaturation patterns in the alkenone series are related to the growth temperature of the haptophyte algae that produce these compounds (Brassell et ak, 1986 Prahl and Wakeham, 1987), and hold great promise as indicators of absolute ocean paleotemperature. 

Mansuy et al. [97] investigated the use of GC-C-IRMS as a complimentary correlation technique to GC and GC-MS, particularly for spilled crude oils and hydrocarbon samples that have undergone extensive weathering. In their study, a variety of oils and refined hydrocarbon products, weathered both artificially and naturally, were analyzed by GC, GC-MS, and GC-C-IRMS. The authors reported that in case of samples which have lost their more volatile n-alkanes as a result of weathering, the isotopic compositions of the individual compounds were not found to be extensively affected. Hence, GC-C-IRMS was shown to be useful for correlation of refined products dominated by n-alkanes in the C10-C20 region and containing none of the biomarkers more commonly used for source correlation purposes. For extensively weathered crude oils which have lost all of their n-alkanes,it has been demonstrated that isolation and pyrolysis of the asphaltenes followed by GC-C-IRMS of the individual pyrolysis products can be used for correlation purposes with their unaltered counterparts [97]. 

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... 

Canuel, E.A., Freeman, K.H., and Wakeham, S.G (1997) Isotopic compositions of lipid biomarker compounds in estuarine plants and surface sediments. Limnol. Oceanogr. 42, 1570-1583. 

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. 

Shi, W., Sun, M.Y., Molina, M., and Hodson, R.E. (2001) Variability in the distribution of lipid biomarkers and their molecular isotopic composition in Altamaha estuarine sediments implications for the relative contribution or organic matter from various sources. Org. Geochem. 32, 453-468. 

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... 

In this chapter the case of the oxygen isotopic composition of the Dales Gorge Member of the Brockman iron formation will be considered (Figure 3). This formation is underlain by shales of the Marra Mamba Formation that contain extractable hydrocarbon biomarkers generated before or during a peak regional metamorphic event 2,450-2,000 Ma (Brocks et al., 1999). It is unlikely that such labile material could have survived the pervasive fluid migration that would... 

Changes in abundance and isotopic composition of biomarker compounds can help delineate relative mass contributions from terrestrial, marine algal, and bacterial OM sources, as well as provide indications of specific processes and environmental conditions in ancient water... 

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. 

Grice K., Schaeffer P., Schwark L., and Maxwell J. R. (1997) Changes in palaeoenvironmental conditions during deposition of the Permian Kupferschiefer (Lower Rhine Basin, northwest Germany) inferred from molecular and isotopic compositions of biomarker components. Org. Geochem. 26, 677-690. 

The molecular distribution and compound-specific carbon-isotopic composition of hydrocarbons can be used to qualify and quantify their sources and pathways in the environment. Molecular source apportionment borrows from molecular methods that were developed and applied extensively for fundamental oil biomarker studies, oil-oil and oil source rock correlation analysis. Additionally, petroleum refinement produces well-defined mass and volatility ranges that are used as indicators of specific petroleum product sources in the environment. Compound-specific carbon-isotopic measurement is a more recent addition to the arsenal of methods for hydrocarbon source apportionment. Carbon isotopic discrimination of i-alkanes, biomarkers, and PAHs has shown that the technique is highly complementary to molecular apportionment methods. 

Jasper, J. P. Gagosian, R. B. 1993. The relationship between sedimentary organic carbon isotopic composition and organic biomarker compound concentration. Geochimica et Cosmochimica Acta, 57, 167-186. 

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