Ambiguities regarding the source and diagenetic behavior of particulate and sedimentary OC raised by bulk elemental, stable and radiocarbon isotopic, and biomarker compositions arise largely because of the “one-dimensional” approach often used. Biomarker data may be interpreted in the absence of corresponding isotopic results; stable isotope compositions and radiocarbon ages are discussed without explicit information on the different types of organic materials present in complex materials. Recent advances in the measurement of molecular stable isotope compositions (¹⁴C) of carefully chosen source specific compounds can reduce complexities inherent in bulk analyses and provide further insight for constraining OC source. Molecular radiocarbon activities (¹⁴C) add a third dimension for assessing the fate of OC in the water column and sediments by providing an age component to the biomarkers of choice for comparison with the more conventional (¹⁴C) ages of bulk OC. Individual compounds are isolated by preparative capillary gas chromatography (PCGC) and their radiocarbon compositions (Δ¹⁴C) are determined by isotope accelerator mass spectrometry (AMS).

Compound-specific ¹³C and ¹⁴C measurements link a biomarker to the source biomass and to environmental conditions and history at the time the compound (biomass) was synthesized. The premise on which this connection is based is that biomarkers are isotopically representative of the original biomass from which they derive and isotopic fractionation does not occur during vertical transport and deposition. Source and age characteristics of specific biomarkers are thus independent of complications associated with concentration- or flux-based interpretations and differential diagenetic and preservation processes.

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