Enhancement of Capabilities for Molecular-Level Radiocarbon Studies of Water Column and Sedimentary Organic Matter

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Since measurements of 14C contents of individual organic compounds isolated from marine sediments were first published almost a decade ago, compound specific radiocarbon analysis (CSRA) has met with increasing interest by the ocean science community. While subsequent applications of this approach have provided important new insights into the cycling of dissolved and particulate organic matter in the ocean, our interpretations remain rudimentary, largely because of the sparse nature of existing data sets. This paucity of molecular-level 14C information manifests itself in two ways -- the limited number of samples investigated thus far, and the narrow range of molecular species that have been isotopically characterized. With funding through this grant, a team of organic geochemists at the Woods Hole Oceanographic Institution will purchase instrumentation that upgrades and enhances their existing capabilities for CSRA, with the goal of (i) expanding the range of compounds amenable to 14C measurement, and (ii) increasing sample throughput. The instrumentation includes a preparative capillary gas chromatography (PCGC) system to replace the preexisting 12-year-old model, and a semi-preparative liquid chromatography/mass spectrometry (LC/MS) system. Together, these instruments will provide broad capabilities that will be shared among, and meet the needs of, the PIs. Future applications include molecular isotopic characterization of refractory macromolecular components of dissolved and particulate organic matter, and of volatile and dissolved halogenated organic compounds. In the near future, natural abundance 14C measurements by continuous-flow accelerator mass spectrometry (CF-AMS) will undoubtedly become reality. Both PCGC and LC represent viable modes of sample introduction for CF-AMS, and the PIs will devote considerable time and effort to developing chromatographic methods compatible with this exciting new technology.Scientific Merit and Broader Impacts. Molecular-level natural abundance 14C measurements have become an important component of biogeochemical studies of marine dissolved and particulate organic matter. This methodological approach, which was born in the ocean sciences, is now finding applications in other fields such as environmental chemistry and archaeology. Through access to the proposed instrumentation, the PIs hope to further expand the applicability and utility of compound specific radiocarbon analysis. The PIs are each active in advising graduate and undergraduate summer students, and the new research capabilities made available through the proposed instrumentation will provide unique and challenging opportunities for students to become involved in, and spearhead, interdisciplinary research. As part of this proposal, a graduate student will play an integral role in exploring the capabilities of the new instrumentation with a view towards developing protocols for molecular-level 14C measurements via CF-AMS