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20 pages, 8 figures, 2 tables, Recent work using compound-specific stable isotopes of amino acids (CSI-AA) in proteinaceous deep-sea corals opens a new realm of high-fidelity reconstruction for biogeochemical and ecological changes in the ocean. However, underlying these CSI-AA paleoceanographic applications are a series of fundamental assumptions, which hold first that baseline-proxy AA isotope values fixed at the base of food webs represent integrated δ13C and δ15N values of primary production, and second they are unaltered during subsequent export and incorporation from particles into corals. We explored long-term δ13C and δ15N CSI-AA data on a sediment trap time series together with contemporaneous, geographically close deep-sea bamboo corals (Isidella sp.) in the California margin, directly testing these assumptions for the first time. Our data show that isotope values of essential (δ13CEAA) and source AAs (δ15NPhe) in sinking particles quantitatively track bulk δ13C and δ15N values of export production. These CSI-AA baseline proxies varied independently of carbon flux, trophic position (TPCSI-AA) and microbial alteration, suggesting that they were well preserved in the sinking particles consumed by corals. Paired comparisons between sinking particles and corals revealed minor elevations of δ13CEAA (by ∼2‰) and δ15NPhe (by ∼1‰) in available coral specimens. We hypothesize that the difference in δ13CEAA is due to the geographic offset in δ13C values of primary production expected between the (more offshore) sediment trap site and (more onshore) coral specimens, whereas the δ15NPhe offset is likely related to expected minor trophic fractionation. Using empirical models derived from the sediment trap time series, we demonstrate for the first time that CSI-AA in proteinaceous deep-sea corals can reconstruct known bulk δ15N values of export production, source nitrogen δ15N values, and exported TPCSI-AA values with very good fidelity. Together, these findings represent a major advance in our understanding of AA isotope behavior in modern and paleoarchives, and can be used to underpin the rapidly evolving use of CSI-AA-based tools in multiple paleoceanographic studies and archives, This study was supported by National Science Foundation (OCE 1635527 to T.G. and M.M). A portion of this work was performed under the auspices of the U.S. Department of Energy (DE-AC52-07NA27344)

Production of oil and gas from shales and other unconventional hydrocarbon-bearing reservoirs has increased dramatically in recent years, largely as a result of technological developments in horizontal drilling and hydraulic fracturing. This increase has been accompanied by growing awareness of the environmental impacts of drilling and production activities, with a particular emphasis on groundwater quality. The presence of natural gas in groundwater is a health and explosion hazard. It also may indicate hydraulic connectivity with deeper hydrocarbon reservoirs, along which formation and drilling fluids that could migrate upward. Gas in groundwater occurs naturally through microbial activity and connection with microbial or thermogenic hydrocarbon accumulations. More rarely, hydrocarbon gases can migrate upward along the annuli of well bores and into shallow aquifers. The ability to distinguish between in situ and migrated natural gas underlies recent baseline water quality regulations in jurisdictions such as the state of Colorado. Stable isotope analysis forms a critical element of natural gas identification and fingerprinting protocols. This chapter reviews analytical and interpretive methods of compound-specific stable isotope analysis of natural gas.

Publisher Summary This chapter focuses on the deep-sea corals. Deep-Sea corals provide a widespread archive of oceanographic processes, with annual- to decadal-resolution records spanning several centuries in length. They are ideally suited to the study of rapid changes, such as that which characterized the Pleistocene–Holocene transition. Deep-sea scleractinians exhibit a wide variety of growth forms, from simple, solitary cup corals to complex, branching colonies. The corallite is lengthened by periodic uplift of the polyp and formation of a new dissepiment. The wall of the corallite is called the theca. A series of thin vertical sheets, the septa, radiate from the theca into the center of the corallite. The key utility of corals in paleoceanography is that long records of ambient conditions are locked into the growing skeleton in successive layers. When dealing with tropical reef scleractinians, massive colonies are selected for climate reconstructions because of the simplicity of their growth banding. Deep-sea scleractinians have more complicated cup and branching morphologies, making it difficult to visualize and sample the growth layers. The chapter discusses the growth and sclerochronology in deep-sea scleractinians, growth and sclerochronology in horny corals, sources of carbon to deep-sea corals, and stable isotopic disequilibria in deep-sea corals.