A Robust and Sensitive In Situ Analyzer for Simultaneous Methane Carbon and Hydrogen Isotopic Measurements in the Deep Sea

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Despite decades of research, study of the marine methane cycle has been hindered by the difficulties of measuring dissolved gases at the tremendous pressure of the deep ocean. Through development of new sensors capable of continuous methane concentration and isotope measurements, this project aims to provide a better understanding of methane cycling and methane sources in the deep sea and thereby complements the understanding of global dynamics of this greenhouse gas. Recently, Quantum cascade laser-based (QCL) sensors have demonstrated an impressive track record for robust, highly precise and exceptionally sensitive chemical and isotopic measurements under demanding environmental constraints. Coupling a QCL-based sensor with a gas-permeable membrane inlet, this project will develop and deploy an in situ methane isotope sensor for deep ocean biogeochemistry. The sensor will be field-tested on a research cruise in collaboration with the Ocean Exploration Trust utilizing the telepresence-enabled Exploration Vessel (E/V) Nautilus and the remotely operated vehicle (ROV) Hercules, facilitating the simultaneous engagement of educators, students, and the general public in ocean engineering, technology, chemistry, exploration, and science. In an effort to design advanced instrumentation for studying sources and biogeochemical cycling of methane (CH4) in the deep ocean, the investigators will develop a Quantum cascade laser-based in situ methane isotope sensor. By combining an off-axis integrated cavity output spectroscopy-based approach with Quantum cascade lasers, this sensor will be capable of measuring in situ methane isotopes. A primary goal of this project is to demonstrate the use of Quantum cascade laser-based instrumentation for deep sea chemical sensing. A newly designed gas inlet system will be implemented to reduce interference by water and to enhance the sensitivity of in situ stable isotopic analyses. The sensor system will be field tested at a deep-sea methane-rich environment using the E/V Nautilus and the ROV Hercules.