Advancing an In situ Laser Spectrometer for Carbon Isotope Analyses in the Deep Ocean

Development of in situ chemical sensors is critical for improving our understanding of deep-ocean biogeochemistry and recent advances in chemical sensors are already expanding the breadth and depth of deep sea/seafloor exploration and research. Although initially developed for high sensitivity measurements of atmospheric gases, laser-based spectroscopic sensors are now being developed for research in the deep sea by incorporating the use of semi-permeable membranes. Here we present on recent deep-sea deployments of an in situ laser-based analyzer of carbon isotopes of methane (δ¹³CH₄), highlighting several advances including a new capability for also measuring δ¹³C of DIC or CO₂ by incorporating a second laser and an in line acidification module. A bubble trapping approach was designed and implemented for the collection and analysis of both CH₄ and CO₂ from deep-sea bubbles. The newly advanced laser spectrometer was deployed at both Kick ‘Em Jenny volcano off of the island of Grenada and in a brine pool in the western Gulf of Mexico (“The Jacuzzi of Despair”) using the E/V Nautilus and the ROV Hercules. At Kick ‘Em Jenny, seafloor measurements were made of both emanating fluids and bubbles from within and around the crater – revealing high levels of magmatic CO₂ with minor amounts of CH₄ and hydrogen sulfide. At the brine pool, spot measurements and depth profile measurements into the brine pool were made for chemical mapping, revealing fluids that were saturated with respect to methane. New technologies such as the laser spectrometer will enable us to obtain high resolution and near real-time, in situ chemical and isotopic data and to make geochemical maps over a range of spatial and temporal scales.