Development and deployment of lander-based multi-channel Raman spectroscopy for in-situ long-term experiments in extreme deep-sea environment

Fluid seepages in deep-sea cold seep and hydrothermal vent areas transport substances and energy from the lithosphere to the hydrosphere, thereby sustaining the seafloor biosphere. The strong inhomogeneity of cold seep and hydrothermal vent systems in terms of time and spatial scales requires in-situ, long-term, and multi-target detection. However, commercial sensors and the developed deep ocean Raman spectrometers have limitations in obtaining a more comprehensive understanding of cold seep and hydrothermal vent systems. Based on a previously developed deep-sea hybrid Raman insertion Probe (RiP), we developed a novel multi-channel Raman insertion probes system (Multi-RiPs) that can simultaneously detect four targets in situ. Multi-RiPs can be used to analyze the geochemistry of fluid seepage, rocks, gas hydrates, and sediment pore water deployed by deep-sea long-term ocean observation platforms (LOOP). The Multi-RiPs was landed with LOOP near an active cold seep vent in the South China Sea and used for in-situ detection of fluids at different depths in the chemosynthetic communities, methane hydrate quickly formed by the cold seep fluids and authigenic carbonates that were exposed to the ambient seawater from June 2, 2020 to June 10, 2020 (8 days). The in-situ long-term Raman spectra acquired by Multi-RiPs indicated a possible novel sulfur transition pathway existing in the chemosynthetic communities, and dynamic evolution of gas hydrate. Overall, the Multi-RiPs has significant potential for long-term multi-target detection and geochemistry analysis in the deep sea.