In situ Raman detection of the deep-sea hydrothermal vent fluids up to 290 °C

Hydrothermal vent fluids play very important role in the deep-sea geochemistry cycle, and support the extreme biological communities. But, there are very few sensors can be used for the in situ measurement of the chemical compositions of the emerging vent fluids. The extremely high temperature and pressure will kill most of them. The traditional sampling technology cannot maintain the sample temperate up to 400 degrees C during sample recovery process from the deep ocean to the lab. In this paper, novel Raman insertions probe for hydrothermal vent fluids (RiP-Hv) has been developed by the Institute of Oceanology, Chinese Academy of Sciences (IOCAS). The design operating temperature can be up to 450 degrees C with the operated depth down to 4500 m. So, it can be directly inserted into the high temperature emerging fluids of the hydrothermal vent. During the sea test cruises at 2015-2016, this RiP-Hv system has been deployed by ROV (remotely operated vehicle) Faxian at the Manus back-arc basin, Papua New Guinea in 2015 and the middle Okinawa Trough back-arc basin in 2016. The in situ Raman spectra of CH4, CO2, H2S, HS-, and SO42- were obtained from the high temperature, focused hydrothermal vents up to 290 degrees C, at water depth down to 1726 m. This probe can also be used for the lower temperature diffuse hydrothermal fluids with the detection limit of 1 mM for CH4. The quantitative analysis models to calculate the concentrations of the high temperature vent fluid compositions are going to set up in the lab simulation experiments. So, the RiP-Hv system provide a very useful tool for investigating the geochemistry of hydrothermal vents fluids, and has extensive applications in other deep-sea research in future.