An in-situ chemical sensor system for cabled ocean observatory applications at hydrothermal vents

An in-situ chemical sensor system was developed for long term monitoring of hydrothermal vent fluids as part of the US NSF Ocean Observatory Initiative (OOI) Regional Scale Nodes (RSN) in the Northeast Pacific Ocean. The sensor wand design is based on Yittria-stabilized zirconia (YSZ) ceramic membrane electrode in conjunction with Ag|AgCl reference electrode, Au or Pt redox electrode and Ag|Ag₂S (H₂S) electrode. The YSZ ceramic electrode was constructed with a titanium tube for the long term deployment application. To achieve high measurement accuracy, the high impedance signal of the YSZ ceramic electrode was converted to the low impedance signal by a pre-amplifier. The instrument utilizes the power supply and bandwidth of the fiber optic ocean cable to conduct continuous monitoring of the hot vent fluids. The instrument was deployed on Regional Scale Nodes (RSN) Axial Seamount site via MJ03C mid-power junction box. A modified version of the instrument was also deployed multi times by DSV Alvin during AT26-17 cruise on Axial Seamount and Main Endeavour Field (MEF) vent field, Juan De Fuca Ridge. This integrated electrochemical system has successfully measured pH, dissolved H₂ and H₂S of hydrothermal vent fluids at 300 °C and 220 bars.