DEEP-SEA HYDROTHERMAL EXPLORATION BASED ON MULTI-SENSOR DATA PROCESSING: A CASE STUDY IN THE OKINAWA TROUGH

To date, multi-beam echo sounder (MBES) equipped on Research vessels and AUVs has been widely accepted as a powerful tool for detecting interception of any rising, buoyant hydrothermal plumes, without water sampling (Nakamura et al., 2015). Although utilization of water column sonar data enabled us to achieve certain results, to find new vents, this approach is not sufficient to distinguish cold seeps and hydrothermal vents, and moreover, it is inadequate to determine hydrothermal plumes with a low gas content.

To improve efficiency and accuracy of exploring hydrothermal plumes and to understand their properties, we use multi-sensor data such as temperature, turbidity, redox potential, and methane concentration. In this presentation, we will introduce data-driven analytical techniques to determine chemical properties of the water masses, and make a comparative review of 3 discrete hydrothermal fields in the Okinawa Trough. Each hydrothermal field has different features: i) Yokosuka Field, the highest temperature vent-site on record in the Okinawa Trough (364.1°C at 2183m depth), shows strong water column acoustic reflections and consistently detectable sharp peaks in turbidity, redox potential, and methane concentration. ii) Futagoyama Field is characterized by its gas seeps, strong water column acoustic reflections, and little change in turbidity and redox potential. iii) hydrothermal field off-Kume Island, which includes at least 9 active hydrothermal vents, is characterized by its acoustically invisible plumes, low H₂S content, as well as sharp peaks in turbidity, redox potential, and methane concentration. These case studies will provide an insight into the feature of each hydrothermal activity, and ensure much more efficient use of deep-submergence assets such as human occupied vehicles and remotely operated vehicles during follow-on studies.