Fluctuation of High-Turbidity Water Measured by Acoustic Doppler Current Profiler at the Izena Calderon in the Okinawa Trough

Abstract

Hydrothermal processes associated with spreading centers of plate-tectonic activity form seafloor massive sulfide (SMS) deposits. Given that the SMS deposits found in the western Pacific have been considered to be potential sources of gold (Au), silver (Ag), cupper (Cu), zinc (Zn), and lead (Pb) including manganese nodules and cobalt-rich manganese crusts, there is a strong possibility that they will be mined in near future. In order to take measures against environmental impact during the mining of SMS deposits, it is important to measure components of hydrothermal origin with high temporal and spatial resolution on site, and to understand the ecosystem in the hydrothermal environment. In this study, we first propose a measurement method of turbidity profiles using an Acoustic Doppler Current Profiler (ADCP). Applying this method to the ADCP measurements in the Izena Calderon with SMS in the Okinawa Trough, we verify that this method can extract turbidity data from echo intensities measured by ADCP. Subsequently, we describe the high-turbidity water in the Izena Calderon measured by ADCP, and present and discuss the turbidity fluctuations estimated by applying time-frequency analysis to these turbidity data.