Characteristics of Deep-Sea Turbulence Intensity (Turbulent Kinetic Energy Dissipation Rate) Estimated by Deep-Sea Turbulence Estimation Method

In the vicinity of the deep seafloor, where deep sea mining takes place, the impact on the ecosystem due to the diffusion and re-sedimentation of suspended particles is a matter of concern. To assess these environmental impacts, it is crucial to understand the dynamics of mixing (turbulence) near the deep seafloor. The authors have developed an estimation method for deep-sea turbulence intensity by utilizing data from the Expendable Vertical Microstructure Profile (VMP-X) and Acoustic Doppler Velocimeter (ADV) to gain insights into the turbulence environment near the seafloor. This method allows for capturing the time variation of turbulence intensity, which was previously limited to single measurements. By applying this method, they investigated the hydrothermal vent area of Myojin Knoll in the Izu-Ogasawara Arc and the cold seep area of Hatsushima Island in the Sagami Bay. The study revealed that turbulence intensity can vary significantly even when average flow velocities are similar, indicating that factors beyond average flow strength, such as complex seafloor terrain in hydrothermal areas, influence turbulence intensity. To understand the spreading of suspended particles and the mixing environment near the deep seafloor accurately, it is crucial to estimate deep-sea turbulence intensity alongside the average flow and to identify the determining factors of the mixing environment, such as tidal currents, complex seafloor terrain, and hydrothermal vents. This knowledge will be instrumental in evaluating the environmental impact of deep-sea mining and resource development activities.