Assessment of gas fluxes from Yokosuka hydrothermal field in the western Pacific Ocean based on in situ observations

The hydrothermal system annually releases a significant amount of gases into the ocean, serving as a crucial factor influencing marine chemical composition and material cycling. The western Pacific region boasts abundant hydrothermal activities, characterized by exceptionally high concentrations of carbon dioxide and methane in hydrothermal fluids due to the interplay of subduction processes and substantial terrestrial input. Such characteristics are scarcely observed in other global hydrothermal regions. However, as of now, there exists no convincingly established dataset for the quantification of carbon dioxide, methane, and other components released through the hydrothermal system in the western Pacific Ocean. In this study, we conducted comprehensive in situ exploration at the Yokosuka hydrothermal field in the western Pacific during the open research cruise NORC2021–582 implemented by R/V “Dongfanghong 3”. In situ Raman spectroscopy was employed to determine the gas composition concentrations of fluids in both the hydrothermal diffuse flow area and the focused flow area. Fluid flow velocities from different vents and the areas of different types of hydrothermal eruption zones were quantified using a turbine flowmeter, high-definition video analysis, and ultra-short baseline positioning techniques. Ultimately, the gas fluxes of CH₄, CO₂, and H₂S in the Yokosuka hydrothermal field were quantitatively assessed as 1.8 × 10⁸ to 2.5 × 10⁹, 2.8 × 10⁹ to 3.8 × 10¹⁰, and 2.0 × 10⁸ to 2.7 × 10⁹ mol/year, respectively, and the heat flux was estimated at 1.7 × 10¹⁰ to 2.1 × 10¹¹ MJ/year. Notably, the gas and heat fluxes from the diffuse flow area accounted for more than 80–90 % of the total volatile and thermal output across the hydrothermal field, clearly dominating the mass and energy transfer to the surrounding seawater and playing a pivotal role in sustaining the hydrothermal ecosystem. Hydrodynamic analysis reveals that under the influence of hydrothermal plumes, the Yokosuka hydrothermal field experiences a higher turbulent kinetic dissipation rate in the deep region, specifically between approximately 1600 to 1900 m, peaking at 10⁻⁵ W/kg. In the surface and intermediate layers of the hydrothermal area, the Kuroshio Current transports Yokosuka hydrothermal materials northeastward, while its impact on material transport in the deep water is relatively minor.