Estimation of Methane Leakage Flux from an Active Cold Seep in the South China Sea: A Case Study at Site F

Methane leakage from submarine cold seeps is an important pathway for inter-layer material and energy exchange, indicating the presence of natural gas hydrates, and significantly contributing to ocean acidification and greenhouse gas effects. However, quantifying methane flux entering the ocean and atmosphere via cold seeps remains challenging due to limitations in observational scope, duration, sampling complexities, and constraints of in-situ environmental laboratory cultivation. This study focuses on Site F in the South China Sea (SCS) to accurately estimate the methane flux from submarine cold seeps. It integrates multidisciplinary research data across various scales, including multibeam bathymetry, side-scan sonar, CTD (conductivity, temperature, depth), and time-series videos, to constrain the physical and chemical characteristics of methane bubbles in seawater. Numerical simulations were applied to quantify the methane flux at Site F. The research findings indicate that the estimated methane flux for Site F is 12.06×10⁻⁶ mol/h temporally and 0.5878 mol/m² spatially, with an annual flux of approximately 6.44×10⁵ mol/yr, which is larger than previous estimates. This suggests that previous assessments of methane leakage from cold seep systems contributing to climate change and carbon cycling may have been severely underestimated.