Quantitative Study of Methane Sequestration by Hydrate-Encapsulated Bubbles at Cold Seeps: Kinetic Characteristics and Environmental Implications

Abstract

Cold seeps are a major source of natural methane emissions from the seafloor and regulate the global ocean carbon cycle. Hydrate formation serves as a key natural barrier restricting methane escape, but its kinetic mechanisms remain poorly quantified due to limited in situ monitoring capabilities. Here, we employ time-series Raman spectroscopy to conduct quantitative monitoring of methane hydrate growth kinetics and coupled methane sequestration behavior across various fluid-bubble flows. Time-resolved spectral data clearly capture real-time variations in the concentration and conversion ratio of multiphase methane during hydrate growth, quantitatively revealing the dynamic evolution patterns and regulatory mechanisms in cold-seep environments. Experimental results indicate that the growth rate accelerates and the occupancy of large cages in cold-seep bubble flows increases by 15% relative to that of small cages influenced by low salinity and small solid particles. Furthermore, field model estimates indicate that the annual methane sequestration by hydrate-encapsulated bubbles at Site F is estimated to be about 0.34–2.77 t/yr, which accounts for roughly 3.3%–26.9% of the total methane leakage flux in this region. These findings fill critical quantitative gaps in understanding cold-seep methane sequestration dynamics and provide key parameters for incorporating hydrate-mediated sequestration into ocean carbon cycle models.