Abstract: The abnormal methane concentration in cold seep water is not only an important indicator of natural gas hydrate occurrence in the seabed, but also of great significance to the study of the marine environment and global climate change. Based on the analysis and study of the characteristics of the existing cold seeps, a inversion method for quantitatively obtaining methane concentration distribution in cold seep water based on single beam sounding data was established. Taking the cold seep area in the northwest slope of the Kurile Basin in the Okhotsk Sea as an example, the concentration of dissolved methane in cold seep water of the study area was calculated by using the 12 kHz and 20 kHz acoustic echo sounding data obtained from the sea trial. Compared with the chromatographic analysis results of the cold seep water samples, the calculation results of this inversion method were in good agreement with the field measured data. And due to the advantages of beam angle and bubble resonance effect, the inversion results corresponding to 12 kHz sounding data were closer to the measured data. At the same time, relevant calculation results showed that the dissolved methane in the water of the survey region mainly came from the free methane gas released from cold seeps. In addition, the field observation results showed that the hydrated crust on the surface of the cold seep bubble in hydrate stability zone could significantly prolong the floating time and distance of the bubbles.

Key words: cold seep, underwater acoustic, single beam sounding, cold seep bubbles, methane