The Okinawa Trough is a natural hydrothermal gas emission field. The flux of CO2 into the water column is dominated by hot hydrothermal CO2-rich vents. The influence of the emitted low-temperatured gas bubbles and droplets (‘condensed phase’) is very likely restricted to the lowermost part of the water column. Despite their proximity the gas composition of the condensed phases varies widely, especially in methane, which is likely caused by diverse phase transformation and thus fractionation below and above the seafloor.