The bubble mechanism for methane transport from the shallow sea bed to the surface: A review and sensitivity study

Bubbles transport methane (CH4) released from the sea bed to the surface while exchanging gas with the surrounding aqueous environment. The fraction of CH4 released at the surface depends upon the release depth, bubble size, dissolved gas concentrations, temperature, surface-active substances, and bulk fluid motions-particularly the upwelling flow. A bubble model was developed to examine the sensitivity of bubble-mediated CH4 transport to these parameters. A strong sensitivity to several environmental parameters was found that must be accurately measured in order to correctly predict bubble-mediated CH4 transport. Strong sensitivities (one or more orders of magnitude, depending upon initial bubble size and depth) were found for both aqueous CH4 concentration and upwelling flows. The equations used to model bubble-mediated gas transfer incorporate parameterizations of bubble motion and gas transfer. A review of the literature on the experimental measurements and theory used to derive these parameterizations is presented, and the approaches used in geophysics and chemical engineering bubble models, are described. This research seeks to provide all the necessary parameterizations and theoretical background to allow modeling of CH4 bubble streams for diverse marine conditions. (C) 2002 Elsevier Science Ltd. All rights reserved.