From the seep to the surface: the ascent and dissolution of methane bubbles in the ocean
Methane, as a strong greenhouse gas, has 21-25 times the warming potential per unit mass than carbon dioxide, and the methane from the oceans can contribute to ~4% of the annual atmosphere methane budget. Large methane bubble plumes have been observed in seep sites globally on shallow continental shelves, and emerging industry of methane hydrates mining causes growing environmental concern on possible disastrous blowout which destabilizes the methane hydrate and releases huge amount of methane gas. To better estimate how much methane in gaseous phase leaked from the seeps can reach the atmosphere, a simplified model is developed to simulate the ascent of a methane bubble from a shallow ocean methane seep, and the methane transfer with the surrounding water. The breakup and coalescence of bubbles are neglected, and the bubble is assumed to remain spherical following a vertical path during the whole rising process. We calculated the survival distance of bubbles with varying initial sizes and depths and the remaining percentage of methane reaching the sea surface, and applied the results to the seep sites in the Shenhu area in the South China Sea. The study can provide insight into the relative significance of different water bodies in contributing to the atmosphere greenhouse gas.