Methane migration and consumption in submarine mud volcanism and their impacts on marine carbon input

Submarine mud volcanoes contribute carbon to the hydrosphere and the atmosphere by releasing methane-rich fluids, and researches on the temporal and spatial distribution of methane migration and chemical transportation at submarine mud volcanoes are the keys to understanding the processes mentioned above. In this paper, a large number of domestic and foreign literatures are systematically investigated, and the strong heterogeneity of methane leakage was recognized in the mud volcano systems. Methane emissions mainly occur during the eruption and dormant periods of mud volcanoes, and only a small amount of leakage occurs in extinct periods. In space, strong methane bubble leakages are usually developed around the centers of mud volcanos, and the chemical transportation efficiencies of methane are low in sediments; the leakages of methane and DIC controlled by fluid flow are mainly developed in the wings, where the rates of anaerobic oxidation of methane and the precipitation rate of authigenic carbonate are the highest. Shallow sediments have the strongest interception to carbon emission; both the intensity and the transportation rate of methane in the edge area are low, and hence a large area of DIC microleakage is developed. Globally, the carbon flux from submarine mud volcanos into shallow sediments is ca. 0.02 Pg C·a⁻¹. The methane and DIC coming from sediments could cause seawater anoxia, acidification, and change air-sea carbon exchange fluxes, which may affect the ocean’s ability to absorb atmospheric carbon dioxide on millennium scale or even in a shorter time, and thus impacts on the global climate environment. In the future, accurate statistics on the number and eruption cycle of submarine mud volcanoes, and detailed investigations on the migration and transportation of methane in typical submarine mud volcanoes with different sizes and development stages, will be helpful to further accurately estimate their total carbon emissions, to study the impacts of bottom-up mud volcanoes’ carbon emissions on the marine carbon cycle, and to improve the marine carbon cycle model.