Oceanic carbon cycle in a symbiotic zone between hydrothermal vents and cold seeps in the Okinawa Trough

• Carbon source, fluxes, and carbon fixation of the cold seeps and hydrothermal vents. • Interaction between the two extreme systems on the seabed of the Okinawa Trough. • Metal reduction driven anaerobic oxidation of methane in the Okinawa Trough. Submarine cold seeps and hydrothermal vents are the key agents of material and energy exchange between the marine lithosphere and outer geospheres. Moreover, they breed natural gas hydrates, massive metal sulfides, and precious genetic resources and are one of the main targets of modern marine scientific research and resource exploration. A series of cold seeps and hydrothermal systems are developed in the Okinawa Trough (OT), a typical back-arc basin in the western Pacific. Due to their geographical proximity, the two extreme environments have evident mutual exchange or influence on the geological structure, material transportation, and ecological community, resulting in a unique carbon cycle model in this region. This study presents a series of recent research results in a symbiotic zone between hydrothermal vents and cold seeps in the OT. First, the genesis, carbon source, fluxes, and carbon fixation of cold seeps in the western slope of the OT are systematically summarized. In addition, characteristics of the carbon source, genesis, and flux in the hydrothermal area, near the spreading center of the basin, are compared and described. Second, the latest discoveries on the interaction between the two extreme systems on the seabed of the OT are illustrated. Furthermore, the evidence and progress of metal reduction driven anaerobic oxidation of methane and the global significance of the Fe–C coupling cycle are presented. Finally, key scientific problems in future research on the submarine symbiotic zone between cold seeps and hydrothermal vents are discussed. This study aims to provide an accurate model for the global marine methane cycle with additional consideration for metal electron receptors to gain further insights into the evolutionary history of the global carbon cycle process.