Supply of Dissolved Organic Carbon from the Cold Seeps-Hydrothermal System and Its Impact on the Deep-Sea Carbon Cycle: An Overview

Dissolved carbon (dissolved organic carbon and dissolved inorganic carbon) is the major component of the ocean carbon cycle, representing one of the largest carbon pools on Earth. Cold seeps and hydrothermal systems serve as the two main windows for the material and energy recycling exchange between the lithosphere and outer spheres (biosphere, hydrosphere and atmosphere). However, recent studies have found that the dynamic activities of fluids in these two extreme systems are a crucial source of ‘new’ carbon in the deep ocean. These carbon sources may become vital contributors to carbon and energy in marine ecosystems, which affect the global deep-sea carbon budget, and the marine ecosystems as well. In this review, we summarize the sources and formation mechanisms of dissolved carbon in the seep fluids from the cold seeps and hydrothermal vents, the contribution of methane oxidation to dissolved carbon, and the characteristics of the carbon isotope composition in the fluid. Furthermore, we analyze and discuss the influence of carbon discharged from seabed on the seawater carbon cycle by comparing and contrasting these two extreme environments. The research may assist in promoting a deeper understanding of the carbon cycle and material interaction in the ocean, particularly further carbon cycle research in the back-arc basin where cold seeps and hydrothermal vents commonly prevail.