Geochemistry of black carbon in marine extreme environments and its environmental implications
Black carbon is one of the carbonaceous materials,it exists ubiquitously in the environment and could be resistant to oxidation and decomposition.Black carbon might strongly affect the global carbon cycle as an important component of recalcitrant organic carbon.The current discrepancy of marine black carbon budgets indicates that there are unknown sources or buried pathways of black carbon in the ocean.It has been confirmed that marine extreme environments,such as abyssal trenches,hydrothermal vents and cold seeps,may be important sources or sinks of marine black carbon with the continuous deepening of the research on black carbon in these environments.In this review,the geochemical characteristics of black carbon in extreme marine environment are summarized.It is found that the unique"V"-shaped terrain of the abyssal trenches is conducive to the accumulation of materials,in which the black carbon is older than the syn-sedimentary organic carbon,and the annual buried amount of black carbon is about(1.0±0.5)Tg.The high-temperature fluid in hydrothermal vents forms in-situ authigenic black carbon by"burning"organic matter,and its annual contribution to the ocean is about 1.6～9.7Tg,which is an important source of marine black carbon.The source and sink process of black carbon in cold seeps remain unclear,but the high abundance of anaerobic methanotrophic archaea in these areas has recently been proved to directly produce black carbon,and its carbon isotope value is negatively below-60‰.As the only microbial source of black carbon found so far,it is an important supplement to the traditional understanding of black carbon types.The overall framework of marine black carbon source and sink process has been established notwithstanding,there is a lack of direct morphological observation and characterization of black carbon in marine extreme environments.It is necessary to clarify the ratio between terrestrial black carbon input and marine authigenic black carbon in extreme marine environments,to further understand the source and sink process of marine black carbon and explore the role of extreme environmental black carbon in marine black carbon budgets in the future.
black carbonmarine extreme environmentsgeochemical characteristicssource-sink processes
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