Marine dissolved organic carbon (DOC), the largest pool of reduced carbon in the oceans, rivals the atmospheric carbon inventory in size, plays an important role in the global carbon cycle and contributes to the regulation of atmospheric oxygen and carbon dioxide abundances. Recent work has suggested that the size of the DOC reservoir may respond to variations in sea temperature and global overturning circulation strength. Moreover, mobilization of marine DOC has been implicated in paleoclimate events including Cryogenian glaciation and Eocene hyperthermals.  Despite its importance in global biogeochemical cycles, the long-term history of the marine DOC reservoir is poorly constrained. The size of DOC reservoiris decided by sources and sinks. Depending on the degradability of DOC (DOCD, defined as 1/[DOC]*d[DOC]/dt , i.e., the reciprocal of the apparent lifetime of the DOC pool). And it is suggested that the combined effects of photochemical and microbial degradation represent the major sinks of DOC. In this study, we focus on the degradation of deep-sea DOC, and designed serial ultraviolet oxidation experiments of DOC at different radiation intensities. The quantitative relationship between DOCD and radiation was obtained by analyzing a series of degradation experiments. The preliminary results show that DOCD and UV radiation are linearly correlated, which indicates that the photochemical degradation of deep-sea DOC will occur only when the radiation exceeds a certain number, corresponding to the solar radiation in a specific geological period, and provides an important basis for analyzing the changes of DOC reservoir over a long time scale.

DOC,carbon cycling,Dissolved Organic Carbon,photochemical degradation,DOC reservoir