Distribution and photodegradation behavior of CDOM along 130°E in the western Pacific Ocean

Photochemical properties and photochemical degradation of chromophoric dissolved organic matter (CDOM) were investigated in the upper water of the western Pacific Ocean during the autumn in 2018. The results showed that the absorption coefficient a(320) of CDOM ranged from 0.025 m⁻¹ to 0.64 m⁻¹, with an average of (0.20 ± 0.08) m⁻¹. The a(320) showed relatively lower values in the surface water, which was mainly related to the photobleaching removal of the surface CDOM. The higher values of a(320) were observed in the 100−200 m water lay-ers, which was mainly related to the biological production in the subsurface layer. The tyrosine-like component C1 and the marine humic-like component C2 were identified by FDOM excitation/emission matrix spectroscopy and a parallel factor analysis. The production of C1 was mainly originated from the production of phytoplankton and the degradation of microorganisms, while C2 was mainly originated from the input of the marine humic brought by Kuroshio. Moreover, the absorption loss spectra of CDOM indicated that the UV radiation was responsible for the photodegradation of CDOM. The tyrosine-like component was more susceptible to photodegradation than the marine humic-like component. The results also indicated that photodegradation was the important removal route of CDOM in the western Pacific Ocean.