Characterization of colored dissolved organic matter in the northeastern South China Sea using EEMs-PARAFAC and absorption spectroscopy

Three-dimensional fluorescence excitation-emission matrix spectroscopy with parallel factor analysis (EEMs-PARAFAC) and absorption spectroscopy were used to characterize the colored dissolved organic matter (CDOM) in the northeastern South China Sea. The results showed that fluorescence components were identified as humiclike, tryptophan-like, tyrosine-like substances. The fluorescence indices indicated the CDOM in deep and subsurface waters had strong autogenous source characteristics, which were significantly affected by the activities of phytoplankton and bacteria in water. CDOM in surface waters was affected by both endogenous and exogenous sources. The content of CDOM in the horizontal spatial gradually decreased and then increased from nearshore areas to far-shore areas, indicating the coastal areas were affected by human activities, and in the open sea, the activities of organisms were strong. The redundancy analysis results showed that total phosphorus, ammonia nitrogen and dissolved oxygen were key environmental factors affecting the distribution of CDOM.