[Distribution and Seasonal Variations of Chromophoric Dissolved Organic Matter(CDOM) in the Bohai Sea and the North Yellow Sea]

UV-Vis spectral data and a fluorescence excitation-emission matrix (EEM) was analyzed for the surface, middle, and bottom layer water samples from the Bohai Sea and North Yellow Sea in April, August, and December of 2016 and February of 2017. Distribution characteristics, influencing factors, and seasonal variation of CDOM in the study area were investigated. The results showed that the horizontal distributions of CDOM are similar in different seasons, showing a characteristic of high levels near shore and low levels in the offshore region. Strong correlations were observed between value a (355) and spectral slope S_275-295, indicating that CDOM is significantly affected by land input. According to the vertical distribution, the CDOM level is the lowest in surface seawater in summer due to strong photo-degradation. In February, controlled by primary productivity, the lowest level of CDOM was found in the bottom seawater. From April 2016 to February 2017, the content of CDOM first increased and then decreased. Its concentration was highest in December. Seasonal variations are mainly controlled by land input and on-site production. According to analysis of the spectral slope S_275-295, the average molecular weight of CDOM in winter was smallest in February, which was mainly related to the drastic reduction of land-based input at that time. The strong photo-degradation in summer resulted in a small average molecular weight of CDOM.