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 S275-295, 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 S275-295, 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

Spatial distribution of colored dissolved organic matter(CDOM) in the Bohai, Yellow and East China Seas in November and December

UV-Vis spectral data was analyzed for the surface,middle, and bottom layer water samples of the Bohai Sea, Yellow Sea and East China Sea in November and December, 2016. The distribution characteristics, sources and influencing factors of CDOM in the study area had been investigated. The results showed that CDOM concentrations in the Bohai Sea were higher than those in the Yellow Sea and the East China Sea. In these three Chinese marginal seas, the CDOM concentration showed a decreased trend from the nearshore to the open sea. Strong correlations were observed between value a_(355) and spectra slope S_(275-295). Considering the distribution patterns of a_(355) and S_(275-295), adominant terrestrial source of CDOM was concluded. In the Bohai Sea, the highest concentration of CDOM was detected in the Yellow River estuary,due to the combining effects of the direct riverine discharge and sediment re-suspension by strong wave movement in winter. The lowest DOC and CDOM concentrations in the Bohai sea were observed in the regions,where the double-center cold-water mass areas occurred in the summer. The invasion of the Taiwan Warm Current,charactered by high salinity and low DOC, resulted in an obvious regional low value of DOC except for CDOM concentration. CDOM and DOC did not show remarkable correlation in the Bohai Sea,Yellow Sea and East China Sea.</p