The Study On Characteristics And Distribution Of Chromophoric Dissolved Organic Matter (CDOM) Based On Absorption And Fluorescence Properties In The Bohai Sea And The Yellow Sea

In this paper, both in situ measure and laboratory analysis were detailedly studiedfor Chromophoric Dissolved Organic Matter （CDOM） in the Bohai Sea and theYellow Sea. Absorption and fluorescence characters of CDOM are utilized to analyseits horizontal and vertical distribution, seasonal change, source, transportation andtransformation, and molecule weight. The CDOM optical properties are studiedquantitatively and qualitatively, and environmental influence factors to spatial andtemporal distribution and trend of CDOM are discussed. The major results are showedas follows:1. To understand the seasonal change of CDOM’s absorption properties in the Bohai Seaand the Yellow Sea, absorption coefficient a₃₅₅, the spectral slopes S275-295、S350-400andthe spectral slope ratio SRwere used. The average values of a₃₅₅in spring and inautumn were0.41m^-1and0.73m^-1and values were decreased from inshore to offshore.Slight spectral slope average values changes were found in spring and in autumn,however, the higher values of S275-295were collected in nearshore for spring samplesbut opposite trend were appeared in autumn. Horizontal distribution of the values ofS350-400had no evident regularity. These results indicated that different factorsinfluented the spring and autumn samples, causing absorption attenuation diversities.The average value of spectral slope ratio SRwas higher in autumn than that in spring,indicating that phytoplankton produced during causing that relative small weightmoleculars were produced by phytoplankton in spring bloom. Through the correlationanalysis between a₃₅₅and salinity, Chl-a and bacterial abundance, it was found thatCDOM kept conservative mixing in the Yellow Sea in autumn because of strikingliner relation. For the rest, no obvious correlation was found. These meaned thatcomplex factors affected the CDOM concentration, expect for biogeochemistryprogresses such as water mixing, phytoplankton production, microbiological and photochemical degradation, and sediment resuspension, human activities also playedan important role.2. The vertical distribution of CDOM was researched on Chengshan Jiao-East Bay and35°N sections. For Chengshan Jiao-East Bay section in spring, input from fresh waterwas the main resource for nearshore, and the spring bloom contributed to lowerCDOM concentration to the offshore. And microbiological processes and sedimentresuspension had important influences on bottom layer CDOM concentration. Inautumn, the distribution character was similar to Chl-a. The field productioncontribution to CDOM was obvious in deep layer for offshore waters, and terrigenousresource was found inshore waters. For35°N section, tidal current strongly impactednearshore in spring, and a₃₅₅in bottom layer was higher than surface layer owing tosediment resuspension. The bottom distribution of a₃₅₅near Huanghai Trough wasconsistent to the regression path of the cold water mass, and can be used to trace thecold water mass movement. The distribution of SRshowed significant effect oncomposition and molecular weight of CDOM when water mass mixed.3. For enrichment study of a₃₅₅and SR, a₃₅₅had similar distribution between themicrolayer and subsurface layer, and distinct enrichment was determined. However,SRwas in a complex situation, obvious differences distribution in microlayer andsubsurface layer, and this might caused by special physical oceanographyenvironment of microlayer. Dissolved organic matters enriched in microlayer with agreat many of changes in structures and proportions of components. Particularly, inspring, there was a loss for the absorption between275and295nm, indicating thatwhen CDOM enriched in microlayer, components which could absorb short waveoccurred photodegradation, or small molecular matter readily undergo polymerizationand lead to absorb red-shift.4. EEMs-PARAFACA method was applied to research the fluorescence character ofCDOM, and four fluorescence components were identified. C1contained amount ofresidual interference, and was ignored. C2was humic-like fluorophore, C3wasprotein-like fluorophore, and C4was complex. C2and C3had similar horizontal distribution to a₃₅₅, higher in nearshore and lower in the far shore, illustrating thatboth had common degeneration in distribution character. The different distributioncharacter of C4indicated that the formation and transformation process was differentto C2and C3. In addition, vertical distribution was analyzed on Chengshan Jiao-EastBay and35°N sections, in the same time, correlation analysis was determinedbetween fluorescence components and a₃₅₅. Complex environmental factorsinfluenced on CDOM fluorescence components, for example, in autumn, there was noobvious correlation both, and the results showed that the source and removal processof CDOM in Bohai Sea and the Yellow Sea was affected by complicated factors inspring and autumn, and production and loss rate influenced fluorescent substancecomponent proportion.