The Distribution And Influence Factors Of Organic Carbon In Qingdao Coastal Waters

Ocean organic carbon cycle is very important in the global carbon cycle.Understand the distribution, transportion and transformation of DOC, POC and Organic Carbon in sediment is of great importance in ocean organic carbon cycle.This paper baseed on the progress of DOC, POC and organic carbon in sediment in shelf and marginal seas,using Total Organic Carbon Analyser, we determined DOC, POC and organic carbon in sediments in Qingdao Coastal waters. In combination with hydrophical,chemical and biological datas, we analysed the distribution and influence factors of DOC, POC and organic carbon in sediment in Qingdao Coastal waters. We also estimated the residence time of POC and the contribution of phytoplankton organic carbon to POC in Qingdao Coastal waters.The main results are following:1. Dissolved Organic Carbon: The concentration of DOC in Qingdao Coastal waters is the highest in summer, followed by spring and autumn and the lowest in winter, in consistent with photoplankton growth seasonal variation. In summer, it was related with terrestrial inputs, oil pollution ,biogical activity and water mass, and was high in surface waters and low in bottom waters. The winter horizontal distribution resembled spring, which was high near the coast and low offshore. The dirtribution characteristics of DOC in Autumn was between Summer and Winter. In Spring, Autumn and Winter, the distribution of DOC resembled TSM, indicated that DOC was mainly controlled by terrestrial inputs, vertical distribution of DOC was uniform, due to sediment respension, DOC in bottom waters was sometimes higher than surface layer and middle layer waters. The diel changes of DOC were controled by tide and biological activity.2. Particulate Organic Carbon: The concentration of POC in Qingdao Coastal waters is the highest in summer, followed by spring and autumn and the lowest in winter, in consistent with photoplankton growth seasonal variation. The horizontal distribution of POC in Qingdao Coastal waters showed that high value of POC was found near the shore and the value decreased seaward. The POC horizontal distribution resembles TSM distribution , indicated that POC was mainly from terrestrial input. During the season of rapid growth of phytoplankton, the contribution of biological activity to the POC was not ignored. The vertical distribution of POC changed little. In summer, because of strong biological activity, the concentration of POC was high in the surface and middle layer and low in the bottom layer, while in other seasons, because of sediment resuspension, the concentration of POC in bottom waters was sometimes high.3. In summer, DOC was inversely correlated with AOU, the contribution of DOC oxidation to AOU below 10m layer is 16.9%, probably due to oxidation of other substrates. The correlation between DOC and chl-a was poor, indicated that the increase of phytoplankton biomas did not result in DOC accumulation.4. POC was well correlated with TSM for all seasons, the correlation in winter was better than in summer. POC was correlated with chl-a, the contribution of phytoplankton to in situ POC was 26.9% and 4.10% in summer and winter, indicated that it was mainly detritus organic carbon in Qingdao Coastal waters. The residence time of POC in Qingdao Coastal waters was short, averaging 10.38d, indicated that the regenerated rate was fast and relative high bioreactivity.5. Organic Carbon in sediment: The main form of C was OC in surface sediment of Qingdao Coastal waters, accounted for 56% of TC. The distribution of OC was low near the shore and increased seaward and was related with sediment type, the OC content was higher in clay than in sand. The OC was inversely correlated with IC, probably due to OC facilitate IC solubility. The correlation between botton POC% and OC in surface sediment was poor, indicated that bottom POC entered into sediment with degradation.