A Study On Particulate Silica In The Changjiang Estuary And Its Adjacent Area And East China Sea Shelf

Particulate Biogenic Silica mainly produced by diatoms is part of global Si cycle.The concentration and distribution of PBSi are impacted by many factors. The EastChina Sea is a perfect place to study Si cycle for it is effected by many water masses,like Yangtze River, Taiwan Strait Warm Water and Kuroshio. In this study, six cruiseswere carried out in the East China Sea (ECS) to understand the factors which affectthe concentration and distribution of PBSi. Some major conclusions are drawn asfollows.1. During June, August and October in2006cruises in the Changjiang (YangtzeRiver) Estuary and its adjacent area. The concentration of PBSi in October was higherthan in August and then higher than in June. The diatom biomass was higher inOctober and August than in June. As a result, the concentration of PBSi is the lowestin June. In October the higher concentration of PBSi was due to resuspension ofseabed sediment related to strong water mixing. The concentration of LSi in Octoberwas higher than in June and then higher than in August, and the concentrations of LSiin near-bottom water were higher than in surface water.On the East China Sea Shelf: in summer the concentration of PBSi in surfaceranged from0.01to6.39μmol/L, which was lower than in near-bottom water wherePBSi ranged from0.24to9.53μmol/L. In autumn the concentration of PBSi insurface ranged from0.03to4.61μmol/L, which was higher than in near-bottom wherePBSi ranged from0.01to4.60μmol/L. In winter the concentration of PBSi in surfaceranged from0.01to0.75μmol/L, which was lower than in near-bottom with PBSiranged from0.002to6.98μmol/L. The concentration of LSi in near-bottom water washigher than that in surface water. This maybe influenced by the resuspension ofseabed sediments. In autumn the concentration of PBSi in surface was higher than innear-bottom but in winter the concentration of PBSi in surface was lower than innear-bottom. In surface the concentration of PBSi was as follows: summer>autumn>winter. Because of the terrigenous sediment discharges from the Changjiangwas higher in summer than in autumn and winter. The concentration of PBSi observedin coastal area was higher than in the offshore area affected by the abundantterrigenous sediment discharge from the Changjiang. LSi were the major part of Si inparticulate (PBSi+LSi) both in autumn and winter. 2. PBSi and LSi in the Changjiang Estuary and its adjacent East China Sea Shelfshow significantly linear relationship with the SPM. The relationship between PBSiand S, POC, Chla and Apparent Oxygen Utility (AOU) were analysed. Because ofdiatoms were dominated in phytoplankton in August and October, the relationshipsbetween these factors and PBSi were significangt, while the relationships were notsignificantly in June.3. Using four distinct LSi-salinity-temperature water mass end-members todetermine the contribution of Changjiang Diluted Water (CDW) to East China Seashelf. The contribution of CDW to the East China Sea Shelf in2003was more thanthat in2006, due to less runoff and sediment discharge in2006.