Dissolved Organic And Inorganic Carbon Nearby Changjiang Estuary

As the biggest carbon reservoir on the earth surface, the oceans play a dominant role in the global carbon cycling. Understanding the distributions, transportations and transformation of DOC and DIC is of great importance in ocean organic carbon cycling.Waters nearby Changjiang Estuary, which is a typical marginal sea, were chosen as our study area. Field observations were carried out in April, May and October 2010, respectivly. Concentration and distribution of organic carbon (DOC) and dissolved inorganic carbon (DIC), as well as their relationships with temperature, salinity, dissolved oxygen and Chla were analyzed. Also, this paper studied coupling relationship between DOC and DIC. The main results are listed as follows:1. In April, DOC was mainly influenced by terrestrial inputs, and the distribution characteristics were higher near the coast and lower offshore. In May, the highest concentration of DOC was located near Changjiang estuary. In the surface and middle waters of south of Changjiang estuary, there were high concentration of DOC, because of the phytoplankton bloom. The distribution characteristics in October, was similar to that in April. Vertical distribution and Seasonal variation was related to terrestrial inputs, biological activities and sediments resuspension.2. Based on the relationships of DOC with S and Chla, we concluded that terrestrial inputs made more sense in surface waters in affecting the distribution of DOC than in middle and bottom waters in April. Terrestrial inputs and biological activities affected DOC simultaneously. While terrestrial inputs played more importance in October.3. The contribution of DOC oxidation to AOU below 10m layer was 49.3%, 32.5% and 14.3% in April, May and October, respectively.4. Like DOC, distributions of DIC in April and October both were higher near shore and lower offshore in April and October. Opposite to DOC, the concentration of DIC in surface and middle waters southern of Changjiang estuary were low. Vertical distribution of DIC was opposite to that of DOC. The data of PCO2 indicated that the study area acted as sources of atmosphere CO2 in April and October, while was a sink in May.5. The relationships between DIC and T, or S showed that DIC was mostly affected by T in April and October. Otherwise, biological activities played more importance in May.6. The contribution of DOC oxidation to DIC below 10m layer was about 2%～10%. The others may be contributed by resuspension and terrestrial inputs.7. 3.67×10~5tC was fixed by phytoplankton during April to May in the water column, penetrating 10 m beneath the sea surface surrounded by Za, Zb and Zc .