As one of the major carbon reservoirs, oceans play an important role in the carbon cycle, which is 50 times more than the atmosphere and 20 times more than the biosphere.So it is very important to study the mechanism of carbon cycle in oceans and to find the oceans’ potential capacity in the uptake of atmospheric CO2.In this paper, we studied the influence of external source nutrient(nitrate and phosphate) coupled with algae cultivation on dissolved inorganic carbon system through simulation experiments in laboratory. There were three experiment groups: (1) nitrate addition; (2) phosphate addition; (3) nitrate-phosphate addition. And each had three concentration grades as follows, which are low (L), middle (M) and high (H).The results showed that the external source nutrient can cause the variation of the inorganic carbon system.During the experiments, dissolved inorganic carbon (DIC) increased slowly with time in all the incubation groups. The concentrations of DIC had the following sequence: nitrate addition groups>nitrate-phosphate addition groups>phosphate addition groups>the control group with algae. HCO-3 had the similar increase tendency and same order as DIC.During the experiments, HCO-3 increased from approximately 2.12 to 3.35%. The variations of Pco2 and CO2-3showed similar tendency with the pH which indicates that Pco2and CO2-3 were determined by the contents of H+ and HCO-3.There was a positive correlation between the nutrient content, DIC, Pco2. The results indicate that the external source nutrient may induce the concentration of inorganic carbon to be increased.In Jiaozhou Bay, because of the increases of nitrogen and phosphorus, DIC has increased about 1μmol/L from 1960s to 1990s, which indicates that it absorbs 1.1t C each year excessively.
