| Continental shelf is a connection between continent and ocean, which plays an important role in marine biogeochemical cycle of carbon and other chemical elements. As the northern marginal seas of China, the Yellow Sea and the Bohai Sea show high necessary in studies on the distribution of the parameters of the carbonate system of seawater and influence factors to this system. Field observation cruise in the Yellow Sea and the Bohai Sea was carried out in November 2013. Three parameters of the carbonate system of seawater, i.e., pH, dissolved inorganic carbon (DIC), total alkalinity (TA) as well as the dissolved calcium ion (Ca2+) in seawater were determined. Other parameters, i.e., partial pressure of carbon dioxide (ρCO2), saturation degree of calcium carbonate and buffer coefficient were calculated using CO2SYS software combining with the temperature and salinity. The distribution features of carbonate system were studied and the physical, chemical and biological factors influencing the carbonate system were discussed.Regional differences observed in the distributions of the parameters of carbonated system in the Bohai Sea and the Yellow Sea. pH (NBS), TA and DIC were in the ranges of 8.03-8.26,2.436-2.614 mmol/L and 2.115-2.434 mmol/L in surface water of the Bohai Sea. The parameters were uniform with depth due to the mixing of seawater in the Bohai Sea. In the Yellow Sea, pH, TA and DIC were in the ranges of 8.06-8.26,2.311-2.428 mmol/L and 1.986-2.320 mmol/L in the surface water. Parameters of carbonate system were uniform in the upper 30 meters, but stratification phenomenon was observed in 30 nr depth obviously in the south Yellow Sea.Concentration of dissolved calcium ion could be expressed using the equation Ca2+(mmol/kg)=CA/2+Φ×(S/1.80655) for seawater samples from the Yellow Sea and the Bohai Sea. The calculated 0 was in the range of 0.460-0.478, while 75% of the values fall in the range of 0.461-0.469. Calcite saturation and aragonite saturation were in the range of 2.25-4.47 and 1.41-2.75. The calculated value of the partial pressure of CO2 (ρCO2) in surface water were ranged from 239 to 414 μatm, with an average value of 328 μatm. Thus, the Bohai Sea and the Yellow Sea showed a weak sink of atmospheric carbon dioxide in late autumn, generally.Due to the discharge of the Yellow River, TA and DIC of surface water in the Bohai Sea were the highest in the observed area. In the south Yellow Sea, TA and DIC of surface water were also high due to the influence of the discharge from the abandoned estuary of the Yellow Sea in the northern Jiangsu coast. Gradients of TA and specific alkalinity (SA) were observed in a station close to the Changjiang Estuary. The influence of the discharge from the Changjiang Estuary to the carbonate system was lower than that from the Yellow River Estuary. Influenced by the water exchange between the Bohai Sea and the South Yellow Sea as well as the discharge of the Yalujiang River, TA and DIC levels were the lowest in the observed area in the north Yellow Sea.Cold water masses were observed from 34°N to 37°N,123°E to 124°E below 50 m depth in the south Yellow Sea and in deep water of a small area in the southwest of the north Yellow Sea. The cold water mass showed low pH and high pCO2 due to decomposition of organic matter in deep water and inhibited vertical exchange between upper and deep waters. Slight influence of biological activity to carbonate system was also found in surface water in late autumn. |
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