Distribution And Air-sea Fluxes Of Dissolved Nitrous Oxide In The Yellow Sea And The East China Sea

Nitrous Oxide （N₂O） is an important greenhouse gas in the atmosphere, whichplays a significant role in global warming and atmospheric chemistry. Oceans are thesecond biggest sources of atmospheric N₂O, and production and emission of N₂O aremore active in coastal areas due to human activities. Researches about N₂Odistribution and the quantification of different sources and sinks are fundamentalapproaches to understand its biogeochemistry processes.Distribution and seasonal variation of N₂O were studies in this dissertation basedon five cruises in2011. Fluxes from air-sea interface and sediment-water interfacewere estimated, and box-model was used to calculate the N₂O budget in the EastChina Sea. The main results are as follows:1. Five cruises were carried out in the Yellow Sea and the East China Sea in March,May, August, October and December2011, respectively. The results indicated thatdissolved N₂O showed high spatial and seasonal variability due to the influence ofcomplex water masses and the variable controlling factors. N₂O concentrations arealmost the same in surface and bottom waters due to the complete vertical mixation inwinter and spring. However, the vertical profiles of N₂O were characterized by anincrease from surface to bottom in the water column in summer and autumn due tostratification. The average concentration of N₂O in the Yellow Sea is higher than thatin the East China Sea, thus water exchange between the Yellow Sea and the EastChina Sea would influence the distribution of N₂O in some degree. Distribution ofdissolved N₂O showed negative correlation with the water temperature. High N₂Oconcentrations were found in bottom waters near the Okinawa Trough, indicating theinfluence from Kuroshio. Kuroshio and Changjiang Dilluted water are importantsources of dissolved N₂O in the East China Sea.2. Saturation of dissolved N₂O in surface waters and air-sea fluxes were evaluated inthe East China Sea. N₂O concentrations were high in spring and low in autumn. N₂O were oversaturated in most stations in spring, summer and winter, while almost half ofthe stations were undersaturated in autumn. In general, the East China Sea is a netsource of atmospheric N₂O, and it is estimated that N₂O emissions from East ChinaSea in2011is0.052⁰.078Tg, which accounted for about1.7%of the annual globaloceanic emission, indicating that the East China Sea is an active area for N₂Oemission.3. Sediment samples were collected in different seasons to quantify the N₂O fluxesbetween sediment and bottom water. The results showed great seasonal variability andmost stations are sources of dissolved N₂O. The fluxes varied a lot and the valueswere high in summer. It is estimated that N₂O emissions from sediment to bottomwater are0.067×10⁹mol in2011.4. Box-model was used to evaluate the N₂O budget in the East China Sea on the basisof our data and former results. It is concluded that Changjiang dilluted water, TaiwanCurrent Warm water and Kuroshio are important sources of N₂O in the East ChinaSea, and their contribution showed great seasonality. N₂O concentration in KuroshioSubsurface Water is higher than that of Kuroshio Surface Water, indicating that theKuroshio Subsurface Water is the main source from Kuroshio. The in situ productionwas the main source of dissolved N₂O, and the production rate of the East China Seain summer and winter were preliminarily estimated to be0.95μmol·m-3·s^-1and0.84μmol·m^-3·s^-1, respectively. The in situ production of N₂O in the East China Sea wereestimated to be1.56×109mol·yr^-1, which indicates great uncertainties and still needfurther research.