| Volatile halocarbons (VHCs) are important atmospheric trace gases, potential greenhouse gases and ozone destructors, which play important roles in global climatic change and environment. Global oceans are net natural sources of atmospheric VHCs. Although coastal regions only occupy a small part of the world ocean, they appear to be responsible for a large part of the oceanic VHCs emission. Therefore, studies on the biogeochemistry of VHCs in coastal water will be helpful to estimate the contribution of oceanic emission to the atmospheric VHCs on global scale, and to predict the influence of oceanic emissions to the global climate change.In the dissertation, the concentration distributions, temporal and spatial variations and sea-to-air fluxes of VHCs were studied systematically in the Bohai Sea (BS) and the Northern Yellow Sea (NYS) in spring and autumn. Meanwhile this paper first discusses the concentration of the VHCs in underlying seawater and sediment pore water, in order to discuss the sediment-over water interface to provide a scientific basis. But in order to better discuss the source of seawater or the removal of volatile halogenated hydrocarbons to provide a scientific basis.The main research results were as follows:(1)Distributions of 4 kinds of VHCs were studied in the BS and NYS during November 2013 (autumn) and April 2014 (spring). The results show that the average concentrations of CHBr2Cl, CHBr3, C2HCl3 and C2Cl4 in the surface seawater of the BS and NYS were 7.03 (4.23～12.63)pmol/L,19.61 (5.99～55.00) pmol/L,20.37 (1.68～58.25) pmol/L and 41.03 (10.84～96.94)pmol/L in autumn and 12.77(0.39～35.64),26.92(3.01-67.41),32.83(10.48～97.49) and 25.18 (15.76～45.18) pmol/L in spring. There was a good correlation between C2HCl3 and C2Cl4 in autumn. But in the spring there were a good correlation between C2HCl3 and C2Cl4, CHBr2Cl and CHBr3, CHBr2Cl and Salinity, C2HCl3 and temperature.Seasonal variations show that the concentrations of CHBr2Cl, CHBr3 and C2HCl3 in spring were higher than those in autumn. But the concentrations of C2Cl4 in autumn were higher than those in spring.(2) The vertical distributions of 4 kinds of VHCs during the antumn and spring were studied. Depth profiles of 4 kinds of VHCs in autumn and spring show near surface and bottom maxima owing to in situ production and the minima appear in the middle-layer of the water column. In addition, the VHCs concentrations exhibited obvious diurnal variation in the surface seawater. The highest concentrations of VHCs appearing around noon time may be associated with biogenic production and photosynthesis of the algae, while the relatively high concentration in the night may be attributed to algal respiration and tidal frequency. The sea-to-air fluxes of 4 kinds of VHCs in the BS and NYS were CHBr2Cl 36.28 (0.13～109.54), CHBr3 85.96(-8.9～308.61), C2HC13 191.71 (0.10～386.67),C2Cl4 285.14(0.19～914.85)nmol/m2·d in autumn and CHBr2Cl 47.17 (-1.16～178.82), CHBr3 56.63 (-24.07～356.70), C2HC13 162.56 (2.23～977.83), C2C14 104.37(1.64～398.39) nmol/m2·d in spring. The results of sea-to-air fluxes of 4 kinds of VHCs elucidate that the investigated area appear to be the source of atmospheric during the study time.(3) The bottom water concentrations of CHBr2Cl, CHBr3, C2HC13 and C2Cl4 were 6.32 (3.86～13.27) pmol/L,18.83 (3.24～43.10) pmol/L,32.05 (0.23～211.87) pmol/L and 43.70 (13.05～154.40)pmol/L in autumn. In the spring the distributions of 4 kinds of VHCs were 12.62(0.49～37.71) pmol/L,23.12 (4.74～82.56) pmol/L, 26.85 (8.42～67.68) pmol/L and 24.03(14.41～45.05)pmol/L.(4) The interstitial water concentrations of CHBr2Cl,CHBr3,C2HCl3 and C2Cl4 were 17.38(5.10～61.00),48.53(4.49-138.16),46.00(14.72～177.60) and 35.57 (20.57～83.59)pmol/L in autumn.In the spring the distributions of 4 kinds of VHCs are 19.37(1.34～70.66),36.87(0.27～91.48),185.52(100.51～392.68) and 75.18(21.38～193.98) pmol/L. In autumn the concentration of CHBr2Cl and CHBr3 in the interstitial water were similar to that in the spring. But the concentrations of C2HC13 and C2Cl4 in spring were significantly greater than in autumn. |
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