| Dimethyl sulfide(DMS), as an important trace gas in the ocean, and its precursor β-dimethyl mercapto propionic acid salt(DMSP) were the hot topics in the study of ocean, however, the research of acrylic acid(AA), another product related to the DMS generative process was almost blank. Distribution of AA concentrations and related parameters in the Bohai Sea and the Yellow Sea were studied from2011to2013. We also summarized the spatial and temporal variations of AA in different sea area and different seasons. Field simulation experiment was conducted to study the production and consumption of AA. The main results are drawn as follows:(1)The concentration of AA in surface water in summer could be0.258μmol/L or higher, which in the Bohai Sea was lower than that in the Yellow Sea. AA/Chlorophyll-a (Chl-a) was0.28mol/g, AA/(DMSP+AA) reached0.61. The production rate of AA would increase in the sea area which has lower temperature and high salinity. In peripheral waters far away from the Changjiang Estuary AA/Chl-a increased. AA/(DMSP+AA) showed the consistency with AA, and in the Yellow Sea Cold Water Mass it has minimum value. In the vertical section from Changjiang Estuary to Jeju Island, the surface AA was especially low, where influenced by the changjiang diluted water; in the middle AA was very high. The distribution of AA/Chl-a was consistent with AA. In the Yellow Sea Could Water Mass vertical section, AA was higher in the surface water than that of the bottom, and in the depth of20m-30m subsurface Chl-a maximum layer was existed obviously, AA also has this feature; the AA/Chl-a had maximum layer in the depth of20m-30m, and in the bottom it also very high. In the northern Yellow Sea and the Bohai Sea, AA in surface is higher than that in bottom, which was similar to Chl-a and AA/Chl-a. Diurnal variation showed that AA concentration during the day was higher than that of the night period, Chl-a had the similar trend; AA/Chl-a was just opposite to Chl-a.(2)In autumn the AA concentration was about0.029μmol/L in the Bohai Sea and the Yellow Sea, which was an order of magnitude lower than that in summer. AA in the Bohai Sea was lower than that in the Yellow Sea, some even below the detection limit. Chl-a was0.5μg/L, and in the middle of the South Yellow Sea it had high value, AA and bacterial abundance were also not low. AA/Chl-a was about0.06mol/g, its distribution was broadly consistent with AA. In the section of the Yellow Sea Cold Water Mass, AA had the maximum in the depth of20m. The distribution of AA/Chl-a was consistent with AA, in60m depth AA/Chl-a also had a high value.(3) In summer AA was higher than that in autumn, and had a significant correlation with the amount of phytoplankton. In summer, DMSP generated more AA with greater biomass than that in autumn. AA had no significant correlation to bacterial abundance. AA/(DMSP+AA) value in summer was higher than that in autumn; while DMS/AA was opposite to AA/(DMSP+AA). The concentrations of AA in China Sea in spring and summer were higher than that in autumn and winter.(4)In surface water, AA/Chl-a showed positive correlations with temperature and salinity. AA and AA/(DMSP+AA) showed no significant correlation with Chl-a, in surface seawater DMS/AA showed a highly significant positive correlation with Chl-a. No matter in surface water or the distribution of vertical section, AA showed a positive correlation with bacterial abundance.(5)Field experiments showed that there were DMSP degradation and AA generation in seawater. At the initial stage of the experiment, the degradation rates of AA was always higher than DMSP, and the higher the initial concentration of DMSP was, the more AA degraded. The degradation rate of AA was proportional to the initial concentration in dark condition, while it was the exact opposite in illumination condition. In photochemical reaction, AA was photo chemically produced in first2h and photo chemically degraded in last2h. |
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