| Dimethylsulfide (DMS) is the most volatile biogenic sulfur compound in the seawater and one of the major natural sources of atmospheric sulfidevolatile. Its emissions to the atmosphere account for about 2/3 of the global marine sulfur release, which play an important role in the global sulfur cycle. As the main precursor of DMS, dimethylsulfoniopropionate (DMSP) is produced by the miniature, macroalgae and halophyte. DMSP can be cracked into DMS and arylic under the action of DMSP lyase released from bacteria or some marine algae in the seawater, which has an important influence on the DMS production and distributions.In the present thesis, we chose the East China Sea (ECS) and Changjiang Estuary and adjacent areas as the study areas. The DMS and DMSP horizontal distributions and influencing factors in the study area were studied. The diel variations and the concentration of DMSPd in sediment porewaters in the ECS were also discussed. Furthermore, the vertical distributions of DMS and DMSP in the Changjiang Estuary typical section, the correlations between DMS(DMSPp) and Chl-or, and the DMS biological production and consumption rates were also analyzed. In addition, the sea-to-air flux of DMS were calculated. The main conclusions were drawn as follows:The concentrations of DMS, DMSPd and DMSPp in the surface water of the ECS during autumn were 4.84 (1.91-8.59),5.84 (1.29-22.36) and 13.01 (2.92-26.51) nmol L-1, respectively. Their concentrations in summer were 5.28 (1.95-10.84),6.58 (2.41-16.98) and 17.37 (4.50-36.89) nmol L-1, respectively. The concentrations of DMS and DMSP in the surface water of the ECS showed a significant seasonal variation with higher values in summer. The horizontal distributions of DMS and DMSP were the same trend in autumn and summer, they were gradually decreased from inshore to offshore sites. The high value area of DMS, DMSPd and DMSPp in autumn and summer were occurred in the coastal waters of the central and southern Zhejiang, which indicated that the human activities and the terrigenous input had an important influence on the coastal marine ecosystem. Besides, their diel variations in summer followed the trend that higher concentrations in day and lower concentrations at night, being consistent with the change trend of Chl-a, which indicated that the light was an important factor of DMSP biosynthesis. The concentrations of DMS, DMSPd and DMSPp in the surface water of the Changjiang Estuary and adjacent areas during dry season were 0.54 (0.20-1.61),2.04 (0.31-5.50) and 6.65 (1.41-23.86) nmol L-1, respectively. Their concentrations in wet season were 3.99 (0.26-15.01), 5.57 (0.50-17.32) and 14.26 (1.16-34.01) nmol L-1,respectively. The high values of two cruises were appeared in Zhoushan waters, which were consistent with the high value of Chl-a. Their low values were appeared near the mouth of the Changjiang. The concentrations of Chl-o, DMS, DMSPd and DMSPp in the surface waters also had the obvious seasonal variation with higher values in wet season, and wet season values were 3.7,7.4,2.7 and 2.2 times higher than dry season values, respectively.The DMSP concentrations in sediment porewater in the ECS during summer and autumn were higher than that in bottom water with the average height of 20 times. The results in autumn showed that the DMSP concentrations decreased rapidly with the increase of the depth, which was related with the marine microorganisms in surface sediment. The above results showed sediment porewater may be a significant source to sea water. But there were not seasonal variation in summer and autumn.According to the vertical distributions of DMS and DMSP concentration in the Changjiang Estuary C-A6 section, our conclusion was that the vertical distributions of DMS and DMSP concentration were more uniform at the station where the water depth was shallow (<20 m) and the upper and lower water exchanged more fully. However, the high values of DMS and DMSP concentration appeared in surface and middle region and the bottom water was small at the station where the water depth was deep, which was mainly because the high turbidity and low light transmission rate lead to the inhibition of phytoplankton photosynthesis so that the synthesis and release of DMS and DMSP were less. In addition, the DMS and DMSPp concentration to Chl-a concentration had a significant positive correlation in dry season, and there was certain correlation for DMSPp concentration to Chl-a concentration in wet season, and DMS concentration to Chl-a concentration was no correlation, which showed that the distributions of DMS and DMSP were influenced by the phytoplankton biomass in dry season. The study also found that the correlation between DMSPp and Chl-a was better than the correlation between DMS and Chl-a. In addition, the experiment of DMS biological production and consumption rates in dry season showed that the DMS biological consumption was the main way to remove it.The sea-to-air fluxes of DMS in the ECS during autumn and summer were 11.63 (0.66-31.73) and 7.45 (1.30-31.84) μmol m-2 d-1, respectively. The sea-to-air fluxes of DMS in the Changjiang Estuary and adjacent areas during dry and wet season were 0.36 (0.02-1.37) and 2.17 (0.06-13.09) μmol m-2 d-1, respectively. DMS sea-to-air flux in autumn was significantly higher than that in summer, and the average value in autumn was 1.56 times higher than that in summer. In the Changjiang Estuary, DMS sea-to-air flux in wet season was 6 times higher than that in dry season. The difference of the sea-to-air flux in the ECS was mainly caused by the different wind speed while it was caused by the difference of the concentration of DMS in the Changjiang Estuary. According to the marine survey results, the DMS emission to the atmosphere was estimated to be 8.58×10-2 Tg S a-1 (Tg=1012 g), accounting for about 0.26%-0.56% of the global ocean emission. Although the ECS account for 0.21% of the world ocean, because of the larger sea-to-air fluxes made that the roles in the global ocean DMS emission contribution can not be ignored. |
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