Study On The Distribution And Enrichment Of Nutrients In The Sea-surface Microlayer Of The East China Sea, The Yellow Sea And The Bohai Sea

As the foundation of growth of marine phytoplankton, the nutrients in seawater play animportant role in controling marine phytoplankton and primary productivity in the ocean. Theconcentrations and ratios of nutrients, such as nitrogen, phosphorus and silicon in seawater,would affect the population dynamics and community structures of phytoplankton. Thesea-surface microlayer （SML）, a thin layer with the thickness of tens to hundreds micrometers,plays a significant role on the exchange of substances and energy between atmosphere and ocean.Due to its particular physicochemical characteristics, the research on SML would be beneficialfor our understanding of the air-sea exchange, flux calculation and climatic change. As thenutrients are generally enriched in SML, the study of structure and enrichment of nutrients inSML plays a remarkable role in realizing the growth and community structure of marinephytoplankton and biogeochemical processes of substances.Based on the data collected in the South Yellow Sea （YS） and the East China Sea （ECS） in2011by the National Basic Research （973） Program of China as well as the data collected in theBohai Sea （BS） and YS in summer2011by the National Natural Science Foundation of Chinsprogram, this thesis discussed the source and spatial distribution of nutrients in SML andsubsurface seawater （SSW） in the China continental self sea and their influencing factorsincluding temperature and salinity. Moreover, the influences of the cold water mass （CWM） inthe YS and the Changjiang diluted water （CDW） on the vertical distribution of nutrients werestudied, and the enrichment factors （EF） of nutrients in SML were calculated to compare thespatio-temporal variation of the enrichment extent among different seasons and sea areas. Fromwhat has been discussed above, the main conclusions are drawn as follows:（1） The concentrations of nutrients in SML and SSW in the BS and the YS in summer displayedhigh levels nearshore and low levels off-shore. Comparing with the BS and south YS, the north YS had higher concentrations of PO₄^3--P. The characteristics of nutrient distributions in SML andSSW of the ECS and the YS were the same, which also had the similar trends to the BS andnorth YS. The stations located near the eustuary of Changjiang River always had highconcentrations of nutrients in the whole year, and the concentrations in the northern part of southYS were low in spring and summer but high in autumn and winter, due to the impact of CWM inthe YS. The CDW and the Kuroshio water were main factors to affect the distributions ofnutrients in the ECS, while the Yellow Sea Warm Current （YSWC） and CWM contributed to thedistributions of nutrients in the YS, leading to the obvious seasonal variation of nitrogen,phosphate and silicate in the investigated sea areas. The structure of DIN in SML and SSW ofthe south YS and the ECS presented seasonal changes, of which the major component wasNO₃^--N in spring, summer and winter and NH+4-N in autumn, respectively.（2） CWM formed the pycnocline to impede the transfer of nutrients from bottom to surface. Itwas found from the research of vertical distributions that stratification occurred in the surfacelayer and vertical mixing characteristics were observed in the bottom. In the vertical distributions,higher concentrations of DIN and SiO₃^2--Si in the north of the Changjiang River estuary occurredin the sea surface compared with the bottom due to the impact of CDW. The D transect, whichextends from the eustuary of Changjiang River to Cheju Island, was affected by CDW the mostin summer, but the vertical mixing characteristics of nutrients were found in autum and winter.The P transect, which extends from the Changjiang River estuary to Okinawa trough, displayedapparent seasonal changes in the distributions of nutrients.（3） All nutrients except NO₃^--N, which included NH₄⁺-N, NO₂^-N, PO₄^3--P, SiO₃^2--Si and DIN,exhibited the obivious enrichment in SML of the BS and the YS in summer, and the average EFsranged from1.37to2.21. The EF values varied following the variation in the sampling areas,time and wind speed. NO₂^--N revealed the highest extent of enrichment and the most significantdifference, while the enrichment of NO₃^--N in the YS and the BS in summer did not presentevident enrichment, presumably due to the biological consumption and photochemical reduction.According to the survey of EFs in four seasons in south YS and ECS, NO₃^--N, NO₂^--N and DINdisplayed remarkable enrichment in the whole year, while NH₄⁺-N displayed an obvious extentin SML in autumn. However, no significant enrichment of PO₄^3--P was observed in SML, inagreement with the previous results in the literature. The enrichment of SiO₃^2--Si in SML appeared in summer and winter.