The Seasonal And Interannual Variations Of Nutrients In The Coastal Sea Of China

Nutrients are the important material basis of primary productivity,which concentrations and structure will directly affect the growth of phytoplankton,thus affecting the productivity of the sea area.China coastal sea,which are the traditional high productivity marginal sea and the global important CO2 sink area,have the representative marine ecosystem.Recently,coastal ecosystems encounter serious problems,such as the nutrient's structure imbalance,high amounts of nitrogen,the lack of silicon and phosphorus,which have result in serious eutrophication phenomenon.For understanding the changes of nutrients in offshore,this study intends to discuss nutrient seasonal trend,variations of the inter-annual and vertical turbulent flux which is contribute to new productivity based on in-situ data of the JODC and SOA from 1975 to 2000 and the cruises,October 2015.We hope that our research can provide basic data support for China marine ecological environment research.The results showed that:(1)Seasonal variations:The seasonal variations of nutrient concentrations in different area and different levels are different.Nutrients concentrations of the surface water is the highest in winter,followed by spring,the third in autumn,and the minimum in summer,and DO is the same.In the bottom,the Bohai Sea nutrients have obvious seasonal variations,the highest in winter,followed by spring and autumn,the lowest in summer,and the same with DO.There are no obvious seasonal variations of nutrient of the bottom in the Yellow Sea and the East China Sea,which remains the maximum values almost all year.DO concentration are the highest in spring and the minimum in autumn.(2)Inter-annual variations:PO4-P concentrations had great change,which reduced in the Bohai Sea in summer,but slightly elevated in winter,which slightly reduced in the North Yellow Sea during the last 25 years,while had a significantly reduced in the South Yellow Sea,which were not obvious in the East China Sea.And SiO3-Si showed a trend of decreasing in China's offshore,especially in the mid-1980s.SiO3-Si concentration was lower than in the 1970s and 1980s.And the DO concentrations also reduced during the last 25 years,especially in the shallow sea of winter is more significant.Also,the DO saturation showed reducing.As a result,the DO concentrations both are controlled by the temperature of seawater and phytoplankton.(3)Spatial variations:the variations of nutrients and DO in different sea during the last 25 years are not exactly the same.The most obvious changes are as follows:For PO4-P,the Bohai Sea decreased but slightly elevated in the North Yellow Sea in the surface of summer.For SiO3-Si,the area of the higher value of surface in summer near the Changjiang estuary of the East China sea was decreasing,while the concentrations of other areas in the East China Sea is not obvious.For DO,the area of the higher value of bottom in summer of the North Yellow Sea is shrinking.(4)Based on the October 2015 in-suit data,we concluded that the vertical eddy diffusivity K? in the East China Sea(10-7-10-2)m2s-1,vertical turbulence nitrate flux at the nitracline range from 0.02 to 3.4 m mol m-2d-1,with other global edge area at the same level.The contribution rate of nutrient provided by vertical flux to the primary productivity is between 4.2%and 24.7%..