Seasonal Variability Of Hydrological Properties And Ecological Effect In The Southern Yellow Sea

Based on the high frequency observation data of hydrology(temperature,salinity),biology(Calanus sinicus)and chemistry(nutrient)collected from field observation in recent years and a large number of field investigations over the years,this paper studies the cold water mass and the process of spring transformation in the Yellow Sea,and the green tide disaster of Enteromorpha prolifera in the Yellow Sea for more than 10 years.The observation of nutrients has a deeper understanding,but there are few reports about the effect of upwelling nutrients on it.Through high frequency and high density nitrate observation,the upwelling nutrients have an important impact on the outbreak and persistence of Enteromorpha proliferata.Due to the limitation of traditional discrete observation and sampling methods,a comprehensive and in-depth study on the effects of various environmental factors on the vertical distribution and migration of zooplankton has been carried out.As a result,many details and mechanisms of the coupling between the vertical distribution of zooplankton and phytoplankton and various ecological factors have not been fully clarified.The distribution pattern of plankton and macroalgae in the Yellow Sea cold water mass should be based on the ecological response to the special physical and chemical conditions of the cold water mass.This paper mainly compares the measured data of 2015-2017(some seasons supplement 2014 and 2019).It is found that the spring and summer yellow sea areas are greatly affected by the previous winter,and the strong cold event causes seasonal water temperature and salinity show inter-annual differences.The Yellow Sea warm currents still exist and there are inter-annual differences in strength and weakness.Therefore,spring has different temperature and salinity characteristics.Under the influence of solar radiation in summer,the water temperature in the Yellow Sea decreases gradually with increasing depth,and a strong thermocline is formed between 10 and 30 m.The bottom layer of the Yellow Sea Cold Water Mass runs from the west to the east from the outside of Haizhou Bay to the Yellow Trough area.The northern Jiangsu shoal is a low-salt area,and the salinity of the upper seawater in other areas of the South Yellow Sea is generally consistent.The cold water masses in the Yellow Sea are mainly distributed near the bottom layer of the saline layer.This area has the characteristics of typical low temperature and high salinity.A strong temperature and salinity front has also been formed in the marginal area of the cold water mass.By comparing historical data of long-term observations of the hydrological environment in spring and summer,it is helpful to carry out multi-angle studies of the Yellow Sea ecosystem,such as system evolution,driving mechanisms and disaster response measures.In spring,due to the influence of the cold water input from the Yellow Sea coastal current,the combined effect of surface water heating and the warm current of the bottom Yellow Sea formed the middle layer cold water outside Qingdao,and gradually evolved to become part of the cold water on the west side of the Yellow Sea Cold Water Mass.The use of observation data for many years shows that the high-nutrient areas in the coastal waters of northern Jiangsu correspond to the low-salinity water areas in general,and a large amount of nutrients are contributed by freshwater input from the land,thus match the nutritional needs of the green tide outbreak.The high-frequency nitrate observation at the 35°N section verifies the existence of the upwelling,carrying nutrients from the(near)bottom layer along the upwelling to the(sub)surface layer;the Yellow Sea is a sea area with typical continental shelf tidal energy dissipation,summer tidal mixing in the Yellow Sea not only controls the boundary of the cold water mass,but also affects the depth of the mixing layer and the structure and strength of the circulation.The existence of the upwelling in the Yellow Sea is also an important way to replenish nutrients during the process of floating Ulva prolifera on the Yellow Sea surface.Through the analysis of the key processes affecting the healthy development of the Yellow Sea ecosystem,we can provide technical support and theoretical basis for the corresponding solutions.Zooplankton is one of the core issues in the study of marine ecosystem dynamics.Calanus sinicus is a key species of zooplankton in the Yellow Sea.In this paper,new observations(high-frequency,in-situ optical observations)are used to try to connect marine dynamic processes with the distribution of dominant zooplankton species.In summer,through preliminary analysis of the Yellow Sea sea area collection time,thermocline intensity changes,the maximum chlorophyll layer depth and tropotrophic layer,and other relevant information,the thermocline strength determines the location and concentration intensity of the chlorophyll maximum layer,often distributed in the thermocline inside or below;the largest layer of chlorophyll is an important food source during the summer of Calanus sinicus,which can basically meet its feeding needs and avoid the damage of high temperature on the surface.The increase in the growth rate of phytoplankton caused by the nutrient layer is called SCML(Subsurface Chlorophyll Maximum Layer)formation mechanism.Calanus sinicus is mainly distributed at the bottom or near the bottom of the cold water mass of the Yellow Sea in summer.Due to the adverse conditions of low water temperature and relatively scarce food in the bottom water,biological individuals often reduce their development rate and reproductive ability to adapt to the existing environment.condition.On-site observations have repeatedly observed that Calanus sinicus appeared in the SCM layer inside the thermocline.It was inferred that from the evening to the early morning,when the thermocline intensity change was small,the largest layer of chlorophyll appeared near the thermocline.A brief feeding on the floor provides convenient conditions.When the environment is suitable and because of the need for energy intake,the rich bait near the jump layer will induce the rise of herbivorous copepods and ingestion to meet their own energy needs.Therefore,for copepods,staying in the SCML layer at night may be a preferred option.