| Aiming at the frontier scientific problems in the process of water environment evolution under the conditions of marine dynamics,many scholars have studied in this field.The Yellow Sea and Bohai Sea(YSBS)is important offshore waters in China.On the basis of the previous research works,this paper adopts the technique route of phenomenon description,mechanism analysis and numerical simulation.And based on the Regional Ocean Modeling System(ROMS),a coupled physical-ecological dynamic model is established which is suitable for the conditions of complex factors in the offshore waters of northern China.The dynamic process describes the physical process according to the Navier-Stokes equation of hydrodynamics,which can well reproduce the hydrodynamic process and provide a reliable background flow for the ecological model.According to the characteristics of ecosystem diversity,the key elements in selecting the necessary ecological processes are in the ecological model.And then,the multi-source observational data of different time-space scales are used to verify the established model and provide a basis for the further study of this paper.The model can be applied to the analysis and research on the hydrodynamic characteristics and the evolution of ecological environment in the relevant sea area and its regularity,which has strong scientific significance and basic application value.The main conclusions are as follows:(1)Based on the large scale calculation results of sea level,the tidal wave processes in northern part of China sea are simulated by the method of a harmonic analysis made for the vertical motion processes of the tidal waves.And then the propagation and distribution characteristics of four tidal components as M2,S2,K1 and O1 tides are given.The simulation results successfully reproduced 4 amphidromic points of the semidiurnal tide component and 2 amphidromic points of the diurnal tide component in the calculated areas.The amplitude is minimal around the amphidromic points and maximal at the free zone of the bay.The propagation property of the longitude direction is less than the latitudinal wave above seas,which is similar to the propagation form of the coastal Kelvin Wave.Moreover,the system of progressive wave revolves independently and rotates respectively anti-clockwise revolving to the left around amphidromic points.(2)Through the comparison of the temporal and spatial evolution of the month-by-month sea surface temperature(SST),the characteristics of the SST have obvious regional and latitudinal spatial distribution.The evolutionary process is mainly influenced by many factors such as solar radiation,Kuroshio,coastal currents,upward temperature transport and river runoff.The distribution of the SST is stable in winter,rising from north to south,and the temperature difference between the north and the south is up to 25 ?.The SST in spring and autumn presents a transitional distribution pattern with small monthly variations.In summer,the SST rises obviously and its distribution structures are complex.The highest sea temperature appears in August and the lowest temperature is generally above 18?,and there exists the structure of cold water band.(3)The South Yellow Sea(SYS)has a unique trough topography.The surface thermal conditions affected by the monsoon,ant it is a strong hydrodynamic conditions in the SYS.According to the calculation results of hydrodynamics,the flow field structure is complicated because of the main driving forces such as the wind stress,tidal dynamic and thermal forcing conditions.These affect both the dynamic process such as the circulation in horizontal and vertical structure,the upwelling and the thermal process such as the SST,fronts and other thermodynamics in the SYS.The surface structure of the Euler's residual flow field is consitstent with the characteristics of the Ekman wind ocean current in July.The direction at 5 m layer is contrary to the surface flow,and the circulation characteristics appear.As the depth of the sea water increases,at the 20 m layer,the structure of a counter clockwise circulation is more obvious.At the bottom layer,the structure of the circulation is lost.The density residual currents are robust and the baroclinity has an important impact on the summertime flow in the SYS.(4)Combined with the topographic features of the section 33.75°N in the SYS,the vertical trajectory of substance transport along the section scale is qualitatively described by the methods of Lagrangian particle tracking experiments.The main driving force of circulation is better understood,discussed the response of substance transport processes to both the dynamic environmental factors such as wind stress,tides,circulation level and vertical structure,vortex and upwelling flows,and the thermal elements such as vertical section temperature and density distribution.It is revealed that the circulation plays a key role in the substance transport and energy transfer,while the secondary circulation and the vortex adjust the particle trajectory in the SYS.(5)According to the characteristics and transformation cycles of the ecological elements,the model of eco-environmental evolution is established in the YSBS through the relationship between the dynamic and thermodynamic process.It is shown that the process of thermocline growth and elimination is an important part of the ecological environment with a distinct seasonal stratification of vertical temperature in the YSBS.Also,the simulated seasonal horizontal distributions of surface phytoplankton indicate a two-peak characteristic of chlorophyll-a concentration in the YSBS,which are theoretically consistent with the biological roles of seasonal stratification.Meanwhile,there is an inverse relationship between nutrient concentration and chlorophyll-a concentration during annual variation cycle. |
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