Effects Of Sea Ice On Coastal Water Exchange In The Bohai Sea During Cold Wave

The Bohai Sea is a semi-closed inland sea.With the increase of coastal economic activities in recent years,the nutrient pollution in its coastal waters has a tendency of aggravating.Ocean can reduce pollutant concentration through its own dynamic conditions,and has a certain physical self-purification function,namely water exchange capacity.In particular,the Bohai Sea has strong winter monsoon and frequent cold wave gales.Previous studies believe that the water exchange capacity in winter is stronger than other seasons.However,the sea surface of the Bohai Sea will freeze rapidly during the cold wave in winter.The formation of sea ice will change the hydrodynamic conditions such as wave,tide and current,and affect the exchange capacity of water body,thus changing the transport and diffusion process of pollutants.Therefore,the establishment of a numerical model to study the influence mechanism of sea ice on the coastal water exchange capacity of bohai Sea during cold wave weather can provide a more reliable and accurate assessment tool and scientific basis for the prevention and control of pollution around the Bohai Sea in winter,which has important scientific significance and application value.In this paper,a fully coupled three-dimensional numerical model of sea ice-ocean-wave water exchange in the Bohai Sea is established based on MCT coupler,FVCOM hydrodynamic model of unstructured grid,sea ice model,SWAN wave model and Lagrange particle tracking model.The effects of sea ice on waves,tides and currents are described by incorporating the ice concentration into the sea surface stress equation with a linear change of weighted percentage.The results of model validation show that the simulated annual maximum sea ice distribution is basically consistent with the satellite remote sensing image.The simulated tidal level,velocity,flow direction and effective wave height are basically consistent with the measured ones,and the maximum error of effective wave height is less than 5%.Lagrange time mean method and Euler time mean method are used to obtain Lagrange residual flow and Euler residual flow respectively.The effects of sea ice on Lagrange residual current,Euler residual current,Stokes drift and water exchange are discussed.The results show that the sea ice hinders the particle discharge from Liaodong Bay,but is beneficial to the particle discharge from Bohai Bay and Laizhou Bay.On this basis,the effects of different initial particle release time and different number of particles on water exchange were analyzed.The Lagrangian particle tracking model was used to read the ice velocity as the driving field to successfully simulate the migration trajectory of the pollutant particles invading the ice body,and the migration trajectory of the pollutant particles invading the ice body with the floating ice was simulated,which provided a new method for the source tracking of the pollutant particles invading the sea ice.