Tidal Characteristics And Its Response To Sea Level Rise In The East China Seas

The east China seas are one of marginal seas with lager continental shelf and strong tidal energy in the northwest of Pacific Ocean.This area is characterized by complex spatial patterns of tidal waves.With the intensification of global greenhouse effect,the rise of sea level caused by global warming is bound to have a huge impact on tidal characteristics of coastal seas.A clearly understanding of the response of tidal characteristics to sea level changes is essential for scientific coastal zone management,disaster reduction and prevention,and long-term sustainable development.Based on the regional ocean modeling system(ROMS),a three-dimensional barotropic numerical model of the East China Sea was developed to simulate the tidal characteristics.The model-observation comparison showed that the model reliably reproduced the tides in the east China seas.The net tidal energy flux of Bohai,Yellow,and East China Seas were about 2.152 GW,96.082 GW,88.33 GW,and the dissipation were about 1.790 GW,95.254 GW,79.168 GW;The bottom friction dissipation and vertical diffusion dissipation accounted for 67.1%and 32.9%of the total dissipation,and the horizontal diffusion dissipation accounted for less than 1%of the total dissipation.The high dissipation areas of the East China Seas were mainly distributed around the coast of the Korean Peninsula,the shoals of North Jiangsu,the Yangtze River subaqueous delta,the Hangzhou Bay and the coast of the Zhejiang and Fujian Provinces.The weak dissipation areas were located in the middle of Bohai Sea,the southwest of Yellow Sea,and the middle of South Yellow Sea.The tidal Eulerian currents in the east China sea showed obvious residual vorticities around the coast of the Korean Peninsula,the shoals of North Jiangsu,the Yangtze River Bank,the coast of the Zhejiang and Fujian Provinces and around the Okinawa trough.The driving mechanisms are coriolis effect and bottom friction effect.Stokes drifts had a larger magnitude and in a direction opposite to the Eulerian residual current in shallow waters,such as the coast of the Korean Peninsula,the shoals of North Jiangsu,the Yangtze River Bank,the coast of the Zhejiang and Fujian Provinces,because of the velocity and water level amplitude were large or the phase difference was close to 90 degrees.Lagrangian residual currents were the sum of Eulerian residual current and stokes drift,were equal to the residual transport velocity only in certain circumstances,but never will they be conceptually the same.The pattern of Lagrangian residual currents were similiar to that of the China coastal currents in many regions of the east China seas.Therefore,the tidal residual current was an important role in the sediment transport over the shelves.Potential changes in the tides caused by mean sea level rise(SLR)are of importance in coastal flooding,and many other applications.Assuming that coastal defenses are constructed along present-day shorelines,a series of numerical experiments were conducted to examine the response of tides to sea-level rise in the east China seas with uniform SLR scenarios from-0.5 m to +2.0 m above present-day sea level.The results showed that the amplitude of the principal M2 and Ki tidal constituents respond to SLR increased and decreased alternately in a spatially nonuniform manner.The change of M2 amplitude was proportional to SLR,while the change of Ki amplitude was complex.The M2 tidal amplitude was the main factor determining the tidal range.Significant tidal amplification mainly occured in the Bohai bay,Liaodong bay,Haizhou bay,Jianghua bay,Subei coast and Weihai or Yantai to the west Korea bay,where high-risk areas of sea intrusion may occur.The amplitude and mean tidal range decreased form estuary of Yangtze River,Hangzhou Bay to Tsushima Strait,in Laizhou Bay and in Taiwan strait.Possible mechanisms responsible for these changes were mainly related to bottom friction decreasing,amphidromic point migration,and resonant effect change.Additionally,the reflectivity of tidal energy flux increased after sea level rise.The dissipation rate increased at the headland with zigzag shoreline and decreased in other areas.The position of the tidal mixing front also shifted.The changes in the amplitude of Ma tide,the tidal current asymmetry,and tidal residual currents,will alter the mass transport processes in the east China seas.