NUMERICAL EXPERIMENTS ON THE WIND-DRIVEN CIRCULATION IN THE BOHAI, HUANGHAI AND EAST CHINA SEAS IN WINTER

A new semi implicit numerical model developed to investigate the wind driven circulation (with inflow and outflow) in the Bohai, Huanghai and East China Sea in winter showed that the open boundary conditions and wind forcing are important in controlling general circulation in wintertime; that open boundary conditions (such as Kuroshio, Changjiang River runoff) are primary factors controlling the East China Sea circulation; and that wind driven current is more important in the upper layer in shallow sea area (such as Bohai Sea, North Huanghai Sea, as well as coastal area) in winter. Two numerical experiments are discussed to demonstrate the circulation responding to the changes of the open boundary conditions.

Preliminary analysis of distribution and variation of perennialmonthly mean water masses in the Bohai Sea,the Huanghai Sea and the East China Sea

On the basis of perennial monthly mean temperature and salinity data, the classification of monthly water masses at the surface and the bottom in the Bohai Sea, the Huanghai Sea and the East China Sea, has been made by using the method of fuzzy cluster from the modified characteristic of water masses in the shallow water area. In this paper, the basic features, growth and decline patterns of water masses in relation to fishing grounds in the whole shelves of the Bohai Sea, the Huanghai Sea and the East China Sea are discussed with emphasis.

Basic characteristics and forming mechanism of the sharp thermocline in the Bohai Sea, Huanghai Sea and northern East China Sea

On the basis of the fact that the sharp thermocHne in the Bohai Sea and the northern Huanghai Sea is often distributed in the deep valley areas, it has been long thought that the reason of the formation of the sharp thermocHne is that the cold water can be easily kept in valleys. But recent investigations carried out in the southern Huanghai Sea in summer show that all of the sharp thermocHne areas were distributed in the shallow sloping-bottom areas but not in the deep valley areas. Only in autumn would the sharp thermoclines translate to the deep valley areas. In summer, they are characterized by shallow upper mixing layer and thin thickness in the southern Huanghai Sea. In addition to entrainment coming from lower boundary of upper mixing layer the entrainment from upper border of bottom homogeneous layer induced by tidal mixing also plays an important role in the growth and decay of thermoclines in these seas.

Sea level change under IPCC-A2 scenario in Bohai, Yellow, and East China Seas

Because of the environmental and socioeconomic impacts of anthropogenic sea level rise （SLR）, it is very important to understand the processes leading to past and present SLRs towards more reliable future SLR projections. A regional ocean general circulation model （ROGCM）, with a grid refinement in the Bohai, Yellow, and East China Seas （BYECSs）, was set up to project SLR induced by the ocean dynamic change in the 21st century. The model does not consider the contributions from ice sheets and glacier melting. Data of all forcing terms required in the model came from the simulation of the Community Climate System Model version 3.0 （CCSM3） under the International Panel on Climate Change （IPCC）-A2 scenario. Simulation results show that at the end of the 21st century, the sea level in the BYECSs will rise about 0.12 to 0.20 m. The SLR in the BYECSs during the 21st century is mainly caused by the ocean mass redistribution due to the ocean dynamic change of the Pacific Ocean, which means that water in the Pacific Ocean tends to move to the continental shelves of the BYECSs, although the local steric sea level change is another factor.

Effects of internal tidal dissipation and self-attraction and loading on semidiurnal tides in the Bohai Sea, Yellow Sea and East China Sea： a numerical study

A parameterized internal tide dissipation term and self-attraction and loading(SAL) tide term are introduced in a barotropic numerical model to investigate the dynamics of semidiurnal tidal constituents M_2 and S_2 in the Bohai Sea, Yellow Sea and East China Sea(BYECS). The optimal parameters for bottom friction and internal dissipation are obtained through a series of numerical computations. Numerical simulation shows that the tide-generating force contributes 1.2% of M_2 power for the entire BYECS and up to 2.8% for the East China Sea deep basin. SAL tide contributes 4.4% of M_2 power for the BYECS and up to 9.3% for the East China Sea deep basin. Bottom friction plays a major role in dissipating tidal energy in the shelf regions, and the internal tide eff ect is important in the deep water regions. Numerical experiments show that artifi cial removal of tide-generating force in the BYECS can cause a signifi cant dif ference(as much as 30 cm) in model output. Artifi cial removal of SAL tide in the BYECS can cause even greater diff erence, up to 40 cm. This indicates that SAL tide should be taken into account in numerical simulations, especially if the tide-generating force is considered.

Pore-water distribution and quantification of diffusive benthic fluxes of nutrients in the Huanghai and East China Seas sediments

The distribution of nitrate, nitrite, ammonia, phosphate and silicate in pore-water and their exchange between sediments and overlying waters （benthic flux） were determined at nine locations on the shelve of Huanghai and East China Seas. On the basis of the redox potential of sediments and nutrients distributions in the pore-waters, it is found that the benthic sediments are being in a suboxic to anoxic environment in the Huanghai and East China Seas. The nutrients distribution in the pore-waters is mainly controlled by the sediment environment, and ammonia is the major inorganic nitrogen in the pore-waters. On the basis of benthic fluxes of nutrients calculated us- ing Fick＇s first law, there is remarkable efflux of ammonia, dissolved inorganic nitrogen（DIN）, phosphate and silicate from the sediments to the overlying waters in the study area, and their benthic fluxes are 299.3-2 214.8, 404.4-2 159.5 , 5.5-18.8 and 541.3-1 781.6 μmol/（m^2·d） respectively, and perhaps they are the major source of dissolved inorganic nitrogen, phosphate and silicate for the overlying water. At most stations, the nitrate flux was from the overlying waters to the sediments, which suggests that suboxic organic matter decomposition via denitrification is dominated in the most area of Huanghai and East China Seas. High benthic fluxes appearing in the coastal area and relatively low benthic fluxes occurring in the shelf area are found and are consistent with pri- mary productivity zoning in the study area. On the other hand, the ammonia flux displays an exponential decrease with water depth increase and an exponential increase with the bottom water temperature. However, others do not display this trend.

Vertical displacement loading tides and self-attraction and loading tides in the Bohai, Yellow, and East China Seas

The loading tides are calculated by means of the Green's function method based on a high-resolution regional ocean tide model, the TOPO7.0 global ocean tide model, and the Gutenberg-Bullen A Earth model. The results show that the maximal amplitude of M2 vertical displacement loading (VDL) tide in the Bohai, Yellow, and East China Seas exceeding 28mm appears 150km off the Zhejiang coast; the second maximum exceeding 20mm appears in Inchon Bay; and the third maximum exceeding 14mm is located in the northeast of the North Yellow Sea. The maximal amplitudes of S2 VDL tide at the above three locations exceed 10, 8, and 4mm, respectively. The maximal amplitudes of the K1 and O1 VDL tides, exceeding 13 and 10 mm respectively, appear near the central and north Ryukyu Islands; the amplitudes tend to decease toward the inward areas. The phases of semidiurnal VDL tides are basically opposite to those of corresponding ocean tides. The phases of diurnal VDL tides are basically opposite to those of corresponding ocean tides in the most part of the East China Sea and the eastern part of the South Yellow Sea. This anti-phase relationship generally does not hold in the rest parts of the Bohai and Yellow Seas. The distribution patterns of self-attraction and loading (SAL) tides are very similar to those of VDL tides. The SAL tides have amplitudes about 1.2-1.7 times of the corresponding VDL tides and their phases are basically opposite to the corresponding VDL tides. The maximal amplitude of M2 SAL tide also appears off the Zhejiang coast, with a magnitude exceeding 42mm.

Study on interaction between the coastal water, shelf water and Kuroshio water in the Huanghai Sea and East China Sea

The main processes of interaction between the coastal water, shelf water and Kuroshio water in the Huanghai Sea (HS) and East China Sea (ECS) are analyzed based on the observation and study results in recent years. These processes include the intrusion of the Kuroshio water into the shelf area of the ECS, the entrainment of the shelf water into the Kuroshio, the seasonal process in the southern shelf area of the ECS controlled alternatively by the Taiwan Strait water and the Kuroshio water intruding into the shelf area, the interaction between the Kuroshio branch water, shelf mixed water and modified coastal water in the northeastern ECS, the water-exchange between the HS and ECS and the spread of the Changjiang diluted water.

Spatial and temporal variations of macro-and mesozoo-plankton community in the Huanghai Sea (Yellow Sea) and East China Sea in summer and winter

The study was conducted during two cruises of June–August 2006 （summer）,and January–February 2007 （winter） in the Huanghai （Yellow） Sea and East China Sea.Spatial and temporal variations of zooplankton abundance,biomass and community structure and its relation to currents and water masses over the continental shelf were examined.A total of 584 zooplankton species/taxa and 28 planktonic larvae were identified during the two surveys.Copepods were the most abundant component among these identified groups.Zooplankton abundance and biomass fluctuated widely and showed distinct heterogeneity in the shelf waters.Five zooplankton assemblages were identified with hierarchical cluster analysis during this study,and they were Huanghai Sea Assemblage,Changjiang Estuary Assemblage,Coastal Assemblage,East China Sea Mixed-water Assemblage and East China Sea Offshore Assemblage.Seasonal changes of zooplankton community composition and its geographical distribution were detected,and the locations of the faunistic areas overlap quite well with water masses and current systems.So we suggest that the zooplankton community structure and its changes were determined by the water masses in the Huanghai Sea and East China Sea.The results of this research can provide fundamental information for the long-term monitoring of zooplankton ecology in the shelf of Huanghai Sea and East China Sea.

Variability of the circulation in the southern Huanghai Sea and East China Sea during the two investigative cruises in June 1999

On the basis of the hydrographic data obtained from June 17 to 25, 1999 on board R/V Eardo , Korea (hereafter'the second cruise'), the circulation in the southern Huanghai Sea and East China Sea is computed by using the modified inverse method. The comparison between the two computed results in the first cruise, which was carried out from June 4 to 19, 1999 on board R/V Xiangyanghong 14, China, and in the second cruise is made. The following results have been obtained. (1) Part of the Kuroshio flows northward through the eastern part of Section E, and its volume transport(VT) is about 6.2×106 m3/s,and its maximum velocity is about 93 cm/s.This shows that most of the Kuroshio flows northward through the region east of Section E.The VT of the offshore branch of Taiwan Warm Current west of the Kuroshio through Section E is about 0.4×106 m3/s. (2) There is the following variability between these two cruises, whose time difference is about two weeks:① The position of the Kuroshio in the second cruise is slightly more east than that in the first cruise; ②The high-density water (HDW) with a cold water occurs in the region south of Cheju Island between 125°30' and 127°E at Sections D and C. The circulation in the region of HDW is cyclonic. Comparing the position of HDW during the second cruise with that during the first cruise,it is found that its position in the second cruise moves slightly northward.(3) The cold and uniform mixing layer occurs in the layer from the 30 m level to the bottom of the middle part of Section A and in the layer from the 20 m level to the bottom of the middle part of Section B,respectively.They are both the southern part of the Huanghai Sea Cold Water Mass (HSCWM). (4) There are higher temperature and lower density with a weaker anticyclonic circulation in the southwestern part of the computed region.Its center is located at the westernmost point of Section E.

Application of biologic silicon in modern sedimentary section to reconstruction of phytoplankton changes in the East China Sea and the Huanghai Sea during last 200 years

Biomarkers had been widely used to reconstruct phytoplankton productivity, and this method was applied in the East China Sea and the Huanghai Sea （Yellow Sea）. In this study, Biologic Silicon （BSi） was used as productivity proxy to reconstruct productivity change of phytoplankton during last 200 years. The results show that the BSi contents of surficial＇sediments were in the range of 0.018%-2.516%, averaging 0.726%, and had a similar variation trend with phytoplankton biomass. The vertical distribution profiles revealed that BSi contents were relatively stable, in accordance with the variations of the contemporary phytoplankton standing crop index. According to the stability analysis of BSi in sediments, BSi was not degradaded for the past two hundred years and remained in sediments steadily. Thus, BSi in sediments had the potential to invert paleoproductivity. To conduct further survey, the linear regression equation between BSi contents and phytoplankton biomass index could be used to calculate the phytoplankton productivity by BSi, so that paleoproduetivity may be reconstructed during last 200 years.

Thermal fronts and cross-frontal heat flux in the southern Huanghai Sea and the East China Sea

Synoptic features in/around thermal fronts and cross-frontal heat fluxes in the southern Huanghai./Yellow Sea and East China Sea （HES） were examined using the data collected from four airborne expendable bathythermograph surveys with horizontal approxmately 35 km and vertical 1 m（from the surface to 400 m deep） spacings. Since the fronts are strongly affected by HES current system, the synoptic thermal features in/around them represent the interaction of currents with surrounding water masses. These features can not be obtained from climatological data. The identified thermal features are listed as follows ： （ 1 ） multiple boundaries of cold water, asymmetric thermocline intrusion, locally-split front by homogeneous water of approxmately 18 ℃, and mergence of the front by the Taiwan Warm Current in/around summertime southern Cheju - Changjiang/Yangtze front and Tsushima front; （2） springtime frontal eddy-like feature around Tsushima front; （3） year-round cyclonic meandering and summertime temperature-inversion at the bottom of the surface mixed layer in Cheju - Tsushima front; and （4） multistructure of Kuroshio front. In the Kuroshio front the mean variance of vertical temperature gradient is an order of degree smaller than that in other HES fronts. The southern Cheju- Changjiang front and Cheju -Tsushima front are connected with each other in the summer with comparable cross-frontal temperature gradient. However, cross-frontal heat flux and lateral eddy diffusivity are stronger in the southern Cheju - Changjiang front. The cross-frontal heat exchange is the largest in the mixing zone between the modified Huanghai Sea bottom cold water and the Tsushima Warm Current, which is attributable to enhanced thermocline intrusions.

The circulation in the southern Huanghai Sea and northern East China Sea in June 1999

On the basis of hydrographic data and current measurement (the mooring system, vessel-mounted ADCP and toward ADCP) data obtained in June 1999, the circulations in the southern Huanghai Sea (HS) and northern East China Sea (ECS) are computed by using the modified inverse method. The Kuroshio flows northeastward through eastern part of the investigated region and has the main core at Section PN, a northward flow at the easternmost part of Section PN, a weaker anti-cyclonic eddy between these two northward flows, and a weak cyclonic eddy at the western part of Section PN. The above current structure is one type of the current structures at Section PN in ECS. The net northward volume transport (VT) of the Kuroshio and the offshore branch of Taiwan Warm Current (TWCOB) through Section PN is about 26.2 x 10(6) m(3)/s in June 1999. The VT of the inshore branch of Taiwan Warm Current (TWCIB) through the investigated region is about 0.4 x 10(6) m(3)/s. The Taiwan Warm Current (TWC) has much effect on the currents over the continental shelf. The Huanghai Sea Coastal Current (HSCC) flows southeastward and enters into the northwestern part of investigated region, and flows to turn cyclonically, and then it flows northeastward, due to the influences of the Taiwan Warm Current and topography. There is a cyclonic eddy south of Cheju Island where the Huanghai Sea Coastal Current flows to turn cyclonically. It has the feature of high dense and cold water. The uniform and cold water is occurred in the layer from about 30 m level to the bottom between Stations C306 and C311 at the northernmost Section C3. It is a southern part of the Huanghai Sea Cold Water Mass (HSCWM).

Four new recorded species of marine nanoplanktonic diatoms found in the East China Sea and Huanghai Sea

In a study of species composition of marine nanoplanktonic diatoms ( < 20 &mu;m) in water samples from the East China Sea and Huanghai Sea (Yellow Sea), four diatom species were identified by TEM as new records for China. They were Thalassiosira oceanica Hasle, Navicula britannica Hustedt et Aleem, Nitzschia leehyi Fryxell and Synedra indica Taylor. Detailed description of the taxonomic characteristics with TEM photographs of the four species and their ecological behavior and distribution is given in this paper.

Impact of the exceptionally high flood from the Changjiang River on the aquatic chemical distributions on the Huanghai Sea and East China Sea shelves in the summer of 1998

On the basis of the field observation in the Huanghai Sea and East China Sea in the summer of 1998, a rare event of exceptionally high discharge from the Changjiang River was described and how this high discharge altered water masses as well as chemical distributions on the shelves of the Huanghai Sea and East China Sea. The maximal extending ranges of the Changjiang diluted water and the nutrients in the freshwater from the Changjiang River were recorded for the first time. It was also found that there was a closed area with high oxygen and pH values in the offshore area of the southern Huanghai Sea and the northern East China Sea, indicating that the extensive spreading of nutrients due to the high discharge led to photosynthesis of phytoplankton mostly taking place in the offshore area far from the river mouth. The presence of ＂excess nitrogen＂ in almost all the northern East China Sea and the south of the Huanghai Sea suggests that these areas are potentially phosphorus-limited rather than nitrogen-limited, manifesting more like an estuarine ecosystem rather than a common marine ecosystem.

Three-dimensional calculations of the currents in the Huanghai Sea and East China Sea during June of 1999

Based on the wind and hydrographic data obtained by R/V Xiangyanghong 14 during June of 1999, the currents in the Huanghai Sea and East China Sea are computed by the three dimensional non-linear diagnostic, semidiagnostic models and prognostic in the a coordinate. The computed results show that the density and velocity fields and so on have been adjusted when time is about 3 days, namely the solution of semidiagnostic calculation is obtained. In the northwest part of the computed region, the Huanghai coastal current flows southeastward, and then it flows out the computed region south of Cheju Island. In the west side of the southern part of the computed region, there is other current, which is mainly inshore branch of Taiwan Warm Current, and it flows cyclonically and turns to the northeast. In the region north of the above two currents, there is a cyclonic eddy southwest of Cheju Island, and it has characteristics of high density and low temperature. There is an offshore branch of Taiwan Warm Current in the west side of the Kuroshio, and it makes a cyclonic meander, then flows northeastward. The Kuroshio in the East China Sea is stronger, and flows northeastward. Its maximum horizontal velocity is 108.5 cm/s at the sea surface, which is located at the northern boundary, and it is 106.1 cm/s at 30 m level, 102.2 cm/s at 75 m level and 85.1 cm/s at 200 m level, respectively, which are all located at the southern boundary. Comparing the results of diagnostic calculation with those of semidiagnostic and prognostic calculations indicates that the horizontal velocity field agrees qualitatively, and there is a little difference between them in quantity. The comparison between the computed velocities and the observed velocities at the mooring station show that they agree each other.

APPLICATION OF THE CLUSTERING METHOD IN ANALYSING SHALLOW WATER MASSES AND MODIFIED WATER MASSES IN THE HUANGHAI SEA AND EAST CHINA SEA

The idea of modified water masses is introduced and a cluster analysis is used for determining the boundary of modified water masses and its variety in the shallow water area of the Huanghai Sea (Yellow Sea) and the East China Sea. According to the specified standards to make the cluster, we have determined the number and boundary of the water masses and the mixed zones.The results obtained by the cluster method show that there are eight modified water masses in this area. According to the relative index of temperature and salinity,the modified water masses are divided into nine different characteristic parts. The water, masses may also be divided into three salinity types. On the TS-Diagram, the points concerning temperature and safinity of different modified mater masses are distributed around a curve, from which the characteristics of gradual modification may be embodied. The variation ranges of different modified water masses are all large, explaining the intensive modification of water masses in

Diagnostic study of the summer thermocline depth in the Huanghai Sea and the East China Sea

In this paper, the depth of the summer thermocline of the South Huanghai Sea and the East China Sea is calculated with two kinds of one-dimentional models, and the formation reasons are explained for the summer thermocline depth distribution characteristics in the study area. It is proved that in the shelf area of the East China Sea, tidal mixing has an important impact on the thermocline depth. And a new explanation for certain phenomena of the so-called coastal upwelling in the East China Sea is proposed.

AN ANALYSIS OF MODIFIED WATER MASSES IN THE YELLOW SEA AND EAST CHINA SEA

The waters in the shallow part of the Yellow Sea and East China Sea are affected greatly by climatic and geographical conditions and fail to possess homogeneity and conservativeness like oceanic waters. They have apparent difference in modified degrees, so we may regard a certain range of mixed water as a relatively independent one. In fact, the study of water masses in the shallow sea means a modified analysis of waters. The idea of modified water masses is introduced, i. e., a water body which holds the similar physical and chemical characters, occupies a certain space, and varies seasonally and regularly. On the T-S diagram, it displays as a certain amount of points aggregated together, the centre of which changes regularly and may have a process of combination and separation.According to the clustering method, there are eight modified water masses in this area. They may also be divided into three salinity types. On the T-S diagram, the points concerning temperature and salinity of different

Assimilating operational SST and sea ice analysis data into an operational circulation model for the coastal seas of China

The prediction of sea surface temperature （SST） is an essential task for an operational ocean circulation model. A sea surface heat flux, an initial temperature field, and boundary conditions directly affect the accuracy of a SST simulation. Here two quick and convenient data assimilation methods are employed to improve the SST simulation in the domain of the Bohai Sea, the Yellow Sea and the East China Sea （BYECS）. One is based on a surface net heat flux correction, named as Qcorrection （QC）, which nudges the flux correction to the model equation; the other is ensemble optimal interpolation （EnOI）, which optimizes the model initial field. Based on such two methods, the SST data obtained from the operational SST and sea ice analysis （OSTIA） system are assimilated into an operational circulation model for the coastal seas of China. The results of the simulated SST based on four experiments, in 2011, have been analyzed. By comparing with the OSTIA SST, the domain averaged root mean square error （RMSE） of the four experiments is 1.74, 1.16, 1.30 and 0.91~C, respectively; the improvements of assimilation experiments Exps 2, 3 and 4 are about 33.3%, 25.3%, and 47.7%, respectively. Although both two methods are effective in assimilating the SST, the EnOI shows more advantages than the QC, and the best result is achieved when the two methods are combined. Comparing with the observational data from coastal buoy stations, show that assimilating the high-resolution satellite SST products can effectively improve the SST prediction skill in coastal regions.