Observed water current and transport through Qiongzhou Strait during August 2010

The velocity structure of the residual current across an entire section of the Qiongzhou Strait(QS) in summer is presented for the fi rst time. Shipboard Acoustic Doppler Current Profi le measurements, from the mid-region of the QS(110.18°E), were collected on 1–4 August 2010. The diurnal tidal currents had their maximum amplitudes between 4.24 and 20.24 m. Their amplitude along the major axis ranged from approximately 0.55 m/s in the middle part of the strait(20.15°N) to 0.84 m/s in the north part of the strait(20.20°N). Both anticlockwise and clockwise tidal current rotations exist in the QS. During the observation period(neap tide), a signifi cant westward residual current occupied almost the entire study section. Two velocity cores of westward current were observed at the northern part and near the deepest trough, although an eastward current appeared in the middle part of the transect. The deepest core was located near 62 m at 20.13°N, with a maximum velocity of-0.34 m/s. The shallower core was located at approximately 16 m at 20.20°N, with a maximum velocity of-0.33 m/s. The estimated total volume of water transported through the QS was-0.16 Sv. This value is an important boundary condition, applicable to numerical models studying coastal ocean circulation in the northwestern South China Sea.     

NUMERICAL STUDY ON THE FORMATION OF THE SOUTH CHINA SEA WARM CURRENT Ⅰ.BAROTROPIC CASE

In this work, Princeton Ocean Model (POM) was used to study the formation of the South China Sea Warm Current (SCSWC) in the barotropic case. Monthly averaged wind stress and the inflow/outflow transports in January were used in the numerical simulation which reproduced the SCSWC. The effects of wind stress and inflow/outflow were studied separately. Numerical experiments showed thatthe Kuroshio intrusion through the Luzon Strait and the slope shelf in the northern SCS are necessary conditions for the founation of the SCSWC. In a flat bottom topography experiment, the wind stress drivennortheast current in the northern SCS is a compensatory current.     

NUMERICAL STUDY ON THE FORMATION OF THE SOUTH CHINA SEA WARM CURRENT Ⅱ. BAROCLINIC CASE

In this part, Levitus‘ climatological temperature and salinity are incorporated in the numerical model developed in Part I. Diagnostic and prognostic experiment on the thermohaline circulation were conducted. The smooth Levitus‘ data do not include any information on the South China Sea Warm Current (SCSWC), so it is not in the model-produced diagnostic thermohaline circulation. Although the SCSWC does not appear in the wind-driven circulation in the barotropic case, it appears in the prognostic wind-driven circulation in the baroclinic case. This implies that the differing circulation pat-terns between barotropic case and bareclinic case are due to the stratification. The prognostic thermohaline circulation with wind stress and inflow/outflow transports at open boundaries are also discussed. Coupling of density and dynamic forces makes the circulation pattern more complicated, Even though the stratification is not always a direct cause of the formation of the SCSWC, it is at least an indirect cause.     

A layered numerical model for simulating the generation and propagation of internal tides over continental slope III. Numerical experiments and simulation

The layered model in Part I was used to simulate the internal tide in a stratified, two layer, and rectangular sea area with step-like topography. The internal tide current velocities of the upper and lower layers and the interfacial elevations were computed and the effect of the upper layer water depth and density difference were studied. Numerical experiments verified that the model can correctly simulate internal tides. The model was also applied to the northwestern part of the South China Sea to simulate the internal tides there with real topography. The distributions of internal tide amplitude in interfaces were delineated. Contribution No. 3590 from the Institute of Oceanology, Chinese Academy of Sciences. Project 49676275 supported by NSFC and also supported by National Special Research Program 97-926-05-02.     

Optimal estimation of zonal velocity and transport through Luzon Strait using variational data assimilation technique

A P-vector method was optimized using variational data assimilation technique, with which the vertical structures and seasonal variations of zonal velocities and transports were investigated. The results showed that westward and eastward flowes occur in the Luzon Strait in the same period in a year. How ever thenet volume transport is westward. In the upper level (0m -- -500m), the westward flow exits in the middle and south of the Luzon Strait, and the eastward flow exits in the north. There are two centers of westward flow and one center of eastward flow. In the middle of the Luzon Strait, westward and eastward flowes appear alternately in vertical direction. The westward flow strengthens in winter and weakens in summer. The net volume transport is strong in winter (5.53 Sv) but weak in summer (0.29 Sv). Except in summer, the volume transport in the upper level accounts for more than half of the total volume transport (0m -- bottom). In summer, the net volum etransport in the upper level is eastward (1.01 Sv), but westward underneath.     

Numerical Study of Water and Suspended Matter Exchange Between the Yellow Sea and the East China Sea

INTRODUCTIONTheYellowSeaandtheEastChinaSea (ECS)aremarginalseasofthenorthwestPacificandhaveexpansivecontinentalshelves .TheuniqueandstrikingfeaturesoftheYellowSeaandtheECSarethattheyhavestrongtidalcurrent;aresubjecttostrongmonsooninfluence ;andreceiveinflowfromthebiggestriverinChina ,theChangjiangRiver ;andthatthefamouswesternboundarycurrent,theKuroshio ,passesthroughtheECS ,withitsbranchesintrudingupwardintothecontinentalshelfareas.Generallyspeaking ,thewaterexchangecapacityofthe…     

Energetics and temporal variability of internal tides in Luzon Strait: a nonhydrostatic numerical simulation

A fully nonlinear,three-dimensional nonhydrostatic model driven by four principal tidal constituents(M2,S2,K1,and O1) is used to investigate the spatial-temporal characteristics and energetics of internal tides in Luzon Strait(LS).The model results show that,during spring(neap) tides,about 64(47) GW(1 GW=109 W) of barotropic tidal energy is consumed in LS,of which 59.0%(50.5%) is converted to baroclinic tides.About 22(11) GW of the derived baroclinic energy flux subsequently passes from LS,among which 50.9%(54.3%) flows westward into the South China Sea(SCS) and 45.0%(39.7%) eastward into the Pacific Ocean,and the remaining 16(13) GW is lost locally owing to dissipation and convection.It is revealed that generation areas of internal tides vary with the spring and neap tide,indicating different source areas for internal solitary waves in the northern SCS.The region around the Batan Islands is the most important generation region of internal tides during both spring and neap tides.In addition,the baroclinic tidal energy has pronounced seasonal variability.Both the total energy transferred from barotropic tides to baroclinic tides and the baroclinic energy flux flowing out of LS are the highest in summer and lowest in winter.     

A COMPARISON OF EASTERN AND WESTERN HONG KONG PHYTOPLANKTON FROM WEEKLY SAMPLES （1997-1999）

Weekly phytoplankton samples were taken from western Hong Kong (Lamma) from Jan. 1997 to Dec. 1999 and from Port Shelter in Eastern Hong Kong from January 1998 to December 1999. During that time diatom blooms occurred repeatedly at both sites but never in synchrony. One species would bloom at one site and then weeks later it or another species would bloom at the other site; while the 1998 red tide of the mucus producing dinoflagellateGymnodinium mikimotoi occurred at both sites. It first occurred at the Port Shelter site in March and did not appear at the Lamma site until April. With the single exception of this species, no other dinoflagellate reached bloom concentrations at the Lamma site. In addition, dinoflagellate abundance at the Lamma site was significantly lower (P<0.05) than that at the Port Shelter site. This was correlated with a significantly higher turbidity (i. e. low Secchi transparency) and higher turbulence (stronger currents) at the Lamma site. Annual variation in surface temperature correlated with total surface phytoplankton abundance at both our sample sites. Phytoplankton abundance increased in spring as water temperatures warmed. In fall, as surface water temperatures began to decline and the monsoon rains became less frequent there was a reduction in phytoplankton abundance associated with the reduction in temperature and light. Because so many variables co-occur with temperature (e. g. the amount of rainfall light intensity and light duration etc.) it is not possible to cite temperature as the causal factor associated weth controlling phytoplankton abundance at our two sample sites. Our data support the rather controversial notion that percentage-wise, there are relatively more harmful bloom forming species in nutrient-rich coastal waters than there are in the world's oceans. 16% of the dinoflagellate species and 10.3% of the diatom species observed at our two sample sites were classed as harmful. These percentages were higher than those cited by Sournia (1995) for the worlds oceans (9.6% and 6.8% respectively). This raises the possibility that there are relatively more toxic species in the nutrient-rich coastal waters of the world than there are in the mid ocean nutrient-poor areas of the world. Some reasons for this are briefly discussed.     

Surface inflow into the South China Sea through the Luzon Strait in winter

We studied the driving force of the Kuroshio intrusion into the South China Sea (SCS) during the winter monsoon, using satellite-tracked drifters entering the Luzon Strait (LS) through the Balintany and Babuyan Channels from the Philippine Sea. Most drifters passing through the Babuyan Channel in winter entered the interior SCS without a significant change in velocity. However, half of the drifters passing through the Balintany Channel entered the SCS at ~30 cm/s, which was faster than when they entered the LS. The other half continued moving northwestward into the Kuroshio and returned to the North Pacific. Quantitative analyses, using surface climatological wind and sea surface height anomaly (SSHa) data explained both the difference in velocity of drifters between the two channels and their acceleration through the Balintany Channel. The results suggest that the positive meridional gradient of sea surface height in the Luzon Strait, caused by the pileup of seawater driven by the Northeast monsoon, as well as Ekman flow, contribute to the Kuroshio intrusion into the SCS through the Babuyan and Balintany Channels. The former may be the main driving force.     

Numerical experiments on the wind-driven circulation in the Bohai, Huanghai and East China Seas in winter

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GEOCHEMICAL STUDY OF THE CORE S01 IN THE SOUTH CHINA SEA

Si, Ti, Al, Fe, Mn, Ca, Mg, K, Na, P and Sr, Ba, Rb, Ga, V, Zr, Cr, Ni, Co, Cu, Zn, Pb,Nb, Y, Th, La in the core S01 were analyzed and the pattems of their enrichment are discussed.Enrichment of Na, Fe, Mn, Ba, Cu elements in the core indicates volcanic material are an importantsoarce of the sediments in the area. The enrichment frequently varying with the deposition processshows bottom volcanism is frequent in the area and that the studied area is a margin basin with distinctoceanic characteristics. The abnormal enrichment of Mn at the layers(0-15 cm and 665-670 cm) of the core could beclosely related to and so, indicate, the wide deposition hiatus that have occurred in the West PacificOcean and adjacent margin seas since Late Pleistocene.     

Numerical study on global motion of Truss Spar in frequency and time domains for the Liwan 3-1 area

Using frequency and time domain analysis, the authors analyzed the hydrodynamics and motion behavior of a Truss Spar platform at a water depth of 1500 m in the Liwan 3-1 area of the South China Sea. Firstly, the seakeeping ability is acquired in the frequency domain by calculating the hull’s hydrodynamics and comparing with a semi-submersible platform. The random wave analysis for 100-year, 10-year and 1-year return periods in Liwan 3-1 distinctly shows lower heave but larger surge and pitch re-sponses of the Truss Spar than those of a semi-submersible. Secondly, 3-hour motions of the Truss Spar are predicted and compared in the time domain under 100-year return period conditions in Liwan 3-1 and the Gulf of Mexico. Thirdly, the hull/mooring line cou-pled and uncoupled models are compared. Finally, the responses of the Truss Spar under 10-year and 1-year return period conditions are assessed. The results reveal that the mooring line damping reflected by the coupled model distinctly decreases the low frequency motion. The maximum heave response for 100-year return period waves is 1.23m and below 0.1m for the case of 1-year return period.     

NUMERICAL STUDY ON THE INTERANNUAL OSCILLATION OF SEA SURFACE TEMPERATURE IN THE SOUTH CHINA SEA

A two and a half layer oceanic model of wind-driven, thermodynamical general circulation is appliedto study the interannual oscillation of sea surface temperature (SST) in the South China Sea (SCS). Themodel consists of two active layers: the upper mixed layer (UML) and the seasonal thermocline, with themotionless abyss beneath them. The governing equations which include momentum, continuity and sea.temperature for each active layer, can describe the physics of Boussinseq approximation, reduced gravityand equatorial β-plane. The formulas for the heat flux at the surface and at the interface between twoactive layers are designed on the Haney scheme. The entrainment and detrainment at the bottom of theUML induces vertical transport of mass,momentum and heat, and couples of dynamic andthermodynamic effect.Using leap-frog integrating scheme and the Arakawa-C grid the model is forced bya time-dependent wind anomaly stress pattern obtained from category analysis of COADS. The numerical results indicate that t     

Effects of tidal currents on nonlinear internal solitary waves in the South China Sea

The propagation and fission process of internal solitary waves (ISWs) with amplitudes of about 170 m are simulated in the northeast of the South China Sea (NSCS) by using the generalized Korteweg-de Vries (KdV) equation under continuous stratification. More attention is paid to the effects of the ebb and flood background currents on the fission process of ISWs. This kind of background current is provided by the composed results simulated in terms of monthly mean baroclinic circulation and barotropic tidal current. It is found that the obtained relation of the number of fission solitons to the water depth and stratification is roughly in accordance with the fission law derived by Djordjevic and Redekopp in 1978; however, there exists obvious difference between the effects of the ebb and flood background currents on the wave-lengths of fission solitons (defined as the distance between two neighboring peaks of ISWs). The difference in nonlinearity coefficient α between the ebb and flood background currents is a main cause for the different wave-lengths of fission solitons.     

Spatial distribution characteristics of surface tidal currents in the southwest of Taiwan Strait

This study was conducted on the spatial distribution characteristics of surface tidal currents in the southwestern Taiwan Strait based on the quasi-harmonic analysis of current data obtained by two high frequency surface wave radar (HFSWR) systems. The analysis shows that the tidal current pattern in the southwestern Taiwan Strait is primarily semi-diurnal and influenced significantly by shallow water constituents. The spatial distribution of tidal current ellipses of M₂ is probably affected by the interaction between two different systems of tide wave, one from the northern mouth of Taiwan Strait and the other from the Bashi Channel. The directions of the major axes of M₂ tidal current ellipses coincide roughly with the axis of the Taiwan Strait. The spatial distribution of the magnitudes of the probable maximum current velocity (PMCS) shows gradual increase of the velocity from northeast to southwest, which is in accordance with the spatial distribution of the measured maximum current velocity (MMCS). The directions of the residual currents are in accordance with the direction of the prevailing monsoon wind at the Taiwan Strait and the direction of the Taiwan warm current during summer. The bathymetry also shows a significant effect on the spatial distribution characteristics of tidal currents.     

渤海海峡亚海鲂属鱼类一新记录种——云纹亚海鲂

2012年12月3日,在渤海海峡的蓬莱近海浅水海域捕获雄性成体鱼1尾,该鱼体长34 cm,体高18cm,体长为体高的1.9倍,体宽4.5 cm,头长12.5 cm,体长为头长的2.7倍,尾柄长4.5 cm,体光滑无鳞。管状侧线前半部弧形,后半部平直,行于体中央。棘状骨板沿背鳍基底两侧各12块,臀鳍基底两侧各8块,每一骨板中央具1棘,向后;胸部6块,自第3骨板开始分左右两行;腹部7块,自第2骨板开始分左右两行,胸腹部骨板棘小,形成锯齿缘。背鳍1个,鳍棘部与鳍条部之间有一深缺刻;鳍棘细长,棘间鳍膜延长成丝状,最长超过尾鳍末端。据其形态特征和测量值,鉴定为云纹亚海鲂(Zenopsis nebulosa Temminck et Schlegel,1847),为该海域首次记录。     

南海海域数种海藻总脂质及脂肪酸含量的比较

研究南海海域盛产的四种褐藻(海带、裙带菜、昆布和亨氏马尾藻)、三种红藻(紫菜、沙菜和江蓠)及来自南海三个不同海区(南沙、惠来和南澳)亨氏马尾藻的总脂质及脂肪酸含量干重,并重点比较其多不饱和脂肪酸的含量.结果表明,供试褐藻类海藻总脂质含量ω在1.81%～6.11%之间,红藻类海藻的总脂质含量ω在1.44%～3.96%之间;紫菜中含有7.548mg/g(干重,下同)的亚油酸(C182);海带含丰富C181,达5.592mg/g;花生四烯酸(C204)在裙带菜中含量为1.606mg/g;在供试藻种中,昆布的EPA(C20.5)和DHA(C226)含量最高,测定值为608μg/g和689μg/g.     

Water masses in the South China Sea and water exchange between the Pacific and the South China Sea

Water masses in the South China Sea (SCS) were identified and analyzed with the data collected in the summer and winter of 1998. The distributions of temperature and salinity near the Bashi Channel (the Luzon Strait) were analyzed by using the data obtained in July and December of 1997. Based on the results from the data collected in the winter of 1998, waters in the open sea areas of the SCS were divided into six water masses: the Surface Water Mass of the SCS (S), the Subsurface Water Mass of the SCS (U), the Subsurface-Intermediate Water Mass of the SCS (UI), the Intermediate Water Mass of the SCS (I), the Deep Water Mass of the SCS (D) and the Bottom Water Mass of the SCS(B). For the summer of 1998, the Kuroshio Surface Water Mass (KS) and the Kuroshio Subsurface Water Mass (KU) were also identified in the SCS. But no Kuroshio water was found to pass the 119.5°E meridian and enter the SCS in the time of winter observations. The Sulu Sea Water (SSW) intruded into the SCS through the Mindoro Channel between 50–75 m in the summer of 1998. However, the data obtained in the summer and winter of 1997 indicated that water from the Pacific had entered the SCS through the northern part of the Luzon Strait in these seasons, but water from the SCS had entered the Pacific through the southern part of the Strait. These phenomena might correlate with the 1998 El-Niño event.     

NUMERICAL STUDY ON THE TIDAL FRONT IN THE WESTERN YELLOW SEA

The formation and evolution of the tidal front in the western Yellow Sea are studied by means of a two-dimensional model in which wind and tide mixing, sun radiation and wind stress, and realistic topography are incorporated. In this numerical study, the schemes employed are stable for time step t= 900 s, so the model can be run for 4 months to simulate the front evolution. The authors examined the effects of mixing and atmospheric forcing on the tidal front under conditions of : mixing and solar heating without wind stress on the sea surface; mixing, solar heating and 50 hours of wind stress; mixing, solar heating and long time periodical wind stress, Results show that (1) the tidal front forms at the beginning of May, and strengthens with the increasing of heat input, (2) the temperature structure in the shallow well-mixed water is dominated by mixing, while in the front and deeper stratified regions, it is controlled by the joint effects of (mainly) mixing and advection, 0) the currents and front all     

Numerical simulation of the structure and variation of upwelling off the east coast of Hainan Island using QuikSCAT winds

The spatial structure and variation of the upwelling in the waters east and northeast of Hainan Island, China during 2000-2007 were investigated using a nested high-resolution Princeton Ocean Model (POM) forced by QuikSCAT winds. The model produced good simulations of the summer upwelling and the seasonal and annual variability. Strong upwelling occurs from mid-July to mid-August with a peak east of Hainan Island associated with the southwesterly monsoon in the South China Sea. Sensitivity experiments indicated that when the local wind stress controls the variability of the upwelling, the large-scale circulation significantly enhances the upwelling northeast of Hainan Island by inducing a local upwelling and transporting cold water northeast-ward along the island’s east coast. The joint effects of the local wind stress and large-scale circulation result in stronger upwelling northeast of Hainan Island. This implies that the annual variation of the upwelling northeast of Hainan Island is controlled not only by the local alongshore wind stress but also by the large-scale circulation. This result will help us investigate the decadal variation of the upwelling in this region in the future.