Chemicohydrographic characteristics of the Yellow Sea Cold Water Mass

Based on the field data obtained during summer cruises in 2006, the overall perspective of chemical and hydrographic characteristics of the Yellow Sea Cold Water Mass （YSCWM） are discussed through the cross- YSCWM transect profiles and horizontal distributions of hydrological and chemical variables, with emphasis on the differences between the northern Yellow Sea Cold Water Mass （NYSCWM） and the southern Yellow Sea Cold Water Mass （SYSCWM）. The results show that YSCWM is characterized by low temperature （〈10℃） and dissolved oxygen （DO） concentration, high salinity （〉32.0） and nutrient concentrations. Compared to the SYSCWM, the NYSCWM possesses lower values of temperature, salinity and nutrient concentrations but higher values of DO. Also its smaller variation ranges of variables （except for temperature） demonstrate that NYSCWM is more uniform than that of SYSCWM. In addition, thermocline is more intensive in the SYSCWM than that of NYSCWM. Furthermore, DO and Chl a maxima appear at the depth of 30 m in the SYSCWM, while these phenomena are not obvious in the NYSCWM.

The temporal and spatial variability of the Yellow Sea Cold Water Mass in the southeastern Yellow Sea, 2009–2011

The Yellow Sea Cold Water Mass （YSCWM） is one of the important water mass in the Yellow Sea （YS）. It is distributed in the lower layer in the Yellow Sea central trough with the temperature less than 10℃ and the salinity lower than 33.0. To understand the variability of the YSCWM, the hydrographic data obtained in April and August during 2009-2011 are analyzed in the southeastern Yellow Sea. In August 2011, relatively warm and saline water compared with that in 2009 and 2010 was detected in the lower layer in the Yellow Sea central area. Although the typhoon passed before the cruise, the salinity in the Yellow Sea central trough is much higher than the previous season. It means that the saline event cannot be explained by the typhoon but only by the intrusion of saline water during the previous winter. In April 2011, actually, warm and saline water （T 〉 10~C, S 〉34） was observed in the deepest water depth of the southeastern area of the Yellow Sea. The wind data show that the northerly wind in 2011 winter is stronger than in 2009 and 2010 winter season. The strong northerly wind can trigger the intrusion of warm and saline Yellow Sea Warm Current. Therefore, it is proposed that the strong northerly wind in winter season leads to the intrusion of the Yellow Sea Warm Current into the Yellow Sea central trough and influenced a variability of the YSCWM in summer.

Seasonal variability of the zooplankton community in the southwest of the Huanghai Sea (Yellow Sea) Cold Water Mass

Samples were collected with a plankton net in the four seasonal cruises during 2006-2007 to study the seasonal variability of the zooplankton community in the southwest part of Huanghai Sea Cold Water Mass （HSCWM, Yellow Sea Cold Water Mass）. The spatial and temporal variations of zooplankton species composition, biomass, abundance and biodiversity were examined. A total of 122 zooplankton species and 30 pelagic larvae were identified in the four cruises. Calanus sinicus and Aidanosagitta crassa were the most dominant species, and Themisto gaudichaudi and Euphau- sia pacifica were widely distributed in the HSCWM area. The spatial patterns of non-gelatinous zooplankton （removing the high water content groups） were similar to those of the total zooplank- ton biomass in autumn, but different significantly in the other three seasons. The seasonal means of zooplankton biomass in spring and summer were much higher than that in autumn and win- ter. The total zooplankton abundance averaged 283.5 ind./m3 in spring （highest）, 192.5 ind./m3 in summer, 165.5 ind./m3 in autumn and 65.9 ind./m3 in winter （lowest）, and the non-gelatinous groups contributed the most total abundance. Correlation analysis suggests that the non-gelatinous zooplankton biomass and abundance had a significant positive correlation in the whole year, but the relationship was insignificant between the total zooplankton biomass and abundance in spring and summer. The diversity index HI of zooplankton community averaged 1.88 in this study, which was somewhat higher than historical results. Relatively low diversity in summer was related to the high dominance of Calanus sinicus, probably due to the strongest effect of the HSCWM in this season.

Seasonal variations of phytoplankton phosphorus stress in the Yellow Sea Cold Water Mass

The Yellow Sea is located between the China Mainland and the Korean Peninsula, representing a typical shallow epicontinental sea. The Yellow Sea Cold Water Mass（YSCWM） is one of the most important physical features in the Yellow Sea. The characteristics of vertical profiles and seasonal variations of biogenic elements in the YSCWM may lead the variations of nutrient availability（e.g., phosphorus） and phosphorus stress of phytoplankton. In this study, the authors surveyed the seasonal variations of phytoplankton phosphorus stress with emphasis on the effect of the YSCWM during the four cruises in April and October 2006, March and August 2007. Using both bulk and single-cell alkaline phosphatase activity（APA） assays, this study evaluated phosphorus status of phytoplankton community, succession of phytoplankton community and ecophysiological responses of phytoplankton to phosphorus in the typical region of the YSCWM. With the occurrence of the YSCWM, especially the variations of concentration of dissolved inorganic phosphorus（DIP）, the results of bulk APA appeared corresponding seasonal variations. Along Transects A and B, the mean APA in August was the highest, and that in March was the lowest. According to the ELF-labeled assay＇s results, seasonal variations of the ELF-labeled percentages within dominant species indicated that diatoms were dominant in March, April and October, while dinoflagellates were dominant in August. During the four cruises, the ELF-labeled percentages of diatoms except Paralia sulcata showed that diatoms were not phosphorus deficient in April 2006 at all, but suffered from severe phosphorus stress in August 2007. In comparison, the ELF-labeled percentages of dinoflagellates were all above 50% during the four time series, which meant dinoflagellates such as Alexandrium and Scrippsiella, sustained perennial phosphorus stress.

The numerical investigation of seasonal variation of the cold water mass in the Beibu Gulf and its mechanisms

A wave-tide-circulation coupled model based on the Princeton Ocean Model is established to explore the seasonal variation of the cold water mass in the Beibu Gulf and its mechanisms. The results show that the cold water mass starts forming in March, reaches the maximum strength during June and July, and fades away since October. Strong mixing in winter transports the cold water from sea surface to bottom. The cold water mass remains in the bottom layer as the thermocline strengthens during spring, except for the shallow water where the themocline is broken by strong tidal mixing, which gradually separate the cold water mass from its surrounding warm water. Further analysis on the ocean current and stream function confirms that the cold water mass in the Beibu Gulf is locally developed, with an anticlockwise circulation caused by a strong temperature gradient. Sensitivity experiments reveal that the cold water mass is controlled by the sea surface heat flux, while the terrain and tidal mixing also play important roles.

Three new species of Genus Cryptonatica (Gastropoda,Naticidae) from Huanghai Sea Cold Water Mass

This report based on the results of investigations conducted in June 2007 and July 2008, respectively, on the benthic community structure and characteristic diversity of the Huanghai Sea （Yellow Sea） Cold Water Mass, as well as that in July 1959 during the national oceanic survey. The Naticidae specimens collected from Cold Water Mass in middle and northern Huanghai Sea were studied through morphological classification and the internal anatomy on radula. Three new species of Naticidae, i.e., Cryptonatica purpurfunda sp. nov., Cryptonatica sphaera sp. nov., and Cryptonatica striatica sp. nov. were identified. The morphological characteristics of the new species are described, and the similarties and differences between the new species and similar species are compared and discussed.

Particle flux through the Huanghai Sea cold water mass

Settling particulate matter （SPM） was collected by using sediment traps at four stations in a survey section from Qingdao to Cheju-do, across the Huanghai Sea cold water mass （HSCWM）, in August 2002. The sediment traps were planted in three layers： the upper layer of the thermocline （ULT） above the HSCWM, the lower layer of the thermocline （LLT）, and the bottom layer of water column （BL）. To determine the particle flux, the contents of organic carbon （POC）, organic nitrogen （PON）, total carbon （PC）, and total phosphorous （PP） in SPM were analyzed, and two flux models （Ⅰ and Ⅱ） were improved to calculate the resuspension ratio, with an assumption in Model Ⅰ that the vertical flux of SPM in the LLT equals the net vertical flux of SPM in the whole water column. An X value, i.e., the fraction of the resuspension flux originating from the surficial sediments nearby the sampling station, was deduced from Model Ⅰ to estimate the contribution of lateral currents to the total resuspension flux. The results showed that inorganic particles, fecal pellets, and miscellaneous aggregates were the major types of SPM in the HSCWM, and the contents of POC, PON, PC, and PP all decreased with water depth. A great deal of fecal pellets found in the LLT indicates that the main space producing biogenic SPM is the thermocline, and especially the LLT, where the C/N ratio is lower than that in the ULT. The resuspension ratios, 90%-96% among stations, imply strong impact ofresuspension on particle flux in the BL. These values were not significantly different between the two flux models, suggesting that the hypothesis in Model Ⅰ that the flux in the LLT equaling the net flux to the bottom is acceptable for shallow waters with stratification like the HSCWM. The POC export ratio from the HSCWM ranges from 35% to 68%. It benefits from the short sinking distance in shallow water. The upwelling in the HSCWM enhanced the POC flux through the water mass, and the lateral currents provides up to being greater than 50% ofresuspension flux in the BL according to evaluation of the X value.

Influence of the northern Yellow Sea Cold Water Mass on picoplankton distribution around the Zhangzi Island,northern Yellow Sea

Picoplankton distribution around the Zhangzi Island（northern Yellow Sea）was investigated by monthly observation from July 2009 to June 2010.Three picoplankton populations were discriminated by flow cytometry,namely Synechococcus,picoeukaryotes and heterotrophic prokaryotes.In summer（from July to September）,the edge of the northern Yellow Sea Cold Water Mass（NYSCWM）resulting from water column stratification was observed.In the NYSCWM,picoplankton（including Synechococcus,picoeukaryotes and heterotrophic prokaryotes）distributed synchronically with extremely high abundance in the thermocline（20 m）in July and August（especially in August）,whereas in the bottom zone of the NYSCWM（below 30 m）,picoplankton abundance was quite low.Synechococcus,picoeukaryotes and heterotrophic prokaryotes showed similar response to the NYSCWM,indicating they had similar regulating mechanism under the influence of NYSCWM.Whereas in the non-NYSCWM,Synechococcus,picoeukaryotes and heterotrophic prokaryotes exhibited different distribution patterns,suggesting they had different controlling mechanisms.Statistical analysis indicated that temperature,nutrients（NO3^and PO4^3-）and ciliate were important factors in regulating picoplankton distribution.The results in this study suggested that the physical event NYSCWM,had strong influence on picoplankton distribution around the Zhangzi Island in the northern Yellow Sea.

The sensitivity of numerical simulation to vertical mixing parameterization schemes: a case study for the Yellow Sea Cold Water Mass

The vertical mixing parameterization scheme,by providing the eff ects of some explicitly missed physical processes and more importantly closing the energy budgets,is a critical model component and therefore imposes signifi cant impacts on model performance.The Yellow Sea Cold Water Mass(YSCWM),as the most striking and unique phenomenon in the Yellow Sea during summer,is dramatically aff ected by vertical mixing process during its each stage and therefore seriously sensitive to the proper choice of parameterization scheme.In this paper,a hindcast of YSCWM in winter of 2006 was implemented by using the Regional Ocean Modeling System(ROMS).Three popular parameterization schemes,including the level 2.5 Mellor-Yamada closure(M-Y 2.5),Generic Length Scale closure(GLS)and K-Profi le Parameterization(KPP),were tested and compared with each other by conducting a series of sensitivity model experiments.The infl uence of diff erent parameterization schemes on modeling the YSCWM was then carefully examined and assessed based on these model experiments.Although reasonable thermal structure and its seasonal variation were well reproduced by all schemes,considerable diff erences could still be found among all experiments.A warmer and spatially smaller simulation of YSCWM,with very strong thermocline,appeared in M-Y 2.5 experiment,while a spatially larger YSCWM with shallow mixed layer was found in GLS and KPP schemes.Among all the experiments,the discrepancy,indicated by core temperature,appeared since spring,and grew gradually by the end of November.Additional experiments also confi rmed that the increase of background diff usivity could eff ectively weaken the YSCWM,in either strength or coverage.Surface wave,another contributor in upper layer,was found responsible for the shrinkage of YSCWM coverage.The treatment of wave eff ect as an additional turbulence production term in prognostic equation was shown to be more superior to the strategy of directly increasing diff usivity for a coastal region.

Weak coupling between heterotrophic nanoflagellates and bacteria in the Yellow Sea Cold Water Mass area

A study was carried out to investigate the grazing pressure of heterotrophic nanoflagellates （HNF） on bac-teria assemblages in the Yellow Sea Cold Water Mass （YSCWM） area in October, 2006. The results show that the HNF abundance ranges from 303 to 1388 mL-1, with a mean of 884 mL-1. The HNF biomass is equivalent to 10.6%-115.6% of that of the bacteria. The maximum abundance of the HNF generally occurred in the upper 30 m water layer, with a vertical distribution pattern of surface layer abundance greater than middle layer abundance, then bottom layer abundance. The hydrological data show that the YSCWM is located in the northeastern part of the study area, typically 40 m beneath the surface. A weak correlation is found be- tween the abundances of HNF and bacteria in both the YSCWM and its above water layer. One-way ANOVA analysis reveals that the abundance of HNF and bacteria differs between inside the YSCWM and in the above water mass. The ingestion rates of the HNF on bacteria was 8.02±3.43 h-1 in average. The grazing rate only represented 22.75%±6.91% of bacterial biomass or 6.55%±4.24% of bacterial production, implying that the HNF razinR was not the major factor contributing to the bacterial loss in the YSCWM areas.

CHARACTERISTICS AND FORMATION CAUSES OF QINGDAO COLD WATER MASS

In this work, the main characteristics of the Qingdao Cold Water Mass were studied by using "the comparison analysis method" based on 1980 temperature,salinity and dissolved oxygen data on the western South Yellow Sea. The formation cause of the water mass was analyzed based on February of 1959 temperature and salinity data for this area and on some other authors’ studies. The results showed that the Qingdao Cold Water Mass has growing and vanishing processes: appears in the last ten days of March; has stable pattern in April; is biggest in its area in May; becomes small in its area in June; vanishes in July. It comes from the northern Shandong Coastal Water and is characterized by low temperature and salinity and high dissolved oxygen. The mass is formed under the joint effects of anticyclonic circulation and solar radiation.

Responses of Yellow Sea Cold Water Mass to Typhoon Bolaven

A two-month seabed-mounted observation(YSG1 area) was carried out in the western Yellow Sea Cold Water Mass(YSCWM) using an RDI-300 K acoustic Doppler current profiler(ADCP) placed at a water depth of 38 m in late summer, 2012. On August 2012, Typhoon Bolaven passed east of YSG1 with a maximum wind speed of 20 m s-1. The water depth, bottom temperature, and profile current velocities(including u, v and w components) were measured, and the results showed that the typhoon could induce horizontal current with speed greater than 70 cm s-1 in the water column, which is especially rare at below 20 meters above bottom(mab). The deepening velocity shear layer had an intense shear velocity of around 10 cm s-1 m-1, which indicated the deepening of the upper mixed layer. In the upper water column(above 20 mab), westward de-tide current with velocity greater than 30 cm s-1 was generated with the typhoon's onshore surge, and the direction of current movement shifted to become southward. In the lower water column, a possible pattern of eastward compensation current and delayed typhoon-driven current was demonstrated. During the typhoon, bottom temperature variation was changed into diurnal pattern because of the combined influence of typhoon and tidal current. The passage of Bolaven greatly intensified local sediment resuspension in the bottom layer. In addition, low-density particles constituted the suspended particulate matter(SPM) around 10 mab, which may be transported from the central South Yellow Sea by the typhoon. Overall, the intensive external force of the Typhoon Bolaven did not completely destroy the local thermocline, and most re-suspended sediments during the typhoon were restricted within the YSCWM.

A Numerical Study on the Density Driven Circulation in the Yellow Sea Cold Water Mass

The circulation of Yellow Sea Cold Water Mass(YSCWM) in the Southern Yellow Sea is investigated using a diagnostic 2D MITgcm model. The resolution of the computational grid is 900 m in the horizontal and 2 m in the vertical where an initial temperature distribution corresponding to a typical measured Yellow Sea Cold Water Mass was applied. The existence of YSCWM that causes fluid density difference, is shown to produce counter-rotating cyclonic horizontal eddies in the surface layer: the inner one is anti-cyclonic(clockwise) and relatively weaker(8–10 cm s-1) while the outer one is cyclonic(anti-clockwise) and much stronger(15–20 cm s-1). This result is consistent with the surface pattern observed by Pang et al.(2004), who has shown that a mesoscale anti-cyclonic eddy(clockwise) exists in the upper layer of central southern Yellow Sea, and a basin-scale cyclonic(anticlockwise) gyre lies outside of the anti-cyclonic eddy, based on the trajectories and drifting velocities of 23 drifters. Below the thermocline, there is an anti-cyclonic(clockwise) circulation. This complex current eddy system is considered to be capable of trapping suspended sediments and depositing them near the front between YSCWM and the coastal waters off the Subei coast, providing an explanation on the sediment depth and size distribution of mud patches in the Southern Yellow Sea. Moreover, sensitive test scenarios indicate that variations of bottom friction do not substantially change the main features of the circulation structure, but will reduce the bottom current velocity, increase the surface current velocity and weaken the upwelling around the frontal area.

Interannual salinity variability of the Northern Yellow Sea Cold Water Mass

This paper discusses the interannual variability of the Northern Yellow Sea Cold Water Mass(NYSCWM) and the factors that influence it,based on survey data from the 1976–2006 national standard section and the Korea Oceanographic Data Center,monthly E-P flux data from the European Centre for Medium-Range Weather Forecasts,and meridional wind speed data from the International Comprehensive Ocean-Atmosphere Data Set. The results show that:1) the mean salinity of the NYSCWM center has a slightly decreasing trend,which is not consistent with the high salinity center; 2) both the southern salinity front and the halocline of the NYSCWM display a weakening trend,which indicates that the difference between the NYSCWM and coastal water decreases; 3) the Yellow Sea Warm Current intrusion,the E-P flux of the northern Yellow Sea,and the strength of the winter monsoon will affect the NYSCWM salinity during the following summer.

Long-term temperature variation of the Southern Yellow Sea Cold Water Mass from 1976 to 2006

This paper discusses the long-term temperature variation of the Southern Yellow Sea Cold Water Mass(SYSCWM)and examines those factors that infl uence the SYSCWM,based on hydrographic datasets of the China National Standard Section and the Korea Oceanographic Data Center.Surface air temperature,meridional wind speed,and sea surface temperature data are used to describe the seasonal changes.Mean temperature of the two centers of the SYSCWM had diff erent long-term trends.The temperature of the center in the west of the SYSCWM was rising whereas that of the center in the east was falling.Mean temperature of the western center was related to warm water intrusion of the Yellow Sea Warm Current,the winter meridional wind,and the winter air temperature.Summer process played a primary role in the cooling trend of temperature in the eastern center.A decreasing trend of salinity in the eastern half of the SYSCWM showed that warm water intrusion from the south might weaken,as could the SYSCWM circulation.Weakened circulation provided less horizontal heat input to the eastern half of the SYSCWM.Less lateral heat input may have led to the decreasing trend in temperature of the eastern center of the SYSCWM.Further,warmer sea surface temperatures and less heat input in the deep layers intensifi ed the thermocline of the eastern SYSCWM.A stronger thermocline had less heat fl ux input from upper layers to this half of the SYSCWM.Stronger thermocline and weakened heat input can be seen as two main causes of the cooling temperature trend of the eastern center of the SYSCWM.

Annual variation in Calanus sinicus abundance and population structure in the northern boundary area of the Yellow Sea Cold Water Mass

The Yellow Sea Cold Water Mass(YSCWM) was suggested as an over-summering site of the dominant copepod species Calanus sinicus in coastal Chinese seas.Population abundance and structure were investigated by monthly sampling along three transects across the northern boundary of the YSCWM during 2009–2010.Results show that thermal stratification existed from June to October and that the vertical thermal difference increased with depth.Generally,total abundance was lowest in October and highest in June,and the female/male sex ratio was highest in February and lowest in August.Evident spatial differences in abundance were observed during the existence of the YSCWM.In June,total abundance averaged 158.8 ind/m3at well-stratified stations,and 532.1 ind/m3at other stations.Similarly,high abundances of 322.0 and 324.4 ind/m3were recorded from July to August inside the YSCWM,while the abundance decreased from 50.4 to 1.9 ind/m3outside the water mass.C.sinicus distribution tended to even out over the study area in September when the YSCWM disappeared.We believe that the YSCWM may retard population recruitment in spring and preserve abundant cohorts in summer.The summer population was transported to neritic waters in autumn.In addition to low temperatures,stable vertical structure was also an essential condition for preservation of the summer population.C.sinicus can survive the summer in marginal areas in high abundance,but the population structure is completely different in terms of C5 proportion and sex ratio.

Simulation of coupled pelagic-benthic ecosystem of the Yellow Sea Cold Water Mass

A one-dimensional coupled pelagic-benthic box model for the Yellow Sea Cold Water Mass (YSCWM) is developed. The model is divided into three boxes vertically according to the depths of thermocline and euphotic layer. It simulates well the oligotrophic shelf ecosystem of the YSCWM considering effects of nu- trients deposition and microbial loop. Main features of vertical structure of various variables in ecosystem of the YSCWM were captured and seasonal variability of the ecosystem was well reconstructed. Calculation shows that the contribution of microbial loop to the zooplankton can reach up to 60%. Besides, input of inorganic nutrients from atmospheric deposition is an important mechanism of production in upper layer of the YSCWM when stratified.

Tidal Effects on the Bottom Thermal Front of North Yellow Sea Cold Water Mass near Zhangzi Island in Summer 2009

Three seabed-mounted TD/CTD chains and two upward-looking acoustic Doppler current profilers (ADCPs) in the southwest of Zhangzi Island are used and a simultaneous cruise observation in the northern North Yellow Sea (NYS) is conducted to study temperature variation in the bottom thermal front zone of the NYS Cold Water Mass (NYSCWM) during the summer of 2009. In the flood-ebb tidal cycles, the bottom temperature decreases (increases) during flood (ebb) tides, which are dominated by the tidal-current induced horizontal advection. The ebb tide-induced temperature increase is larger than the flood tide-induced tempera- ture decrease due to seasonal warming. In the spring-neap tidal cycles, the temperature and the vertical temperature structure show notable fortnightly variation from 16 July to 25 August. The bottom temperature increases from neap to spring tides and decreases from spring to neap. The Richardson number demonstrates strengthened vertical mixing during spring tides but enhanced stratifica- tion during neap tides. The spring-neap variation in vertical shear caused by tidal current is the dominant factor that induces the fort- nightly variation in vertical mixing and thus bottom temperature.

Effects of wave-current interaction on the waves, cold-water mass and transport of diluted water in the Beibu Gulf

Wave-current interaction and its effects on the hydrodynamic environment in the Beibu Gulf(BG) have been investigated via employing the Coupled Ocean–Atmosphere–Wave–Sediment Transport(COAWST) modeling system. The model could simulate reasonable hydrodynamics in the BG when validated by various observations.Vigorous tidal currents refract the waves efficiently and make the seas off the west coast of Hainan Island be the hot spot where currents modulate the significant wave height dramatically. During summer, wave-enhanced bottom stress could weaken the near-shore component of the gulf-scale cyclonic-circulation in the BG remarkably, inducing two major corresponding adjustments: Model results reveal that the deep-layer cold water from the southern BG makes critical contribution to maintaining the cold-water mass in the northern BG Basin.However, the weakened background circulation leads to less cold water transported from the southern gulf to the northern gulf, which finally triggers a 0.2℃ warming in the cold-water mass area;In the top areas of the BG, the suppressed background circulation reduces the transport of the diluted water to the central gulf. Therefore, more freshwater could be trapped locally, which then triggers lower sea surface salinity(SSS) in the near-field and higher SSS in the far-field.

The baroclinic circulation structure of Yellow Sea Cold Water Mass

A theoretic solution of one-dimensional heat transfer equation and a numerical simula-tion of 3D baroclinic circulation by MOM2 are investigated to understand the roles of bottom boundary mixing and the Topographic Heat Accumulation Effect (THAE) in the Yellow Sea Cold Water Mass (YSCWM) circulation. Our results show: (i) The time scale of heat transfer changes from days to weeks and from shallow to deep water column. Strong bottom boundary mixing makes the thermocline domed. (ii) The circulation of YSCWM has a two-layer structure. The upper layer is cyclonic, while the lower layer is anticyclonic, and the lower layer is thinner (about 10—20 m) and weaker than the upper layer. The depth-integrated (net) circulation is cyclonic. (iii) The strength of the bottom boundary mixing influences the temperature structures greatly but has less effect on the velocity structure.