Phytoplankton pigment patterns and community composition in the northern South China Sea during winter

Phytoplankton pigment patterns and community composition were investigated in the northern South China Sea using high-performance liquid chromatography and the CHEMTAX software from February 11 to 23, 2009. We recognized four different vertical distribution patterns of pigments: chlorophyll a (Chl a)-like type, divinyl chlorophyll a (DV Chl a) type, even distribution type, and surface type. The average value of ratios of accessory photo-protective pigments (APP) to accessory photo-synthetic pigments was 0.8...     

Phytoplankton pigment patterns and community composition in the northern South China Sea during winter

Phytoplankton pigment patterns and community composition were investigated in the northern South China Sea using high-performance liquid chromatography and the CHEMTAX software from February 11 to 23, 2009. We recognized four different vertical distribution patterns of pigments: chlorophyll a (Chl a)-like type, divinyl chlorophyll a (DV Chl a) type, even distribution type, and surface type. The average value of ratios of accessory photo-protective pigments (APP) to accessory photo-synthetic pigments was 0.89±0.63 in the upper 50 m and 0.16±0.06 below 50 m depth. With increasing depth, APP decreased and photo-synthetically active radiation was attenuated. There was an obvious succession in the phytoplankton community from inshore to the open sea. Diatoms were dominant in the inshore region, while pelagophytes, Prochlorococcus, cyanobacteria and prymnesiophytes were dominant in the open sea. The vertical distribution of phytoplankton also differed greatly from inshore to the open sea. In the coastal and shelf region, diatoms were important components in the whole water column. Cyanobacteria also had a high abundance at the Subsurface Chlorophyll a Maxima (SCM) in the shelf region. In the slope and open sea, Prochlorococcus and cyanobacteria were important groups above the SCM, while pelagophytes dominated below the SCM.     

Statistical analysis of surface hydrography and circulation variations in northern South China Sea

1 INTRODUCTIONThe South China Sea (SCS) is a semi-enclosedmarginal sea in western North Pacific Ocean withvery complex topography and is the important pas-sage connecting the Pacific and Indian Oceans. Ithas great impact to the global climate and a greatinterest of many oceanography researchers. Twodominant surface hydrographic and circulation fea-tures in the northern SCS are a strong fresh waterexpansion and a warm and high-salinity seawaterintrusion such as the SCS Diluted Water…     

The modeled atmospheric and oceanic response to the South China Sea SST anomaly

The sensitivity of the global atmospheric and oceanic response to sea surface temperature anomaly (SSTA) throughout the South China Sea (SCS) is investigated using the Fast Ocean-Atmosphere Model (FOAM). Forced by a warming SST, the experiment explicitly demonstrates that the responses of surface air temperature (SAT) and SST exhibit positive anomalous center over SCS and negative anomalous center over the Northern Pacific Ocean (NPO). The atmospheric response to the warm SST anomalies is characterized by a barotropical anomaly in middle-latitude, leading to a weak subtropical high in summer and a weak Aleutian low in winter. Accordingly, Indian monsoon and eastern Asian monsoon strengthen in summer but weaken in winter as a result of wind convergence owing to the warm SST. It is worth noting that the abnormal signals propagate poleward and eastward away in the form of Rossby Waves from the forcing region, which induces high pressure anomaly. Owing to action of the wind-driven circulation, an anomalous anti-cyclonic circulation is induced with a primary southward current in the upper ocean. An obvious cooling appears over the North Pacific, which can be explained by anomalous meridional cold advection and mixing as shown in the analysises of heat budget and other factors that affect SST.     

Currents and mixing in the northern South China Sea

We investigated the vertical distribution of current velocity data of the entire water column at a site on the continental shelf of the northern South China Sea (SCS) from August 4 to September 6, 2007, and found that the characteristics of barotropic and baroclinic tides are mainly diurnal. During the observation period, we also estimated the mixing before and after the passage of Typhoon Pabuk. We found that the internal-wave-scale dissipation rate, the turbulent dissipation rate, and the mixing rate in every water layer increased by about an order of magnitude after the typhoon passage. We analyzed a case of abrupt strong current and calculated the mixing rate before, during, and after the typhoon event. The results show that the internal-wave-scale dissipation rate and the mixing rate in every water layer increased by about two orders of magnitude during the event, while the turbulent dissipation rate increased by about an order of magnitude. Passage of the abrupt strong current could also have increased the mixing rate of affected seawater by more than an order of magnitude. However, the passage of the typhoon differed in that there was an increase in mixing only in the lower layer where the abrupt strong current was particularly strong. The variation of the mixing rate may help us to understand the effects of typhoons and abrupt strong currents on the mixing of seawater.     

Characteristics of Light Transmission in Summer and Winter and Its Relation to Sediment Transport in the East China Sea

INTRODUCTIONTheSubeiShoalandtheChangjiangRiverestuarineareainthewestoftheHuanghaiandEastChinaSeasisoneofthemarginalseasintheworld ,wheresuspendedmatterisextremelyhigh .Here ,notonlyistheretheTaiwanWarmCurrentoneoftheKuroshio’sbranchesintheEastChinaSea,butalsotheHuanghaiCoastalCurrent,andChangjiangDilutedWater.Sothestrongmixingbetweenthecoastalandoffshorewaterscomplicatessuspendedmatterdistributioninthisarea.HowthesuspendedmatterdischargedfromtheChangjiangRiverandtheabandonedHuan…     

MODEL OF UPPER OCEANIC CIRCULATIONS IN THE SOUTH CHINA SEA DURING NORTHEAST MONSOON

MODUrnONTheS0uthChinaSea(SCS)isabophalrnarginalbasinwhereEastAsiamonsoonsprevail.0bviousadjustInentSoftheupperocanoccurduetOthealtematingsurnxneandwintermonsoons.ThemostboohantaspchoflargeanlecurmtSintheSesaretheupperoonnicresponsetothemonsoons(Dale,l956).MostpreviousmrehesfocusedondiagnostiesandmodelingofsuffocecurmtS.Wwti(l96l)plotalsurfacentsbasedonshipdriflsintheNAGAReportNo.2anddescritaltheperiodicallysdri-annualreversingofwindsandrtinthisarea.Xuetal.(l982)calculatalthedy-naAn…     

Spatio-temporal variations in the siphonophore community of the northern South China Sea

To understand how hydrological and biological factors affect near-to off-shore variations in the siphonophore community,we sampled zooplankton at 82 stations in the northern South China Sea during summer,winter,and spring.Forty-one species of siphonophore were collected by vertical trawling.The species richness of siphonophores increased from the nearshore to offshore regions in all three seasons of investigation,with maximum richness in summer and minimum richness in winter.The abundance of siphonophores was also higher in summer than in spring and winter,concentrated in the nearshore region in the warm season and scattered in the offshore region in the cold season.Four siphonophore groups were classified according to the frequency of occurrence:nearshore,near-offshore,offshore,and tropical pelagic.Among them,the nearshore group had higher abundance nearshore compared with the offshore.The tropical pelagic group had higher species number offshore than nearshore.Spatial and temporal fluctuations in taxonomic composition and abundance of siphonophores were due to the influence of the coastal upwelling and surface ocean currents of the South China Sea,driven by the East Asia monsoonal system.     

Vorticity budget study on the seasonal upper circulation in the northern South China Sea from altimetry data and a numerical model

Based on the EOF analyses of Absolute Dynamic Topography satellite data,it is found that,in summer,the northern South China Sea(SCS) is dominated by an anticyclonic gyre whilst by a cyclonic one in winter.A connected single-layer and two-layer model is employed here to investigate the dynamic mechanism of the circulation in the northern SCS.Numerical experiments show that the nonlinear term,the pressure torque and the planetary vorticity advection play important roles in the circulation of the northern SCS,whilst the contribution by seasonal wind stress curl is local and limited.Only a small part of the Kuroshio water intrudes into the SCS,it then induces a positive vorticity band extending southwestward from the west of the Luzon Strait(LS) and a negative vorticity band along the 200 m isobath of the northern basin.The positive vorticity field induced by the local summer wind stress curl is weaker than that induced in winter in the northern SCS.Besides the Kuroshio intrusion and monsoon,the water transports via the Sunda Shelf and the Sibutu Passage are also important to the circulation in the northern SCS,and the induced vorticity field in summer is almost contrary to that in winter.The strength variations of these three key factors(Kuroshio,monsoon and the water transports via the Sunda Shelf and the Sibutu Passage) determine the seasonal variations of the vorticity and eddy fields in the northern SCS.As for the water exchange via the LS,the Kuroshio intrusion brings about a net inflow into the SCS,and the monsoon has a less effect,whilst the water transports via the Sunda Shelf and the Sibutu Passage are the most important influencing factors,thus,the water exchange of the SCS with the Pacific via the LS changes dramatically from an outflow of the SCS in summer to an inflow into the SCS in winter.     

Spatial pattern of the air-sea interaction near the South China Sea during winter

mODUCnONTheSOuthChinaSea(SCS)isasend-enclosedoceanbasinlocatednearthewesternPeripheryofthePacificOcean.SpreadingfIDmtheeqUatorto20"Nands~ngzonallaboutl5'inlooptUde,theSCSlocatesbetweenthesouthChinacoastandtheInaritha6continent,andissurroundedbyInanislandcountries.Duringwinter,S0UthwwhmedngcoldSUrges,mwhfiedbytheSST,affectthepressure,tempethe,andwindfieldsneartheInaritimecontinent,andsomeInayeveninIluencetheS0uthernHdrispheremonsoon(Davids0netal.,1983).msuniqUegeOpophyoftheSCS…     

Characteristics of nonlinear internal waves observed in the northern South China Sea

The South China Sea (SCS) is one of the most active areas of internal waves. We undertook a program of physical oceanography in the northern South China Sea from June to July of 2009, and conducted a 1-day observation from 15:40 of June 24 to 16:40 of June 25 using a chain of instruments, including temperature sensors, pressure sensors and temperature-pressure meters at a site (117.5°E, 21°N) northeast of the Dongsha Islands. We measured fluctuating tidal and subtidal properties with the thermistor-chain and a ship-mounted Acoustic Doppler Current Profiler, and observed a large-amplitude nonlinear internal wave passing the site followed by a number of small ones. To further investigate this phenomenon, we collected the tidal constituents from the TPXO7.1 dataset to evaluate the tidal characteristics at and around the recording site, from which we knew that the amplitude of the nonlinear internal wave was about 120 m and the period about 20 min. The horizontal and vertical velocities induced by the soliton were approximately 2 m/s and 0.5 m/s, respectively. This soliton occurred 2–3 days after a spring tide.     

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.     

Variation in downwelling diffuse attenuation coefficient in the northern South China Sea

The diffuse attenuation coefficient for downwelling irradiance （Kd（λ）） is an important parameter for ocean studies. Based on the optical profile data measured during three cruises in the northern South China Sea in autumn from 2003 to 2005, variations in the Kd（λ） spectra were analyzed. The variability of Kd（λ） shows much distinct features in both magnitude and spectra pattern, it is much higher in coastal waters than that of open oceanic waters; and the blue-to-green （443/555） ratio of Kd（λ） tends to increase with chlorophyll a concentration （[Chl-a]） from open ocean to coastal waters. These characteristics can be explained most by the increase of aw＋p（443）/aw＋p（555） with [Chl-a]. In short waveband, the relation between Kd（λ）-Kw（λ） and [Chl-a] can be well described by a power law function, indicating the large contribution of phytoplankton to the variations in Kd（λ）. As for the spectral model of the diffuse attenuation coefficient, there are good linear relationships between Kd（490） and Kd（λ） in other wavelengths with own slope and intercept of a linear functions in the spectral range 412-555 nm. Kd（490） is well correlated with the spectral ratio of remote sensing reflectance; and should enough measurement data are given, this empirical algorithm would be used in the Kd（λ） retrieval from ocean color satellite data. The variation in Kd（λ） provides much useful information for us to study the bio-optical property in the northern South China Sea.     

Estimation of potential distribution of gas hydrate in the northern South China Sea

Gas hydrate research has significant importance for securing world energy resources, and has the potential to produce considerable economic benefits. Previous studies have shown that the South China Sea is an area that harbors gas hydrates. However, there is a lack of systematic investigations and understanding on the distribution of gas hydrate throughout the region. In this paper, we applied mineral resource quantitative assessment techniques to forecast and estimate the potential distribution of gas hydrate resources in the northern South China Sea. However, current hydrate samples from the South China Sea are too few to produce models of occurrences. Thus, according to similarity and contrast principles of mineral outputs, we can use a similar hydrate-mining environment with sufficient gas hydrate data as a testing ground for modeling northern South China Sea gas hydrate conditions. We selected the Gulf of Mexico, which has extensively studied gas hydrates, to develop predictive models of gas hydrate distributions, and to test errors in the model. Then, we compared the existing northern South China Sea hydrate-mining data with the Gulf of Mexico characteristics, and collated the relevant data into the model. Subsequently, we applied the model to the northern South China Sea to obtain the potential gas hydrate distribution of the area, and to identify significant exploration targets. Finally, we evaluated the reliability of the predicted results. The south seabed area of Taiwan Bank is recommended as a priority exploration target. The Zhujiang Mouth, Southeast Hainan, and Southwest Taiwan Basins, including the South Bijia Basin, also are recommended as exploration target areas. In addition, the method in this paper can provide a useful predictive approach for gas hydrate resource assessment, which gives a scientific basis for construction and implementation of long-term planning for gas hydrate exploration and general exploitation of the seabed of China.     

An isopycnic-coordinate internal tide model and its application to the South China Sea

A three-dimensional isopycnic-coordinate ocean model for the study of internal tides is presented. In this model, the ocean interior is viewed as a stack of isopycnic layers, each characterized by a constant density. The isopycnic coordinate performs well at tracking the depth variance of the thermocline, and is suitable for simulation of internal tides. This model consists of external and internal modes, and barotropic and baroclinic motions are calculated in the two modes, respectively. The capability of simulating internal tides was verified by comparing model results with an analytical solution. The model was then applied to the simulation of internal tides in the South China Sea (SCS) with the forcing of M2 and K1 tidal constituents. The results show that internal tides in the SCS are mainly generated in the Luzon Strait. The generated M2 internal tides propagate away in three different directions (branches). The branch with the widest tidal beam propagates eastward into the Pacific Ocean, the most energetic branch propagates westward toward Dongsha Island, and the least energetic branch propagates southwestward into the basin of the SCS. The generated K1 internal tides propagate in two different directions (branches). One branch propagates eastward into the Pacific Ocean, and the other branch propagates southwestward into the SCS basin. The steepening process of internal tides due to shoaling effects is described briefly. Meridionally integrated westward energy fluxes into the SCS are comparable to the meridionally integrated eastward energy fluxes into the Pacific Ocean.     

Estimation of potential distribution of gas hydrate in the northern South China Sea

Gas hydrate research has significant importance for securing world energy resources, and has the potential to produce considerable economic benefits. Previous studies have shown that the South China Sea is an area that harbors gas hydrates. However, there is a lack of systematic investigations and understanding on the distribution of gas hydrate throughout the region. In this paper, we applied mineral resource quantitative assessment techniques to forecast and estimate the potential distribution of gas hydrate resources in the northern South China Sea. However, current hydrate samples from the South China Sea are too few to produce models of occurrences. Thus, according to similarity and contrast principles of mineral outputs, we can use a similar hydrate-mining environment with sufficient gas hydrate data as a testing ground for modeling northern South China Sea gas hydrate conditions. We selected the Gulf of Mexico, which has extensively studied gas hydrates, to develop predictive models of gas hydrate distributions, and to test errors in the model. Then, we compared the existing northern South China Sea hydrate-mining data with the Gulf of Mexico characteristics, and collated the relevant data into the model. Subsequently, we applied the model to the northern South China Sea to obtain the potential gas hydrate distribution of the area, and to identify significant exploration targets. Finally, we evaluated the reliability of the predicted results. The south seabed area of Taiwan Bank is recommended as a priority exploration target. The Zhujiang Mouth, Southeast Hainan, and Southwest Taiwan Basins, including the South Bijia Basin, also are recommended as exploration target areas. In addition, the method in this paper can provide a useful predictive approach for gas hydrate resource assessment, which gives a scientific basis for construction and implementation of long-term planning for gas hydrate exploration and general exploitation of the seabed of China.     

Distribution and origin of sediments on the northern Sunda Shelf, South China Sea

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