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.     

Dimethylsulfide in the South China Sea

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SEAWATER FLUX OF THE SOUTH CHINA SEA

The South China Sea water can be divided according to depth into three boxes by the pycnoclineand a sill.Using a box model with matter balance,the net seawater fluxes were calculated to be317.9×10~4 m~3/s in box Ⅰ for the upper homogeneous layer outflowing to the adjoining oceans;67×10~4 m~3/s in box Ⅲ for the water entering the basin;240×10~4 m~3/s in box Ⅱ for water entering theSouth China Sea.The upward speed of basin water was calculated to be 8.4×10~(-5) cm/s and that ofseawater flowing up along the pycnocline was calculated to be 8.9×10~(-5) cm/s.     

Long term sea level change and water mass balance in the South China Sea

Sea level anomalies observed by altimeter during the 1993–2006 period, thermosteric sea level anomalies estimated by using subsurface temperature data produced by Ishii and SODA reanalysis data, tide gauge records and HOAPS freshwater flux data were analyzed to investigate the long term sea level change and the water mass balance in the South China Sea. The altimeter-observed sea level showed a rising rate of (3.5±0.9) mm yr-1 during the period 1993–2006, but this figure was considered to have been highly d...     

Deep-sea geohazards in the South China Sea

Various geological processes and features that might inflict hazards identified in the South China Sea by using new technologies and methods.These features include submarine landslides,pockmark fields,shallow free gas,gas hydrates,mud diapirs and earthquake tsunami,which are widely distributed in the continental slope and reefal islands of the South China Sea.Although the study and assessment of geohazards in the South China Sea came into operation only recently,advances in various aspects are evolving at full speed to comply with National Marine Strategy and‘the Belt and Road’Policy.The characteristics of geohazards in deep-water seafloor of the South China Sea are summarized based on new scientific advances.This progress is aimed to aid ongoing deep-water drilling activities and decrease geological risks in ocean development.     

Trace metal anomalies in bleached Porites coral at Meiji Reef,tropical South China Sea

Coral bleaching has generally been recognized as the main reason for tropical coral reef degradation, but there are few long-term records of coral bleaching events. In this study, trace metals including chromium(Cr), copper(Cu), molybdenum(Mo), manganese(Mn), lead(Pb), tin(Sn), titanium(Ti), vanadium(V), and yttrium(Y), were analyzed in two Porites corals collected from Meiji Reef in the tropical South China Sea(SCS) to assess differences in trace metal concentrations in bleached compared with unbleached coral growth bands. Ti, V, Cr, and Mo generally showed irregular fluctuations in both corals. Bleached layers contained high concentrations of Mn, Cu, Sn, and Pb. Unbleached layers showed moderately high concentrations of Mn and Cu only. The different distribution of trace metals in Porites may be attributable to different selectivity on the basis of vital utility or toxicity. Ti, V, Cr, and Mo are discriminated against by both coral polyps and zooxanthellae, but Mn, Cu, Sn, and Pb are accumulated by zooxanthellae and only Mn and Cu are accumulated by polyps as essential elements. The marked increase in Cu, Mn, Pb, and Sn are associated with bleaching processes, including mucus secretion, tissue retraction, and zooxanthellae expulsion and occlusion. Variation in these trace elements within the coral skeleton can be used as potential tracers of short-lived bleaching events.     

Freshening of the intermediate water of the South China Sea between the 1960s and the 1980s

Variation in intermediate water salinity in the South China Sea (SCS) between the 1960s and 1980s was studied using historical hydrographic data. The results demonstrate that the water was significantly fresher in the 1980s than in the 1960s, indicating that vertical mixing at intermediate water depth was reduced in the 1980s. This was partially because of the change of the SCS meridional overturning circulation (MOC) connecting local intermediate water with deep water. Data assimilation showed a 0.5Sv (1 Sv=10 6m 3/s) reduction in the strength of the MOC, which is about one third of the mean SCS MOC. Because the SCS MOC is linked to the Pacific Ocean, such an interdecadal variation in the intermediate water SCS may reflect anthropogenic climate change in the world ocean.     

A NUMERICAL STUDY OF THE TIDE-SURGE INTERACTION IN THE EAST CHINA SEA AND THE SOUTH CHINA SEA

Nearshore sea levels in the East China Sea(ECS) and the South China Sea(SCS) during tropical cyclones-Typhoon 8007(Joe, 1980) and Typhoon 7209(Betty 1972) were simulated. The tide-surge interactions in the two regions are remarkable and locally produced. The corresponding nonlinear effects were derived from the different nonlinear terms. The contribution of the quadratic friction term is the most important, the shallow term comes second the convective term is the least; the phases of the interactions generated by the various nonlinear terms are asynchronous. Both the quadratic friction and the convective term can stimulate and aggravate the surge structure with more peaks. The bottom friction features have crucial influences on tides and surges, and the interaction is sensitive to the changes of tide and surge.     

THE NOMENCLATURE OF THE SOUTH CHINA SEA ISLANDS IN ANCIENT CHINA

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Definition of the South China Sea summer monsoon onset

We analyze statistically different definitions of the South China Sea summer monsoon (SCSSM) onset are to establish a SCSSM onset time series that is more recognizable by a majority of indicators. With the acknowledged index, we determine a key area (105°E–112.5°E, 7.5°N–12.5°N) and define the zonal wind component in this key area as a new SCSSM onset index, using daily mean reanalysis data of the National Center for Environmental Prediction/National Center for Atmospheric Research. The atmospheric circulations before and after the onset of the SCSSM determined using the index defined in this paper are preliminarily studied. Results show that the Somalia cross-equatorial flow is enhanced, the strongest westerly wind in the tropical Indian Ocean shifts northward, the cyclone couple in the Bay of Bengal and the Southern Hemisphere weaken and move eastward, convection over the South China Sea increases, and the subtropical high retreats from the South China Sea after the outbreak of the SCSSM. By analyzing the atmospheric circulation, it is found that in 1984 and 1999, the SCSSM broke out in pentads 29 and 23, respectively, which is consistent with the onset times determined using our index.     

Observations of Kuroshio intrusion into the South China Sea

To discuss the intrusion of the Kuroshio into the SCS, we examined the mixing between the North Pacific and South China Sea (SCS) waters based on in-situ CTD data collected in August and September 2008 and the moored ADCP data taken from mid September 2008 to early July 2009. The CTD survey included four meridional sections from 119°E to 122°E around the Luzon Strait, during which pressure, temperature, and salinity were measured. The CTD data show that the isopycnal surface tilted from the SCS to the North Pacific; and it was steeper in the lower layers than in the upper ones. Meanwhile, we found strong vertical mixing taken place in the areas near 121°E. The Kuroshio in high temperature and salinity intruded westward through Luzon Strait. The frequency of buoyancy was one order of magnitude greater than that of the common ones in the ocean, suggesting stronger stratification in the northeastern SCS. On the other hand, the long-term ADCP data show that before late October 2008, the direction of water flow in the SCS was eastward, and from November 2008 to late February 2009, it turned northwestward in the layers shallower than 150 m, while remained unchanged in deep layers from 200 to 450 m. From March to June 2009, the direction shifted with increasing depth from northward to southward, akin to the Ekman spiral. EOF analysis of the current time series revealed dominant empirical modes: the first mode corresponded to the mean current and showed that the Kuroshio intrusion occurred in the upper layers only from late December to early March. The temporal coefficient of the first and the second mode indicated clearly a dominant signal in a quasi-seasonal cycle.     

Pathways of mesoscale variability in the South China Sea

The propagation of oceanic mesoscale signals in the South China Sea (SCS) is mapped from satellite altimetric observations and an eddy-resolving global ocean model by using the maximum cross-correlation (MCC) method. Significant mesoscale signals propagate along two major bands of high variability. The northern band is located west of the Luzon Strait, characterized by southwestward eddy propagation. Although eddies are the most active in winter, their southwestward migrations, steered by bathymetry, occur throughout the year. Advection by the mean flow plays a secondary role in modulating the propagating speed. The southern eddy band lies in the southwest part of the SCS deep basin and is oriented in an approximately meridional direction. Mesoscale variability propagates southward along the band in autumn. This southward eddy pathway could not be explained by mean flow advection and is likely related to eddy detachments from the western boundary current due to nonlinear effects. Our mapping of eddy propagation velocities provides important information for further understanding eddy dynamics in the SCS.     

STUDY OF WATER—TRANSPORT THROUGH SOME MAIN STRAITS IN THE EAST CHINA SEA AND SOUTH CHINA SEA

OCCAM global ocean model results were applied to calculate the monthly water transport through 7 straits around the East China Sea(ECS)and the South china Sea(SCS).Analysis of the features of velocity profiles and their variations in the Togara Strait,Luzon Strait and Eastern Taiwan Strait showed that;1)the velocity profiles had striped pattern in the Eastern Taiwan Strait,where monthly flux varied from 22.4 to 28.1 Sv and annual mean was about 25.8 Sv;2)the profiles of velocity in the Togara Strait were characterized by core structure,and monthly flux varied from 23.3 to 31.4 Sv,with annual mean of about 27.9 Sv;3)water flowed from the SCS to the ECS in the Taiwan Strait,with maximum flux of 3.1 Sv in July and minimum of 0.9 Sv in November;4)the flux in the Tsushima Strait varied by only about 0.4 Sv by season and its annual mean was about 2.3 Sv;5)Kuroshio water flowed into the SCS in the Luzon Strait throughout the year and the velocity profiles were characterized by multi-core structure.The flux in the Luzon Strait was minimun in June(about 2.4 Sv)and maximum in February(about 9.0 Sv),and its annual mean was 4.8 Sv;6)the monthly flux in the Mindoro Strait was maximum in December(3.0 Sv)and minimum in June(Only 0.1 Sv),and its annual mean was 1.3 Sv;7)Karimata Strait water flowed into the SCS from May to August,with maximum in-flow flux of about 0.75 Sv in June and flowed out from September to April at maximum outflow flux of 3.9 Sv in January.The annual mean flux was about 1.35 Sv.     

南海周边国家的海洋划界立法与实践

介绍了南海周边国家根据1982年《联合国海洋法公约》精神颁布的海洋法律,并叙述了这些国家的管辖区域主张以及与海洋划界有关的领海基线和基点等方面的问题。指出:南海周边国家之间若要划出专属经济区和大陆架边界线,包括我国在内的所有周边国家政府都应当修正不适宜的划界主张,并在划界原则、理论和方法上趋向一致,为早日划好边界,促进南海地区的经济发展和和平稳定而努力。     

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.     

Some new species of radiolaria from surface sediments of the East China Sea and the South China Sea

Fourteen species of Radiolaria described in this paper were discovered from surface sediments of the East China Sea, the South China Sea and the cores of the Okinawa Trough. Type specimens are deposited in the Second Institute of Oceanography, SOA.