2000 Vol. 19, No. 3

Display Method:
Hydrological analysis of Kuroshio water intrusion into the South China Sea
Xu Jianping, Su Jilan
2000, (3): 1-21.
Using CTD and ADCP data collected by four research vessels from both sides of the Taiwan Strait in the northeastern area of the South China Sea in August-September 1994 and incorporating with CTD data collected in the same area in March 1992 and some historical hydrologic data,the water features and the intrusion of Kuroshio water into the South China Sea are discussed,which shows that the water mass distribution in the survey period was similar to that in the cruise of late winter and early spring (March 1992),that is,the water structure in the northeast of the sea and in the Northwest Pacific had their own independent features of temperature and salinity.Though the intrusion of Kuroshio water into the sea was found,it was very weak.Therefore there would be no direct Kuroshio branch into the sea in the late summer and early autumn.Even the Kuroshio water intrusion from the Bashi Channel into the Taiwan Strait,its influence was also very weak.Analysis of isopycnic surface and geostrophic current and the observed ADCP data show that there was a rather strong northward flow in the southeast part of the survey area which flowed northward along the west coast of Philippines,rounded the northwest comer of Luwn Island and then flowed north-eastward.Some kind of mixing with Kuroshio water was shown in the Bashi Channel.The water mass was obviously of high temperature and low salinity in winter and comparatively low temperature and low sainity in summer.
Mild-slope equation for water waves propagating over non-uniform currents and uneven bottoms
Huang Hu, Ding Pingxing, Lü Xiuhong
2000, (3): 23-31.
A time-dependent mild-slope equation for the extension of the classic mild-slope equation of Berkhoff is developed for the interactions of large ambient currents and waves propagating over an uneven bottom,using a Hamiltonian formulation for irrotational motions.The bottom topography consists of two compon}ts:the slowly varying component which satisfies the mild-slope approximation,and the fast varying component with wavelengths on the order of the surface wavelength but amplitudes which scale as a small parameter describing the mild-slope condition.The theory is more widely applicable and contains as special cases the following famous mild-slope type equations:the classical mild-slope equation,Kirby's extended mild-slope equation with current,and Dingemans's mild-slope equation for rippled bed.Finally,good agreement between the classic experimental data concerning Bragg reflection and the present numerical results is observed.
Eddies along front of warm winter current off the north coast of Spain and at Jovellanos Seamount
Huang Weigen
2000, (3): 33-43.
Two kinds of eddies in the Bay of Biscay were observed in 1990 by the use of satellite imagery and in-situ measurements.Frontal eddies in the warm winter current off the north coast of Spain persist for about 3 months and have a vertical scale of 700 m and diameters of 80 to 150 km.According to our interpretation,these eddies are mainly generated by baroclinic instability of the warm winter current.The anticycolonic eddy at the Jovellanos Seamount is about 200 km in scale and has a lifetime of 7 months.The possible mechanisms for the generation of the eddy are baroclinic instability of the mean current,topographic interaction and atmospheric forcing.
Three-dimensional numerical calculations of currents east of Taiwan Island in December 1997
Wang Huiqun, Yuan Yaochu, Su Jilan, Liu Yonggang
2000, (3): 45-63.
Based on the wind and hydrographic data obtained from the cruise of China-Japan Cooperative Research on Subtropical Gyre during December 1997,the Kuroshio east of Taiwan Island and the currents southeast of the Ryūkyū-guntō are computed by using three-dimensional diagnostic,semidiagnostic and prognostic models in the σ coordinate.The computed results show that:(1) The density and velocity fields have been adjusted when time is about 15 d,namely,the solution of semidiagnostic calculation is obtained.The quasi-steady state solution has been reached after 300 d,thus and the results of prognostic calculation got. (2) From the diagnostic calculation,the following main results can be obrained-1) There is a stronger cyclonic eddy with tongue-shaped in the region south of Taiwan Island,and the Kuroshio is located east of this cyclonic eddy.Compared with the results in July 1997,the position of the main axis of the Kuroshio moves eastward.2) There is an anticyclonic eddy south of Miyakojima,and there is a cyclonic eddy near the middle of the southern computational boundary.3) The upwelling dominates in an area of the Kuroshio near Taiwan Island.(3) Comparing the results of diagnostic calculation with those of semidiagnotic and prognostic calculations indicates that the horizontal velocity fields agree qualitatively,and there is a little difference between them in quantity.For example,the maximum horizontal velocities of the Kuroshio at the sea surface at t=0d (diagnostic),15 d (semidiagnostic) and 300 d (prgnostic) are 88.6,98.0 and 97.0 cm/s,respectively.As to the distributions of vertical components of velocity,there are some differences between them,which shows that the semidi-agnostic and prognostic results can coincide with better the salinity and temperature distributions.
Characteristics of low-frequency oscillations in course of SCS summer monsoon onset
Mao Jiangyu, Xie An, Song Yanyun, Ye Qian
2000, (3): 65-72.
Some of the low-frequency oscillation (LFO) characteristics of summer monsoon onset over the South China Sea (SCS) are examined based on NCEP/NCAR reanalysis data and OLR from NOAA in the period of 1979-1996.It is found that the SCS summer monsoon is characterized by predominance of low-frequency activities with significant interannual variability closely related with onset time.The LFOs over the SCS strengths after onset.Composite analyses for LFO components of OLR and kinetic energy indicate that the eastward propagation of LFO over the equatorial Indian Ocean and LFO owning from the western Pacific strongly affect the physical processes responsible for the SCS summer monsoon onset.The SCS is the place where the Indian Ocean LFO links with low-frequency activities over the western Pacific during summer monsoon onset.
Concentrative function and its primary application
Wang Zhiren, Yu Zhouwen, Song Jiaxi, Song Xuejia, Bao Chenglan, Jiang Dayong
2000, (3): 73-80.
In this paper,a concentrative function used in statistics is designed to present the extent in which an elementary field concentrates in the spatial distribution.Its characteristics are discussed and its availability proved.From its application in the atmospheric and oceanic sciences,we can find some interesting phenomena.For example,there is a clear seasonal concentricity in the occurrence of storms in every oceanic area in a year.The storm-dense-months correspond to such an geographical place that goes around anti-clockwise in the tropical oceanic areas.The spatial concentricity of SST and that of cloud change with time in a year in a similar way,that is,the higher occurrence of storms,the higher concentricity of SST and cloud,maybe the higher possibility of floods,which shows possibly that SST and its distribution play an important role in the formation of cloud and that the formation of storms contributes to the concentration of the cloud.
Satellite infrared remote sensing observation of surface circulation of the northeast South China Sea in winter
Xu Jianping
2000, (3): 81-92.
Based on several images taken by,the NOAA-11 and-12 advanced very high resolution radiometer (AVHRR/2) during 1989-1993,and combined with a larger-scale of oceanographic investigation during 8-27 March 1992,some related questions of the physical oceanography in the South China Sea have been discussed.The results show that there were a more complementary action for the investigation and study on the physical oceanographic phenomena in the South China Sea using the satellite imageries and in-situ data,and the distribution and variation of the satellite-derived sea surface temperatore field in the northeast South China Sea basically mirrored the results obtained from in-situ investigation.Some of the large-scale and meso-scale marine phenomena varied with the long and medium periods,for instance,an anticyclonic meandering of the Kuroshio path when it flowed through the Bashi Channel,the warmer water with high temperature along the west coastline of Luwn Island,the western and northern warmer water tongues off the southwest of Taiwan Island,China,as well as the thermal front along the continental shelf off Guangdong,were well presented in both the satellite imageries and in-situ data.Then,there also can be revealed some marine phenomena with a short period,or in the further large area using the satellite imageries,which will provide scientific basis for planning and carrying out the effective marine investigation.Finally,a map of surface circulation pattern in the northeast South China Sea in winter is sketched according to the comprehensive analysis of the satellite and in-situ data.
Distribution of organochlorine compounds in water, porewater and sediments in Xiamen Harbour
Zhang Zulin, Hong Huasheng, Khalid Maskaoui, Chen Weiqi, Zhou Junliang, Xu Li
2000, (3): 93-102.
The Concentrations of 18 organochlorine pesticides and 12 polychlorinated biphenyls (PCBs)in water,porewater and sediments from the Xiamen Harbour were analyzed quantitatively.It shows that,the levels of all organochlorine insecticides varied from 6.60 to 19.6 ng/dm3 (in water),11.9-78.5 ng/dm3(in porewater) and not detected(ND)-0.58 ng/g dry weight (in sediments),and those of total DDTs were in the range ND-0.06 ng/g dry weight.Concentrations of PCBs and insecticides in porewater were higher than in surface water,due to the higher affinity of these hydrophobic compound for sedimentary phase than to water.It implies there would be a potential flux of pollutants from sediments to ovenerlying water.Compared with the concentrations of these polutants measured in the Xiamen Harbour in 1993,it is one to several magnitude order lower,which suggests their inputs have been decreased in recent years and possible degradation of these compounds.The levels of these pollurants were also compared with other estuaries.
Characteristics of seismic reflections in central region of the South China Sea and their geological significance
Liu Jianhua, Jin Xianglong
2000, (3): 103-113.
More than 4 000 km 48-channel seismic reflection data from the central region of the South China Sea have been interpreted.Five seismic interfaces have been distinguished,named T1,T2,T4,T6 and T8 respectively.Meanwhile,five seismic sequences numbered Ⅰ-Ⅴ have been divided with the ages of Quaternary and Pliocene, Later Miocene,Earlier and Middle Miocene, Oligocene and PreOligocene separately.Sequences Ⅰ-Ⅱ overlie all parts of the area.In the continental slope and island slope,Sequences Ⅲ-Ⅴ are mainly found in the grabens.Sequence Ⅲ is found at most profiles of the deep-sea basin,and Sequence Ⅳ is seen not only at the margins of the east subbasin but also at the margins of the southwest subbasin.Strong reflection from Moho is found at most profiles of the deep-sea basin.The depth of Moho varies between 10 and 12 km,with a thickness of 6-8 km for the crust.Calculated by age-basement depth correlation formula,the age of basaltic basement in the southwest subbasin is 51-39 Ma.It is indicated that the evolution of the southwest subbasin is simultaneous with or earlier than that of the east subbasin.
Origin and evolution of alkali basaltic magma in the Okinawa Trough
Zhang Jiaqiang, Sun Yongfu, Jiang Xiaoli
2000, (3): 115-129.
The contents of major element cromposition of the phenocrysts and the matrix glass as well as the spinel inclusions and the melt inclusion in the phenocrysts of the basalt dredged from Station 133 of the Okinawa Trough are determined by electron microprobe.The results show that the basalt is a dorgalite consisting of phenocrysts of bytownite, chrysolite, clinopyroxene and magnetite as well as labradorite microcrystal,matrix glass and a few bits of broken vein quartz.Glassy melt inclusion and chromohercynite or chrompleonaste exist in bytownite and chrysolite.The formation of the spinels is related to partial melting of mantle.The melt inclusions stand for a primary alkali dorgalitic magma,whose composition corresponds to olivine gabbro.The basaltic magma was generated from partial melting of spinel-lherzolite of the upper mantle and evolved in a process of "alkali dorgalitic magma→trachybasaltic magma→basaltic trachytic magma→trachytic magma".Assimilation and hybridization of crustal material may exist during magma upwelling in every evolutionary stage.
Abrupt changes of radiolarian fauna at 600 and 120 ka B. P. in the southern South China Sea and their paleoceanographic implications
Wang Rujian, Andrea Abelmann
2000, (3): 131-138.
Abrupt changes in radiolarian composition are discovered over the last 600 and 120 ka B.P.based on quantitative analyses of radiolarians in Core 17957-2 of the southern South China Sea.The distinct changes at 600 ka B.P.could correspond to the onset of the 100 ka cycle during the glacial and interglacial periods.This abrupt change in the 100 ka cyclicity at 600 ka B.P.occurred also in the magnetic susceptibility signal that is obtained from loess and plaeosol sequences of the China Loess Plateau.The larger amplitude and stronger cyclicity in the susceptibility signal after 600 ka B.P. reflect the prominent change in the intensity of the monsoon,induced by an enhancement of the monsoon circulation.Stronger seasonality during the glacial period in the South China Sea,resulted from strengthening of winter monsoon,might lead to the changes in the radiolarian composition at 600 and 120 ka B.P.It can be suggested that only species adapted to a broader temperature range might have been able to live in this environment.Therefore,the abrupt changes in radiolarian composition at 600 and 120 ka B.P.could be attributed to the stronger SST differences between summer and winter that were caused by the striking change in the intensity of the monsoon circulation.
Study on biological oceanography charateristics of planktonic copepods in waters north of Taiwan Ⅱ. Community characteristics
Yang Guanming, He Dehua, Wang Chunshen, Miao Yutian, Yu Honghua
2000, (3): 139-152.
The paper is the succession of the study on abundance distribution of planktonic copepods in the waters north of Taiwan,and the emphasis is laid on the analysis and discussion of the wnstructions and features of copepod community and the relationships with water environment.The results show as follows:a total of 237 species were identified and the construction of communtity was complex.The percentage of annual present species was only 32 0%.The mean values of diversity and homogeneity of the copepod community were 3.714 and 0.690 respectively,and their horiwntal distribution patterns were higher in outshore area than in nearshore area. The copepods of the area could be divided into five ecotypes.Warm-water outshore high temperature and lower saline group and tropic oceanic high temperatore and saline group could indicate the seasonal changes of the Taiwan Strait water and the Kuroshio surface water respectively.According to the various aspects of calculation and analysis,winter was different from other three seasons in environmental conditions.In spring,summer and autumn,Undinula valgaris was the most dominant species and salinity was the main factor that affected the community feature values.The communities in the three seasons had the subtropic-tropic characteristics in which warm-water outshore species were dominant and tropic oceanic species accounted for also certain proportion.While in winter,the dominant species was Euohaeta marina and temperature was the main factor influencing the c}nrrmnity feture values.The community had the tropic oceanic characteristics in which tropic oceanic species were dominant.