花岗岩风化壳的不均一性与海岸带的可蚀性研究——以南海北大陆海岸带为例

海岸带岩土动力学特征的差异是影响海岸侵蚀过程与方向的重要因素之一。南海北大陆海岸带主要由花岗岩风化边坡组成。通过对该海岸带的北东翼及西南翼典型花岗岩风化壳剖面的黏土矿物及风化指标研究发现,两者存在不均一性:横向上,北东翼黏土矿物主要以高岭石、伊利石为主;西南翼黏土矿物主要以高岭石、伊利石和绿泥石为主,两翼均未见较明显的蒙脱石。相同层位比较,西南翼黏土矿物总量高于北东翼。垂向上,自地表到深部,北东翼黏土矿物组合及总量无明显的分层性,而西南翼则呈明显的分层性且地表含量明显高于深部。海岸带的风化作用也存在明显的不均一性:表现为横向上,北东翼海岸带风化程度要稍弱于西南翼;垂向上,北东翼化学风化指标n(Al2O3)/n(SiO2),n(Fe2O3+Al2O3)/n(SiO2),n(TiO2)/n(Al2O3)、CIA在风化壳中呈无规律变化,而西南翼则呈明显的分层性,这种分层基本与表土层、红土层及砂土层成一定的对应关系。从化学可蚀性指标来看,由南海北大陆海岸带花岗岩风化壳演化而成的土壤均为强抗蚀性,但相同层位比较,北东翼可蚀性要稍弱于西南翼剖面。研究认为,组成南海北大陆海岸带的花岗岩风化壳之黏土矿物与风化作用的不均一性可很大程度影响海岸带的可蚀性。

南海北陆架坡表面沉积物的物理力学性质初探

南海北部陆坡工程地质环境复杂,并分布有大量油气资源,对该区海底沉积物的物理力学性质的研究是不可缺少的研究工作。本文利用2015年6月于"实验3"号科考船南海北部航次获得的箱式样和柱状样样品,在室内进行了含水率、天然密度、比重、微型扭力十字板以及微型贯入试验和压缩试验,获得了该处沉积物的粒度分布特征及物理力学性质参数。研究表明,南海北陆坡架表层沉积物类型以粉砂质黏土和黏土质粉砂为主,具有较高的含水率和较低的湿密度,抗剪强度、贯入阻力、压缩性等力学性质较差。沉积物的各项土工参数随深度呈现一定规律性的变化,且沉积环境、粒度成分和沉积年代等因素对其存在一定影响。

南海北坡ODP1146站第四纪粘土矿物记录:洋流搬运与东亚季风演化

南海北部ODP1146站第四纪粘土矿物学分析表明,伊利石、绿泥石和高岭石含量在冰期时增高,而蒙脱石含量在间冰期时增高.蒙脱石/(伊利石+绿泥石)比率和蒙脱石丰度变化可以作为东亚季风演化的矿物学标志.在万年时间尺度上,间冰期盛行的西南表层洋流将更多的蒙脱石由南部和东部向北搬运,表现为加强的夏季风;冰期盛行的逆时针表层洋流将大量伊利石和绿泥石由台湾以及流经吕宋海峡的长江物源搬运至南海北坡,表现为强盛的冬季风.就10万年时间尺度而言,蒙脱石/(伊利石+绿泥石)比率与沉积速率的对应关系,指示2000～1200和400-0 ka期间南海北部盛行冬季风,而1200-400ka期间表现为加强的夏季风.夏季风演化的强弱与北半球夏季目射量基本呈线性关系,表明东亚季风演化的天文驱动机制.

南海北村口岸鼠密度及种群调查

本文报道了1994年夏、秋季南海北村口岸啮齿类动物种群构成。布放有效鼠夹867只,捕获啮齿类动物180只,隶属2目2科3属5种,密度为20.76%。以褐家鼠为优势鼠种。

《齐桓公伐楚》“北海”“南海”考释

《齐桓公伐楚》中的“北海”“南海”之“海”,并不表“大海”义,它是指从“大海”义衍生出的极远之地;“北海”“南海”也不是今日的渤海、南海,它们是指北方、南方极远之地。“海”从本义“大海”衍生出极远之地,其文化背景是古人以中国之四周皆为海的传统观念,而达成这种指称对象转移的机制则是转喻。通过转喻机制,“海”由本指大海或四海转而指与之空间上相邻的极远之地,此亦《齐桓公伐楚》“北海”“南海”义指北方、南方极远地之语义演化的主要理据。

Distribution and composition of tintinnids ciliates in the northern South China Sea during summer

Tintinnids were enumerated and identified in samples collected from 36 stations between 18°-22°N, 107°-122 °E in the northern South China Sea （NSCS）. 44 species belonging to 24 genera of tintinnids were recorded. The dominant species were He/icostome/la /onga and Tintinnopsis radix. Tintinnids abundance ranged from 0 to 2 200 cell/L, and mean abundance was 221cell/L in the surface water. Tintinnids abundance and species numbers decreased from coast to offshore. Upwelling and Pearl River discharge influenced the distribution of tintinnids by regulating nutrients supply. Maximum abundance （2 200 cell/L） was found in the surface water of A1. Tintinnids abundance showed positive relationship with chlorophyll a （Chl a） concentration, and no significant relationship was found between tintinnids abundance and temperature.

The 3D magnetic structure beneath the continental margin of the northeastern South China Sea

Understanding the continental margin of the Northeastern South China Sea is critical to the study of deep structures, tectonic evolution, and dynamics of the region. One set of important data for this endeavor is the total-field magnetic data. Given the challenges associated with the magnetic data at low latitudes and with remanent magnetism in this area, we combine the equivalent-source technique and magnetic amplitude inversion to recover 3D subsurface magnetic structures. The inversion results show that this area is characterized by a north-south block division and east-west zonation. Magnetic regions strike in EW, NE and NW direction and are consistent with major tectonic trends in the region. The highly magnetic zone recovered from inversion in the continental margin differs visibly from that of the magnetically quiet zones to the south. The magnetic anomaly zone strikes in NE direction, covering an area of about 500 km × 60 km, and extending downward to a depth of 25 km or more. In combination with other geophysical data, we suggest that this strongly magnetic zone was produced by deep underplating of magma associated with plate subduction in Mesozoic period. The magnetically quiet zone in the south is an EW trending unit underlain by broad and gentle magnetic layers of lower crust. Its magnetic structure bears a clear resemblance to oceanic crust, assumed to be related to the presence of ancient oceanic crust there.

Vegetation Evolution in the Northern South China Sea Region Since 40 ka BP - An Attempt to Reconstruct Palaeovegetation Based on Biomization

Vegetation evolution in the northern South China Sea region since 40 500 a BP is reconstructed using biomization procedure based on pollen data from deep sea core 17940. The result shows that, it is feasible to reconstruct palaeovegetation using biomization procedure, when pollen, particularly Pinus pollen, transported by mind over long distance is excluded. Results from factor analysis suggest that humidity and temperature are the two main factors determining vegetation evolution on land around the northern South China Sea. From 40 500 a BP to 11 100 a BP, broad-leaved evergreen forest (WAMF), and montane conifers(MGRF) occurred on hills and low mountains; while steppe (STEP) predominated on the exposed shelf. The main feature of the vegetation evolution is the frequent alternation between MGRF (or WAMF) and STEP, implying abrupt changes in millennium scale between humid/cold and dry/temperate climate. All abrupt climate events could be broadly correlated with Henrich events and Dansggard-Oscherge events. One of the events around 12 700 a BP, sees the occurrence of MGRF, suggesting that climate turned humid and cold rapidly. This may be correlated with the Younger Dryas event; Broad-leaved evergreen (WAMF) predominates since 11 000 a BP. During the early Holocene and late Holocene tropical rainforest (TRFO) or tropical seasonal forest (TSFO) occurred several times.

Internal tides in the northern South China Sea from 20-day in-situ mooring observations in 1998

20-day in-situ ADCP current and CTD data are used to investigate the characteristics and energy of the internal tides in the northern South China Sea （NSCS）. The results show that the O1, K1, M2 and S2 constituents of internal tides are energetic and diurnal constituents （O1 and K1） are dominating. In the observational period, the current vectors of these four constituents all rotate clockwise and the maximum semi-major axe of internal tidal ellipses is more than 14 cm/s. The variation of ocean temperature shows that the internal tides present obvious quasi-diurnal oscillation and the average amplitude reaches 50 m. Furthermore, these internal tides carry high energy and appear to be intermittent. The maximum values of KE （PE） during the observational period are up to 2 （3.5） k J/m^2 for diurnal internal tides, and up to 1 （1.5） k J/m^2 for semidiurnal internal tides.

Development of Sedimentary Environment in the Northeastern South China Sea Since the Last Glacial Stage

Core D （21°23′02″N, 116°47′13″E, water depth 405 m） was sampled from the upper slope from the northeastern South China Sea （SCS） and applied to analyze the sedimentary environmental change in this sea area since the last glacial stage. The results of grain size analysis, diatom analysis and detrital mineral analysis were well matched. We divided the core D into two layers. The surface sand layer （0 - 2 cm） consisted of residual sediments, which might be originally the sediment in the late Pleistocene and later suffered from being transformed in the post glacial transgression. The lower layer （2 - 130 cm） was quite different from the surface one, which might mainly result from a neritic sedimentary environment in the last glacial stage. Two sedimentary cycles could be detected in the core D： regression during Marine isotope stage （MIS） 4 to transgression during MIS 3 and regression during MIS 2 to transgression during the post glacial.

Population parameters and dynamic pool models of commercial fishes in the Beibu Gulf, northern South China Sea

Length-frequency data of eight commercial fish species in the Beibu Gulf （Golf of Tonkin）, northern South China Sea, were collected during 2006-2007. Length-weight relationships and growth and mortality parameters were analyzed using FiSAT II software. Five species had isometric growth, two species had negative allometric growth, and one species had positive allometric growth. Overall, the exploitation rates of the eight species were lower in 2006 2007 than in 1997-1999： for four species （Saurida tumbil, Saurida undosquamis, Argyrosomus macrocephalus, and Nemipterus virgatus） it was lower in 2006-2007 than in 1997 1999, for two species （Parargyrops edita and Trichiurus haumela） it remained the same, and for the other two species （Trachurus japonicus and Decapterus maruadsi） it was higher in 2006~007 than in 1997-1999. The exploitation rates might have declined because of the decline in fishing intensity caused by high crude oil prices. The optimum exploitation rate, estimated using Beverton-Holt dynamic pool models, indicated that although fishes in the Beibu Gulf could sustain high exploitation rates, the under-size fishes at first capture resulted in low yields. To increase the yield per recruitment, it is more effective to increase the size at first capture than to control fishing effort.

Marine Atmospheric Boundary Layers Associated with Summer Monsoon Onset over the South China Sea in 1998

The variations of the marine atmospheric boundary layer (MABL) associated with the South China Sea Summer Monsoon were examined using the Global Positioning System (GPS) sounding datasets obtained four times daily during May-June 1998 on board Research Vessels Kexue 1 and Shiyan 3. The MABL height is defined as the height at the lowest level where virtual potential temperature increases by 1 K from the surface. The results indicate that the MABL height decreased over the northern South China Sea (SCS) and remained the same over the southern SCS, as sea surface temperature (SST) fell for the northern and rose for the southern SCS after the monsoon onset. Over the northern SCS, a decrease in both the SST and the surface latent-heat flux after the onset resulted in a reduction of the MABL height as well as a decoupling of MABL from clouds. It was found that MABL height reduction corresponded to rainfall occurrence. Over the southern SCS, a probable reason for the constant increase of SST and surface heat flux was the rainfall and internal atmospheric dynamics.

Observation of interactions between internal tides and near-inertial waves after typhoon passage in the northern South China Sea

During the observational period of our study, Typhoon Hagupit passed over the mooring site and induced strong near-inertial waves （NIWs）, which provided an opportunity to investigate the interactions between internal tides （ITs） and NIWs. Based on the mooring data, we compared the current spectra during the typhoon period and non-typhoon period in the northern South China Sea, and found that the high- frequency waves （fD1 and fD2） were evident during the former. Moreover, the observations of the current revealed that fD1 and fD2 occurred near the depth of strong vertical shear in the NlWs. In order to confirm the generation mechanism of fD1 and fD2, we compared the positions of strong vertical shear in the NIWs and strong vertical velocity in the ITs. It was established that the vertical shear of the horizontal current of the NIWs and the vertical current of the ITs contributed to the generation of fDt and fD2.

Bottom Currents Observed in and Around a Submarine Valley on the Continental Slope of the Northern South China Sea

Bottom currents at about 1000m depth in and around a submarine valley on the continental slope of the northern South China Sea were studied by a 14-month long experiment from July 2013 to September 2014. The observations reveal that bottom currents are strongly influenced by the topography, being along valley axis or isobaths. Power density spectrum analysis shows that all the currents have significant peaks at diurnal and semi-diurnal frequencies. Diurnal energy is dominant at the open slope site, which is consistent with many previous studies. However, at the site inside the valley the semi-diurnal energy dominates, although the distance between the two sites of observation is quite small （11 kin） compared to a typical horizontal first-mode internal tide wavelength （200 km）. We found this phenomenon is caused by the focusing of internal waves of certain frequencies in the valley. The inertial peak is found only at the open slope site in the first deployment but missing at the inside valley site and the rest of the de- ployments. Monthly averaged residual currents reveal that the near-bottom currents on the slope flow southwestward throughout the year except in August and September, 2013, from which we speculate that this is a result of the interaction between a mesoscale eddy and the canyon/sag topography. Currents inside the valley within about 10mab basically flow along slope and in the layers above the 10mab the currents are northwestward, that is, from the deep ocean to the shelf. The monthly mean current vectors manifest an Ek- man layer-like vertical structure at both sites, which rotate counter-clockwise looking from above.

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.

Phytoplankton size class derived from phytoplankton absorption and chlorophyll-a concentrations in the northern South China Sea

A previously developed model was modified to derive three phytoplankton size classes (micro-, nano-, and pico-phytoplankton) from the overall chlorophyll-a concentration, assuming that each class has a specific absorption coefficient. The modified model performed well using in-situ data from the northern South China Sea, and the results were reliable and accurate. The relative errors of the size-fractioned chlorophyll-a concentration for each size class were: micro-:21%, nano-:41%, pico-:26%, and nano+pico:23%. The model was then applied on ocean color remote sensing data to examine the distribution and variation of phytoplankton size classes in northern South China Sea on a large scale.

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.

Accumulation and exploration of gas hydrate in deep-sea sediments of northern South China Sea

The large deep-sea area from the southwestern Qiongdongnan Basin to the eastern Dongsha Islands,within the continental margin of northern South China Sea,is a frontier of natural gas hydrate exploration in China.Multiform of deep-sea sedimentations have been occurred since late Miocene,and sediment waves as a potential quality reservoir of natural gas hydrate is an most important style of them.Based on abundant available data of seismic,gravity sampling and drilling core,we analyzed the characteristics of seismic reflection and sedimentation of sediment waves and the occurrence of natural gas hydrate hosted in it,and discussed the control factors on natural gas hydrate accumulation.The former findings revealed the deep sea of the northern South China Sea have superior geological conditions on natural gas hydrate accumulation.Therefore,it will be of great significance in deep-sea natural gas hydrate exploration with the study on the relationship between deep-sea sedimentation and natural gas hydrate accumulation.

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.

A continuously stratified nonlinear model for internal solitary waves in the northern South China Sea

A continuously stratified nonlinear model is set up to study the impact of topographical character on the generation of internal solitary waves over a sill by tidal flow.One of the reasons why almost all of the generated internal solitary waves propagate westward in the northern South China Sea is explained.The model simulations describe the generation and propagation of internal waves well.When the strength of imposed barotropic tides and the water stratification stay unchanged,the steepness of the sill slope can control both(a) whether or not the waves induced over a sill by tidal flow are linear internal waves or nonlinear internal solitary waves,and(b) the amplitude of the internal solitary waves generated.If the steepness of the sill is asymmetric,the nonlinear internal solitary waves may be induced on the steeper side of the sill.These conclusions are supported by a numerical experiment with a monthly-mean stratification and an actual seafloor topography from the Luzon Strait.