Nansha Area Research Articles

Study on Microstructure and Silting Characteristics of Soft Soil: A Case Study of Nansha District, Guangzhou

With the development of society and economy, land subsidence in soft soil areas has become a prominent geological disaster in our country’s coastal area. Land subsidence has the characteristics of irreversibility, wide influence range, long aging, etc., and these characteristics are closely related to the characteristics of soft soil, such as physical and mechanical parameters, microstructure characteristics, etc. The Nansha District of Guangzhou was taken as the study area in this paper. Through the collection of preliminary data, two-dimensional scanning electron microscopy, and three-dimensional Computed Tomography (CT), the micro-structure characteristics of soft soil are expounded and its plugging characteristics are further analyzed. The results show that the study area’s soft soil has a honeycomb, granular, and flocculent structure. From the perspective of pore scale distribution, the number of macropores and ultramicro pores is small, and the continuity is poor. In most small and medium pores, namely the aggregate and granular pores. The siltation of soft soil is closely related to the microstructure of soil and can be treated according to the effect of siltation characteristics on the consolidation settlement of soft soil. The research results of this paper can provide targeted prevention and control suggestions for the soft land subsidence disaster in the Nansha area, and also provide a reference for other similar research.

Cadmium Enrichment and Bioavailability of Quaternary Profiles in Nansha District, Guangzhou, China

Comprehending the distribution pattern and enrichment rule of the heavy metal cadmium (Cd) in soil and grasping its activity and influencing factors is crucial for guaranteeing the soil environment safety of agricultural and construction land and improving the overall quality of the soil environment. The concentration of heavy metal Cd in the quaternary profile of Nansha was measured, and the pollution level was evaluated using the geographical accumulation index (Igeo) and potential ecological risk index (Er). Then, we determined the correlation between the total amount of Cd and the physicochemical properties of the soil using factor analysis (FA-MLR). The results showed that the average content of Cd in shallow soil (0-20 cm) in the Nansha area was 0.54 mg·kg-1, and the soil was mainly weakly acidic and neutral. The average content of Cd in deep soil (150-200 cm) was 0.42 mg·kg-1, and the soil was mainly neutral. At the same time, the variation coefficient of Cd content in shallow soil was significantly greater than that in deep soil, and Cd content tended to be consistent with the increase in depth. The Cd content of quaternary sediments showed a bimodal distribution with depth, reaching a peak at 20-25 m and 5-10 m, respectively, whereas the core sediments in this section were mostly marine sediments of silt and silty clay, with high cation exchange capacity and organic matter. The Igeo and Er of Cd in the fine-grained sediments dominated by clayey soil were significantly higher than those in the coarse-grained sediments dominated by sandy soil. The difference in soil pH value led to the different trend of Cd content with depth; the migration amount and vertical migration depth of Cd in deep soil were greater in the acidic environment. The influence of pH change on the migration and transformation of Cd was not completely reflected in the influence on the total amount of Cd, but more importantly, it changed the effective state of Cd, thus affecting the bioavailability of Cd. The unstable Cd composed of water-soluble, ion-exchangeable, and carbonate states accounted for 37.92%-49.10% of the total Cd, resulting in a strong instability of soil Cd. Further investigation on the migration and toxicity of heavy metals associated with human health risks is needed in future studies.

Adsorption and pH Values Determine the Distribution of Cadmium in Terrestrial and Marine Soils in the Nansha Area, Pearl River Delta.

Cadmium is a toxic element with a half-life of several decades, which can accumulate in the human body by entering the food chain and seriously harm health. The cadmium adsorption and desorption processes in the soil directly affect the migration, transformation, bioavailability, and ecotoxicity of this element in soil-plant systems. Coastal zones are located in the transitional zone between land and sea, and large amounts of terrigenous material input have important environmental effects on this ecosystem. The pH, hydrodynamic conditions, soil organic matter (SOM), and other factors defining the sea-land interaction within the sedimentary environment are significantly different from those defining land facies. In order to study the key factors affecting cadmium adsorption in soils at the sea-land interface in the Nansha area of the Pearl River Delta, a test was conducted on a column of undisturbed soil. The results showed that the adsorption constant KF and the Cd2+ adsorption capacity of marine soils were higher than those of terrestrial soils. However, the saturation adsorption of cadmium in terrestrial sediments was higher than in marine sediments. Soil pH was an important factor affecting cadmium adsorption capacity in both terrestrial and ma-rine sediments. Neutral and alkaline topsoil conditions inhibited the vertical migration of cadmium, while the acidic environment favored it. The higher the clay and SOM were, the stronger the Cd2+ adsorption capacity of the soil was. These findings suggest that the distribution of cadmium in marine and continental sedimentary soils is not only related to adsorption, but also to the physical and chemical processes occurring in different sedimentary environments.

High-Frequency Motions in the Southeastern South China Sea During Winter–Spring 2018/2019

High-frequency motions in the southeastern South China Sea (SCS) have rarely been investigated due to sparse field observations. The vertical distribution and temporal variation of internal tides (ITs) and near-inertial waves (NIWs) near the Nansha area in the southeastern SCS were studied using a mooring current dataset from December 2018 to June 2019 in this study. Results showed that ITs were mainly dominated by O1, K1, and M2. Tidal energy analysis indicates that the diurnal ITs were the most energetic components, followed by the semidiurnal ITs. Modal decomposition reveals that diurnal ITs were dominated by mode-3, rather than mode-1, as reported by previous studies. The horizontal kinetic energy (HKE) of diurnal ITs fluctuated within a limited range, almost unaffected by the background field. However, the HKE of semidiurnal ITs was dominated by mode-1 and more affected by the background field, especially at the end of March. Most observations showed the phase of the NIWs propagating upward and the energy propagating downward. During the northeast monsoon period, the near-inertial energy had a large magnitude due to strong wind forcing. In addition, the near-inertial energy peaked from the middle of March to the beginning of April because of the input of NIWs from afar. Overall, near-inertial energy was found concentrated above a 500–600 m depth in the southeastern SCS.

Genetic Structure and Haplotype Pattern of Marine Planktonic Ostracod (Porroecia spinirostris) from South China Sea Based on Mitochondrial COI Gene

Ostracods (Crustacea, Ostracoda) are small bivalved crustaceans, contributing to the marine zooplankton community. They are widely distributed and are relatively abundant components of the marine mesozooplankton worldwide, playing an important role in the transport of organic matter to deep layers. By analysing the mitochondrial COI gene, we explored the population genetic structure and haplotype pattern of Porroecia spinirostris which is the dominant ostracod in the South China Sea. We investigated the population genetic structure of ostracods at medium spatial scales in the absence of physical barriers. Our data provides evidence of the importance of both long-distance dispersal as well as genetic isolation in determining the seascape genetic structure of this species. Our data suggest that P.spinirostris can achieve long distance dispersal and specific haplotypes were successful in colonizing habitats from the Xisha to the Nansha area. A total of 36 haplotypes were defined from 85 individuals with most of these haplotypes occurring only once. The dominant haplotype was found in twelve sampling sites. The largest distance between two sampling sites harbouring this haplotype is more than 700 km. Our findings of long distance dispersal in the South China Sea combined with mild genetic differentiation among fifteen sampling sites (average ΦST = 0.167) are in line with a scenario where population genetic structure is strongly impacted by colonization patterns. The seascape genetic structure of P.spinirostris in the South China Sea reflects both the importance of long distance dispersal as well as of reduced levels of gene flow, likely caused by colonization events followed by demographic expansions.

Sedimentary budget of the Southwest Sub‐basin, South China Sea: Controlling factors and geological implications

Calculation of the sediment budget in the South China Sea abyssal basin lacks constraints from drilling data and reinterpretation of seismic data. On the basis of six multichannel seismic profiles across the Southwest Sub‐basin (SWSB) and the drilling data from International Ocean Discovery Program Expedition 349, we divided the Cenozoic sediments into four sedimentary units. The sedimentary budget of the abyssal basin at different geological times was calculated. The previous works in the Mekong continental shelf and slope areas were integrated to calculate the sediment budget of the whole SWSB. Our researches show that the sediment budget in the SWSB increased during the Palaeogene and reached its first peak because of intensified erosion, which might have resulted from the continued uplift of the Tibetan Plateau and accelerated southeastward extrusion of the Indo‐China Peninsula. Since the Late Miocene, the sediment budget was mainly influenced by the East Asia monsoon, that is, the intensified winter monsoon decreased the sediment budget of the entire area during the Late Miocene, whereas the strengthened summer monsoon increased the sediment budget during the Pliocene and reached a peak during the Pleistocene. The sediment budgets of the Mekong continental shelf, the Mekong continental slope, and the abyssal basin have distinct characteristics, relating to the infilling sequence of the terrestrial sediments in different regions. The sediment provenance of the SWSB was mainly from the Indo‐China Peninsula, the Nansha area, and the Palawan before the Late Miocene. After that time, sediments were mainly transported from the modern Mekong River.

Study on the Cooperation Mechanism of Nansha Area and National Free Trade Areas along “The Belt and Road” <br/>—Taking Financial Business as an Example

This paper investigates the development orientation, advantages and features of the Free Trade Zone Nansha Area, combs through the development and experience of national free trade areas (FTAs) along “the Belt and Road”, analyzes the comparative advantages between the two and explores the cooperation in the following areas: management inspiration of the national FTAs along the “the Belt and Road” to the Nansha area; fields and patterns of cooperation between national FTAs along “the Belt and Road” and Nansha Area to help Chinese enterprises “go out” to countries along “the Belt and Road”; the contents of the key industry positioning and cooperation in the Nansha Area on the basis of the cooperation with the national FTAs along “the Belt and Road”.

Preliminary study on the nautical area scattering coefficient and distribution of mesopelagic fish species in the central-southern part of the South China Sea

PDF HTML阅读 XML下载 导出引用 引用提醒 南海中南部中层鱼资源声学积分值及时空分布初探 DOI: 作者: 作者单位: 中国水产科学研究院 南海水产研究所, 农业部南海渔业资源开发利用重点实验室, 农业部南海渔业资源环境科学观测实验站, 广东 广州 510300 作者简介: 张俊(1984-),男,助理研究员,从事海洋渔业声学研究.E-mail:zkexin0901@126.com 通讯作者: 中图分类号: S932 基金项目: 农业部财政专项项目（NFZX2013）；国家重点基础研究发展计划项目（2014CB441500）；农业部财政专项项目（2009-2016）；中央级公益性科研院所基本科研业务费专项资金项目（2014TS18）；农业部南海渔业资源开发利用重点实验室开放基金（FREU2016-01）. Preliminary study on the nautical area scattering coefficient and distribution of mesopelagic fish species in the central-southern part of the South China Sea Author: Affiliation: South China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences;Key Laboratory of South China Sea Fishery Resources Exploitation & Utilization, Ministry of Agriculture;Scientific Observing and Experimental Station of South China Sea Fishery Resources & Environments, Ministry of Agriculture, Guangzhou 510300, China Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:本研究利用Simrad EK60科学探鱼仪（38 kHz）于2013年春季和2014年春季采集的南沙和中沙、西沙海域渔业声学数据，结合中层拖网取样，采用回声积分法研究了南海中南部中层鱼的资源量及其时空分布特征。结果显示，2014年春季中、西沙海域9次中层拖网作业共捕获和鉴定鱼类和头足类79种，隶属于3纲16目37科60属，其中硬骨鱼纲的种类最多（65种），鞘亚纲次之（13种），软骨鱼纲1种，硬骨鱼纲中巨口鱼科、灯笼鱼科和钻光鱼科的种类最多，分别有20种、13种和6种；南沙海域中层鱼声学积分值（nautical area scattering coefficient，m2/nmi2）显著低于中沙、西沙及邻近海域，前者夜间向上迁移的强度高于后者；2013年春季南沙海域夜间10~200 m和白天200~1000 m声学积分值构成没有显著差异（<0.01）；南沙海域白天200~1000 m不同纬度组间中层鱼声学积分值构成有极显著差异（<0.01）；南海中南部中层鱼声学积分值是（2387±601）m2/nmi2，基于现存公开发表的中层鱼的声学目标强度数据并取其均值，推算南海中南部中层鱼资源量是（8200±2100）万t。研究表明，南海中南部中层鱼声学积分值比全球平均值高约29.2%，可能是我国未来具有开发价值的大宗生物资源。 Abstract:Two acoustical surveys were conducted using a Simrad EK60 scientific echosounder (38 kHz split-beam transducer) in the Nansha, Zhongsha, and Xisha areas during spring 2013 and 2014 to explore the abundance and spatiotemporal distribution of mesopelagic fish species in the central-southern part of the South China Sea. The abundance and distribution were estimated using the echo-integration method based on acoustic data and mid-water trawl samples. We identified 79 fish and squid species in 60 genera, 37 families, 16 orders, and 3 classes in the Zhongsha and Xisha areas during spring 2014. Osteichthyes was the most abundant (65 species), followed by Coleoidea (13 species), and Chondrichthyes was only represented by one species. Stomiidae, Myctophidae, and Gonostomidae (Osteichthyes) were the most abundant families and were represented by 20, 13, and 6 species, respectively. The nautical area scattering coefficient (NASC, m2/nmi2) of mesopelagic fish in the Nansha area was much lower than that in the Zhongsha and Xisha areas, and the former presented more obvious ascending intensity at night. The NASC composition of fish living in 10-200 m depth range at night was not different from that of fish living in 200-1000 m during the day in the Nansha area in spring of 2013, but the difference was significant in the Zhongsha and Xisha areas in spring of 2014. The NASC composition values of fish living in 200-1000 m during the day for the different latitude scopes in the Nansha, Zhongsha, and Xisha areas were significantly different. The NASC of mesopelagic fish in the central-southern part of the South China Sea was (2387±601) m2/nmi2. We estimated the abundance of mesopelagic fish in the central-southern part of the South China Sea to be (82±21) million tons based on the existing mesopelagic fish target strength parameters and the median value. These results indicate that the NASC of mesopelagic fish in the central-southern part of the South China Sea was 29.2% higher than the global average. Mesopelagic fish are a potential major strategic fishery resource and are very important for China to develop. 参考文献 相似文献 引证文献

Seasonal variability in mixed layer depth in Nansha area in 2013

Seasonal variability in mixed layer depth in Nansha area in 2013

Community characteristics of pelagic copepods in Nansha area before and after onset of Southwest Monsoon

Community characteristics of pelagic copepods in Nansha area before and after onset of Southwest Monsoon

Population structure of purpleback flying squid (Sthenoteuthis oualaniensis) in Nansha area in spring

Population structure of purpleback flying squid (Sthenoteuthis oualaniensis) in Nansha area in spring

A preliminary study on biology of Glowfish (Gnathodentex aureolineatus) in Yongshu Reef of Nansha area in the South China Sea

A preliminary study on biology of Glowfish (Gnathodentex aureolineatus) in Yongshu Reef of Nansha area in the South China Sea

An integrated geophysical study on the Mesozoic strata distribution and hydrocarbon potential in the South China Sea

A series of drilling, dredge, and seismic investigations indicate that Mesozoic sediments exist in the South China Sea (SCS) which shows a bright prospect for oil and gas exploration. In order to study the distribution of Mesozoic strata and their residual thicknesses in the SCS, we carried out an integrated geophysical study based mainly on gravity data, gravity basement depth and distribution of residual Mesozoic thickness in the SCS were obtained using gravity inversion constrained with high-precision drilling and seismic data. In addition, the fine deep crustal structures and distribution characteristics of Mesozoic thicknesses of three typical profiles were obtained by gravity fitting inversion. Mesozoic strata in the SCS are mainly distributed in the south and north continental margins, and have been reformed by the later tectonic activities. They extend in NE-trending stripes are macro-controlled by the deep and large NE-trending faults, and cut by the NW-trending faults which were active in later times. The offset in NW direction of Mesozoic strata in Nansha area of the southern margin are more obvious as compared to the north margin. In the Pearl River Mouth Basin and Southwest Taiwan Basin of the north continental margin the Mesozoic sediments are continuously distributed with a relatively large thickness. In the Nansha area of the south margin the Mesozoic strata are discontinuous and their thicknesses vary considerably. According to the characteristics of Mesozoic thickness distribution and hydrocarbon potential analyses from drilling and other data, Dongsha Uplift-Chaoshan Depression, Southwest Taiwan Basin-Peikang Uplift and Liyue Bank have large thickness of the Mesozoic residual strata, have good hydrocarbon genesis capability and complete source–reservoir–cap combinations, show a bright prospect of Mesozoic oil/gas resources.

Tectonic Analysis of the Breakup and Bollision Unconformities in the Nansha Block

AbstractThe Nansha block is located to the east of the Tingjar fault (or the Baram Line) and is conjugate to the Northern continental margin, of which the research will contribute greatly to the understanding of the evolution of the South China Sea. Seismic profile interpretation and regional tectonic analysis suggested that two unconformities, the Breakup Unconformity (BU) and Collision Unconformity (CU), are two most important boundaries, which constitute the evolutionary frame of the Nansha area. This work attempts to reveal the main tectonic processes of the two major boundaries in the Nansha block by analysis of seismic profiles constrained with drilling data and mathematical modeling. The results show that BU is a diachronic boundary and dated as early Miocene in the Liyue basin to the east, while to the west in Beikang and Nanweixi basin it is dated as middle Miocene around 16 Ma, where BU is synchronous with CU. The CU in the east of the Nansha block is of age around 16 Ma. In Nansha block, the boundaries after CU are also synchronous, but the rifting boundaries before BU might also be diachronic. Analyzing the depth as well as the Empty Basin subsiding Rate (EBSR) simulation, we found that the Nansha block experienced deflection since Tg in the middle and west parts accompanied with the subduction and the collision thereafter. On profiles 90N09 and 94N07, the top of the forebulgo increased to the highest around 16 Ma. The deflection is strong in the west and weak in the east, the position of the forebulgo migrates differently. We conjecture that the deflection of the block might be controlled by factors such as collision time, lithospheric strength, and oceanic width of the subducted proto South China Sea.

Effect of Soil Conditions on the Strength of Cemented Soil with Deep Bidirectional Mixing

Soil condition is a major impact factor on the strength of cemented soil. In order to study the relationship between the soil conditions and the strength of cemented soil in deep mixing column under the circumstance of thick soft clay in the Nansha area, the uniaxial and unconfined compressive strength tests were carried out, from which stress-strain curves of the cemented soil and strength-depth curves of column body were obtained under three different soil conditions. Analyzing these curves, conclusions can be made that the strength of different parts of cement soil from deep mixing pile varies greatly in the Nansha area. Among the samples, the cement mixed with silty clay has the highest strength, while the lowest one is the cement mixed with mud. Besides the above results, compressive strength values(fcu)of cement soil is determined, which can be of great significance to calculate the bearing capacity of deep mixing piles.

The study of a method of regional environmental risk assessment

Regional environmental risk assessment can be defined as risk assessment which deals with a spatial scale that contains multiple habitats with multiple sources of many stressors affecting multiple endpoints. The characteristics of the landscape also affect the estimated risk. In this paper, an information diffusion method based on a grid system is proposed to assess regional environmental risk. The risk information on a single environmental risk source can be diffused effectively by using fuzzy set theory. Regional environmental risk values obtained from information diffusion can be clustered on classification criteria and different environmental risk levels can be depicted in a spatial partition map. Huangge Town and Nansha Town located in the Nansha Area of Guangzhou City in China were selected as model cases. The results derived from this information diffusion method will help the local government to optimize the distribution of industrial areas and establish risk prevention measurements and emergency management procedures.

Remanence magnetic records of the recent 130 000 years from the sediments in Nansha area, South China Sea

Two hundred and eighty-one samples, collected from drilling core NS93-5 located in the Nansha area of the South China Sea, were used to study the magnetic characteristics of the sediments in the sea. Detailed rock magnetic results show that the magnetic minerals of the sediments were dominated by ferrimagnetic minerals such as magnetite, and a small contribution of hematite and maghematite also existed. The sediments recorded three negative values of remanence magnetic inclination at the depth: 191–206 cm, 232–248 cm, and 292–308 cm. The corresponding ages of these negative values were 65.87–68.7 ka B.P., 73.4–80.8 ka B.P. and 108.4–113.6 ka B.P., respectively, according to stratigraphy of oxygen isotope, 14C, and the age of a volcanic ash layer. The negative value during 108.4–113.6 ka B.P. may be the record of a Blake event in the sediments of the Nansha area.

High-precision TIMS U-series and AMS 14C dating of a coral reef lagoon sediment core from southern South China Sea

Accurate dating of lagoon sediments has been a difficult problem, although lagoon profiles, usually with high deposition rates, have a great potential for high-resolution climate reconstruction. We report 26 high-precision TIMS U-series dates (on 25 coral branches) and five AMS 14C dates (on foraminifera) for a 15.4-m long lagoon core from Yongshu Reef, Nansha area, southern South China Sea. All the dates are in the correct stratigraphical sequence, providing the best chronology so far reported for lagoon deposits. The results reveal a ∼4000-a continuous depositional history, with sedimentation rates varying from 0.8 to 24.6 mm a −1, with an average of 3.85 mm a −1, which corresponds to an average net carbonate accumulation rate of ∼2700 g CaCO 3 m −2 a −1, significantly higher than the mean value (800±400 g CaCO3 m −2 a −1) used for lagoons in general in previous studies of global carbonate budget. Episodes of accelerated depositions within the last 1000 years correlate well with strong storm events identified by U-series dates of storm-transported coral blocks in the area. However, in the longer term, the sedimentation rates during the past 1000 years were much higher than earlier on, probably due to more vigorous wave–reef interaction as a result of relative sea-level fall since 500 AD and expansion of reef flat area, supplying more sediments. The coral TIMS U-series ages and foraminifera AMS 14C dates reveal intriguing apparent “radiocarbon reservoir ages” (R) from 572 to 1052 years, which are much higher than global mean values of ∼400 years.

U-series dating of dead Porites corals in the South China sea: Evidence for episodic coral mortality over the past two centuries

High-precision (up to ±1–2 years) U-series dating of dead in situ massive Porites corals on the reef flats of Yongshu and Meiji Reefs, Nansha area, southern South China Sea reveals that mortality of these massive corals occurred many times over the past two centuries, many of which appear to correlate in time with historic El Niño events. Despite different habitats of corals, at least six mortality events occurred simultaneously on both reefs (e.g. in 1869–1873, 1917–1920, 1957–1961, 1971, 1982–1983 and 1999–2000 AD), reflecting the occurrence of large-scale regional events. We speculate that many of such mortality events, especially those dated at 1998–2000, 1991, 1982–1983, 1971, and 1957–1958 AD with an overall uncertainty of ±1–2 years, are probably due to high temperature bleaching during El Niño years (e.g. 1997–1998, 1991–1992, 1982–1983, 1972–1973 and 1957–1959 AD). This study demonstrates that individual colonies of massive corals have died at different times over the past two centuries and mass spectrometric U-series dating of very young corals with a precision of up to ±1–2 years is likely to become a powerful tool for reconstruction of past coral mortality history and investigation of global warming and coral bleaching.

Storm cycles in the last millennium recorded in Yongshu Reef, southern South China Sea

Large storm-relocated Porites coral blocks are widespread on the reef flats of Nansha area, southern South China Sea. Detailed investigations of coral reef ecology, geomorphology and sedimentation on Yongshu Reef indicate that such storm-relocated blocks originated from large Porites lutea corals growing on the spurs within the reef-front living coral zone. Because the coral reef has experienced sustained subsidence and reef development during the Holocene, dead corals were continuously covered by newly growing coral colonies. For this reason, the coral blocks must have been relocated by storms from the living sites and therefore the ages of these storm-relocated corals should approximate the times when the storms occurred. Rapid emplacement of these blocks is also evidenced by the lack of coral overgrowth, encrustation or subtidal alteration. U-series dating of the storm-relocated blocks as well as of in situ reef flat corals suggests that, during the last 1000 years, at least six strong storms occurred in 1064±30, 1210±5–1201±4, 1336±9, 1443±9, 1685±8–1680±6, 1872±15 AD, respectively, with an average 160-year cycle (110–240 years). The last storm, which occurred in 1872±15 AD, also led to mortality of the reef flat corals dated at ∼130 years ago. Thus, the storm had significant impacts on coral reef ecology and morphology.