Paleogene transgression process and environmental evolution in the deepwater area of the Baiyun Depression in the northern South China Sea

Multiple borehole samples are collected from the Baiyun Depression in deep-water area of the northern South China Sea(SCS)in an effort to reconstruct transgression processes during the Paleogene based on palynalgal analysis.This study indicates that the Baiyun Depression generated a large group of palynopore assemblages and fluvial/lacustrine-related algae during the early and middle Eocene when the Wenchang Formation was deposited.The entire depression was dominated by fluvial and lacustrine facies before transgression.Its eastern and southeastern sags transitioned to shallow marine environment by generating a large abundance of marine dinoflagellates during the Enping deposition of the late Eocene.Meanwhile,the southern uplift zone simply yielded fluvial/lacustrine-related palynopores and algae,and was dominated by the fluvial and lacustrine environment during the early stage of the Enping Formation,prior to shifting into transitional setting in the later period.Northwestern sags remained extensive fluvial and delta facies without existence of marine dinoflagellates.It was until the depositional stage of the Zhuhai Formation(Oligocene)that the overall depression was strongly impacted from transgression process.Both eastern and southeastern sags were mainly under deep marine setting on a continental slope while northwestern and southern areas developed transitional facies.Although distribution and accumulation patterns varied greatly among sub-sags,the overall Baiyun Depression was characterized by widespread development of marine dinoflagellates.It should be noted that the northwestern sag also partly generated large-scale river delta deposits.Due to the eustatic rise and change of SCS spreading axis,the overall Baiyun Depression was mostly influenced by the deep marine environment on a continental slope during the early Miocene.Both northwestern sag and southern uplift zone were found plentiful marine dinoflagellates.In summary,transgression initiated from the eastern and southeastern Baiyun Depression before subsequently progressing into the farther west.Evolution of transgression process is also greatly consistent with the gradual westward expansion of the SCS.

Uncertainty analysis for the calculation of marine environmental design parameters in the South China Sea

The calculation results of marine environmental design parameters obtained from different data sampling methods,model distributions,and parameter estimation methods often vary greatly.To better analyze the uncertainties in the calculation of marine environmental design parameters,a general model uncertainty assessment method is necessary.We proposed a new multivariate model uncertainty assessment method for the calculation of marine environmental design parameters.The method divides the overall model uncertainty into two categories:aleatory uncertainty and epistemic uncertainty.The aleatory uncertainty of the model is obtained by analyzing the influence of the number and the dispersion degree of samples on the information entropy of the model.The epistemic uncertainty of the model is calculated using the information entropy of the model itself and the prediction error.The advantages of this method are that it does not require many-year-observation data for the marine environmental elements,and the method can be used to analyze any specific factors that cause model uncertainty.Results show that by applying the method to the South China Sea,the aleatory uncertainty of the model increases with the number of samples and then stabilizes.A positive correlation was revealed between the dispersion of the samples and the aleatory uncertainty of the model.Both the distribution of the model and the parameter estimation results of the model have significant effects on the epistemic uncertainty of the model.When the goodness-of-fit of the model is relatively close,the best model can be selected according to the criterion of the lowest overall uncertainty of the models,which can both ensure a better model fit and avoid too much uncertainty in the model calculation results.The presented multivariate model uncertainty assessment method provides a criterion to measure the advantages and disadvantages of the marine environmental design parameter calculation model from the aspect of uncertainty,which is of great significance to analyze the uncertainties in the calculation of marine environmental design parameters and improve the accuracy of the calculation results.

Physical characteristics of high concentrated gas hydrate reservoir in the Shenhu production test area,South China Sea

High concentrated and heterogeneous distribution of gas hydrates have been identified in the gas hydrate production test region in the Shenhu area,South China Sea.The gas hydrate-bearing sediments with high saturation locate at two ridges of submarine canyon with different thickness and saturations just above the bottom simulating reflection.The crossplots of gamma ray,acoustic impedance(P-impedance)and porosity at four sites show that the sediments can be divided into the upper and lower layers at different depths,indicating different geotechnical reservoir properties.Therefore,the depositional environments and physical properties at two ridges are analyzed and compared to show the different characteristics of hydrate reservoir.High porosity,high P-wave velocity,and coarse grain size indicate better reservoir quality and higher energy depositional environment for gas hydrate at Sites W18 and W19 than those at Sites W11 and W17.Our interpretation is that the base of canyon deposits at Sites W18 and W19 characterized by upward-coarsening units may be turbidity sand layers,thus significantly improving the reservoir quality with increasing gas hydrate saturation.The shelf and slope sliding deposits compose of the fine-grained sediments at Sites W11 and W17.The gas hydrate production test sites were conducted at the ridge of W11 and W17,mainly because of the thicker and larger area of gas hydrate-bearing reservoirs than those at Sites W18 and W19.All the results provide useful insights for assessing reservoir quality in the Shenhu area.

Phytoplankton community structure and environmental parameters in aquaculture areas of Daya Bay,South China Sea

Environmental characteristics and phytoplankton community structure were investigated in two aquaculture areas in Dapeng Cove of Daya Bay, South China Sea, between April 2005 and June 2006. Phytoplankton abundance ranged between 5.0 and 8877.5 cells/mL, with an average of 751.8 cells/mL. The seasonal cycle of phytoplankton were demonstrated by frequent oscillations, with recurrent high abundances from late spring to autumn and a peak stage in late winter. Diatoms were the predominant phytoplankton group, accounting for 93.21% of the total abundance. The next most abundant group was the dinoflagellates, which made up only 1.24% of total abundance. High concentrations of Alexandrium tamarense （Lebour） Balech with a maximum of 603.0 cells/mL were firstly recorded in this area known for high rates of paralytic shellfish poisoning （PSP） contamination. Temperatures and salinities were within the suitable values for the growth of phytoplankton, and were important in phytoplankton seasonal fluctuations. The operation of the Daya Bay Nuclear Power Station （DNPS） exerts influences on the phytoplankton community and resulted in the high abundances of toxic dinoflagellate species during the winter months. Dissolved inorganic nitrogen （DIN） and dissolved silicate （DSi） were sufficient, and rarely limited for the growth of phytoplankton. Dissolved inorganic phosphorus （DIP） was the most necessary element for phytoplankton growth. The enriched environments accelerated the growth of small diatoms, and made for the shift in predominant species from large diatom Rhizosolenia spp. to chain-forming diatoms such as Skeletonema costatum, Pseudo-nitzschia spp. and Thalassiosira subtilis.

Distribution of meiofaunal abundance in relation to environmental factors in Beibu Gulf,South China Sea

This study aims to explore the distribution of meiofaunal abundance in relation to environmental factors in the Beibu Gulf, a natural semi-enclosed part of the South China Sea, surrounded by China and Vietnam. Meiofauna and ten benthic environmental factors were determined at 27 sampling stations in the Beibu Gulf in four surveys during 2006 2007. The results show a clear geographical trend in meiofaunal abundance, water depth, salinity and clay content. The meiofaunal abundance and the clay content decreased, whereas the water depth and the salinity increased from the north to the south of the Gulf. The percentage of meiofaunal abundance in the 0 2 cm layer increased, whereas in the 2-5 cm and 5 10 cm layers it decreased from the north to the south of the Gulf. Correlation analysis show significant negative correlations between meiofaunal abundance and water depth, benthic temperature, salinity and pH, but significant positive correlations between meiofaunal abundance and dissolved oxygen, chlorophyll a and clay content.

Preliminary results of environmental monitoring of the natural gas hydrate production test in the South China Sea

Natural gas hydrate (NGH)is considered as one of the new clean energy sources of the 21st century with the highest potential.The environmental issues of NGH production have attracted the close attention of scientists in various countries.From May 10 to July 9,2017,the first offshore NGH production test in the South China Sea (SCS)was conducted by the China Geological Survey.In addition,environmental security has also been effectively guaranteed via a comprehensive environmental monitoring system built during the NGH production test.The monitoring system considered sea-surface atmosphere methane and carbon dioxide concentrations,dissolved methane in the sea water column,and the seafloor physical oceanography and marine chemistry environment.The whole process was monitored via multiple means, in multiple layers,in all domains,and in real time.After the production test,an environmental investigation was promptly conducted to evaluate the environmental impact of the NGH production test. The monitoring results showed that the dissolved methane concentration in seawater and the near-seabed environment characteristics after the test were consistent with the background values,indicating that the NGH production test did not cause environmental problems such as methane leakage.

Distribution of chlorophyll a, photosynthesis and their relations to the environmental factors in the Central South China Sea

Some studies have been made on the variation of primary productivity in the Central South ChinaSea. This paper studies comprehensively the characteristics of chlorophyll a distributions in time andspace and the primary productivity, as well their relations to the environmental factors.Materals and methods During the comprehensive investigation in the Central South China Sea from September 1983 toDecember 1984, the distributions of chlorophyll a and primary productivity were studied. Figure 1shows the sampling stations and their range of investigation.

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.

Geological environment in the South China Sea

The South China Sea(SCS),situated in southern China,at the junction of the Pacific Plate,the Eurasian Plate,and the Indian Ocean Plate,is a northeast-southwest trending semi-enclosed sea.It spans an area of approximately 3.5 million square kilometers and has an average water depth of about 1200 m,its deepest point reaching 5559 m.In 2021,a scientific expedition(called as U1 voyage)in the South China Sea was organized by the Innovation Research Team of Guangdong Special Key Program from March to April,this marks the first comprehensive scientific research voyage to the southern Uboundary corridor.Consisting of a total of 30 papers,this special issue is to share a portion of the research findings from this scientific expedition U1 voyage,covering six aspects:1)characteristics of the marine ecosystem in the SCS and its response to marine dynamic processes;2)multi-scale marine dynamic processes,sea-air interactions,and forecasting techniques in the SCS;3)geomorphology and geological structure;4)sedimentary processes and resource potential in the SCS;5)geostrategy,rights and interests maintenance and strategic countermeasures in the SCS;6)marine scientific instruments.By integrating the scientific research with the study of history,jurisprudence and international strategies,this issue presents new insights into the formation history and scope evolution of the SCS,and it also seeks to establish a new scientific framework based on the marine governance and development of the SCS.

A Preliminary Study on the Diversity of Fish Species and Marine Fish Faunas of the South China Sea

There are 3048 species of fish occurring in the China Seas （CS）, of which at least 2321 species are found in the South China Sea （SCS）, belonging to 35 orders, 236 families and 822 genera. The fish species diversity is analyzed in this paper based on biogeography, biostatistics, fishing methods, etc. It is found that the regional environment, especially biological factors, plays an important role in the distribution of faunas, and there are two fish faunas in the SCS, one in the north and another in the center and south. This regional division is of value for sustainable fishery production and eiTlcient management of fishery resources.

Geochemical characteristics of cold-seep carbonates in Shenhu area,South China Sea

Cold seeps spread worldwide along the continental margins,which are closely related to the exploration of gas hydrates.Cold-seep carbonates have been reported to record the nature of seepage,including fluid source,sedimentary environment,and variation of seepage activity.We investigated the morphology,mineralogy,element compositions,and carbon and oxygen isotopes of 15 cold-seep carbonates collected from the Shenhu area,and compared them with 2 carbonates from the Haima cold seep,the South China Sea(SCS),to promote our knowledge of cold-seep system in SCS.Most of the Shenhu carbonates exhibit crust morphology,and some are in the form of chimneys and blocks.Their absolute(20%–65%)and relative carbonate mineral contents(mainly aragonite and calcite,with minor samples containing dolomite)vary significantly,indicating the multi-stage methane leakage in our study area.Some samples show a slight negative Ce anomaly,suggesting either the mixing of seawater or variation of the redox condition during the precipitation;the cooccurrence of strongly enriched U and Mo demonstrates anoxic condition during precipitation.The mixed genetic methane source was interpreted by δ^(13)C of the Shenhu carbonates to range from-22.34‰to-59.30‰Vienna PeeDee Belemnite(VPDB),and the slight ^(18)O-enrichment imprinted on the carbonates suggests the possible influence from hydrate dissociation.The Haima carbonates,with biogenic methane as the main gas source,were presumably formed in a stronger fluid flux by compared with our Shenhu samples.

Diatom assemblages in surface sediments from the South China Sea as environmental indicators

We studied diatom distribution from 62 samples from the uppermost 1 cm of sedimem in the South China Sea （SCS）, using grabs or box corers in three cruises between 2001-2007. Fifty six genera, 256 species and their varieties were identified. Dominating species included Coscinodiscus africanus, Coscinodiscus nodulifer, Cyclotella stylorum, Hemidiscus cuneiformis, Melosira sulcata, Nitzschia marina, Roperia tesselata, Thalassionema nitzschioides, Thalassiosira excentrica, and Thalassiothrix longissima. Most surface sediments in the SCS were rich ill diatoms, except for a few coarse samples. Average diatom abundance in the study area was 104 607 valve/g. In terms of the abundance, ecology, and spatial distribution, seven diatom zones （Zones 1-7） were recognized. Zone 1 （northern continental shelf） is affected by warm currents, SCS northern branch of the Kuroshio, and northern coastal currents; Zone 2 （northwestern continental shelf） is affected by intense coastal currents; Zone 3 （Xisha Islands sea area） is a bathyal environment with transitional water masses; Zone 4 （sea basin） is a bathyal-to-deep sea with stable and uniform central water masses in a semi-enclosed marginal sea; Zone 5 （Nansba Islands marine area） is a pelagic environment with relatively high surface temperature; Zone 6 （northern Sunda Shelf） is a tropical shelf environment; and Zone 7 （northern Kalimantan Island shelf area） is affected by warm waters from the Indian Ocean and coastal waters. The data indicate that these diatom zones are closely related to topography, hydrodynamics, temperature, nutrients and especially the salinity. Better understanding of the relationship between diatom distribution and the oceanographic factors would help in the reconstruction of the SCS in the past.

Response of Spatio-temporal Distribution of Fishery Resources to Mairne Environment in the Northern South China Sea

[Objective] The paper was to investigate the spatio-temporal distribution of fishery resources in the northern South China Sea and to provide reference for scientific evaluation and effective protection of fishery resources in the northern South China Sea. [Methods] Based on monitoring data and satellite remote sensing data [including Sea Surface Temperature(SST), Chlorophyll a concentration(Chl a) and Sea Surface Wind(SSW)] in winter(January to February) and summer(August to September) in the northern South China Sea, the relationship between spatio-temporal distribution of fishery resources and marine environment was investigated by using Generalized Linear Models(GLM), fishing ground gravity and correlation analysis. [Results] The suitable SST and Chl a of light falling-net fishing ground in winter were 17-23°C and 0.2-0.6 mg/m3, respectively. The suitable SST and Chl a in summer were approximately 28°C and 0.2-1.0 mg/m3. Standardized Catch Per Unit Effort(SCPUE) was higher in summer(2-4) and lower in winter(1-3). From winter to summer, the fishing ground gravity migrated to the east about 1 °E. [Conclusion] The spatio-temporal distribution of fishery resources is related to eastern Hainan-western Guangdong upwelling and the coastal flow, caused by the monsoon in the northern South China Sea, and the major catch species of light falling-net.

Vulnerability Assessment of Tourism Environment in the South China Sea Islands : Construction of Evaluation Model Based on Interpretation System of Formation Mechanism

Tourism vulnerability research is an important theoretical basis for sustainable research of tourism.In this study,it hopes to establish a comprehensive evaluation index system for vulnerability of tourism environment in the South China Sea Islands,to achieve the sound development of island tourism in the South China Sea.Therefore,based on the study of the geographical environment and geographical background of the South China Sea Islands,the mechanism analysis method is used to form three interpretation systems.First,interpretation system of meridional causality mechanism.4 evaluation levels and 52 indicators are screened out,and the mathematical and physical criteria for each indicator is established.Second,interpretation system of latitudinal factor relationship mechanism.The AHP is used to obtain the weights of each index,and the contribution rate of factor at each level to the vulnerability is determined.Third,sharing platform of connecting meridional and latitudinal interpretation system.Likert 5-level scale is used to make the factors belong to different orders of magnitude,and factors from different systems could be comparable.Finally,through the formulation of mathematical and chemical standards of indexes and weights of evaluation indexes,a comprehensive evaluation model for vulnerability of tourism environment in the South China Sea Islands is established.

The second natural gas hydrate production test in the South China Sea

Clayey silt reservoirs bearing natural gas hydrates(NGH)are considered to be the hydrate-bearing reservoirs that boast the highest reserves but tend to be the most difficult to exploit.They are proved to be exploitable by the first NGH production test conducted in the South China Sea in 2017.Based on the understanding of the first production test,the China Geological Survey determined the optimal target NGH reservoirs for production test and conducted a detailed assessment,numerical and experimental simulation,and onshore testing of the reservoirs.After that,it conducted the second offshore NGH production test in 1225 m deep Shenhu Area,South China Sea(also referred to as the second production test)from October 2019 to April 2020.During the second production test,a series of technical challenges of drilling horizontal wells in shallow soft strata in deep sea were met,including wellhead stability,directional drilling of a horizontal well,reservoir stimulation and sand control,and accurate depressurization.As a result,30 days of continuous gas production was achieved,with a cumulative gas production of 86.14×104 m3.Thus,the average daily gas production is 2.87×10^4 m^3,which is 5.57 times as much as that obtained in the first production test.Therefore,both the cumulative gas production and the daily gas production were highly improved compared to the first production test.As indicated by the monitoring results of the second production test,there was no anomaly in methane content in the seafloor,seawater,and atmosphere throughout the whole production test.This successful production test further indicates that safe and effective NGH exploitation is feasible in clayey silt NGH reservoirs.The industrialization of hydrates consists of five stages in general,namely theoretical research and simulation experiments,exploratory production test,experimental production test,productive production test,and commercial production.The second production test serves as an important step from the exploratory production test to experimental production test.

Current status and cause analysis of microplastic pollution in sea areas in China

As a new type of pollutants in the marine environment,microplastics have attracted increasing attention from scientific researchers and environmental protection workers in China and abroad.However,for the microplastic pollution in sea areas in China,there are a very limited number of studies on its current status and few reviews of research on the microplastics.This paper reviews the surveys and researches of microplastics in the Bohai Sea,the Yellow Sea,the East China Sea,the South China Sea,and main estuaries in China carried out in recent years and proposes an outlook for future work,aiming to provide research suggestions and solutions for ecological protection against microplastic pollution in sea areas in China.Previous studies have shown that microplastics are widely distributed in water bodies and sediments in sea areas and major estuaries in China.The Pearl River Estuary,in the South China Sea suffers the most serious microplastic pollution,followed by the Bohai Sea.In contrast,the microplastic pollution in the Yellow Sea and the East China Sea is comparatively slight.Microplastics in sea areas in China are mainly fibrous and are concentrated in offshore areas with developed industry and a dense population(especially around estuaries and bays).In addition,they are widely affected by human activities,such as shipping,aquaculture,industry,and sewage discharge.Here the authors suggest unifying measurement units and research methods and developing related standard systems to carry out researches related to microplastics.Furthermore,this paper also suggests further deepening researches on both the source-sink process of microplastics and nanoscale microplastics while enhancing the development and implementation of related policies,aiming to promote researches and control of microplastics in sea areas in China.

Belt and Road Initiative and Possible Impacts on the SouthChina Sea Issue

Since China proposed the Belt and Road Initiative （BRI） in late 2013, the impacts of the 21st century Maritime Silk Road （MSR） construction on the South China Sea （SCS） issue become a focal point of both academic research and public concern. There are plenty of divergent opinions on whether the MSR will mean an opportunity for settling the SCS issue, or it will face the challenge of intensified maritime conflicts in this region. This paper first of all analyzes the significance of the BRI in the general picture of China＇s foreign policy. To ensure neighborhood diplomacy be in line with the BRI, China adjusts its SCS policy through rebuilding and consolidating political mutual trust with countries which have been involved into conflicts with China on the SCS issue; meanwhile, China promotes pragmatic cooperation under MSR framework to cultivate positive atmosphere and sense of community with a shared destiny. Both MSR construction and the addressing of the SCS issue are long-term issues, while the MSR provides an innovative approach to surpass existing disputes and focus on regional development cooperation. Hence, the MSR could be an opportunity to accelerate the resolving of maritime disputes.

南海渔业资源可持续发展的中国方案建构

有效治理南海渔业资源问题,应以现实需求为导向探寻南海渔业资源可持续发展的总基调,这是建构中国特色治理方案的根本前提。同时,要不失时机地从立法、执法、司法角度深刻反思现有治理措施的缺陷,紧追全球海洋治理大势,借鉴地中海渔业合作治理经验,形成符合南海海洋治理需求的体系化方案。该方案需具有吸引力、感召力与引导力且全面展示中国在南海问题上的基本立场。中国可通过加强科学管理与法规建设、注重生态修复与增殖养护、推动国际合作与区域治理等可行途径实现南海渔业资源的可持续发展。

南海海洋环境保护的法治保障研究

南海作为中国三大边缘海之一,以其特殊的地理位置和战略意义备受国际关注,随着蓝色海洋和经济转型的不断发展,南海海洋环境保护问题频发。文章在阐释南海海洋环境保护的重要性基础上,分析南海的国际国内地位以及相应的法律规定,通过海洋污染、海洋保护区的国内外法律规制方面展开讨论南海现存的海洋环境保护的法治现状,从国际、国内双视角分析现存南海海洋环境保护的法治问题,主张在国际上实现区域协同合作、制定环境保护法规,在国内建立环境保护专门性机构、加强具体法律规制以及协调划分职权范围等方面探讨南海海洋环境保护的法治保障路径,促进南海海洋环境良性发展,实现海洋蓝色经济高质量转型。