South China Sea Area Research Articles

Origin of anomalous subsidence along the Northern South China Sea margin and its relationship to dynamic topography

Mantle induced dynamic topography may have a significant effect on the accomodation space in sedimentary basins, especially close to “slab burial grounds”, but its magnitude and relevance is controversial. We use five Cenozoic stratigraphic sections and 56 wells from the northern South China Sea margin to assess all mechanisms contributing to Late Tertiary tectonic subsidence in this area and to ground-truth the dynamic topography output of a mantle convection model. The computed dynamic topography decreases on average by about 300 m from 20 Ma to the present in the northern South China Sea area. Post-rift anomalous subsidence is computed as the discrepancy between observed and predicted post-rift subsidence based on modeling exponential thermal cooling following earlier lithospheric thinning events. In shallow water areas its magnitude is similar to that predicted by the mantle convection model, confirming that the change in dynamic topography through time since 20 Ma agrees well with subsidence unaccounted for by a conventional rift model. However, this mechanism does not explain the rapid increase of anomalous subsidence towards the deep water areas in the Qiongdongnan and Pearl River Mouth basins. In the deep water (>500 m) part of the Qiongdongnan and Pearl River Mouth basins, post-rift anomalous subsidence ranges from 900 to 1200 m, whereas in the continental shelf area of the basins it ranges from 700 to 300 m and decreases landwards, to less than 250 m in the Beibuwan Basin. This rapid subsidence event, preceded by minor uplift, is interpreted as a thermal cooling episode induced by a late magmatic event. In the Yinggehai Basin anomalous subsidence during the post-rift stage is about 300–500 m in the northwestern part of the basin, substantially less than that in the middle and southeastern parts, where it ranges from 900 to 1200 m. The distinct subsidence anomaly in the Yinggehai Basin may originate from a combination of the dextral movement of marginal faults since the Late Miocene and the effect of dynamic topography.

Legal and Environmental Regime of Islands in the South China Sea: Status under International Law

The Spratly islands comprised an area of hundred and fifty features in the South China Sea (SCS) and on of the littoral States which have obtained their claims to sovereignty to them. The present article analyses under the rules of international law of the sea, the rules that govern the regime of islands. We should take in consideration that all the boundary States has claimed to sovereign over ths islands. China has put forward much documentation supporting the chinese claim based on historical and discovery occupation in the region. Taiwan demonstrates legal bases of claims in the SCS establishing a physical presence on the Spratlys after the japanese withdrawal after world war II. Other States that includes activities in the area of SCS is Vietnam, Philippines, Brunei and Malaysia. There is also explained that a discusses of a continental shelf, the maritime zones, the purpose of the boundary solution has involved also another point of analysis: the protection of the environment in the Spratly region and especially after the 1997. Governments of the region should have start to think and act seriously on environmental questions as a new consequences of various crisis in the last years.

High-quality hydrocarbon source rock in the Paleogene sequence of the Ping Chau Formation, Hong Kong

Although petroleum exploration is being conducted in the Hong Kong region, high-quality hydrocarbon source rocks have never been found in this area. The Ping Chau Formation is only Mesozoic-Cenozoic sedimentary rock exposed in Hong Kong and its surrounding areas. The hydrocarbon source rock of the Ping Chau Formation is very rich in organic matters, which has an average total organic carbon (TOC) of 1.9% and chloroform bitumen “A” range from 0.14% to 0.24%. The total hydrocarbon content varies from 880 to 1800 ppm and the transformation ratio is specific from 5 to 9. The index of pyrolytic hydrogen is up to about 600 mgHC/gTOC. These data demonstrate the characteristics of the high-quality hydrocarbon source rock. The lamalginite is the major maceral of the source rock of the Ping Chau Formation, and geochemical characteristics also suggest that the organic materials of the source rock are of type I and type II1, with abundant gammacerane, γ, β-carotane and C24 tetracyclic terpane, which indicate that it was formed in the salt water and brackish water sedimentary environment, and the source rock has evolved into a mature phase. The organic inclusions are found within calcite veins in cracks of the source rock, indicating that hydrocarbon has been generated and a secondary migration has happened. The source rock in the Ping Chau Formation is about 200–300 m thick, thus having considerable hydrocarbon potential. The discovery of the high quality hydrocarbon source rock in the Ping Chau Formation will certainly provide insight on hydrocarbon resource exploration in the South China Sea area.

Carbon isotopic record of foraminifers in surface sediments from the South China Sea and its significance

The study is based on stable carbon isotopic measurements of 112 foraminiferal samples from surface sediments at 40 sites in the South China Sea (SCS). δ13C of foraminifers and Δδ13C between planktonic and benthic foraminiferal species exhibit a low value area at the north-eastern and southern ends of the SCS. It is correlated with the nutrient distributional pattern in the SCS and circumjacent area, the influence of the northeastern and southwestern monsoons on water flow and water chemistry in the SCS. The monsoons have not only brought nutrients to the upper part of the sea but also disturbed water and decreased difference between the surface and bottom water. Its influence is most obvious at both ends, which resulted in the low value areas in δ13C and Δδ13C at the ends. The distributional pattern of the stable carbon isotope in the SCS is a reflection of the East Asian monsoons.

Zonal propagation of kinetic energy and convection in the South China Sea and Indian monsoon regions in boreal summer

Zonal propagation of kinetic energy (KE) and convection in the South China Sea (SCS) and Indian summer monsoon areas are examined in present study. Results suggest that the SCS and Indian summer monsoon prevailed regions (5–15°N) are dominated by the southwesterly wind, however, the disturbances of KE at 850 hPa and convection are observed mainly coming from the western Pacific Ocean (140-150°E), after passing through the SCS, and westward propagated into the Bay of Bengal (90-100°E). In the Indian summer monsoon domain, where the disturbances of KE are found mainly coming from the Arabian Sea (AS) and eastward propagated into the Bay of Bengal. Therefore, the SCS and the Indian summer monsoon are quite different in zonal propagation of KE and convection. The SCS summer monsoon is mainly affected by the KE and convection coming from the tropical western Pacific. The Indian summer monsoon, however, can be partly influenced by the AS and the SCS summer monsoon. The analysis also suggests that the interaction region between the SCS and the Indian summer monsoon is around 90–95°E, rather than 105°E as proposed by earlier studies.

Cross-strait interactions on the South China Sea issues: a need for CBMs.

Recent developments in the South China Sea (SCS) and the actions expected to be taken by China and member states of ASEAN in accordance with the Declaration on the Conduct of Parties in the SCS have the potential to further marginalize Taiwan's role in any serious discussion on SCS issues and then deprive Taiwan of its legitimate rights and interest in the area. These developments will also force Taiwan to respond by taking more active actions for the sole purpose of safeguarding its sovereignty and maritime jurisdiction in the SCS. This article discusses a number of possible confidence-building measures that could be considered for adoption by China to help engage Taiwan in the regional security dialogue process and enable Taiwan to participate in the planned joint co-operative activities in the SCS. The co-operative actions taken in the SCS area could enhance mutual trust between the two sides of the Taiwan Strait.

Holocene megathermal abrupt environmental changes derived from 14C dating of a coral reef at Leizhou Peninsula, South China Sea

A depth profile of a Goniopora coral reef at Leizhou Peninsula, South China Sea, was radiocarbon dated using liquid scintillation counting (LSC) and accelerator mass spectrometry (AMS). The time of formation, during 6600–7400 cal BP, can be divided into nine stages, each terminated by abrupt growth cessation of Goniopora and appearance of Ostrea shells. The results show that, during the Holocene megathermal (8.2–3.3 ka BP), large climatic changes have occurred in the South China Sea area.

Biological markers and their carbon isotopes as an approach to the paleoenvironmental reconstruction of Nansha area, South China Sea, during the last 30 ka

Paleoenvironmental changes over the last 30 ka have been documented for the Nansha area, South China Sea, from the biomarkers and their carbon isotopic composition of 314 sediment samples from core 17962. The concentrations of marine lipids indicate that the paleoceanographic and paleoclimatic conditions were not stable in the Nansha area during the last glacial period. The accumulation rates of C 37 alkenones and C 30 alkyl diols show that marine paleoproductivity was higher during the last glaciation than in the Holocene, and correlate well with those of terrestrial biomarkers. Simultaneous variations in accumulation rates of marine biomarkers and terrigenous long-chain compounds during the last glacial period suggest that this enhancement of marine productivity was caused by an increase in terrestrial nutrient supply from the Sunda Shelf. The stable carbon isotopic composition of terrigenous long-chain compounds, such as n-alkanes ( δ 13C=−28.6∼−34.2‰), n-alkanoic acids ( δ 13C=−27.1∼−31.8‰) and n-alkanols ( δ 13C=−26.6∼−35.3‰), indicates that these compounds were derived from C 3 plants, and the surrounding area of southern South China Sea was not dry during the last glacial.

A Pleistocene paleoceanographic record from the north slope of the Spratly Islands, southern South China Sea

A 1.4 my paleoceanographic history for offshore north central Spratly Islands, southern South China Sea, is reconstructed using stable isotope, carbonate content, coarse fraction, and planktonic foraminifera census data from gravity core SO95-17957-2. The chronological framework for SO95-17957-2 is based on stable oxygen isotope correlation with open ocean records and constrained with AMS- 14C dates, floral and faunal bioevents, and a Pleistocene microtektite event. Stable oxygen isotope composition of surface water reflects mainly changes in high latitude ice volume but also riverine water influx from surrounding land. Stable carbon isotope record suggests that surface water δ 13C in the southern South China Sea has been modulated primarily by global changes in atmospheric CO 2 since the early Pleistocene. Dissimilarities between δ 18O patterns in SO95-17957-2 and those in various cores from the rest of the South China Sea indicate that between 60 and 120 Ka surface water chemistry at offshore north central Spratly Islands may be affected by different mechanisms. Those differences likely reflect unknown hydrological conditions during stages 4 and 5. Carbonate content is lower during the interglacial periods than during the glacial–deglacial periods, which are opposite to the general trend in the shallow South China Sea areas during the same period. Faunal composition, RSP and various dissolution indices suggest that productivity is the most important factor controlling carbonate preservation. Dissolution above the lysocline may modify the productivity signal but cannot reverse the entire pattern. Faunal composition and carbonate flux suggests productivity is higher during glacial–deglacial than during interglacial. Stronger glacial winter monsoon induces stronger upwelling and deep mixing and enhances nutrient cycling in the surface ocean, which in turn increases productivity. Estimated summer sea surface temperature (SST) based on transfer function FP-12E agrees with δ 18O and is consistently between 28 and 29°C during most of the last 1.4 my Winter SST reflects geographic location and changes in surface hydrology, and fluctuates between 25 and 28°C. During the last glacial period disconnection of the South China Sea from the Indian Ocean and the influx of temperate water through the Bashi Channel allowed winter SSTs to vary by as much as 3.5°C. Comparison of modern and estimated SST and SST estimates based on different methods suggest that G. bulloides and G. menardii are probably overweighed in transfer function FP-12E, which cause discrepancies in SST estimation.

A possible mechanism effecting the earlier onset of southwesterlymonsoon in the South China Sea compared to the Indian monsoon

A possible mechanism effecting the earlier onset of the South China Sea (SCS) southwesterly (summer) monsoon compared to the Indian monsoon is revealed by use of the NCAR/NCEP reanalysis data during the 1998 South China Sea Monsoon Experiment (SCSMEX). It is found that the fundamental cause might be the different spatial distributions and time variations of the surface sensible heat (SH) fluxes in the two areas. In the SCS area, positive surface sensible heating exists all the time in both the tropics and the subtropics with the latter being dominant after March. While in the India Peninsula (IP) area, the tropical heating is the dominant one at the early period before May and the subtropical heating is smaller and even negative. It is further found that the west-east contrasts of the SH fluxes at middle latitudes are also favorable to the earlier onset of the SCS monsoon.

A contrast and comparison of near-sea surface air temperature/humidity from GMS and SSM/I data with an improved algorithm

With data sets gained from Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave/Imager (SSM/I) microwave channels, Geostationary Meteorological Satellite (GMS-5) infrared channels, and ship-measured data, the statistical algorithms to estimate sea surface temperature and near-sea surface air humidity around Taiwan and the South China Sea areas are developed. Then a new, improved method to estimate near-sea surface air temperature based on the algorithm proposed by Konda et al. (1996) is established in this study. The results estimated with SSM/I data show that the root mean square error (RMSE) of SST, near-sea surface air humidity and air temperature over the oceans around Taiwan and the South China Sea are 1.2 K,1.43 g/kg, and 1.6 K, respectively. The results with GMS data are 1.7 K,1.71 g/kg and 1.7 K, respectively. The results also show that the improvements in the algorithm of Konda et al. simplify the computation scheme, improve the accuracy, and match the regional ocean-atmosphere properties in retrieving near-sea surface air temperature. The estimate produced using SSM/I and GMS data also show good consistency between them, both in temporal and spatial variations. Basically, the accuracy of this result implies strong potential for application of satellite data to relative studies and operational work in the ocean-atmosphere interaction.

A phylogenetic and biogeographic study of Euniphysa (Eunicidae, Polychaeta)

Fourteen species have either been described in, or referred to, the genus Euniphysa. Seven of these are here re-described based on type material and two new species, E. quadridentata and E. filibranchia, are described. Euniphysa oculata is found to be a subjective synonym of E. spinea, and E. unicusa is a subjective synonym of E. aculeata. Euniphysa taiwanensis and E. megalodus are correctly assigned to the genus, but cannot be described due to lack of material. Euniphysa misakiensis, E. tubicola and E. tubifex are transferred to Eunice. A key is given to the nine identifiable species retained in Euniphysa. Coding strategies for polymorphic and inapplicable characters, as well as problems associated with shared absences, are discussed. A phylogenetic analysis of Euniphysa based on 24 morphological characters yielded two most parsimonious trees (CI = 0.902, RI = 0.905). The tree topology separates Euniphysa into two distinct groups. Group I includes E. filibranchia n. sp., E. italica, E. jeffreysii, E. quadridentata n. sp. and E. spinea, it is supported by five equivocal similarities. Group II is supported by five unequivocal synapomorphies and two equivocal similarities, it includes E. aculeata, E. auriculata, E. falciseta and E. tridontesa. Based on the phylogenetic topology, Paraeuniphysa and Heterophysa are considered as junior synonyms of Euniphysa. The recognition of a separate family for Euniphysa is not warranted. All species of Euniphysa are fragile, shallow, warm water species. They have been collected mainly from sandy sediments of the Northern Hemisphere. The greatest diversity is from the South China Sea area; other species are found throughout the Indian Ocean, the Mediterranean Sea and the East Atlantic Ocean coasts suggesting the genus may have originated in the Tethys Sea. A few species have also been found in the Gulf of Mexico and the West Atlantic Ocean coast again suggesting a Tethyan origin associated with the westward drift of the North American continent.

ABSTRACT: Gas exploration potential in deep water area of South China Sea

ABSTRACT: Gas exploration potential in deep water area of South China Sea

Moisture Flux and Water Balance over the South China Sea During Late Boreal Spring and Summer

The moisture flux and water balance over the South China Sea (SCS) during late boreal spring and summer are studied using the reanalysis data of the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP/NCAR). It is shown that the SCS is a water vapor sink during that period of time. Climatologically, the SCS works like a “reservoir of water vapor” for its special geographical location. In early May, water vapor is brought into the SCS area through its eastern, southern, and western boundaries, and is transported out of that area through its northern boundary. From June to August, the western and southern boundaries of the SCS are inflow passes of moisture flux to that region, while the northern and eastern boundaries are outflow passes. It is the intense convergence of moisture to the SCS area that maintains the local heavy precipitation. The northward branch of moisture flux feeds the precipitation over eastern China.

Numerical simulation of principal tidal constituents in the South China Sea, Gulf of Tonkin and Gulf of Thailand

The principal tidal constituents M 2, S 2, K 1 and O 1 in the South China Sea, Gulf of Tonkin and Gulf of Thailand are simulated simultaneously using the numerical scheme of Kwok et al. (1995 Proceedings of the 1st Asian Computational Fluid Dynamics Conference, pp. 16–19). The average differences between the computed and observed harmonic constants are mostly within 5 cm and 10° for amplitudes and phase-lags, respectively. The simulated tidal regimes in the present model are believed to be more accurate than the previous numerical results. Our studies confirm that a clockwise rotating M 2 amphidromic system lies in the southeast of the Gulf of Thailand and an S 2 amphidromic system at the near-shore area of the northeast South China Sea. The linear tidal energy equation developed by Garrett (1975 Deep-Sea Research 22, 23–35) is generalized to the nonlinear case. Based on the numerical results, the energy budgets in the South China Sea and its subareas, namely the Taiwan Strait, the Gulf of Tonkin, the Gulf of Thailand and the remaining area are investigated. The tidal motion in the Taiwan Strait is maintained mainly by the energy fluxes from the East China Sea for both semidiurnal and diurnal species and partially from the Luzon Strait for semidiurnal species. For the other parts of the South China Sea, the tidal motion is mainly maintained by the energy fluxes through the Luzon Strait. The energy inputs from the tide-generating force are negative for semidiurnal species and positive for diurnal species.

Evolution of intraseasonal oscillation over the tropical western pacific / south china sea and its effect to the summer precipitation in southern china{1{

In this paper, the evolution of intraseasonal oscillation over the South China Sea and tropical western Pacific area and its effect to the summer rainfall in the southern China are studied based on the ECMWF data and TBB data) analyses. A very low-frequency waves exist in the tropics and play an important role in dominating intraseasonal oscillation and lead to special seasonal variation of intraseasonal oscillation over the South China Sea / tropical western Pacific area. The intraseasonal oscillation (convection) over the South China Sea and tropical western Pacific area is closely related to the summer rainfall (convection) in the southern China. Their relationship seems to be a seesaw feature, and this relationship resulting from the different pattern of convection in those two regions is caused by the differnt type of local meridional circulation.

Deep-sea benthic foraminiferal recolonization of the 1991 Mt. Pinatubo ash layer in the South China Sea

A census count of Rose Bengal stained benthic foraminifera from the surface area on top of a 2 to 6 cm thick ashfall layer at three deep water stations along the western margin of the Philippines exhibits a unique assemblage composition of benthic foraminifera. The total number of benthic foraminifera is low and the ratio of living individuals to empty tests is high. Specific diversity is low, with a significant dominance of infaunal morphotypes including species of the genus Reophax ( R. scorpiurus, R. bilocularis and R. dentaliniformis), which are regarded as successful recolonizers. Assemblages below the ash layers are diverse and contain many epifaunal suspension-feeding agglutinated and calcareous foraminifera. The 1991 Mt. Pinatubo eruption caused mass mortality of benthic foraminifera in a vast area of the eastern South China Sea followed by step-wise recolonization of the ash substrate. Three years after the eruption, the benthic foraminiferal community structure is still far from recovery to background levels.

Tectono-stratigraphic terranes and detachment faulting of the South China Sea and Sulu Sea

Geoscientific data acquired from the South China Sea and Sulu Sea areas by BGR since 1977 are compiled and interpreted as comprehensive data sets, together with available information of commercial wells and drillsites of the Ocean Drilling Program (ODP). Generalized stratigraphy and lithology are discussed and correlated with the interpreted seismic profiles. On the basis of the stratigraphic and structural analysis 5 main tectono-stratigraphic terranes are defined for the South China Sea and 4 main terranes for the Sulu Sea, respectively. The Dangerous Grounds, Reed Bank, Palawan-NW Borneo Trough and Palawan Island represent terranes of continental origin which developed on the proto-China margin by uniform-sense, low-angle, simple shearing within the crust in Late Cretaceous to Early Paleocene. This rift was abandoned and a new westward propagating rift system developed north of the Dangerous Grounds-Reed Bank area from the middle Eocene to the Oligocene/Early Miocene together with seafloor spreading in the South China Sea Basin. The leading edge of the southward drifting continental terranes collided with the Late Cretaceous to Early Eocene subduction complex of the northernmost terrane of the proto-Sulu Sea. Continuous convergence of these terranes, back-arc spreading creating the SE Sulu Sea terrane and the assumed anti-clockwise rotation of Borneo are responsible for the complex collision-compression structures of the Sulu Sea terranes, including the formation of splinters of oceanic crust. Major right-lateral wrench systems are NNW-SSE running, up to 500 km long and cut across most of the identified terranes. Wrenching presumably ceased 12 to 16 Myr ago.

The geology of Sarawak deepwater and surrounding areas

A geological and geophysical investigation of several key transects ofthe 1989 vintage seismic grid in the Sarawak deepwater was conducted in order to understand the sedimentation history and structural geology of the area. In the study area, two tectonostratigraphic provinces can be recognised, namely the North Luconia and West Luconia Provinces. The deep sedimentary basin of North Luconia is filled with 7-8 km of Tertiary sediments and are characterised by NNE-SSW trending extensional fault bounded features, buried hills and local occurrences of forced folds. On the eastern boundary, a major, NNE-SSW trending basin boundary fault separates it from the Northwest Sabah Platform. The latter by contrast is an attenuated crustal terrain characterised by NE-SW trending rift systems and generally thinner sedimentary cover of about only 2-4 km thick. To the southeast, the West Luconia Province which is a thick sedimentary basin with up to about 13 km of sediments, contains a very thick pile of post mid Miocene sedimentary section and is characterised by E-W trending growth faults and °a series of slumps and toe thrusts formed by gravity gliding. These overlie an older normal-faulted section at a mid Miocene unconformity. Generally, the crustal extension in the South China Sea and peripheral areas have generated various patterns of rift orientation and extensional axes. In North Luconia the NNE-SSW trending extensional elements parallel some of the basin axes in the N am Con Son Basin, offshore Vietnam. Finally, based on sequence stratigraphic framework, up to five sub-megasequences are recognised in the Sarawak deepwater. The age determination from well controls and correlation with the episodic crustal rifting and seafloor spreading in the South China Sea Basin has provided some insight on the tectonic evolution.

The impact of maritime boundary delimitation on the development of offshore mineral deposits

Many developing countries are keen to promote investments in maritime areas that are subject to overlapping claims or are even the subject of sovereignty disputes. The link between attracting investment for development of such areas and the settlement of the dispute concerned is the delimitation of the boundaries of the area. The settlement of overlapping claims in maritime zones has led to the development of hard mineral and petroleum deposits in border areas. This has been clearly demonstrated in the North Sea and the Persian Gulf in the case of petroleum. Where there is a failure to settle overlapping claims, as in the South China Sea and Aegean Sea areas, investors tend to avoid such areas. However, in a growing number of cases, coastal states have resorted to the joint development of mineral deposits in areas of overlapping claims in the absence of an agreement to settle their claims, as is evidenced in the Red Sea region with respect to minerals (Sudan and Saudi Arabia) and the Timor Sea in the case of petroleum (Indonesia and Australia).