The Shenhu area is one of the most favorable places for the occurrence of gas hydrates in the northern continental slope of the South China Sea. Pore water samples were collected in two piston cores (SH-A and SH-B) from this area, and the concentrations of sulfate and dissolved inorganic carbon (DIC) and its carbon isotopic composition were measured. The data revealed large DIC variations and very negative δ¹³C-DIC values. Two reaction zones, 0–3 mbsf and below 3 mbsf, are identified in the sediment system. At site SH-A, the upper zone (0–3 mbsf) shows relatively constant sulfate and DIC concentrations and δ¹³C-DIC values, possibly due to bioturbation and fluid advection. The lower zone (below 3 mbsf) displays good linear gradients for sulfate and DIC concentrations, and δ¹³C-DIC values. At site SH-B, both zones show linear gradients, but the decreasing gradients for δ¹³C-DIC and SO₄²⁻ in the lower zone below 3 mbsf are greater than those from the upper zone, 0–3 mbsf. The calculated sulfate-methane interface (SMI) depths of the two cores are 10.0 m and 11.1 m, respectively. The depth profiles of both DIC and δ¹³C-DIC showed similar characteristics as those in other gas hydrate locations in the world oceans, such as the Blake Ridge. Overall, our results indicate an anaerobic methane oxidation (AMO) process in the sediments with large methane flux from depth in the studied area, which might be linked to the formation of gas hydrates in this area.

The upper oceanic heat budget in the South China Sea (SCS) is studied on the basis of ocean surface heat flux, upper sea heat storage and horizontal oceanic heat transport calculated from Comprehensive Ocean and Atmosphere Data Set. Several useful conclusions can be obtained and they are helpful for us to understand the climatologically thermal condition in the SCS. The annual variation of net heat budget reflects the adjustment and sudden change of the monsoon circulation over the SCS. The variation of upper oceanic heat storage of the SCS is tightly connected with the oceanic heat transport as well as the vertical movement in the SCS and so on.

The formation of the South China Sea (SCS) deep basin warm-core and cool-core eddies was studied numerically using the Princeton Ocean Model (POM) with 20 km horizontal resolution and 23 sigma levels conforming to a realistic bottom topography. Numerical integration was divided into pre-experimental and experimental stages. During the pre-experimental stage, we integrated the POM model for three years from zero velocity and April temperature and salinity climatological fields with climatological monthly mean wind stresses, restoring type surface salt and heat fluxes, and observational oceanic inflow/outflow at the open boundaries. During the experimental stage, we integrated the POM model for another 16 months under three different conditions: one control and two sensitivity runs (no-wind and no lateral transport). We take the fields of the last 12 months for analysis. The simulation under control run agrees well with earlier observational studies on the South China Sea surface thermal variabilities. In addition, the sensitivity study further confirms that the wind effect is the key factor for generation of the SCS deep basin warm/cool eddy and that the lateral boundary forcing is the major factor for the formation of the strong western boundary currents, especially along the southeast Chinese coast during both summer and winter monsoon seasons.

Based on the stable isotopic analysis of more than 1000 samples of planktonic and benthic foraminifers from ODP Site 1148 in the northern South China Sea (SCS), the oxygen isotope stratigraphy has been applied to the last 3 million years for the first time in the SCS. Furthermore, the paleoceanographic changes in the northern SCS during the last 6 million years have been unraveled. The benthic foraminiferal δ¹⁸O record shows that before δ3.1 Ma the SCS was much more influenced by the warm intermediate water of the Pacific. The remarkable decrease in the deepwater temperature of the SCS during the period of 3.1-2.5 Ma demonstrates the formation of the Northern Hemisphere ice-sheet. However, the several sea surface temperature (SST) reductions during the early and middle Pliocene, reflected by the planktonic foraminiferal δ¹⁸O, might be related to the ice-sheet growth in the Antarctic region. Only those stepwise and irreversible SST reductions during the period of δ2.2-0.9 Ma could be related to the formation and growth of the Northern Hemisphere ice-sheet.

This is a quantitative method for studying the fractal character of magnetic anomaly fields and delineating tectonic elements using fractal theory. For an area with different geological and geophysical features, the definition of Hausdorff dimension is used to calculate the fractal dimension of the area’s magnetic field, then delineate geological tectonic elements by comparing this value. Use of 1978–1986 geophysical survey data in this method applied to the South China Sea yieled three first grade tectonic elements and nine second grade ones, in six of which subsecond grade elements were found.

A new species,Clathrocorys gracilis nov. spec. of Tripocyrtidae (Radiolarians: Nassellaria) from surface water in northern South China Sea, is described in this paper. The new species has four radial beams arising from the cephalic base centre, each foot with cup-shaped structure and ramified bar in the proximal section (near cephalic base), and each wing with a large mesh in the middle, a medium mesh and a small mesh on each side respectively.

Based on an analysis of drifter data from the World Ocean Circulation Experiment during 1979–1998, the sizes of the eddies in the North subtropical Pacific are determined from the radii of curvature of the drifter paths calculated by using a non-linear curve fitting method. To support the drifter data results, Sea Surface Height from the TOPEX/POSEIDON and ERS2 satellite data are analyzed in connection with the drifter paths. It is found that the eddies in the North Pacific (18°–23°N and 125°–150°E) move westward at an average speed of approximately 0.098 ms⁻¹ and their average radius is 176 km, with radii ranging from 98 km to 298 km. During the nineteen-year period, only 4 out of approximately 200 drifters (2%) actually entered the South China Sea from the area adjacent to the Luzon Strait (18°–22°N and 121°–125°E) in the winter. It is also found that eddies from the interior of the North Pacific are unlikely to enter the South China Sea through the Luzon Strait.

A distinct echo-character was assigned to sedimentation processes, which were then verified using data from surface sediment samples and piston cores. Of echo types on the continental slope perfectly reflecting both sediment erosion and deposition, four sedimentary types have been recognized: (1) submarine slides distributed on the shelfbreak and characterized by high silt and water content, loose structure, poor consolidation and low shearing strength; (2) slumps occurring on the shelfbreak, middle slope channel and reef margin near Dongsha Islands, but having different origins; (3) debris flow occurring either in sea areas around Dongsha Atoll, or on the continental slope's three channels, where the transparent debris flow deposits often overlie or abruptly truncate highly stratified hemipelagic sediments; are of limited to local extent, ranging from a few square kilometers to hundreds of square kilometers in area; but on the lower slope, usually occur as 1000 km², about 100km² individual complexes; and (4) turbidites, limited on the continental slope; some occurring as migrating waves of sediments at the toe of the slope, and are rhythmically-bedded, coarse-grained. Their migration is a result of overbank flow downslope through the submarine channel at the west. The slope faces are dominated by mass wasting deposition, and a few turbidite current sediments. Mass wasting is an important process. Some debris flow complexes on the west are buried by well-stratified conformable sediments, whereas others on the east appear on the present seafloor and therefore are relatively recent.

We utilized ²³⁴Th, a naturally occurring radionuclide, to quantify the particulate organic carbon (POC) export rates in the northern South China Sea (SCS) based on data collected in July 2000 (summer), May 2001 (spring) and November 2002 (autumn). Th-234 deficit was enhanced with depth in the euphotic zone, reaching a subsurface maximum at the Chl-a maximum in most cases, as commonly observed in many oceanic regimes. Th-234 was in general in equilibrium with ²³⁸U at a depth of ∼100 m, the bottom of the euphotic zone. In this study the ²³⁴Th deficit appeared to be less significant in November than in July and May. A surface excess of ²³⁴Th relative to ²³⁸U was found in the summer over the shelf of the northern SCS, most likely due to the accumulation of suspended particles entrapped by a salinity front. Comparison of the ²³⁴Th fluxes from the upper 10 m water column between 2-D and traditional 1-D models revealed agreement within the errors of estimation, suggesting the applicability of the 1-D model to this particular shelf region. 1-D model-based ²³⁴Th fluxes were converted to POC export rates using the ratios of bottle POC to ²³⁴Th. The values ranged from 5.3 to 26.6 mmol C m⁻²d⁻¹ and were slightly higher than those in the southern SCS and other oligotrophic areas. POC export overall showed larger values in spring and summer than in autumn, the seasonality of which was, however, not significant. The highest POC export rate (26.6 mmol C m⁻²d⁻¹) appeared at the shelf break in spring (May), when Chl-a increased and the community structure changed from pico-phytoplankton (<2 µm) dominated to nano-phytoplankton (2–20 µm) and micro-phytoplankton (20–200 µm) dominated.

The first attempt is made to evaluate quantitatively the changes of accumulation rates in the South China Sea during the last glaciation and Holocene, based on the data of 72 sediment cores taken from six areas deeper than 100 m. As shown from the calculations, the accumulation rate during the last glaciation is much higher than that during the Holocene. The southern and northern continental slopes are distinguished from other areas by the highest accumulation rates, with different features of sedimentation for aifferent stages: The Glacial-Holocene contrast in accumulation rate of terrigenous material is more distinct in the southern slope, while the contrast in biogenic sedimentation rate is more remarkable in the northern slope.