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Based on NCEP/CFSR 0.5° reanalysis data and the best track data from the Japan Tokyo Typhoon Center, composite and comparative analyses demonstrate the asymmetrical structures of the temperature and humidity in tropical cyclones over the Western North Pacific and the South China Sea from 1979 to 2010. The results are shown as follows. (1) With intensifying tropical cyclones, the flow field tends to become gradually more axisymmetric; however, the asymmetry of the specific humidity in the outer regions is more obvious. (2) In general, tropical cyclones have a non-uniform, vertical, “double warm-core” structure. The “warm-cores” in the lower level of weak tropical cyclones and in the higher level of strong tropical cyclones are the stronger of the two. (3) The distribution area of a “warm-core” is enhanced with cyclone intensification and tends to become more axisymmetric. At 200 hPa, the “warm-core” of a weak cyclone has a weak anticyclone in the center, whereas that of a strong cyclone has a weak cyclone in the center. (4) The “wet-core” of a tropical cyclone is primarily located in the lower level (700–850 hPa). With the cyclone’s intensification, the intensity of the “wet-core” increases and the scope of the 0.8 g⋅kg−1 specific humidity anomaly tends to expand to higher levels. (5) With the cyclone’s deepening, the pseudo-equivalent potential temperature at different levels in different regions increases. In addition, the largest warming rates at each intensity level in the different regions occur in the core area, followed in turn by the envelope and outer areas. [ABSTRACT FROM AUTHOR]

Four types of tourmaline in the Qitianling granitic batholith, South China, were identified in this study: euhedral disseminated tourmaline (DT type) in the early stage of granite consolidation; typical interstitial nodular tourmaline (NT type) formed late in the crystallization history; radial tourmaline veinlet (RT type) and vein tourmaline (VT type) of hydrothermal origin. We performed major and trace element analysis by in situ electron microprobe and laser ablation inductively coupled plasma mass spectrometry on these four tourmaline types. Compositionally, these tourmalines fall into the alkali group and schorl-dravite solid solution series. There is clear correlation between trace and major elements in VT-type tourmalines, likely related to co-variations of these elements in the hydrothermal fluid from which the tourmaline precipitated. Tourmaline from granites displays low REE abundances and negative LREE trends, positive Eu anomalies, and HREE below or close to their detection limits. The DT-type tourmalines show a positive Eu anomaly, which is probably due to a preferential incorporation of Eu over Eu. REE depletion in NT-type tourmalines may reflect co-crystallization of REE-rich minerals. The positive Eu anomaly in NT-type tourmalines is due to late-stage release of Eu caused by tourmaline replacement of early feldspar. Vein tourmalines (RT and VT type) display similar slopes from La to Nd, without an Eu anomaly. The chondrite-normalized REE patterns in tourmalines from veins display a concave upward-shaped, MREE-depleted pattern, with minimum values at Ho increasing steadily to Lu, and may reflect the REE characteristics of the precipitated medium. HREE enrichment in hydrothermal fluid can be attributed to the formation of REE-fluoride complexes during the internal fluid evolution. [ABSTRACT FROM AUTHOR]

The Qiongdongnan Basin is one of the target areas for marine gas hydrate exploration in the northern margin of the South China Sea. In this study, major anion (e.g., SO, Cl, Br, I), cation (e.g., Ca, Mg, K, Na), and trace element (e.g., Sr, Ba) concentrations of pore water samples collected from site HQ-1PC in the Qiongdongnan Basin were analyzed. These geochemical data suggest that the process of AOM (Anaerobic Oxidation of Methane) is dominant in sulfate-reduction zone in this site due to high upwelling iodine flux and strong microbial activities. The iodine-rich fluids, which may carry methane for the gas hydrate formation, pass through the gas hydrate stability zone, mix with brine released during gas hydrate formation, and cause the geochemical anomalies observed at site HQ-1PC. The pore water geochemical characteristics and anomalies in the Qiongdongnan Basin are quite similar to those found in other gas hydrate locations in the Shenhu area in the northern South China Sea, and a genetic link is suggested with the possibility of gas hydrate occurrence in the study area. [ABSTRACT FROM AUTHOR]

Shenhu Area is one of the most promising areas for gas hydrate exploration in the northern South China Sea (SCS). Pore water sulfate gradient, sulfate-methane interface (SMI) depth, and sulfate flux were analyzed at 53 sites in this area. SO gradient ranges between 0.33 and 4.43 mmol L m. SMI depths are from 7.7 to 87.9 mbsf. Sulfate flux varies between 2.0 and 26.9 mmol m yr, with a mean of 11.7 mmol m yr. Correlation coefficient between SMI depth and methane flux for the 53 sites is −0.80, implying that methane flux regulates the rate of anaerobic methane oxidation (AMO), SMI depth, and sulfate flux. Twelve anomalous fields with high methane flux and steep sulfate gradients were recognized. Bottom simulating reflector (BSR) is distributed mainly in areas where SMI depth is less than 50 mbsf or places with sulfate flux larger than 3.5 mmol m yr. It is suggested that the Baiyun Sag and the Southern Uplift are potential areas for gas hydrate exploration. [ABSTRACT FROM AUTHOR]

Gravity flow deposits form a significant component of the stratigraphic record in ancient and modern deep-water basins worldwide. Analyses of high-resolution 3D seismic reflection data in a predominantly slope setting, the southern slope of Qiongdongnan Basin, South China Sea, reveal the extensive presence of gravity flow depositional elements in the Late Pliocene−Quaternary strata. Three key elements were observed: (1) mass transport deposits (MTDs) including slumps and debris flows, (2) turbidity current deposits including distributary channel complexes, leveed channel complexes and avulsion channel complexes, and (3) deep-water drapes (highstand condensed sections). Each depositional element displays a unique seismic expression and internal structures in seismic profiles and attribute maps. Based on seismic characteristics, the studied succession is subdivided into six units in which three depositional cycles are identified. Each cycle exhibits MTDs (slump or debris) at the base, overlain by turbidities or a deep-water drape. The genesis of these cycles is mainly controlled by frequent sea-level fluctuations and high sedimentation rates in the Late Pliocene-Quaternary. Moreover, tectonics, differential subsidence, and paleo-seafloor morphology may have also contributed to their formation processes. The present study is aimed to a better understanding of deep-water depositional systems, and to a successful hydrocarbon exploration and engineering-risk assessment. [ABSTRACT FROM AUTHOR]

The Shenhu area is one of the promise target areas for marine gas hydrate exploration in the northern margin of the South China Sea. Pore water samples were collected from two piston cores (8.75 and 8.52 m) in site HS-A and site HS-B in the Shenhu area, and their major anion and cation contents and trace element contents have been analyzed in this study. Cl- concentrations in pore waters are similar to the seawater value and no systematic change along depth profiles has been found for the Cl- content in both sites. In site HS-A, the SO42- contents show a limited range in pore waters from 0 to 3 m depths, but a dramatic decrease is documented in depth below 3 m. Other elements such as Ca2+, Mg2+ and Sr2+ show similar variation patterns as the SO42-, i.e., no variation in 0-3 m, but large decrease in depth below 3 m. In site HS-B, both the SO4 and Ca2+, Mg2+ and Sr2+ display a decrease pattern along the depth profile, but in 0-3 m the variation is less significant than those in depth below 3 m. In both sites HS-A and HS-B, I contents show a dramatic increase along depth profiles. Calculations show that the SMI depths are very shallow (10 and 11 m) in both sites, and the sulfate flux and I flux are very high. These geochemical characteristics and anomalies at Shenhu are quite similar to those found in other gas hydrate locations in the world, and a genetic link is suggested to be related to the gas hydrate occurrence at depths in the study area. In summary, we suggest that combined geochemical parameters in shallow sediment pore waters are useful indicators to indicate the gas hydrate occurrence at depths. [ABSTRACT FROM AUTHOR]

Abstract: Trace element and rare earth element (REE) concentrations in cold seep carbonates from the northern continental slope of the South China Sea are used in this study to indicate source fluid characteristics and redox conditions. Carbonate samples from the two study areas (Shenhu and Dongsha) all show low total REE concentrations (mostly 10–20ppm). In the Shenhu area, the shale-normalized REE patterns of the chimney carbonates display slight light REE enrichment, positive Ce anomaly, and a consistently positive Gd anomaly. These carbonate chimneys show a two-stage formation history, with a slight increase in the positive Ce anomaly from the rim to core. Trace and rare earth element data suggest that the core may have formed in a more anoxic condition than the rim. In the Dongsha area, seep carbonate samples show a slight heavy REE enrichment, with both negative and positive Ce anomalies, and more positive Gd anomalies, which are consistent with precipitation in an anoxic environment. Redox sensitive trace elements, such as Mo, U, Ni, V and Co, also indicate anoxic conditions for this cold seep carbonate precipitation. [ABSTRACT FROM AUTHOR]