The characteristic differences of tropical cyclones forming over the western North Pacific and the South China Sea

The best track dataset of tropical cyclones in the western North Pacific （WNP） and the South China Sea （SCS） from 1977 to 2005 during the satellite era, the NCEP/NCAR reanalysis dataset and the extended reconstructed sea surface temperature dataset are employed in this study. The main climatological characteristics of tropical cyclone formation over the WNP and the SCS are compared. It is found that there is obviously different for the locations of tropical cyclone origins, achieving the lowest central pressure and termination points between over the WNP and over the SCS. The annual number of tropical cyclones forming over the SCS is obviously less than over the WNP, and there is a significant negative correlation with the correlation coefficient being - 0.36 at the 5% significance level between over the WNP and over the SCS. The mean speed of tropical cyclone moving is 6.5 m/s over the WNP and 4.6 m/s over the SCS. The mean lowest central pressure of tropical cyclones is obviously weaker over the SCS than over the WNP. The tropical cyclone days per year, mean total distance and total displacement of tropical cyclone traveled over the WNP are all obviously longer than those over the SCS. Tropical cyclone may intensify to Saffir - Simpson hurricane scale 5 over the WNP, but no tropical cyclone can intensify to Saffir - Simpson hurricane scale 3 over the SCS. The changing ranges of the radii （R15,R16） of the 15.4 m/s winds them and the 25.7 m/s winds over the WNP are obviously wider than those over the SCS, and the median values of the radii over the WNP are also larger than those over the SCS. For the same intensity of tropical cyclones, both radii have larger medians over the WNP than over the SCS. The correlations of annual mean tropical cyclone size parameters between over the WNP and over the SCS are not significant. At the same time, the asymmetric radii of tropical cyclones over the WNP are different from those over the SCS.

Mass movements in small canyons in the northeast of Baiyun deepwater area, north of the South China Sea

The process of mass movements and their consequent turbidity currents in large submarine canyons has been widely reported, however, little attention was paid to that in small canyons. In this paper, we document mass movements in small submarine canyons in the northeast of Baiyun deepwater area, north of the South China Sea （SCS）, and their strong effects on the evolution of the canyons based on geophysical data. Submarine canyons in the study area arrange closely below the shelf break zone which was at the depth of -500 m. Within submarine canyons, seabed surface was covered with amounts of failure scars resulted from past small-sized landslides. A complex process of mass transportation in the canyons is indicated by three directions of mass movements. Recent mass movement deposits in the canyons exhibit translucent reflections or parallel reflections which represent the brittle deformation and the plastic deformation, respectively. The area of most landslides in the canyons is less than 3 km2. The trigger mechanisms for mass movements in the study area are gravitational overloading, slope angle and weak properties of soil. Geophysical data indicate that the genesis of submarine canyons is the erosion of mass movements and consequent turbidity currents. The significant effects of mass movements on canyon are incision and sediment transportation at the erosion phases and fillings supply at the fill phases. This research will be helpful for the geological risk assessments and understanding the sediment transportation in the northern margin of the SCS.

The destiny of the North Pacific Intermediate Water in the South China Sea

The previous studies show that the spreading path of the subtropical salinity minimum of the North Pacific Intermediate Water （NPIW） is southwestward pointing to the Luzon Strait. Based on the P -vector method and generalized digital environmental model （GDEM） data, the volume transport of NPIW through Luzon Strait and the upward transport on the NPIW lower and upper boundaries are calculated to examine the destiny of NPIW in the South China Sea （SCS）. On the annual mean, the estimation of NPIW transport into the SCS through the Luzon Strait is 1.72 Sv （1Sv=10 6 m 3 /s）. The upward transport over the SCS is 0.31 Sv on the NPIW upper boundary and 1.31 Sv on the NPIW lower boundary. There is no strait or passage deeper than the surface for the NPIW to extend, except for the Luzon Strait. For the volume balance in the SCS NPIW, the volume transport of 2.72 Sv has to flow out of the SCS NPIW layer through the Luzon Strait.

Eddies in the Northwest Subtropical Pacific and Their Possible Effects on the South China Sea

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.

Associations between the Western North Pacific Monsoon and the South China Sea Monsoon

Based on the interannual variability of convection over the tropical western North Pacific (WNP), a region of 130°—160°E, 10°—20°N, a composite analysis is performed on the fields of surface temperature, outgoing longwave radiation and 850 hPa zonal wind. The composite results show that the weaker (stronger) WNP convection is related to the El Nino (La Nina)—pattern sea surface temperature (SST) anomalies in the preceding winter and in spring. A comparison with previous results indicates that a similar spatial and temporal distribution of SST anomalies is also associated with the onsets of both the WNP and South China Sea (SCS) monsoons. The composite results also show that the weaker (stronger) convection over the WNP corresponds to the easterly (westerly) anomalies that extend westward from the WNP into the Bay of Bengal. A numerical experiment by an atmospheric general circulation model shows a similar result. In addition, during weaker (stronger) convection summer, the convection over the WNP and lower-level zonal winds over the SCS exhibit a small (large) extent of seasonal evolution.

Vorticity Budget Study on the Seasonal Upper Circulation in the Northern South China Sea from Altimetry Data and a Numerical Model

Based on the EOF analyses of Absolute Dynamic Topography satellite data, it is found that, in summer, the northern South China Sea （SCS） is dominated by an anticyclonic gyre whilst by a cyclonic one in winter. A connected single-layer and two-layer model is employed here to investigate the dynamic mechanism of the circulation in the northern SCS. Numerical experi- ments show that the nonlinear term, the pressure torque and the planetary vorticity adveetion play important roles in the circulation of the northern SCS, whilst the contribution by seasonal wind stress curl is local and limited. Only a small part of the Kuroshio water intrudes into the SCS, it then induces a positive vorticity band extending southwestward from the west of the Luzon Strait （LS） and a negative vorticity band along the 200 m isobath of the northern basin. The positive vorticity field induced by the local summer wind stress curl is weaker than that induced in winter in the northern SCS. Besides the Kuroshio intrusion and monsoon, the water trans- ports via the Sunda Shelf and the Sibutu Passage are also important to the circulation in the northern SCS, and the induced vorticity field in summer is almost contrary to that in winter. The strength variations of these three key factors （Kuroshio, monsoon and the water transports via the Sunda Shelf and the Sibutu Passage） determine the seasonal variations of the vorticity and eddy fields in the northern SCS. As for the water exchange via the LS, the Kuroshio intrusion brings about a net inflow into the SCS, and the monsoon has a less effect, whilst the water transports via the Sunda Shelf and the Sibutu Passage are the most important influencing factors, thus, the water exchange of the SCS with the Pacific via the LS changes dramatically from an outflow of the SCS in summer to an inflow into the SCS in winter.

Tertiary Calcareous Nannofossil Biostratigraphy in the North Part of the South China Sea

The marine Tertiary sequence in the north part of the South China Sea may be divided into 18 LateOligocene to Pliocene calcareous nannofossil zones and one unnamed Eocene assemblage based on an analysisof calcareous nannofossils from 40 offshore boreholes. The unnamed Eocene assemblage has been found onlyon the northeast margin of the Zhujiangkou basin. The 18 cakareous nannofossil zones of the Late Oligoceneto Pliocene were deposited in succession, but their development degrees are different. Among the 18 calcareousnannofossil zones, those corresponding to Martini's (1971) NN4- NN5 zones, NN11 zone and NN13-NN15zones are well developed, relatively persistent laterally and also widely distributed. They are the importantmarkers for the stratigraphical subdivision and correlation of the Upper Tertiary between the various basins inthe north part of the South China Sea. Based on the calcareous nannofossils and the sedimentsry features coup-led with the foraminifer zonation in certain basins, the present paper discusses the sedimentary characteristicsof the marine Tertiary and as well as the distribution and development of the sedimentary hiatus in the region.The calcareous nannofossil markers for the Upper / Lower Tertiary and the Quaternary / Tertiary boundaries,and the characteristics and geological significance of the reworked calcareous nannofossils are also discussed inthe paper.

The evolution of the coral reefs in the middle and north parts of the South China Sea and its relation with tectonic and eustatic movements

In this paper, the morphogenesis, stratigraphic sequences and dates of the coral reefs in the middle and north parts of the South China Sea are discussed, the position of the distributary regions of Cenozoic coral reefs in plate tectonics, the relationships of coral-reef evolutionary characteristics and dates with sea-basin spreading. Neogene sea-water transgression and Quaternary global climate-eustatic fluctuation are expounded and proved, and the latitudinal variation of the distribution of coral reefs in various geologic times are summed up.

Effects of South China Sea/western North Pacific summer monsoon on tropospheric biennial oscillation （TBO）

Several theories have been developed to explain tropical biennial oscillation （TBO）, as an air-sea interactive system to impact Asian and global weather and climate, and some models have been established to produce a TBO. A simple 5-box model, with almost all the key processes associated with TBO, can produce a TBO by including airsea interactions in the monsoon regions. Despite that, the South China Sea/western North Pacific summer monsoon （SCS/WNPSM）, a very important monsoon subsystem, is neglected. In this paper, based on the dynamical framework of 5-box model, the term of SCS/WNPSM has been added and a 6-box model has been developed. Comparing the difference of TBO sensibilities with several key parameters, air-sea coupling coefficient α, SST-thermocline feedback coefficient γand wind-evaporation feedback coefficient λ, between the modified model and original model, TBO is more sensible to the parameters in the new model. The results imply that the eastern Pacific and local wind-evaporation play more important roles in the TBO when including SCS /WNPSM.

Low-frequency variability of the shallow meridional overturning circulation in the South China Sea

The low-frequency variability of the shallow meridional overturning circulation（MOC） in the South China Sea（SCS） is investigated using a Simple Ocean Data Assimilation（SODA） product for the period of 1900-2010. A dynamical decomposition method is used in which the MOC is decomposed into the Ekman, external mode, and vertical shear components. Results show that all the three dynamical components contribute to the formation of the seasonal and annual mean shallow MOC in the SCS. The shallow MOC in the SCS consists of two cells： a clockwise cell in the south and an anticlockwise cell in the north; the former is controlled by the Ekman flow and the latter is dominated by the external barotropic flow, with the contribution of the vertical shear being to reduce the magnitude of both cells. In addition, the strength of the MOC in the south is found to have a falling trend over the past century, due mainly to a weakening of the Luzon Strait transport（LST） that reduces the transport of the external component. Further analysis suggests that the weakening of the LST is closely related to a weakening of the westerly wind anomalies over the equatorial Pacific, which leads to a southward shift of the North Equatorial Current（NEC） bifurcation and thus a stronger transport of the Kuroshio east of Luzon.

Liquid-plastic Limit of Surface Sediments in North Slope of South China Sea

1 Introduction China has a vast area of continental shelf and is very rich in marine resources,but because of the complex geological environment and frequent geological disasters,the utilization of marine resources and the construction of marine engineering are limited(Zhu et al.,2016).As the

Surface Sediment Density and Moisture Content in North slope of South China Sea

Marine engineering geology is mainly based on the actual project to study the seabed.This provides a variety of engineering geological parameters for the development of marine engineering(Zhu et al.,2016).This is an early

Effects of topography on the sub-tidal circulation in the southwestern Huanghai Sea(Yellow Sea)in summer

A nested circulation model system based on the Princeton ocean model （POM） is set up to simulate the currentmeter data from a bottom-mounted Acoustic Doppler Profiler （ADP） deployed at the 30 m depth in the Lunan（South Shandong Province, China） Trough south of the Shandong Peninsula in the summer of 2008, and to study the dynamics of the circulation in the southwestern Huanghai Sea （Yellow Sea）. The model has reproduced well the observed subtidal current at the mooring site. The results of the model simulation suggest that the bottom topography has strong steering effects on the regional circulation in summer. The model simulation shows that the Subei （North Jiangsu Province, China）coastal current flows north- ward in summer, in contrast to the southeastward current in the center of the Lunan Trough measured by the moored currentmeter. The analyses of the model results suggest that the southeastward current at the mooring site in the Lunan Trough is forced by the westward wind-driven current along the Lunan coast, which meets the northward Subei coastal current at the head of the Haizhou Bay to flow along an offshore path in the southeastward direction in the Lunan Trough. Analysis suggests that the Subei coastal current, the Lunan coastal current, and the circulation in the Lunan Trough are independent current systems con- trolled by different dynamics. Therefore, the current measurements in the Lunan Trough cannot be used to represent the Subei coastal current in general.

3D Velocity Structure and Its Tectonic Implications in the East China Sea and Yellow Sea

3D structure of the crust and upper mantle in the studied area has been analyzed from surface wave tomography. The velocity distribution in the uppermost crust is symmetrical on two sides of the central line of the sea, and coincides with the structure of crystalline basement. The essential difference in tectonics between the East China Sea and the Yellow Sea mainly lies in that the velocity structures of their lower crust and upper mantle are identical to those of South China and North China respectively. In the upper mantle there exists a high-velocity zone with a nearly EW strike from the Hangzhou Bay, China, to the Tokara Channel, Japan, along about the latitude of 30°N. It is found that between the East China Sea and the Yellow Sea there are systematical differences in geomorphology, geology, seismicity, heat flow, quality factor and gravity and aeromagnetic anomalies, which is related to both left-lateral shear dislocation and right-lateral tear of the Benioff zone from the Hangzhou Bay to the Tokara Channel.It is inferred that the East China Sea was formed by Cenozoic back-arc extension. The boundary between the North China and South China crustal blocks stretches along the southern piedmont of Mts. Daba-Dabie-Hangzhou Bay-Tokara Channel, and the subduction zone at the Okinawa trench is the eastern boundary of the South China crustal block. The movements of the Pacific plate, Indian plate and upper mantle rather than the Philippine plate subduction have played a dominant role for the modern tectonic movements in East Asia.

Response of the western North Pacific subtropical ocean to the slow-moving super typhoon Nanmadol

Based on in-situ observation,satellite and reanalysis data,responses of the western North Pacific subtropical ocean(WNPSO)to the slow-moving category 5 super typhoon Nanmadol in 2011 are analyzed.The dynamical response is dominated by near-inertial currents and Ekman currents with maximum amplitude of 0.39m/s and 0.15m/s,respectively.The near-inertial currents concentrated around 100m below the sea surface and had an e-folding timescale of 4 days.The near-inertial energy propagated both upward and downward,and the vertical phase speed and wavelength were estimated to be 5m/h and 175m,respectively.The frequency of the near-inertial currents was blue-shifted near the surface and redshifted in ocean interior which may relate to wave propagation and/or background vorticity.The resultant surface cooling reaches-4.35℃ and happens when translation speed of Nanmadol is smaller than 3.0m/s.When Nanmadol reaches super typhoon intensity,the cooling is less than 3.0℃ suggesting that the typhoon translation speed plays important roles as well as typhoon intensity in surface cooling.Upwelling induced by the slow-moving typhoon wind leads to typhoon track confined cooling area and the right-hand bias of cooling is slight.The mixed layer cooling and thermocline warming are induced by wind-generated upwelling and vertical entrainment.Vertical entrainment also led to mixed layer salinity increase and thermocline salinity decrease,however,mixed layer salinity decrease occurs at certain stations as well.Our results suggest that typhoon translation speed is a vital factor responsible for the oceanic thermohaline and dynamical responses,and the small Mach number(slow typhoon translation speed)facilitate development of Ekman current and upwelling.

Variations in High-frequency Oscillations of Tropical Cyclones over the Western North Pacific

Variations in the high-frequency oscillations of tropical cyclones （TCs） over the western North Pacific （WNP） are studied in numerical model simulations. Power spectrum analysis of maximum wind speeds at 10 m （MWS10） from an ensemble of 15 simulated TCs shows that oscillations are significant for all TCs. The magnitudes of oscillations in MWS10 are similar in the WNP and South China Sea （SCS）; however, the mean of the averaged significant periods in the SCS （1.93 h） is shorter than that in the open water of the WNP （2.83 h）. The shorter period in the SCS is examined through an ensemble of simulations, and a case simulation as well as a sensitivity experiment in which the continent is replaced by ocean for Typhoon Hagupit （2008）. The analysis of the convergence efficiency within the boundary layer suggests that the shorter periods in the SCS are possibly due to the stronger terrain effect, which intensifies convergence through greater friction. The enhanced convergence strengthens the disturbance of the gradient and thermal wind balances, and then contributes to the shorter oscillation periods in the SCS.

High resolution Porites Mg/Ca thermometer for the north of the South China Sea

High resolution Mg/Ca ratios in the skeleton of a Porites lutea from the coastal area in the North of the South China Sea were precisely analyzed by ICP-MS. Compared with the instrument measured SST records, the Mg/Ca ratios strongly correlate with the SSTs, even in time of 1982/83 EI N(?)io. Therefore, a coral Mg/Ca thermometer for the North of the South China Sea was established.Based on ICP-MS technique it can report sea surface temperatures to an accuracy of±0.5℃.

Springtime Convective Quasi-Biweekly Oscillation and Interannual Variation of Its Intensity over the South China Sea and Western North Pacific

This study investigates characteristics of the convective quasi-biweekly oscillation(QBWO) over the South China Sea(SCS) and western North Pacific(WNP) in spring, and the interannual variation of its intensity. Convective QBWO over the WNP and SCS shows both similarities and differences. Convective QBWO over the WNP originates mainly from southeast of the Philippine Sea and propagates northwestward. In contrast, convective QBWO over the SCS can be traced mainly to east of the Philippines and features a westward propagation. Such a westward or northwestward propagation is probably related to n = 1 equatorial Rossby waves. During the evolution of convective QBWO over the WNP and SCS, the vertical motion and specific humidity exhibit a barotropic structure and the vertical relative vorticity shows a baroclinic structure in the troposphere. The dominant mode of interannual variation of convective QBWO intensity over the SCS–WNP region in spring is homogeneous. Its positive phase indicates enhanced convective QBWO intensity accompanied by local enhanced QBWO intensity of vertical motion throughout the troposphere as well as local enhanced(weakened) QBWO intensity of kinetic energy, vertical relative vorticity,and wind in the lower(upper) troposphere. The positive phase usually results from local increases of the background moisture and anomalous vertical shear of easterlies. The latter contributes to the relationship between the dominant mode and QBWO intensities of kinetic energy, vertical relative vorticity, and wind. Finally, a connection between the dominant mode and the sea surface temperature anomalies in the tropical Pacific Ocean is demonstrated.

Lithospheric Thermal Isostasy of North Continental Margin of the South China Sea

Accompanied with rifting and detaching of the north continental margin of the South China Sea, the crust and the lithosphere become thinner away from the continental margin resulting from the tectonic activities, such as tensile deformation, thermal uplift, and cooling subsidence, etc.. Integrated with thermal, gravimetric, and isostatic analysis techniques, based on the seismic interpretation of the deep penetration seismic soundings across the northern margin of the South China Sea, we reconstructed the lithospheric thermal structure and derived the variation of the crust boundary in the east and west parts of the seismic profile by using gravity anomaly data. We mainly studied the thermal isostasy problems using the bathymetry of the profiles and calculated the crust thinning effect due to the thermal variety in the rifting process. The results indicate that the thermal isostasy may reach 2.5 km, and the compositional variations in the lithospheric density and thickness may produce a variation of 4.0 km. Therefore, the compositional isostatic correction is very important to recover the relationship between surface heat flow and topography. Moreover, because of the high heat flow characteristic of the continental margin, building the model of lithospheric geotherm in this region is of great importan for studying the Cenozoic tectonic thermal evolution of the north passive continental margin of the South China Sea.

Stable isotopic records of the glacial deep-water properties in the South China Sea

Based on the oxygen and carbon stable isotopic records of benthic foraminifera in nine deep-sea cores of the South China Sea (SCS), the bathymetric profiles of δ 18O and δ 13C since the last glacial maximum (LGM) are preliminarily established. The bathymetric gradients of deep-water δ 18O and δ 13C in the SCS are obviously greater during the LGM than during the Holocene, showing the existence of the deep thermocline and nutricline at water depth of about 2 000 m. Particularly, the differences in δ 18O and δ 13C between the LGM and Holocene, from which the ice-volume effect and the global mean shift have been subtracted respectively, are positive values at water depths of 1 000-2 500 m in the SCS. This indicates the existence of deep-water mass with relatively cool temperature or higher salinity, better ventilation and more δ 13C within the water depth range of the SCS during the LGM, which is distinctly different from that at present. These changes further confirm the existence of the glacial "North Pacific Deep Water" which, however, is possibly confined to the water depth range of 1 000-2 500 m.