Fine-grained Pleistocene deepwater turbidite channel system on the slope of Qiongdongnan Basin, northern South China Sea

Recently, as oil exploitation has become focused on deepwater slope areas. more multi-channel high resolution 2D and 3D seismic data were acquired in the deepwater part of the Qiongdongnan Basin, northern South China Sea. Based on 3D seismic data and coherence time slice, RMS and 3D visualization, a series of deepwater channels were recognized on the slope that probably developed in the late Quaternary period. These channels trend SW-NE to W-E and show bifurcations, levees, meander loops and avulsions. High Amplitude Reflections (HARs), typical for channel-levee complexes, are of only minor importance and were observed in one of the channel systems. Most of the detected channels are characterized by low-amplitude reflections, and so are different from the typical coarse-grained turbidite channels that had been discovered worldwide. The absence of well data in the study area made it difficult to determine the age and lithology of these channels. Using a neighboring drill hole and published data about such depositional systems worldwide, the lithology of these channels is likely to be dominated by mudstones with interbedded thin sandstones. These channels are formed by turbidity currents originated from the little scale mountain river of mid-Vietnam in SW direction and were probably accompanied by a relative sea level drop in the last glacial age. These channels discovered on the northern South China Sea slope are likely to be fine-grained, mud-dominant and low N:G deposits in a deepwater paleogeographic setting. (C) 2009 Elsevier Ltd. All rights reserved.

Geomorphology, sedimentary processes and development of the Zenisu deep-sea channel, northern Philippine Sea

The Zenisu deep-sea channel originates on the Izu-Ogasawara island arc, and disappears in the Shikoku Basin of the Philippine Sea. The geomorphology, sedimentary processes, and the development of the Zenisu deep-sea channel were investigated on the basis of swath bathymetry, side-scan sonar imagery, submersible observations, and seismic data. The deep-sea channel can be divided into three segments according to the downslope gradient and channel orientation. They are the Zenisu Canyon, the E-W fan channel, and the trough-axis channel. The sediment fill is characterized by turbidite and debrite deposition and blocky-hummocky avalanche deposits on the flanks of the Zenisu Ridge. In the Zenisu Canyon and the Zenisu deep-sea channel, sediment transport by turbidity currents generates sediment waves (dunes) observed during the Shinkai 6500 dive 371. The development of the Zenisu Canyon is controlled by a N-S shear fault, whereas the trough-axis channel is controlled by basin subsidence associated with the Zenisu Ridge. The E-W fan channel was probably affected by the E-W fault and the basement morphology.

Modification to the Hardisty equation, regarding the relationship between sediment transport rate and particle size

Bagnold-type bed-load equations are widely used for the determination of sediment transport rate in marine environments. The accuracy of these equations depends upon the definition of the coefficient k(1) in the equations, which is a function of particle size. Hardisty (1983) has attempted to establish the relationship between k(1) and particle size, but there is an error in his analytical result. Our reanalysis of the original flume data results in new formulae for the coefficient. Furthermore, we found that the k(1) values should be derived using u(1) and u(1cr) data; the use of the vertical mean velocity in flumes to replace u(1) will lead to considerably higher k(1) values and overestimation of sediment transport rates.

On the relationships between the radial tidal current field and the radial sand ridges in the southern Yellow Sea: a numerical simulation

The ori-in of the radial sand ridges (RSRs) in the southern Yellow Sea has been a controversial problem since they were discovered in the early 1960s. To resolve the problem, two key questions need to be answered: (1) was the radial tidal current field in the RSR area generated by the submarine topography, or (2) did it exist before the RSRs occurred? In this study, the M-2 tide and tidal currents in the RSR area were simulated with a two-dimensional tidal model using a flat bottom and a shelving slope topography, the results being then compared with the field data. It is demonstrated that the radial tidal current field in the southern Yellow Sea is independent of bottom topography, and may thus be the controlling factor generating the RSRs. The radial tidal current field probably existed before the RSRs were formed.

Geomorphic and hydrodynamic responses in salt marsh-tidal creek systems, Jiangsu, China

Salt marsh-tidal creek systems as a coastal geomorphological unit represent an important natural resource. The present study on Jiangsu salt marshes, eastern China, shows that variations in tidal current velocities in salt marsh creeks are controlled by the local tidal wave characteristics and the bed slope and elevation of the salt marshes and creeks. Likewise, the tidal currents modify the geomorphology of the salt marsh-tidal creek systems by transporting sediments and causing erosion/deposition. Storm events, which appear to have cyclical changes in their intensity relating to sunspot activities, can affect the geomorphic evolution of such systems. Further, in response to accelerated sea-level rise, accretional rates on salt marshes may increase. The tidal creeks have the function of transporting water and sediment onto the salt marsh surface; further, the energy of tidal currents and waves are dissipated within the salt marsh-tidal creek system. Hence, this coastal system has a potential value for coastal protection.

Mineral provinces and matter provenance of the surficial sediments in the western Philippine Sea: implication for modern sedimentation in West Pacific marginal basin

The characteristics and distribution patterns of detrital minerals (0.063 similar to 0.125 mm) in marine sediments provide a significant indicator for the identification of the origin of sediment. The detrital mineral composition of 219 surface sediment samples was analysed to identify the distribution of sediments within the western Philippine Sea. The area can be divided into three mineral provinces: ( 1) province east of the Philippine Trench, the detrital minerals in this province are mainly composed of calcareous or siliceous organisms, with the addition of volcanogenic minerals from an adjacent island arc; (II) middle mineral province, clastic minerals including feldspar, quartz and colorless volcanic glass, sourced from seamounts with intermediate-acid volcanic rock, or erupting intermediate-acid volcano; (III) province west of the Palau-Kyushii Ridge, the matter provenance within this province is complex; the small quantity of feldspar and quartz may be sourced from seamounts or erupting volcano with intermediate - acid composition, with a component of volcanic scoria sourced from a volcano erupting on the Palau-Kyushu Ridge. it is suggested that, ( I) Biogenic debris of the study area is closely related to water depth, with the amount of biogenic debris controlled by carbonate lysocline. (2) Volcaniclastic matter derived from the adjacent island are can be entrained by oceanic currents and transported towards the abyssal basin over a short distance. The weathering products of volcanic rocks of the submarine plateau ( e. g. I Benham Plateau) and adjacent ridges provide an important source of detrital sedimentation, and the influence scope of them is constrained by the intensity of submarine weathering. (3) Terrigenous sediments from the continent of Asia and the adjacent Philippine island arc have little influence on the sedimentation of this study area, and the felsic mineral component is probably sourced from volcanic seamounts of intermediate-acid composition.

A preliminary study on fingerprinting approach in marine sediment dynamics with the rare earth elements

Locating the quantitized natural sediment fingerprints is an important work for marine sediment dynamics study. The total of 146 sediment samples were collected from the Shelf of the East China Sea and five rivers, including Huanghe (Yellow), Changjiang (Yangtze), Qiantang, Ou and Min River. The sediment grain size and the contents of rare earth elements (REEs) were measured with laser particle size analyzer and ICP-MS technology. The results show that absolute REE content (Sigma REE) and the concentration ratio of light REEs to heavy REEs (L/HREE) are different in the sediments among those rivers. There are higher REE contents in being less than 2 m and 2-31 mu m fractions in the Changjiang Estuary surface sediments. The REE contents of bulk sediment are dominated by the corresponding values of those leading size-fractions. Sigma REE of sediment is higher close to the estuaries and declines seaward on the inner shelf of the East China Sea (ECS). The L/HREE ratio has a tendency of increase southward from 28 degrees N. Hydrodynamic conditions plays a predominate role on spacial distributions of the surficial sediment's REE parameters. In some situations, the currents tend to remove the coarser light grains from initial populations, as well as the deposit of the finer heavy mineral grains. In other situations, the currents will change the ratio of sediment constituents, such as ratio between silts and clays in the sediments. As a result, the various values of Sigma REE or L/HREE ratio in different bulk sediments are more affected by the change of size-fractions than source location. Under the long-term stable hydrodynamic environment, i.e., the East China Sea Shelf, new sediment transport model based on the size and density gradation concept may help to understand the spatial distribution patterns of REE parameters.

Observational evidence of the Yellow Sea warm current

The Yellow Sea Warm Current (YSWC) is one of the principal currents in the Yellow Sea in winter. Former examinations on current activity in the Yellow Sea have not observed a stable YSWC because of the positioning of current meters. To further understand the YSWC, a research cruise in the southern Yellow Sea was carried out in the winter of 2006/2007. Five moorings with bottom-mounted acoustic Doppler current profilers (ADCP) were deployed on the western side of the central trough of the Yellow Sea. The existence and distributional features of the YSWC were studied by analyzing three ADCP moorings in the path of the YSWC in conjunction with conductivity-temperature-depth (CTD) data over the observed area in the southern Yellow Sea. The results show the following. (1) The upper layer of the YSWC is strongly influenced by winter cold surge; its direction and speed often vary along a south-north axis when strong cold surges arrive from the north. (2) The YSWC near the bottom layer is a stable northwest flowing current with a speed of 4 to 10 cm/s. By combining the analyses of the CTD data, we speculate that the core of the YSWC may lie near the bottom. (3) On a monthly average timescale, the YSWC is stably oriented with northward flow from the sea surface to the sea floor.

A unified criterion for initiation of sediment motion and inception of sheet flow under water waves

A unified criterion is developed for initiation of non-cohesive sediment motion and inception of sheet flow under water waves over a horizontal bed of sediment based on presently available experimental data. The unified threshold criterion is of the single form, U-o = 2 pi C[1 + 5(T-R/T)(2)](-1/4), where U-o is the onset velocity of sediment motion or sheet flow, T is wave period, and C and T-R are the coefficients. It is found that for a given sediment, U-o initially increases sharply with wave period, then gradually approaches the maximum onset velocity U-o = 2 pi C and becomes independent of T when T is larger. The unified criterion can also be extended to define sediment initial motion and sheet flow under irregular waves provided the significant wave orbital velocity and period of irregular waves are introduced in this unified criterion.

Long-Wave Dynamics of Sea Level Variations during Indian Ocean Dipole Events

Long-wave dynamics of the interannual variations of the equatorial Indian Ocean circulation are studied using an ocean general circulation model forced by the assimilated surface winds and heat flux of the European Centre for Medium-Range Weather Forecasts. The simulation has reproduced the sea level anomalies of the Ocean Topography Experiment (TOPEX)/Poseidon altimeter observations well. The equatorial Kelvin and Rossby waves decomposed from the model simulation show that western boundary reflections provide important negative feedbacks to the evolution of the upwelling currents off the Java coast during Indian Ocean dipole (IOD) events. Two downwelling Kelvin wave pulses are generated at the western boundary during IOD events: the first is reflected from the equatorial Rossby waves and the second from the off-equatorial Rossby waves in the southern Indian Ocean. The upwelling in the eastern basin during the 1997-98 IOD event is weakened by the first Kelvin wave pulse and terminated by the second. In comparison, the upwelling during the 1994 IOD event is terminated by the first Kelvin wave pulse because the southeasterly winds off the Java coast are weak at the end of 1994. The atmospheric intraseasonal forcing, which plays an important role in inducing Java upwelling during the early stage of an IOD event, is found to play a minor role in terminating the upwelling off the Java coast because the intraseasonal winds are either weak or absent during the IOD mature phase. The equatorial wave analyses suggest that the upwelling off the Java coast during IOD events is terminated primarily by western boundary reflections.

Remote sensing of ocean waves by along-track interferometric synthetic aperture radar

A new wave retrieval method for the Along-Track Interferometric Synthetic Aperture Radar (AT-InSAR) phase image is presented. The new algorithm, named parametric retrieval algorithm (PRA), uses the full nonlinear mapping relations. It differs from previous retrieval algorithms in that it does not require a priori information about the sea state or the wind vector from scatterometer data. Instead, it combines the observed AT-InSAR phase spectrum and assumed wind vector to estimate the wind sea spectrum. The method has been validated using several C-band and X-band HH-polarized AT-InSAR observations collocated with spectral buoy measurements. In this paper, X-band and C-band HH-polarized AT-InSAR phase images of ocean waves are first used to study AT-InSAR wave imaging fidelity. The resulting phase spectra are quantitatively compared with forward-mapped in situ directional wave spectra collocated with the AT-InSAR observations. Subsequently, we combine the parametric retrieval algorithm (PRA) with X-band and C-band HH-polarized AT-InSAR phase images to retrieve ocean wave spectra. The results show that the ocean wavelengths, wave directions, and significant wave heights estimated from the retrieved ocean wave spectra are in agreement with the buoy measurements.

Numerical calculation of the response of the south China sea to typhoon imbudo

The response of the South China Sea (SCS) to Typhoon Imbudo was examined using POM model. The results indicated that SST decreased by 2-6 degrees C with a rightward-biased response as Typhoon Imbudo passed across the SCS. Due to a strong mixing process, the mixed layer (ML) depth deepened as much as 10-60 m and ML heat budget lost 824.78 W/m(2), which was OF dominated by the vertical mixing. By the response of upper ML heat transport, the temperature below the ML increased and oscillated near the inertial period. Furthermore, strong inertial currents were generated by the storm with the max currents up to 1.4 m/s in the upper ML.

Dynamics of the buoyant plume off the Pearl River Estuary in summer

Field measurements of salinity, wind and river discharge and numerical simulations of hydrodynamics from 1978 to 1984 are used to investigate the dynamics of the buoyant plume off the Pearl River Estuary (PRE), China during summer. The studies have shown that there are four major horizontal buoyant plume types in summer: Offshore Bulge Spreading (Type I), West Alongshore Spreading (Type II), East Offshore Spreading (Type III), and Symmetrical Alongshore Spreading (Type IV). River mouth conditions, winds and ambient coastal currents have inter-influences to the transport processes of the buoyant plume. It is found that all of the four types are surface-advected plumes by analysing the vertical characteristic of the plumes, and the monthly variations of the river discharge affect the plume size dominantly. The correlation coefficient between the PRE plume size and the river discharge reaches 0.85 during the high river discharge season. A wind strength index has been introduced to examine the wind effect. It is confirmed that winds play a significant role in forming the plume morphology. The alongshore wind stress and the coastal currents determine the alongshore plume spreading. The impact of the ambient currents such as Dongsha Current and South China Sea (SCS) Warm Current on the plume off the shelf has also assessed. The present study has demonstrated that both the river discharge and wind conditions affect the plume evolution.

Influence of the earth rotation on the interfacial wave solutions and wave-induced tangential stress in a two-layer fluid system

Interfacial waves and wave-induced tangential stress are studied for geostrophic small amplitude waves of two-layer fluid with a top free surface and a flat bottom. The solutions were deduced from the general form of linear fluid dynamic equations of two-layer fluid under the f-plane approximation, and wave-induced tangential stress were estimated based on the solutions obtained. As expected; the solutions derived from the present work include as special cases those obtained by Sun et al. (2004. Science in China, Set. D, 47(12): 1147-1154) for geostrophic small amplitude surface wave solutions and wave-induced tangential stress if tire density of the upper layer is much smaller than that of the lower layer. The results show that the interface and the surface will oscillate synchronously, and the influence of the earth's rotation both on the surface wave solutions and the interfacial wave solutions should be considered.

The effects of random surface waves on the steady Ekman current solutions

The response of near-surface current profiles to wind and random surface waves are studied based on the approach of Jenkins [1989. The use of a wave prediction model for driving a near surface current model. Dtsch. Hydrogr. Z. 42,134-149] and Tang et al. [2007. Observation and modeling of surface currents on the Grand Banks: a study of the wave effects on surface currents. J. Geophys. Res. 112, C10025, doi:10.1029/2006JC004028]. Analytic steady solutions are presented for wave-modified Ekman equations resulting from Stokes drift, wind input and wave dissipation for a depth-independent constant eddy viscosity coefficient and one that varies linearly with depth. The parameters involved in the solutions can be determined by the two-dimensional wavenumber spectrum of ocean waves, wind speed, the Coriolis parameter and the densities of air and water, and the solutions reduce to those of Lewis and Belcher [2004. Time-dependent, coupled, Ekman boundary layer solutions incorporating Stokes drift. Dyn. Atmos. Oceans. 37, 313-351] when only the effects of Stokes drift are included. As illustrative examples, for a fully developed wind-generated sea with different wind speeds, wave-modified current profiles are calculated and compared with the classical Ekman theory and Lewis and Belcher's [2004. Time-dependent, coupled, Ekman boundary layer solutions incorporating Stokes drift. Dyn. Atmos. Oceans 37, 313-351] modification by using the Donelan and Pierson [1987. Radar scattering and equilibrium ranges in wind-generated waves with application to scatterometry. J. Geophys. Res. 92, 4971-5029] wavenumber spectrum, the WAM wave model formulation for wind input energy to waves, and wave energy dissipation converted to currents. Illustrative examples for a fully developed sea and the comparisons between observations and the theoretical predictions demonstrate that the effects of the random surface waves on the classical Ekman current are important, as they change qualitatively the nature of the Ekman layer. But the effects of the wind input and wave dissipation on surface current are small, relative to the impact of the Stokes drift. (C) 2008 Elsevier Ltd. All rights reserved.