Cross-shelf circulation in the Yellow and East China Seas indicated by MODIS satellite observations

Ocean color and sea surface temperature data from Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Terra satellite are used to study the cross-shelf circulation and transport of suspended sediments in the Yellow and the East China Seas. The ocean color images show a significant turbid water plume extending in the southeast direction from the Subei coasts of China to the shelf edge south of Cheju during fall-winter, suggesting significant cross-shelf currents in the Yellow Sea/East China Sea in winter. The currents transport suspended sediments from the area of the old Huanghe mouth into the Okinawa Trough. Part of the turbid plume joins the Yellow Sea Warm Current to enter the Yellow Sea trough in winter. The satellite images suggest that the time scales of cross-shelf transport and surface-to-subsurface descending of the suspended sediments are a few weeks. The turbid plume grows in fall, reaches its maximum expansion and intensity in winter-spring, and subsides in late spring. In summer, the plume becomes coastally trapped. Substantial interannual variations of the intensity and coverage of the turbid plume are indicated by the observations. In comparison, the Changjiang Diluted Water in summer only transports a small amount of the Changjiang suspended sediment to the outer shelf south of Cheju, which does not enter the Yellow Sea owing to the weak intrusion of the Yellow Sea Warm Current in summer. The dynamics of the cross-shelf circulation in the Yellow Sea in winter are hypothesized to be associated with (1) the convergence of the Yellow Sea Coastal Current and the Taiwan Warm Current off the Changjiang mouth and (2) the time-dependent forcing of the northerly wind bursts that drives the intrusion of the Yellow Sea Warm Current. (C) 2007 Elsevier B.V. All rights reserved.

Atmospheric cu and pb deposition and transport in lake sediments in a remote mountain area；northern China

IEECAS SKLLQG

The effects of sediment transport on grain-size distributions

Changes in statistics (mean, sorting, and skewness) describing grain-size distributions have long been used to speculate on the direction of sediment transport. We present a simple model whereby the distributions of sediment in transport are related to their source by a sediment transfer function which defines the relative probability that a grain within each particular class interval will be eroded and transported. A variety of empirically derived transfer functions exhibit negatively skewed distributions (on a phi scale). Thus, when a sediment is being eroded, the probability of any grain going into transport increases with diminishing grain size throughout more than half of its size range. This causes the sediment in transport to be finer and more negatively skewed than its source, whereas the remaining sediment (a lag) must become relatively coarser and more positively skewed. Flume experiments show that the distributions of transfer functions change from having a highly negative skewness to being nearly symmetrical (although still negatively skewed) as the energy of the transporting process increases. We call the two extremes low-energy and high-energy transfer functions , respectively. In an expanded sediment-transport model, successive deposits in the direction of transport are related by a combination of two transfer functions. If energy is decreasing and the transfer functions have low-energy distributions, successive deposits will become finer and more negatively skewed. If, however, energy is decreasing, but the initial transfer function has a high-energy distribution, successive deposits will become coarser and more positively skewed. The variance of the distributions of lags, sediment in transport, and successive deposits in the down-current direction must eventually decrease (i.e., the sediments will become better sorted). We demonstrate that it is possible for variance first to increase, but suggest that, in reality, an increasing variance in the direction of transport will seldom be observed, particularly when grain-size distributions are described in phi units. This model describing changes in sediment distributions was tested in a variety of environments where the transport direction was known. The results indicate that the model has real-world validity and can provide a method to predict the directions of sediment transport

Diagnostic experiments for transport mechanisms of suspended sediment discharged from the Yellow River in the Bohai Sea

Five diagnostic experiments with a 3D baroclinic hydrodynamic and sediment transport model ECOMSED in couple with the third generation wave model SWAN and the Grant-Madsen bottom boundary layer model driven by the monthly sediment load of the Yellow River, were conducted to separately diagnose effects of different hydrodynamic factors on transport of suspended sediment discharged from the Yellow River in the Bohai Sea. Both transport and spatio-temporal distribution of suspended sediment concentration in the Bohai Sea were numerially simulated. It could be concluded that suspended sediment discharged from the Yellow River cannot be delivered in long distance under the condition of tidal current. Almost all of sediments from the Yellow River are deposited outside the delta under the condition of wind-driven current, and only very small of them are transported faraway. On the basis of wind forcing, sediments from the Yellow River are mainly transported north-northwestward, and others which are first delivered to the Laizhou Bay are continuously moved northward. An obvious 3D structure characteristic of sediment transport is produced in the wind-driven and tide-induced residual circulation condition. Transport patterns at all layers are generally consistent with circulation structure, but there is apparent deviation between the depth-averaged sediment flux and the circulation structure. The phase of temporal variation of sediment concentration is consistent with that of the bottom shear stress, both of which are proved to have a ten-day cycle in wave and current condition.

Diversity and spatial distribution of amoA-encoding archaea in the deep-sea sediments of the tropical West Pacific Continental Margin

The ecological characteristics of the deep-sea amoA-encoding archaea (AEA) are largely unsolved. Our aim was to study the diversity, structure and distribution of the AEA community in the sediments of the tropical West Pacific Continental Margin, to develop a general view of the AEA biogeography in the deep-sea extreme environment. Archaeal amoA clone libraries were constructed. Diverse and novel amoA sequences were identified, with the Bohol Sea, Bashi Strait and Sibuyan Sea harbouring the highest and the Bicol Shelf the lowest AEA diversity. Phylogenetic and statistical analyses illustrate a heterogeneous distribution of the AEA community, probably caused by the differential distribution of the terrestrial or estuarine AEA in the various sampling sites. The deep-sea sedimentary environments potentially harbour diverse and novel AEA in the tropical West Pacific Continental Margin. The stations in the Philippine inland seas (including station 3043) may represent AEA assemblages with various terrestrial influences and the stations connected directly to the open Philippine Sea may represent marine environment-dominant AEA assemblages. Our study indicates the potential importance of geological and climatic events in the transport of terrestrial micro-organisms to the deep-sea sedimentary environments, almost totally neglected previously.

Quantitatively distinguishing sediments from the Yangtze River and the Yellow River using delta Eu-N-I REEs pound plot

Sediment samples were collected from the lower channel of the Yangtze River and the Yellow River and the contents of rare earth elements (REEs) were measured. In addition, some historical REEs data were collected from published literatures. Based on the delta Eu-N-I REEs pound plot, a clear boundary was found between the sediments from the two rivers. The boundary can be described as an orthogonal polynomial equation by ordinary linear regression with sediments from the Yangtze River located above the curve and sediments from the Yellow River located below the curve. To validate this method, the REEs contents of sediments collected from the estuaries of the Yangtze River and the Yellow River were measured. In addition, the REEs data of sediment Core 255 from the Yangtze River and Core YA01 from the Yellow River were collected. Results show that the samples from the Yangtze River estuary and Core 255 almost are above the curve and most samples from the Yellow River estuary and Core YA01 are below the curve in the delta Eu-N-I REEs pound plot. The plot and the regression equation can be used to distinguish sediments from the Yangtze River and the Yellow River intuitively and quantitatively, and to trace the sediment provenance of the eastern seas of China. The difference between the sediments from two rivers in the delta Eu-N-I REEs pound plot is caused by different mineral compositions and regional climate patterns of the source areas. The relationship between delta Eu-N and I REEs pound is changed little during the transport from the source area to the river, and from river to the sea. Thus the original information on mineral compositions and climate of the source area was preserved.

Benthic foraminiferal distribution in surface sediments along continental slope of the southern Okinawa Trough: dependance on water masses and food supply

Benthic foraminiferal analysis of 29 samples in surface sediments from the southern Okinawa Trough is carried out. The results indicate that benthic foraminiferal abundance decreases rapidly with increasing water depth. Percentage frequencies of agglutinated foraminifera further confirm the modem shallow carbonate lysocline in the southern Okinawa Trough. From continental shelf edge to the bottom of Okinawa Trough, benthic foraminiferal fauna in the surface sediments can be divided into 5 assemblages: (1) Continental shelf break assemblage, dominated by Cibicides pseudoungerianus, corresponds to subsurface water mass of the Kuroshio Current; (2) upper continental slope assemblage, dominated by Cassidulina carinata, Globocassidulina subglobosa, corresponds to intermediate water mass of the Kuroshio Current; (3) intermediate continental slope assemblage, dominated by Uvigerina hispida, corresponds to the Okinawa Trough deep water mass above the carbonate lysocline; (4), lower continental slope - trough bottom assemblage, dominated by Pullenia bulloides, Epistominella exigua and Cibicidoides hyalinus, corresponds to deep water mass of the Okinawa Trough; and (5) trough bottom agglutinated assemblage, dominated by Rhabdammina spp., Bathysiphon flavidus, corresponds to I strongly dissolved environment of the trough bottom. The benthic foraminiferal fauna in the southern Okinawa Trough are controlled jointly by water masses and food supply. Water temperature, oxygen concentration and carbonate dissolution of the water masses are important controlling factors especially for the continental shelf break and trough bottom assemblages. The food supply also plays an important role in these benthic foraminiferal assemblages along the western slope. of the Okinawa Trough. Both the abundance and the 5 assemblages of benthic foraminifera correspond well to the organic matter supply along the continental slope and a lateral transport of TSM (total suspended matter) and POC (particulate organic carbon) from the shelf break to the deep water is also an important food supply for benthic fauna in this region.

Geochemical character and material source of sediments in the eastern Philippine Sea

Based upon analyses of grain-size, rare earth element (REE) compositions, elemental occurrence phases of REE, and U-series isotopic dating, the sediment characteristics and material sources of the study area were examined for the recently formed deep-sea clays in the eastern Philippine Sea. The analytical results are summarized as follows. (1) Low accumulation rate, poor sorting and roundness, and high contents of grains coarser than fine silt indicate relatively low sediment input, with localized material source without long distance transport. (2) The REE Contents are relatively high. Shale-normalized patterns of REE indicate weak enrichment in heavy REE (HREE), Ce-passive anomaly, and Eu-positive anomaly. (3) Elemental occurrence phases of REE between the sediments with and without crust are similar. REE mainly concentrate in residual phase and then in ferromanganese oxide phase. The light REE (LREE) enrichment, Ce-positive anomaly, and Eu-positive anomaly occur in residual phase. Ferromanganese oxide phase shows the characteristics of relatively high HREE content and Ce-passive anomaly. (4) There are differences in each above mentioned aspect between the sediments with and without ferromanganese crust. (5) Synthesizing the above characteristics and source discriminant analysis, the study sediments are deduced to mainly result from the alteration of local and nearby volcanic materials. Continental materials transported by wind and/or river (ocean) flows also have minor contributions.

SUSPENDED SEDIMENT TRANSPORT IN THE OFFSHORE NEAR YANGTZE ESTUARY

Based on the Estuarine, Coastal and Ocean Modeling System with Sediments (ECOMSED) model, a 3-D hydrodynamic-transport numerical model was established for the offshore area near the Yangtze Estuary in the East China Sea. The hydrodynamic module was driven by tide and wind. Sediment module included sediment resuspension, transport and deposition of cohesive and non-cohesive sediment. The settling of cohesive sediment in the water column was modeled as a function of aggregation (flocculation) and deposition. The numerical results were compared with observation data for August, 2006. It shows that the sediment concentration reduces gradually from the seashore to the offshore area. Numerical results of concentration time series in the observation stations show two peaks and two valleys, according with the observation data. It is mainly affected by tidal current. The suspended sediment concentration is related to the tidal current during a tidal cycle, and the maximum concentration appears 1 h-4 h after the current maximum velocity has reached.

Preliminary study of the dynamic origin of the distribution pattern of bottom sediments on the continental shelves of the Bohai Sea, Yellow Sea and East China Sea

The bottom sediment types in the Bohai Sea, Yellow Sea and East China Sea (BYECS) are diversified, and their distribution pattern is very complicated. However, the bottom sediment types can be simplified to be sandy sediment, clayey sediment and mixed sediment, which comprise the complicated distribution pattern of bottom sediment in the BYECS. The continental shelves of the BYECS are broad, with shallow water depths and tidal currents which are permanent and dominate the marine dynamics in the BYECS. Based on numerical simulation of tidal elevations and currents in the BYECS, the rates of suspended load transport and bed load transport during a single tidal cycle for sediments of eight different grain size ranges are calculated. The results show that any sediment, whose threshold velocity is less than that of tidal current, has the same transport trend. Suspended load transport rare, bed load transport rate, and the ratio of the former to the latter decrease with grain size becoming coarser and coarser. The erosion/accretion patterns of sediments with different grain sizes are determined by the sediment transport rate divergences, and the results show that the patterns are the same for sediments with different grain sizes. Three main bottom sediment types, i.e. sandy sediment mainly composed of fine sand, clayey sediment mainly composed of silty clay, and mixed sediment mainly composed of fine sand, silt, and clay, are obtained by computation. The three bottom sediment types and their distribution pattern are consistent not only with sediment transport field and the sea bed erosion/accretion pattern obtained by simulation, but also with field data of bottom sediment types and divisions. In the BYECS, sand ridges form mainly in the areas with strong rectilinear tidal currents, sand sheets form mainly in the areas dominated by strong rotatory tidal currents, and clayey sediments, i.e. mud patches, form mainly in the areas with weak tidal currents. Hence, not only the sandy sediments but also the clayey sediments in the BYECS are formed under the control of the whole tidal current field of the BYECS. The three main bottom sediment types are not isolated respectively-in fact, they constitute a whole tidal depositional system. Under the condition with no cyclonic cold eddy, the clayey sediments in the BYECS can form in weak tidal current environments. Therefore, a cold eddy is not necessary for the deposition of clayey sediments in the BYECS. (C) 2000 Academic Press.

Growth of Silicon Carbide Bulk Crystals by Physical Vapor Transport Method and Modeling Efforts in the Process Optimization

Silicon carbide bulk crystals were grown in an induction-heating furnace using the physical vapor transport method. Crystal growth modeling was performed to obtain the required inert gas pressure and temperatures for sufficiently large growth rates. The SiC crystals were expanded by designing a growth chamber having a positive temperature gradient along the growth interface. The obtained 6H-SiC crystals were cut into wafers and characterized by Raman scattering spectroscopy and X-ray diffraction, and the results showed that most parts of the crystals had good crystallographic structures.

Thermoelastic Stresses in SiC Single Crystals Grown by the Physical Vapor Transport Method

A finite element-based thermoelastic anisotropic stress model for hexagonal silicon carbide polytype is developed for the calculation of thermal stresses in SiC crystals grown by the physical vapor transport method. The composite structure of the growing SiC crystal and graphite lid is considered in the model. The thermal expansion match between the crucible lid and SiC crystal is studied for the first time. The influence of thermal stress on the dislocation density and crystal quality is discussed.

Modeling Ammonothermal Growth of GaN Single Crystals: The Role of Transport

Single crystal gallium nitride (GaN) is an important technological material used primarily for the manufacture of blue light lasers. An important area of contemporary research is developing a viable growth technique. The ammonothermal technique is an important candidate among many others with promise of commercially viable growth rates and material quality. The GaN growth rates are a complicated function of dissolution kinetics, transport by thermal convection and crystallization kinetics. A complete modeling effort for the growth would involve modeling each of these phenomena and also the coupling between these. As a first step, the crystallization and dissolution kinetics were idealized and the growth rates as determined purely by transport were investigated. The growth rates thus obtained were termed ‘transport determined growth rates’ and in principle are the maximum growth rates that can be obtained for a given configuration of the system. Using this concept, a parametric study was conducted primarily on the geometric and the thermal boundary conditions of the system to optimize the ‘transport determined growth rate’ and determine conditions when transport might be a bottleneck.