Relationship between in situ sound velocity and granular characteristics of seafloor sediments in the Qingdao offshore region

The sound velocity of seafloor sediments from shallow seas can provide important information for harbor design, and ocean and seacoast engineering projects. In this study, in situ measurements were used to obtain accurate sediment sound velocities at 45 stations offshore of Qingdao. The relationships between the sound velocity and granular properties of the seafloor sediments were analyzed. Sound velocity showed an increase with the sand content, sand-clay ratio, and sorting coefficient; and a nonlinear decreasing trend with increasing mean grain size and clay content. We plotted a sound velocity distribution map, which shows that the sound velocity was closely related to the geological environment. Previous empirical equations suggested by Hamilton, Anderson, and Liu were used to calculate the velocity with grain size. A comparison between the measured and calculated velocities indicates that the empirical equations have territorial limitations, and extensive data are essential to establish global empirical equations. Future work includes the calibration of the laboratory acoustic measurements with an in situ technique.     

Tests of new in-situ seabed acoustic measurement system in Qingdao

A new in-situ seabed acoustic measurement system is developed for direct in-situ measurement of sediment geoacoustic properties （compressional wave velocity and attenuation）. The new in-situ system consists of two parts： the deck control unit and the underwater measurement unit. The underwater measurement unit emits sonic waves that propagate through the seafloor sediment, receives the returning signals, and transmits them to the deck control unit for waveform display and analysis. The entire operation is controlled and monitored in real time by the deck control unit on the research vessel and can provide recording of full waveforms to determine the sound velocity and attenuation. This paper outlines the design of the system, the measurement process, and demonstrates its application in tests carded out on seabed sediment off the Qingdao coast, China. The test results show that the system performed well and rapidly provided accurate in-situ acoustic velocity and attenuation estimates of the seafloor sediment.     

Distribution and generic composition of culturable marine actinomycetes from the sediments of Indian continental slope of Bay of Bengal

Actinomycetes population from continental slope sediment of the Bay of Bengal was studied. Samples were collected during two voyages of FORV Sagar Sampada in 2004 （May-June） and 2005 （July） respectively from 11 transects （each transect had ca. 200 m, 500 m, and 1 000 m depth stations）. The physicochemical parameters of overlying water, and sediment samples were also recorded. The actinomycete population ranged from 5.17 to 51.94 CFU/g dry sediment weight and 9.38 to 45.22 CFU/g dry sediment weight during the two cruises respectively. No actinomycete colony was isolated from stations in 1 000 m depth. Two-way analysis of variance showed significant variation among stations （ANOVA two-way, P〈0.05）, but no significance was found between the two cruises （ANOVA two-way, P〈0.05）. Populations in stations in 500 m depth in both cruises were higher than that of 200 m depth stations with statistically insignificant difference （ANOVA two-way, P〉0.05）. Three actinomycetes genera were identified. Streptomyces was found to be the dominating one in both the cruises, followed by Micromonospora, and Actinomyces. The spore of Streptomyces isolates showed the abundance in spiral spore chain. Spore surface was smooth. Multiple regression analysis revealed that the influencing physico-chemical factors were sediment pH, sediment temperature, TOC, porosity, salinity, and pressure. The media used in the present study was prepared with seawater. Thus, they may represent an autochthonous marine flora and deny the theory of land runoff carriage into the sea for adaptation to the salinity of the seawater and sediments.     

Biogenic silicate accumulation in sediments, Jiaozhou Bay

1 INTRODUCTION Silicate, or silicic acid (H4SiO4), is a very im- portant nutrient in the ocean. Unlike other major nu- trients such as phosphate and nitrate or ammonium, which are needed by almost all marine plankton, silicate is an essential chemical req…     

Influence of Seawater Temperature on Phytoplankton Growth in Jiaozhou Bay, China

The phytoplankton reproduction capacity (PRC), as a new concept regarding chlorophyll-a and primary production (PP) is described. PRC is different from PP, carbon assimilation number (CAN) or photosynthetic rate ( P^B ) . PRC quantifies phytoplankton growth with a special consideration of the effect of seawater temperature. Observation data in Jiaozhou Bay, Qingdao, China, collected from May 1991 to February 1994 were used to analyze the horizontal distribution and seasonal variation of the PRC in Jiaozhou Bay in order to determine the characteristics, dynamic cycles and trends of phytoplankton growth in Jiaozhou Bay; and to develop a corresponding dynamic model of seawater temperature vs. PRC. Simulation curves showed that seawater temperature has a dual function of limiting and enhancing PRC. PRC‘s periodicity and fluctuation are similar to those of the seawater temperature. Nutrient silicon in Jiaozhou Bay satisfies phytoplankton growth from June 7 to November 3. When nutrients N, P and Si satisfy the phytoplankton growth and solar irradiation is sufficient, the PRC would reflect the influence of seawater temperature on phytoplankton growth. Moreover, the result quantitatively explains the scenario of one-peak or two-peak phytoplankton reproduction in Jiaozhou Bay, and also quantitatively elucidates the internal mechanism of the one- or two-peak phytoplankton reproduction in the global marine areas.     

Benthic nutrient recycling in shallow coastal waters of the Bohai Sea

Sediment-water fluxes of N and P species in the Bohai Sea were investigated in September-October 1998 and April-May 1999. The benthic fluxes of nutrient species were determined by incubating sediment core samples with bottom seawater bubbled with air or nitrogen. NO^-2,NH4, dissolved organic nitrogen (DON) and phosphorus (DOP), total dissolved nitrogen (TDN) and phosphorus (TDP), and PO4^3- showed a net exchange flux from seawater to sediment, while NO^-3, dissolved inorganic nitrogen (DIN) and SiO3^2- were released from sediment to seawater in the Bohai Sea. Sediment-water nutrient exchange increases DIN and reduces the phosphorus load in the Bohai Sea. The release of silicate from sediment to overlying seawater reduces potential silicate limitation of primary production resulted from decrease of riverine discharge.The exchange flux of nutrients showed no obvious seasonal variation. The present study showed that the concentrations and composition of nutrients in the water column were affected by suspended sediment, and that not all the exchangeable phosphate in sediment could be released via sediment resuspension.     

压力及温度对碳酸盐岩声波速度与频谱特征的影响实验

碳酸盐岩声波传播特征具有重要的应用价值,系统性地分析流体类型、流体压力、温度及围压对碳酸盐岩声波速度与频谱特性影响的研究仍需加强。选取四川盆地合川-潼南地区灯影组缝洞碳酸盐岩,开展了不同条件下的声波透射实验,分析了围压、孔隙压力、压力差、温度及流体类型对碳酸盐岩样品声波速度的影响及不同条件下透射声波的主频特征。研究结果表明:饱和地层水时声波速度对压力变化的敏感度较饱和氮气时低。压力变化过程中,声波速度变化幅度与岩样孔隙度为正相关关系。实验温度范围内,随着温度逐渐升高,饱和地层水、氮气岩心纵波速度、横波速度均小幅降低。当差应力较低时,通过改变孔隙压力来改变差应力的方式对应的声波速度大于通过改变围压来改变差应力方式对应的声波速度,当差应力较高时,结论相反。相同差应力条件下,声波速度对围压变化较孔隙压力变化更为敏感。定围压变孔隙压力与定孔压变围压曲线所对应的2条声波速度-差应力关系曲线的夹角及斜率差可定性反映岩样动态Biot有效应力系数相对大小。随着差应力增大,孔隙压力对有效应力的贡献逐渐降低。随着孔隙压力增大,纵波主频幅值、横波主频幅值均逐渐下降,随着围压增大,纵波主频幅值、横波主频幅值均逐渐增大,随着温度逐渐升高,纵波主频幅值、横波主频幅值均逐渐增大。研究结果有助于基于测井声波信息开展碳酸盐岩地层孔隙压力预测相关理论研究及工程应用。      

Flow variability along a vegetated natural stream under various sediment transport rates

The influence of vegetation and sediment on flow characteristics in open channels cannot be neglected. To study the flow variability under the effects of the instream natural vegetation and sediment supply, experiments were conducted with varied water and sediment supply in a movable bed of a river prototype. The instantaneous three-dimensional velocities near two types of vegetation patches (the shrub and the weed) and along the centerline of the main channel with vegetation belts were measured using a 3-D side-looking acoustic Doppler velocimetry. The experimental results show that both the instream vegetation and sediment supply strongly affect the flow and turbulence characteristics. In the case of vegetation patches, both the shrub and weed have a considerable influence on the distribution of the streamwise velocity and turbulence intensity of their surrounding water. The streamwise velocity distribution followed as J-shape and linear shape around the weed and shrub under different experimental conditions. The turbulence intensity was large at the top of the weed and shrub; the shrub had its greatest influence on the downstream water flow. In the case of vegetation belts, the streamwise velocity along the centerline of the main channel exhibited an S-shape, J-shape and linear shape at different locations under varied water, vegetation structures and riverbed configurations. The turbulence intensity along the centerline of the main channel ranged from 0.0 to 0.1. The upstream turbulence intensity was affected considerably by a sediment supply, while the downstream turbulence intensity changed with the varied vegetation characteristics and riverbed topography. The second flow coefficient M-value increased longitudinally and was almost positive along the centerline of the main channel, implying that the rotational direction of the secondary current cell was clockwise.     

Estimation of suspended sediment concentrations using Pulse-coherent Acoustic Doppler Profiler （PCADP）

The objective of the study is to investigate the suitability of using Pulse-coherent Acoustic Doppler Profiler (PCADP) to estimate suspended sediment concentration (SSC). The acoustic backscatter intensity was corrected for spreading and absorption loss, then calibrated with OBS and finally converted to SSC. The results show that there is a good correlation between SSC and backscatter intensity with R value of 0.74. The mean relative error is 22.4%. Then the time span of little particle size variation was also analyzed to exclude the influence of size variation. The correlation coefficient increased to 0.81 and the error decreased to 18.9%. Our results suggest that the PCADP can meet the requirement of other professional instruments to estimate SSC with the errors between 20% and 50%, and can satisfy the need of dynamics study of suspended particles. Supported by National High Technology Research and Development Program of China (863 Program, No. 2008AA09Z113)     

Bacterial diversity and community structure in the East China Sea by 454 sequencing of the 16S rRNA gene

The 454 sequencing method was used to detect bacterial diversity and community structure in the East China Sea. Overall, 149 067 optimized reads with an average length of 454 nucleotides were obtained from 17 seawater samples and five sediment samples sourced in May 2011. A total of 22 phyla, 34 classes, 74 orders, 146 families, and 333 genera were identified in this study. Some of them were detected for the first time from the East China Sea. The estimated richness and diversity indices were both higher in the sediment samples compared with in the seawater samples. All the samples were divided by their diversity indices into four regions. Similarity analysis showed that the seawater samples could be classified into six groups. The groups differed from each other and had unique community structure characteristics. It was found that different water masses in the sampling areas may have had some influence on the bacterial community structure. A canonical correspondence analysis revealed that seawater samples in different areas and at different depths were affected by different environmental parameters. This study will lay the foundation for future research on microbiology in the East China Sea.     

Contrast between the climatic states of the warm pool in the Indian Ocean and in the Pacific Ocean

Based on the analysis of Levitus data, the climatic states of the warm pool in the Indian Ocean (WPIO) and in the Pacific Ocean (WPPO) are studied. it is found that WPIO has a relatively smaller area, a shallower bottom and a slightly lower seawater temperature than those of WPPO. The horizontal area at different depths, volumes, central positions, and bottom depths of both WPIO and WPPO show quite apparent signals of seasonal variation. The maximum amplitude of WPIO surface area’s seasonal variation is 58% larger over the annual mean value. WPIO’s maximum volume variation amplitude is 66% larger over the annual mean value. The maximum variation amplitudes of the surface area and volume of WPPO are 20.9% and 20.6% larger over the annual mean value respectively. WPIO and WPPO show different temporal and spatial characteristics mainly due to the different wind fields and restriction of ocean basin geometry. For instance, seasonal northern displacement of WPIO is, to some extent, constrained by the basin of the Indian Ocean, while WPPO moves relatively freely in the longitudinal direction. The influence of WPIO and WPPO over the atmospheric motion must be quite different.     

EXAMINATION OF SILICATE LIMITATION OF PRIMARY PRODUCTION IN JIAOZHOU BAY, CHINA Ⅰ. SILICATE BEING A LIMITING FACTOR OF PHYTOPLANKTON PRIMARY PRODUCTION

Jiaozhou Bay data collected from May 1991 to February 1994, in 12 seasonal investigations, and provided the authors by the Ecological Station of Jiaozhou B ay, were analyzed to determine the spatiotemporal variations in temperature, light, nutrients (NO-3-N, NO-2-N, NH+4-N, SiO2-3-Si, PO3-4-P), phytoplankton, and primary production in Jiaozhou Bay. The results indicated that only silicate correlated well in time and space with, and had important effects on, the characteristics, dynamic cycles and trends of, primary production in Jiaozhou Bay. The authors developed a corresponding dynamic model of primary production and silicate and water temperature. Eq.(1) of the model shows that the primary production variation is controlled by the nutrient Si and affected by water temp erature; that the main factor controlling the primary production is Si; that water temper ature affects the composition of the structure of phytoplankton assemblage; that the different populations of the phytoplankton assemblage occupy different ecologica l niches for C, the apparent ratio of conversion of silicate in seawater into phytoplankton biomas and D, the coefficient of water temperature's effect on phytoplankton biomass. The authors researched the silicon source of Jiaozhou Bay , the biogeochemical sediment process of the silicon, the phytoplankton predominan t species and the phytoplankton structure. The authors considered silicate a limit ing factor of primary production in Jiaozhou Bay, whose decreasing concentration of silicate from terrestrial source is supposedly due to dilution by current and up take by phytoplankton; quantified the silicate assimilated by phytoplankton, the intrins ic ratio of conversion of silicon into phytoplankton biomass, the proportion of silicate uptaken by phytoplankton and diluted by current; and found that the primary production of the phytoplankton is determined by the quantity of the silicate assimilated by them. The phenomenon of apparently high plant-nutrient concentrations but low phytoplankton biomass in some waters is reasonably explained in this paper.     

GNSS SNR信号反演大坝水位变化

通过采集GNSS信噪比(SNR)数据,基于水面反射的GNSS多路径信号特性,分析信号频率、高度角范围及弧段长度等因素对大坝水位反演结果的影响。结果表明,大坝水位变化反演结果与实测水位数据具有良好的一致性,相关系数在0.9以上,GPS反演精度为0.1~0.15 m,BDS反演精度为0.35~0.45 m,GPS和BDS联合反演精度为0.1~0.13 m,优于单系统反演精度。     

Prediction for potential landslide zones using seismic amplitude in Liwan gas field,northern South China Sea

The Liwan (Lw) gas field located in the northern slope of the South China Sea (SCS) is extremely complex for its sea-floor topograghy, which is a huge challenge for the safety of subsea facilities. It is economically impractical to obtain parameters for risk assessment of slope stability through a large amount of sampling over the whole field. The linkage between soil shear strength and seabed peak amplitude derived from 2D/3D seismic data is helpful for understanding the regional slope-instability risk. In this paper, the relationships among seabed peak, acoustic impedance and shear strength of shallow soil in the study area were discussed based on statistical analysis results. We obtained a similar relationship to that obtained in other deep-water areas. There is a positive correlation between seabed peak amplitude and acoustic impedance and an exponential relationship between acoustic impedance and shear strength of sediment. The acoustic impedance is the key factor linking the seismic amplitude and shear strength. Infinite slope stability analysis results indicate the areas have a high potential of shallow landslide on slopes exceeding 15° when the thickness of loose sediments exceeds 8 m in the Lw gas field. Our prediction shows that they are mainly located in the heads and walls of submarine canyons.     

Simulation of seafloor electrical resistivity measuring equipment based on 3D finite element method

In order to explore the mineral resources buried in sea mud,it is necessary to use seabed resistivity measuring equipment,which works closer to the sediments than ordinary ship-based geophysical measuring equipment. Because of the harsh environment of seafloor,high pressure and highly conductive seawater,marine magnetotelluric method developed slowly. The sea floor environment is similar to the environment of logging, According to the design of dual lateral logging equipment,a new equipment for seafloor electrical resistivity measurement is designed. Four 3D FEM models that contain resistivity abnormal targets are built to test the ability of this equipment to locate different shape of shallow buried resistivity abnormal targets in sea mud. The authors propose the method to correct the response curve while the bottom surface of this equipment is suspended or not parallel to the seafloor. The resistivity of targets can be calculated accurately.     

Influence of temperature and frequency on microwave dielectric properties of lunar regolith simulant

The dielectric constant of the lunar regolith can directly influence the reflection coefficient and the trans-mission coefficient of the Moon′s surface, and plays an important role in the Moon research. In order to study the di-electric properties of the lunar regolith, the lunar regolith simulant was made according to the making procedure of the CAS-1 simulant made by Chinese Academy of Sciences. Then the dielectric constants of the lunar regolith simulant were measured with 85070E Aiglent Microwave Network Analyzer in the frequency ranging from 0.2 GHz to 20.0 GHz and at temperature of 25.1℃, 17.7℃, 13.1℃, 11.5℃, 9.6℃, 8.0℃, 4.1℃, -0.3℃, -4.7℃, -9.5℃, -18.7℃, -27.7℃, and -32.6℃, respectively. The Odelevsky model was employed to remove the influence of water in the air on the final effective dielectric constants. The results indicate that frequency and temperature have apparent influences on the dielectric constants of the lunar regolith simulant. The real parts of the dielectric constants increase fast over the range of 0.2 GHz to 3.0 GHz, but decrease slowly over the range of 4.0 GHz to 20.0 GHz. The opposite phenomenon occurs in the imaginary parts. The influences of the frequency and temperature on the brightness temperature were also estimated based on the radiative transfer equation. The result shows that the variation of the frequency and temperature results in great changes of the microwave brightness temperature emitting from the lunar regolith.     

EXAMINATION OF SILICATE LIMITATION OF PRIMARY PRODUCTION IN JIAOZHOU BAY, CHINA I. SILICATE BEING A LIMITING FACTOR OF PHYTOPLANKTON PRIMARY PRODUCTION

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Numerical simulation of mechanical compaction of deepwater shallow sediments

To study the compaction law and overpressure evolution in deepwater shallow sediments, a large-strain compaction model that considers material nonlinearity and moving boundary is formulated. The model considers the dependence of permeability and material properties on void ratio. The modified Cam-Clay model is selected as the constitutive relations of the sediments, and the deactivation/reactivation method is used to capture the moving top surface during the deposition process. A one-dimensional model is used to study the compaction law of the shallow sediments. Results show that the settlement of the shallow sediments is large under their own weight during compaction. The void ratio decreases strictly with burial depth and decreases more quickly near the seafloor than in the deeper layers. The generation of abnormal pressure in the shallow flow sands is closely related to the compaction law of shallow sediments. The two main factors that affect the generation of overpressure in the sands are deposition rate and permeability of overlying clay sediments. Overpressure increases with an increase in deposition rate and a decrease in the permeability of the overlying clay sediment. Moreover, an upper limit for the overpressure exists. A two-dimensional model is used to study the differential compaction of the shallow sediments. The pore pressure will still increase due to the inflow of the pore fluid from the neighboring clay sediment even though the deposition process is interrupted.     

Influence of fine sediment on the fluidity of debris flows

Debris flows include a great diversity of grain sizes with inherent features such as inverse grading, particle size segregation, and liquefaction of fine sediment. The liquefaction of fine sediment affects the fluidity of debris flows, although the behavior and influence of fine sediment in debris flows have not been examined sufficiently. This study used flume tests to detect the effect of fine sediment on the fluidity of laboratory debris flows consisting of particles with various diameters. From the experiments, the greatest sediment concentration and flow depth were observed in the debris flows mixed with fine sediment indicating increased flow resistance. The experimental friction coefficient was then compared with the theoretical friction coefficient derived by substituting the experimental values into the constitutive equations for debris flow. The theoretical friction coefficient was obtained from two models with different fine-sediment treatments: assuming that all of the fine sediments were solid particles or that the particles consisted of a fluid phase involving pore water liquefaction. From the comparison of the friction coefficients, a fully liquefaction state was detected for the fine particle mixture. When the mixing ratio and particle size of the fine sediment were different, some other cases were considered to be in a partially liquefied transition state. These results imply that the liquefaction of fine sediment in debris flows was induced not only by the geometric conditions such as particle sizes, but also by the flow conditions.     

Cumulative impact of dam constructions on streamflow and sediment regime in lower reaches of the Jinsha River,China

The cumulative effect of cascade hydropower stations on river ecological environment has been widely concerned because of the significant streamflow hydrology change induced by dam constructions. The characteristics of the change in the lower reaches of the Jinsha River, China are analyzed based on long-term(1952–2015) hydrological and sedimentological data. The averaging coefficient, reservoir regulation coefficient(RRC), incoming sediment coefficient(ISC), and sediment transport modulus(STM), which reflect the variation of streamflow and sediment regimes, are defined and calculated. The results show that the construction and regulation of reservoirs reduces flow in flood season, increases flow in dry season, significantly altering the monthly discharge regimes. These alterations also led directly to changes in the timing of extreme flows at Pingshan Station. The monthly flow records at the basin outlet are reconstructed using stepwise regression, to reduce reservoir impacts. Comparisons of observed and reconstructed monthly flows demonstrate that the previous studies overestimated the cumulative effects of cascade reservoirs on flow processes. Furthermore, this study clearly illustrates that the reduction in sediment trapping and sediment transportation capacity together lead to the sharp reduction in annual sediment yield at the Pingshan Station. The earlier constructed reservoirs have more obvious effects on the ISC and STM than the more recent reservoirs and the effect of sediment trapping is related to reservoir location, on the main stream versus tributaries.