Global Crust-Mantle Density Contrast Estimated from EGM2008, DTM2008, CRUST2.0, and ICE-5G

We compute globally the consolidated crust-stripped gravity disturbances/anomalies. These refined gravity field quantities are obtained from the EGM2008 gravity data after applying the topographic and crust density contrasts stripping corrections computed using the global topography/bathymetry model DTM2006.0, the global continental ice-thickness data ICE-5G, and the global crustal model CRUST2.0. All crust components density contrasts are defined relative to the reference crustal density of 2,670 kg/m³. We demonstrate that the consolidated crust-stripped gravity data have the strongest correlation with the crustal thickness. Therefore, they are the most suitable gravity data type for the recovery of the Moho density interface by means of the gravimetric modelling or inversion. The consolidated crust-stripped gravity data and the CRUST2.0 crust-thickness data are used to estimate the global average value of the crust-mantle density contrast. This is done by minimising the correlation between these refined gravity and crust-thickness data by adding the crust-mantle density contrast to the original reference crustal density of 2,670?kg/m³. The estimated values of 485 kg/m³ (for the refined gravity disturbances) and 481?kg/m³ (for the refined gravity anomalies) very closely agree with the value of the crust-mantle density contrast of 480?kg/m³, which is adopted in the definition of the Preliminary Reference Earth Model (PREM). This agreement is more likely due to the fact that our results of the gravimetric forward modelling are significantly constrained by the CRUST2.0 model density structure and crust-thickness data derived purely based on methods of seismic refraction.     

电动机械取心钻具反扭装置实验台设计及实验

大扭矩反扭装置是研制铠装电缆冰下基岩电动机械取心钻具的主要部分之一,该装置的失效将导致钻进无法进行,甚至将造成钻具脱落等严重的孔内事故。设计了铠装电缆钻具反扭装置实验台,并就实验装置的设计思想、设计原则、主要结构参数及初步实验结果进行了详细介绍。该实验台可以测试反扭装置在不同温度冰层和不同孔径任意组合下所能提供的反扭矩大小以及产生的下滑阻力。初步实验验证,该实验台工作性能良好,可以为更好的选择反扭装置类型及最优的使用参数提供重要依据。     

Magnetostratigraphy of Cave Sediments: Application and Limits

The application of the magnetostratigraphy for dating of clastic and chemogenic cave sediments has been limited by the complex conditions underground and the lack of age constraints on these deposits for correlation with geomagnetic polarity timescale (GPTS). Without age constraints any correlation of obtained results cannot be explicit. Additionally, the dynamic character of cave infilling, exhumation and fossilisation expressed by unconformities within preserved sedimentary profiles can hide a substantial part of the geological time. The detailed internal division of deposits (breaks in deposition and related processes) and scarcity of fossils make the correlation of obtained magnetostratigraphic log with geomagnetic polarity timescales sometimes problematic. The analytical results confirmed that the complete step/field procedure offered by demagnetisation methods must be applied. The application of complete analysis only to pilot samples and shortened, selected field/step approach, to other samples did not offer sufficient data set for reliable interpretation.     

An ANN application for water quality forecasting

Rapid urban and coastal developments often witness deterioration of regional seawater quality. As part of the management process, it is important to assess the baseline characteristics of the marine environment so that sustainable development can be pursued. In this study, artificial neural networks (ANNs) were used to predict and forecast quantitative characteristics of water bodies. The true power and advantage of this method lie in its ability to (1) represent both linear and non-linear relationships and (2) learn these relationships directly from the data being modeled. The study focuses on Singapore coastal waters. The ANN model is built for quick assessment and forecasting of selected water quality variables at any location in the domain of interest. Respective variables measured at other locations serve as the input parameters. The variables of interest are salinity, temperature, dissolved oxygen, and chlorophyll-a. A time lag up to 2Deltat appeared to suffice to yield good simulation results. To validate the performance of the trained ANN, it was applied to an unseen data set from a station in the region. The results show the ANN's great potential to simulate water quality variables. Simulation accuracy, measured in the Nash-Sutcliffe coefficient of efficiency (R(2)), ranged from 0.8 to 0.9 for the training and overfitting test data. Thus, a trained ANN model may potentially provide simulated values for desired locations at which measured data are unavailable yet required for water quality models.     

Concentrations and Seasonal Trends of Extracellular Microcystins in Freshwaters of the Czech Republic – Results of the National Monitoring Program

The first outcomes of the national monitoring program on cyanobacteria and their toxins in the Czech Republic are reported. The concentrations of extracellular microcystins (MCs, analyzed by ELISA) in 206 water samples collected from 94 localities have been investigated. Observed MC concentrations were relatively high in comparison with the literature data, although weather conditions during the covered season (year 2004) were less favorable for the cyanobacterial water blooms. Detectable MCs (>0.125 μg/L) were found in 145 waters (70% of all samples) with a median concentration of 0.67 μg/L. The total median, including samples with no detectable MCs, was 0.26 μg/L. The seasonal trend showed an increase from July to September at most localities (maximum concentrations of about 8 μg/L and extremes up to 37 μg/L). However, a peak at the beginning of the season or continuously elevated MC concentrations were also observed at some localities. Positive correlations between increasing concentrations of MCs and the dominancy of Microcystis spp. have been observed. The survey provides the first large-scale study of the occurrence and seasonal variability of extracellular microcystins that are of particular interest for drinking water management.     

Submesoscale eddies in Peter the Great Bay of the Japan/East Sea in winter

Ocean Dynamics - Cold-core (T < 0 °C) domes of dense water σθ > 27.24 kg/m3 were observed in the near-bottom layer at the...     

The forced and free response of the South China Sea to the large-scale monsoon system

Non-tidal sea level anomalies (SLAs) can be produced by many different dynamical phenomena over many time scales, and they can induce serious damages in coastal regions especially during extreme events. In this work, we focus on the SLAs in the South China Sea (SCS) to understand whether and how they can be related to the large-scale, seasonal monsoon system which dominates the SCS circulation and dynamics. We have two major objectives. The first one is to understand whether the NE (winter) and SW (summer) monsoons can be responsible for the persistent SLAs, both positive and negative, observed at the SCS ends along the main monsoon path. The second objective is to understand the SCS response as a free system upon onset/relaxation or sudden changes in the forcing wind. It is well known that sudden changes in the forcing mechanism induce free oscillations, or seiches, in closed, semi-enclosed basins and harbors, and we want to identify the possible seiche modes of the SCS. To our knowledge, these two objectives have not been previously addressed. We address these objectives both through observational analysis and modeling simulations. Multi-year tide-gauge data from stations along the coastal regions of the SCS are analyzed examining their spatial correlations. Strong negative correlations are found between the northeast and southwest stations at the two ends of the SCS under the path of the NE/SW monsoons. They correspond to wind-induced positive/negative sea level set-ups lasting for the entire monsoon season and changing sign from winter to summer. Short periods of negative correlations are also found between the SLAs at eastern and western stations during El Niño years in which the monsoons are weaker and have an enhanced E/W component inducing corresponding sea level set-ups. The tide-gauge station at Tanjong Pagar at the southwest SCS end near Singapore is chosen to study four extreme SLAs events in the observational record during 1999. Modeling simulations are carried out to reproduce them. The observed and modeled extreme SLAs agree quite well, both in the amplitude of the highest peak and in phase. Three main peaks are identified in the observational energy spectrum of the de-tided SLAs at the same station in 1999. Using Merian’s formula to evaluate the periods of seiches in idealized basins Wilson (Adv Hydrosci 8:1–94, 1972) the first two peaks (24.4 h and 11.9 h) are found to correspond to the first two seiche modes in the direction of the main, longer axis of the SCS. The third peak (8.5 h) is found to correspond to the seiche in the transversal, shorter axis. Finally, modeling simulations are carried out by suddenly dropping a circular bump of water in the quiescent basin at different locations to excite the seiches. The periods of the modeled peaks agree quite well with the observational ones, the first two periods being actually identical.