Magnetic polarity sequences from downhole measurements in ODP holes 998B and 1001A,leg 165, Caribbean Sea

The magnetostratigraphy of sediments drilled at two sites (998 and 1001) in the Caribbean Sea during the Ocean Drilling Program (ODP) Leg 165 is established directly from downhole measurements. For the first time in the ODP, the magnetostratigraphy of sediments is determined from both logging magnetic data and paleomagnetic analysis of core material for an age interval of about 16 m.y. across the Cretaceous/Tertiary boundary. The total magnetic induction and the susceptibility of the surrounding sediment were recorded in situ and continuously by the GHMT (Geological High-sensitivity Magnetic Tool). The aim of processing these data is to determine the magnetic polarity. At Site 998 (Cayman Rise), no paleomagnetic results are available from the recovered cores given a hard secondary overprint. Nonetheless, a magnetostratigraphic sequence from early Miocene to late Oligocene is proposed from the analysis of the GHMT data. The comparison with biostratigraphic results shows the accuracy of the resulting magnetic polarity. At Site 1001 (Hess escarpment), cores were recovered in two holes thus allowing the comparison of the magnetostratigraphic results obtained from the GHMT data and from paleomagnetic analysis of core samples over a length of 200 m representing about 16 m.y. from early Eocene to late Cretaceous times. The sedimentation rates computed from the determined magnetochrons are very similar and correspond to the ones obtained from shipboard biostratigraphic results. One of the most striking result obtained from the magnetostratigraphic results, especially the GHMT data, at Site 1001, is the abrupt decrease in the sedimentation rate across the K/T boundary. This suppressed sedimentation lasted at least 4 Ma after the K/T event.     

Heave compensation system of lifting pipeline for deep-sea mining based on combined action of vibration absorber and accumulator

ABSTRACT

A heave compensation system combined with a vibration absorber and accumulator is proposed, with regard to the requirement for poly-metallic nodule mining systems at an ocean depth of 6,000?m in China. The principle of the compensation system was analyzed, its main parameters were designed, and its mathematical model was established. The system performance was simulated and analyzed in MATLAB, and the frequency domain characteristics and compensation rate of the system with different volume accumulators, and with or without vibration absorbers, were compared. A simulation test of the compensation system was conducted. The proposed compensation system had a better compensation effect for a random wave interference under level-6 sea conditions, and the compensation rate being more than 72% with optimal system parameters.     

Modified approach to evaluation of undrained shear strength from piezocone tests in soft clays

This paper proposes a modified-theoretical approach to interpreting the undrained shear strength from piezocone tests in clays. Assuming the shear and normal stresses on the cone face to be the friction at the cone–soil interface and the ultimate expansion pressure, respectively, an expression of the tip resistance is first derived at force equilibrium. The undrained shear strength is then determined by combining the derived expression of tip resistance with the formulation for pore pressure at the cone shoulder position. Many factors, such as the penetration rate and the cone roughness, are considered in this model. Different shaped model penetrometers, including cone- and ball-shaped ones, are adopted in centrifuge tests to investigate the validity of the proposed method. The undrained shear strength estimated from the piezocone test is found to agree well with that from ball penetrometer test. Case studies are also presented to show the application of the proposed method. Comparisons between the predicted and measured values of undrained shear strength indicate that the proposed approach is generally applicable for nonfissured clays, especially intact clays.     

集装箱船货舱区结构设计和强度评估研究

基于NAPA Steel软件,实现某集装箱船货舱区的3D结构设计,并输出2D的CAD图纸.同时,在结构设计模型的基础上直接生成三舱段结构的初始有限元模型,参照CCS规范要求对模型进行修改完善后,应用MSC.Nastran软件对其进行了强度分析和屈曲计算,获得了该舱段结构强度的详细信息,并根据评估结果来完善结构设计.与传统的2D结构设计模式相比较,3D结构设计方法能有效地提高设计质量和效率.     

Target localization and tracking from Doppler-shift measurements

It is possible to localize a nonmaneuvering moving source radiating a constant frequency tone from measurements of the Doppler-shifted frequency at several sensors. Due to the nonlinear nature of the problem, it is necessary to find the solution by grid searches. However, if measurements of the rates of frequency changes are available, the search is only in three dimensions instead of the normal five in source frequency, its x-y positions, and speeds. The validity of combining frequency and frequency-rate measurements is confirmed with simulation studies. The overall system includes a least-squares track-sort algorithm to differentiate the true track from the extraneous track, and a Kalman tracker for the prediction of future source positions, thereby reducing the grid search size. An error analysis relating localization accuracy to uncertainties in frequency measurements and sensor positions is also given     

海洋中天然气水合物的成矿机理与资源评价概述

本文综述了近年来国内外关于天然气水合物成矿机理研究的新进展，阐明了作为一种非常规的天然气矿藏，其形成和稳定存在除了需要特定的温、压条件外，更需要合适的成矿地质条件，包括沉积构造环境、充足的气源、有效的运移通道、有效的储集层和保存条件等．文中还介绍了天然气水合物资源评价方法及国外研究者对全球气体水合物中甲烷量的估算值，由于其结果相差几个数量级，表明目前还没有成熟的天然气水合物资源定量评价方法．     

Pitch-roll buoy mean wave directions from heave acceleration, bow magnetism, and starboard magnetism

This paper describes the refinement of a previously published procedure for estimating Mean Wave Direction using azimuth, pitch, and roll derived from only the bow and starboard components of the earth magnetic field. To demonstrate the effectiveness of this refined procedure, it is applied to sensor time series records taken over a single twenty-minute period aboard a pitch-roll buoy, and results are presented. On the assumption that the method will be verified by additional data, practical means to apply it operationally are outlined.     

陆源污染生态损害评估及其补偿标准研究——以象山港为例

陆源污染是半封闭海湾环境恶化的主要原因,评估海湾地区陆源污染的生态损害,对目前迫切需要制定的海洋生态损害补偿政策以及生态修复计划具有重要的现实意义。本文以象山港为研究区域,运用生态恢复评估与生态服务价值评估相结合的方法,构建陆源污染生态损害评估模型,进行陆源污染对海湾生态服务损害评估与补偿标准研究。结果显示:(1)象山港陆源污染造成的生态服务损害价值为38 342.81万元,执行损害评估的费用约为20万元;以生态损害评估的总费用作为补偿标准,生态补偿费用共计38 362.81万元,单位面积补偿价值为0.42万元/hm~2·a。(2)象山港陆源污染所导致的海洋生态系统初始性修复成本为零,恢复期内损害价值主要以养分循环和净化环境为主,分别为19 740.72万元和13 938.13万元;美学景观损害价值为3 798.59万元,占比为9.91%;生物多样性维持损害价值598.66万元,占比为1.56%;食物生产的损害价值最小,为266.72万元。     

Estimation of bottom scattering strength from measured and modeledmid-frequency sonar reverberation levels

Hamilton-type geoacoustic models were developed for Area Foxtrot, a shallow water test bed south of Long Island, for emerging active sonar systems where the surface sediment type is highly spatially variable. Reverberation levels (RL) were modeled using the finite-element parabolic equation (FEPE) propagation model to augment the generic sonar model (GSM) propagation model because the bottom loss model in GSM did not estimate transmission loss (TL) accurately in shallow water. FEPE estimates reveal that there is a greater than 15 dB difference between TL for sand and that for silt-day sediments in Area Foxtrot. The comparison between modeled RL and measured RL (from a 1991 active sonar exercise) enabled bottom scattering strength kernels to be developed for Area Foxtrot. Bottom scattering strength was found to be a function of sediment type. Hard sand sediment has a bottom scattering strength which obeys Lambert's law (sin² &thetas;) while that of silt-clay sediment is consistent with sub-bottom volume scattering (sine). The RLs in Area Foxtrot are azimuth-dependent and are a function of TL and bottom scattering strength (and hence bottom sediment type). Sonar beams steered towards the hard sand show higher RLs than for silt-clay, and knowledge of the sediment type and its spatial variation must be known to model RL accurately. A method to determine sediment type using measured RLs and RL slopes is given     

Experiments on the ocean sequestration of fossil fuel CO2: pH measurements and hydrate formation

We have carried out a series of in situ experiments to investigate the formation of a CO₂ hydrate (CO₂:5.75 H₂O) for the purpose of evaluating scenarios for ocean fossil fuel CO₂ disposal with a solid hydrate as the sequestered form. The experiments were carried out with a remotely operated vehicle in Monterey Bay at a depth of 619 m. pH measurements made in close proximity to the hydrate–seawater interface showed a wide range of values, depending upon the method of injection and the surface area of the hydrate formed. Rapid injection of liquid CO₂ into an inverted beaker to form a flocculant mass of hydrate resulted in pH initially as low as 4.5 within a few centimeters of the interface, decaying slowly over 1–2 h towards normal seawater values as dense CO₂ rich brine drained from the hydrate mass. In a second experiment, slower injection of the liquid CO₂ to produce a simple two-layer system with a near planar interface of liquid CO₂ with a thin hydrate film yielded pH values indistinguishable from the in situ ocean background level of 7.6. Both field and laboratory results now show that the dissolution rate of a mass of CO₂ hydrate in seawater is slow but finite.     

Physical modeling and swirling strength analysis of vortex shedding from near-bed piggyback pipelines

The vortex shedding from near-bed piggyback pipelines in a steady flow has been investigated experimentally in a large water flume. A specially arranged PIV system with upward-illumination of pulsed laser arrays from the flume bottom was employed for the flow visualization and quantitative measurement of the lee-wake flow in a sub-critical regime around the piggyback pipelines in the proximity of a plane boundary. Based on dimensional analyses, a dimensionless maximum swirling strength (W_m) is used for analyzing the vortex shedding intensity and its frequency. Time-averaged swirling strength analyses indicate that the lee-wake patterns for the near-bed piggyback pipelines are dependent on the configuration factors, including the gap-to-diameter ratio (e/D), the spacing-to-diameter ratio (G/D), and the diameter ratio of two pipes (d/D), etc. The swirling strength in the lee-wake is obviously asymmetric for piggyback pipelines with bed proximity. For the fixed values of G/D and d/D, the maximum swirling strength decreases with the decrease of e/D. Moreover, for the examined G/D range (0 ≤ G/D ≤ 0.5), minimum values of W_m and corresponding VIV amplitude for the piggyback pipelines are evidently within the same range of spacing-to-diameter ratio G/D ≈ 0.05–0.20.     

Observations of suspended sediment from ADCP and OBS measurements in a mud-dominated environment

The ability of a 1.2-MHz Acoustic Doppler Current Profiler (ADCP) to measure suspended sediment concentration (SSC) and particle size variation in a mud-dominated environment has been investigated. Experiments were conducted in the Bay of Banten, Indonesia, where clays and silts in the range of 3–55 μm are prevalent. The ADCP backscatter depends both on SSC and on the size of the scatterers. Over the time span of several separate deployments, which lasted 20 days at most, SSC was found to be proportional to the acoustically normative grain size squared. Using this relation, the ADCP could be calibrated to yield depth profiles of SSC. The obtained calibrations, however, were spatially and seasonally dependent. Differences between the calibrations could not be completely ascribed to variation in grain size distributions, due to the largely unknown influences of aggregates and organic scatterers. The ADCP backscatter measurements provided insight into diurnal events of erosion and subsequent deposition. An increase or decrease of SSC generally coincided with a raise or decline of the average grain size in the sediment suspension (respectively).     

Age and growth rates of ferromanganese concretions from the gulf of Finland derived from 210Pb measurements

The formation of ferromanganese concretions on continental shelves is a widespread recent biogeochemical process, which is particularly intense in the Baltic Sea. The proposed new technique for dating ferromanganese concretions is based on the equilibrium ²¹⁰Pb, which is produced immediately within them due to the decay of ²²⁶Ra, which is intensely sorbed by concretions from the seawater. This method is principally different from the traditional dating of bottom sediments using nonequilibrium ²¹⁰Pb, which represents a decay product of atmospheric Ra. A mathematical tool for the calculation of the concretion ages is proposed. The latter is used for calculating the ages and growth rates of ferromanganese concretions belonging to two morphological varieties. The age and average growth rates of spheroidal concretions are estimated to be 670–850 years and 0.014 mm/year, respectively. The central part of a pancake-shaped concretion is dated back to 2500–3800 years, and its calculated respective horizontal and vertical growth rates are approximately 0.028 and 0.004 mm/year.     

Chemical leaching and specific surface area measurements of marine sediments in the evaluation of mercury contamination near cinnabar deposits

This paper investigates mercury contamination in recent marine sediment of the Tyrrhenian continental shelf near the mouths of three rivers draining an area with cinnabar deposits (M. Amiata, Italy). By means of chemical leaching, two fractions of the total mercury were distinguished: a ‘non-leachable’ fraction, consisting of mercury held in relatively stable forms and a ‘leachable’ fraction, composed of forms that are more weakly bound to the sediments. The two Hg fractions are correlated to the organic matter content, the distribution of which is strictly dependent on the sediment surface area.In order to eliminate the effects of grain size variations among the samples, the Hg concentrations were normalized to the unit of surface area (ng/m²). Following this procedure, the ‘non-leachable’ Hg was found to be concentrated mostly in a belt along the coast, while the ‘leachable’ Hg fraction was shown to accumulate largely in the zones with high depositional dynamics near the mouths of the rivers.Hypotheses to account for the discrepancy between the low concentrations of ‘leachable’ Hg in the sediment of the outer continental shelf and the high concentrations in the fauna of the same area, reported in previous papers, are presented.     

GPS浮标数据反演海浪谱的理论仿真与试验验证

GPS浮标作为一种新型的海洋测量设备,近年来在海面高度现场测量和星载高度计定标方面取得了重要应用。通过仿真试验对反演海浪谱的方法和流程进行研究,旨在探索从GPS浮标测量的海面高度序列中提取海浪谱的方法。首先,使用Longuest模型生成了海浪波面位移时间序列,并通过Pierson-Moscowitz风浪谱对波面位移的统计特性进行约束,其随机性由相位引入。结合典型潮汐和GPS浮标仪器噪声的仿真时间序列,合成了仿真时间长度1h的1Hz(每秒1次)随机海面高度序列。然后,利用自相关函数法,进行高通滤波和数据压缩,得到了仿真的海浪谱。该仿真结果和理论海浪谱非常接近,可满足海浪谱反演的需求。最后,通过山东石岛外海的GPS浮标现场试验,验证了本文提出的反演方法的适用性。本文的研究解决了GPS浮标反演海浪谱的关键问题,丰富了海浪谱反演的手段,拓展了GPS浮标的应用领域,有望为未来我国的星载波谱仪定标服务。     

卫星重力估计陆地水和冰川对全球海平面变化的贡献

重力场恢复与气候试验（GRACE）卫星为高分辨率地监测全球海洋质量变化提供了一种新的手段。利用2003年1月至2014年12月Level-2 RL05的GRACE产品,进行去相关误差滤波、高斯滤波和海洋-陆地信号泄漏改正后,得到了全球陆地和海水质量变化,并分析了陆地水和冰川的质量变化对海平面长期变化的贡献。研究表明,全球陆地水和冰川的质量变化对海平面的贡献约为（2.09±0.54）mm/a,与卫星测高扣除海洋温盐数据比热容变化得到的海水质量长期变化（2.07±0.62）mm/a有着很好的一致性,其中全球陆地水储量对全球质量项海平面变化的贡献为（0.15±0.25）mm/a,南极冰盖对全球质量项海平面变化的贡献为（0.59±0.10）mm/a,格陵兰岛冰盖对全球质量项海平面变化的贡献为（0.72±0.12）mm/a,山地冰川对全球质量项海平面变化的贡献为（0.63±0.09）mm/a。并进一步讨论了不同分析中心GRACE重力场系数,一阶项系数和二阶项对质量项海平面变化的影响。结果表明,一阶项对质量项海平面的影响为（0.10±0.08）mm/a,二阶项对质量项海平面的影响为（0.16±0.04）mm/a,美国德克萨斯大学空间研究中心和德国地学研究中心分析结果较为一致,而美国国家航空航天局喷气推进实验室的结果则稍稍偏小。     

Calorimetric study of the thermodynamics of formation of MgSO4 and NaSO4− ion pairs at the ionic strength of seawater

The formation of the ion pairs MgSO₄ and NaSO₄^? was investigated calorimetrically at 0.75 M ionic strength, 25°C, 1 atm. Simultaneous determinations of enthalpy changes, ΔH₁⁰, and stability constants, K₁, were not possible, and values of K₁ determined independently had to be introduced for the calculation of ΔH₁⁰. The values of ΔH₁⁰ obtained were 1–3 kJ mol^?1 for MgSO₄ and 0 kJ mol^?1 for NaSO₄^?.