苏北浅滩钙结核的特征及其环境指示意义

对采自苏北浅滩的钙结核样品进行了岩石学、矿物学和碳氧同位素的分析。样品富含石英和长石砂屑,碳酸钙胶结,其碳和氧同位素组成分别为-8.38‰~-8.19‰V-PDB及-5.23‰~-5.03‰V-PDB。根据样品的氧同位素组成,利用碳酸盐-水体系氧同位素方程,结合现今底层水温度,并考虑可能存在的温度变化,计算得到古沉淀流体的δ18 O水范围为-4.72‰~-4.52‰VSMOW,较正常海水偏负,认为钙结核的形成可能受到了淡水影响。根据结核中碎屑矿物的成分及其成熟度,判断其包含的碎屑矿物源自古黄河,认为这些结核样品可能形成于海陆交互环境,形成时间约为7~6.5ka BP左右,当时古海平面高度比现今低10m左右,古黄河河道可能位于苏北浅滩附近。     

伊犁尼勒克剖面烧失量变化特征及影响因素

对新疆伊犁尼勒克黄土剖面513个样品进行了550℃和950℃高温烧失量分析以及X射线衍射矿物学分析,并将其烧失量与剖面中碳酸盐、有机质、4μm的黏粒含量进行了相关性分析。结果表明:对于位于西风区的伊犁尼勒克黄土,550℃高温烧失量变化可以反映土壤中有机质和束缚水的含量变化,而黏粒成分对550℃高温烧失量贡献较大;950℃高温烧失量变化可以用来反映伊犁地区黄土碳酸盐的变化趋势。根据碳酸盐含量变化所指示的气候环境意义推断出高的950℃高温烧失值反映冷干的气候环境,低的950℃高温烧失值反映比较湿润的气候环境,这对于研究伊犁地区黄土古土壤形成时期的古气候环境有重要的意义,同时证明了可以将烧失量这一简便、快捷的方法用于西风区黄土堆积序列的研究中。     

黄土-古土壤磁化率述评

黄土－古土壤是研究亚洲大陆内部过去２．６０Ｍａ间古环境变化的最好记录,特别是研究其与季风气候形成的密切关系,以及黄土扩展到日本甚至广泛的太平洋区域（北半球）等重大气候环境现象。其研究对第四纪古环境恢复具有极大的意义。最近基于黄土－古土壤而进行的古环境研究取得了很大的进展,一是因为黄土－古土壤磁化率的变化与深海沉积物的氧同位素比的变化非常一致,指示陆相沉积物亦可作为古气候的良好代用指标。另一方面,为什么黄土－古土壤中的磁化率存在差别,特别是古土壤磁化率为什么增大等问题,已成为这１０ａ间岩石磁学研究的中心课题。磁化率不单单只与强磁性矿物的含量成比例,同时也与不同种类的强磁性矿物的粒径分布有很大关系。发现在土壤化过程中形成的０．１μｍ以下的单畴－超顺磁性颗粒是造成古土壤磁化率增强的主要原因,它是否与生物作用有关目前仍不确定,但不论哪种情况,都可以肯定暖湿气候是古土壤磁化率增加的共同原因。磁化率增强的系统理论明确建立以来,使得从磁化率的变化来推算降水量,以及建立古气候复元的定量模型等都已成为可行。     

渭南黄土剖面中的稀土元素

对渭南黄土－古土壤序列中稀土元素含量和分布特征的研究结果表明：古土壤比黄土层的∑REE表现丰度高,这主要是古土壤中碳酸盐遭到强烈淋滤造成的相对富集。实际上,在成土过程中稀土元素本身有淋失。黄土层和古土壤层的稀土元素组合模式彼此相似,并且与黄河中游黄土也极相似,这反映了中国黄土的物质来自于相似的源区。黄土中稀土元素对古气候变化的响应主要表现在Ce的异常程度、各种稀土的组成和稀土总量的表现丰度上。因而,δCe、∑Ce/∑Y和∑REE也能从一个方面气候环境的变化。     

宜昌庙河钙结岩记录的古环境变化

对位于三峡地区黄陵背斜核部的宜昌庙河钙结岩体进行了沉积学、岩石学分析,识别出土壤钙结岩和地下水钙结岩。对土壤钙结岩进行了胶结物的分离、ESR年龄测试和碳氧稳定同位素分析,结果表明,庙河土壤钙结岩中方解石胶结物的δ13 C值相对围岩而言明显偏负,多数样品δ18 O值则呈不同程度偏正的趋势。土壤钙结岩主要形成于冰期,计算表明它们形成时期的古气温多为8~12℃,年均降雨量多为760~770mm,C4植物占约84%的绝对优势。由于钙结岩的形成过程涉及到诸多影响碳酸盐化学过程和相应土壤碳酸盐稳定同位素组成的因素,得出的认识可能存在一定程度的不确定性。     

中国粉尘源区表土碳酸盐含量与碳氧同位素组成

在中国的主要沙漠和戈壁等粉尘源区采集了地表沙或土壤(统称为表土)样品,分析了样品的碳酸盐含量和碳酸盐的碳氧同位素组成。结果表明,中国粉尘源区表土碳酸盐含量在空间上随着年降水量的增加而逐渐减少,大致呈现自西向东逐渐降低的趋势;碳酸盐δ^13C值在空间上随着年降水量的增加而逐渐偏负．δ^18O值缺乏规律性;塔克拉玛干沙漠细颗粒物质中碳酸盐含量相对偏高,但不同粒级颗粒中碳酸盐的δ^13C值基本一致,表明风蚀时粒度的分选并不影响源区的同位素组成特征;由于粉尘源区表土碳酸盐含量和δ^13C值均具有区域特征,因此利用大气粉尘的碳酸盐含量和δ^13C值示踪不同的源区是可能的。     

利用黄土中的碳同位素半定量地重建古温度

在相对稳定的气候阶段,土壤中的CO2与其中的碳酸盐之间处于同位素平衡状态,这意味着二者的碳同位素分馏值可作为地质温度计估算古温度。对中国洛川黄土剖面的10组黄土-古土壤序列L1-1-S8同时做了碳酸盐和有机质的碳同位素分析。由于这些地层单元可以与深海氧同位素记录的2-21阶段对比,其中L1-1-L2可与南极Vostok冰心的大气CO2浓度记录对比,由此通过相关分析确定了各地层形成时的平均大气CO2浓度及其δ^183C值,再根据Cerling模型,用有机质δ^13C值代替土壤呼吸CO2的δ^13C,算出土壤CO2的δ^13值。将该值与次生碳酸盐的δ^13C值代入Deines分馏方程可算出各地层单元的古温度。该温度代表了平均深度约30cm处的土壤温度,相当于当时的夏季大气温度。所有数据与黄土-古土壤地层学记录的气候变化吻合,定量地反映了近800ka来黄土高原古气候的变化。     

硼同位素地球化学应用研究进展

硼的2个稳定同位素(10 B和11B)间较大的同位素相对质量差导致自然界明显的硼同位素分馏,加上硼易溶于水和活泼的化学性质,使其在不同的地质环境下具有不同的同位素组成.现已查明自然界硼同位素组成(δ11 B)的变化范围为-70‰～+75‰.较负的δ11B值见于非海相蒸发硼酸盐矿物和某些电气石,而较正的δ11 B值见于盐湖卤水和蒸发海水.20世纪80年代以来,随着硼同位素测量方法的建立和改进,硼同位素地球化学研究领域不断拓宽.目前,硼同位素已成功地应用于判别沉积环境、示踪地下水污染、研究矿床成因、示踪海水入侵、重建古海洋与古气候条件和研究大陆化学风化等方面.综合概述了硼同位素的分馏机理、硼同位素在自然界的分布及其硼同位素在地球化学领域研究中取得的成果、最新进展以及研究中存在的问题,以促进硼同位素地球化学研究在我国的进一步发展.     

大西洋中脊TAG热液活动区海底热液沉积物的硫同位素组成及其？…

对１９８８年取自大西洋中脊ＴＡＧ热液活动区的海底表层热液沉积物中３６件硫化物样品进行了硫同位素组成分析。结合ＯＤＰＬｅｇ１５８的近期成果,对ＴＡＧ区热液沉积物的硫同位素组成及其时空演变、硫源、硫同位素偏重的原因和硫的演化进行了探讨,得出如下结论：（１）ＴＡＧ区表层热液喾物的δ＾３４Ｓ值从２．９‰－７．６‰变化,均值为５．９８‰,与其它洋中论脊热液合活动区相比明显偏重,（２）从海底表层区到蚀变玄武岩     

南海北部海域沉积物中生物钡、碳氮同位素的组成特征及其与表层水体初级生产之间的关系

通过对采集自南海北部的D06和S0612两个短柱状沉积物样品中的不同赋存形态钡、有机碳和生物硅的含量以及有机质碳氮同位素组成的分析，结果表明沉积物中的钡主要以碎屑钡和自生的生物钡形式存在。沉积物中生物钡的含量在10.3~385.2 μg/g之间，平均值为177.0 μg/g，据此计算的新生产力在12.3~146.7 mg/（d·m2）（以碳计）之间，平均为78.9 mg/（d·m2）；D06站计算的结果和附近站位的实测值相当。沉积物中有机碳的含量在0.64%~1.34%之间，平均值为0.89%，C/N比值为4.96~5.93，平均值为5.54。有机碳的δ13C值在-22.98‰~-20.73‰之间，平均值为-21.46‰，依据端元组份同位素组成计算的陆源有机质比率显示，D06站位的有机质主要来自海洋生物，而S0612站位则受陆源有机质的影响较大。沉积物中有机质的δ15N值在3.96‰~6.29‰之间，平均值为5.26‰，反映的是该海区氮源的同位素组成，而不受硝酸盐利用率的影响。     

Microbial Biomass and Organic Nutrients in the Deep-Sea Sediments of the Central Indian Ocean Basin

In order to assess the impact of deep-sea mining on the in situ benthic life, we measured the microbial standing stock and concentration of organic nutrients in the deep-sea sediments of the Central Indian Ocean Basin in the Indian pioneer area. Sediments were collected using box core and grab samples during September 1996. The total bacterial numbers ranged from 10 10 -10 11 cells per g -1 dry weight sediment. There was a marginal decrease in the number of bacteria from surface to 30 cm depth, though the subsurface section registered a higher number than did the surface. The highest numbers were encountered at depths of 4-8 cm. The retrievable number of bacteria were two orders less in comparison with the direct total counts of bacteria. An almost homogeneous distribution of bacteria, total organic carbon, living biomass, and lipids throughout the depth of cores indicates active microbial and benthic processes in the deep sea sediments. On the other hand, a uniform distribution of total counts of bacteria, carbohydrates, and total organic carbon in all the cores indicates their stable nature and suggests that they can serve as useful parameters for long-term monitoring of the area after the benthic disturbance. Further studies on temporal variability in this region would not only verify the observed norms of distribution of these variables but would also help to understand restabilization processes after the simulated benthic disturbance.     

Assessing the Validity of Seismo-Acoustic Predictor Equations for Obtaining Seabed and Sub-Surface Sediment Physical Properties

The interdependence between the seismo-acoustic properties of a marine sediment and its geotechnical/physical parameters has been known for many years, and it has been postulated that this should allow the extraction of geotechnical information from seismic data. Though in the literature many correlations have been published for the surficial layer, there is a lack of information for greater sediment depths. In this article, a desktop study on a synthetic seafloor model illustrates how the application of published near-surface prediction equations to subsurface sediments (up to several tens of meters burial depth) can lead to spurious predictions. To test this further, acoustic and geotechnical properties were measured on a number of sediment core samples, some of which were subjected to loading in acoustically-equipped consolidation cells (oedometers) to simulate greater burial depth conditions. For low effective pressures (representing small burial depths extending to around 10 meters subsurface), the general applicability of established relationships was confirmed: the prediction of porosity, bulk density, and mean grain size from acoustic velocity and impedance appears generally possible for the investigated sedimentary environments. As effective pressure increases through, the observed relationships deviate more and more from the established ones for the near-surface area. For the samples tested in this study, in some instances increasing pressure even resulted in decreasing velocities. There are several possible explanations for this abnormal behavior, including the presence of gas, overconsolidation, or bimodal grain size distribution. The results indicate that an appropriate depth correction must be introduced into the published prediction equations in order to obtain reliable estimates of physical sediment properties for greater subsurface depths.     

海上大直径钢管桩打桩过程中桩周土强度弱化研究

海上大直径钢管桩打桩过程中,桩周土体受到强烈扰动而发生强度弱化,掌握桩周土体强度弱化规律对于准确预测打桩过程、保证工程安全具有重要意义。为研究土体强度弱化规律,开展了环剪试验模拟打桩对桩周土体的扰动,测试土体强度随剪切速率的变化规律,建立了描述土体强度弱化规律的拟合公式,引入到打桩分析软件中。研究结果表明：土体的强度折减程度不仅与土体本身的性质有关还受到土体的埋深和剪切速率的影响,埋深越深土体强度折减程度越低,剪切速率越高土体强度折减越高,在打桩分析中可采用这里推荐的线性折减方法来模拟不同深度处土体强度的折减规律。     

Geoacoustic Inversion via Genetic Algorithm and Its Application to Manganese Sediment Identification

An acoustic inversion method using a wide-band signal and two near field receivers is proposed and applied to multiple layered seabed models including a manganese sediment. The inversion problem can be formulated into a probabilistic model comprised of signals, a forward model, and additive noise. The forward model simulates wide-band signals, such as chirp signals, and is chosen to be the source-waveletconvolution plane wave modeling method. The wavelet matching technique, using weighted least-squares fitting, estimates the sediment sound-speed and thickness on which determination of the possible numerical ranges for a priori uniform distribution is based. The genetic algorithm is applied to a global optimization problem to find a maximum a posteriori solution for determined a priori search space. Here the object function is defined by an L 2 norm of the difference between measured and modeled signals. Not only the marginal pdf but also its statistics are calculated by numerical evaluation of integrals using the samples selected during importance sampling process of the genetic algorithm.     

Interannual Sea Level Variations and Annual Tides in the Northwestern Pacific

Specific properties of the interannual sea level variations and annual tides in the Northwestern Pacific were studied. Several tide stations were monitored. The monthly mean sea level for the year of 1995 was analyzed at each tide station. A seismic event in 1995, some tectonic activity around the subject area, and the Kuroshio (the oceanic western boundary current) may possibly contaminate results which would have occurred from the astronomical annual tide alone.     

Deep-Sea Sediment Compression Curves: Some Controlling Factors, Spurious Overconsolidation, Predictions, and Geophysical Reproduction

Oedometer tests have been carried out on 70 undisturbed surficial clays (at approximately 250 mm below the mudline), mostly collected by free-fall corers from sites widely scattered throughout the deep-sea North Atlantic. Acoustic measurements were also made, initially on contiguous samples and ultimately on the same sample using a geophysically instrumented oedometer which also collected electrical resistivity data. Apart from those quiescent areas below the carbonate compensation depth, such as north of the West Indies where very fine clays exist, most of the samples are silty clays whose geotechnical-geophysical properties are dependent on the type of clay minerals present (and their ability to take in moisture), the sand-size fraction, and the quantity of carbonate present. Thus the pure clays have high compressibilities which decrease on the addition of coarse particles, while the converse is true for the acoustic parameters, these increasing with the sand fraction. Using the notion of the intrinsic compression line for all samples, and comparison to it of the measured compression curves, it is clear that, contrary to some previously held ideas, most deep-sea clays are normally consolidated; the addition of carbonate has the effect of creating an open, stronger sediment skeleton. Interestingly, where information is available, the variation with depth of a sample's acoustic velocity follows the void ratio pressure relationship of the compression curve. This allows the construction of an in-situ sediment compression curve using the in-situ geophysical observations.     

Phylogenetic diversity and phenotypic characterization of cultivable bacterioplankton isolated from polar oceans

A set of 27 marine planktonic bacteria isolated from the polar regions was characterized by 16S rDNA sequencing and physiological and biochemical testing. More than half of these bacteria were positive for caseinase, gelatinase and 13-glucosidase, and could utilize glucose, maltose or malic acid as carbon source for cell growth. Twelve isolates expressed nitrate reduction activities. Except for one antarctic isolate BSwlO175 belonging to Actinobacteria phylum, these isolates were classified as γ-Proteobacteria, suggesting that γ-Proteobacteria dominated in cultivable marine bacterioplankton at both poles. Genus Pseudoalteromonas was the predominant group in the Chukchi Sea and the Bering Sea, and genus ShewaneUa dominated in cultivable bacterioplankton in the Prydz Bay. With sequence similarities above 97%, genus Psychrobacter was found at both poles. These 27 isolates were psychrotolerant, and significant 16S rDNA sequence similarities were found not only between arctic and antarctic marine bacteria （ 〉 99% ）, but also between polar marine bacteria and bacteria from other aquatic environments （ ≥ 98.8% ）, including temperate ocean, deep sea, pond and lake, suggesting that in the polar oceans less temperature-sensitive bacteria may be cosmopolitan and have a bipolar, even global, distribution at the species level.     

Flow Cytometric Analysis of Coastal Lagoon Bacterioplankton and Picophytoplankton: Fixation and Storage Effects

The effect of different fixation and storage protocols on the flow cytometric (FCM) simultaneous analysis of bacterioplankton and phytoplankton in coastal seawater samples (Mediterranean coastal lagoons) was investigated. FCM measurements (cell number, fluorescence and scatter characteristics) were obtained through DAPI staining. Three fixatives [glutaraldehyde (GA), formaldehyde (FA) and paraformaldehyde (PFA)] and two storage (3 months duration) methods (5 °C and −196 °C) were tested. Two dominant populations were detected in studied samples: bacteria and eukaryotic picophytoplankton. Adding fixatives (2% final concentration) appears necessary to obtain FCM exhaustive counts of all the bacteria and phytoplanktonic cells. This was related to the permeation effect of fixatives which allowed a better DAPI staining of the cells. Maximum fluorescence, i.e. optimal staining of the cells was obtained with FA or PFA, and significant lower fluorescences with GA. Fixed samples stored at 5 °C induced rapid cell loss. Only storage in liquid nitrogen of samples fixed with FA or PFA, allows mid-term (≥4 months) preservation of bacteria or picophytoplankton cell numbers, and limited evolution of DAPI-induced fluorescence and scatter characteristics.