Mechanism of variations in environmental magnetic proxies of lake sediments from Nam Co, Tibet during the Holocene

High-resolution environmental records from the Tibetan Plateau are essential to understand past global climatic and environmental changes. Magnetic minerals in lake sediments are important proxies to reconstruct environmental and climatic changes. Nam Co (lake) is a typical great lake in the transitional region of southwest monsoon in the Tibetan Plateau. Previous studies have extensively focused on geochemistry, microfossils, sedimentology and biochemistry analysis of Nam Co, which provides sound interpretation of paleoclimatic and paleoenvironmental changes. However, up to now, no systematic environmental magnetic studies have been carried out. Therefore, high-resolution and systematic magnetic studies combined with geochemical parameters were carried on lake sediments of core NC 08/01 from Nam Co for the Holocene period (11.3 cal ka BP) in order to explore how magnetic properties of the sediments respond to climatic changes. Based on variations of magnetic proxies, the sequence can be separated into 3 units. Unit 1 (236-199 cm, 11.3-7.8 cal ka BP) contains dominantly coarse-grained magnetite with homogeneous grain size. A positive correlation between magnetite and Ti strongly suggests that these coarse-grained detrital magnetites reflect detrital input signals due to insignificant effects of postdepositional dissolution processes on these coarse-grained magnetite particles. For Unit 2 (198-102 cm, 7.8-2.1 cal ka BP), magnetic grain size is finer and the corresponding concentration of magnetite is also reduced. This is mainly due to significant dissolution of these fine-grained detrital magnetite particles, which were transported under reduced water flow conditions during this period. For Unit 3 (101-0 cm, 2.1-0 cal ka BP), the bulk magnetic properties are dominated by a mixture of single domain biogenic magnetite and detrital magnetite. The concentration of magnetic minerals is not correlated with the Ti content. In conclusion, the preservation of magnetic minerals in the lake sediment and thus the corresponding magnetic properties are related to the initial grain size. Combination of magnetic properties (including variation of grain size and concentration) and other proxies of detrital inputs (e.g. Ti) can be used to infer the variation of redox conditions in Nam Co. These results provide a viable framework for reconstructing the paleoenvironmental changes of this lake.     

东海陆架表层沉积物的磁性测量及其油气勘探意义

本文通过对东海陆架盆地平湖地区表层沉积物的系统磁性测量和化探指标分析,揭示烃类微渗漏对沉积物磁性特征的影响,探讨磁性测量方法在表层油气勘探中的应用前景。研究表明,平湖地区表层沉积物中主要的磁性矿物为磁铁矿,一般磁性较弱沉积物中磁铁矿晶粒以单畴（ＳＤ）为主,而磁性较强的沉积物中以较烃的假单畴／多畴（ＰＳＤ／ＭＤ）为主,磁性参数与化探数据酸解烃,蚀变碳酸盐存在明显的相关性,表明磁性测量可作为油气勘探的     

Magnetic response to atmospheric heavy metal pollution recorded by dust-loaded leaves in Shougang industrial area,western Beijing

Fifty-five evergreen tree＇s leaves growing less than one year were collected from Shougang industrial area in western suburb of Beijing, including steel plants and its ambient residential areas, recreational parks and farmlands. Rock magnetic properties and heavy metal contents were studied. The results show that the magnetic properties of leaf samples are predominated by Iow-coercivity magnetite, and both the concentration and grain size of magnetite particles gradually decreased with the distance from the main pollution source increases. Moreover, there is a significant linear relationship between magnetic parameters （the low-field magnetic susceptibility, saturation isothermal remanent magnetization and anhysteretic remanent magnetization） and heavy metals contents （Fe, Pb, V, Cr and Zn） （0.73≤ R≤ 0.88）. Hence, the magnetic parameters of leaves can serve as a proxy for quick detecting of the recent atmospheric metallic pollution.     

Magnetic granulometry of recent sediments from the Huguang Maar and its implication for provenience

To understand the origin and its climatic implications of the Huguang Maar sediments, we conducted laser grain size analysis and rock mangtic measurement for the recent deposits from the Huguang Maar and for the volcanic rocks of the caldera for comparison. The grain size distributions are dominated by clayey silts for both the bulk sediments and magnetic separates. Acquisition of isothermal remanent magnetization (IRM) and thermal demagnetization of IRM suggest (titano) magnetite as the dominating magnetic mineral in the sediments; high coercivity minerals are not detected. Therefore, the ratio of the susceptibility of anhysteretic remanent magnetization (k _ARM) to the weak field magnetic susceptibility (k), k _ARM/k can be used to estimate the grain size of magnetite. The sediments and volcanic rocks yield values of 13.7 and 11.8 for the k _ARM/_k, respectively, corresponding to grain size values of ～0.03 µm and ～0.05 µm. The magnetic granulometry of lake sediments is distinctive from one of the Chinese loess, in which published data suggest a value of 6.0 for k _ARM/_k, and grain size of ～0.1 µm, but is akin to the nearby volcanic rocks. Although a Loess Plateau source of the lake sediments cannot be fully ruled out, the catchment is most probably the main source. We explain the slightly finer magnetite grain size in sediments than in the volcanic rocks as being disintegrated of particles during erosion and transportation. We conclude that there is no evidence for aeolian input of the Loess Plateau dusts into the Huguang Maar, and the relationship between magnetic parameters of the lake sediments and winter monsoon intensity is probably more complicated than previously thought.     

Magnetic properties of different grain-sized particles of sediments from the Okinawa Trough and their relationships to sedimentary environment

Multiple magnetic parameters were measured for nine different grain-sized fractions separated from the sediment samples that are representatives of four different sedimentary environments of the Okinawa Trough. Based on the measured results, the contributions of different grain-sized particles to total magnetic susceptibility of bulk sediments, the magnetic mineral assemblage and magnetic domain state as well as their relationships to sedimentary environment were discussed. Our research shows that the magnetic mineral is dominated by magnetite with a small amount of hematite and is primarily in pseudo-single-domain state. That indicates that the different sedimentary environments in the Okinawa Trough have certain correlation in material provenance. The magnetic minerals enrich in different grain-sized particles in response to different sedimentary environments. The contribution of the grain sizes from coarse to fine to coarse and fine to the magnetic susceptibility from the west to the east is in accordance with terrigenous material transportation from continental shelf of the East China Sea to the Okinawa Trough. It also shows difference in magnetic properties as a result of some environmental factors.     

TJ-1模拟月壤颗粒几何特性

颗粒几何特性是颗粒材料的一个重要物理性质,是决定颗粒材料力学性质的一个重要因素.针对软着陆模型试验所用的TJ-1模拟月壤颗粒进行了体视显微镜扫描,获取数字图像后用图形处理软件对各粒径组的颗粒进行了几何特性各指标参数的量化统计,获得了模拟月壤颗粒在延伸度、圆度和凹凸度等的具体数值,为进一步研究TJ-1模拟月壤物理力学性质与颗粒几何特性的关系提供了相关试验数据.试验结果表明:TJ-1模拟月壤颗粒具有棱角、钩角、锯齿等不规则结构,表面相对凹凸,大粒径颗粒具有明显的蜂窝状气孔结构;颗粒形状各异,主要形状有长条状、类三角形和类四边形.最后对TJ-1模拟月壤颗粒和真实月壤颗粒在几何特性方面进行了对比分析.     

Magnetic properties of highroad-side pine tree leaves in Beijing and their environmental significance

This is a report on magnetic properties of highroad-side tree (Pinus pumila Regel) leaves collected along an expressway linking Beijing City and the Capital International Airport and further focus on their environmental contributions. A series of rock magnetic experiments show that the primary mag-netic mineral of leaf samples was identified to be magnetite,in the pseudo-single domain (PSD) grain size range 0.2―5.0 μm. On the other hand,magnet-ite concentration and grain size in leaves are ascer-tained to decrease with increasing of sampling dis-tance to highroad asphalt surface,suggesting that high magnetic response to traffic pollution is localized within a distance of some two meters away from highroad asphalt surface. Although magnetic suscep-tibility is ordinarily regarded as a simple,rapid and low-cost method for monitoring traffic pollution,saturation isothermal remanent magnetization (SIRM) can be treated as a valid proxy for monitoring air par-ticulate matter (PM) when samples are magnetically weak. It is believed that a synthetic rock magnetic study is an effective method for determining concen-tration and grain size of ferromagnets in the atmos-pheric PM,and then it should be a rapid and feasible technique for monitoring atmospheric pollution.     

高密度磁记录纳米颗粒膜磁性的蒙特-卡罗模拟

用蒙特－卡罗方法对Co-C和CoPt-C纳米颗粒膜的磁特性进行模拟研究。模拟中，假设磁性颗粒为球形、单畴，易轴随机取向。对包含hcp结构、直径为3nm的Co颗粒的Co-C膜给出了湿度从3K到300K的磁滞回线，超顺磁驰豫的截止温度约20K；对包含fct结构CoPt的CoPt-C膜给出了300K时平均颗粒尺寸从4nm到6nm，对应于不同尺寸分布下的磁滞回线。模拟显示，由于fct结构CoPt-C有特大的各向异性，因而具备超高的矫顽力，可以满足超高密度磁记录的需要。以上模拟的结果与Co-C颗粒膜和CoPt-C颗粒膜的实验结果一致。     

Magnetostratigraphy of borehole EY02-2 in the southern Yellow Sea and its paleoenvironmental significance

Various media are used for the study of paleoenvi- ronment. Among them, ice-core, loess and marine sediments are the most important for long time re- cording[1]. In all kinds of researches of paleoenviron- ment, age determination of the sediments is the m…     

Magnetite defines a vertebrate magnetoreceptor

The key behavioural, physiological and anatomical components of a magnetite-based magnetic sense have been demonstrated in rainbow trout (Oncorhynchus mykiss). Candidate receptor cells located within a discrete sub-layer of the olfactory lamellae contained iron-rich crystals that were similar in size and shape to magnetite crystals extracted from salmon. Here we show that these crystals, which mapped to individual receptors using confocal and atomic force microscopy, are magnetic, as they are uniquely associated with dipoles detected by magnetic force microscopy. Analysis of their magnetic properties identifies the crystals as single-domain magnetite. In addition, three-dimensional reconstruction of the candidate receptors using confocal and atomic force microscopy imaging confirm that several magnetic crystals are arranged in a chain of about 1 microm within the receptor, and that the receptor is a multi-lobed single cell. These results are consistent with a magnetite-based detection mechanism, as 1-microm chains of single-domain magnetite crystals are highly suitable for the behavioural and physiological responses to magnetic intensity previously reported in the trout.     

多晶体晶粒尺度三维组织建模及可视化

采用基于Monte Carlo Potts模型的仿真技术对单相多晶体各向同性晶粒组织进行了三维建模,利用OpenGL图形接口,在所建多晶体组织模型数据结构的基础上进而实现了三维可视化和任意角度观测,结果表明,所建几何图像模型可以很好地仿真预定细观组织结构参数的三维多晶体组织,不但满足模型化研究所要求的统计意义上的准确性,而且非常符合实际材料显微组织的多变性特征,可望用作细观尺度多晶材料加工过程数值模拟和细观力学计算的基本组织模型。     

磁性参数的环境指示意义

介绍了岩石磁学研究中常用的能够指示环境变迁和气候变化的几种磁性参数及其组合。研究表明：磁化率是气候变化的代用指标之一，其值的高低反映气候的暖冷和沉积颗粒的细粗，用参数HSIRM，Bcr,HSIRM/k可以识别磁性矿物类型，较多磁铁矿的存在指示暖湿的沉积环境，反映沉积物颗粒细；而较多赤铁矿的存在则指示干冷的沉积环境，反映沉积物颗粒粗。HARM，Ber,HSIRM/k，S比(HSIRM-100mT/HSIRM)在环境监测中有重要的意义。     

Use of environmental magnetic measurements to characterize and correlate tephra-A case study in Iceland

A set of environmental magnetic parameters(i.e. magnetic susceptibility, xARM, IRMs, hysteresis loops and thermomagnetic curves) has been applied to two soil sections from SE Iceland. Results demonstrate that the main magnetic minerals in the tephras are ferrimagnetic minerals (e.g.magnetite) and canted antiferromagnetic minerals (e.g.haematite), with abundant paramagnetic material also present. Cross plots of Mrs/Ms vs. (B0)cr/(B0)c and xfd% vs.xARM/SIRM indicate that the main magnetic grain sizes in tephras are pseudo single domain (PSD) and multidomain(MD). Initial correlation of tephra layers was achieved, usingall the measured magnetic parameters, by use of the multi-variate statistical measures of Similarity Coefficient (SC) andEuclidean Distance (ED). This demonstrates that magnetictechniques can potentially assist in the identification andcorrelation of distal tephra.     

Magnetic characteristics and its environmental implications of core YSJD-86GC sediments from the southern South China Sea

Sediments of core YSJD-86GC （referred to as 86GC） collected from the southern South China Sea were selected for environmental magnetic studies. Combined with the published chronological framework, sediment magnetic properties were revealed for the study area since the MIS3 stage. The rock magnetic results indicate that low-coercivity magnetite is the main magnetic mineral within the sediments. Also, a certain amounts of hematite are present. The King plot and Day plot, which reflect the magnetic particle size, show that fine-grained pseudo-sin- gle-domain phase magnetic particles dominate the magnetic minerals in the sediments. Comparison of magnetic parameters and geochemical indicators show that magnetic properties of core 86GC sediments reflect a terrigenous input. Simultaneously, magnetic characteristics of the stud- ied sediment are influenced by the quantity of terrigenous sediment input, oxidation-reduction conditions of the provenance area, and the transportation environment and distance. Sea level fluctuation caused by global climate change was the main factor for variation in concentration of magnetic minerals and magnetic particle size of thestudied core sediments. Thus, variation of sediment magnetic properties in the study area can be used as an indirect indicator of sea level fluctuation.     

Effects of composition and microstructure on intergrain interactions of nanocomposite Pr2 Fe14B/α-Fe material

The effects of contents of Fe and B and microstructure on the intergrain interactions in the nanocomposite Pr2Fe14 B/a-Fe permanent magnetic materials are investigated by measuring the δM-H curves. The intergrain interactions become stronger with the increase in the content of Fe. The larger δM value of the ribbon samples corresponds to the smaller grain size and uniform grain size distribution, which are favorable factors strengthening the intergrain interactions and exchange-coupling. The non-ferromagnetic phase Pr1.1Fe4B4 is found in grain boundaries when the content of B is larger, which weakens the intergrain interactions.     

不同尺寸Fe3O4磁性颗粒的制备和表征

在水溶液体系中用溶胶-凝胶的方法通过改变各反应物的浓度制备不同尺寸的Fe3 O4磁性颗粒,用X-射线衍射(XRD)、X-透射电子显微镜(TEM)、电子衍射(ED)对不同大小的颗粒进行了结构和形貌的表征,此外还运用了振动样品磁强计(VSM)对其进行磁学特性测量.结果表明,这种方法能够制备不同粒径的立方尖晶石结构的Fe3 O4磁性颗粒,并且粒径不同的Fe3 O4磁性颗粒形貌、磁性均有所不同.     

Susceptibility variations of multiple origins of loess from the Ily Basin (NW China)

The magnetic susceptibility of loess from the Ily Basin,northwestern China shows maximum values in S0 paleosols but minimum values in other paleosols,the mechanism of which has been well debated.In this work,systematic magnetic measurements were made on a representative section from Neleke county.The results show that the loess horizons(L1,L2 and L3) have multi-domain magnetite grains of aeolian origin,S0 is characterized by production of pedogenetic ultrafine-grained ferrimagnetic minerals,and the other paleosols(S1,S2,and S3) are characterized by the formation of nonferrimagnetic minerals associated with waterlogging.The correlation between the low concentration of ferrimagnets,high paramagnetic content,high magnetic coercivity remanence,fine ferrimagnetic grain size and intensified pedogenesis suggest two competing processes of pedogenetic enhancement and pedogenetic depletion in the lower paleosols.Pedogenetic depletion dominates and is responsible for the low susceptibility.Changes in magnetic grain size distribution occur during pedogenetic depletion.The susceptibility variations are of multiple origins in the loess of the Ily Basin.Pedogenetic enhancement,pedogenetic depletion,and allochthonous input of magnetic minerals should all be taken into account to explain the variations of magnetic parameters.     

电流变抛光液中固相粒子间结合模型研究

电流变抛光液中的固相极化后形成复杂的微观结构并改变其流变性能。通过超景深三维显微系统观察了电流变抛光液在外加电场作用下形成的微观结构。根据粒子介电极化模型和抛光液中固相粒子间的作用力,建立了混有不同粒度磨料颗粒的电流变抛光液中固相粒子的结合模型,分析了颗粒粒度和粒子间作用力等因素对粒子结合模型的影响。     

Magnetic properties of street dust and topsoil in Beijing and its environmental implications

Environmental magnetic measurements were carried out on the sanrhples of street dust and topsoil, which were collected along the roadway in the urban and suburb of Beijing, including magnetic susceptibility （X）, anhysteretic remanent magnetization （ARM）, isothermal remanent magnetization （IRM） of all samples and temperature-dependence of magnetic susceptibilities and magnetic hysteresis parameters of representative samples. Obvious differences exist between the samples of street dust and those of topsoil. Compared with topsoil samples, the concentration of magnetic particles and high-coercivity components in street dust samples are higher, and the magnetic grains are coarser. Both dust and topsoil samples are dominated by ferrimagnetic minerals, and iron particles are only detected in some dust samples. These results suggest that street dust samples reflect the characteris- tic of particles produced by industrial and traffic activities, and the magnetic property of topsoil sam- ples represents the characteristic of particles from both anthropogenic and natural sources. The distribution of magnetic parameters is influenced by the environment where the samples are collected, like industry, traffic density and other road conditions. Hard isothermal remanent magnetization （HIRM） may be used as an indicator of particles produced by traffic activity. Dust storm samples collected on 17 and 18 April, 2006 have different magnetic properties from street dust and natural particles, like loess and paleosol, which indicate that the dust storm might be mixed with anthropogenic particulates during transport and falling.     

Environmental magnetism and paleoclimatic interpretation of the Sanmenxia loess-paleosol sequence in the southeastern extremity of the Chinese Loess Plateau

This is a report of multi-parameter mineral magnetic results of the Sanmenxia loess-pa-leosol couplets in the SE extremity of the Chinese Loess Plateau (CLP) over the interval of L1- L13 spanning the last 1 Ma. These results show that mass-specific magnetic susceptibility (X), XARM and SIRM and their ratios exhibit parallel stratigraphic variations. Since superparamagnetic (SP) particles have significant contribution to X but no contribution to remanence, e.g., ARM and SIRM, the strong linear correlations between X and remanence (e.g., ARM and SIRM) suggest that the pedogenesis-produced magnetic grains are predominantly in small single domain range. Consequently, the significant contribution of SP particles to the bulk X as supposed in previous studies has been obviously overestimated. XARM/X data in Sanmenxia and median grain size records of typical loess sections from the hinterland of the CLP display a strong resemblance, implying that XARM/X may be regarded as a reliable indicator for monitoring the variations of ferrimagnetic grain sizes. The results of S-ratio and HIRM ((SIRM IRM-0.3T)/2) measurements indicate that there is significant enhancement of both soft magnetite/maghemite and hard hematite/goethite in paleosols associated with pedogenesis.