Geomagnetic secular variation from recent lake sediments,ancient fireplaces and historical measurements in southeastern Australia

Compilations of historical observations, archaeomagnetic data from ancient fireplaces and palaemagetic results from short cores of sediment from lakes in southeastern Australia, particularly Lake Keilambete, provide a detailed record of the geomagnetic secular variation during the last 3000 years. The independent sets of data are in good agreement if the radiocarbon time scale for the lacustrine record is about 450 years too old. The error is attributed to systematic incorporation of ancient carbon into the lake floor sediments, mainly through erosion of sediment on the crater walls at times of low water level. A significant lag between deposition and the acquisition of stable magnetic remanence is ruled out. Inclination has been abnormally steep during the last 500 years but remained fairly close to the axial dipole field value prior to that. During the last 1000 years the predominant sense of looping of the magnetic vector corresponds to westward drift of the nondipole field. Secular variations on a time scale of ～ 100 years can be resolved by the lacustrine record.     

Evidence for recent palaeomagnetic secular variation in lake sediments from the New Guinea Highlands

Palaeomagnetic declination and inclination data are reported from Mackereth mini cores taken from three lake sites in Papua New Guinea. ¹³⁷Cs, ²¹⁰Pb and ¹⁴C dating provide a timescale for the palaeomagnetic oscillations. Tephrastratigraphy aids correlation between lakes. The palaeomagnetic data resemble the geomagnetic secular variation pattern deduced from historical observations. The new results greatly extend the latitudinal coverage of palaeomagnetic secular variation recorded in the last 10⁴ yr. Their significance in assessing secular variation source models is discussed. The data suggest that the edge of the Pacific region of low non-dipole field activity has remained near New Guinea during the last 10⁴ yr.     

Geomagnetic secular variation and motion of the earth's core

Summary A general theory of a time-dependent magnetic dipole in the earth is discussed. On the basis of the weastward drift of the «equatorial» dipole in the two eccentric dipoles model due toH. G. Macht, the impossibility of the origin of geomagnetic secular variation being in a deep interior of the earth's core is established from the standpoints of the shielding effect and the motions in the core. But the westward drift of the core's top layer relative to the mantle seems to be quite reasonable, even if we take into account the shielding effect of the mantle.     

The recent secular variation of declination and inclination in Kenya

Oriented specimens of very young lavas have been collected from 3 volcanic sites in Kenya in order to determine the declination and inclination angles at the times the lavas cooled. TheseD andI values have been tentatively fitted to a time scale extending over the past 1000 years based on historical, geological and vegetational evidence. A plot of declination against inclination for this period takes the form of a partial loop, somewhat similar to those obtained at other places.     

The secular geomagnetic variation. Statistical methods for paleomagnetic directions in sediments

Understanding the character of variations in the magnetic field of the Earth in the geological past requires a mathematically substantiated method for testing the statistical hypotheses against the real paleomagnetic data. As known, the paleomagnetic data from lava flows are sort of momentary snapshots of the state of the ancient magnetic field. Being quite fragmentary in time and space, these data compose what is referred to as a sample in statistics: on the close discrimination of the lava flows, the internal correlations in the data are absent. It is well known that the distributions of the paleomagnetic directions from the sedimentary data differ from the distributions in lavas, which is mainly due to the effect of averaging of the magnetization over the time interval corresponding to the accumulation of sedimentary layers represented in the rock specimen. Assuming the rate of sedimentation to be known for each specimen, one can suggest the method for the quantitative testing the statistical consistency of the paleomagnetic data in the sediments with the model variations of the magnetic field of the Earth in terms of the Giant Gaussian Process (GGP). It turned out that the averaging effect can well be allowed for by the coefficients of GGP, and the scheme of the further testing is in this case identical to the scheme of testing the paleomagnetic data obtained from lavas.     

Measurements of recent geomagnetic secular variation in southeastern Australia and the question of dipole wobble

Archaeomagnetic and radiocarbon measurements on a series of ancient Aboriginal fireplaces and burnt tree-stump sites in southeastern Australia are presented, and an outline of changes in the local direction of the earth's magnetic field over the last 1500 years is offered.An analysis of these new data from the southern hemisphere and published data for the northern hemisphere indicates that a large change occurred in the orientation of the geomagnetic dipolar axis between about 1400 and 1650 A.D.     

Helical core flow from geomagnetic secular variation

Fluid flow below the core-mantle boundary is inferred from geomagnetic secular variation data, assuming frozen magnetic flux and a new physical assumption termed helical flow, in which the tangential divergence correlates with the radial vorticity. Helical flow introduces streamfunction diffusion and removes non-uniqueness in the inversion of the magnetic induction equation. We combine helical flow with tangential geostrophy and compare the following physical assumptions: tangential geostrophy, strong helicity, weak helicity and columnar flow, using geomagnetic field models from the 2000 Oersted and 1980 Magsat satellites. Our solutions contain some features found in previous core flow models, such as large mid-latitude vortices, westward drift in most of the southern hemisphere, and suggested polar vortices. However, our solutions contain significantly more flow along contours of the radial magnetic field than previous core flow models.     

IGRF-11描述的2005-2010年中国地区地磁长期变化及其误差分析

第11代国际地磁参考场(IGRF-11)是国际地磁学与高空物理学联合会(IAGA)于2009年12月提出的最新与比较准确的IGRF.根据IGRF-11模型,计算了2005-2010年中国地区地磁长期变化(SVC).IGRF-11所描述的2005-2010年中国地区地磁长期变化与实际观测的地磁长期变化(SVO)是基本一致的,但亦有明显差异.分析比较了在中国地区34个台站上的SVO与SVC之间的差异,并得到了它们之间的差值及其均方误差σ,对于地磁偏角和倾角,σ分别为0.35′/a与0.53′/a;对于地磁总强度、水平分量、北向分量、东向分量与垂直分量,σ分别为5.12nT/a,8.91nT/a,8.89nT/a,3.27nT/a与3.59nT/a.引起IGRF-11所描述的2005-2010年中国地区地磁长期变化的误差原因是:中国地区的区域性与局部性的磁异常、IGRF忽略了外源场与IGRF模型的截断阶数、全球台站与测点的分布不均匀、地磁观测误差等因素.由于中国地磁模型(CGM)优于IGRF模型,并能比较准确地描述中国地区地磁场及其长期变化,故在实际应用中应选用CGM.     

An estimate of late Pleistocene geomagnetic intensity variation from Sulu Sea sediments

Sediments from Site 769 of the Ocean Drilling Program's Leg 124 provide a record of geomagnetic intensity variation over the past 110 ky. Using continous shipboard measurements exclusively, I estimate the variation in the geomagnetic field strength by employing low-field magnetic susceptibility as a normalization parameter for the measured remanence intensity. By calibrating the resultant relative paleointensity record against previously available Holocene age estimates of absolute paleointensity, I derive an estimate of virtual dipole moment since 110 ka. The record obtained from these Sulu Sea sediments is strikingly like that previously obtained from sediments of a similar age in the Mediterranean Basin with distinct intervals of low intensity near 15, 20, 40 and 65–70 ka. The Sulu sediments also indicate a low-intensity feature near 108 ka. Important differences in paleointensity estimates obtained from these different regions for the interval between 30 and 20 ka suggest that a relatively large non-dipolar component of the geomagnetic field might have been present at that time.     

Long term variation in the secular love number

Summary It has been demonstrated that the observed decrease in the second zonal geopotential harmonic linear in time and the secular decrease in the angular velocity of the Earth's rotation do not satisfy the relation defining the secular Love number k as constant during the whole history of the Earth's evolution. The discrepancy disappears if it is assumed thatdk/dt=–2.4×10^–6 cy^–1 .

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aa, m a ¶rt;a au m aauunmuaa u u a ¶rt;a u mu au u ¶rt;mm mu, n¶rt; u a a nm mu umuu u. a uam, u ¶rt;nmumdk/dt=–2,4·10 ^–6 (mmu)^–1 .

     

Persistent organochlorine residues in sediments from the Black Sea

The extent of contamination of the Black Sea by selected organochlorine compounds has been assessed through the analysis of surficial sediments taken from throughout the region. Concentrations of HCHs at sites influenced by the Danube delta are among the highest recorded on a global basis (up to 40 ng g(-1) dry wt). The ratio between the alpha- and gamma-isomers was relatively low indicating contamination through the use of lindane. Concentrations of DDTs (0.06-72 ng g(-1) dry wt) and PCBs (0.06-72 ng g(-1) dry wt) were not especially high in comparison to levels reported from throughout the world. The DDE/DDT ratio was, however, low indicating fresh inputs and hence current usage of DDT within the Black Sea region.     

地磁场长期变化和日长十年尺度变化的周期特征

根据历史地磁场模型GUFM1、第10代国际参考地磁场（IGRF10）模型和日长资料,采用小波变换方法,分析了地磁场磁矩、能量、西向漂移等参数的长期变化和日长十年尺度变化的周期分量及其时变特征.结果表明,1800～2005年期间,偶极子磁场长期变化有82年和48年准周期分量,它们与日长变化的周期没有直接关系.非偶极子磁场参数的长期变化与日长变化有66年和32年准周期分量,66年准周期比32年准周期强.在66年准周期分量,西向漂移比日长变化超前8.8年,非偶极子磁场能量比日长变化滞后15.6年.日长十年尺度波动和地磁场长期变化的起源不存在因果关系.     

Paleomagnetic records of secular variation from Lake Michigan sediment cores

Continuous measurements of the natural remanent magnetization of six cores from central Lake Michigan have been made, using a cryogenic magnetometer designed to permit the passage of long cores through its sensing region. The output of each of the three-component sensors is deconvolved with the appropriate system response function and combined to yield continuous records of inclination, declination and intensity with a resolution of approximately 6 cm. The paleomagnetic record extends to about 13,500 years B.P. and includes two features which may be excursions of the earth's field. Other features may be correlated between different cores, and the magnetic sequence is, in general, consistent with the stratigraphic sequence. There is an indication of a repeated sequence of field changes, which is somewhat reminiscent of the solar field cycle.     

中国地区地磁长期变化研究

采用2000~2004年中国地区34个台站的地磁日均值数据, 计算了通日和静日的平均年变率,以及静日的拟合年变率.应用上述年变率, 建立了2000.0~2005.0年代中国地区地磁场长期变化泰勒多项式模型和曲面样条模型.分析讨论了该泰勒多项式模型和曲面样条模型与国际地磁参考场长期变化模型(IGRF-SV)的异同, 结果表明,中国地区地磁长期变化的泰勒多项式模型与曲面样条模型的形态与数值是一致的,而且与IGRF-SV长期变化的趋势也是一致的,但中国地区地磁长期变化具有区域特征.     

The distribution of mercury in the surficial sediments of the northern Tyrrhenian sea

Marine sediments are the ultimate recipient of mercury introduced into aquatic ecosystem either by man or by weathering. In the surficial sediments of the northern Tyrrhenian sea high concentrations of this metal were found in an area close to the effluent of a chlor-alkali plant and in the bays of La Spezia and Leghorn, which receive wastes from numerous industries and from port activities.The sediments of a much larger marine area off the mouths of the Ombrone, Albegna and Fiora rivers also contain high levels of Hg, part of which derives from the weathering of the rich cinnabar deposits of Mount Amiata and part from mining and processing the cinnabar.     

利用小波分析重力的长期变化

运用小波滤波方法估算Chandler和周年项的潮汐因子.本文分析了四个台站(Brussels, Boulder, Membach以及Strasbourg)的观测记录,运用合成潮方法得到重力残差后,用Daubechies小波带通滤波器滤波残差,得到256～512 d时间尺度上的序列,根据标准差最小原则确定观测极潮周年和Chandler项的周期,然后利用最小二乘法估算它们的潮汐因子,同时给出未经模型改正的周年重力.由于高阶Daubechies小波构造的滤波器具有良好的频率响应,且能压制信号中的高阶异常成分,使滤波的信号更加光滑,因此计算结果具有更小的均方差,更加可靠.     

南海磁场特征研究

建立客观的磁力ΔT异常,获得可信的磁力ΔZ_⊥异常、居里面成果, 在此基础上开展综合地质地球物理研究,对于解决南海资源等相关的地质、地球物理问题意义重大.本文汇集我国历年在南海取得的磁力实测资料,重新处理、校正、整合,特别是追溯南海周边的国际地磁台的日变资料进行日变改正,形成的南海磁力ΔT异常,其资料品质得到了极大提高.采用全磁纬变倾角化极技术,获得磁力ΔZ_⊥异常,其与实测证实的磁性海山、海岛有非常好的匹配关系,建立起可以直接用于反演处理解释的南海磁力ΔZ_⊥异常.选择磁力ΔZ_⊥异常的小波多尺度分解四阶逼近,采用单一磁性界面反演技术进行深度反演,获得居里面又称磁性底界面.建立了认识、解释南海的磁场基础体系,证实了南海基性岩浆岩分布区与磁力ΔZ_⊥异常的正磁异常高密切相关,区域性的磁力ΔZ_⊥异常负磁异常区可能与居里面深度相关.     

A recent history of metal accumulation in the sediments of Rijeka harbor, Adriatic Sea, Croatia

We studied metal pollution in the sediments of Rijeka harbor, including anthropogenic influence during recent decades and at the present time. Sediment profiles were collected at ten sampling points. The concentrations of 63 elements in bulk sediment were obtained using ICP-MS, and the concentrations of selected elements were evaluated by statistical factor analyses. We also calculated metal-enrichment factors and geoaccumulation indices and constructed spatial-distribution maps.Mercury (Hg) was the heaviest pollutant, with concentrations exceeding 4 mg/kg. Silver (Ag) was the second most important pollutant, with constantly increasing values. The average concentrations of the most toxic elements were comparable to those found in sediments of other ports throughout the world, and their toxicity ranged from threshold values [chromium (Cr), arsenic (As)] and midrange-effect values [cadmium (Cd), lead (Pb), copper (Cu), zinc (Zn), nickel (Ni)] to extreme-effect values (Hg). Metal pollution has decreased during recent decades, except for Ag and barium (Ba).     

Rapid secular variation recorded in thick Eocene flows from the Absaroka Mountains of northwest Wyoming

Stable reversed remanence carried by pseudo-single-domain magnetite shows systematic direction changes in three thick ( 70m) Eocene basalt flows from the Absaroka Mountains of Wyoming. Three cores were collected at each of 24 sites in the lower flow, 26 sites in the middle flow, and nine sites in the upper flow. Cores in the two lower flows were oriented by sun compass and in the upper flow with a magnetic compass. Although remanent directions do not change smoothly through the entire thickness of the flows, portions of the record indicate that the field direction was changing as rapidly as 0.5° per year during remanence acquisition. Rough paleointensity estimates suggest that this behavior occurred while the field was in a stable reversed state rather than during a transitional period. Paleomagnetic studies of flows should avoid sampling the upper parts, because the declination record may be distorted by rotations of portions of the crust.