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1.
Variations in the ratio of18O/16O as measured in shells of marine calcareous microfossils are primarily dominated by changes in global ice volume; hence these variations provide a set of global time lines in deep-sea sediments. It is likely that the timing of major changes in oxygen isotope values is strongly influenced, if not controlled, by variations in the geometry of the Earth's orbit. Since the variation of orbital parameters can be accurately calculated, the opportunity exists for transforming this orbital chronology into a geological chronology.Through careful correlation of oxygen isotope records in a set of deep-sea cores from the sub-Antarctic, South Atlantic and equatorial Pacific, we have assembled a composite isotopic section spanning the last 750,000 years with an average sedimentation rate of 2.3 cm/1000 years. A new chronology for this time period was developed by adjusting the ages of the oxygen isotope stage boundaries in this composite section so as to extend the consistent phase relationships that exist between variations in oxygen isotope ratios and changes in obliquity and precession during the last 300,000 years to the entire 750,000-year record. Previously identified difficulties in phase locking precession with the filtered isotopic signal between 365,000 and 465,000 years B.P. have been resolved with the recognition that precessional variations have an average period of 19,000 years and not 23,000 years during this interval. Since this new age model yields the best match between variations in obliquity and precession and their corresponding frequency components in the oxygen isotope record, we believe that it presents the most accurate chronology yet developed for deep-sea sediments.With this new age model providing the time control, power spectral analyses of South Atlantic and sub-Antarctic chemical and biotic indices show that there is a strong tendency for variance to be concentrated at frequencies corresponding to periods of ～ 100,000, 41,000 and 23,000 years. 相似文献
2.
K. Perrot J. Francheteau M. Maia C. Tisseau 《Earth and Planetary Science Letters》1998,160(3-4):593-607
The distributions of crustal depths as a function of age have been analysed for the southeast Pacific region, along the East Pacific Rise, between the Equator and the Easter microplate (23°S). Using age data and a new compilation of bathymetric data, subsidence rates (for both eastern and western flanks), asymmetry of subsidence and zero-age depths, are computed within flow-line corridors on the Nazca and Pacific plates. Variations of subsidence rates, axial depths and subsidence asymmetry are examined both in space (within corridors) and time (within several age intervals). The variability in these parameters along the strike of the East Pacific Rise is systematic and serves to define several orders of ridge segmentation. The largest variations of these parameters are correlated with the large-scale segmentation of the ridge axis (i.e. transform faults and very large overlapping spreading centres) and are interpreted as related to variations in mantle heterogeneities mainly dependent upon temperature. Smaller variations of subsidence parameters are correlated with second- (and sometimes third-) order segmentation of the ridge axis, which could be related to variations in axial magmatic supply. Across-strike variations of subsidence suggest the existence of small lateral temperature and density variations in the mantle. When analysing the slope of the distribution of depth versus square root of age within corridors, we have observed the existence of changes in the slope which occur at specific age limits. We have estimated the subsidence over different age ranges in order to determine the temporal evolution of subsidence parameters (rates and asymmetry). Such an analysis may inform on the past axial segmentation and on the persistence of axial discontinuities in time. A linear relationship between subsidence rates and axial depths is determined for each age range and suggests that shallower segments subside faster than deeper segments. Although a similar, statistically defined linear relationship exists for any mid-ocean spreading ridge (both for intermediate or fast–ultrafast spreading), the resultant slopes of this relationship vary from ocean to ocean and show that this relationship is not universal over all oceans. 相似文献
3.
Used to test the Milankovitch theory over the last glacial-interglacial cycles, the Louvain-la-Neuve two-dimension Northern Hemisphere climate model shows that orbital and CO2 variations induce, in the climate system, feedbacks sufficient to generate the low frequency part of the climatic variations over the last 200 kyr. Initiation and termination of glacial cycles cannot indeed be explained without invoking both the fast feedbacks associated with atmospheric processes (water vapor, cloud, snow and sea ice) and the slower feedbacks associated with coupling to other parts of the climate system, in particular the land ice-sheet buildup and disintegration. This model shows that long-term changes in the Earth's orbital parameters lead to variations in the amount of solar radiation received at the top of the atmosphere, which in turn act as a pacemaker for climatic variations at the astronomical frequencies, through induced albedo-temperature and greenhouse gases-temperature feedbacks. Spectral analysis of the Northern Hemisphere global ice volume variations simulated under both insolation and CO2 forcings reproduces correctly the relative intensity of the peaks at the orbital frequencies as seen in SPECMAP data. Except for variations with time scales shorter than 5 kyr, the simulated long-term variations of total ice volume are comparable to that reconstructed from deep-sea cores. For example, the model simulates glacial maxima of similar amplitudes at 134 kyr BP and 15 kyr BP, followed by abrupt deglaciations. 相似文献
4.
TIAN Jun WANG Pinxian CHENG Xinrong WANG Rujian & SUN Xiangjun . State Key Laboratory of Marine Geology Tongji University Shanghai China . Institute of Geology Geophysics Chinese Academy of Sciences Beijing China . Institute of Botany Chinese Academy of Sciences Beijing China 《中国科学D辑(英文版)》2005,48(10)
The variations of the Earth’s geometry (ETP) pre-dominate climate changes such as monsoon on the Earth[1], serving as its external forcing. The loess/ paleosol sequence in Central China provides a good record of terrestrial deposition to study the evolution of the east Asian monsoon[2―4]. However, the deep sea deposition, due to its high resolution dating and abun-dant climate proxies, should be able to provide more climatic information in the geological time, such as the forcing mechanis… 相似文献
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6.
Based on the published analysis of the average monthly variations in solar activity and temperature of the upper atmosphere in the region of the mesopause and lower thermosphere (after elimination of the average long-term variations during different 11-year cycles), it was indicated that the periods and amplitudes of the observed quasibiennial variations monotonically decrease in the course of time. The regularity of these variations is described by the Airy function, which represents a wave train with decreasing amplitude and period and reflects cyclic hydrodynamic processes in the Sun’s interior. A spectral analysis of the quasibiennial variations modelly described by the Airy function has been performed. It has been revealed that the period amplitudes near the average value for 2.25 years (27 months) are distributed normally with a dispersion of ～0.5 years. According to several publications, similar periods are obtained by analyzing measurements of long-term variations in solar activity and parameters of the lower and middle atmosphere. This indicates that the values of the periods are obtained randomly. Therefore, a standard Fourier analysis does not make it possible to determine a real character of the quasibiennial variations since a real physical process is not revealed in the course of this analysis. 相似文献
7.
Yu. A. Nagovitsyn 《Geomagnetism and Aeronomy》2014,54(6):673-679
Prolonged variations in the duration of the Schwabe-Wolf (～11 years) and Suess (～200 years) cycles have been analyzed using different experimental data. It was shown that the duration of the Schwabe-Wolf cycle on a 2000-year time scale varied monotonically (on average, increasing) and cyclically (with a period of several hundred years); periods of 10.4, 11.0, and 11.4 years predominate on the occurrence frequency histogram. The Suess cycle duration was 200–290 years during the Holocene and tended to increase in the past. This was accompanied by cyclic variations with a period of 2300–2500 years corresponding to the Hallstatt cycle. Arguments for the assumption that the Suess cycle duration decreased by a factor of more than 1.5 over the past half billion years are presented. This may indicate that the solar rotation characteristics and convection zone parameters varied on long time scales during the Sun’s evolution on the main sequence. 相似文献
8.
为了研究1976年唐山地震的磁效应,本文在文献[1]的基础上,利用北京测区六年(1975——1981)的磁测资料,分析了北京地区地磁场长期变化的局部差异,正常(无强震)时期地磁统计量的变化特性,以及长期变化局部差异对地磁统计量的影响.正常时期与地震前后地磁统计量的对比分析表明,唐山地震对北京地区地磁场总强度统计量的影响是显著的.通过不同区域测点、测线的各种组合,计算了地震前后统计量的空间分布,以确定测区信息最强的区域.唐山地震在北京地区所产生的磁效应的统计性质如下:1.异常信息不是短期的波动,而是呈趋势性变化,其持续时间至少一年;2.离震中较近的 S 区异常显著,其主要根据是,地磁统计量 Smj,bsn和Fk2在 S 区变化显著.特别是统计信息的局部差异与长期变化明显不同,前者呈东西分布,后者主要呈北南走向;3.趋势性异常变化的平均空间差异随时间的变化在测区总体并不显著,但在 S 区这种差异的时间变化,在震前1976年3——6月却是显著的. 相似文献
9.
I. M. Demina Yu. G. Farafonova A. Sas-Uhrynowski E. Welker 《Geomagnetism and Aeronomy》2006,46(1):129-138
The model of the main geomagnetic field sources, including 12 more dipoles in addition to the main dipole, is presented. The source parameters have been determined for the 100-year-long period at an interval of 5 years. The problem is solved using the iteration method proposed and developed by the authors. Six more sources have been included in the iteration process at its current step. This made it possible to substantially smooth the time variations in the dipole parameters obtained previously and, on the other hand, to describe all global anomalies of the main geomagnetic field using this model. A change in the parameter values can be approximated by rather smooth functions describing specific features of development of the sources operating for 20–30 years. However, the short duration of the obtained series (21 points) makes the problem of prediction substantially more difficult. The parameters of 13 dipoles, extrapolated for 2000 using the linear prediction filter, are in good agreement only with the general development of the sources. 相似文献
10.
O. Yu. Vinogradova 《Izvestiya Physics of the Solid Earth》2012,48(7-8):572-586
The load Love numbers, Green’s functions, and oceanic tidal loading effect over the territory of Europe are calculated for the PREM and IASP91 models of the Earth and CSR3 ocean-tide model. Computations were carried out for the reference periods of 1 s, 12 h, and 24 h. It is established that the corrections to gravity acceleration for the M2 wave significantly differ in different models. 相似文献
11.
N. I. Alekseevskii D. V. Magritskii P. K. Koltermann P. A. Toropov D. I. Shkol’nyi P. A. Belyakova 《Water Resources》2016,43(1):1-14
Inundatios on the Black Sea coast of Krasnodar krai between 1945 and 2013 have been analyzed. The main genetic types of inundations on the coast have been identified. The specific features and regularities of inundation wave transformation along the rivers and over time have been studied. Seasonal and maximal runoff of Black Sea rivers has been analyzed over a long-term period. Regularities in the variations of the number of inundatios and their characteristics over the coastal area have been revealed both at the annual and long-term scales. Quantitative estimates are given to the hazard and damage to the population and economic activity due to inundations in the valleys of Black Sea rivers. 相似文献
12.
Roger Kantin Maria G.Z. Baumgarten Marcelo Cabeda Antonio C. Beaumord Tabajara L. De Almeida 《Marine pollution bulletin》1981,12(2):50-53
The concentration of anionic detergents, polyphosphates, ammonia, seston and dissolved oxygen have been determined in a small bay near the principal sewage discharge of the city of Rio Grande. The results show great variations in the concentrations, as a function of the time of the day. The highest concentrations in anionic detergents were observed between 09.00 and 10.00 in the morning, and from 18.00 to 21.00. The other parameters present an erratic distribution, except the dissolved oxygen, showing a net increase in the second half of the sampling period. 相似文献
13.
The effect of the mutual orientation of the Poynting vector P of the electromagnetic energy density in the solar wind and the vector M of the Earth’s magnetic moment (taking into account its orbital and diurnal motions) on the geomagnetic activity has been
examined for the first time using the measurements of the solar wind parameters on the Earth orbit in 1963–2005. The component
P
m of the vector P along the vector M is shown to have a pronounced annual variation with the extrema in November and May and a diurnal variation with the extrema
at ∼6 and 18 UT. The phases of the variations are shown to be determined only by the geometric parameters and are independent
of the sign of the sector structure of the interplanetary magnetic field. The experimental data on the planetary and high-latitude
geomagnetic activity, which is a response to changes in the orientation of P relative to M, are presented. The power of the sources of the electromagnetic energy of the solar wind during strong geomagnetic disturbances
is also estimated. 相似文献
14.
D. Altadill 《Annales Geophysicae》1996,14(7):716-724
The presence and persistence of an 18-day quasi-periodic oscillation in the ionospheric electron density variations were studied. The data of lower ionosphere (radio-wave absorption at equivalent frequency near 1 MHz), middle and upper ionosphere (critical frequencies f0E and f0F2) for the period 1970–1990 have been used in the analysis. Also, solar and geomagnetic activity data (the sunspot numbers Rz and solar radio flux F10.7 cm, and aN index respectively) were used to compare the time variations of the ionospheric with the solar and geomagnetic activity data. Periodogram, complex demodulation, auto- and cross-correlation analysis have been used. It was found that 18-day quasi-periodic oscillation exists and persists in the temporal variations of the ionospheric parameters under study with high level of correlation and mean period of 18–19 days. The time variation of the amplitude of the 18-day quasi-periodic oscillation in the ionosphere seems to be modulated by the long-term solar cycle variations. Such oscillations exist in some solar and geomagnetic parameters and in the planetary wave activity of the middle atmosphere. The high similarities in the amplitude modulation, long-term amplitude variation, period range between the oscillation of investigated parameters and the global activity of oscillation suggests a possible solar influence on the 18-day quasi-periodic oscillation in the ionosphere. 相似文献
15.
The variations in the rigidity spectrum and anisotropy of cosmic rays in December 2006 have been studied based on the surface measurements of the cosmic ray intensity at the global network of stations, using the method of global spectrographic survey. It has been indicated that the highest degree of anisotropy (to ～50%) with the maximal intensity of particles with a rigidity of 4 GV in the direction from the Sun (an asymptotic direction of about ?25° and 160°) was observed at 0400 UT on December 13. The parameters of the cosmic ray rigidity spectrum, which reflect the electromagnetic characteristics of the heliospheric fields during the studied period, have been determined when the surface and satellite measurements of protons in the energy range from several megaelectronvolts to several tens of gigaelectronvolts were jointly analyzed. The observed anisotropy and variations in cosmic rays in a wide energy range have been explained based on an analysis of the results. 相似文献
16.
Coastal erosion is an immense economic and social problem that has been receiving increased attention in recent years. A number of devices have been developed to determine the sediment stability in coastal areas: laboratory and field flumes; a range of different erosion devices; shear vanes and fall cone penetrometers. The cohesive strength meter (CSM) erosion device was developed to determine in situ the temporal and spatial variations in the erosion threshold of muddy intertidal sediments. Technological developments have enabled considerable improvements to be made to the original design over the last 15 years. 相似文献
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18.
The continuous spatial-temporal model of variations in the main geomagnetic field in the 20th century has been elaborated. All available data—from the navigation to the satellite surveys at the beginning and end of the century, respectively—have been used to construct the model. Since the accuracy of measurements was different during the century and the data are nonuniformly distributed over the Earth’s surface, the methods for regulating solutions based on global parameters of the magnetic field and its secular variation, invariant on the simulation interval, have been used to correct the model. The secular variation model has been represented as the sum of the models obtained by means of expansion in terms of natural orthogonal components. The conclusions that the character of field variations is complex have been made and the spatial and temporal characteristics of the secular variations of different origin have been estimated based on the simulation results. 相似文献
19.
Piotr Tucholka 《Earth and Planetary Science Letters》1980,48(2):379-384
A simple method of calculating running means over different intervals within palaeomagnetic records has been used to identify short-period secular variations of the geomagnetic field. The records from Polish lake sediments reveal variations in declination with a period between 290 and 372 years. The periodicity of variations in the inclination has been estimated to be between 522 and 670 years. 相似文献
20.
N. A. Barkhatov S. E. Revunov G. G. Vertogradov V. G. Vertogradov V. A. Valov V. P. Uryadov 《Geomagnetism and Aeronomy》2006,46(1):84-93
The algorithm for predicting one of the main parameters of the ionospheric HF radio channel—maximum observed frequency (MOF)—for the interval 0.5–3 h has been synthesized based on the technology of artificial neural networks (ANNs). The data of oblique-incidence LFM sounding obtained on the Inskip (England)-Rostov-on-Don path have been used for this purpose. The studies have been performed under different geophysical conditions. The relation of MOF to the variations in the key parameters of the solar wind and IMF, responsible for the succession of development of magnetospheric-ionospheric disturbances leading to a change in the HF radiocommunication conditions, has been established. The time scales of the ionospheric response have been determined. The practical value of the performed work consists in that the obtained results are used to increase the reliability of ionospheric HF radiocommunication. 相似文献