Axial and equatorial rotations of the Earth's cores associated with the Quaternary ice age     

Masao Nakada 《Physics of the Earth and Planetary Interiors》2006,154(2):113-147

The differential axial and equatorial rotations of both cores associated with the Quaternary glacial cycles were evaluated based on a realistic earth model in density and elastic structures. The rheological model is composed of compressible Maxwell viscoelastic mantle, inviscid outer core and incompressible Maxwell viscoelastic inner core. The present study is, however, preliminary because I assume a rigid rotation for the fluid outer core. In models with no frictional torques at the boundaries of the outer core, the maximum magnitude of the predicted axial rotations of the outer and inner cores amounts to ∼2° year⁻¹ and ∼1° year⁻¹, respectively, but that for the secular equatorial rotations of both cores is ∼0.0001° at most. However, oscillating parts with a period of ∼225 years are predicted in the equatorial rotations for both cores. Then, I evaluated the differential rotations by adopting a time-dependent electromagnetic (EM) torque as a possible coupling mechanism at the core-mantle boundary (CMB) and inner core boundary (ICB). In a realistic radial magnetic field at the CMB estimated from surface magnetic field, the axial and equatorial rotations couple through frictional torques at the CMB, although these rotations decouple for dipole magnetic field model. The differential rotations were evaluated for conductivity models with a conductance of 10⁸ S of the lowermost mantle inferred from studies of nutation and precession of the Earth and decadal variations of length of day (LOD). The secular parts of equatorial rotations are less sensitive to these parameters, but the magnitude for the axial rotations is much smaller than for frictionless model. These models, however, produce oscillating parts in the equatorial rotations of both cores and also in the axial rotations of the whole Earth and outer and inner cores. These oscillations are sensitive to both the magnitude of radial magnetic field at the CMB and the conductivity structure. No sharp isolated spectral peaks are predicted for models with a thin conductive layer (∼200 m) at the bottom of the mantle. In models with a conductive layer of ∼100 km thickness, however, sharp spectral peaks are predicted at periods of ∼225 and ∼25 years for equatorial and axial rotations, respectively, although these depend on the strength of radial magnetic field at the CMB. While the present study is preliminary in modelling the fluid outer core and coupling mechanism at the CMB, the predicted axial rotations of the whole Earth may be important in explaining the observed LOD through interaction between the equatorial and axial rotations.  相似文献   

Advanced Micro-XRF Method to Separate Sedimentary Rhythms and Event Layers in Sediments: Its Application to Lacustrine Sediment from Lake Suigetsu,Japan     

Nagayoshi Katsuta  Masao Takano  Shin-ichi Kawakami  Shoji Togami  Hitoshi Fukusawa  Mineo Kumazawa  Yoshinori Yasuda 《Journal of Paleolimnology》2007,37(2):259-271

Event-related sedimentary layers, which are deposited occasionally due to volcanic eruptions, earthquakes or heavy rains, are often contained in the rhythmical sequences of lacustrine and marine sediments. We have developed an analytical method for separating the sedimentary rhythms and the event layers identified using the scanning X-ray analytical microscope (SXAM) and obtained sequential profiles of seven elements Al, Si, K, Ca, Ti, Mn, and Fe in the lacustrine sediment from Lake Suigetsu, Japan. Two types of event layers could be detected from the elemental composition of 33 layers of sediment: three known volcanic ash layers and 30 clay layers containing 12 turbidites. The recurrence interval of the latter, which may potentially be initiated and archived by locally important earthquakes, is estimated to be an average of 640 ± 160 years by using Sompi event analysis (SEA) based on an autoregressive (AR) model. After removing those portions that represented event layers from the elemental profiles, we obtained event-removed (ER) temporal profiles based on the tephrochronology of the three volcanic ash layers. The ER temporal profiles of manganese and iron, probably representing the siderite content, showed a millennial-scale variation in the Holocene that corresponded well with ice-rafting events in the North Atlantic.  相似文献   

Characteristics of deep currents off Cape Shiono-misaki before and after formation of the large meander of the Kuroshio in 1981     

Masao Fukasawa  Toshihiko Teramoto 《Journal of Oceanography》1986,42(1):53-68

Deep currents measured by moored current meters over the shelf-slope off Cape Shiono-misaki, Kii Peninsula during the period from 28 April, 1981 to 4 May, 1982 are analyzed to determine characteristics of the deep current before and after the large meander of the Kuroshio formed. The observed deep currents show some different characteristics between the periods before and after the formation of the large meander of the Kuroshio,i.e.:

1. The mean current direction over the shelf slope changed to westward after the meander was formed, though it was eastward at two offshore stations before the meander was formed.
2. The eddy kinetic energy, \(ke((\overline {u'^2 } + \overline {\upsilon '^2 } )/2)\) became large at all stations after the meander formed.
3. It appears that there were current variations in the period band shorter than 10 days which propagated offshore before the meander formed but inshore after the meander formed.
4. After the meander formed, the current variations with a period of O(25 days) were amplified at two of the three stations. The current variations in this period band showed high coherence among the three stations.

Data from tidal stations showed that sea level variations with a period of O(30 days) were also amplified along the south coast of Japan after the meander was formed. But sea level variations were not coherent with current variations in this period band.  相似文献   

Seasonal and Interannual Variation of DIC in Surface Mixed Layer in the Oyashio Region: A Climatological View     

Tsuneo?OnoEmail author  Hiromi?Kasai  Takashi?Midorikawa  Yusuke?Takatani  Kazuhiro?Saito  Masao?Ishii  Yutaka?W.?Watanabe  Katsuyuki?Sasaki 《Journal of Oceanography》2005,61(6):1075-1087

Eight-year observation results of DIC from 1996 to 2003 in the Oyashio region have been analyzed to obtain a climatological view of its seasonal variation and interannual variation. Data of DIC obtained by several institutes are synthesized to give a dataset with an uncertainty lower than 5 μmol/kg. The obtained climatology of NDIC seasonal variation in the Oyashio mixed layer shows a seasonal amplitude of 176 μmol/kg, with a maximum in January and a minimum in September. These features closely resemble those observed in the southern half of the western subarctic North Pacific (WSNP) including Station KNOT, although the timing of the NDIC maximum is slightly advanced in the case of the Oyashio. Analysis using a quasi-conservative tracer Cp0 (NDIC - 106NP) shows that among 176 μmol/kg of NDIC seasonal variation, only 16 μmol/kg is attributed to hydrographic processes while the remaining 160 μmol/kg is attributed to biological processes. The Cp0 value in the Oyashio mixed layer also resembles that of the WSNP mixed layer during the months May to November, suggesting further resemblance of the Oyashio water mass to that of WSNP in terms of carbon dynamics. The present results also suggest that a single data obtained in Oyashio mixed layer contains 30 μmol/kg of potential uncertainty for the representativity of this region, which leads to a note about a need to treat with caution results obtained by a single observation in this region.  相似文献   

The causes of forest cover loss in the hill forests in Bangladesh   总被引：1，自引：0，他引：1  

Md. Abdus Salam  Toshikuni Noguchi  Masao Koike 《GeoJournal》1999,47(4):539-549

The Hill Forests in Bangladesh have been depleted and degraded in volume, area, and quantity, thus requiring urgent forest protection by identifying the causes of forest loss. This study seeks to identify the fundamental causes of the shrinking forest cover in the Hill Forests in Bangladesh. The results indicate four sets of causes: (i) indigenous forest dwellers, having their own types of problems; (ii) migrants, who, because of problems in their places of origin, have decided to move to the forests; (iii) the timber industry, which, legal or not, are cutting too many trees; and (iv) the government through its Forest Department which is not able or willing to implement suitable policies to regulate the cutting trees and to prevent illegal cutting. Because it is a time consuming task to mitigate the first and second sets of factors, we recommend to involve forest dwellers in forestry practices as much as possible and taking necessary steps to alleviate the third and fourth sets and thereby reduce the rate of forest depletion. Accordingly, a number of strategies that should be adopted to halt the loss of remaining forest cover are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Effect of the viscoelastic lithosphere on polar wander speed caused by the Late Pleistocene glacial cycles     

Masao Nakada 《Geophysical Journal International》2000,143(1):230-238

Previous studies of the wander of the rotation pole associated with the Late Pleistocene glacial cycles indicate that the predicted polar wander speed is sensitive to the density jump at the 670 km discontinuity, the thickness of the elastic lithosphere, and the lower mantle viscosity. In particular, the M1 mode related to the density jump at 670 km depth has been shown to contribute a dominant portion of predicted polar wander speed for sufficiently small lower mantle viscosities. In this study, we examine the sensitivity of polar wander to variations in the viscosity of the viscoelastic lithosphere using simplified compressible Maxwell viscoelastic earth models. Model calculations for earth models with a viscoelastic lithosphere of finite viscosity indicate that the contribution of the M1 mode is similar to those associated with the density discontinuity at the core–mantle boundary (C0 mode) and the lithosphere (L0 mode). We speculate that this is due to the interaction between the M1 mode and the transient mode associated with the viscoelastic lithosphere, which reduces the magnitude of polar wander rates. Therefore, the M1 mode does not contribute a dominant portion of the predicted polar wander speed for earth models with a viscoelastic lithosphere of finite viscosity. In this case, predictions of polar wander speed as a function of lower mantle viscosity exhibit the qualitative form of an 'inverted parabola', as predicted for the J ˙₂ curve. We caution, however, that these results are obtained for simplified earth models, and the results for seismological earth models such as PREM may be complicated by the interaction between the M1 mode and the large set of transient modes.  相似文献   

Trends of water resource development and utilization in arid north-west China   总被引：12，自引：0，他引：12  

Q. Feng  G. D. Cheng  M. K. Masao 《Environmental Geology》2000,39(8):831-838

 From an analysis of the current water resources and their development and utilization in arid north-west China, the authors conclude the extent of channelled water accounts for only 56.0% of the total, exploitable surface-water resources of arid north-west China. The utilization ratio of canal systems is 42%, and farmland use is 0.8. When the ground and surface waters of river basins in the region are comprehensively developed, the channelled water will reach its climax, accounting for 80% of the total, exploitable surface-water resources, which would constitute a 91% increase over current levels in surface-water resource development. In the future, the utilization ratio of canal system as well as the utilization ratio of farmland water will reach 0.9 with the help of scientific and technological advancements. The channelled water is the same as the comprehensive development and utilization stages, but the total water use will be increased by 247×10⁸ m³, and will reach 756.8×10⁸ m³, accounting for 88.2% of the total, exploitable surface-water resources in arid north-west China. Also, the authors suggest that the scientific and technological measures to increase the water-use ratio include improving management, strengthening protection of water resources and the environment, and increasing studies of water saving techniques. Received: 11 January 1999 · Accepted: 6 July 1999  相似文献   

山区林地粗糙度的推求   总被引：2，自引：2，他引：0  

冯起  张艳武  苏永红  司建华  常宗强  席海洋  MIKAMI Masao 《中国沙漠》2006,26(6):1046-1051

应用实测资料计算复杂地面森林冠层的动量、潜热和粗糙参数以及动量总体输送系数（CM）、热量总体输送系数（CH）和水汽总体输送系数（CE）的参数。使用最大相关法计算本地风的粗糙度Z0M与零通量面d0M,同样结果较满意。在假设θS=θRAD的情况下计算水汽粗糙度Z0H,表明斯坦顿系数S-1t=ln（Z0M/Z0H）/K比过去的调查结果大。温度的零通量计算结果为d0H=（11.9）,该值与d0M值（=12.8）相近。通过修改后方程计算表面湿度参数α,表面湿度参数α的值为0.61,该值与冠层的相对湿度相近。因此α的值可以用冠层顶部的相对湿度来计算。计算森林区粗糙度的方法和模型可推广应用到黑河流域。  相似文献   

Modeling low salinity waters along the coast around Japan using a high-resolution river discharge dataset     

L. Shogo Urakawa  Masao Kurogi  Kei Yoshimura  Hiroyasu Hasumi 《Journal of Oceanography》2015,71(6):715-739

  相似文献   

Contamination status of POPs and BFRs and relationship with parasitic infection in finless porpoises (Neophocaena phocaenoides) from Seto Inland Sea and Omura Bay, Japan     

Isobe T  Oshihoi T  Hamada H  Nakayama K  Yamada TK  Tajima Y  Amano M  Tanabe S 《Marine pollution bulletin》2011,63(5-12):564-571

Contamination status of brominated flame retardants (BFRs) and persistent organic pollutants (POPs) in blubber of finless porpoises (Neophocaena phocaenoides) stranded along the coasts of Seto Inland Sea and Omura Bay in Japan were investigated. Levels of PCBs, DDTs and CHLs were significantly higher than those of HCHs, HCB, PBDEs and HBCDs. Concentrations of PBDEs and HBCDs, as well as organochlorine compounds in males increased with body length (p<0.05). Among 14 PBDE congeners analyzed, BDE-47 was the predominant, which is similar to those generally reported in biota. PBDEs, HBCDs and PCBs showed no obvious temporal trend in concentrations during the study period, suggesting continuous environmental release of these chemicals. On the other hand, levels of DDT, CHLs and HCHs have decreased. Concentrations of PCBs in liver trematode infected individuals were significantly higher than those in not infected individuals, implying there could be a relationship between contaminant levels and parasitic infection.  相似文献