Library

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Regional Correlation Analysis between Seismic Heterogeneity in the Lower Mantle and Subduction in the Last 180 Myr: Implications for Mantle Dynamics and Rheology (1998)
    Springer
    Pure and applied geophysics 151 (1998), S. 527-537 
    Details
    ISSN: 1420-9136
    Keywords: Key words: Correlation analysis, seismic velocity heterogeneities, subduction history.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract. —We have carried out a regional correlation analysis between the seismic structure of the lower mantle and the reconstructions of subduction sites in the past 180 Myr with the aim of estimating individual styles of slab motion over different parts of the earth. The correlation patterns obtained for three subduction branches (West Pacific, East Pacific and Alpine-Himalayan) are remarkably different. In the West Pacific, the subducting slabs tend to be stagnant beneath the 660-km discontinuity, while basically no subducted lithosphere has been detected below the depth of 1000 km. In contrast, the lithosphere subducted beneath the Americas seems to penetrate through the lower mantle continuously, showing correlation peaks at depth intervals of 800–1100 km and 1900–2500 km. In the Alpine-Hi malayan region, significant correlation has been found below the 660-km discontinuity for recent subduction and in the mid-mantle for subduction younger than 120 Myr. An increase in the correlation close to the core-mantle boundary nevertheless indicates that, under certain circumstances, the slabs can reach the bottom of the mantle in the West Pacific and in the Alpine-Himalayan regions as well. The correlation peak at a depth of around 1000 km is common to all the subduction branches. However, its depth rather varies for different subduction zones and, thus, it is not clear whether this correlation maximum may be associated with a global mid-mantle discontinuity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000240050127
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    New Perspectives on Mantle Dynamics from High-resolution Seismic Tomographic Model P1200 (1998)
    Springer
    Pure and applied geophysics 151 (1998), S. 503-525 
    Details
    ISSN: 1420-9136
    Keywords: Key words: Geodynamics, seismic tomography, spectral analysis, inferences of viscosity from geoid, mantle convection.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —Recently a high-resolution tomographic model, the P1200, based on P-wave travel times was developed, which allowed for detailed imaging of the top 1200 km of the mantle. This model was used in diverse ways to study mantle viscosity structure and geodynamical processes. In the spatial domain there are lateral variations in the transition zone, suggesting interaction between the lower-mantle plumes and the region from 600 km to 1000 km. Some examples shown here include the continental region underneath Manchuria, Ukraine and South Africa, where horizontal structures lie above or below the 660 km discontinuity. The blockage of upwelling is observed under central Africa and the interaction between the upwelling and the transition zone under the slow Icelandic region appears to be complex. An expansion of the aspherical seismic velocities has been taken out to spherical harmonics of degree 60. For degrees exceeding around 10, the spectra at various depths decay with a power-law like dependence on the degree, with the logarithmic slopes in the asymptotic portion of the spectra containing values between 2 and 2.6. These spectral results may suggest the time-dependent nature of mantle convection. Details of the viscosity structure in the top 1200 km of the mantle have been inferred both from global and regional geoid data and from the high-resolution tomographic model. We have considered only the intermediate degrees (l = 12–25) in the nonlinear inversion with a genetic algorithm approach. Several families of acceptable viscosity profiles are found for both oceanic and global data. The families of solutions for the two data sets have different characteristics. Most of the solutions asociated with the global geoid data show the presence of asthenosphere below the lithosphere. In other families a low viscosity zone between 400 and 600 km depth is found to lie atop a viscosity jump. Other families evidence a viscosity decrease across the 660 km discontinuity. Solutions from oceanic geoid show basically two low viscosity zones one lying right below the lithosphere; the other right under 660-km depth. All of these results bespeak clearly the plausible existence of strong vertical viscosity stratification in the top 1000 km of the mantle. The presence of the second asthenosphere may have important dynamical ramifications on issues pertaining to layered mantle convection. Numerical modelling of mantle convection with two phase transitions and a realistic temperature- and pressure-dependent viscosity demonstrates that a low viscosity region under the endothermic phase transition can indeed be generated self-consistently in time-dependent situations involving a partially layered configuration in an axisymmetric spherical-shell model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000240050126
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Microbial activities in soils of a healthy and a declining reed stand (2000)
    Springer
    Hydrobiologia 418 (2000), S. 45-55 
    Details
    ISSN: 1573-5117
    Keywords: reed dieback ; eutrophication ; decomposition processes ; denitrification ; carbon dioxide ; methane ; nitrous oxide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Microbial processes were investigated in the soil of a declining, more eutrophic (Rožmberk West) and a healthy looking, less eutrophic (Rožmberk East) freshwater reed stand. Soil was sampled monthly from June to September 1997. Glucose induced carbon dioxide (CO2) production in oxic and anoxic conditions, methane (CH4) production, nitrification and denitrification activities were measured in laboratory conditions in suspensions prepared from homogenised soil samples. Within a stand the proportion of anaerobic (as opposed to aerobic) microbial activity was greatest in June. Potential methanogenesis was highest in June and decreased later in both stands. Methane production was approximately the same in June at both stands but it was higher at Rožmberk East than at Rožmberk West stand in later months. Denitrifying activity was higher in August than July at both stands. Nitrifying activity was undetectable at both stands over the entire study period. Generally Rožmberk West was more anaerobic than Rožmberk East, with lower redox potential, higher amounts of oxygen-consuming organic matter and a lower ratio of CO2 production in oxic conditions to CO2 production in anoxic conditions. Microbial activity was apparently restricted at Rožmberk West stand in comparison to Rožmberk East. The shift from aerobic to anaerobic microbial metabolism and a coinciding restriction of metabolic activities at Rožmberk West are thought to be indicative of a strengthened oxygen stress in the soil, associated with accumulation of metabolites toxic to both the microorganisms and the reed. Possible links between eutrophication, microbial characteristics and reed performance are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003836015918
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...