ALBERT

Beschreibung: The use of stable isotopes as climate proxies is widely accepted for climate reconstruction. Re-establishing climate signals, e.g. temperature, from isotope values of biological materials requires some knowledge of the system’s response behaviour. The related problems are discussed in conjunction with stable isotopes of two different terrestrial archives: carbon isotope data of tree rings from southern Germany and oxygen isotope data of diatoms from Lake Holzmaar, Germany. Carbon isotope temperature coefficients (Δδ13C/ΔT) derived from tree rings were chosen as an example for non-linear transformation of environmental signals through biological systems explaining negative and positive temperature coefficients. Thin radial tree ring sections taken from tree rings of different species (poplar, beech and oak) show carbon isotope variations of up to 3‰ with a characteristic, annually recurring isotope pattern. This behaviour is discussed in view of time resolution, isotope signature conservation and the question of storage and remobilisation of photosynthates with time. For Lake Holzmaar it is shown that isotope proxy signals derived from diatoms may not be unambiguously translated into abiotic environmental forcing factors, such as for example temperature. Corresponding measurements reveal that the isotopic input signal varies considerably and nonlinearly with temperature.

Beschreibung: In this study, we present an interpretation of seismic refraction profiles from the PISCO 94 experiment in northern Chile. As the PISCO experiment was a combined active and passive seismological study, we also discuss results of the passive part in the context of the seismic refraction model. Previous seismic refraction and gravimetric studies indicate a maximum crustal thickness of about 70 km beneath the Pre- and Western Cordillera. The new seismic refraction data lead to a differentiated image of the Andean crust which shows strong varying characteristics. The crustal discontinuities (up to five are detected) dip from W to E. The upper crust has a thickness of 18 km (Precordillera) to 23 km (magmatic arc) underlain by the recent middle crust down to 35-45 km where the velocity increases to about 7 km/s at its base. This crustal level is interpreted as old continental lower crust and its base as blurred continental (paleo) Moho. Beneath the Precordillera, a strong discontinuity at 70 km depth with a velocity increase to about 8 km/s was detected, interpreted as the recent geophysical Moho. For the magmatic arc, this deep discontinuity could not be found by active seismic measurements. The tomographic models of the seismological studies, in general, confirm the seismic refraction results. Anomalously high vp/vs rations in the deeper part of the forearc indicate a hydrated mantle wedge consisting of serpentine and amphibole-bearing peridotite and the 70 km discontinuity is interpreted as the boundary between these two different stages of the hydrated mantle wedge. A zone of high attenuation (Qp) and high vp/vs ratios beneath the magmatic arc coincides with the low velocity zones and indicates partially molten rocks from a depth of 20 km down to the asthenospheric wedge.

Beschreibung: Combined geological, structural, petrological and radiometric investigations provide constraints for the polyphase Variscan tectonothermal evolution of the Pulo de Lobo Zone in SW Spain. First phase deformation structures are intensively overprinted and only preserved in microlithons of the second Variscan phase. As Late Devonian overstep sequences are undeformed by the first Variscan deformation, this phase can be dated around the Frasnian/Famennian boundary. It argues for an early accretion of the Pulo do Lobo Zone to the Ossa-Morena Zone which was terminated in the late Devonian. During the Early Carboniferous the Pulo do Lobo Zone was successively deformed and sandwiched inbetween the Ossa-Morena Zone and the South Portuguese Zone. Oblique convergence resulted in a prominent phase of transpression. This stage comprises the second and third Variscan deformation phase, both with SSW directed thrusting and left-lateral displacement. Synkinematic intrusions started to ascend contemporaneously. Their final emplacement occured between the second and third deformation phase, cooling of the intrusions outlasted the third Variscan phase. The regional metamorphism of the Pulo do Lobo Zone reaches in the basal units upper greenschist to lower amphibolite facies conditions. The metamorphism is connected with the second Variscan deformation phase. As it is closely associated with a wide-spread contact metamorphism, the Spanish part of the Pulo do Lobo Zone appears widely underlain by synkinematic intrusions. The timing of transpression in the Pulo do Lobo Zone can be constrained by 40Ar/39Ar and 87Rb/86Sr isotope dates of synkinematic intrusions which range between 337 Ma and 328 Ma. They are interpreted as cooling ages and can be related to microstructural observations in the contact aureole of the intrusives. According to this Variscan transpression. low-grade metamorphism and magmatism occured almost contemporaneously in the late Visean and was terminated by the end of the Early Carboniferous. The Variscan deformation of the Pulo do Lobo Zone ended with left-lateral movements along previously generated thrusts during the late Carboniferous.

Beschreibung: Abstract: A new experimental technique for the study of deformation processes in rocks in transmitted light under the microscope uses a modified sapphire anvil cell in which one of the sapphire anvils can be rotated and thus permit the deformation of a thin solid sample disc. The deformation can be observed during the experiment through the anvils using a polarizing microscope stage. The technique is applicable up to 450 Celsius degree and up to 2 GPa confining pressure in the central part of the sample.

Beschreibung: Short-period, three-component recordings of the seismic wave field of peaceful nuclear explosions recorded on deep seismic sounding profiles (Quartz and Ruby-I, collected in 1984 and 1988, respectively) in northern Russia are used to constrain the nature of the high-frequency teleseismic Pn phase, which can be observed for receiver distance of 〉3000 km. We suggest that this phase is caused by velocity fluctuations in the upper mantle acting as scatterers. To test this hypothesis and to determine the properties of the upper mantles scatterers, the elastic reflectivity method (one-dimensional isotropic models) was used to model the coda of the high-frequency teleseismic Pn phase. Both the observed data and the synthetic record sections were analyzed by examining the coda decay rates of the teleseismic Pn phase at 5 Hz. Synthetic seismograms are computed for different models based on the global model IASP91 with an added zone of randomly distributed velocity fluctuations (lamellae) just below the crust-mantle boundary. These models may be characterized by the thickness of the scattering layer L, the vertical heterogeneity correlation length a, and the heterogeneity standard deviation sigma. The numerical simulation of the wave propagation in these models generated a high-frequency teleseismic Pn. Comparing the coda decay rates of synthetic seismograms with the observation, we tried to constrain the properties of the velocity model containing fluctuations in the upper mantle, L, a and sigma. In the distance range of the uninterfered high-frequency teleseismic Pn phase beyond 1300 km, the coda decay rates for our best fitting model are similar to the observed ones. This model has a 75 km thick zone of scatterers below the Moho, containing lamellae with an average thickness of 2 km and a RMS velocity perturbation of 5%. The modeling results show also that two other possible models, the whispering gallery phase along the crust-mantle boundary and scattering in the lower crust, taken alone are not able to explain the coda properties of the high-frequency teleseismic Pn phase.

Beschreibung: Single zircons from two orthogneiss complexes, the 'Grey Gneiss' and 'Red Gneiss', the lowermost tectonic units in the Erzgebirge, were dated. The zircon ages document a distinct late Proterozoic phase of granitoid magmatism, similar in age to granitoids in the Lusatian block farther north-east. However, Palaeozoic deformation as well as medium pressure metamorphism (approx 8 kbar/600-650 degrees C) are identifical in both gneiss units and distinguish these rocks from the Lusatian granitoids. They grey and red gneisses were overthrust by units with abundant high-pressure relicts and a contrasting P-T evolution. -from Authors

Beschreibung: A seismological characterization of crust and upper mantle can refer to large-scale averages of seismic velocities or to fluctuations of elastic parameters. Large is understood here relative to the wavelength used to probe the earth. In this paper we try to characterize crust and upper mantle by the fluctuations in media properties rather than by their average velocities. As such it becomes evident that different scales of heterogeneities prevail in different layers of crust mantle. Although we cannot provide final models and an explanation of why these different scales exist, we believe that scales of inhomogeneities carry significant information regarding the tectonic processes that have affected the lower crust, the lithospheric and the sublithospheric upper mantle. We focus on four different types of small-scale inhomogeneities: (1) the characteristics of the lower crust, (2) velocity fluctuations in the uppermost mantle, (3) scattering in the lowermost lithosphere and on (4) heterogeneities in the mantle transition zone.

Beschreibung: Five Andean countries (Bolivia, Peru, Ecuador, Colombia, Venezuela) and four European countries (Italy, Spain, Holland, Germany) cooperated in the PILOTO program ("Test area for earthquake monitoring and seismic hazard assessment"), launched under GSHAP and sponsored by the European Union (Ct.94-0103) to produce a unified SHA for the Andean region. Activities included the integration of national earthquake catalogues and source zonings in common regional databases and joint technical workshops for the assessment of the regional hazard, expressed in terms of expected peak ground acceleration with 10% exceedance probability in 50 years.

Beschreibung: Ocean isotope tracers of intermediate residence time are becoming of increasing importance in studies of paleo-ocean circulation, global weathering fluxes, and trace pollutant dispersion in ocean basins. While analytical models exist that predict the way in which conservative tracers are dispersed in ocean gyres, the lateral movement of reactive tracers has not yet received much attention. Here we present time-dependent numerical simulations of the lateral mixing process (advection-diffusion-reaction) of reactive tracers with different residence times in gyres with varying Péclet number, diffusivity, western boundary intensification, and source geometry. Our main conclusions are that in our model gyre (1) homogenization of tracer concentrations and also of isotopic ratios in those cases where the isotopes have different pathways (e.g., atmospherically deposited cosmogenic 10Be, continent-derived 9Be depends largely on the residence time and eddy diffusivity and isonly a weak function of Péclet number; (2) western intensification influences homogenization only in the case of short residence times and large Péclet numbers; (3) homogenization of isotopic ratios of continent-sourced tracers (e.g., 206Pb/204Pb, 143Nd/144Nd) is favored by high water velocities and hence shallow ocean levels; (4) boundary scavenging can result in significant lateral redistribution of output fluxes for even very short residence time tracers (e.g., 230Th) if Péclet numbers are high; (5) the width of source and scavenging regions exerts a strong control over the actual tracer concentrations, but the spatial distribution and degree of tracer homogenization is not affected. The space dependence of input and scavenging is applicable to several reactive isotope tracers such as Be, Pb, Nd, Hf, Th, or Pa. Relative uniformity in their isotope ratios has been observed by mapping of these tracers in individual ocean basins (von Blanckenburg and Igel, 1999). Such uniformity would not be necessarily expected since the isotopes concerned enter through entirely different pathways. The simulations presented here demonstrate that homogenization of such short residence time tracers in ocean gyres is a feasible mechanism that can account for these observations.

Beschreibung: In this paper we describe a new design for an optically pumped tandem magnetometer situated at the GeoForschungsZentrum Potsdam. A tandem magnetometer combines the fast response of a self-oscillating vapour magnetometer with the accuracy of a narrow line Mz-type magnetometer. A newly patented method of coupling the two sensors avoids any stray magnetic fields and so allows a compact design of the instrument itself, as well as facilitating its operation in close proximity to other magnetometers. A prototype Cs-K tandem magnetometer for use in magnetic observatories is described. We then show typical results of a long-term comparison with both a second type of optically pumped magnetometer and an Overhauser proton magnetometer. Finally, a resumé is given of four years of continuous operation of this new type of magnetometer with respect to the data quality produced and its operational reliability.

Beschreibung: This paper presents two concepts for the detection of different objects from high spatial resolution satellite imagery like MOMS-02. The first method is a supervised image segmentation technique which allows a target oriented search for smaller objects. Based on the variation of threshold parameters, different regions are formed by pixel aggregation and selected by a shape classification using artificial neural networks or template matching. In the second approach, large objects such as field structures are extracted. Previously developed recognition methods for aerial imagery are limited to the detection of objects with simple regular shapes like houses and streets. Other objects which include fine details and complex outlines cannot be extracted but are also of great interest for many applications. Therefore, a new hierarchical technique is introduced which deletes small details and preserves the essential object shapes. The obtained results confirm that shape based algorithms are capable of detecting different objects.

Beschreibung: P- and S-wave modelling of the data obtained during the seismic refraction wide angle reflection experiment of the URSEIS 95 project demonstrate the presence of a 15-18 km thick crustal root beneath the Magnitogorsk-Tagil zone in the central part of the Urals orogen. However, the centre of this crustal root is displaced by 50-80 km to the east of the present-day maximum topography. Also beneath the Magnitogorsk-Tagil island arc zone, an upper crustal body with a high P-wave velocity of 6.3 km s(hoch)-1 at 4-9 km depth can be interpreted as consisting of mafic and/or ultramafic rocks. This, in turn, would help to explain the positive Bouguer gravity anomaly and the surface heat-flow minimum associated with the zone, and would also be consistent with the known surface geology of the zone. Another major feature of the seismic model is the presence of high P- and S-wave velocities (7.5 and 4.2 km s(hoch)-1, respectively) at the base of the crustal root. If the deeper parts of the thickened crust also have high densities (small density contrast of about -0.1 g cm(hoch)-3 with respect to the uppermost mantle) then this helps to explain the absence of a pronounced gravity minimum associated with the root. These high velocities and densities can be most easily explained by mafic rocks or a mix of mafic and ultramafic rocks. Within the structural framework of Berzin et al. (1996) these rocks would belong to the lower Russian plate, which was being subducted beneath the Siberian plate during the Uralian orogeny. It is possible that the crustal root is formed from the remnants of oceanic crust or a mix of oceanic crust and mantle attached to the Russian plate. This would mean that little or no continental crust has been subducted or that subduction, and hence the Uralian orogeny, stopped when there was no more oceanic crust or when an attempt was made to subduct lighter continental crust.

Beschreibung: An analysis of the steady-state heat conduction model for the Earth's crust and the upper mantle revealed that the main difficulties in the downward continuation of subsurface geothermal measurements q were connected with an estimation of the heat flow density q"SUB M" at the Moho boundary and of the source distribution f. Solving the steady-state heat conduction equation numerically by means of finite differences (finite elements), we can describe the relation between q, q"SUB M" and f by a linear algebraic system. To overcome the non-uniqueness and instability, a least squares approach is suggested to solve these systems. Bounds for the square-means of the unknown parameters q"SUB M" and f are introduced, whereby it is possible to find solutions with appropriate mean properties. A two-dimensional geothermal profile crossing Central Europe is used to demonstrate this method. The difficulties in estimating reasonable mantle heat flow density and optimal heat source models from geothermal measurements only are pointed out.-Authors