ALBERT

Beschreibung: Ice-rafted debris (IRD) (〉2 mm), input in eight sediment cores along the Eurasian continental margin (Arctic Ocean), have been studied over the last two glacial/interglacial cycles. Together with the revised chronologies and new micropaleontological data of two cores from the northern Barents Sea (PS2138) and northeastern Kara Sea (PS2741) spanning Marine Isotope Stages (MIS) 6 to 1, the IRD data give new insights into the glacial history of northern Eurasian ice-sheets over the last 150 ka. The chronologies of the cores are based on stable isotope records, AMS 14C datings, paleomagnetic and biostratigraphic data. Extensive episodes of northern Barents Sea ice-sheet growth, probably to the shelf edge, occurred during the late Weichselian (MIS 2) and the Saalian (MIS 6). Major IRD discharge at the MIS 4/3-transition hints to another severe glaciation, probably onto the outer shelf, during MIS 4. IRD-based instabilities of the marine-based ice margin along the northern Barents Sea between MIS 4 and 2 are similar in timing with North Atlantic Heinrich events and Nordic Seas IRD events, suggesting similar atmospheric cooling over a broad region or linkage of ice-sheet fluctuations through small sea-level events. In the relatively low-precipitation areas of eastern Eurasia, IRD peak values during Termination II and MIS 4/3-transition suggest a Kara Sea ice-sheet advance onto the outer shelf, probably to the shelf edge, during glacial MIS 6 and 4. This suggests that during the initial cooling following the interglacials MIS 5, and possibly MIS 7, the combined effect of sustained inflow of Atlantic water into the Arctic Ocean and penetration of moisture-bearing cyclones into easterly direction supported major ice build-up during Saalian (MIS 6) and Mid-Weichselian (MIS 4) glaciation. IRD peak values in MIS 5 indicate at least two advances of the Severnaya Semlya ice-sheet to the coast line during the Early Weichselian. In contrast, a distinct Kara Sea ice advance during the Late Weichselian (MIS 2) is not documented by the IRD records along the northeastern Kara Sea margin.

Beschreibung: The influence of Fe on the reaction clinochlore + kyanite ó magnesiochloritoid + talc (1) was determined experimentally as a function of pressure (1.6 - 2.6 GPa) and composition at 600 and 540oC. Analytical electron microscopy (AEM) was used to determine the compositions of the coexisting phases in these complex multiphase run products. Within the compositional range studied (xFebulk = 0.12 0.34) chlorite solid solutions were always richer in magnesium than the coexisting chloritoid solid solutions. Fractionation of Fe into the chloritoid extends the stability field of the assemblage chloritoid plus talc towards lower pressures. However, the extent of the stability field for increasing xFe is less than one would expect for ideal mixing behaviour in chloritoid and chlorite and indicates a moderate, positive deviation from ideality for chloritoid solid solutions. The thermodynamic data for magnesiochloritoid given in Simon et al. (1997) and in Vidal et al. (1999) are in good agreement with the present experiments, those of Holland & Powell (1998) yield pressures much too high at least compared with the experiments at 600 oC.

Beschreibung: Aim of the report consists in describing basic methodology for future small satellite system designated for measuring with high accuracy and spatial resolution parameters of the atmosphere and ionosphere as a communication media. This system will use radio occultation method in different schemes: satellite-to-satellite, satellite-ground, satellite-air-plane (or helicopter) in the atmosphere with purposes of analyzing corresponding communication channels and influences on characteristics of the channels meteorological and ionospheric phenomena, effects of radio waves propagation including multibeam, refraction, diffraction and wave guide mechanisms. The basic methodology may be applied for developing small satellites that will use radio sygnals emitted by radio navigation, radio communication satellites for precise measuring effects of radio waves propagation at low elevation angles and for global monitoring radio communication channels passed through the atmosphere and ionosphere. The second task consists in revealing new information on wave phenomena in the atmosphere and ionosphere that are important for telecommunication conditions in the difficult accessible regions (communications with air-planes in polar and sea zones, communications through the ionosphere between two satellites using high frequency band), observing dangerous atmospheric processes and ecological changes. Nowadays near Earth's space is broadly used for telecommunication and radio navigation. The near Earth's space as radio communication media now may be studied by using signals of existing satellites designed for television, radio navigation and communication. This signals may be received by small satellite system for analysis of parameters of corresponding information channels. Also signals emitted from the Earth's surface may be received by small satellite system for investigation ground-satellite communication channel. The small satellite systems for this purposes are now under development. During 1990-1998 in Russia practical testing of radio occultation method for monitoring atmosphere and ionosphere channels between the orbital station 'MIR' and geo-stationary (GEO) satellite had been provided at wavelength of 2 and 32 cm. Experiments of radio occultation measurements of altitude distribution of the electron density in the ionosphere and the refraction in the neutral atmosphere had been carried out in USA during 1995-1999 using two frequency in decimeter range. High precision radio fields emitted by GPS navigational system and a small satellite known as Micro-Lab-1 were used for verification. It was established that radio occultation in decimeter wavelength range allows to determine the physical parameters of the media important for telecommunication: the temperature altitude profile in the atmosphere and electron density distribution in the ionosphere. As it followed from combining phase and amplitude GPS/MET data analysis, vertical resolution of 0.3 - 0.5 km may be achieved in the upper atmosphere region. Combined phase and amplitude analysis reveals wave-like structures with spatial periods from 1-2 km to 8-10 km in the vertical electron density distribution in the D-and E-layers. Variations in the gradient of the electron density from ±5×103 to ±8×103 electrons/(cm3km) at the altitudes of 72 - 95 km were observed. Also wave structures in the E-layer (height interval 102-110 km) with vertical period 0.5-2 km and amplitude 2-3×103 electrons×cm-3 were revealed. These wave-like structures are important for understanding the role of gravity waves and their contribution to the dynamics of the mesosphere. The structures in the electron density distribution may be connected with neutral wind velocity profile. Maximums in electron density distribution correspond to minimum neutral wind velocity values, thus determining vertical positions of wind shears in the upper atmosphere. The examples of application of the derived methodology to radio occultaion data analysis show it usefulness for future small satellite systems.

Beschreibung: GFZ has started together with other large research centers of the German Helmholtz Association the "GPS Atmosphere Sounding" Project (GASP) on using ground-based (Subproject 1) and space-based (Subproject 2) GPS observations for applications in numerical weather prediction, climate research and space weather monitoring. Operational precision determination of water vapor in near real-time within dense German GPS network (~ 70 sites) is being carried out since May 2000 and has demonstrated an accuracy of better than 2 mm with a standard deviation at the level of better than +- 1 mm. The results are validated regulary with the local weather model LM1 of German Weather Service. Assimilation studies are in preparation. Space-based GPS sounding of the atmosphere and ionosphere is entering a new era with the German CHAMP sattelite: CHAMP is the first mission aiming at the quasi-continous monitoring of the atmosphere with GPS. Launched last summer, the satellite has only recently delivered its first set of atmospheric data. Once in full operation, CHAMP will deliver about 200-250 daily vertical profiles of temperature, tropospheric humidity and ionospheric electron content. Some first results and intercomparisons will be presented.

Beschreibung: The 1.3 Ma Purico complex is part of an extensive Neogene-Pleistocene ignimbrite province in the central Andes. Like most other silicic complexes in the province, Purico is dominated by monotonous intermediate ash-flow sheets and has volumetrically minor lava domes. The Purico ignimbrites (total volume 80-100 km3) are divided into a Lower Purico Ignimbrite (LPI) with two extensive flow units, LPI I and LPI II; and a smaller Upper Purico Ignimbrite (UPI) unit. Crystal-rich dacite is the dominant lithology in all the Purico ignimbrites and in the lava domes. It is essentially the only lithology present in the first LPI flow unit (LPI I) and in the Upper Purico Ignimbrite, but the LPI II flow unit is unusual for its compositional diversity. It constitutes a stratigraphic sequence with a basal fall-out deposit containing rhyolitic pumice (68-74 wt% SiO2) overlain by ignimbrite with dominant crystal-rich dacitic pumice (64-66 wt% SiO2). Rare andesitic and banded pumice (60-61 wt% SiO2) are also present in the uppermost part of the flow unit. The different compositional groups of pumice in LPI II flow unit (rhyolite, andesite, dacite) have initial Nd and Sr isotopic compositions that are indistinguishable from each other and from the dominant dacitic pumice ()Nd=-6.7 to -7.2 and 87Sr/86Sr=0.7085-0.7090). However, two lines of evidence show that the andesite, dacite and rhyolite pumices do not represent a simple fractionation series. First, melt inclusions trapped in sequential growth zones of zoned plagioclase grains in the rhyolite record fractionation trends in the melt that diverge from those shown by dacite samples. Second, mineral equilibrium geothermometry reveals that dacites from all ignimbrite flow units and from the domes had relatively uniform and moderate pre-eruptive temperatures (780-800 �C), whereas the rhyolites and andesites yield consistently higher temperatures (850-950 �C). Hornblende geobarometry and pressure constraints from H2O and CO2 contents in melt inclusions indicate upper crustal (4-8 km) magma storage conditions. The petrologic evidence from the LPI II system thus indicates an anomalously zoned magma chamber with a rhyolitic cap that was hotter than, and chemically unrelated to, the underlying dacite. We suggest that the hotter rhyolite and andesite magmas are both related to an episode of replenishment in the dacitic Purico magma chamber. Rapid and effective crystal fractionation of the fresh andesite produced a hot rhyolitic melt whose low density and viscosity permitted ascent through the chamber without significant thermal and chemical equilibration with the resident dacite. Isotopic and compositional variations in the Purico system are typical of those seen throughout the Neogene ignimbrite complexes of the Central Andes. These characteristics were generated at moderate crustal depths (〈30 km) by crustal melting, mixing and homogenization involving mantle-derived basalts. For the Purico system, assimilation of at least 30% mantle-derived material is required.

Beschreibung: The chromium-bearing kyanite specimen U-158, extracted from a kyanite-eclogite xenolith in a Yakutian kimberlite pipe was studied by transmission electron microscopy TEM. This specimen has an analysed composition (Al1.989Cr0.014Fe0.007Ti0.001)Ó=2.011 [O/Si0.990O4] and has been examined by electronic absorption and fluorescence spectroscopy (Platonov et al ., 1998). The (010) oriented foil previously studied by spectroscopy, shows areas of dark diffraction contrast which were found to originate from incipient alumina-type exsolutions forming platelets about 2 nm thick and 5-10 nm wide. They are intergrown with the kyanite matrix and have the orientation relationships [011]ky // [0110]cor and (100)ky // (0001)cor. The volume fraction of these exsolution precursors is estimated to be less than 0.1 vol. %. Elemental mapping using inelastically scattered electrons in the EELS spectra (Al-L3 and Si-L3 edges) demonstrated Si-depletion and Al-enrichment in the exsolution precursors. Furthermore, EDX analysis with a nominal spot size of 4 nm confirmed the areas with dark contrasts to be more Al-rich than the kyanite matrix without these contrasts, while chromium contents were the same. The EDX analysis is evidently a superposition of the chemical composition of both the kyanite matrix and the additional phase identified by TEM. In any case, the chemical analysis confirms the crystallographic inferences about composition. The results confirm the presence of a precursor of an Al-rich, chromium-bearing corundum-type exsolution as previously suggested to explain two greatly differing crystal fields for Cr3+ in the studied chromium-bearing kyanite.

Beschreibung: GFZ has started together with other large research centers of the German Helmholtz Association the "GPS Atmosphere Sounding" Project (GASP) on using ground-based (Subproject 1) and space-based (Subproject 2) GPS observations for applications in numerical weather prediction, climate research and space weather monitoring. Operational precision determination of water vapor in near real-time within dense German GPS network (~ 70 sites) is being carried out since May 2000 and has demonstrated an accuracy of better than 2 mm with a standard deviation at the level of better than +- 1 mm. The results are validated regulary with the local weather model LM1 of German Weather Service. Assimilation studies are in preparation. Space-based GPS sounding of the atmosphere and ionosphere is entering a new era with the German CHAMP sattelite: CHAMP is the first mission aiming at the quasi-continous monitoring of the atmosphere with GPS. Launched last summer, the satellite has only recently delivered its first set of atmospheric data. Once in full operation, CHAMP will deliver about 200-250 daily vertical profiles of temperature, tropospheric humidity and ionospheric electron content. Some first results and intercomparisons will be presented.

Beschreibung: High-resolution analyses of rock magnetic and sedimentological parameters were conducted on an 11 m long sediment core from Lama Lake, Northern Siberia, which encompasses the late Pleistocene and the Holocene epochs. The results reveal a strong link between the median grain size of the magnetic particles, identified as magnetite, and the oxidation state of the sediment. Reducing conditions associated with a relative high total organic carbon (TOC) content of the sediment characterize the upper 7 m of the core ( Holocene), and these have led to a partial dissolution of detrital magnetite grains, and a homogenization of grain-size-related rock magnetic parameters. The anoxic sediments are characterized by significantly larger median magnetic grain sizes, as indicated, for example, by lower median destructive fields of the natural remanent magnetization (MDFNRM) and lower ratios of saturation remanence to saturation magnetization (MSR/MS). Consequently, estimates of relative geomagnetic palaeointensity variations yielded large amplitude shifts associated with anoxic/oxic boundaries. Despite the partial reductive dissolution of magnetic particles within the anoxic section, and consequent minimal variations in magnetic concentration and grain size, palaeointensity estimates for this part of the core were still lithologically distorted by the effects of particle size (and subsidiary TOC) variations. Anomalously high values coincide with an interval of significantly more fine-grained sediment, which is also associated with a decrease in TOC content, which may thus imply a decreased level of magnetite dissolution in this interval. Calculation of relative palaeointensity estimates therefore seems to be compromised by a combined effect of shifts in the particle size distribution of the bulk sediment and by partial magnetite dissolution varying in association with the TOC content of the sediment.

Beschreibung: Thirty-three earthquakes occurred in Central Apennines (Italy) with Ml ranging from 2.4 to 3.7 have been spectrally analysed using digital recordings from twelve stations of the Rete Sismometrica Marchigiana (RSM) network. Data corrected for geometrical spreading and quality factor Q have been inverted by means of the Generalised Inversion Technique. Site responses have been compared with those obtained by H/V ratio. Site amplifications have been observed both at stations placed on Pleistocene sediments and at one station located at 1800 m of altitude. Source parameters have been calculated by fitting the spectra with an automatic procedure adopting the w2 source model. The seismic moments range from 9.23*10^19 to 4.28*10^21 dyne-cm with average Mo (S) to Mo (P) ratio of 1.13 plus minus 0.38. The stress drops are generally low and they vary between 1.1 and 10.2 bar when estimated by using S source spectra, and between 0.5 and 7.1 bar when the P source spectra are fitted. For the considered range of seismic moments we observe that the stress drop does not have significant dependence on event size.

Beschreibung: La Pacana caldera in the Central Andes of northern Chile is one of the largest and best exposed resurgent calderas in the world. The caldera had previously been recognised as the source of the regionally-extensive Atana ignimbrite, but additional field and stratigraphic evidence, along with new K–Ar age determinations and geochemical data have led to a revision of the geology and development of this major Andean caldera. In particular, this information allows more realistic estimates of eruptive volumes and has implications for the style of ignimbrite eruption. Two major ignimbrites appear to have originated from La Pacana caldera, based on their thickness variations, lateral distributions and stratigraphic relations: the crystal-poor, rhyolitic Toconao ignimbrite (4–5 Ma) and the crystal-rich, dacitic Atana ignimbrite (4 Ma). Following caldera collapse and formation of the resurgent Atana block, several crystal-rich dacitic–rhyolitic domes formed along the margin of the resurgent block. New K–Ar ages show that this post-caldera volcanism continued from 4 to 2 Ma, indicating that the La Pacana magmatic system was active for at least 2 Ma after the main eruption. The Atana ignimbrite extends west, south and east of La Pacana caldera. Our work shows that the ignimbrite sequence northeast of the caldera, formerly mapped as Atana outflow, represents two new units which we name the upper and lower Tara ignimbrites. The distribution of the Tara ignimbrites points to a source to the north. The upper Tara ignimbrite comprises four flow units with interbedded surge and fall deposits and a characteristic, heterogeneous pumice population. It occurs in the La Pacana moat and onlaps the resurgent block. These field relations and a new K–Ar age of 3.8 Ma show convincingly that this ignimbrite erupted after formation of La Pacana caldera. The lower Tara ignimbrite is a single extensive flow unit, and has an age of 5.6 Ma. Two outcrops of lag breccia occur adjacent to the caldera topographic margin and these are interpreted as vent areas for the Atana ignimbrite. This indicates that the structural caldera margin does not coincide with the resurgent block as previously thought, but is close to the topographic margin. Combining this redefinition of caldera geometry with the revised distribution of the Atana ignimbrite implies an overall trap-door-like configuration of caldera collapse, with a hinge to the north and maximum subsidence in the south. The new volume estimate of 2500 km3 for the caldera-forming Atana ignimbrite, including intracaldera and outflow facies, places it among the most voluminous ignimbrites of the world.

Beschreibung: The Kalman filter has been applied extensively in the area of kinematic geodetic positioning. The reliability of the linear filtering results, however, is reduced when the kinematic model noise is not accurately modeled in filtering or the measurement noises at any measurement epoch are not normally distributed. A new adaptively robust filtering is proposed based on the robust M (maximum-likelihood-type) estimation. It consists in weighting the influence of the updated parameters in accordance with the magnitude of discrepancy between the updated parameters and the robust estimates obtained from the kinematic measurements and in weighting individual measurements at each discrete epoch. The new procedure is different from functional model-error compensation; it changes the covariance matrix or equivalently changes the weight matrix of the predicted parameters to cover the model errors. A general estimator for an adaptively robust filter is developed, which includes the estimators of the classical Kalman filter, adaptive Kalman filter, robust filter, sequential least-squares adjustment and robust sequential adjustment. The procedure can not only resist the influence of outlying kinematic model errors, but also controls the effects of measurement outliers. In addition to the robustness, the feasibility of implementing the new filter is achieved by using the equivalent weights of the measurements and the predicted state parameters. A numerical example is given to demonstrate the ideas involved.