ALBERT

Beschreibung: Despite the large number of successful applications of laser ablation, elemental and isotopic fractionation coupled to inductively coupled plasma mass spectrometry (ICP-MS) remain as the main limitations for many applications of this technique in the fields of analytical chemistry and Earth Sciences. A substantial effort has been made to control such fractionations, which are well-established features of nanosecond laser ablation systems. Technological advancements made over the past decade now allow the ablation of solids by femtosecond laser pulses in the deep ultraviolet (UV) region at wavelengths less than 200 nm. Here the use of femtosecond laser ablation and its effects on elemental and isotopic fractionation is investigated. The Pb/U system is used to illustrate elemental fractionation and stable Fe isotopes are used to illustrate isotopic fractionation. No elemental fractionation is observed beyond the precision of the multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) measurements. Without a matrix match between standard and sample, elemental fractionation is absent even when using different laser ablation protocols for standardization and samples (spot versus raster). Furthermore, we found that laser ablation-induced isotope ratio drifts, commonly observed during nanosecond laser ablation, are undetectable during ultraviolet femtosecond laser ablation. So far the precision obtained for Fe isotope ratio determinations is 0.1‰ (2 standard deviation) for the 56Fe/54Fe ratio. This is close to that obtainable by solution multiple-collector inductively coupled plasma mass spectrometry. The accuracy of the results appears to be independent of the matrix used for standardization. The resulting smaller particle sizes reduce fractionation processes. Femtosecond laser ablation carries the potential to solve some of the difficulties encountered during the two prior decades since the introduction of laser ablation.

Beschreibung: Although satellite electromagnetic induction studies have usually assumed a symmetric magnetospheric ring current source described by Y10, there is growing evidence for significant source asymmetry. Balasis et al. (2004) and Balasis and Egbert (2006) presented evidence for at least an additional Y21 quadrupole term that introduces some local time asymmetry in the source. This component is correlated with the traditional axial dipole source variations, and oriented so that meridional magnetic fields peak in the dusk sector (at 19:30 LT). The time-domain, spherical harmonic-finite element method developed by Velimsky and Martinec (2005) has recently been applied to 1-D inverse modeling of CHAMP satellite data assuming only storm-time, axially symmetric ring-current excitation (Velimsky et al., 2006). We attempt to apply the method to model the electromagnetic response of the Earth to the source field incorporating higher degree non-zonal terms. It is noted that a multi-satellite mission would offer the opportunity to compare and combine simultaneous measurements over different local times. This could help in mapping more accurately the fields of the system of external currents used for estimating electromagnetic induction transfer functions. Therefore the foreseen SWARM constellation will be essential to the task of developing improved source models for induction studies. Ultimately, data assimilation methods which combine physics-based models of the magnetosphere and ionosphere with all available data offer the greatest hope for accurate modeling of external sources for global inductionstudies with satellite data.

Beschreibung: A fortuitous sequence of closely spaced earthquakes in the Rana region of northern Norway, during 2005, has provided an ideal natural laboratory for investigating event detectability using waveform correlation over networks and arrays at regional distances. A small number of events between magnitude 2.0 and 3.5 were recorded with a high SNR by the Fennoscandian IMS seismic arrays at distances over 600 km and three of these events, including the largest on 24 June, displayed remarkable waveform similarity even at relatively high frequencies. In an effort to detect occurrences of smaller earthquakes in the immediate geographical vicinity of the 24 June event, a multi-channel correlation detector for the NORSAR array was run for the whole calender year 2005 using the signal from the master event as a template. A total of 32 detections were made and all but 2 of these coincided with independent correlation detections using the other Nordic IMS array stations; very few correspond to signals detectable using traditional energy detectors. Permanent and temporary stations of the Norwegian National Seismic Network (NNSN) at far closer epicentral distances have confirmed that all but one of the correlation detections at NORSAR in fact correspond to real events. The closest stations at distances of approximately 10 km can confirm that the smallest of these events have magnitudes down to 0.5 which represents a detection threshold reduction of over 1.5 for the large-aperture NORSAR array and over 1.0 for the almost equidistant regional ARCES array. The incompleteness of the local network recordings precludes a comprehensive double-difference location for the full set of events. However, stable double-difference relative locations can be obtained for eight of the events using only the Lg phase recorded at the array stations. All events appear to be separated by less than 0.5 km. Clear peaks were observed in the NORSAR correlation coefficient traces during the coda of some of the larger events; the local stations confirm that these are in fact aftershocks exhibiting very similar waveforms to the main events. Many of the more marginal correlation detections are not made when the calculations are repeated using shorter signal segments, fewer sensors or more distant stations. We demonstrate in addition how these almost repeating seismic sources have been exploited to detect and measure timing anomalies at individual sites within the arrays and network.

Beschreibung: Active continental margins are the Earth's principal regions of active deformation and significant earthquake hazard. We apply the enhanced method called Scan Sythetic Aperture Radar (ScanSAR) interferometry to quantify active surface deformation in the coastal region of the South American active margin in central Chile between 22° S and 27° S. Here, as in other active margin settings, crustal deformation may reach far inland and affects hundreds of square kilometre wide areas. The "normal" ENVISAT ASAR Strip-Mode covers a 100 km wide stripe and will therefore not be sufficient for such deformation study. We use the ENVISAT ASAR Wide Swath (WS) data that cover in generally an area of 400 x 400 km2. Because of this we investigate the potential of WS data to monitor such wide-stretched surface displacement. Therewith a high spatiotemporal surface deformation monitoring in active margin settings can be given.

Beschreibung: Tectonic studies made in intraplate Europe have shown that this area is more active than would be expected from its location far away from plate boundaries.The first strength map showed that the European lithosphere is characterized by major spatial mechanical strength variations, with a pronounced contrast between the strong lithosphere of the East-European Platform (EEP) east of the Tesseyre-Tornquist Zone (TTZ) and the relatively weak lithosphere of Western Europe. In order to improve the results previously obtained, we have constructed a new crustal model, in which we implement the results of recent seismic studies. The new crustal model consists for continental realms, of two or three crustal layers and an overlying sedimentary cover layer, whereas for oceanic areas one crustal layer is used. The results of deep seismic reflection and refraction and/or receiver function studies are used to define the depth of the crustal interfaces and P-wave velocity distribution. The Moho depth variations are reconstructed by merging the most recent maps compiled for the European regions (e.g. Ziegler and Dèzes, 2002, Kozlovskaja et al, 2004) and by ourselves using published interpretations of seismic profiles (e.g. in the Vøring and Lofoten basins). To each layer of the model we associate a density value and corresponding lithology. Strong differences in the crustal structure are found between the areas east and west of the TTZ, respectively. The eastern region is mostly characterized by high velocity of the lowest layer (Vp~7.1km/s) and thick crust, e.g. over the Baltica region (42-44km) with a maximum of over 60 km in the Baltic Shield. By contrast, crustal structure is more heterogeneous to the west from TTZ, being characterized by Variscan crust with slower P-wave velocity in the lower crust (Vp~6.8km/s) and an average thickness of 30-35 km, orogens (e.g. the Alps and the Pyrenees), where the crustal thickness is increased up to 45-50 km, and locally by strong extensional deformation, which resulted in a very thin crust in the Pannonian Basin (~25 km) and in the Tyrrhenian Sea (~10 km). Concerning the oceanic domain, the crustal thickness is generally decreased towards the ridge (up to 10 km in the most western part), with local maxima up to 20-25 km (e.g. in the Vøring and Lofoten basins) and up to 35-40 km beneath the islands (e.g. Iceland and Faeroe islands), on account of mantle underplating. Seismic tomography data are used to get the location of the lithosphere-astenosphere boundary and calculate the temperature distribution. These results, jointly with the new crustal model, allowed us to refine the previous strength map. Furthermore, the gravity effect of the crustal model is calculated and removed from the observed gravity field in order to get residual mantle anomalies. These anomalies distribution are compared with the new strength results. Negative mantle gravity anomalies and relative low strength values characterize Western Europe, while the reverse is true for Eastern Europe. Large differences exist also for specific tectonic units: a pronounced contrast in lithosphere properties is found between the strong Adriatic plate and the weak Pannonian Basin area, as well as between the Baltic Shield and the North Sea rift system.

Beschreibung: Mantle flow models that do not consider the effects of latent heat on phase boundaries typically predict dynamic surface topography too large to be compatible with observations. Here these effects were implemented in a mantle flow model and resulting changes in dynamic topography and topography of phase boundaries were computed. Inclusion of these effects was found to reduce the rms amplitude of dynamic topography by about 50–60 m, still leaving a substantial misfit from observations in most cases considered. Generally, it also leads to a slight improvement of correlation with dynamic surface and phase boundary topography constrained by observations. Results thus indicate that the model implemented here is applicable to the Earth, but that other effects need to be considered as well in order to fully explain phase boundary and dynamic surface topographies.

Beschreibung: Seismic and volcanic activities in Central Java, Indonesia, the area of interest of this study, are directly or indirectly related to the subduction of the Indo-Australian plate. In the framework of the MERapi AMphibious EXperiments (MERAMEX), a network consisting of about 130 seismographic stations was installed onshore and offshore in Central Java and operated for more than 150 days. In addition, 3-D active seismic experiments were carried out offshore. In this paper, we present the results of processing combined active and passive seismic data, which contain traveltimes from 292 local earthquakes and additional airgun shots along three offshore profiles. The inversion was performed using the updated LOTOS-06 code that allows processing for active and passive source data. The joint inversion of the active and passive data set considerably improves the resolution of the upper crust, especially in the offshore area in comparison to only passive data. The inversion results are verified using a series of synthetic tests. The resulting images showan exceptionally strong low-velocity anomaly (−30 per cent) in the backarc crust northward of the active volcanoes. In the upper mantle beneath the volcanoes, we observe a low-velocity anomaly inclined towards the slab, which probably reflects the paths of fluids and partially melted materials in the mantle wedge. The crust in the forearc appears to be strongly heterogeneous. The onshore part consists of two high-velocity blocks separated by a narrow low-velocity anomaly, which can be interpreted as a weakened contact zone between two rigid crustal bodies. The recent Java Mw = 6.3 earthquake (2006/05/26-UTC) occurred at the lower edge of this zone. Its focal strike slip mechanism is consistent with the orientation of this contact.

Beschreibung: Tropical mountain areas may undergo rapid land degradation as demographic growth and intensified agriculture cause more people to migrate to fragile ecosystems. To assess the extent of the resulting damage, an erosion rate benchmark against which changes in erosion can be evaluated is required. Benchmarks reflecting natural erosion rates are usually not provided by conventional sediment fluxes, which are often biased due to modern land use change, and also miss large, episodic events within the measuring period. To overcome this, we combined three independent assessment tools in the southern Ecuadorian Andes, an area that is severely affected by soil erosion. First, denudation rates from cosmogenic nuclides in river sediment average over time periods of 1–100 k.y. and establish a natural benchmark of only 150 ± 100 t km-2 yr-1. Second, we find that land use practices have increased modern sediment yields as derived from reservoir sedimentation rates, which average over periods of 10–100 yr to as much as 15 × 103 t km-2 yr-1. Third, our land cover analysis has shown us that vegetation cover exerts first-order control over present-day erosion rates at the catchment scale. Areas with high vegetation density erode at rates that are characteristically similar to those of the natural benchmark, regardless of whether the type of vegetation is native or anthropogenic. Therefore, our data suggest that even in steep mountain environments sediment fl uxes can slow to near their natural benchmark levels with suitable revegetation programs. A set of techniques is now in place to evaluate the effectiveness of erosion mitigation strategies.

Beschreibung: Southern Africa and its southern continental margin offer an unrivalled region, where continental accretion, continental breakup and magmatic processes over a period of more than 3.5 billion years can be studied. The Agulhas-Karoo Geoscience Transect is part of the South African - German cooperative research project "Inkaba ye Africa", which aims to investigate this part of the continent and ocean in a cone-shaped sector from core to space. Geophysical and geological data and samples were collected along this transect which spans from the Agulhas Plateau across the Agulhas-Falkland fracture zone, the Outeniqua Basin, the Cape Fold Belt, the Namaqua-Natal Belt onto the Karoo Craton. A combined onshore-offshore deep crustal seismic reflection and refraction survey as well as several magnetotelluric surveys provide information about tectonic and magmatic structures and constraints for physical parameters from sedimentary sequences to the upper mantle. The main objectives include an understanding of the crustal nature of the Agulhas Plateau, the processes accompanying and succeeding the crustal shearing process along the Agulhas-Falkland Transform/Fracture Zone, the offshore basin formation in relation to breakup, the deep-seated tectonics of the Cape Fold Belt, and the geometries and sources of the Beattie Magnetic Anomaly and the Southern Cape Conductivity Belt. The geophysical data are integrated with geological, petrological and geochemical analysis on rock composition, age and alteration history to form an overarching geodynamic model of the evolution of this region and its sedimentary, tectonic and magmatic units.

Beschreibung: A spherical harmonic degree 60, global internal field model is described (called BGS/G/L/0706). This model includes a degree 15 core and piecewise-linear secular variation model and is derived from quiet-time Ørsted and CHAMP satellite data sampled between 2001.0 and 2005.0. For the satellite data selection, a wide range of geomagnetic index and other data selection filters have been used to best isolate suitably quiet magnetospheric and ionospheric conditions. Only a relatively simple, degree one spherical harmonic, external field model is then required. It is found that a new ‘Vector Magnetic Disturbance’ index (VMD), the existing longitude sector A indices, the auroral zone index IE, and the polar cap index PC are better than Kp and Dst at rejecting rapidly varying external field signals at low, middle, auroral and polar latitudes. The model quality is further enhanced by filling spatial and temporal gaps in the quiet data selection with a second selection slightly more disturbed data. It is shown that VMD provides a better parametrization than Dst of the large-scale, rapidly changing, external field. The lithospheric field model between degrees 16 to 50 is robust and displays good coherence with other recently published models for this epoch. BGS/G/L/0706 also shows crustal anomalies consistent with other studies, although agreement is poorer in the southern polar cap. Inter-model coherency reduces above about degree 40, most likely due to incompletely filtered signals from polar ionospheric currents and auroral field aligned currents. The absence of the PC index for the southern hemisphere for 2003 onwards is a particular concern.

Beschreibung: The NCAR Whole Atmosphere Community Climate Model, version 3 (WACCM3), is used to study the atmospheric response from the surface to the lower thermosphere to changes in solar and geomagnetic forcing over the 11-year solar cycle. WACCM3 is a general circulation model that incorporates interactive chemistry that solves for both neutral and ion species. Energy inputs include solar radiation and energetic particles, which vary significantly over the solar cycle. This paper presents a comparison of simulations for solar cycle maximum and solar cycle minimum conditions. Changes in composition and dynamical variables are clearly seen in the middle and upper atmosphere, and these in turn affect terms in the energy budget. Generally good agreement is found between the model response and that derived from satellite observations, although significant differences remain. A small but statistically significant response is predicted in tropospheric winds and temperatures which is consistent with signals observed in reanalysis data sets.

Beschreibung: During the strategy fund program SEAL (Sea Level Change: an Integrated Approach to its Quantification) of the Helmholtz Community of German Research Centers (HGF), a global data base for late-glacial and Holocene sea-level indicators (SLIs) was established at the GeoForschungsZentrum Potsdam (GFZ). The aim was to interpret sea-level variations on a global scale over the last 20,000~a with respect to glacial-isostatic adjustment (GIA), to infer the Earth's mantle viscosity and to predict the GIA contribution to the present-day sea-level rise (e.g. Hagedoorn et al., 2006) and gravity change observed by GRACE. In contrast to the standard information, such as position, age and former sea-level height characterizing a specific SLI, a more complete suite of information about each SLI is included in the data base. Its main advantage is that it allows a more sophisticated inference of former sea-level height from SLIs (e.g. Hagedoorn, 2005, STR 05/13 GFZ-Potsdam; Klemann & Wolf, 2007, PAGEOPH; Wolf et al., 2006, Surv. Geophys.). The poster presents the status quo of the data base: The data consist at present of 14,000 SLIs which are stored in a relational data-base system and sorted with respect to geographical regions. It is based on compilations by Kevin Fleming (Far Field), Art Dyke (North America), Ian Shennan (Britain), Glushankova (Siberia) and additional compilations for Antarctica, Patagonia, Barents Sea and Fennoscandia based on a scrutiny of the relevant literature.

Beschreibung: Monthly mean gravity fields solely based on GRACE satellite tracking data are found to provide reliable ocean mass anomalies down to 500 km regional averages when comparing them to mass observations obtained from sterically corrected Jason 1 altimetry and simulated mass anomalies derived from the Ocean Model for Circulation and Tides (OMCT). Beside the assessment of systematic shortcomings of GRACE, Jason 1 and OMCT estimates, robust signals of mass anomalies in the North Pacific and in various regions of the Southern Ocean are identified in all three independent datasets. Correlations of up to 0.8 and rms values of differences of around 2 hPa indicate that uncertainties are well below the expected monthly mean mass signals of up to 6 hPa rms in these regions. By means of output of the numerical ocean model, mass anomalies are related to changes in barotropic ocean currents, providing in turn the opportunity to infer barotropic current anomalies from GRACE observations, and therefore principally allowing to monitor climate relevant changes of ocean currents from satellite observations.

Beschreibung: One of the projects within the framework of Inkaba yeAfrica, an earth system science initiative between German and South African research communities, is the Agulhas-Karoo transect. This 800 km north-south off-onshore transect runs from the offshore Agulhas Plateau onto the South African coast, across the Cape Fold Belt, Beattie Magnetic Anomaly, the Karoo Basin, the Great Escarpment and into the Kaapvaal Craton. Among the numer of geophysical measurements taken along the transect are two wide-angle on-shore seismic lines collected in April and May 2005. The lines run roughly parallel to each other approximately 200 km apart, starting at Mossel Bay and St. Francis, and running about 200 km north to Fraserburg and Graaf Reinet, respectively. At each line 48 seismic receivers were used to record data from 13 shots. The profiles cross a wide variety of geological terrains, such as the siliciclastic sequences of the Paleozoic - Mesozoic Karoo and Oudtshoorn basin, the lower Paleozoic Cape Fold Belt, and the Eocanbrian Kango and Kaaimans inliers. They also cross the Beattie Magnetic Anomaly, a large east-west orientated crustal feature within the upper crust, and more than 1000 km long, first reported almost a century ago, but still not fully understood. The overall quality of seismic data is very good. First (P-wave) arrivals were manually picked on the available traces, and tomographic inversion was done using these travel times. The ray coverage made it possible to create the P-wave velocity model to depths of up to 25 km. We find excellent correlation of the shallow features with surface rock type. Deeper down we can identify both stratigraphic and tectonic contacts between geological groups. These include an inferred possible blind Paleozoic thrust fault, and the uncontormity between the Cape Supergroup and the Namaqua-Natal Metamorphic Complex. The normal listric geometry of the Kango and Gramtoos Faults is clearly seen to a minimum depth of 15 km. We also observe a high velocity anomaly within the NNMC at ~ 10 km depth that we relate to the source of the source of the Beattie Magnetic Anomaly.

Beschreibung: 3D Density and Temperature Distribution at Passive Continental Margins –an Example from the North Atlantic Magdalena Scheck-Wenderoth and Yuryi Maystrenko GeoForschungsZentrum Potsdam, Sect. 4.3: Organic geochemistry, Telegrafenberg C423 D-14473 Potsdam, Germany The physical state of passive continental margins is controversial concerning the mode and level of isostatic compensation and the configuration of the lithosphereasthenosphere boundary. One of the few passive continental margins where the detailed structure of the crustal part of the system from the continental onshore, over the continental margin offshore and across the continent ocean transition to the oceanic part is well explored, is the Norwegian margin of the northern Atlantic. This provides constraints for the 3D conductive thermal field and the density distribution across the margin in the crust and in the lithospheric mantle. To evaluate which configuration of the lithosphere asthenosphere boundary is consistent with the observed crustal configuration and with measured temperatures in the sedimentary part of the margin, we test different scenarios. We use a present-day 3D structural model of the Vшring and Mшre segments of the Norwegian margin which is constrained by seismic, well and gravity data. 3D gravity modelling and isostatic calculations revealed that the lithospheric mantle below the ocean is less dense than below the continent. Subsequently, we calculate the temperature distribution for the 3D structural model of the margin and compare the results to measured temperatures in deep wells on the margin and in two ODP wells on the oceanic crust. Our results indicate higher temperatures in the oceanic mantle than in the continental mantle.

Beschreibung: A problem that arises when investigating the spatial representation of the monthly gravity-field solutions from the Gravity Recovery and Climate Experiment (GRACE) space mission is the presence of north-south oriented striped noise. This is a result of the high inclination of the GRACE spacecrafts (89.5degree) and the configuration of the GRACE satellites, resulting in less-dense sampling in the east-west direction. We compare the results from the application of three different post-processing filters to the GRACE gravity-field solutions, and their ability to reduce the characteristic "striping". These are: (1) a statistical filter, where temporal trends inferred from the time series of the GRACE solution Stokes coefficients are tested for their statistical reliability, (2) an order-dependent filter, as applied by Swenson and Wahr (2006), and (3), an anisotropic moving average filter applied to the solutions in the spatial domain. We discuss the similarities and limitations of each filter, and their benefits for various aspects of GRACE analysis.