ALBERT

Beschreibung: Lateglacial and Holocene faunal and stable-isotope records from benthic foraminifers in the eastern Mediterranean Sea (EMS) suggest a high spatiotemporal variability of deep-water oxygenation and biogeochemical processes at the sea floor during that time. Changes in the oxygenation and food availability of the deep-sea ecosystems are closely linked to the hydrology of the EMS borderlands; they reflect orbital and suborbital climate variations of the high northern latitudes and the African monsoon system. During the last glacial maximum, cool surface waters and high evaporation resulted in maximum convection and oxic deep-waters in all sub-basins. Strong wind-induced mixing fostered surface-water production with seasonal phytodetritus fluxes. During the glacial termination and the Holocene, oxygenation and food availability of deep-sea benthic ecosystems were characterized by a pronounced regional differentiation. Local deep-water formation and trophic conditions were particularly variable in the northern Aegean Sea as a response to changes in riverine runoff and Black Sea outflow. During the interval of sapropel S1 formation in the early Holocene, average oxygen levels decreased exponentially with increasing water depth, suggesting a basin-wide shallowing of vertical convection superimposed by local signals. In the northernmost Aegean Sea, deep-water ventilation persisted during the early period of S1 formation, owing to temperature-driven local convection and the absence of low-salinity Black Sea outflow. At the same time, severe temporary anoxia occurred in the eastern Levantine basin at water depths as shallow as 900 m. This area was likely influenced by enhanced nutrient input of the Nile river that resulted in high organic matter fluxes and related high oxygen-consumption rates in the water column. In the southern Aegean and Levantine Seas, we observe a gradual increase in deep-water residence times, preceding S1 formation by approximately 1–1.5 kyr. Once oxygen levels fell below a critical threshold, the benthic ecosystems collapsed almost synchronously with the onset of S1 deposition. The recovery of benthic ecosystems during the terminal phase of S1 formation is controlled by subsequently deeper convection and re-ventilation over a period of approximately 1500 years. After the re-ventilation of the various sub-basins had been completed during the middle and late Holocene, deep-water renewal was more or less similar to recent rates. During that time, deep-sea ecosystem variability was driven by short-term changes in food quantity and quality as well as in seasonality, all of which are linked to millennial-scale changes in riverine runoff and associated nutrient input.

Beschreibung: Comparing the organic matter (OM) composition of modern and past lake sediments contributes to the understanding of changes in lacustrine environments over time. We investigate modern plant and lake-water samples as well as modern and ancient sediment samples from the Tswaing Crater in South Africa using biomarker and stable carbon isotope analyses on bulk OM and specific biomarker compounds. The characteristic molecular markers for higher land plants (predominantly C3-type deciduous angiosperms) in Lake Tswaing are long-chain n-alkanes (n-C27−33), n-alkanols (n-C28+30), stigmasterol, β-sitosterol, β-amyrin, α-amyrin and lupeol. The C17 n-alkane, tetrahymanol, gammaceran-3-one and C29 sterols dominate the lipid fraction of autochthonously produced OM. By comparing stable carbon isotope analyses on bulk OM and the characteristic biomarkers, we follow the modern carbon cycle in the crater environment and find indications for methanotrophic activity in the lake from isotopically depleted moretene. A comparative study of core sediments reveals changes in the terrestrial (C3 versus C4) and aquatic bioproductivity and allows insights into the variability of the carbon cycle under the influence of changing climatic conditions for the time from the end of the last glacial (Termination I) to the late Holocene, ca. 14,000–2,000 calibrated years before present (years BP). The most pronounced changes occur in the aquatic realm after ca. 10,000 years BP when our results imply climate swings from more humid to more arid and after 7,500 years BP to gradually more humid conditions again, which can be related to a shift in the position of the Inter-Tropical Convergence Zone or to changes in the tropical atmosphere–ocean interaction. Long-chain alkenones (LCAs) have been identified in ancient lake sediments from Africa for the first time. They occur in samples older than 7,500 years BP and their distribution (dominance of C38 and of tri- over tetra-unsaturated LCAs) is distinctly different from other published records suggesting a to date unknown source organism.

Beschreibung: Der Wasserspiegel des Toten Meeres sinkt rapide um durchschnittlich einen Meter pro Jahr. Dadurch hat der Salzsee bereits ein Drittel seiner Oberfläche verloren. Dies hat u. a. dramatische Auswirkungen auf die einzigartige Ökologie. Entlang der ausgedörrten Ufer bilden sich täglich neue so genannte Erdfälle oder Sinkholes, die bis zu 20 Meter tief sind. Gut 1000 dieser plötzlich einfallenden Sinkholes haben sich inzwischen an der Küstenlinie des Toten Meeres gebildet. Während der Messkampagne zum Dead Sea Integrated Research Project (DESIRE) 2007 wurde das Küstengebiet südlich von Ein Gedi zusätzlich mit einem Laser Mirror Scanner der Firma RIEGL beflogen, um entsprechende Sinkholes zu detektieren. Das Gebiet besitzt eine Ausdehnung von etwa 20 mal 4 km. Die Datenakquirierung erfolgte durch Befliegung in Nord-Süd-Richtung in 20 Streifen und einer Überdeckung von 50%. Für die Auswertung stand die Software TopPIT der Firma Trimble Geospatial zur Verfügung. Ziel der Befliegung ist neben der Berechnung eines Digitales Geländemodells (DGM) die Schaffung einer Bestandsaufnahme bestehender Sinkholes, durch die Veränderungen im Vergleich mit zukünftigen Aufnahmen aufgedeckt werden können. Zudem soll die Leistungsfähigkeit der eingesetzten Messmethode als geeignetes Verfahren nachgewiesen werden.

Beschreibung: Although studies on stable-carbon isotopes in trees from temperate zones provide abundant paleoclimatic data, tropical trees are still understudied in this context. Therefore this study examined the variability of intra- and inter-annual stable-carbon isotopic pattern in several tree species from various tropical climates. The delta C-13 Values of samples of 12 broadleaved trees (seven species) from various paleotropical and neotropical sites along a climatic moisture gradient were investigated. The inter-annual variability between species and sites was studied. Further the relationship between delta C-13 and precipitation time series was analyzed. Results show that tropical tree species show a similar variability in carbon isotopic composition as temperate tree species. Significant correlations between annual precipitation and tree-ring delta C-13 time series were negative. Successful crossdating of a tree-ring delta C-13 time series highlights the potential of carbon isotope measurements for tropical tree-ring analytical studies. Tropical broadleaved trees are able to capture a carbon isotopic signal in their annual rings even under everwet conditions and show good potential for paleoclimatic research.

Beschreibung: This study reveals the first analyses of the composition and activity of the microbial community of a saline CO2 storage aquifer. Microbial monitoring during CO2 injection has been reported. By using fluorescence in situ hybridisation (FISH), we have shown that the microbial community was strongly influenced by the CO2 injection. Before CO2 arrival, up to 6 × 106 cells ml−1 were detected by DAPI staining at a depth of 647 m below the surface. The microbial community was dominated by the domain Bacteria that represented approximately 60% to 90% of the total cell number, with Proteobacteria and Firmicutes as the most abundant phyla comprising up to 47% and 45% of the entire population, respectively. Both the total cell counts as well as the counts of the specific physiological groups revealed quantitative and qualitative changes after CO2 arrival. Our study revealed temporal outcompetition of sulphate-reducing bacteria by methanogenic archaea. In addition, an enhanced activity of the microbial population after five months CO2 storage indicated that the bacterial community was able to adapt to the extreme conditions of the deep biosphere and to the extreme changes of these atypical conditions.

Beschreibung: In order to assess the importance of different pollution sources for the increase in element concentration and accumulation, historical changes in selected elements were studied in the annually laminated sediment of Lake Korttajärvi in Central Finland (62°20′N; 25°41′E). The sediment chronology based on varve counting (256 BC to AD 2005) provided a unique opportunity to explore and date signals of metal emissions, including the ancient metallurgical activities of the Roman Empire at the beginning of the Current Era. Records of this kind are mostly lacking in Finland and northernmost Europe. The stratigraphic sequence of element concentrations did not reflect any major changes in the lake, but changes in element accumulation rates provided distinct pollution signals caused by airborne fallout, catchment erosion, and to some extent municipal wastewater loading. The maximum bulk sedimentation recorded in the twentieth century was 11-fold and organic sedimentation 4-fold higher than the mean background sedimentation rate (256 BC to AD 1019). The increase in the accumulation rates of the majority of the elements, such as Cd, Sn, Pb, Si, Ni, B, Cu, Zn, Sr, Na, K, Sb, Ca, Cr, U and Mg, in descending order, was at least equal to that of bulk sedimentation or much greater, especially for Cd, Sn, and Pb. Changes in the accumulation of Co, Fe, Mn, Mo and As were small and mainly followed those of organic sedimentation. The earliest pollution signals were those of Pb recorded in AD 1055–1141. A weak signal of Pb pollution from the Roman Era was detected in metal concentrations, but this could not be confirmed by the accumulation rate data for Pb.

Beschreibung: Many studies on ecosystem resilience often lack sufficiently long time scales to determine potential cycles of landscape response. In this paper we review some examples on how palaeoecology has provided an important aid to modern ecology in understanding ecosystem resilience. We focus some of these ideas on two Holocene sites from Southern Spain (Zoñar and Gádor) where current plant diversity is very high. Both sites presented resilient pattern at centennial and millennial time scales with several stable phases. Vegetation in Zoñar proved to be very sensitive to environmental changes, especially moisture availability while forest in Gádor responded elastically to fire and drought to a threshold level when the forest recede to a more open landscape. We conclude that any serious attempt to understand ecosystem resilience should include the long-term perspective.

Beschreibung: The isotope composition of iron in soils bears a signature of the environmental conditions that formed this soil. But plants extract only the mobile iron from soil, which is a small fraction of the soils total iron. Yet this fraction is notoriously difficult to extract experimentally. Here we provide evidence that this signature is provided readily in the form of strategy II plants (grasses). To this end we determined the stable Fe isotope signature of iron pools in two agronomic soils with two different sequential extraction methods. The Fe isotopic composition of the following soil mineral pools was resolved: exchangeable iron, iron of poorly-crystalline (oxyhydr)oxides, iron in organic matter, iron of crystalline oxides and silicate bound iron. We found variations of about 1 per mil in δ56Fe (δ56Fe/[‰] = [(56/54Fesample/56/54FeIRMM-014) -1] • 103) in the iron isotopic composition between the different soil mineral pools. The pools that are identified to contribute most to plant nutrition are water-extractable- and exchangeable iron, iron in organic matter and iron of poorly-crystalline (oxyhydr)oxides. These fractions are about 0.3 per mil lighter than the bulk soils. Silicates in our soils have a δ56Fe of up to 0.4 ‰, suggesting preferential loss of light iron during weathering. We compared the isotope composition of the plant-available Fe to that of typical strategy I and strategy II plants, grown on the soils. While redox and other transformation processes in the rhizosphere enrich strategy I plants to varying degrees in light iron isotopes, strategy II plants exhibit a uniform Fe isotopic composition and are only slightly enriched in the heavier iron isotopes by about 0.3 ‰. Therefore these plants may record the Fe isotope composition of plant-available iron in soils, to which the composition of strategy I plants can be compared to. Keywords: Fe isotopes, higher plants, MC-ICP-MS, isotope fractionation, soils

Beschreibung: The Seferihisar–Balçova Geothermal system (SBG) is characterized by complex temperature and hydrochemical anomalies. Previous geophysical and hydrochemical investigations suggest that hydrothermal convection in the faulted areas of the SBG and recharge flow from the Horst may be responsible for the observed patterns. A numerical model of coupled fluid flow and heat transport processes has been built in order to study the possible fluid dynamics of deep geothermal groundwater flow in the SBG. The results support the hypothesis derived from interpreted data. The simulated scenarios provide a better understanding of the geophysical conditions under which the different fluid dynamics develop. When recharge processes are weak, the convective patterns in the faults can expand to surrounding reservoir units or below the seafloor. These fault-induced drag forces can cause natural seawater intrusion. In the Melange of the Seferihisar Horst, the regional flow is modified by buoyant-driven flow focused in the series of vertical faults. As a result, the main groundwater divide can shift. Sealing caprocks prevent fault-induced cells from being overwhelmed by vigorous regional flow. In this case, over-pressured, blind geothermal reservoirs form below the caprocks. Transient results showed that the front of rising hot waters in faults is unstable: the tip of the hydrothermal plumes can split and lead to periodical temperature oscillations. This phenomenon known as Taylor–Saffman fingering has been described in mid-ocean ridge hydrothermal systems. Our findings suggest that this type of thermal pulsing can also develop in active, faulted geothermal systems. To some extent, the role of an impervious fault core on the flow patterns has been investigated. Although it is not possible to reproduce basin-scale transport processes, this first attempt to model deep groundwater geothermal flow in the SBG qualitatively supported the interpreted data and described the different fluid dynamics of the basin.

Beschreibung: A passive seismic array which operated between December 2007 and November 2010 has been deployed in the southern Puna plateau between 25°S to 28°S latitude and 65W to 70W longitude in Argentina and Chile to address fundamental questions on the processes that form, modify and destroy continental lithosphere and control lithospheric dynamics along Andean-type continental margins. This experiment consisted of 75 stations has been conducted by Argentine, Chilean, German and US scientists and was designed to improve our understanding of the evolution of the Central Andean plateau in an area where there is a very little geophysical data available.We present here some preliminary results form P and S receiver functions that enables us to address fundamental questions about the role of crustal and mantle lithospheric delamination in the evolution of plateau regions and the evolution of the continental crust in general. Our aim is to determine the seismic structure and thickness of the continental crust and the lithospheric mantle beneath the southern Puna plateau.We also want to determine the thickness of the mantle transition zone beneath the southern Puna and constrain the geometry and rheology of the subducting slab. As a collaborative project, our network has been designed to use other standard broadband seismological methods besides receiver function involving surface wave tomography, tomographic travel time inversion, and shear wave splitting analysis.

Beschreibung: High-quality observations have been obtained from a number of magnetic satellites, complementing the ground available data for the last decade. We present here the issues regarding observatory and satellite data, in order to show how these modern measurements have brought new insights in understanding the Earth's magnetic field. It is only when combined with ground-based data that satellite measurements can provide additional opportunities for studies ranging from core flow, mantle conductivity and lithospheric composition to the dynamics of the ionospheric and magnetospheric currents. Therefore, in this paper a case is presented for the necessity of continuous monitoring of geomagnetic field from ground and space. This contribution is mainly based on some recent work and publications we are co-authoring.

Beschreibung: The Dead Sea Transform (DST) is a system of left-lateral strike-slip faults that accommodates the relative motion between the African and Arabian plates. Furthermore the water level of the Dead Sea is sinking rapidly at an average of one meter per year. Because of this the salt lake has already lost one third of its surface and along the parched shores are formed daily new sinkholes that are up to 20 meters deep. About 1000 of these sudden incident sinkholes have formed in the meanwhile the shoreline of the Dead Sea. They represent danger both to life and property, disrupt life in the area, and aversely affect building and development. During the measurement campaign for the Dead Sea Integrated Research Project (DESIRE) 2007 the coastal area was flown to the south of En Gedi also with a laser mirror scanner constructed by RIEGL to detect relevant sinkholes. The airborne survey area covers a surface of approximately 20 by 4 km. The data acquisition was done by flights in North-South direction in 20 strips with an overlap of 50 percent. For the data analysis focused on the software TopPIT of Trimble Geospatial was used. The aim of the airborne survey was the calculation of a digital terrain model (DTM) but also the creation of an inventory of existing sinkholes, that can be used to detect temporal changes by comparison with future recordings. Moreover, the efficiency of the method used should be demonstrated as an appropriate procedure compared with traditional field data collection.

Beschreibung: Stable oxygen isotope analyses at annual, 2-, 5- and 10-varve sample resolution were carried out on two selected varve intervals from the interglacial sediment record of the Piànico palaeolake. These sediments are particularly suitable for ultra-high resolution isotope analyses on lacustrine endogenic calcite because of the exceptionally well-preserved varve structure. A bias through detrital contamination can be excluded because microscopically controlled sampling enabled selecting detrital-free samples. The studied sediment intervals comprise 352 and 88 continuous varve series formed during periods of rapid climate change at the onset and end of a marked millennial-scale cool interval during the Piànico interglacial. The most intriguing result is a pronounced short-term oscillation in the bi-annually resolved isotope record superimposed on the general decreasing and increasing δ18O trends at the climatic transitions that is recorded at lower sample resolution. Spectral analyses of the bi-annual time series reveal periodicities indicating solar and NAO controls on the δ18O record. Multiple δ18O measurements from endogenic calcite of individual varves showed variations of up to 0.6 ‰, thus larger than the observed inter-annual variability and most likely explained by seasonal effects.

Beschreibung: The Sumatra-Andaman earthquake with a magnitude of 9.3, and the subsequent destructive tsunami which caused more than 225 000 fatalities in the region of the Indian Ocean, happened on 26 December 2004. Less than one month later, the United Nations (UN) World Conference on Disaster Reduction took place in Kobe, Japan to commemorate the 1995 Kobe earthquake. The importance of preparedness and awareness on regional, national and community levels with respect to natural disasters was discussed during this meeting, and resulted in the approval of the Hyogo Declaration on Disaster Reduction. Based on this declaration the UN mandated the Intergovernmental Oceanographic Commission (IOC) of UNESCO (United Nations Education, Science and Cultural Organization), taking note of its over 40 years of successful coordination of the Pacific Tsunami Warning System (PTWC), to take on the international coordination of national early-warning efforts for the Indian Ocean and to guide the process of setting up a Regional Tsunami Early Warning System for the Indian Ocean.

Beschreibung: Holocene palaeomagnetic secular variation (PSV) in inclination and declination recorded in the sediment remanent magnetization of two small lakes, Lake Lehmilampi (63°37'N, 29°06'E) and Lake Kortejärvi (63°37'N, 28°56'E) in eastern Finland is presented. As an outcome of systematic coring, eight cores, 300–753 cm in length, were investigated. All samples (Lehmilampi n= 1320, Kortejärvi n= 943) were subjected to palaeo- and mineral magnetic analyses. The directions of the characteristic remanent magnetization (ChRM) were obtained from progressive alternating field demagnetization of the natural remanent magnetization (NRM) followed by principle component analysis. The younger sections of the sediment columns in the studied lakes are annually laminated, providing detailed chronologies for dating PSV features back to 5100 cal. BP. The underlying older sections of the cores were dated by palaeomagnetic pattern matching in respect to varve-dated Lake Nautajärvi PSV data (Ojala & Saarinen 2002), thus yielding a composite age model covering nearly the whole Holocene epoch. Average sedimentation rates ranging from ∼0.68 to 0.74 mm yr−1 enabled recording of changes in the geomagnetic field at decadal resolution. The carriers of remanence are dominantly magnetite of stable single-domain to pseudo-single-domain grain size, accompanied by magnetic minerals of harder coercivity. The sediments from both lakes exhibit strong and stable single-component magnetizations nearly throughout the whole cores. The sediment magnetization lock-in delay is estimated to range between 80 and 100 yr. PSV data were transformed into time-series and subsequently stacked to comprise North Karelian stack, and Fisher statistics were used to calculate mean directions together with the 95 per cent confidence level (α95). A comparison of declination and inclination features of the North Karelian stack with previously published data expresses remarkable similarity, therefore confirming the similar source behind the changes in the NRM directional records. The high quality of the PSV data extracted from Lehmilampi and Kortejärvi, in terms of dating as well as amplitude reconstruction, have a high potential to improve existing and future geomagnetic field models.

Beschreibung: A high-resolution geochemical profile from a 5,500-year-old sediment core of Lake Lehmilampi in eastern Finland was analyzed to study long-term trends and variability in element concentrations and accumulation rates. The accumulation rates of all studied elements followed the same trend, responding to changes in the total sedimentation rate. Concentration profiles differed among elements and showed considerable variation over time. Principal components analysis (PCA) was used on the concentration data to identify groups of elements that have similar geochemical controls. The first principal component was influenced by changes in mineral matter accumulation, and it incorporated elements that are associated with stable allochthonous minerals (such as Mg, K, Cs, Rb, Li, Ti and Ga), as well as elements in forms that become diluted when mineral matter increases (e.g., S, Fe and Mn). The second and third principal components showed that a large proportion of the variance was accounted for by elements with continuously increasing or decreasing concentrations related to pedogenetical development of the catchment soil. In the case of Hg, Pb and Cd, however, accumulation rates increased faster at the surface than is simply accounted for by changes in total sedimentation rates. For Cu, Cr, Ni and Zn, concentrations increased over the past 150 years, but there were no indications of a significant addition due to atmospheric deposition. These elements had more variable concentrations before the mid nineteenth century than after, as did elements that are often used for normalization. These findings suggest that lake sediments may not properly reflect the history of atmospheric metal deposition in remote areas.

Beschreibung: Thinning is the main forestry measure to increase tree growth by reducing stand tree density and competition for resources. A thinning experiment was established in 1993 on a 32-year-old Pinus nigra Arn. stand in central Spain. The response of growth, climate-growth relationships and intrinsic water use efficiency (WUEi) to a stand density reduction were compared between moderate thinned plots and a control plot by a combined analysis of basal area increments (BAI), and C and O stable isotope ratios (delta C-13(c) and delta O-18(c)). BAI in the control plot showed a decreasing trend that was avoided by thinning in the thinned plot. Thinning also partially buffered tree-ring response to climate and trees were less sensitive to precipitation although more sensitive to temperature. Delta C-13(c) in the thinned plot was not modified indicating that stomatal conductance (g) and photosynthetic capacity (A) did not change or change in the same direction. However, delta O-18(c) decreased in the control plot (unrelated to delta O-18 of precipitation) but not in the thinned plot, suggesting a relative increase of temperature and irradiance and/or a decrease of air humidity after reducing the density consistent with an increase in A, g and BAI. As WUEi did not increase in the thinned plot, faster growth in this plot was caused by higher abundance of resources per tree. The trend of WUEi in both plots indicated low-moderate CO2-induced improvements. Thinning might be a useful adaptation measure against climate change in these plantations reducing their vulnerability to droughts. However, because WUEi was not affected, the positive growth response might be limited if droughts and warming continue and certain thresholds are exceeded.

Beschreibung: Central and Northern Asia is a key natural laboratory for the study of active intra-continental deformation in response to the ongoing far-field collision of India and Eurasia. The induced tectonic processes strongly depend on the thermo-mechanical and compositional (density and thickness) structure of the lithosphere. In particularly, density anomalies within the crust and upper mantle are important factors that control Earth deformations at shallow and deep levels. Moreover, the inherited heterogeneity is responsible also for the local and regional stress field. The main aim of this collaborative research project is to construct new high-resolution 3-D models of the compositional, thermal and rheological structure of the lithosphere of the study area. These models will be constructed by combining and jointly analysing satellite gravity data with terrestrial data (seismic velocity distributions, seismic tomography, GPS derived surface deformations, heat flow measurements and terrestrial gravity). These models will be the basis for subsequent 3-D numerical modelling of the intra-plate stress and strain fields in Central and Northern Asia. Here we present a new crustal model including Moho and seismic velocity distribution for Central and Northern Asia. This model is primarily based on seismic data. Where data coverage is insufficient additional data such as topography and outline of the main tectonic provinces is used to obtain homogeneous models. The new crustal model will be used for the construction of the gravity, thermal, compositional and rheological models of the lithosphere. In the next phase of the project, the new model, combined with a thermal model of the crust and upper mantle, will be used to assess the 3D rheological strength (in)homogeneity of the lithosphere. Probing possible rheological strength variations is essential for a successful quantitative assessment of the present-day intra-plate deformation of the study area.

Beschreibung: Hyperspectral satellite remote sensing may considerably contribute to the mapping and monitoring of dryland plant communities in nature reserve areas. This is especially true in areas that are not otherwise accessible and are undergoing rapid changes due to land use conversion such as the nature reserve “Döberitzer Heide”. For the purpose of mapping and understanding dynamic vegetation structures within dryland habitats multidimensional vegetation samples were transformed into comprehensive data spaces, using non metric multidimensional scaling. The resulting topology of field samples, consisting of species abundance could be interpreted as the distribution of species similarities along environmental gradients. A spatially explicit prediction of these gradients could be achieved by generating deterministic models from a PLS1 regression between ordination axis metrics and spectral variables derived from field measurements and applying the resulting models to image spectra, recorded from the HyMap airborne scanner. A four dimensional color interpolation scheme enabled the visualization of variable transition zones in species composition. Furthermore spectral field measurements were used as input variables to a random Forest classification based on vegetation clusters within the resulting ordination space. The final decision tree, which is determined by an overall accuracy of 82 %, was applied to the same digital image data. The external validation as well as an interpretation of predicted vegetation structures indicates the potential of combining both methods to extract valuable additional information for the monitoring of dryland habitats.

Beschreibung: Within the framework of the German - South African geo-scientific research initiative Inkaba yeAfrica several magnetotelluric (MT) field experiments were conducted along the Agulhas- Karoo Transect in South Africa. This transect crosses several continental collision zones between the Cape Fold Belt, the Namaqua Natal Mobile Belt and Kaapvaal Craton. Along the profile we can identify areas (〉 10km) with phases over 90◦. This phenomenon usually occurs in presence of electrical anisotropy. Due to the dense site spacing we are able to observe this behaviour consistently at several sites. In this presentation we focus on the profile section between Prince Albert and Mosselbay. With isotropic 2D inversion we are able to explain most features in the MT data but not the abnormal phase behavior. With several anisotropic forward modelling studies we have tested the influence of anisotropy parameters on the MT responses. In a first step we use simple 2D models with embedded zones of electrical anisotropy to get a basic understanding of anisotropic responses. In a second step isotropic 2D inversion results serve as background models in which we included anisotropic zones, e.g. to fit the abnormal phase curves. These resolution tests are necessary and important for the future development of a 2D inversion with spatially constraint anisotropy.

Beschreibung: We present the second generation of the GFZ Reference Internal Magnetic Model (GRIMM-2), that was derived for the preparation of the GFZ candidate for the 11th generation of the IGRF. The model is built by fitting a vector data set made of CHAMP satellite and observatory data, spanning the period 2001.0 to 2009.5. The data selection technique and the model parametrization are similar to that used for the the derivation of the GRIMM model (Lesur et al., 2008). The obtained model is robust over the time span of the data. However, the secular variation above spherical harmonic degree 13 becomes less controlled by the data and is constrained by the applied regularisation before 2002 and after 2008.5. At best, only the spherical harmonic degrees 3 to 6 are robustly estimated for the secular acceleration. The problem associated with the first two spherical harmonic degrees of the secular acceleration model arise from the difficulty in separating the core field signal from the external fields and their internally induced counterparts. The regularization technique applied smoothes the magnetic field model in time. This affects all spherical harmonic degrees, but starts to be significant at spherical harmonic degree 5.