Einige Ergebnisse der geologischen Landesaufnahme in den Westtiroler Zentralalpen

Ohne Zusammenfassung     

Sediments of Lake Vens (SW European Alps,France) record large-magnitude earthquake events

We studied sediment cores from Lake Vens (2,327 m asl), in the Tinée Valley of the SW Alps, to test the paleoseismic archive potential of the lake sediments in this particularly earthquake-sensitive area. The historical earthquake catalogue shows that moderate to strong earthquakes, with intensities of IX–X, have impacted the Southern Alps during the last millennium. Sedimentological (X-ray images, grain size distribution) and geochemical (major elements and organic matter) analyses show that Lake Vens sediments consist of a terrigenous, silty material (minerals and organic matter) sourced from the watershed and diatom frustules. A combination of X-ray images, grain-size distribution, major elements and magnetic properties shows the presence of six homogenite-type deposits interbedded in the sedimentary background. These sedimentological features are ascribed to sediment reworking and grain sorting caused by earthquake-generated seiches. The presence of microfaults that cross-cut the sediment supports the hypothesis of seismic deposits in this system. A preliminary sediment chronology is provided by ²¹⁰Pb measurement and AMS ¹⁴C ages. According to the chronology, the most recent homogenite events are attributable to damaging historic earthquakes in AD 1887 (Ligure) and 1564 (Roquebillière). Hence, the Lake Vens sediment recorded large-magnitude earthquakes in the region and permits a preliminary estimate of recurrence time for such events of ~400 years.     

Experimental determination of REE fractionation between liquid and vapour in the systems NaCl–H2O and CaCl2–H2O up to 450 °C

Fractionation of selected REE between brine and vapour was experimentally determined using a large-volume rocking Ti-autoclave that allowed quasi-isobaric sampling of liquid-vapour pairs. Samples were extracted along the 350, 400 and 450 °C-isotherms of the H₂O-NaCl system, and along the 400 °C isotherm of the CaCl₂ system. Total salt concentrations were either 6.6 and 10 wt% NaCl or CaCl₂, respectively, and total REE concentrations were about 2 ppm of each REE. Starting pH at room temperature was 1.8, added as HCl. In another series of experiments, REEs were added in amounts of 312 ppm. Here, the starting pH at room temperature was 0.5, added as HNO₃:HCl=1:2. Liquid-vapour pairs (L-V) were analysed for REE by ICP-MS methods. L-V-partitioning of REE along a particular isotherm follows broadly the partitioning of the main salt components, NaCl or CaCl₂. D_REE=REE^V/REE^L decrease rapidly from the critical point with decreasing pressure (equivalent to increasing salinity of the liquid) as the solvus opens. This is independent of the total amount of the added REE. Log D_REE values show approximately linear correlations with decreasing pressure from the critical point to salt-saturated conditions where the L-V curve meets the liquid + vapour + solid boundary. At given P and T, we found a systematic variation of D_REE along the La-Lu suite. HREE are enriched in the vapour phase relative to LREE. Fractionation coefficients K_D=(HREE^V/HREE^L)/(LREE^V/LREE^L) increase linearly with (P=P_crit-P along a particular isotherm. At the 450 °C isotherm, K_D (Lu/La) at the critical point (425 bar and 10 wt% NaCl) is 1; about 2.5 at 350 bar (33 wt% NaCl in the liquid); and about 5 if extrapolated to salt-saturation (250 bar and 52 wt% NaCl in the liquid). The REE fractionation behaviour is similar along the CaCl₂-H₂O solvus boundaries. Existing equations of state and thermodynamic databases of REE species cannot predict this behaviour at L-V-equilibrium conditions. That HREE are preferentially fractionated over LREE into the vapour phase has important petrogenetic consequences. In boiling hydrothermal systems, brines will be depleted in HREE relative to LREE. Isobaric cooling is ineffective for fractionation because the solvus closes and the system eventually shifts into the one-phase field. Fractionation is most effective in systems undergoing isothermal or adiabatic decompression. In an open system, where vapour may escape through cavities, fractionation is probably controlled by a Rayleigh fractionation process, resulting in larger overall fractionation effects. Similar fractionations probably occur during magma degassing at very shallow intrusion levels.     

Mutagenicity of Baltic seawater and the relation to certain chemical and microbiological parameters.

The presented work investigates the mutagenicity of seawater with regard to its distribution along the German Baltic Sea coastline. Further on in this paper the relationship between mutagenic activity and certain chemical, microbiological and physical parameters is analysed. Water samples were drawn from eight places between Eckernf?rde and Ribnitz-Damgarten. Seawater was concentrated using XAD-2/7 resin. Extracts of up to 3-l per plate were tested with the Salmonella mutagenesis assay employing the strains TA 98 and TA 100 with and without addition of S9-mixture for metabolic activation. Samples from Weissenhaus, Travemünde and Wismar demonstrated a mutagenic activity with the strain TA 98. Tested filter sediment was not mutagenic. The sum of six polycyclic aromatic hydrocarbons (PAH) concentrated by XAD resin and obtained by high performance liquid chromatography (HPLC) were between 0.03 and 34.11 ng/l seawater. No correlation of measured mutagenicity and chemical or physical parameters could be established. The sampling place Wismar with one mutagenic sample had the highest number of colony forming units of Escherichia coli.     

Application of a hydrometeorological model chain to investigate the effect of global boundaries and downscaling on simulated river discharge

In the current study, two regional climate models (MM5 and REMO) driven by different global boundary conditions (the ERA40 reanalysis and the ECHAM5 model) are one-way coupled to the uncalibrated hydrological process model PROMET to analyze the impact of global boundary conditions, dynamical regionalization and subsequent statistical downscaling (bilinear interpolation, correction of subgrid-scale variability and combined correction of subgrid-scale variability and bias) on river discharge simulation. The results of 12 one-way coupled model runs, set up for the catchment of the Upper Danube (Central Europe) over the historical period 1971–2000, prove the expectation that the global boundaries applied to force the RCMs strongly influence the accuracy of simulated river discharge. It is, however, noteworthy that all efficiency criteria in case of bias corrected MM5 simulations indicate better performance under ERA40 boundaries, whereas REMO-driven hydrological simulations better correspond to measured discharge under ECHAM5 boundaries. Comparing the hydrological results achievable with MM5 and REMO, the application of bias-corrected MM5 simulations turned out to allow for a more accurate simulation of discharge, while the variance in simulated discharge in most cases was better reflected in case of REMO forcings. The correction of subgrid-scale variability within the downscaling of RCM simulations compared to a bilinear interpolation allows for a more accurate simulation of discharge for all model configurations and all discharge criteria considered (mean monthly discharge, mean monthly low-flow and peak-flow discharge). Further improvements in the hydrological simulations could be achieved by eliminating the biases (in terms of deviations from observed meteorological conditions) inherent in the driving RCM simulations, regardless of the global boundary conditions or the RCM applied. In spite of all downscaling and bias correction efforts described, the RCM-driven hydrological simulations remain less accurate than those achievable with spatially distributed meteorological observations.     

A 4D sedimentological approach to reconstructing the flood frequency and intensity of the Rhône River (Lake Bourget,NW European Alps)

A high-resolution sedimentological study of Lake Bourget was conducted to reconstruct the flood frequency and intensity (or magnitude) in the area over the last 350 years. Particular emphasis was placed on investigating the spatio-temporal distribution of flood deposits in this large lake basin. The thicknesses of deposits resulting from 30 flood events of the Rhône River were collected over a set of 24 short sediment cores. Deposit thicknesses were compared with instrumental data for the Rhône River discharge for the period from 1853 to 2010. The results show that flood frequency and intensity cannot be reliably reconstructed from a single core because of the inhomogeneous flood-deposit geometry in such a large lake. From all documented flood-deposit thicknesses, volumes of sediment brought into the lake during each flood event were computed through a Kriging procedure and compared with the historical instrumental data. The results show, in this study, that reconstructed sediment volumes are well correlated to maximal flood discharges. This significant correlation suggests that the increase of embankment and dam settlements on the Rhône River during the last 150 years has not significantly affected the transport of the smallest sediment fraction during major flood events. Hence, assessment of the flood-sediment volumes deposited in the large Lake Bourget is the only way to reliably reconstruct the flood frequency and intensity.     

I. Erdöl Ergebnisse der erdölgeologischen Erforschung Nordwestdeutschlands 1932–1947, ein Überblick

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Seychelles coral record of changes in sea surface temperature bimodality in the western Indian Ocean from the Mid-Holocene to the present

We report fossil coral records from the Seychelles comprising individual time slices of 14–20 sclerochronological years between 2 and 6.2 kyr BP to reconstruct changes in the seasonal cycle of western Indian Ocean sea surface temperature (SST) compared to the present (1990–2003). These reconstructions allowed us to link changes in the SST bimodality to orbital changes, which were causing a reorganization of the seasonal insolation pattern. Our results reveal the lowest seasonal SST range in the Mid-Holocene (6.2–5.2 kyr BP) and around 2 kyr BP, while the highest range is observed around 4.6 kyr BP and between 1990 and 2003. The season of maximum temperature shifts from austral spring (September to November) to austral autumn (March to May), following changes in seasonal insolation over the past 6 kyr. However, the changes in SST bimodality do not linearly follow the insolation seasonality. For example, the 5.2 and 6.2 kyr BP corals show only subtle SST differences in austral spring and autumn. We use paleoclimate simulations of a fully coupled atmosphere–ocean general circulation model to compare with proxy data for the Mid-Holocene around 6 kyr BP. The model results show that in the Mid-Holocene the austral winter and spring seasons in the western Indian Ocean were warmer while austral summer was cooler. This is qualitatively consistent with the coral data from 6.2 to 5.2 kyr BP, which shows a similar reduction in the seasonal amplitude compared to the present day. However, the pattern of the seasonal SST cycle in the model appears to follow the changes in insolation more directly than indicated by the corals. Our results highlight the importance of ocean–atmosphere interactions for Indian Ocean SST seasonality throughout the Holocene. In order to understand Holocene climate variability in the countries surrounding the Indian Ocean, we need a much more comprehensive analysis of seasonally resolved archives from the tropical Indian Ocean. Insolation data alone only provides an incomplete picture.     

The sensitivity of the Indian summer monsoon to a global warming of 2��C with respect to pre-industrial times

In this study the potential future changes in different aspects of the Indian summer monsoon associated with a global warming of 2°C with respect to pre-industrial times are assessed, focussing on the role of the different mechanisms leading to these changes. In addition, these changes as well as the underlying mechanisms are compared to the corresponding changes associated with a markedly stronger global warming exceeding 4.5°C, associated with the widely used SRES A1B scenario. The study is based on two sets of four ensemble simulations with the ECHAM5/MPI-OM coupled climate model, each starting from different initial conditions. In one set of simulations (2020?C2200), greenhouse gas concentrations and sulphate aerosol load have been prescribed in such a way that the simulated global warming dioes not exceed 2°C with respect to pre-industrial times. In the other set of simulations (1860?C2200), greenhouse gas concentrations and sulphate aerosol load have been prescribed according to observations until 2000 and according to the SRES A1B scenario after 2000. The study reveals marked changes in the Indian summer monsoon associated with a global warming of 2°C with respect to pre-industrial conditions, namely an intensification of the summer monsoon precipitation despite a weakening of the large-scale monsoon circulation. The increase in the monsoon rainfall is related to a variety of different mechanisms, with the intensification of the atmospheric moisture transport into the Indian region as the most important one. The weakening of the large-scale monsoon circulation is mainly caused by changes in the Walker circulation with large-scale divergence (convergence) in the lower (uppper) troposphere over the Indian Ocean in response to enhanced convective activity over the Indian Ocean and the central and eastern Pacific and reduced convective activity over the western tropical Pacific. These changes in the Walker circulation induce westerly (easterly) wind anomalies at lower (upper) level in the Indian region. The comparison with the changes in the Indian summer monsoon associated with a global warming of 4.5°C reveals that both the intensification of the monsoon precipitation and the weakening of the large-scale monsoon circulation (particularly in the lower troposphere) are relatively strong (with respect to the magnitude of the projected global warming by the end of the twentieth century for the two scenarios) in the scenario with a global warming of 2°C. The relatively strong intensification of the monsoon rainfall is related to rather strong increases in evaporation over the Arabian Sea and the Bay of Bengal, while a rather weak amplification of the meridional temperature gradient between the Indian Ocean and the land areas to the north contributes to the relatively strong reduction of the large-scale monsoon flow.