Die Glazialerscheinungen in Äquatorial- und Südafrika

Ohne Zusammenfassung     

Relationship between oil pollution and psammolittoral meiofauna density of two South African beaches

The effects of stranded oil from a tanker collision off the South African coast on the meiofauna ratio and density have been monitored over a period of 1 year on two sandy beaches. The perturbation of two beaches was judged against reference beach meiofauna density behaviour. In the undisturbed beach, oil deposited in sediment depressed harpacticoid copepod numbers, while numbers of nematodes stayed similar to those of the reference levels. Removal of surface sand in the mechanically disturbed beach had a greater influence on the density of animals than oil. Both beaches showed recovery after six months, but evidence of pollution by oil of unknown origin was found.     

Die ostafrikanische Bruchtreppe

Ohne ZusammenfassungVortrag auf der Mitgliederversammlung der Geologischen Vereinigung Januar 1937.     

Variations in trace metal content of the mussel Choromytilus meridionalis (Kr.) with season and sex

Trace metal contents of whole bodies of mussels are presented. The metal concentrations are correlated with each other and variations between individuals and sexes with season and stage in sexual cycle are discussed.     

Quantifying the impact of chemicals on stable carbon and oxygen isotope values of raw pollen

Purification protocols to extract pollen from lake sediments contain chemicals that alter the carbon and oxygen pollen-isotope values according to pollen characteristics and family affiliation. Modern (raw) pollen of broad-leaved (Alnus glutinosa, Betula pendula, Carpinus betulus, Corylus avellana, Fagus sylvatica and Quercus robur) and coniferous tree species (Picea abies and Pinus sylvestris) were treated with potassium hydroxide (KOH), hydrofluoric acid (HF), sodium hypochlorite (NaClO) and sulphuric acid (H₂SO₄) to test the impact on δ¹³C_pollen and δ¹⁸O_pollen and assess the applicability in purification protocols. Pollen of broad-leaved and coniferous trees reacted differently to chemical exposure, but response patterns are generally alike. Alterations of δ¹³C_pollen values vary between + 1.0‰ (B. pendula, NaClO-treatment) and −5.0‰ (P. sylvestris, H₂SO₄-treatment). The δ¹³C_pollen values of raw and chemically treated samples seem to be related after treatments with KOH, NaClO and HF, whereas the application of H₂SO₄ led to inconsistent changes among species. The impact of chemicals on δ¹⁸O_pollen are more diverse and offsets range between +1.1‰ (C. avellana, NaClO-treatment) and −17.9‰ (P. sylvestris, H₂SO₄-treatment). In general, the use of isotope-altering chemicals in purification protocols should be brought to a minimum, but the application of KOH and NaClO seems mostly unproblematic before δ¹³C_pollen and δ¹⁸O_pollen analysis.     

Water balance estimation under the challenge of data scarcity in a hyperarid to Mediterranean region

Water budget analyses are important for the evaluation of the water resources in semiarid and arid regions. The lack of observed data is the major obstacle for hydrological modelling in arid regions. The aim of this study is the analysis and calculation of the natural water resources of the Western Dead Sea subsurface catchment, one which is highly sensitive to rainfall resulting in highly variable temporal and spatial groundwater recharge. We focus on the subsurface catchment and subsequently apply the findings to a large‐scale groundwater flow model to estimate the groundwater discharge to the Dead Sea. We apply a semidistributed hydrological model (J2000g), originally developed for the Mediterranean, to the hyperarid region of the Western Dead Sea catchment, where runoff data and meteorological records are sparsely available. The challenge is to simulate the water budget, where the localized nature of extreme rainstorms together with sparse runoff data results in few observed runoff and recharge events. To overcome the scarcity of climate input data, we enhance the database with mean monthly rainfall data. The rainfall data of 2 satellites are shown to be unsuitable to fill the missing rainfall data due to underrepresentation of the steep hydrological gradient and temporal resolution. Hydrological models need to be calibrated against measured values; hence, the absence of adequate data can be problematic. Therefore, our calibration approach is based on a nested strategy of diverse observations. We calculate a direct surface runoff of the Western Dead Sea surface area (1,801 km²) of 3.4 mm/a and an average recharge (36.7 mm/a) for the 3,816 km² subsurface drainage basin of the Cretaceous aquifer system.     

Numerical Solutions of Three-Dimensional Pressure-Bounded Magnetohydrostatic Flux Tubes

We present a three-dimensional technique for the solution of the magnetohydrostatic equations when we are modeling structures bounded by a current sheet that is free to move to satisfy pressure balance. The magnetic field is expressed in terms of Euler potentials and the equations are transformed to flux coordinates, greatly simplifying the problem of locating the free boundary. Multi-grid techniques are used to rapidly solve the resulting nonlinear elliptic partial differential equations. The method is tested against Low's (1982) exact solution of a bipolar plasma loop. It is shown that fast, accurate solutions can be found.     

The effect of dike geometry on different resistivity configurations

Geoelectrical profiling with multi-electrode systems has become an important tool for monitoring dike embankments bordering rivers. Profiles running perpendicular to the dike axis are affected by the dike topography, with the amplitude of this effect dependent on the surface geometry and the choice of the electrode configuration. Investigations using seven different electrode configurations have shown that some configurations are less sensitive to the topography than others.The topography correction method (TCM) is an important tool for processing data from measurements at river dikes. This method is generally recommended for flank angles steeper than 10°. The topography effect is calculated by two-dimensional finite element modelling. The resulting synthetic data of a homogeneous dike body are used to apply a topographic correction for each measurement.The topographic effect and correction procedure is demonstrated for synthetic dike data and for a data set from a river dike in Thai Binh province (Vietnam). The topography can be ignored for flank angles less than 25° if an averaged Half-Wenner electrode configuration is used. This configuration has proved to be less affected by undulated topography and the focusing effect of averaging the two data sets provides reliable structural information without the need for time-consuming data inversion.