Microscale investigations of microbial communities in coastal surficial sediments

The upper millimeters of sediments are considered major locations of microbial colonization and activity. The goal of our study was to investigate variations of microbial communities in the uppermost sediment layers of the coastal Baltic Sea with emphasis on the complex interplay between microbiology and physico‐chemical sediment properties. We selected a high‐resolution methodological approach that combined the cryolanding sampling technique (spatial resolution of 250 μm) with microsensor‐, spectrophotometric and microscopic analyses. While the oxygen penetration depths in dark conditions ranged from 1.4 mm to 2.6 mm during the study period, this zone expanded by about 1 mm in light and could be divided into three micro‐horizons: (i) an upper zone with a high net O₂ production, (ii) an intermediate zone with increased O₂ consumption on account of light‐stimulated respiration and (iii) a lower zone with lower O₂ consumption. Time‐series experiments revealed a rapid response of the benthic microbial community to altered light intensities. In May and July, the net O₂ budget in the porewater of sediments was positive within 35 and 22 min after illumination, respectively, whereas in June O₂ production exceeded O₂ consumption after 112 min. The thickness of the O₂ production and O₂ consumption micro‐zones decreased from May to July coinciding with an increase in temperature. In May, sites of enhanced O₂ consumption were closely associated with subsurface maxima of microbial numbers and enzymatic activities indicating a tight coupling between photoautotrophic and heterotrophic processes between 1‐ and 2‐mm depth. In June and July, the microbial abundance and enzymatic activity hardly varied with depth. Spatial and temporal microheterogeneity of microbial distribution and activity in O₂ gradients was seen as a reflection of the complex interplay between microbiology and physico‐chemical sediment properties.     

Origin and regional significance of late Precambrian and early Palaeozoic granitoids in the Pan-African belt of Somalia

Granitoids within the Precambrian basement of north-eastern and southern Somalia are subdivided on the basis of geology, geochronology and petrology into three different assemblages. The post-kinematic assemblage in north-eastern Somalia ( 630 Ma) comprises granodiorites and granites which belong to a medium-K calc-alkaline suite. Average initial Sr, Nd and Pb isotopic ratios [Sr_i = 0.7048, _Nd = –1.8,²⁰⁶Pb/²⁰⁴Pb(i) = 17.704 and²⁰⁷Pb/²⁰⁴Pb(i) = 15.611] indicate that these melts were derived from a mantle or juvenile crustal source with only slight involvement of pre-existing crust as a contaminant. Two different assemblages are found in southern Somalia. The older assemblage is composed of crustal anatectic, synkinematic, parautochthonous granites ( 600 Ma) related to amphibolite facies retrogression of an intensively reworked pre-Pan-African crust [Sr_i = 0.7100, _Nd = –8.4,²⁰⁶Pb/²⁰⁴Pb(i) = 15.403 and²⁰⁷Pb/²⁰⁴Pb(i) = 15.259]. These monzo- and syenogranites are moderately potassic and peraluminous. The younger assemblage ( 470 Ma) consists of post-kinematic monzonites to syenogranites with A-type affinities. Initial Sr, Nd and Pb isotopic data for this metaluminous assemblage [Sr_i = 0.7114, _Nd = –13.1,²⁰⁷Pb/²⁰⁴Pb(i) = 16.913 and²⁰⁷Pb/²⁰⁴Pb(i) = 15.512] indicate a significant lower crustal component but, however, also a mantle signature. The late Proterozoic to early Palaeozoic granitoids in Somalia thus express contrasting regimes, characterized by strong juvenile input in the north, close to the Arabian-Nubian Shield, whereas intense crustal reworking with little addition of juvenile material prevailed in the south. Somalia was definitively not a cratonic area during the Pan-African, but a zone of high crustal mobility.     

Field campaign for the comparison of SOUSY radar wind measurements with rawinsonde and model data

A field campaign was carried out from 26 October to 7 November 1992, using the SOUSY-VHF radar and a mobile rawinsonde system installed and operated nearby to produce vertical wind profiles. The purpose of this campaign was to compare the two types of wind measurements with one another and with results from forecast models. Numerical algorithms were developed and applied to the radar data in order to eliminate random errors, correct for velocity aliasing, and calculate the effective zenith angle of the off-vertical beams. Differences between wind profiler data and rawinsonde or model results depend not only upon the errors of the different systems, but also on temporal and spatial variations of the wind field. Therefore, methods for the comparison of radar and rawinsonde data were developed which take into consideration these variations. The practical potential of these methods is demonstrated by comparisons of rawinsonde and radar wind profiles. The comparison of radar data and model output shows excellent agreement in the direction and in the speed of the wind at virtually all altitudes. An evaluation of the quality of wind profiler measurements is possible using the estimation of variance and variability of wind components.     

Analysis and interpretation of VHF-radar data

Doppler measurements have been carried out during a variety of observational campaigns using the stationary and the mobile SOUSY-VHF-Radars. The general data reduction procedure is presented in some detail. Particular emphasis is placed upon possible problems arising from contaminated data and solutions are proposed. Some results from measurements at tropospheric and mesospheric heights are presented.     

Vibration of a thin-walled prolate dome under external water pressure

The paper reports on a theoretical and an experimental investigation carried out on a thin-walled hemi-ellipsoidal prolate dome in air and also under external water pressure. The investigation found that there was good correlation between experiment and theory. The theoretical investigation was carried out using the finite element analysis to model both the structure and the fluid. The theoretical investigation used two different programs, one of which was the giant computer program ANSYS and the other was an in-house program developed by Ross. For the shell structure, the ANSYS program used 2 different doubly curved thin-walled shell elements, while the in-house program used a simpler axisymmetric thin-walled shell element. This axisymmetric element allowed a sinusoidal variation of the displacements in the circumferential direction, thus, decreasing preparation and computational time. Agreement between the 3 different finite elements was found to be good. This was found particularly encouraging for the in-house software, as it only took a few hours to set up the computer model, and a few seconds to analyse the vessel, whereas the ANSYS software took several weeks to set up the computer model, and several minutes to analyse the shell dome. The ANSYS software, however, did have the advantage in producing excellent graphical displays in both the pre-processing and post-processing modes.     

Über den Bleigehalt des Kaolins von Hirschau-Sehnaittenbaeh und die Bleierzlagerstätte von Freihung in der Oberpfalz

Zusammenfassung Der Bleigehalt des Hirschau-Schnaittenbacher Kaolins (ca. 0.1% Pb) wird aus dem Entstehungszyklus der kaohnhaltigen Buntsandstein-Arkosen hergeleitet. Die Bleierzlagerstätte von Freihung kann als örtliche Konzentration des Bleigehaltes der Trias-Arkosen gedeutet werden.Herrn Professor Dr. Dr. h. c.C. W. Correns zum 70. Geburtstag gewidmet.     

Ein Beitrag zur Geochemie und Entstehung der Oberpfälzischen Kaolin-Feldspat-Lagerstätten

The plagioclase of the kaolinised granite of Tirschenreuth is decomposed quantitatively and the biotite almost quantitatively, on the contrary potassium feldspar and mucovite of the parent rock remained unaffected by kaolinisation. The quantity of produced kaolinite is equivalent to the quantity of decomposed plagioclase and biotite. The rare elements Pb, Cu, Cr, Ni, P, and Ti from the kaolinised minerals are adsorbed quantitatively by the kaolin. All other elements are diminished, no element has been added to the kaolin from other sources than from parent rock material. The selective decomposition of plagioclase and biotite in the kaolin-feldspar deposit of Tirschenreuth and the association of rare elements in the kaolin are explainable by weathering processes only. Kaolins from Hirschau-Sehnaittenbach are characterised by extremely high concentrations of the rare elements Ba, Sr, Pb, Cu, and P. The association of rare elements of the kaolin has been originated from the decomposed potassium feldspar of the kaolinised arcoses. The rare elements Pb, Cu, Cr, and P are adsorbed quantitatively by the kaolin. The other elements are diminished, Ba and Sr inclusive and in spite of their high absolute concentrations. The composition of the arcoses of Hirschau-Schnaittenbach prior to kaolinisation is calculated to 56% of quartz and 44% of potassium feldspar by means of the quantities of the elements Pb and Cu analysed in the feldspar and in the kaolin. The kaolin of Hirschau-Schnaittenbach has originated by weathering of the potassium feldspar of the Triassic arcoses. The kaolinisation is of Triassic age because kaolins of the Hirschau-Schnaittenbach type were redeposited near Ehenfeld in the Cenomanian. Kaolin deposits of hydrothermal origin are characterised by a zonal structure and are associated by ores. They are different in geological behaviour and mineral association from kaolin deposits which originated by weathering of feldspathic rocks like the deposits of Tirschenreuth and Hirschau-Schnaittenbach (Upper Palatinate, Bavaria).     

Structure and evolution of the volcanic rift zone at Ponta de São Lourenço,eastern Madeira

Ponta de São Lourenço is the deeply eroded eastern end of Madeira’s east–west trending rift zone, located near the geometric intersection of the Madeira rift axis with that of the Desertas Islands to the southeast. It dominantly consists of basaltic pyroclastic deposits from Strombolian and phreatomagmatic eruptions, lava flows, and a dike swarm. Main differences compared to highly productive rift zones such as in Hawai’i are a lower dike intensity (50–60 dikes/km) and the lack of a shallow magma reservoir or summit caldera. ⁴⁰Ar/³⁹Ar age determinations show that volcanic activity at Ponta de São Lourenço lasted from >5.2 to 4 Ma (early Madeira rift phase) and from 2.4 to 0.9 Ma (late Madeira rift phase), with a hiatus dividing the stratigraphy into lower and upper units. Toward the east, the distribution of eruptive centers becomes diffuse, and the rift axis bends to parallel the Desertas ridge. The bending may have resulted from mutual gravitational influence of the Madeira and Desertas volcanic edifices. We propose that Ponta de São Lourenço represents a type example for the interior of a fading rift arm on oceanic volcanoes, with modern analogues being the terminations of the rift zones at La Palma and El Hierro (Canary Islands). There is no evidence for Ponta de São Lourenço representing a former central volcano that interconnected and fed the Madeira and Desertas rifts. Our results suggest a subdivision of volcanic rift zones into (1) a highly productive endmember characterized by a central volcano with a shallow magma chamber feeding one or more rift arms, and (2) a less productive endmember characterized by rifts fed from deep-seated magma reservoirs rather than from a central volcano, as is the case for Ponta de São Lourenço.     

Carbonate diagenesis and feldspar alteration in fracture-related bleaching zones (Buntsandstein,central Germany): possible link to CO<Subscript>2</Subscript>-influenced fluid–mineral reactions

Fracture-related bleaching of Lower Triassic Buntsandstein red beds of central Germany was related to significant carbonate diagenesis and feldspar alteration caused by CO₂-rich fluids. Using cathodoluminescence microscopy and spectroscopy combined with electron microprobe analysis and stable carbon isotope study, two major fluid–mineral interactions were detected: (1) zoned, joint-filling calcites and zoned pore-filling calcite cements, the latter replacing an earlier dolomite, were formed during bleaching. During the calcite formation and dolomite–calcite transformation, iron was incorporated into the calcite cement crystal cores due to Fe availability from the coeval bleaching. The dedolomitisation was ultimately associated with a volume increase. The related permeability decrease implies a certain degree of sealing and increasing retention of CO₂, and the volume increase offers a minor CO₂ sink. Carbonate-rich sandstone, therefore, can provide advantages for underground CO₂ storage especially when situated in the fringes of the reservoir. (2) Alkali-feldspar alteration due to the bleaching fluids is reflected in cathodoluminescence spectra predominantly by the modulation of a brown luminescence emission peak (~620 nm). This peak represents a newly discovered effect related to alkali-feldspar alteration not solely associated with bleaching. Its modulation by the bleaching is interpreted to be due to Na depletion or a lattice defect in the Si–O bonds of the SiO₄-tetrahedron. Alteration reflected by this luminescence feature has a destructive effect on the feldspars implying the possibility of diminished rock integrity due to bleaching and, hence, CO₂-rich fluids. Two further CL spectral changes related to bleaching occur, (a) decreased intensity between around 570 nm assigned to Mn-depletion, and (b) increased amplitude and wavelength shift of the red (~680 nm) band. Converging evidence from carbonate and feldspar diagenesis, stable carbon isotope data and analysis of fracture directions suggests that CO₂ fluids contributed to a significant extent to the bleaching phenomena and alteration in the studied Buntsandstein strata.