Modelling of the vertical fluxes of nitric acid,ammonia, and ammonium nitrate

Results from numerical investigations regarding the exchange of HNO₃, NH₃, and NH₄NO₃ between the atmosphere and the biosphere are presented. The investigations were performed with a modified inferential method which is based on the generally accepted micrometeorological ideas of the transfer of momentum, sensible heat and matter near the Earth's surface and the chemical reactions among these nitrogen compounds. This modified inferential method calculates the micrometeorological quantities (such as the friction velocity and the fluxes of sensible and latent heat), the height-invariant fluxes of the composed chemically conservative trace species with group concentrationsc ₁=[HNO₃]+[NH₄NO₃] (total nitrate),c ₂=[NH₃]+[NH₄NO₃] (total ammonia), andc ₃=[HNO₃]-[NH₃] as well as the fluxes of the individual nitrogen compounds. The parameterization of the fluxes is based on the flux-gradient relationships in the turbulent region of the atmospheric surface layer. The modified inferential method requires only the data of wind velocity, temperature, humidity and concentrations (HNO₃, NH₃, and NH₄NO₃) measured at a reference height by stations of a monitoring network.     

Präparationstechnik für Aufbereitungsprodukte zur quantitativen erzmikroskopischen Untersuchung

Zusammenfassung Mikroskopische Anschliffe feinkörniger Aufbereitungsprodukte können nur dann quantitativ ausgewertet werden, wenn ihre Schliffqualität so hoch ist, daß auch feinste Partien sicher zu bestimmen sind. Daneben muß gewährleistet sein, daß die an der Schliffoberfläche erfaßten Körner die tatsächliche Verteilung der Mineralien der Probe repräsentieren. Diese Forderung kann nur durch zweckentsprechende Präparation, die dem eigentlichen Schleif- und Polierprozeß vorausgeht, erfüllt werden. Als günstigste Lösung erscheint es, das Korngemisch exakt als Einkornschicht zu präparieren und anschließend wie Stückproben anzuschleifen. Die Schliffe können dann nach den gleichen statistischen Gesetzmäßigkeiten ausgewertet werden, wie sie bei praktisch zweidimensionalen Dünnschliffen oder bei Streupräparaten nichtopaker Korngemische vorliegen.

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Quantitative examination of fine-grained ore dressing products depends on good quality of the sections and on whether very small particles and areas of grains can be determined. Besides, it must absolutely be guaranteed that the grains at the section surface represent the actual distribution of the minerals in the sample. This condition can only be realized by suitable grain mounting prior to grinding and polishing. The best method for this purpose appears to be the preparation of a mono-grain layer. The polished sections can then be examined according to the same statistical laws as two-dimensional thin sections or immersion-liquid slides of non-opaque mixtures of grains.

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Mitteilung Nr. 141 aus dem Forschungsinstitut für Aufbereitung der Deutschen Akademie der Wissenschaften zu Berlin, Freiberg (Sachsen). Direktor: Prof. Dr.-Ing. habil. H. Kirchberg.     

Benthic foraminiferal distribution and sedimentary structures suggest tectonic erosion at the Costa Rica convergent plate margin

ABSTRACT Distribution patterns of benthic foraminiferal faunas from ODP Leg 170 Sites 1041 and 1042 show that the Costa Rican convergent margin subsided from coastal to abyssal depth from Middle Miocene to Present. This favours the model of a margin undergoing active subduction erosion. We propose that subduction erosion leads to the removal of material from the base of the forearc wedge and, as a consequence, to progressive subsidence of the forearc. A mean subsidence rate is estimated to be approximately 0.4 mm yr⁻¹.     

The ‘land-locked’ viewpoint

While the Draft Convention still leaves the land-locked states with very considerable disadvantages, it can be said to represent a success for such states in so far as the notion of land-locked states forms a definite part of the proposed law of the sea and therefore provided them with the power to influence further developments.     

Elektronenstrahl-Mikroanalyse des Meteoriten von Steinbach

Zusammenfassung Eine uns vom Naturhistorischen Museum in Wien freundlicherweise zur Verfügung gestellte Probe des Meteoriten von Steinbach wurde mit einem Elektronenstrahl-Mikroanalysator vom Typ CAMECA qualitativ und quantitativ auf die chemische Zusammensetzung der einzelnen Phasen untersucht.Besonders eingehend wurde dabei die Metallphase analysiert, da diese sich durch die Anwesenheit einer gut ausgebildeten Widmanstättenschen Struktur in Gegenwart von Tridymit als Druckindikator auszeichnet.Die nichtmetallischen Phasen wurden ebenfalls quantitativ bestimmt und ergeben leicht abweichende Ergebnisse von den Analysen vonN. Story-Maskelyne, O. Winkler undF. Heide. Interessant sind vor allem der relativ hohe Mangangehalt in Bronzit und Chromit sowie der Chromgehalt des Troilits.Die Anwendung der neuen Berechnungen über die Abkühlungsgeschichte der Meteoritenmutterkörper vonWood auf unsere quantitativen Analysen ergab eine Abkühlungsgeschwindigkeit von 10°/Million Jahre, was einem Mutterkörper von ca. 50–90 km Durchmesser und einem Zentraldruck von 200 b entspricht.

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Summary A sample of the meteorite of Steinbach, made available by the Naturhistorisches Museum at Vienna, has been analyzed qualitatively and quantitatively by a CAMECA electron-beam microanalyzer.Detailed examination has been made on the structure of the metal phase, as the presence of a well-grown Widmanstätten-structure in contact with trydimite as a pressure-indicator is a direct proof for the formation of the Widmanstätten-structure without pressure.The nonmetallic phases have been analyzed quantitatively and the results are slightly different from those ofStory-Maskelyne, Winkler andHeide. Very interesting is the relatively high content of manganese in bronzite and chromite, also the chromium content of troilite.The application of the new computations ofWood, dealing with the cooling history of meteorite-parentbodies to our quantitative analyses indicate a cooling rate of 10° C/Million years, according to a parentbody of appr. 50–90 km diameter and a central pressure of appr. 200 b.

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Mit 8 Textabbildungen

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Herrn Professor Dr.F. Machatschki zum 70. Geburtstag gewidmet.     

The world''s large lake basins as denudation-accumulation systems and implications for their lifetimes

The mechanical denudation rates of 81 large lake basins (lake area > 500 km²) were determined from long-term river loads and erosion maps. Using the drainage area/lake area ratios the mean sedimentation rates of the lakes were calculated for a porosity of 0.3. The mean sedimentation rates of different lake types vary between 0.1 mm/a (glacial lakes, lowland) and 5.4 mm/a (mostly sag basin lakes). The calculated lifetimes of the lakes are based on the lake volumes and mean sedimentation rates, assuming steady-state conditions and solely clastic material. On average, glacial lakes in highlands and fault-related lakes show the shortest lifetimes (c. 70 ka), glacial lakes in lowlands and rift lakes have the longest lifetimes (c. 1 Ma). Some lakes remain unfilled for very long time spans due to rapid subsidence of their basin floors. The calculated lifetimes are compared with those derived from sediment core studies. Most core studies indicate lower mechanical sedimentation rates than the calculated ones because a major part of the incoming sediment is trapped in deltas. However, a number of lakes (e.g., the Great Lakes of North America) show the opposite tendency which is largely caused by extensive shoreline erosion and resuspension. The lifetimes of large glacial lakes often exceed the duration of interglacials. Hence, their lifetimes are restricted by glaciation and not by sediment infill. Rift lakes persist for long time periods which exceed the calculated lifetimes in some cases. Time-dependent subsidence, basin extension, as well as the impact of climate change are briefly described.