Entweichgeschwindigkeiten und Mittlere Geschwindigkeiten in Stern- und Galaxienhaufen

The ratio of the escape velocity at the centre to the mean velocity amounts to 2.5 for open star clusters, 2.7 for globular clusters, and 2.8 for the Coma cluster of galaxies.

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Mitteilungen Serie A.     

One-millimeter brightness temperatures of the planets

New values for the 1-mm brightness temperatures of Mercury, Venus, Jupiter, Saturn, Uranus, and Neptune have been determined using Mars as the absolute photometric standard.     

Simulated global-scale response of the climate system to Dansgaard/Oeschger and Heinrich events

By using an Earth system model of intermediate complexity we have studied the global-scale response of the glacial climate system during marine isotope stage (MIS) 3 to perturbations at high northern latitudes and the tropics. These perturbations include changes in inland-ice volume over North America, in freshwater flux into the northern North Atlantic and in surface temperatures of the tropical Pacific. The global pattern of temperature series resulting from an experiment in which perturbations of inland ice and freshwater budget are imposed at high northern latitudes only, agree with paleoclimatic reconstructions. In particular, a positive correlation of temperature variations near Greenland and variations in all regions of the Northern Hemisphere and some parts of the southern tropics is found. Over the southern oceans a weak negative correlation appears which is strongest at a time lag of approximately 500 years. Further experimentation with prescribed temperature anomalies applied to the tropical Pacific suggests that perturbation of tropical sea-surface temperatures and hence, the tropical water cycle, is unlikely to have triggered Dansgaard/Oeschger (D/O) events. However, together with random freshwater anomalies prescribed at high northern latitudes, tropical perturbations would be able to synchronize the occurrence of D/O events via the mechanism of stochastic resonance.     

Synthesis, properties and stability of end member boromuscovite, KAl2[BSi3O10](OH)2

End member boromuscovite, with nearly the ideal composition, was synthesized as a single phase from mixtures of its own composition, or with excess boron and water, at high pressures of between 15 and 30 kbar at 700 °C. The mica synthesized consists of a mixture of 2M₁ and 1M polytypes with the cell dimensions of 2M₁: a=5.071(4), b=8.786(4), c=19.830(89) Å, #=95.84(12)°, V=878.5(1.4) ų; and 1M: a=5.059(5), b=8.819(6), c=10.025(17) Å, #=101.39(57)°, V=438.4(1.3) Å. The IR spectrum shows characteristic differences relative to that of muscovite. DTA registers an endothermic peak due to dehydration breakdown above 680 °C. Seeded experiments indicate that boromuscovite is a high-pressure phase requiring minimum pressures of 3 to 10 kbar at temperatures that concomitantly increase from 300 to 750 °C. At lower pressures, the anhydrous solid assemblage K-feldspar + Al-borate (probably Al₄B₂O₉) coexists with a vapor rich in boric acid. The conversion of this assemblage to boromuscovite is connected with increases in the coordination number of B from [3] to [4], and of Al from [4] to [6]. Above 10 kbar, the boromuscovite stability field is limited along its high-temperature side by congruent (or incongruent?) melting of the mica, starting near 750 °C and 10 kbar and increasing to about 900 °C at 50 kbar, although, at such very high pressures a supercritical fluid may be present. Because, even in the presence of excess-boron fluid, the synthetic mica shows invariable X-ray properties, it is concluded that one B atom per formula unit represents the maximum, and - contrary to olenitic tourmalines - no further substitution of Si by B linked with addition of hydrogen takes place. In contrast to muscovite, KAl₂[AlSi₃O₁₀](OH)₂, end member boromuscovite is not stable under normal P-T conditions of the Continental Crust along a 30 °C/km geotherm, and especially not during the intrusion of acidic igneous rocks including their pegmatites, which may explain its scarcity in nature. However, it may form in the waning hydrothermal stages of deep-seated (>10.5 km) pegmatites and - providing sufficient boron is available - in HP/LT subduction zone environments, where it may carry boron to considerable depths.     

Composition of Volcanic Tuffs,Neotectonics, and Structure of the Upper Sedimentary Cover of the Osborn Plateau (Indian Ocean)

Oceanology - The Osborn Plateau is a large intraplate elevation in the eastern Indian Ocean, which has been poorly studied by geological and geophysical methods. On cruise SO258/1 aboard the R/V...     

Resolution issues in numerical models of oceanic and coastal circulation

The baroclinic and barotropic properties of ocean processes vary on many scales. These scales are determined by various factors such as the variations in coastline and bottom topography, the forcing meteorology, the latitudinal dependence of the Coriolis force, and the Rossby radius of deformation among others. In this paper we attempt to qualify and quantify scales of these processes, with particular attention to the horizontal resolution necessary to accurately reproduce physical processes in numerical ocean models. We also discuss approaches taken in nesting or down-scaling from global/basin-scale models to regional-scale or shelf-scale models. Finally we offer comments on how vertical resolution affects the representation of stratification in these numerical models.     

A new relation between the central spectral solar H I Lyman α irradiance and the line irradiance measured by SUMER/SOHO during the cycle 23

The spectral irradiance at the center of the solar H I Lyman α (, referred to as Lyα in this paper) line profile is the main excitation source responsible for the atomic hydrogen resonant scattering of cool material in our Solar System. It has therefore to be known with the best possible accuracy in order to model the various Lyα emissions taking place in planetary, cometary, and interplanetary environments. Since the only permanently monitored solar irradiance is the total one (i.e. integrated over the whole Lyα line profile), Vidal-Madjar [1975. Evolution of the solar Lyman alpha flux during four consecutive years. Solar Phys. 40, 69-86] using Orbiting Solar Observatory 5 (OSO-5) satellite Lyα data, established a semi-empirical formula allowing him to deduce the central spectral Lyα irradiance from the total one. This relation has been extensively used for three decades. But, at the low altitude of the OSO-5 orbit, the central part of the solar line profile was deeply absorbed by a large column of exospheric atomic hydrogen. Consequently, the spectral irradiance at the center of the line was obtained by a complex procedure confronting the observations with simulations of both the geocoronal absorption and the self-reversed shape of the solar Lyα profile. The SUMER spectrometer onboard SOHO positioned well outside the hydrogen geocorona, provided full-Sun Lyα profiles, not affected by such an absorption [Lemaire et al., 1998. Solar H I Lyman α full disk profile obtained with the SUMER/SOHO spectrometer. Astron. Astrophys. 334, 1095-1098; 2002. Variation of the full Sun Hydrogen Lyman α and β profiles with the activity cycle. Proc. SOHO 11 Symposium, ESA SP-508, 219-222; 2004. Variation of the full Sun Hydrogen Lyman profiles through solar cycle 23. COSPAR 2004 Meeting], making it—for the first time—possible to measure the spectral and total Lyα solar irradiances directly and simultaneously. A new relation between these two quantities is derived in an expression that is formally similar to the previous one, but with significantly different parameters. After having discussed the potential causes for such differences, it is suggested that the new relation should replace the old one for any future modeling of the numerous Lyα absorptions and emissions observed in the Solar System.     

Experimental study of platinum solubility in silicate melt to 14 GPa and 2273 K: Implications for accretion and core formation in Earth

We determined the solubility limit of Pt in molten haplo-basalt (1 atm anorthite-diopside eutectic composition) in piston-cylinder and multi-anvil experiments at pressures between 0.5 and 14 GPa and temperatures from 1698 to 2223 K. Experiments were internally buffered at ∼IW + 1. Pt concentrations in quenched-glass samples were measured by laser-ablation inductively coupled-plasma mass spectrometry (LA-ICPMS). This technique allows detection of small-scale heterogeneities in the run products while supplying three-dimensional information about the distribution of Pt in the glass samples. Analytical variations in ¹⁹⁵Pt indicate that all experiments contain Pt nanonuggets after quenching. Averages of multiple, time-integrated spot analyses (corresponding to bulk analyses) typically have large standard deviations, and calculated Pt solubilities in silicate melt exhibit no statistically significant covariance with temperature or pressure. In contrast, averages of minimum ¹⁹⁵Pt signal levels show less inter-spot variation, and solubility shows significant covariance with pressure and temperature. We interpret these results to mean that nanonuggets are not quench particles, that is, they were not dissolved in the silicate melt, but were part of the equilibrium metal assemblage at run conditions. We assume that the average of minimum measured Pt abundances in multiple probe spots is representative of the actual solubility. The metal/silicate partition coefficients (D^met/sil) is the inverse of solubility, and we parameterize D^met/sil in the data set by multivariate regression. The statistically robust regression shows that increasing both pressure and temperature causes D^met/silto decrease, that is, Pt becomes more soluble in silicate melt. D^met/sil decreases by less than an order of magnitude at constant temperature from 1 to 14 GPa, whereas isobaric increase in temperature produces a more dramatic effect, with D^met/sil decreasing by more than one order of magnitude between 1623 and 2223 K. The Pt abundance in the Earth’s mantle requires that D^met/sil is ∼1000 assuming core-mantle equilibration. Geochemical models for core formation in Earth based on moderately and slightly siderophile elements are generally consistent with equilibrium metal segregation at conditions generally in the range of 20-60 GPa and 2000-4000 K. Model extrapolations to these conditions show that the Pt abundance of the mantle can only be matched if oxygen fugacity is high (∼IW) and if Pt mixes ideally in molten iron, both very unlikely conditions. For more realistic values of oxygen fugacity (∼IW − 2) and experimentally-based constraints on non-ideal mixing, models show that D^met/sil would be several orders of magnitude too high even at the most favorable conditions of pressure and temperature. These results suggest that the mantle Pt budget, and by implication other highly siderophile elements, was added by late addition of a ‘late veneer’ phase to the accreting proto-Earth.