Viscosity of andesitic melts—new experimental data and a revised calculation model

The viscosity of a synthetic andesite-like melt was measured in the low viscosity range (10¹-10⁶ Pa s) using the falling sphere(s) method and in the high viscosity range (10⁸-10¹³ Pa s) using parallel-plate viscometry. Falling sphere experiments with melts containing 2.3 and 5.6 wt.% H₂O were carried out in an internally heated gas pressure vessel (IHPV) at 500 MPa confining pressure. The sinking velocity of Pt and Pd spheres and in one case of a corundum sphere was used to measure the melt viscosity. In addition, a creep experiment was performed at ambient pressure using a glass containing 2.73 wt.% H₂O . A more water-rich glass (5.6 wt.% H₂O ) was investigated with a high pressure parallel-plate viscometer at 400 MPa confining pressure in an IPHV. By combining our new data with previous results for a similar melt composition we derived the following expression to describe the viscosity η (in Pa s) as a function of temperature T (in K) and water content w (in wt.%)

     

The SAURON project – VII. Integral-field absorption and emission-line kinematics of 24 spiral galaxy bulges

We present observations of the stellar and gas kinematics for a representative sample of 24 Sa galaxies obtained with our custom-built integral-field spectrograph SAURON operating on the William Herschel Telescope. The data have been homogeneously reduced and analysed by means of a dedicated pipeline. All resulting data cubes were spatially binned to a minimum mean signal-to-noise ratio of 60 per spatial and spectral resolution element. Our maps typically cover the bulge-dominated region. We find a significant fraction of kinematically decoupled components (12/24), many of them displaying central velocity dispersion minima. They are mostly aligned and co-rotating with the main body of the galaxies, and are usually associated with dust discs and rings detected in unsharp-masked images. Almost all the galaxies in the sample (22/24) contain significant amounts of ionized gas which, in general, is accompanied by the presence of dust. The kinematics of the ionized gas are consistent with circular rotation in a disc co-rotating with respect to the stars. The distribution of mean misalignments between the stellar and gaseous angular momenta in the sample suggests that the gas has an internal origin. The [O  iii ]/Hβ ratio is usually very low, indicative of current star formation, and shows various morphologies (ring-like structures, alignments with dust lanes or amorphous shapes). The star formation rates (SFRs) in the sample are comparable with that of normal disc galaxies. Low gas velocity dispersion values appear to be linked to regions of intense star formation activity. We interpret this result as stars being formed from dynamically cold gas in those regions. In the case of NGC 5953, the data suggest that we are witnessing the formation of a kinematically decoupled component from cold gas being acquired during the ongoing interaction with NGC 5954.     

Pillow lavas as a habitat for microbial life

The upper oceanic crust consists predominantly of pillow lavas that, soon after their eruption, are colonized by microbes when the ambient temperature ameliorates. During the process of microbial interaction with the glassy rims of pillows several types of bio-traces are generated, of which micro-textures are the most spectacular. Microbial textures are most useful for mapping the depth of the oceanic biosphere, and in the search for the earliest life on Earth.     

Line-of-sight velocity distributions of low-luminosity elliptical galaxies

The shape of the line-of-sight velocity distribution (LOSVD) is measured for a sample of 14 elliptical galaxies, predominantly low-luminosity ellipticals. The sample is dominated by galaxies in the Virgo cluster but also contains ellipticals in nearby groups and low-density environments. The parametrization of the LOSVD given by Gerhard and van der Marel & Franx is adopted, which measures the asymmetrical and symmetrical deviations of the LOSVD from a Gaussian by the amplitudes h ₃ and h ₄ of the Gauss–Hermite series. Rotation, velocity dispersion, h ₃ and h ₄ are determined as a function of radius for both major and minor axes. Non-Gaussian LOSVDs are found for all galaxies along the major axes. Deviations from a Gaussian LOSVD along the minor axis are of much lower amplitude if present at all. Central decreases in velocity dispersion are found for three galaxies. Two galaxies have kinematically decoupled cores: NGC 4458 and the well-known case of NGC 3608.     

Impact-generated dust clouds surrounding the Galilean moons

Tenuous dust clouds of Jupiter's Galilean moons Io, Europa, Ganymede and Callisto have been detected with the in-situ dust detector on board the Galileo spacecraft. The majority of the dust particles have been sensed at altitudes below five radii of these lunar-sized satellites. We identify the particles in the duut clouds surrounding the moons by their impact direction, impact velocity, and mass distribution. Average particle sizes are between 0.5 and 1 μm, just above the detector threshold, indicating a size distribution with decreasing numbers towards bigger particles. Our results imply that the particles have been kicked up by hypervelocity impacts of micrometeoroids onto the satellites' surfaces. The measured radial dust density profiles are consistent with predictions by dynamical modeling for satellite ejecta produced by interplanetary impactors (Krivov et al., 2003, Planet. Space Sci. 51, 251-269), assuming yield, mass and velocity distributions of the ejecta from laboratory measurements. A comparison of all four Galilean moons (data for Ganymede published earlier; Krüger et al., 2000, Planet. Space Sci. 48, 1457-1471) shows that the dust clouds of the three outer Galilean moons have very similar properties and are in good agreement with the model predictions for solid ice-silicate surfaces. The dust density in the vicinity of Io, however, is more than an order of magnitude lower than expected from theory. This may be due to a softer, fluffier surface of Io (volcanic deposits) as compared to the other moons. The log-log slope of the dust number density in the clouds vs. distance from the satellite center ranges between −1.6 and −2.8. Appreciable variations of number densities obtained from individual flybys with varying geometry, especially at Callisto, are found. These might be indicative of leading-trailing asymmetries of the clouds due to the motion of the moons with respect to the field of impactors.     

Palaeoecological constraints on late Glacial and Holocene ice retreat in the Southern Andes (53°S)

Late Glacial to Holocene ice retreat was investigated along a 120 km long fjord system, reaching from Gran Campo Nevado (GCN) to Seno Skyring in the southernmost Andes (53°S). The aim was to improve the knowledge on regional and global control on glacier recession with special emphasis on latitudinal shifting of the westerlies. The timing of ice retreat was derived from peat and sediment cores, using mineralogical and chemical characteristics, and pollen as proxies. Stratigraphy was based on ¹⁴C-AMS ages and tephrochronology. The ice retreat of the Seno Skyring Glacier lobe is marked by an ice rafted debris layer which was formed around 18,300 to 17,500 cal. yr B.P. Subsequently, fast glacier retreat occurred until around 15,000 to 14,000 cal. yr B.P. during which around 84% of Skyring Glacier were lost. This fast recession was probably also triggered by an increase of the Equilibrium Line Altitude (ELA) from 200 to 300 m. Subsequently, the ice surface was lowered below the ELA in an area that previously made up more than 50% of the accumulation area. Much slower retreat and glacier fluctuations of limited extent in the fjord channel system northeast of GCN occurred between around 14,000 to 11,000 cal. yr B.P. during both the Antarctic Cold Reversal and the Younger Dryas. This slow down of retreat indicates a decline in the general warming trend and/or increased precipitation, due to a southward migration of the westerlies. After around 11,000 cal. yr B.P. pollen distribution shows evolved Magellanic Rainforest and similar climate as at present, which lasted throughout most of the Holocene. Only Late Neoglacial moraine systems were formed in the period 1220–1460 AD, and subsequently in the 1620s AD, and between 1870 and 1910 AD. The results indicate that the Gran Campo Nevado ice cap has reacted more sensitive and partly distinct to climate change, compared to the Patagonian Ice Field.     

A comparative study of uranium–thorium accumulation at the western edge of the Arabian Peninsula and mineral deposits worldwide

Jordan, located at the western edge of the Arabian Plate, stands out from the remaining part of the Arabian Peninsula by its abundance in radioactive elements, mainly uranium, in a way so far not found elsewhere on the Arabian Peninsula. Uranium (U) and thorium in Jordan are concentrated in eight different types of ore mineralization: (1) intrusive-related (intramagmatic), (2) vein-type, (3) superficial, (4) sandstone-hosted (5) limestone-hosted, (6) U-Th-REE placer-type, (7) black shales, and (8) phosphorites. The major concentration of radioactive elements are synsedimentary and diagenetic in nature, mainly in near-shore marine depositional environments where uranium contents are abnormally high in the late Cretaceous to Paleogene phosphorites and increasing towards the mobile shelf of the Tethys ocean. These uraniferous phosphorites form the source of uranium that was redeposited within terrigenous chemical residues of lacustrine-fluvial depositional systems in Central Jordan (calcretes). Faultbound radiometric anomalies are caused by hot brines being vented along with the Jordan-Dead-Sea rifting. Presumably, low-grade U accumulation in (hot) black shales and marls of Silurian age are responsible for these radiometric anomalies. In the present paper, the Jordanian uranium concentrations are compared with reference types of uranium deposits elsewhere in the world to get an idea if the geological, chemical, and mineralogical features of analogue uranium mineralization in Jordan are indicative of economic targets. The uranium concentration in Jordanian phosphorites has been tracked beyond the border into Syria, Iraq, Israel, and Saudi Arabia. The uranium potential in neighboring countries is assessed based on the current geological data available for the Mediterranean Phosphorite Belt which is poised to become a another string to the bow with respect to energy supply on the Arabian Peninsula.     

Carbon,nitrogen and phosphorus dynamics in nine sub-systems of the Sylt-Rømø Bight ecosystem,German Wadden Sea

Flow networks of nine sub-systems consisting of 59 components each of the Sylt-Rømø Bight, German Wadden Sea, were constructed depicting the standing stocks and flows of material and energy within and between the sub-systems. Carbon, nitrogen and phosphorous were used as currencies for each sub-system, thus resulting in 27 network models, which were analyzed by ecological network analytical protocols. Results show substantial variability in the dynamics of these elements within and between the nine sub-systems, which differ in habitat structure, species diversity and in the standing stocks of their constituent living and non-living components. The relationship between the biodiversity and selected information indices and ratios, derived from ecological network analysis, of individual sub-systems is variable and differ substantially between them. Ecosystem properties such as the structure and magnitude of the recycling of these elements, number of cycles, and total sub-system activity were calculated and discussed, highlighting the differences between and complexity of the flow of C, N and P in a coastal marine ecosystem. The average number of cycles increase from 179 for C, to 16,923 and 20,580 for N and P respectively, while the average amount of recycled material, as measured by the Finn Cycling Index (FCI), increase from 17% for C, to 52% for P and to 61% for N. The number of cycles and the FCI vary considerably between the sub-systems for the different elements. The largest number of cycles of all three elements was observed in the muddy sand flat sub-system, but the highest FCIs were computed for both C (32%) and N (85%) in the Arenicola Flats, and in sparse Zostera noltii sea grass beds for P (67%). Indices reflecting on the growth, organization and resilience of the sub-systems also showed considerable variability between and within the inter-tidal ecosystems in the Bight. Indices such as, for example, the relative ascendency ratios increase on average from C to N to P, whereas others, such as the Average Mutual Information and Flow Diversity indices, were found to be higher in the N models than in the C or P ones.