Visible spectral reflectance measurements (0.33–1.1 μm) of the Galilean satellites at many orbital phase angles

One hundred eighty-seven reflectance spectra (0.33–1.10 μm) of the Galilean satellites have been obtained. Solar phase angle color correction coefficients were derived and the spectra corrected to a solar phase of 6°. Solar phase angle coefficients beyond 0.55 μm are presented for the first time. The spectra as a function of orbital phase angle are presented in the form of images to display hemispheric spectral variations. Io and Europa are redder on their trailing hemispheres while Callisto is redder on its leading hemisphere. Ganymede shows small longitudinal color variations despite the complex albedo structure visible in Voyager images. Comparisons of these data with previous measurements reveal that most differences can be attributed to the solar calibration. Reflectance measurements of Io at 0.73 μm observed 8.5 years apart show a 6% global reflectance decrease. However, it is difficult to unambigously attribute this particular decrease in reflectance to a change in Io's surface composition.     

Die mit einer Drehwaage messbare Massenwirkung eines „zweidimensionalen” Parallelepipeden in der vertikalen Ebene

Summary The gravimetric effect of a two dimensional parallelepipedon measurable by Torsion Balance in the vertical plane is examined. It is found that the places of the equal gradients and curvatures of a rectangle stretching into the infinity are orthogonal circles. The gradients and curvatures of a parallelogramm (stretching into the infinity) which has the finite side in common with the rectangle are expressed by those of the latter, their extreme values lie along isosceles hyperbolas.

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Riassunto Si esamina l'azione gravimetrica di un parallelepipedo bidimensionale in base agli elementi misurabili con la bilancia di torsione nel piano verticale. Risulta che il luogo dei punti di eguali gradienti e curvature di un parallelogrammo pure estendentesi all'infinito con il lato finito in comune col rettangolo sono esprimibili a mezzo degli analoghi elementi di quest'ultimo ed 1 loro valori estremi risultano distribuiti lungo iperboli isosceli.

     

The influence of turbulence on drag

The use of the Reynolds number as the only correlating factor for drag force measurements may be inadequate in circumstances involving highly turbulent flows. The results of previous investigations relating to the effects of turbulence scale and intensity are examined. Of special interest is the possibility of a drag minimum, even at low Reynolds number, for a free-stream turbulence intensity of about 5%. This appears to be the result of interaction between the free stream and the boundary layer. As intensity increases beyond 5%, the minimum may be succeeded by an increase in drag to values exceeding the laminar flow values. Further elucidation of the subject is required, particularly because of its importance in various problems related to geophysical flows.     

Filter-feeding ascidians (Ciona intestinalis) in a shallow cove: Implications of hydrodynamics for grazing impact

The grazing impact by a dense population of filter-feeding ascidians Ciona intestinalis on horizontally flowing water (driven by density circulation) in a shallow cove (Kertinge Nor, Denmark) has been described and quantified by means of a simple one-dimensional numerical model. The agreement between observations and modelled predictions was satisfactory. The applied numerical model has the following analytical solution in the idealized case: Cx = C₀e^−(fx/Y₂), where C_x = algal concentration at a downstream distance x, C₀ = initial concentration, f = F/v_c; F = area specific population filtration rate; v_c = current velocity; Y₂ = depth of mixed layer below halocline. The numerical model quantifies the actual grazing impact while the analytical model illustrates the governing physics in well-known terms. To describe situations with no current (i.e. stagnant water), we performed simulation studies in the laboratory and measured vertical profiles of algal cells over filter-feeding C. intestinalis. The results showed that phytoplankton became reduced in a near-bottom water layer of 20–30 cm thickness. Such water layers may develop in stagnant water (calm days and no advective currents), thus uncoupling the pelagic food and the filter feeders which within a short time will experience extremely meagre food conditions.     

Spatial variation of nutrients and primary productivity in the Rufiji Delta mangroves,Tanzania

Determinations of spatial and temporal variations in organic matter and nutrient dynamics in water and sediments are crucial for understanding changes in aquatic bodies. In this study, we (i) determine the spatial dynamics of dissolved inorganic nutrients, during the transition from the dry to the rainy season, and (ii) provide future productivity predictions for the Rufiji Delta mangroves, Tanzania, based on the input of various nutrients. Water samples were collected from six locations, three times per year between April 2012 and January 2014, and analysed for dissolved nutrients, total organic and inorganic carbon, chlorophyll a, chlorophyll b and total carotenoids. The prediction of future net primary productivity in the Rufiji mangroves was undertaken using the software STELLA. The mean nutrient concentrations were of the order: nitrate > phosphate > ammonium > silica > dissolved organic carbon. The study revealed that high nutrient concentrations occurred in the northern part of the Rufiji Delta as a result of anthropogenic influence in the watershed. Modelling of nutrient inputs into the delta indicated enhanced primary productivity, which is expected to increase the vulnerability of water quality in the near future due to eutrophication.     

The Sponge Community in a Semi-Submerged Temperate Sea Cave: Density, Diversity and Richness

Abstract. The sponge communities inhabiting a temperate semi-submerged sea cave were investigated at Lough Hyne Marine Nature Reserve, Co. Cork, Ireland. Thirty-one species of sponge were reported, the majority of which exhibited either an encrusting or massive morphology. Sponge density (averaged over depth) increased with horizontal distance (5  m intervals) into the cave until approximately 30  m, corresponding to the maximum algal intrusion (algal information from Norton et al. , 1971) . Species diversity and richness (averaged over depth) were highest at 10  m horizontal distance from the cave entrance. Variability in sponge density, diversity and richness was observed with increasing vertical depth (0.5  m intervals) at most horizontal intervals sampled (5  m apart). These three variables increased initially with depth, but then decreased towards the seabed. Bray-Curtis Similarity Analysis and Multi-Dimensional Scaling (MDS) showed cave sponge community composition to have greater similarity (50 %) with local loose rock habitats than the nearby cliffs. Similar processes structuring cave and loose rock sponge communities may account for this situation. Information collected from this and previous studies on the biotic (algal communities, other fauna and competition) and abiotic factors (water flow rate, depth, aerial exposure, light, cave morphology, nutrient depletion and humidity) affecting this and other caves is discussed with respect to its influence on the sponges inhabiting different parts of the cave. Although horizontal zonation patterns have been considered analogous to vertical distribution patterns for algal communities (due to similar decreases in light), this was not the case for the studied sponge communities.     

Nitrogen cycling in deep-sea sediments of the Porcupine Abyssal Plain, NE Atlantic

Rates of transformation, recycling and burial of nitrogen and their temporal and spatial variability were investigated in deep-sea sediments of the Porcupine Abyssal Plain (PAP), NE Atlantic during eight cruises from 1996 to 2000. Benthic fluxes of ammonium (NH₄) and nitrate (NO₃) were measured in situ using a benthic lander. Fluxes of dissolved organic nitrogen (DON) and denitrification rates were calculated from pore water profiles of DON and NO₃, respectively. Burial of nitrogen was calculated from down core profiles of nitrogen in the solid phase together with ¹⁴C-based sediment accumulation rates and dry bulk density. Average NH₄ and NO₃-effluxes were 7.4 ± 19 μmol m⁻² d⁻¹ (n = 7) and 52 ± 30 μmol m⁻² d⁻¹ (n = 14), respectively, during the period 1996–2000. During the same period, the DON-flux was 11 ± 5.6 μmol m⁻² d⁻¹ (n = 5) and the denitrification rate was 5.1 ± 3.0 μmol m⁻² d⁻¹ (n = 22). Temporal and spatial variations were only found in the benthic NO₃ fluxes. The average burial rate was 4.6 ± 0.9 μmol m⁻² d⁻¹. On average over the sampling period, the recycling efficiency of the PON input to the sediment was 94% and the burial efficiency hence 6%. The DON flux constituted 14% of the nitrogen recycled, and it was of similar magnitude as the sum of burial and denitrification. By assuming the PAP is representative of all deep-sea areas, rates of denitrification, burial and DON efflux were extrapolated to the total area of the deep-sea floor (>2000 m) and integrated values of denitrification and burial of 8 ± 5 and 7 ± 1 Tg N year⁻¹, respectively, were obtained. This value of total deep-sea sediment denitrification corresponds to 3–12% of the global ocean benthic denitrification. Burial in deep-sea sediments makes up at least 25% of the global ocean nitrogen burial. The integrated DON flux from the deep-sea floor is comparable in magnitude to a reported global riverine input of DON suggesting that deep-sea sediments constitute an important source of DON to the world ocean.     

The cumulus and post-cumulus evolution of chrome-spinels in ultrabasic layered intrusions: evidence from the Cuillin Igneous Complex,Isle of Skye,Scotland

Chrome-spinels from the layered Peridotilte Series of the unmetamorphosed, anorogenic 60 Ma Cuillin Igneous Complex, Isle of Skye, display a wide variety of compositions. Cumulus (within seams) chrome-spinels from the lowest exposed portion of the Peridotite Series exhibit features indicative of textural equilibrium, are rich in Al and Mg, and have low values of the ratio Cr/(Cr+Al). Cumulus chrome-spinels from higher up in the series are different from these: particularly, textural disequilibrium is evident, intercumulus plagioclase and olivine are present, and the chrome-spinels are rich in Cr, Fe and Ti, with high values of the ratio Cr/(Cr+Al). Intercumulus (dispersed) chrome-spinels tend towards anhedral forms and define enrichment trends towards Fe (both Fe²⁺ and Fe³⁺) with decreasing Mg, Cr and Al, and towards Al, with decreasing Fe²⁺ and Cr (and increasing Mg). Individual crystals are completely homogeneous and are devoid of reaction rims. The observed textural characteristics and compositional data of the chrome-spinels documented here suggest that the semi-quantitative peritectic reaction: aluminous chrome-spinel + meltplagioclase + olivine + chromian chrome-spinel, is responsible for the observed parageneses, and that both the environment of crystallization (eumulus or intercumulus) and the role of plagioclase ±olivine crystallization are critical parameters for this geochemical trend in spinels within upper crustal magmatic systems. The effects of pyroxene crystallization on the development of this geochemical trend are also considered. This investigation highlights the need to consider the role of post-cumulus mineral-melt reactions and their influences upon the final compositions of major oxide and silicate phases within layered intrusions.     

High-resolution atmospheric observations by the Mars Odyssey Thermal Emission Imaging System

High-resolution observations of atmospheric phenomena by the Mars Odyssey Thermal Emission Imaging System (THEMIS) during its first mapping year are presented. An atmospheric campaign was implemented on the basis of previous spacecraft imaging. This campaign, however, proved of limited success. This appears to be due to the late local time of the Odyssey orbit (the locations of activity at 4–6 p.m. appear to be different from those at 2 p.m.). Ironically, images targeting the surface were more useful for study of the atmosphere than those images specifically targeting atmospheric features. While many previously recognized features were found, novel THEMIS observations included persistent clouds in the southern polar layered deposits, dust or condensate plumes on the northern polar layered deposits, dust plumes as constituent parts of local dust storms, and mesospheric clouds. The former two features tend to be aligned parallel and normal to polar troughs, respectively, suggesting a wind system directed normal to troughs and radially outward from the center of the polar deposits. This is consistent with katabatic drainage of air off the polar deposits, analogous to flow off Antarctica. The observation of dust lifting plumes at unprecedented resolution associated with local dust storms not only demonstrates the importance of mean wind stresses (as opposed to dust devils) in initiation of dust storms, but is also seen to be morphologically identical to dust lifting in terrestrial dust storms. As Odyssey moves to earlier local times, we suggest that the atmospheric campaign from the first mapping year be repeated.