Effects of hydrostatic pressure on microbial alteration of sinking fecal pellets

We used a new experimental device called PASS (PArticle Sinking Simulator) during MedFlux to simulate changes in in situ hydrostatic pressure that particles experience sinking from mesopelagic to bathypelagic depths. Particles, largely fecal pellets, were collected at 200 m using a settling velocity NetTrap (SV NetTrap) in Ligurian Sea in April 2006 and incubated in high-pressure bottles (HPBs) of the PASS system under both atmospheric and continuously increasing pressure conditions, simulating the pressure change experienced at a sinking rate of 200 m d⁻¹. Chemical changes over time were evaluated by measuring particulate organic carbon (POC), carbohydrates, transparent exopolymer particles (TEP), amino acids, lipids, and chloropigments, as well as dissolved organic carbon (DOC) and dissolved carbohydrates. Microbial changes were evaluated microscopically, using diamidinophenylindole (DAPI) stain for total cell counts and catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH) for phylogenetic distinctions. Concentrations (normalized to POC) of particulate chloropigments, carbohydrates and TEP decreased under both sets of incubation conditions, although less under the increasing pressure regime than under atmospheric conditions. By contrast, dissolved carbohydrates (normalized to DOC) were higher after incubation and significantly higher under atmospheric conditions, suggesting they were produced at the expense of the particulate fraction. POC-normalized particulate wax/steryl esters increased only under pressure, suggesting biochemical responses of prokaryotes to the increasing pressure regime. The prokaryotic community initially consisted of 43% Bacteria, 12% Crenarchaea and 11% Euryarchaea. After incubation, Bacteria dominated (90%) the prokaryote community in all cases, with γ-Proteobacteria comprising the greatest fraction, followed by the Cytophaga–Flavobacter cluster and α-Proteobacteria group. Using the PASS system, we obtained chemical and microbial evidence that degradation by prokaryotes associated with fecal pellets sinking through mesopelagic waters is limited by the increasing pressure they experience.     

Meteorologically-induced mesoscale variability of the North-western Alboran Sea (southern Spain) and related biological patterns

Hydrographic mesoscale structures in the North-western Alboran Sea show a high variability induced by a number of different factors. One of the most important is the differences in atmospheric pressure over the Mediterranean basin when compared to the Gulf of Cádiz. This difference modulates the zonal wind field in the Alboran Sea and the intensity of the Atlantic inflow through the Strait of Gibraltar, also affecting the formation and extension of the Western Alboran Gyre (WAG). When westerly winds are dominant, lower atmospheric pressure in the Mediterranean enhances the inflow of Atlantic waters causing the Atlantic Jet to be located in the vicinity of the Spanish shore, creating a well-defined frontal zone in front of Estepona Cove. In this situation, the coastal upwelling is enhanced, leading to a minimum in sea surface temperature and a maximum of surface nutrient concentrations located in the coastal area. The vertical position of the chlorophyll maximum found in these circumstances appeared to be controlled by the nutrient availability. On the other hand, when easterly winds prevail, higher atmospheric pressure in the Mediterranean leads to a reduced inflow and the oceanographic and biological structures are clearly different. The Atlantic Jet moves southward flowing in a south-eastern direction, changing the structure of the currents, resulting in an enhanced cyclonic circulation extending throughout the North-western Alboran Sea basin. These physical alterations also induce changes in the distribution of biogeochemical variables. Maximum nutrient and chlorophyll concentrations are located further off the coast in the central area of the newly created cyclonic gyre. During these easterlies periods coastal upwelling stops and the distribution of phytoplankton cells seems to be mainly controlled by physical processes such as advection of coastal waters to the open sea.     

Post-rift volcanism and high heat-flow at the ocean-continent transition of the eastern Gulf of Aden

A high heat-flow (∼900 mW m⁻²) has been observed over a volcanic structure at the Ocean-Continent Transition in the Eastern Gulf of Aden (Oman margin). The anomaly is superposed to a progressive increase of heat-flow across the margin and can be interpreted either by (1) heat refraction, (2) fluid discharge or (3) cooling magma. The two first explanations cannot be ruled out definitely by modelling analysis, but require unlikely thermal conductivity or permeability values. The third one implies that the latest activity of the volcano was about 100 000 years old and therefore continued c. 18 Ma after the break-up of Africa and Arabia. This potential mechanism is consistent with other lines of evidence of post-rifting activity in the Gulf of Aden and could invalidate the conventional assumption that rifted-margins become passive after the break-up of continents.     

Release of neutral sodium atoms from the surface of Mercury induced by meteoroid impacts

Meteoroid impact has been shown to be a source of sodium, and most likely of other elements, on the Moon. The same process could be also relevant for Mercury. In this work we calculate the vapor and neutral Na production rates on Mercury due to the impacts of meteoroids in the radius range of 10⁻⁸-10⁻¹ m. We limit our calculations to this size range, because meteoroids with radius larger than 10⁻¹ m have not to be found important for the daily production of the exosphere. This work is based on a new dynamical model of the meteoroid flux at the heliocentric distance of Mercury, regarding objects in the size range 10⁻²-10⁻¹ m. This size range, never investigated before, is not affected by nongravitational forces, such as the Poynting-Robertson effect, which is dominant for particles smaller than 10⁻² m. In order to evaluate the release of neutral sodium atoms also for smaller meteoroids we have used the distribution reported by M.J. Cintala [1992. Impact-induced thermal effects in the lunar and mercurian regoliths. J. Geophys. Res. 97, 947-973] calculated for particle size range 10⁻⁸-10⁻³ m. We have extrapolated this distribution up to 10⁻² m and we have based the impact calculations on a new surface composition assuming 90% plagioclase and 10% pyroxene. The results of our model are that (i) the total mass of vapor produced by the impact of meteoroids in the size range 10⁻⁸-10⁻¹ m is 4.752×¹⁰⁸ g per year, and (ii) the production rate of neutral sodium atoms is 1.5×¹⁰²² s⁻¹.     

Scaling laws and coherent structures in the solar wind

The interplanetary medium is characterized by a very high Reynolds number and is pervaded by fluctuations providing information on a wide range of scales, from fractions of second up to the solar rotation period. In the past decade or so, turbulence in the solar wind has been used as a large wind tunnel to investigate scaling laws of turbulent fluctuations and multifractal models. Moreover, new interesting insights in the theory of turbulence have been derived from the point of view which considers a turbulent flow as a complex system, a sort of benchmark for the theory of dynamical systems. Important finding like the lack of a strict self-similarity of the fluctuations with the consequent nonapplicability of strict scale invariance, the strong anisotropy of velocity and magnetic field fluctuations, the clear lack of equipartition between magnetic and kinetic fluctuations all contributed to suggest the idea that interplanetary fluctuations could possibly be due to a mixture of propagating waves and static structures convected by the wind. In this paper we further discuss this point and bring new evidence about the fact that the presence of a background magnetic field introduces not only a symmetry breaking in interplanetary space but also organizes fluctuations about its large scale orientation.     

lemomaf: Lensed Mock Map Facility

We present the Lensed Mock Map Facility ( lemomaf ), a tool designed to perform mock weak-lensing measurements on numerically simulated chunks of the Universe. Coupling N -body simulations to a semi-analytical model of galaxy formation, lemomaf can create realistic lensed images and mock catalogues of galaxies, at wavelengths ranging from the ultraviolet to the submillimetre. To demonstrate the power of such a tool, we compute predictions of the source–lens clustering (SLC) effect on the convergence statistics, and quantify the impact of weak lensing on galaxy counts in two different filters. We find that the SLC effect skews the probability density function of the convergence towards low values, with an intensity which strongly depends on the redshift distribution of galaxies. On the other hand, the degree of enhancement or depletion in galaxy counts due to weak lensing is independent of the SLC effect. We discuss the impact on the two-point shear statistics to be measured by future missions like SNAP and LSST . The SLC effect would bias the estimation of σ₈ from two-point statistics up to 5 per cent for a narrow redshift distribution of mean   z ∼ 0.5  , and up to 2 per cent in small angular scales for a redshift distribution of mean   z ∼ 1.5  . We conclude that accurate photometric redshifts for individual galaxies are necessary in order to quantify and isolate the SLC effect.     

Equilibration Scales in Silicic to Intermediate Magmas Implications for Experimental Studies

Experimental phase equilibrium studies are increasingly beingused for the determination of intensive variables (P, T, fH₂O,fO₂ ) in silicic to intermediate magmas. In contrast, silicicigneous bodies are now perceived as open, periodically recharged,systems involving only limited chemical equilibration. Thus,the use of laboratory-determined crystal–liquid equilibriumdata needs clarification. Here we review the field, petrologicaland geochemical evidence concerning states and scales of chemicalequilibrium in silicic magma bodies. It is concluded that totalchemical equilibrium is generally not the rule. However, a subsystemin local equilibrium (the reactive magma) can be identified.Equilibration scales in silicic magmas are rate-limited eitherby diffusive flux in crystals (DICL regime) or by diffusiveflux in the melt (MD regime). The recognition that equilibriumin magmas is limited to a reactive subsystem requires phaseequilibrium studies to be chemically scaled. Experiments, eitherof total or partial equilibrium type, should aim at a closereproduction of equilibrium states specific to natural systems.The laboratory reconstruction of the natural equilibrium statesguarantees a precise determination of the pre-eruptive parametersand a reliable application of the experimental data to activevolcanic systems. KEY WORDS: silicic magmas; chemical equilibrium; timescales; experimental studies     

Imposex levels and concentrations of organotin compounds (TBT and its metabolites) in Nassarius nitidus from the Lagoon of Venice

Specimens of Nassarius nitidus were collected in seven stations of the Venice Lagoon to assess the levels of tributyltin (TBT) and its metabolites monobutyltin and dibutyltin in the tissues and monitor their effect on organisms, in particular the phenomenon of imposex (superimposition of male sexual characteristics on females). The following values of population indices were found: vas deferens sequence: 1.2 ± 0.7–4.0 ± 0.5; relative penis length: 6–47%. The least impacted station was situated in the northern part of the Lagoon, where females without imposex were found and Butyltin (BuTs) concentrations in the organisms (average sum of BuTs = 43 ± 14 ng Sn g⁻¹ w.) were significantly lower than in the other stations (range of average sum of BuTs: 101 ± 22–217 ± 27 ng Sn g⁻¹ d.w.). Population indices were found to be related to the TBT content in the tissues. In particular VDSI had a significant logarithmic correlation: r = 0.95, n = 8, p < 0.05.     

Thermodynamic behaviour of the high-temperature P\bar 1{\text{-}}I\bar 1 phase transition along the CaAl2Si2O8–SrAl2Si2O8 join

In situ high-temperature synchrotron radiation powder diffraction patterns were taken from room temperature to T = 740°C from synthetic feldspars along the join CaAl₂Si₂O₈–SrAl₂Si₂O₈ (An–SrF). Three samples of composition An₉₅SrF₅, An₉₀SrF₁₀ and An₈₅SrF₁₅ were investigated, and the evolution of cell parameters with T was determined by Rietveld analysis of powder X-ray diffraction patterns. The high-temperature $P\bar 1{\text{-}}I\bar 1$ phase transition, previously observed with T _c = 241°C in anorthite, was found in An₉₅SrF₅, An₉₀SrF₁₀ and An₈₅SrF₁₅ feldspars at T _c = 233(5)°, 195(2)° and 174(2)°C respectively. The transition was revealed by the disappearance of critical reflections and variations in the rate of change of cell parameters with temperature. A significant, although small (between 0.0025 and 0.0012 at room temperature), spontaneous strain could be measured, allowing the thermodynamic behaviour of the transition to be modelled. A second-order trend for An₉₀SrF₁₀ and An₈₅SrF₁₅ [β = 0.504(7) and 0.505(7) respectively] or nearly second-order for An₉₅SrF₅[β = 0.458(4)] was observed in contrast with tricritical behaviour of end member anorthite. An extrapolation of the T _c versus composition to room temperature indicates that the critical composition for the $P\bar 1$ phase is An₆₀SrF₄₀.