Discriminating the long distance dispersal of fine ash from sustained columns or near ground ash clouds: The example of the Pomici di Avellino eruption (Somma-Vesuvius,Italy)

Ash samples from tephra layers correlated with the Pomici di Avellino (Avellino Pumice) eruption of Somma-Vesuvius were collected in distal archives and their composition and particle morphology investigated in order to infer their behaviour of transportation and deposition. Differences in composition and particle morphologies were recognised for ash particles belonging to the magmatic Plinian and final phreatomagmatic phases of the eruption. The ash particles were dispersed in opposite directions during the two different phases of the eruption, and these directions are also different from that of coarse-grained fallout deposits. In particular, ash generated during magmatic phase and injected in the atmosphere to form a sustained column shows a prevailing SE dispersion, while ash particles generated during the final phreatomagmatic phase and carried by pyroclastic density currents show a general NW dispersion. These opposite dispersions indicate an ash dispersal influenced by both high and low atmosphere dynamics. In particular, the magmatic ash dispersal was first driven by stratospheric wind towards NE and then the falling particles encountered a variable wind field during their settling, which produced the observed preferential SE dispersal. The wind field encountered by the rising ash clouds that accompanied the pyroclastic density currents of the final phreatomagmatic phase was different with respect to that encountered by the magmatic ash, and produced a NW dispersal. These data demonstrate how ash transportation and deposition are greatly influenced by both high and low atmosphere dynamics. In particular, fine-grained particles transported in ash clouds of small-scale pyroclastic density currents may be dispersed over distances and cover areas comparable with those injected into the stratosphere by Plinian, sustained columns. This is a point not completely addressed by present day mitigation plans in case of renewal of activity at Somma-Vesuvius, and can yield important information also for other volcanoes potentially characterised by explosive activity.     

Heat budget for a shallow,sinuous salt marsh estuary

An experimental study of temperature cycles and the heat budget in the Duplin River, a tidal creek bordered by extensive intertidal salt marshes, was carried out in late summer of 2003 and spring of 2004 near Sapelo Island on the central Georgia coast in the southeastern US. Three water masses are identified with differing temperature and salinity regimes, the characteristics of which are dictated by channel morphology, tidal communication with the neighboring sound, ground water hydrology, the extent of local intertidal salt marshes and side channels and the spring–neap tidal cycle (which controls both energetic mixing and, presumably, ground water input). For the first experiment, heat budgets are constructed for the upper (warmer) and lower (cooler) areas of the Duplin River showing the diminishing importance of tidal advection away from the mouth of the creek along with the concomitant increase in the importance of both direct atmospheric fluxes and of interactions with the marsh and side creeks. The second experiment, in the spring of 2004, reexamines the heat budget on seasonal and daily averaged scales revealing the decreased importance of advective fluxes relative to direct atmospheric fluxes on this scale but the constant importance of marsh/creek interactions regardless of time scale or season. Short period temperature fluctuations which affect larval development are examined and analogies are drawn to use heat to understand the marsh as a source of sediment, carbon and other nutrients.     

Magnetic field transforms with low sensitivity to the direction of source magnetization and high centricity

Magnetic data interpretation faces difficulties due to the various shapes of magnetic anomalies and the positions of their extrema with respect to the causative bodies for different directions of the source magnetization. The well‐known transforms — reduction to the pole, pseudogravity field, and analytic signal (total gradient) — help in reducing the problem. Another way to achieve the required effect is the transformation of magnetic data, ΔT or Z, into values of the anomalous magnetic intensity T. In this respect, we have found some transforms based on differential operators such as the gradient of T and its modulus R = |?T|, the Laplacian L = ?²T, the product T ?²T and its square root Q, and the Laplacian ?²(T²) and its square root E, to be useful. They are slightly sensitive to the magnetization orientation and their extrema occur above the sources. For a 2D anomaly of a homogeneous causative body, the proposed transforms do not depend on the inclination of magnetization. In the 3D case, such independence does not exist even for the elementary field of a point dipole. The influence of the magnetization direction is estimated by an integral coefficient of sensitivity. This coefficient takes values of up to 2.0 for ΔT or Z anomalies, while their transforms T, R, E, Q and L have values of less than 0.28, 0.29, 0.24, 0.16 and 0.07, respectively, i.e. on average, 10 times less. The estimation of the centricity is carried out using the relative deviation of the principal extremum of the anomaly or its transforms from the epicentre of the model body at a depth equal to 100 units. For a ΔT anomaly this deviation is up to 67%; for the L transform it is less than 8%; for Q, E, R and T it is less than 10%, 15%, 20% and 25%, respectively. The proposed transforms take only non‐negative values. With respect to their shape, the peripheral magnetic extrema are removed, the anomalous configuration is simplified and the resolution of complicated interference patterns is improved. Their calculation does not require additional data for the direction of magnetization, which is an essential advantage over the reduction‐to‐the‐pole and pseudogravity‐field transforms. A joint analysis of the measured field and its transforms T, E and L offers possibilities for more confident separation of the anomalous effects and direct correlation to their sources. The model tests performed and the 3D field applications to real magnetic data confirm the useful properties of the transforms suggested here.     

Bacterial response to seasonal changes in labile organic matter composition on the continental shelf and bathyal sediments of the Cretan Sea

Bacterial abundance, biomass and cell size were studied in the oligotrophic sediments of the Cretan Sea (Eastern Mediterranean), in order to investigate their response to the seasonal varying organic matter (OM) inputs. Sediment samples were collected on a seasonal basis along a transect of seven stations (ranging from 40 to 1570 m depth) using a multiple-corer. Bacterial parameters were related to changes in chloroplastic pigment equivalents (CPE), the biochemical composition (proteins, lipids, carbohydrates) of the sedimentary organic matter and the OM flux measured at a fixed station over the deep basin (1570 m depth). The sediments of the Cretan Sea represent a nutrient depleted ecosystem characterised by a poor quality organic matter. All sedimentary organic compounds were found to vary seasonally, and changes were more evident on the continental shelf than in deeper sediments. Bacterial abundance and biomass in the sediments of the Cretan Sea (ranging from 1.02 to 4.59 × 10⁸ cells g⁻¹ equivalent to 8.7 and 38.7 μgC g⁻¹) were quite high and their distribution appeared to be closely related to the input of fresh organic material. Bacterial abundance and biomass were sensitive to changes in nutrient availability, which also controls the average cell size and the frequency of dividing cells. Bacterial abundance increased up to 3-fold between August '94 and February '95 in response to the increased amount of sedimentary proteins and CPE, indicating that benthic bacteria were constrained more by changes in quality rather than the quantity of the sedimentary organic material. Bacterial responses to the food inputs were clearly detectable down to 10 cm depth. The distribution of labile organic compounds in the sediments appeared to influence the vertical patterns of bacterial abundance and biomass. Cell size decreased significantly with water depth. Bacterial abundance and biomass were characterised by clear seasonal changes in response to seasonal OM pulses. The strong coupling between protein flux and bacterial biomass together with the strong bacterial dominance over the total biomass suggest that the major part of the carbon flow was channelled through the bacteria and the benthic microbial loop.     

Constraining the cosmic equation of state from old galaxies at high redshift

New limits on the cosmic equation of state are derived from age measurements of three recently reported old high-redshift galaxies (OHRG). The results are based on a flat Friedmann–Robertson–Walker (FRW) type cosmological model driven by non-relativistic matter plus a smooth component parametrized by its equation of state p _x ωρ _x ( ω −1). The range of ω is strongly dependent on the matter density parameter. For Ω_M∼0.3, as indicated from dynamical measurements, the age estimates of the OHRG restrict the cosmic parameter to ω −0.27. However, if Ω_M is the one suggested by some studies of field galaxies, i.e., Ω_M≃0.5, only a cosmological constant ( ω =−1) may be compatible with these data.     

Crystal-chemistry of clinopyroxenes from potassic and ultrapotassic rocks in central Italy: implications on their genesis

The clinopyroxenes mentioned have been investigated by single crystal X-ray diffraction combined with electron microprobe analysis. The aim of this study was to characterize the crystal-chemical variations of clinopyroxenes in order to delineate the intracrystalline constraints which are characteristic of specific magmatic environments. Clinopyroxenes (cpx) crystallized from peralkaline ultrapotassic melt with kamafugitic and lamproitic affinities are characterized by high Si contents, which are insensitive to variations in silica abundance and silica saturation of the melt. The high Si occupancy in clinopyroxenes from kamafugitic magma is coupled to large M1 (i.e. Mg and Fe²⁺) and M2 (high Ca occupancy) sites, whereas in clinopyroxenes from magmas with lamproitic affinity, high Si content is combined with large M1 but small M2 sites. Clinopyroxenes from Romantype alkaline potassic and ultrapostassic rocks are characterized by an expanded tetrahedron (high ^IVA1 content) and small M1 site which is combined with small M2 polyhedron in clinopyroxenes from the potassic rocks and large M2 site in those from the ultrapotassic rocks.     

New Reference Materials and Assessment of Matrix Effects for SIMS Measurements of Oxygen Isotopes in Garnet

Accurate ion microprobe analysis of oxygen isotope ratios in garnet requires appropriate reference materials to correct for instrumental mass fractionation that partly depends on the garnet chemistry (matrix effect). The matrix effect correlated with grossular, spessartine and andradite components was characterised for the Cameca IMS 1280HR at the SwissSIMS laboratory based on sixteen reference garnet samples. The correlations fit a second‐degree polynomial with maximum bias of ca. 4‰, 2‰ and 8‰, respectively. While the grossular composition range 0–25% is adequately covered by available reference materials, there is a paucity of them for intermediate compositions. We characterise three new garnet reference materials GRS2, GRS‐JH2 and CAP02 with a grossular content of 88.3 ± 1.2% (2s), 83.3 ± 0.8% and 32.5 ± 3.0%, respectively. Their micro scale homogeneity in oxygen isotope composition was evaluated by multiple SIMS sessions. The reference δ¹⁸O value was determined by CO₂ laser fluorination (δ¹⁸O_LF). GRS2 has δ¹⁸O_LF = 8.01 ± 0.10‰ (2s) and repeatability within each SIMS session of 0.30–0.60‰ (2s), GRS‐JH2 has δ¹⁸O_LF = 18.70 ± 0.08‰ and repeatability of 0.24–0.42‰ and CAP02 has δ¹⁸O_LF = 4.64 ± 0.16‰ and repeatability of 0.40–0.46‰.     

Zircon formation during fluid circulation in eclogites (Monviso, Western Alps): implications for Zr and Hf budget in subduction zones

The zircons from an eclogite and an enclosed eclogite-facies vein from the Monviso ophiolite (Western Alps) display contrasting chemical and morphologic features and document different stages of the evolution of the ophiolite. The zircons from the eclogite show a typical magmatic zoning and are enriched in heavy rare earth elements (HREEs) over middle rare earth elements (MREEs) and have an accentuated negative Eu anomaly, which indicates that the grains co-crystallised with plagioclase. These magmatic zircons document the formation of oceanic crust at 163 ± 2 Ma. In contrast, zircons from the vein contain inclusions of garnet, omphacite, and rutile, which indicate that they crystallised under eclogite-facies conditions. The vein zircons have Th/U ratios < 0.09, lack Eu anomalies, and are only weakly enriched in HREE with respect to MREE. These features are consistent with a garnet-bearing, plagioclase-free, i.e., eclogite-facies paragenesis. Vein zircons yield an age of 45 ± 1 Ma, which is evidence for Eocene subduction-zone metamorphism of the Monviso ophiolite.In the vein, the apparent coexistence of zircon, omphacite, and garnet permits the determination of a set of trace element distribution coefficients among these minerals at high pressure. This set of partitioning can demonstrate chemical equilibrium among these phases in rocks that show less clear evidence of textural equilibrium. In addition, zircon age can now be linked to sensors of metamorphic pressure-temperature conditions. The presence of zircon and rutile in the vein is another example of high field strength element (HFSE) mobility over short distances in aqueous fluids at eclogite-facies conditions. However, the concentrations of Zr and Hf in the aqueous fluid are estimated to be at least a factor of 10 less than primitive mantle values.Mass balance calculations demonstrate that zircon hosts > 95% of the bulk Zr, 90% of Hf, and ∼25% of U in the vein. Zircon is a residual phase in subducted basalts and sediments up to temperatures of at least 800 to 900 °C. Therefore, residual zircon in subducted crust, together with rutile, control the HFSE in liberated subduction zone fluids/melts and might be partly responsible for negative Zr and Hf anomalies in subduction zone magmas.     

Stellar wind models with Alfvén waves

It is known that stellar winds from late type stars are of mixed thermal and magnetic origin. The stellar wind model presented in this work uses the hydrodynamic equations of mass and momentum conservation and closes the system of equations with a detailed energy equation. Both momentum and energy equations have terms due to the effects of Alfvén waves. A smooth transition between the two regimes for Alfvén wave propagation, the undamped and the damped modes, is achieved by considering the geometrical mean of both wave amplitudes. It will be shown that the initial push on the plasma is provided by the mechanical heating input, and that further out the Alfvén waves take over energetically.