Spatial and temporal prokaryotic variability in the northern Adriatic Sea

The prokaryotic community, both in terms of abundance and activity (exoenzymatic hydrolysis of proteins, polysaccharides and phosphorylated molecules and leucine uptake), was investigated seasonally for a 3‐year period (2004–2006) in the Gulf of Venice (northern Adriatic Sea). By focusing on spatial and temporal variability, the prokaryote dynamics showed significant variations on a horizontal and seasonal scale, but no substantial differences were observed among years. The basin‐scale variability was mainly influenced by allochthonous inputs from the Po river and the Venice Lagoon, which were the main source of nutrients, acting as a ‘bottom up’ control on prokaryotes. On a seasonal scale, all the microbial parameters (except the polysaccharide degradation) showed significant variations following the temperature fluctuations. The annual rate of change was very low for all the chemical, physical and biological parameters and only the abundance and phosphatase activity of the prokaryotes differed significantly among years.     

Combining relative and absolute gravity measurements to enhance volcano monitoring

To achieve a balance between uncertainty and efficiency in gravity measurements, we have investigated the applicability of combined measurements of absolute and relative gravity as a hybrid method for volcano monitoring. Between 2007 and 2009, three hybrid gravity surveys were conducted at Mt Etna volcano, in June 2007, July 2008, and July 2009. Absolute gravity data were collected with two absolute gravimeters, which represent the state of the art in recent advances in ballistic gravimeter technology: (1) the commercial instrument FG5#238 and (2) the prototype instrument IMGC-02. We carried out several field surveys and confirmed that both the absolute gravimeters can still achieve a 10 μGal or better uncertainty even when they are operated in severe environmental conditions. The use of absolute gravimeters in a field survey of the summit area of Mt Etna is unprecedented. The annual changes of the gravity measured over 2007–2008 and 2008–2009 provide unequivocal evidence that during the 2007–2009 period, two main phenomena of subsurface mass redistribution occurred in distinct sectors of the volcano, accompanying different eruptive episodes. From 2007 to 2008, a gravity change of ?60?μGal was concentrated around the North-East Rift. This coincided with a zone affected by strong extensional tectonics, and hence might have been related to the opening of new voids. Between 2008 and 2009, a North-South elongate feature with a maximum gravity change of +80?μGal was identified in the summit craters area. This is interpreted to indicate recharge of a deep-intermediate magma storage zone, which could have occurred when the 2008–2009 eruption was still ongoing.     

Lava flow simulations using discharge rates from thermal infrared satellite imagery during the 2006 Etna eruption

Techniques capable of measuring lava discharge rates during an eruption are important for hazard prediction, warning, and mitigation. To this end, we developed an automated system that uses thermal infrared satellite MODIS data to estimate time-averaged discharge rate. MODIS-derived time-varying discharge rates were used to drive lava flow simulations calculated using the MAGFLOW cellular automata model, allowing us to simulate the discharge rate-dependent spread of lava as a function of time. During the July 2006 eruption of Mount Etna (Sicily, Italy), discharge rates were estimated at regular intervals (i.e., up to 2 times/day) using the MODIS data. The eruption lasted 10 days and produced a ~3-km-long lava flow field. Time-averaged discharge rates extracted from 13 MODIS images were utilized to produce a detailed chronology of lava flow emplacement, demonstrating how infrared satellite data can be used to drive numerical simulations of lava flow paths during an ongoing eruptive event. The good agreement between simulated and mapped flow areas indicates that model-based inundation predictions, driven by time-varying discharge rate data, provide an excellent means for assessing the hazard posed by ongoing effusive eruptions.     

Ground and marine magnetic surveys of the lower eastern flank of Etna volcano (Italy)

In 1996 and 1997, two high-resolution magnetic surveys, one on land and the other at sea, were carried out on the lower eastern flank of Mount Etna. The magnetic surveys, covering an area of about 400 km², aimed to elucidate the relationships between the main tectonic and morphologic features of this flank of Mount Etna. Major features include widespread NNW- and NNE-trending active faults and the Valle del Bove, a depression considered to be the source area of the Chiancone deposit, the largest Etnean volcaniclastic sequence. Magnetic surveys show anomalies that roughly follow the trend of active main structures. Although few magnetization measurements are available for the most representative outcrops of the lower eastern side of Mount Etna, interpretation of the anomalies defines the underground geometry of the Chiancone deposit and its relationship with volcano stratigraphic units and the underlying sedimentary rocks. In particular, a volume of about 14 km³ was ascribed to the Chiancone deposit. Such a large amount of material was likely produced by a catastrophic event, and deposited at different periods at the exit of the Valle del Bove in an area produced by the interaction, on a regional scale, of the main tectonic structures affecting this flank of the volcano.     

Residual electron density at theM2 site inC2/c clinopyroxenes: Relationships with bulk chemistry and sub-solidus evolution

The systematic study of both natural and synthetic clinopyroxenes often indicates the presence in the difference Fourier map of a maximum of residual density of up to 0.8 electrons, here labelledM2′, close to theM2 site along the diad axis, defining a square pyramid co-ordination polyhedron. To investigate the nature and the crystalchemical implications of this feature, a limited but representative set of clinopyroxenes of volcanic, metamorphic and synthetic origin has been investigated by X-ray structure refinement (at 0.7 and 0.4 Å resolution), by microprobe analysis and by transmission electron microscopy. The most important results are: a) at increasing resolution, the height of theM2′ peak increases while its co-ordinates move towardM2; b) as (Ca + Na) content approaches 1.0 atom per formula unit,M2′ vanishes; c)M2′ has been found in clinopyroxenes which show differing incipient exsolution microstructures, from spinodal decomposition to non-periodic fluctuations, as well as in homogeneous specimens. The presence ofM2′ is interpreted in terms of the simultaneous coexistence in the crystals of two different structural models, approximately diopside and clinoenstatite. An accurate evaluation of the totalM2 + M2′ site occupancy is strongly suggested in XREF work, particularly when thermodynamic and kinetic considerations have to be obtained with accurate determinations of site occupancy factors as a starting point.     

Evolution of the REE mineralogy in HP–LT metapelites of the Sebtide complex, Rif, Morocco: Monazite stability and geochronology

REE mineralogy was characterized at the micrometer scale (using scanning electron microscopy) in the four tectono-metamorphic units of the Beni Mzala window, Sebtide Complex, Internal Rif, Morocco, which sample a HP-LT metamorphic gradient from subgreenschist to blueschist/eclogite facies. These tectonic units are composed of garnet-free metapelites (and associated synmetamorphic veins) from the same homogeneous aluminium-rich and calcium-poor protolith. In that context, mineralogical differences between units are assumed to result from contrasted pressure and temperature histories. Light REE-bearing Al-phosphates of the crandallite group with florencite-rich composition and variable goyazite content are the dominant LREE minerals in the lowest-grade units, Tizgarine (300 °C, 3 kbar as peak conditions) and Boquete de Anjera (350 °C, 10 kbar). In the latter unit, metamorphic florencite is associated with MREE-rich monazite. In the schist of the highest-grade units, Beni Mzala 2 (420–450 °C, 12 kbar) and Beni Mzala 1 (550 °C, 16 kbar), associations of allanite-rich epidote and synchisite (a LREE-fluorocarbonate) are found whereas florencite and monazite are no longer observed. At the wall of the quartz–kyanite veins, retrograde monazite-(Ce) with grain size of 20 to 50 μm is the only LREE-bearing mineral. Th–Pb and U–Pb SIMS data on some of these grains yield ages of 21.3 ± 1.7 Ma and 20.9 ± 2.1 Ma, respectively, consistent with previous K–Ar ages obtained on retrograde clay–mica mixtures in rocks from the same locality. The identification of a stability field for monazite in high-pressure aluminous metapelites with an upper thermal-limit below 450 °C as well as the derivation of meaningful U–Pb and Th–Pb SIMS ages demonstrates the monazite potential for dating HP-LT metapelites. However, since, under these conditions, monazite growth occurs below its admitted closure-temperature, these ages must be interpreted on the basis of monazite textural relationships.     

Effects of non-stoichiometry on the spinel structure at high pressure: Implications for Earth’s mantle mineralogy

A non-stoichiometric sample of spinel with composition ^T(Mg_0.4Al_0.6)^M(Al_1.8□_0.2)O₄ was investigated by single-crystal X-ray diffraction in situ up to about 8.7 GPa using a diamond anvil cell. The P(V) data were fitted using a third-order Birch-Murnaghan equation of state and the unit-cell volume V₀, the bulk modulus K_T0 and its first pressure derivative K′ were refined simultaneously providing the following coefficients: V₀ = 510.34(6) Å³, K_T0 = 171(2) GPa, K′ = 7.3(6). This K_T0 value represents the lowest ever found for spinel crystal structures. Comparing our data with a stoichiometric and natural MgAl₂O₄ (pure composition) we observe a decrease in K_T0 by about 11.5% and a strong increase in K′ by about 33%. These results demonstrate how an excess of Al accompanied by the formation of significant cation vacancies at octahedral site strongly affects the thermodynamic properties of spinel structure. If we consider that the estimated mantle composition is characterized by 3-5% of Al₂O₃ this could imply an Mg/Al substitution with possible formation of cation vacancies. The results of our study indicate that geodynamic models should take into account the potential effect of Mg/Al substitution on the incompressibility of the main mantle-forming minerals (olivine, wadsleyite, ringwoodite, Mg-perovskite).     

Magnetic features of the magmatic intrusion that occurred in the 2007 eruption at Stromboli Island (Italy)

Significant changes in the local magnetic field marked the resumption of eruptive activity at Stromboli volcano on February 27, 2007. After differential magnetic fields were obtained by filtering out external noise using adaptive filters and seasonal thermal noise using temperature data, we identified step-like changes of 1–4 nT coincident with the opening of eruptive fissures in the upper part of the Sciara del Fuoco. The magnetic variations detected at two stations are closely related to the propagation of a shallow NE–SW magmatic intrusion extending beyond the summit craters area. These observations are consistent with those calculated using piezomagnetic models in which stress-induced changes in rock magnetization are produced by the magmatic intrusion. No significant magnetic changes were observed when the first fractures opened along the NE crater rim. Indeed, the stress-induced magnetization caused by this magmatic activity is expected to be too low because of the structural weakness and/or thermal state of the summit area. The continuous long-term decay characterizing the post-eruptive magnetic pattern can be related to a time-dependent relaxation process. A Maxwell rheology was assumed and the temporal evolution of the piezomagnetic field was evaluated. This allowed us to estimate the rheological properties of the medium; in particular, an average viscosity ranging between 10¹⁶ and 10¹⁷ Pa⋅s was a relaxation time τ of about 38 days.