ALBERT

Beschreibung: We present calculations of the early stages of the formation of Jupiter via core nucleated accretion and gas capture. The core begins as a seed body of about 350 kilometers in radius and orbits in a swarm of planetesimals whose initial radii range from 15 meters to 100 kilometers. We follow the evolution of the swarm by accounting for growth and fragmentation, viscous and gravitational stirring, and for drag-induced migration and velocity damping. Gas capture by the core substantially enhances the cross-section of the planet for accretion of small planetesimals. The dust opacity within the atmosphere surrounding the planetary core is computed self-consistently, accounting for coagulation and sedimentation of dust particles released in the envelope as passing planetesimals are ablated. The calculation is carried out at an orbital semi-major axis of 5.2 AU and an initial solids' surface density of 10/g/cm^2 at that distance. The results give a core mass of 7 Earth masses and an envelope mass of approximately 0.1 Earth mass after 500,000 years, at which point the envelope growth rate surpasses that of the core. The same calculation without the envelope gives a core mass of only 4 Earth masses.

Beschreibung: Methane plays an important role in the Earth’s atmospheric chemistry and radiative balance being the most important greenhouse gas after carbon dioxide. It has recently been established that geogenic gases contribute significantly to the natural CH4 flux to the atmosphere (Etiope et al., 2008). Volcanic/geothermal areas contribute to this flux, being the site of widespread diffuse degassing of endogenous gases (Chiodini et al., 2005). In such an environment soils are a source rather than a sink for atmospheric CH4 (Cardellini et al., 2003; Castaldi and Tedesco, 2005; D’Alessandro et al., 2009; 2011; 2013). Due to the fact that methane soil flux measurements are laboratory intensive, very few data have been collected until now in these areas. Preliminary studies (Etiope et al., 2007) estimated a total CH4 emission from European geothermal and volcanic systems in the range 4-16 kt a-1. This estimate was obtained indirectly from CO2 or H2O output data and from CO2/CH4 or H2O/CH4 values measured in the main gaseous manifestations. Such methods, although acceptable to obtain order-of-magnitude estimates, completely disregard possible methanotrophic activity within the soil. At the global scale, microbial oxidation in soils contributes for about 3-9% to the total removal of methane from the atmosphere. But the importance of methanotrophic organisms is even larger because they oxidise the greatest part of the methane produced in the soil and in the subsoil before its emission to the atmosphere. Environmental conditions in the soils of volcanic/geothermal areas (i.e. low oxygen content, high temperature and proton activity, etc.) have been considered inadequate for methanotrophic microrganisms. But recently, it has been demonstrated that methanotrophic consumption in soils occurs also under such harsh conditions due to the presence of acidophilic and thermophilic Verrucomicrobia. These organisms were found in Italy at the Solfatara di Pozzuoli (Pol et al., 2007), in New Zealand at Hell’s Gate (Dunfield et al., 2007) and in Kamchatka, Russia (Islam et al., 2008). Both the Italian and the Hellenic territories are geodynamically very active with many active volcanic and geothermal areas. Here we report on methane flux measurements made at Pantelleria (Italy) and at Sousaki and Nisyros (Greece). The total methane output of these three systems is about 10, 19 and 1 t a-1, respectively (D’Alessandro et al., 2009; 2011; 2013). The total emissions obtained from methane flux measurements are up to one order of magnitude lower than those obtained through indirect estimations. Clues of methanotrophic activity within the soils of these areas can be found in the CH4/CO2 ratio of the flux measurements which is always lower than that of the respective fumarolic manifestations, indicating a loss of CH4 during the travel of the gases towards earth’s surface. Furthermore laboratory methane consumption experiments made on soils collected at Pantelleria and Sousaki revealed, for most samples, CH4 consumption rates up to 9.50 µg h-1 and 0.52 µg h-1 respectively for each gram of soil (dry weight). Only few soil samples displayed no methane consumption activity. Finally, microbiological and molecular investigations allowed us to identify the presence of methanotrophic bacteria belonging to the Verrucomicrobia and to the Alpha- and Gamma-Proteobacteria in the soils of the geothermal area of Favara Grande at Pantelleria. While the presence of the former was not unexpected due to the fact that they include acidophilic and thermophilic organisms that were previously found in other geothermal environments, the latter are generally considered not adapted to live in harsh geothermal environments. Their presence in the soils of Pantelleria could be explained by the fact that these soils do not have extremely low pH values (〉5). Indeed thermotollerant methanotrophic Gamma-proteobacteria, have been previously found in the sediments of thermal springs in Kamchatka (Kizilova et al., 2012). Such species could find their niches in the shallowest part of the soils of Favara Grande were the temperatures are not so high and they thrive on the abundant upraising hydrothermal methane.

Beschreibung: Published

Beschreibung: Patras, Greece

Beschreibung: 4.5. Studi sul degassamento naturale e sui gas petroliferi

Beschreibung: open

Beschreibung: Like other geodynamically active areas also the Hellenic territory is affected by a large number of geogenic gas manifestations. These occur either in form of point sources (fumaroles, mofettes, bubbling gases) or as diffuse soil gas emanations. Geogenic sources release huge amounts of gases, which, apart from having important influences on the global climate, could have strong impact on human health. Gases have both acute and chronic effects. Carbon Dioxide and Hydrogen Sulphide are the main gases responsible for acute mortality due to their asphyxiating and/or toxic properties. Gas hazard is often disregarded because in fatal episodes connected to geogenic gases the death cause is often not correctly attributed. Due to the fact that geodynamic active areas can release geogenic gases for million years over wide areas, it is important not to underestimate potential risks. The present work produced a first catalogue of the geogenic gas manifestations of the whole Hellenic territory also considering literature data. Carbon dioxide dominated manifestations are the majority (61 out of 81). Most of them are found along the South Aegean Active Volcanic Arc. Many sites are also found in northern Greece and along the Sperchios basin - north Evia graben (central Greece) which are characterised by extensional tectonic activity. A preliminary estimation of the gas hazard has been made for the time period of the last 20 years considering the whole population of Greece. In this period at least two fatal episodes with a total of three victims could be certainly attributed to geogenic gases (specifically carbon dioxide). This would give a risk of 1.3 10-8 fatalities from geogenic gas manifestations per annum. Of course this risk is unevenly distributed along the whole Hellenic territory and it will depend on many factors. The most important factor will be the geographical distribution of the natural gas manifestations while also the strength of the source, the chemical composition of the gases, the meteorological conditions and the topography of the area will contribute to the determination of the local risk. The assessment of the geographical distribution of the risk levels is a difficult task, but the present catalogue of the gas manifestations of the natural gas manifestations of Greece will be a contribution to its determination. Since deaths due to natural gases are often wrongly attributed we cannot exclude that some fatal episode has not be recognized and thus that the risk is somewhat higher than that here assessed. Although very low this risk has not to be neglected, not only because possibly underestimated but also because simple countermeasures could be adopted. Dangerous area can be easily identified and delimited by geochemical prospections and their hazard properly evidenced.

Beschreibung: Published

Beschreibung: Kagoshima, Japan

Beschreibung: 4.5. Studi sul degassamento naturale e sui gas petroliferi

Beschreibung: open

Beschreibung: Methane plays an important role in the Earth’s atmospheric chemistry and radiative balance being the most important greenhouse gas after carbon dioxide. It is released to the atmosphere by a wide number of sources, both natural and anthropogenic, with the latter being twice as large as the former. It has recently been established that significant amounts of geological methane, produced within the Earth’s crust, are currently released naturally into the atmosphere. Active or recent volcanic-geothermal areas represent one of these sources of geological methane. Due to the fact that methane flux measurements are laboratory intensive, very few data have been collected until now and the contribution of this source has been often indirectly estimated. Both the Italian and the Hellenic territories are geodynamically very active with many volcanic and geothermal areas. Here we report on methane flux measurements made at Pantelleria (Italy), Sousaki and Nisyros (Greece). The total outputs of these three systems are about 10, 19 and 2 t a-1 respectively. These figures are up to one order of magnitude lower than those obtained through indirect estimations. At the global scale, microbial oxidation in soils contributes to the total removal of methane from the atmosphere. Environmental conditions in the soils of volcanic/geothermal areas (i.e. low pH, high temperature, etc.) have been considered inadequate for methanotrophic microrganisms. But recently, it has been demonstrated that methanotrophic consumption in soils occurs also under such harsh conditions due to the presence of thermo-acidophilic Verrucomicrobia. Here we present the results of laboratory incubation experiments on soil samples collected at the main exhalative areas that highlighted methanotrophic activity also at Pantelleria and Sousaki. Soil metagenomic DNA was extracted from some of the Pantelleria samples and analysed using Temporal Temperature Gradient Electrophoresis (TTGE) of the amplified Bacterial 16S rRNA gene in order to evaluate the total bacterial diversity. Soil DNA amplification with primers targeting Proteobacterial and Verrucomicrobial methane monooxygenase genes (pmmo) revealed the presence of methanotrophs affiliated to both phyla up to a depth of 11 cm and a temperature of 80°C. The diversity of proteobacterial methanotrophs was investigated by creating a clone library of the amplified methane mono-oxygenase encoding gene, pmmoA. The clone sequences are close to those of uncultured type I methanotrophic proteobacteria. An attempt to isolate methanotrophs was carried out on soils from Pantelleria, sampled at different depths, by enrichment cultures on a mineral medium in a methane-enriched atmosphere. No isolates were obtained from enrichments carried out at 65°C while incubation at 37°C allowed to isolate a few methanothropic strains that were identified as Methylocystis spp.

Beschreibung: Published

Beschreibung: Kagoshima, Japan

Beschreibung: 4.5. Studi sul degassamento naturale e sui gas petroliferi

Beschreibung: open

Beschreibung: Pantelleria is an active volcanic complex, at present in quiescent status, hosting a high enthalpy geothermal system. Explorative geothermal wells tapped exploitable water-dominated reservoirs at 600-800 m depth with maximum measured temperatures of 250°C. Five field campaigns for soil gas measurements were made in the period from July 2005 to October 2006. CO2 flux was measured with the accumulation chamber method at 807 sites, CO2 concentration and Rn activity in soil atmosphere were measured at 50 cm depth at 728 and 358 sites, respectively. The first campaign covered the whole island (about 83 km2) with an approximately sample density of 3.5 points per km2 for CO2 (flux and concentration) measurements and of 1.6 points per km2 for Rn measurements. The distribution of the sampling points was as far as possible evenly distributed. Only few limited areas resulted uncovered due to accessibility problems (inhabited areas, airport, steep or rough topography). In the following four surveys nine areas were studied with greater detail with sample densities of up to 100 points per km2. Flux measurements for the whole surveys gave values in the range 〈 0.1 - 4700 gCO2 m-2 day-1 (Fig. 1). Organic contribution could not be distinguished with statistical methods and in the present study was considered negligible above 30 g m-2 day-1. The sites displaying flux values above this threshold, representing about 32% of the total population, are almost all located within the 50 ka old caldera. The highest values correspond to the areas of Favara Grande and of the lake Specchio di Venere (Fig. 1), which have long been recognized as sites of anomalous degassing with the presence of active fumarolic vents with temperatures of about 100 °C in the former and thermal springs with abundant bubbling gases and a mofette in the latter. A new anomalous degassing area with very high output values has been identified on the southern flank of Mt. Grande (MGS in Fig. 1). In this area the vegetation cover strongly contrasts with that of the neighboring areas, consisting of scrubby low growing plants, mosses and bare land. Indeed, high CO2 flux values are always measured as long as such vegetation cover is found, abruptly decreasing when higher growing plants are present. The contrast is particularly evident in springtime and can be used as a good marker to individuate anomalous degassing areas. Further areas were studied in detail being sites of fumarolic manifestations. All of them are also sites of anomalous CO2 fluxes although of limited areal extension. The area of the last subaerial volcanic activity (Mursia) was also studied but the measurements were all far below the anomaly threshold. The total CO2 output of the anomalous degassing areas was estimated through geostatistical methods considering only values above the anomaly threshold. Results evidence that most of the output (87%) of the island is due to 3 of the anomalous degassing areas (Lake, MGS and Favare), the first of which accounts for more than 50%. Summing up the contribution of all anomalous areas we obtained a total output of about 0.3 kg s-1 (26 t day-1) over an area of about 0.58 km2. Concentrations of CO2 ranged from 0.039 (atmospheric value) up to 95 % (Fig. 1). The distribution of the values on a probability plot evidenced two statistically distinct populations with an inflection point at about 0.8 %. The values below the threshold (65 % of the population) can be considered as derived from organic activity while those above of magmatic/geothermal origin. The spatial distribution of the sites with anomalous concentrations closely resembles those of anomalous CO2 fluxes. Radon222 activity in the soil ranged from 〈 0.1 to 〉1000 kBq m-3 (Fig. 1). The distribution of the values on a probability plot evidenced three statistically distinct populations with inflection points at 40 and 400 kBq m-3. The lower population (74% of the entire population) probably corresponds to close to equilibrium values in soils with different contents of parent isotopes of the 238U decay chain and could be considered as background population. The values of the other two populations have to be considered anomalous and their high activity values have to be related either to sustained fluxes of a carrier gas (CO2) or/and to enhanced release from the soil due to fumarolic alteration. These anomalous values generally correspond to elevated CO2 flux values and are found close to active or fossil fumarolic areas. The close relationship with fumarolic alteration is confirmed by the contrasting behavior of two of the areas displaying the highest CO2 flux values, namely Favare and Lake. In the former area the high soil temperatures, testifying for anomalous fluxes of hydrothermal fluids, are reflected in a high percentage of anomalous values of soil 222Rn activity. On the contrary at the lake area, where the highest CO2 fluxes are measured, soil temperatures are much lower and consequently also soil 222Rn activity. The only high soil 222Rn activity values are measured along the southern shores of the lake where seeps of thermal water with about 60 °C are present. At Mursia, where recent basaltic lavas and scorias crop out, soil 222Rn activity is particularly low due to the low content of parent radioactive elements in these rocks. Finally, the present study evidenced a few areas were the gas hazard due to both CO2 and radon is elevated with either acute or chronic health issues for humans. These are the western shores of the lake and the village of Rekale the only inhabited area close to an anomalous degassing area.

Beschreibung: Published

Beschreibung: Patras, Greece

Beschreibung: 4.5. Studi sul degassamento naturale e sui gas petroliferi

Beschreibung: open

Beschreibung: Like other geodynamically active areas, Greece is also affected by a large number of geogenic gas manifestations. These occur either in the form of point sources (fumaroles, mofettes, bubbling gases) or as diffuse soil gas emanations. Geogenic sources release huge amounts of gases, which, apart from having important influences on the global climate, could also have a strong impact on human health. Gases have both acute and chronic effects. Carbon dioxide (CO2) and hydrogen sulphide are the main gases responsible for acute mortality due to their asphyxiating and/or toxic properties. Methane instead represents a risk for its explosive properties. Gas hazards are often disregarded because in fatal episodes connected to geogenic gases, the cause of death is often not correctly identified. Due to the fact that geodynamically active areas can release geogenic gases for millions of years over wide areas, it is important to realistically estimate potential risks. The present work produced a first catalogue of the geogenic gas manifestations of the whole Greek territory including relevant literature data. A preliminary estimation of the correlated risk has been made for the time period of the last 20 years considering the whole population of Greece. In this period, at least two fatal episodes with a total of three victims are likely due to exposure to geogenic gases (specifically CO2). This would give a risk of 1.3 9 10-8 fatality from geogenic gas manifestations per annum. This value, although probably underestimated, is much lower than most other natural or anthropogenic risks.

Beschreibung: Published

Beschreibung: 1987–2004

Beschreibung: 4.5. Studi sul degassamento naturale e sui gas petroliferi

Beschreibung: JCR Journal

Beschreibung: restricted

Beschreibung: Passive samplers were used to measure the atmospheric concentrations of SO2 naturally emitted at three volcanoes in Italy (Etna, Vulcano and Stromboli) and of H2S naturally emitted at three volcanic/geothermal areas in Greece (Milos, Santorini and Nisyros). The measured concentrations and dispersion patterns varied with the strength of the source (open conduits or fumaroles), the meteorological conditions and the area topography. At Etna, Vulcano and Stromboli, SO2 concentrations reach values that are dangerous to people affected by bronchial asthma or lung diseases (〉1000 μg m−3). H2S values measured at Nisyros also exceed the limit considered safe for the same group of people (〉3000 μg m−3). The data obtained using passive samplers represent time-averaged values over periods from a few days up to 1 month, and hence concentrations probably reached much higher peak values that were potentially also dangerous to healthy people. The present study provides evidence of a peculiar volcanic risk associated with tourist exploitation of active volcanic areas. This risk is particularly high at Mt. Etna, where the elderly and people in less-than-perfect health can easily reach areas with dangerous SO2 concentrations via a cableway and off-road vehicles

Beschreibung: Published

Beschreibung: 1-13

Beschreibung: 4.5. Studi sul degassamento naturale e sui gas petroliferi

Beschreibung: JCR Journal

Beschreibung: restricted