Explosion craters associated with shallow submarine gas venting off Panarea island, Italy

Explosions of hot water, steam, and gas are common periodic events of subaerial geothermal systems. These highly destructive events may cause loss of life and substantial damage to infrastructure, especially in densely populated areas and where geothermal systems are actively exploited for energy. We report on the occurrence of a large number of explosion craters associated with the offshore venting of gas and thermal waters at the volcanic island of Panarea, Italy, demonstrating that violent explosions similar to those observed on land also are common in the shallow submarine environment. With diameters ranging from 5 to over 100?m, the observed circular seafloor depressions record a history of major gas explosions caused by frequent perturbation of the submarine geothermal system over the past 10,000?years. Estimates of the total gas flux indicate that the Panarea geothermal system released over 70?Mt of CO₂ over this period of time, suggesting that CO₂ venting at submerged arc volcanoes contributes significantly to the global atmospheric budget of this greenhouse gas. The findings at Panarea highlight that shallow submarine gas explosions represent a previously unrecognized volcanic hazard around populated volcanic islands that needs to be taken into account in the development of risk management strategies.     

Application of stable isotope analysis for improved understanding of the methane budget: comparison of TROICA measurements with TM3 model simulations

Presented is a detailed comparison of CH₄ and δ¹³C–CH₄ measurements with simulations of the global transport model TM3. Experimental data were obtained during campaigns along the Trans-Siberian railroad in the framework of the TROICA project. Two summer (1999 and 2001) and one spring (2003) expeditions are evaluated. Model simulations include sensitivity tests to further investigate the isotopic composition of natural gas and emissions from Siberian wetlands. Comparison of the average mixing ratio of methane and its isotopic composition (δ¹³C) has been performed for different geographic zones, including the European part of Russia, Western Siberia and Central Siberia. Simulations are in reasonable agreement with the measurements for the European part of Russia and confirm a high contribution of natural gas to the observed methane levels. An increase of emission from bogs shifts the simulated methane isotopic composition closer to the observations. The relative importance of the Western Siberia emissions in current inventories is underestimated in comparison with other wetland regions in the former USSR. Simulated average mixing ratios are in a good agreement with the observations in Central Siberia, while ¹³C(CH₄) values tend to be higher than measured in all considered scenarios. These results point to a bias in the modeled source mixture over Russia, which could be repaired by shifting emissions from isotopically heavy methane sources (e.g. coal, oil or biomass burning) to light sources (e.g. wetlands, ruminants, waste treatment). Alternatively, the average isotopic signature of Siberian wetlands may be lighter than expected.     

Lightning activity related to satellite and radar observations of a mesoscale convective system over Texas on 7–8 April 2002

A multi-sensor study of the leading-line, trailing-stratiform (LLTS) mesoscale convective system (MCS) that developed over Texas in the afternoon of 7 April 2002 is presented. The analysis relies mainly on operationally available data sources such as GOES East satellite imagery, WSR-88D radar data and NLDN cloud-to-ground flash data. In addition, total lightning information in three dimensions from the LDAR II network in the Dallas–Ft. Worth region is used.GOES East satellite imagery revealed several ring-like cloud top structures with a diameter of about 100 km during MCS formation. The Throckmorton tornadic supercell, which had formed just ahead of the developing linear MCS, was characterized by a high CG+ percentage below a V-shaped cloud top overshoot north of the tornado swath. There were indications of the presence of a tilted electrical dipole in this storm. Also this supercell had low average CG− first stroke currents and flash multiplicities. Interestingly, especially the average CG+ flash multiplicity in the Throckmorton storm showed oscillations with an estimated period of about 15 min.Later on, in the mature LLTS MCS, the radar versus lightning activity comparison revealed two dominant discharge regions at the back of the convective leading edge and a gentle descent of the upper intracloud lightning region into the trailing stratiform region, apparently coupled to hydrometeor sedimentation. There was evidence for an inverted dipole in the stratiform region of the LLTS MCS, and CG+ flashes from the stratiform region had high first return stroke peak currents.     

A new assessment of climate change impacts on food production shortfalls and water availability in Russia

While previous studies have focused on impacts of average climate change on Russian agriculture and water resources, this study takes into account the impact of changing frequency and spatial heterogeneity of extreme climate events, and the reliance of most of Russia on a few food producing regions. We analyze impacts of the IPCC A2 and B2 climate scenarios with the use of the Global Assessment of Security (GLASS) model (containing the Global Agro-Ecological Zones (GAEZ) crop production model and the Water-Global Assessment and Prognosis (WaterGAP 2) water resources model). As in previous studies we find that decreased crop production in some Russian regions can be compensated by increased production in others resulting in relatively small average changes. However, a different perspective on future risk to agriculture is gained by taking into account a change in frequency of extreme climate events. Under climate normal conditions it is estimated that “food production shortfalls” (a year in which potential production of the most important crops in a region is below 50% of its average climate normal production, taking into account production in food-exporting regions) occur roughly 1–3 years in each decade. This frequency will double in many of the main crop growing areas in the 2020s, and triple in the 2070s. The effects of these shortfalls are likely to propagate throughout Russia because of the higher likelihood of shortfalls occurring in many crop export regions in the same year, and because of the dependence of most Russian regions on food imports from a relatively few main crop growing regions. We estimate that approximately 50 million people currently live in regions that experience one or more shortfalls each decade. This number may grow to 82–139 million in the 2070s. The assessment of climate impacts on water resources indicates an increase in average water availability in Russia, but also a significantly increased frequency of high runoff events in much of central Russia, and more frequent low runoff events in the already dry crop growing regions in the South. These results suggest that the increasing frequency of extreme climate events will pose an increasing threat to the security of Russia's food system and water resources.     

Modelling of hydrocyclone performance based on spray profile analysis

Spray profile measurements can be used to calculate the underflow rate, and consequently, be related to hydrocyclone performance. The flow geometry of the spray discharge is found to arise from velocity patterns at the outlet orifice. Through a videographic example of an industrial hydrocyclone, it is shown that underflow profiles are typically parabolic, a feature which is indicative of the velocity at which the fluid exits. The inclusion of gravity in this model clearly highlights deficiencies in currently used models. Moreover, an intimate knowledge of factors affecting the profiles of the underflow of a cyclone is essential for the correct interpretation of videographic images. Subsequently, image data are used to estimate outlet velocities, which give an excellent insight into various fluid mechanical phenomena that are not appreciated by analysing basic operational variables. The exit velocities are used to calculate underflow rates, which are related to mass recovery in the underflow.     

Deuterated water: partition functions and equilibrium constants

HDO and D₂O are thought to be present in significant quantities in the coldest regions of the Universe. Partition functions are calculated for these species and used to calculate temperature dependent equilibrium constants for the most important fractionation reactions involving water. HDO may also be a key indicator of the absence of deuterium burning in very low mass stars. The HDO partition function calculation is extended to high  ( T ≤ 6000 K)  temperatures for this purpose.     

Land-use-mediated <Emphasis Type="Italic">Escherichia coli</Emphasis> concentrations in a contemporary Appalachian watershed

A high-spatial resolution study design was used to investigate the relationship between land use practices, stream physicochemistry, hydroclimate, and stream Escherichia (E) coli concentrations in a mixed-land-use watershed in the Appalachian region. Stream samples were collected daily from six monitoring sites and analyzed for total E. coli counts using an enzyme metabolism indicator method. Statistical comparison of E. coli concentration time series showed significant (p?<?0.05) differences between study sites. Although highest average E. coli concentrations were observed at two agricultural sites (534 and 582 colony-forming counts (CFU) per 100 mL, respectively), highest total loadings were observed within the receiving stream, with values increasing downstream (2?×?10¹² and 4.2?×?10¹² study total CFU for bracketed upstream and downstream sites, respectively). No single physical variable displayed a significant correlation (p?<?0.05) with observed E. coli concentration at every site. However, sites displayed different patterns of significant correlations (p?<?0.05) between E. coli concentration and both physicochemical (e.g. pH, dissolved oxygen saturation) and hydroclimate variables (e.g. streamflow and precipitation). Percent agricultural land cover was the only land use category that showed significant (p?<?0.04) correlation with study average E. coli concentrations, thereby emphasizing the importance of land use practices to stream pathogen regimes. Results validate the analytical method and provide high-resolution, detailed, quantitative characterizations of stream E. coli regimes, thereby supplying land and water resource managers with science-based information to advance management decisions and improve public health.     

Biogeochemistry and bacteriology of ferrous iron oxidation in geothermal habitats

A survey of hot, acid springs in Yellowstone Park has shown that high concentrations of ferrous and ferric iron are often present. Total ionic iron concentrations in different springs ranged from less than 1 ppm to greater than 200 ppm, and up to 50% of the ionic iron was in the ferrous form. Some of these springs also have high concentrations of reduced sulfur species (S^2? and S⁰). Significant populations of the bacterium Sulfolobus, acidocaldarius, an autotrophic organism able to live and oxidize sulfur compounds at low pH and high temperature, were present in most of these springs. The role of this organism in the oxidation of ferrous iron was investigated by incubating natural samples of water and assaying for disappearance of ferrous iron. Controls in which bacterial activity was inhibited by addition of 10% NaCl were also run. Bacterial oxidation of ferrous iron occurred in most but not all of the spring waters. The temperature optimum for oxidation varied from spring to spring, but significant oxidation occurred at temperatures of 80–85°C, but not at 90°C. Thus, 85–90°C is the upper temperature at which bacterial iron oxidation occurs; a similar upper limit has previously been reported for sulfur oxidation in the same kinds of springs. The steady-state concentrations of ferrous and ferric iron are determined by the rate at which these ions move into the spring pools with the ground water (flow rate), by the rate at which ferric iron is reduced to the ferrous state by sulfide, and by the rate of bacterial oxidation. The bacterial oxidation rate is faster than the flow rate, so that the rate of reduction of ferric iron is probably the rate-controlling reaction. In several springs, no decrease in ferrous iron occurred, even though high bacterial populations were present. It was shown that in these springs, ferrous iron oxidation occurred but the ferric iron formed was reduced back to the ferrous state again. These springs were all high in suspended sediment and the reductant was shown to be present in the sediment. X-ray diffraction revealed that the sediment contained three major ingredients, elemental sulfur, natroalunite, and quartz. Chemical analyses showed a small amount of sulfide, too little to reduce the ferric iron. Elemental sulfur itself did not reduce ferric iron but when elemental sulfur was removed from the sediment by CS₂ extraction, the activity of the sediment was abolished. It is hypothesized that the sulfide present in the sediment (possibly bound to natroalunite) reacts with elemental sulfur to form a reductant for ferric iron. The results show that bacteria can have a profound influence on the ferrous/ferric ratios of geothermal systems, but that temperature and mineral composition of the water may significantly influence the overall result.