Search

In the north of the shallow East Siberian Arctic Shelf (the Laptev and East Siberian seas), based on CDP (common depth point) seismic data for 71 lines with total length of 15 630 km, velocities of refracted waves propagation in the upper part of the section were studied. Fundamentally new information was obtained on the state of the shelf permafrost and significant decrease of the zone of possible occurrence of frozen ground and methane hydrates was substantiated. Based on the comprehensive analysis of areas of subsea frozen ground degradation in the Laptev, East Siberian, Chukchi and Beaufort seas, the low probability of a significant contribution of methane, released due to gas hydrates dissociation, to global climate change was substantiated. [ABSTRACT FROM AUTHOR]

Passive rift systems are often characterized by CO 2 degassing, witnessed by the presence of mineral and thermal springs, bubbling pools, mofetes. Despite these field manifestations, the quantitative estimation of the CO 2 budget released to the atmosphere from these geodynamic structures is not well constrained. Here, we examine the chemistry of 169 springs, the isotopic composition of the dissolved carbon (δ13C TDIC) of 33 springs and the dissolved gases composition of 6 springs from the French Massif Central, part of the European Cenozoic Rift System (ECRIS), in order to describe the CO 2 degassing process and to compute the CO 2 emission rate released from groundwaters at regional scale. Water-gas-rock models reveal that the separation of gas from the liquid phase occurs at P-T conditions between 10 bar-180 °C and 1 bar-10 °C. The carbon mass and isotopic balance of spring waters of the French Massif Central allow us to compute a total deeply-sourced CO 2 emission rate of 1.52 ± 0.14 × 109 mol yr−1, suggesting that the CO 2 release from passive rift systems is significant at global scale and should be considered in the present-day global Earth degassing budget. The comparison of our data to other continental rift systems shows a high variability of CO 2 emission rates, highlighting that more detailed studies are needed to constrain the CO 2 flux from this geodynamic setting that, at present, is likely underestimated. [ABSTRACT FROM AUTHOR]

This work presents findings of deep geological and geophysical studies, which have revealed new and often unexpected features of the structure of the Earth's crust and the upper mantle of the continents and oceans, not easily explainable by current geodynamic concepts. For example, deepwater drilling has shown the old age of the oceanic crust and its inhomogeneous composition. Seismic studies of long-range profiles with nuclear explosions and laboratory studies of mantle xenoliths at high pressures and temperatures have revealed that the advection of energy-intensive and geochemically active deep fluids is central to the formation of the upper mantle structure. A comprehensive analysis of these data provides a geodynamic model for the natural transformation of the upper mantle substance influenced by deep fluids and the formation of continents and oceans as a result of unevenly distributed degassing of the Earth. The global variability of the deep fluid advection intensity led to formation of two hemispheres: the Indo Atlantic Hemisphere where almost all continents are located and the Pacific Hemisphere that consists of oceans. This formation of the hemispheres can be explained by the specific features of the Earth's rotation in the Earth-Moon-Sun system. This work provides a review and analysis of these data and then offers a possible explanation based on an integrated geodynamic model. • Deep drilling in oceans and seismic studies revealed unexpected lithosphere features. • The crust of oceans is old and subcontinental lithosphere was found in all oceans. • Lithosphere roots of continents are composed of depleted decreased density material. • Earth degassing with energy-intensive fluids transformed the upper mantle material. • Earth's rotation in the Earth-Moon-Sun system formed the oceanic Pacific Hemisphere. [ABSTRACT FROM AUTHOR]

Abstract: We describe the results of a detailed hydrogeochemical campaign on the groundwater circulating in two regional aquifers located in the area of the Abruzzo 2009 earthquakes. The influx of deeply derived CO2 rich gases into the two aquifers is highlighted by the 13C isotopic composition of dissolved carbon species. The source of the gas is roughly localised beneath the epicentral area of the earthquakes where the presence of sources of fluids under high pressure is suggested by seismological investigations. The carbon isotopic-mass balance of the aquifers indicates that the amount of the deep CO2 dissolved and transported by the groundwaters is ~530t/day. The chemical and isotopic composition of the gas entering the aquifers, named Abruzzo gas, has been derived by comparing the data measured in the springs with the results of a gas–water–rock reaction model, that simulates the evolution of the chemical and isotopic composition of groundwater affected by the input of a deeply-derived CO2 rich gas phase. The composition of Abruzzo gas is compared to that of 40 large gas emissions located in central Italy. The gas becomes progressively richer in radiogenic elements (4He and 40Ar) and in N2, from the volcanic complexes in the west to the Apennines in the east. The Abruzzo gas, in agreement with its location, well matches the composition of the gases emitted in the pre-Apennine region. These geochemical features, consistent with the structural setting of the region, indicate increasing residence times of the gas in the crust moving from west to east. In particular we suggest that the strong increase in radiogenic crustal gases reflects the occurrence of deep traps where the gas is stored at high pressures for a long time and that such high pressure gas pockets play a major role in the generation of Apennine earthquakes. [Copyright &y& Elsevier]

This article describes the results of a comprehensive analysis of the causes of intensive gas emission over a large zone (ca. 80 × 220 km) of the Central Laptev shelf area. The upper parts of 28 sections of common depth point (CDP) seismic lines acquired by the JSC MAGE, covering a total length of 5930 km over an area of 55,000 km2, were interpreted and 519 anomalous objects potentially connected with gas saturation were revealed. For the first time, the boundary between frozen and thawed sediments was defined in the Laptev Sea. The absence of subsea permafrost and gas hydrates in the intensive gas seepage zone was determined. The connection between gas seeps and deep-seated faults identified in seismic sections was substantiated. This study demonstrated that seismotectonic factors caused a large spatial window of long-term Earth degassing with direct intensive migration of deep thermogenic gas to the hydrosphere through a system of faults. A zone of potential gas hydrate distribution was observed on the continental slope. • Permafrost and gas hydrates are not predicted in the zone of gas seeps in the Central Laptev area. • Gas seeps in the Central Laptev area are connected with deep-seated faults. • Seismotectonic factors must contribute to gas seepage in the Central Laptev area. • Gas hydrates are predicted on the continental slope of the Laptev Sea. [ABSTRACT FROM AUTHOR]

Abstract: The CO2 degassing process from a large area on the Tyrrhenian side of central Italy, probably related to the input into the upper crust of mantle fluids, was investigated in detail through the geochemical study of gas emissions and groundwater. Mass-balance calculations and carbon isotopes show that over 50% of the inorganic carbon in regional groundwater is derived from a deep source highlighting gas−liquid separation processes at depth. The deep carbonate−evaporite regional aquifer acts as the main CO2 reservoir and when total pressure of the reservoir fluid exceeds hydrostatic pressure, a free gas phase separates from the parent liquid and escapes toward the surface generating gas emissions which characterise the study area. The distribution of the CO2 flux anomalies and the location of high PCO2 springs and gas emissions suggest that the storage and the expulsion of the CO2 toward the atmosphere are controlled by the geological and structural setting of the shallow crust. The average CO2 flux and the total amount of CO2 discharged by the study area were computed using surface heat flow, enthalpy and CO2 molality of the liquid phase circulating in the deep carbonate−evaporite aquifer. The results show that the CO2 flux varies from 1×104 mol y−1 km−2 to 5×107 mol y−1 km−2, with an average value of 4.8×106 mol y−1 km−2, about five times higher than the value of 1×106 mol y−1 derived by Kerrick et al. [Kerrick, D.M., McKibben, M.A., Seward, T.M., Caldeira, K., 1995. Convective hydrothermal CO2 emission from high heat flow regions. Chem. Geol. 121, 285–293] as baseline for terrestrial CO2 emissions. The total CO2 discharged from the study area is 0.9×1011 mol y−1, confirming that Earth degassing from Tyrrhenian central Italy is a globally relevant carbon source. [Copyright &y& Elsevier]

Geochemical and isotopic studies have been undertaken to assess the origin of CO2-rich waters issuing in the northern part of Portugal. These solutions are hot (76°C) to cold (17°C) Na–HCO3 mineral waters. The δ2H and δ18O signatures of the mineral waters reflect the influence of altitude on meteoric recharge. The lack of an 18O-shift indicates there has been no high temperature water–rock interaction at depth, corroborating the results of several chemical geothermometers (reservoir temperature of about 120°C). The low 14C activity (up to 9.9 pmC) measured in some of the cold CO2-rich mineral waters (total dissolved inorganic carbon) is incompatible with the presence of 3H (from 1.7 to 4.1 TU) in those waters, which indicates relatively short subsurface circulation times. The δ13C values of CO2 gas and dissolved inorganic carbon range between −6‰ and −1‰ versus Vienna-Peedee Belemnite, indicating that the total carbon in the recharge waters is being diluted by larger quantities of CO2 (14C-free) introduced from deep-seated (upper mantle) sources, masking the 14C-dating values. The differences in the 87Sr/86Sr ratios of the studied thermal and mineral waters seem to be caused by water–rock interaction with different granitic rocks. Chlorine isotope signatures (−0.4‰ < δ37Cl < +0.4‰ versus standard mean ocean chloride) indicate that Cl in these waters could be derived from mixing of a small amount of igneous Cl from leaching of granitic rocks. [ABSTRACT FROM AUTHOR]

Both the shallow (organic-derived) and deep (mantellic–magmatic–metamorphic) fluxes of CO2 [ΦCO2, mass time-1] and specific fluxes of CO2 [ϕCO2 mass time-1 surface-1] dissolving in the shallow groundwaters of the volcanic areas of Amiata, Vulsini-Vico-Sabatini, Albani, Roccamonfina, Vesuvio, Vulture, and Etna were evaluated by partitioning the composed population of total dissolved inorganic carbon in two individual populations and subsequent subtraction of local background population.The flux of deep CO2 released from the geothermal fields of Piancastagnaio (Amiata), Torre Alfina, Latera, Marta, Bracciano south, Cesano, and Mofete and from the Overall Northern Latium Hydrothermal Reservoir were also evaluated by means of the total surface heat flux and the enthalpy and CO2 molality of the single liquid phase circulating in each geothermal reservoir.These data suggest that the ϕCO2 released to the atmosphere varies from 9.5×106 to 3.0×106 mol year-1 km-2, over the geothermal fields of Bracciano south and Cesano, respectively, and that a total ΦCO2 of 3.8×108 mol year-1 is cumulatively released from the geothermal fields of Torre Alfina, Latera and Cesano extending over an area of only 66 km2.In addition, a flux of ∼2.2×1011 to 3.8×1011 mol year-1 of gaseous CO2 entering the atmosphere is obtained for the entire anomalous area of central Italy, extending from the Tyrrhenian coastline to the Apennine chain (45,000 km2). Thus terrestrial CO2 emission in central-southern Italy appears to be a significant carbon source. [Copyright &y& Elsevier]