51 research outputs found
The Effect of Lunar Declination on CO2 degassing from Central Italian Apennines
The periodical degassing from CO2 over-pressured reservoirs may have serious
consequences for the environment making urgent understanding the processes and
forecasting the frequency. Prediction though needs methods that depends from
temporal and spatial properties of hydro-chemical and physical reservoir
characteristics that unfortunately are often lacking. We have analyzed surface
emissions of CO2 attributed to over-pressured CO2-rich reservoirs in the
Central Italian Apennines a zone characterized by significant periodical CO2
degassing. Here aquifers are hosted in Mesozoic limestone with high pCO2
groundwater and travertine deposits. We analyzed a 10-year temporal series and
found that in the Apennines, CO2 flux and aquifer fluid composition are
correlated with the lunar tides specific to the geographic zone. In particular,
our study reveals that low CO2 flux corresponds with low lunar tidal potential
values. We found a similar trend for dissolved calcium and water alkalinity,
while pH values display a linear correlation with tidal cycles. The forces
associated with tidal potentials are not capable of fracturing rock. However,
they can, under certain conditions, drive the flow of fluids in over-pressured
reservoirs, triggering sub-surface fluid movements that in turn modify the
water-rock reactivity. In the central Apennines, these movements result in
increased dolomite dissolution and an eventual return to calcite equilibrium.
In this case, dolomite dissolution breaks the rock releasing calcium into
ground water, which leads to calcite equilibrium and in turn to the formation
of significant quantities of travertine and the concomitant release of CO2 in
the atmosphere.Comment: 12 pages, 6 figure
Fossichnus solus and Oichnus simplex, two peculiar ichnospecies in modern benthic foraminifera from a polluted area in SW coast of Sardina, Italy
The modern benthic foraminiferal tests collected from a coastal area of south-western Sardinia (Portoscuso-Portovesme) that is heavily polluted by industrial activity reveal intense and widespread bioerosional structures induced by diversified microborers. A large number of the foraminifera reveals microscopic round holes (1-60 ÎĽm in diameter) and roundish concavities (25x40 ÎĽm in external diameter) on their surface that belong, respectively, to the ichnospecies Oichnus simplex Bromley, 1981, and Fossichnus solus Nielsen et al., 2003. These traces just occur in the tests of the foraminifera which are heavily infested by microendolithic cyanobacteria, algae and fungi suggests comparable ethological behaviour between the ichnospecies Fossichnus and Oichnus and the microbial euendoliths that are ascribed to individual biological taxa. The greater occurrence of F. solus and O. simplex in the high-Mg foraminiferal porcelanaceous tests than in the low-Mg foraminiferal hyaline tests reveals that the bioerosional processes seem to be related to the Mg/Ca ratio, as well as to morphological structures of the tax
A living forest of Tibetan Juniper trees as a new kind of astronomical and geophysical observatory
The trajectory of Earth about the Sun is perturbed by torques exerted by the
Moon and Sun, and also the four giant planets. These provoke variations of
insolation at Earth surface, known as kyr-long Milankovi\'c cycles. The concept
has been extended to the shorter time scales of years to centuries, that are
relevant to tree growth. This paper focuses on iSSA of results of the
dendro-chronological study of a forest of long-lived Tibetan junipers. From
this, we determine a median curve of tree growth rates, that is analyzed by
iSSA. We obtain a rich set of (pseudo-) periods, from 3.3 yr up to more than
1000 years, that compare with the specific spectral signature found in the
sunspot and length-of-day time series. We discuss in detail the record from a
single tree that spans almost completely the 357-2000 AD interval. The 90 yr
Gleissberg, 22 yr and 30 yr components are quite prominent. The Oort, Wolf,
Sp\"orer, Maunder and Dalton climate extrema all correspond quite precisely to
extrema of the Gleissberg cycle. The well-known Medieval Climate Optimum,
Little Ice Age and Modern Climate Optimum all seem to be mainly forced by
variations in the envelope of the Gleissberg cycle. The Gleissberg cycle is
strongly modulated with a period of 500-600 years. The node near a small gap in
the data is very close to the Medieval Climate Optimum. Observations in
different parts of Earth are in favor of a global extension of the MCO. In the
same way that the Milankovic mathematical theory of climate allows one to
relate climate change and length of day, through changes in inclination of
Earth's rotation axis and solar insolation, it is reasonable to propose that
the set of pseudo-periods that are evidenced in the Tibetan tree ring growth
rates simply corresponds to short period Milankovi\'c cycles. The Dulan forest
could be considered as a good candidate for a continuous, global geophysical
observatory.Comment: 26 pages, 15 figure
Comportement des elements en trace dans les fluides geothermaux (exemple du strontium)
SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 78743 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc
Evaluation d'une perturbation oxydante en milieu argileux (mécanisme d'oxydation de la pyrite)
PARIS7-Bibliothèque centrale (751132105) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF
Nanogéochimie (mécanismes d'altération des micas à l'échelle moléculaire)
PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF
Effects of CO2 injections on calcite precipitation in brine aquifers: An overall kinetic rate law
International audienc
Contribution of the reactive mineral surface area on CO2 mineralization under natural conditions
A natural hydrothermal field is considered to be a useful analogue of carbon dioxide mineralization because it integrates the long-term interaction signal. The hydrothermal field of Galicia is characterized fluids resulting from a granit reservoir with pCO2 from 103 to 105 Pa and pH from 10 to 6. Fluids are characterized by an increase of major elements correlated to pCO2. We evaluated the effect of deep CO2 perturbation We evaluated the effects of deep CO2 perturbation on the fluid-rock interaction system. Mineral reactivity which produces changes in the fluid mineral composition is mainly dependent on the 'real' reactive surface area. The mineral surface area participating in reactions resulting from this pCO2 gradient was estimated by an inverse model approach. Input data was based on the chemical composition of the fluids we sampled. The rate of mineral dissolution was estimated by the observed pH and equilibrium conditions. Moreover, the major elemental concentrations allowed us to quantify the variation of the reactive surface area of minerals involved with the overall water-rock interaction. The irreversible mass transfer process, ruled by the continuum equilibrium condition, was defined by the overall degree of reaction advancement, using a set of polynomial equations solved independently of time scale.We found that reactive surface area of calcite, albite and K-feldspar increases by 2 orders of magnitude over the entire CO2 fluid-rock interaction process, while the reactive surface area of biotite increases by 4 orders of magnitude. This shows that fluid neutralisation and consequent CO2 mineralization under the form of carbonate species is greatly dependent on the behaviour of the reactive surface area of the mineral association in this geological context. We propose that biotite plays a basic role on the pH stabilisation and redox control of environmental perturbation and CO2 mineralization
An integrated approach for determining the origin of magnetite nanoparticles
International audienceThe criteria to assess the origin of magnetite are of prime importance because of their significance as biomarkers for extraterrestrial life and paleoenvironmental indicators. It is still unclear if morphology and magnetic properties of crystals do quantitatively allow differentiating abiotic from biotic magnetite crystals of nanometer size. In this study, inorganic magnetite nanocrystals synthesized under controlled experimental aqueous conditions are compared with biogenic magnetite of similar size and morphology formed by magnetotactic (intracellular magnetite) and other (extracellular magnetite) bacteria. Structural properties such as oxygen isotope fractionations and crystal size distributions were explored. Not surprisingly, none of the single properties are able to differentiate inorganic crystals from those having a bacterial origin, either specifically extracellular or specifically intracellular. However, oxygen isotope fractionation allows the differentiation between abiotic and biotic magnetite when the temperature of formation is known and when it does not fall into a crossing region (35≤T (°C)≤55) while crystal size distributions discriminate inorganic from intracellular magnetite. Therefore, a combination of these two properties may be a successful tool for an accurate determination of a reliable biogenicity criterion
Risk evaluation of uranium mining: a new kinetic approach
International audienc
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