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 μm in diameter) and roundish concavities (25x40 μm 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

Aspects mécanistiques de la réaction de précipitation de la calcite et mouvements de fluide supercritique dans une matrice calcitique (implications au stockage minéral du C02)

La quantité de CO2 présente dans l'atmosphère terrestre s'est accrueconstamment depuis les débuts de la révolution industrielle au point quun réchauffement significatif et des changements climatiques ont étéattribués à lactivité anthropogénique. La séquestration géologique du CO2apparaît donc comme lune des stratégies les plus pertinentes pour laréduction à long terme des émissions atmosphériques de ce gaz à effets deserre. Lexcès de CO2 peut être stocké dans les formations géologiques dedifférentes manières. La solution qui apparaît comme la plus stable est defaire réagir des fluides riches en CO2 avec les minéraux des roches (ou lamatière organique) des formations géologiques encaissantes et de produireune nouvelle matrice solide carbonatée. Les cinétiques des réactionsimpliquées dans la minéralisation du CO2 ont donc été étudiées.La première partie de cette étude sest donc attachée à décrire lesaspects mécanistiques de la réaction de précipitation de la calcite parune approche cinétique permettant dobtenir précisément les vitesses etles constantes cinétiques des réactions ainsi que des informations sur lesmécanismes réactionnels en faisant varier la température (5 à 70C) ainsique la composition de la solution (degré de sursaturation et présencedinhibiteur : Mg2+ et SO42-). Les résultats de cette étude ont montré quele rôle de la température ne se limite pas à uniquement à un simple effetcatalyseur mais que les changements de mécanismes cinétiques, que latempérature génère, déterminent aussi les quantités de Magnésium quipeuvent sincorporer dans la calcite. Par extension à cette étude, nousavons établi une loi empirique globale décrivant la variation du taux deprécipitation en fonction de la concentration en carbonate et desdifférents paramètres physico-chimiques influençant la réaction deformation de la calcite (PCO2, salinité, température, inhibiteurs, matièreorganique). La température qui peut faire augmenter de 3 ordres degrandeurs le taux de précipitation mais uniquement dans des conditions dedéséquilibre important contrairement à la pression partielle de CO2 qui aune influence égale proche et loin de léquilibre dans des solutionspourtant complètement tamponnée. Dans la deuxième partie, létude sest focalisée sur les mouvements defluides supercritiques à lintérieur dune matrice solide calcitique. Nousavons montré que des bulles de CO2 supercritiques piégées dans desinclusions fluides contenues dans une matrice polycristalline de calcitepouvaient circuler jusquà la surface du cristal. Ces mouvements ont lieuà travers les joints de grain des cristaux à une vitesse de 10 ordres degrandeurs supérieure à la diffusion cristalline dans les conditions detempérature et de pression standard. De plus, nous avons montré que cephénomène altère de manière significative les propriétés de surface descalcites et il doit être pris en compte lors de la modélisation prédictivede la réactivité et du transport des fluides dans le milieu de stockagePARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF