Vertical profiling of SO2 and SO above Venus’ clouds by SPICAV/SOIR solar occultations

New measurements of sulfur dioxide (SO₂) and monoxide (SO) in the atmosphere of Venus by SPICAV/SOIR instrument onboard Venus Express orbiter provide ample statistics to study the behavior of these gases above Venus’ clouds. The instrument (a set of three spectrometers) is capable to sound atmospheric structure above the clouds in several observation modes (nadir, solar and stellar occultations) either in the UV or in the near IR spectral ranges. We present the results from solar occultations in the absorption ranges of SO₂ (190–230 nm, and at 4 μm) and SO (190–230 nm). The dioxide was detected by the SOIR spectrometer at the altitudes of 65–80 km in the IR and by the SPICAV spectrometer at 85–105 km in the UV. The monoxide’s absorption was measured only by SPICAV at 85–105 km. We analyzed 39 sessions of solar occultation, where boresights of both spectrometers are oriented identically, to provide complete vertical profiling of SO₂ of the Venus’ mesosphere (65–105 km). Here we report the first firm detection and measurements of two SO₂ layers. In the lower layer SO₂ mixing ratio is within 0.02–0.5 ppmv. The upper layer, also conceivable from microwave measurements by Sandor et al. (Sandor, B.J., Todd Clancy, R., Moriarty-Schieven, G., Mills, F.P. [2010]. Icarus 208, 49–60) is characterized by SO₂ increasing with the altitude from 0.05 to 2 ppmv, and the [SO₂]/[SO] ratio varying from 1 to 5. The presence of the high-altitude SO_x species could be explained by H₂SO₄ photodissociation under somewhat warmer temperature conditions in Venus mesosphere. At 90–100 km the content of the sulfur dioxide correlates with temperature increasing from 0.1 ppmv at 165–170 K to 0.5–1 ppmv at 190–192 K. It supports the hypothesis of SO₂ production by the evaporation of H₂SO₄ from droplets and its subsequent photolysis at around 100 km.     

Atomic oxygen on the Venus nightside: Global distribution deduced from airglow mapping

The Visible and Infra-Red Thermal Imaging Spectrometer (VIRTIS) instrument on board the Venus Express spacecraft has measured the O₂(a¹Δ) nightglow distribution at 1.27 μm in the Venus mesosphere for more than two years. Nadir observations have been used to create a statistical map of the emission on Venus nightside. It appears that the statistical 1.6 MR maximum of the emission is located around the antisolar point. Limb observations provide information on the altitude and on the shape of the emission layer. We combine nadir observations essentially covering the southern hemisphere, corrected for the thermal emission of the lower atmosphere, with limb profiles of the northern hemisphere to generate a global map of the Venus nightside emission at 1.27 μm. Given all the O₂(a¹Δ) intensity profiles, O₂(a¹Δ) and O density profiles have been calculated and three-dimensional maps of metastable molecular and atomic oxygen densities have been generated. This global O density nightside distribution improves that available from the VTS3 model, which was based on measurements made above 145 km. The O₂(a¹Δ) hemispheric average density is 2.1 × 10⁹ cm^?3, with a maximum value of 6.5 × 10⁹ cm^?3 at 99.2 km. The O density profiles have been derived from the nightglow data using CO₂ profiles from the empirical VTS3 model or from SPICAV stellar occultations. The O hemispheric average density is 1.9 × 10¹¹ cm^?3 in both cases, with a mean altitude of the peak located at 106.1 km and 103.4 km, respectively. These results tend to confirm the modeled values of 2.8 × 10¹¹ cm^?3 at 104 km and 2.0 × 10¹¹ cm^?3 at 110 km obtained by Brecht et al. [Brecht, A., Bougher, S.W., Gérard, J.-C., Parkinson, C.D., Rafkin, S., Foster, B., 2011a. J. Geophys. Res., in press] and Krasnopolsky [Krasnopolsky, V.A., 2010. Icarus 207, 17–27], respectively. Comparing the oxygen density map derived from the O₂(a¹Δ) nightglow observations, it appears that the morphology is very different and that the densities obtained in this study are about three times higher than those predicted by the VTS3 model.     

Interactions climat-eustatisme-tectonique. Les enseignements et perspectives du Crétacé supérieur (Cénomanien-Coniacien)

Résumé

Une analyse de séries sédimentaires d’âge Crétacé supérieur dans le Sud-Est de la France a été entreprise et intégrée dans un cadre de stratigraphie séquentielle. Les limites Cénomanien–Turonien et la limite Turonien–Coniacien sont marquées par des variations rapides et de fortes amplitudes du niveau marin relatif. La comparaison effectuée avec d’autres bassins mondiaux nous amène à envisager le problème dans un cadre global. On constate : (1) le synchronisme d’événements à haute fréquence dans des contextes géodynamiques différents. (2) les effets de la superposition de cycles eustatiques hiérarchiquement différents, c’est-à-dire la superposition d’oscillations à haute fréquence sur une composante de 3^e ordre. Ces observations sont confrontées à deux hypothèses : le glacio-eustatisme et la tectonique à haute fréquence. © Elsevier, Paris.     

Sedimentology and sequence stratigraphy of Aquitanian and Burdigalian stratotypes in the Bordeaux area (southwestern France)

The historical stratotypes of the Aquitanian and Burdigalian in the Aquitaine Basin are studied here by using the tools of facies sedimentology and the concept of sequence stratigraphy. This analytical method combines recognition and sequential organization of facies, and several types of stratigraphic markers. This method allows identification of at least six depositional sequences within the Miocene of the Saucats area: the four lower ones belong to the Aquitanian, the fifth one to the whole Burdigalian, while the sixth sequence corresponds to the Serravallian. In addition, this method provides evidence of a period of emersion before each transgression, suggesting potential fluvial erosion. Nevertheless, these phases are of lower amplitude than those observed in the Rhodano-Provençal Basin.

Résumé

Les stratotypes historiques de l’Aquitanien et du Burdigalien, en Aquitaine, sont étudiés ici en termes de sédimentologie de faciès et de stratigraphie séquentielle. Cette méthode d’analyse combine la reconnaissance et l’organisation séquentielle des faciès à plusieurs types de repères stratigraphiques. Elle permet d’identifier au moins six séquences de dépôt dans le Miocène de la région de Saucats : les quatre premières dans l’Aquitanien, la cinquième pour le Burdigalien et la dernière pour le Serravallien. Elle a également permis de mettre en évidence des phases d’émersion anté-transgression, suggérant de possibles érosions fluviatiles, mais d’ampleurs inférieures à celles reconnues dans le Bassin miocène rhodano-provençal.     

The density of the upper martian atmosphere measured by Lyman-α absorption with Mars Express SPICAM

Absorption of interplanetary Lyman-α emission by Mars’ nightside lower thermosphere was observed by Mars Express Spectrometer for Investigation of Characteristics of the Atmosphere of Mars (SPICAM), and is analyzed to derive the CO₂ density at 110 km during a martian year. The observed density seasonal variability is consistent with recent observations obtained by stellar occultations, proving that this method, though not as accurate as stellar occultations could be used complementary to them to characterize large variations of thermospheric density on Mars and provide a better spatial coverage by Lyman-α imagery.     

A layer of ozone detected in the nightside upper atmosphere of Venus

To date, ozone has only been identified in the atmospheres of Earth and Mars. This study reports the first detection of ozone in the atmosphere of Venus by the SPICAV ultraviolet instrument onboard the Venus Express spacecraft. Venusian ozone is characterized by a vertically confined and horizontally variable layer residing in the thermosphere at a mean altitude of 100 km, with local concentrations of the order of 10⁷–10⁸ molecules cm⁻³. The observed ozone concentrations are consistent with values expected for a chlorine-catalyzed destruction scheme, indicating that the key chemical reactions operating in Earth’s upper stratosphere may also operate on Venus.     

Cl and Na Fluxes in an Andean Foreland Basin of the Peruvian Amazon: An Anthropogenic Impact Evidence

The dissolved load of the Amazon River is generally considered to be lowly impacted by anthropogenic activities. In this work, based on the chemical and hydrological database of the Environmental Research Observatory—HYBAM (http://www.ore-hybam.org), we explore the importance of the Peruvian Foreland petroleum activity on the dissolved Na and Cl fluxes of the Amazon River. The main result of this study allows us suggesting that oil extraction activity, concentrated in the El Tigre River basin, a small foreland watershed in the Peruvian Amazon, influenced drastically the Na and Cl exportation of the Amazon River during the 2006–2007 period. During these years,  the dissolved exportations of this basin represented almost 20 % of the annual dissolved Cl Amazon flux and almost 12 % of the annual dissolved Na Amazon flux for a mean annual discharge <1 % of the Amazon River discharge. Since the last decades, the anthropogenic activities are increasing over the whole Amazon basin, especially in Andean countries. In this context, our results demonstrate that extractive activity cannot be considered as negligible on the hydro-chemistry of the Amazonian Rivers especially for the weathering budget estimation based on river-dissolved loads. Moreover, Cl and Na can be used to trace the formation waters derived from oil extraction at a large spatial scale. The environmental impacts of contaminants associated with deep water released to the hydrosystem (polycyclic aromatics hydrocarbons, metallic trace elements, etc.) at local and regional scales are still underestimated and should be monitored to map their local and regional influence and to prevent their risks on human health.     

Les flux de matières dissoutes et particulaires exportés des Andes par le Rio Béni (Amazonie Bolivienne), en période de crue

Résumén

Le Rio Béni est l’un des principaux formateurs andins du Rio Madeira, le plus important des affluents méridionaux de l’Amazone. La station hydrométrique de “Angosto del Bala” sur le Rio Béni contrôle un bassin andin de 67500 km², aux caractéristiques géomorpho-climatiques très contrastées.

Afin de connaître l’évolution temporelle des teneurs relatives des éléments des phases dissoutes et particulaires, un suivi hydrologique et hydrogéochimique a été réalisé à cette station en mars 1988, période de hautes eaux où une crue de fréquence annuelle a été observée. Les résultats obtenus montrent l’existence d’une grande variabilité temporelle des concentrations, mais présentant un cortège hydrogéochimique stable au cours de la crue.

Enfin, l’importance quantitative de cette période de hautes eaux sur le bilan moyen annuel des flux exportés est souligné.     

Lower Palaeozoic unconformities in an intracratonic platform setting: glacial erosion versus tectonics in the eastern Murzuq Basin (southern Libya)

The stratigraphic record of the eastern Murzuq Basin has been importantly influenced by deformation resulting in angular and/or deeply erosional unconformities, though the overall context is intracratonic. Major transgressive events and the Ordovician glaciation are nevertheless documented, allowing the delineation of tectonic-, eustasy- or climate-driven unconformities. Lower Palaeozoic key events and related unconformities that characterize the North Gondwana platform have therefore a signature in the eastern Murzuq Basin. The basement/cover unconformity, also known as the infra-Tassilian surface, truncates all the deformed and metamorphosed Lower Cambrian and older rocks. Above is a ?Middle Cambrian to Lower Ordovician megasequence (Murizidié and Hasawnah Fms.), which is in turn truncated by an intra-Ordovician, angular unconformity. This megasequence is unconformably overlain by a Middle Ordovician (Hawaz Fm.) to Silurian (Tanzzuft and Akakus Fms) megasequence, which includes the Upper Ordovician glaciogenic unit (Mamuniyat Fm.), bounded at the base by a polygenic glacial erosion surface showing corrugated glacial lineations, tillites, and glaciotectonic structures. The Middle Ordovician to Silurian megasequence is finally truncated by a base-Devonian, angular unconformity overlain by fluvial sandstones. Regarding the possibility that those fluvial deposits may be as younger as Late Devonian in the eastern Murzuq Basin based on palaeoflora, the so-called Caledonian unconformity might be here a much younger (mid-Eifelian?) surface, and the occurrence of the Lower Devonian “Tadrart Fm.” is questioned. The Upper Ordovician glacial erosion surface, which is sometimes referred to as the Taconic unconformity, usually truncates Middle Ordovician strata in the Murzuq Basin but reaches significantly deeper stratigraphic levels in places that have been previously involved in the intra-Ordovician deformation event. In the Murizidié (southeastern Murzuq Basin), the infra-Tassilian surface, the intra-Ordovician unconformity, and the Upper Ordovician glacial erosion surface amalgamate together. Here, an estimate of the glacial erosion depth cannot be derived from the stratigraphic hiatus beneath the glacial incision, the main part of which relate to the intra-Ordovician tectonic event. The Upper Ordovician climate-related glacial erosion surface is not a valid unconformity for a sequence hierarchy framework of the Lower Palaeozoic, although it presents most of the physical attributes of tectonic-driven unconformities.     

The O2 nightglow in the martian atmosphere by SPICAM onboard of Mars-Express

We present observations of the O₂(a¹Δ_g) nightglow at 1.27 μm on Mars using the SPICAM IR spectrometer onboard of the Mars Express orbiter. In contrast to the O₂(a¹Δ_g) dayglow that results from the ozone photodissociation, the O₂(a¹Δ_g) nightglow is a product of the recombination of O atoms formed by CO₂ photolysis on the dayside at altitudes higher than 80 km and transported downward above the winter pole by the Hadley circulation. The first detections of the O₂(a¹Δ_g) nightglow in 2010 indicate that it is about two order of magnitude less intense than the dayglow (Bertaux, J.-L., Gondet, B., Bibring, J.-P., Montmessin, F., Lefèvre, F. [2010]. Bull. Am. Astron. Soc. 42, 1040; Clancy et al. [2010]. Bull. Am. Astron. Soc. 42, 1041). SPICAM IR sounds the martian atmosphere in the near-IR range (1–1.7 μm) with the spectral resolution of 3.5 cm^?1 in nadir, limb and solar occultation modes. In 2010 the vertical profiles of the O₂(a¹Δ_g) nightside emission have been obtained near the South Pole at latitudes of 82–83°S for two sequences of observations: L_s = 111–120° and L_s = 152–165°. The altitude of the emission maximum varied from 45 km on L_s = 111–120° to 38–49 km on L_s = 152–165°. Averaged vertically integrated intensity of the emission at these latitudes has shown an increase from 0.22 to 0.35 MR. Those values of total vertical emission rate are consistent with the OMEGA observations on Mars-Express in 2010. The estimated density of oxygen atoms at altitudes from 50 to 65 km varies from 1.5 × 10¹¹ to 2.5 × 10¹¹ cm^?3. Comparison with the LMD general circulation model with photochemistry (Lefèvre, F., Lebonnois, S., Montmessin, F., Forget, F. [2004]. J. Geophys. Res. 109, E07004; Lefèvre et al. [2008]. Nature 454, 971–975) shows that the model reproduces fairly well the O₂(a¹Δ_g) emission layer observed by SPICAM when the large field of view (>20 km on the limb) of the instrument is taken into account.