[1] Observations with the FUV imagers on board the IMAGE satellite have been used to map the auroral electron and proton energy fluxes during the summer and winter solstices of 2000, in order to construct a statistical view of the global auroral proton precipitation. The distribution for electrons compare well both in morphology and in magnitude with those obtained previously with the Polar-UVI instruments and with an empirical auroral precipitation model based on DMSP data. The proton morphology also closely resembles the statistical ion oval derived from DMSP data, showing a ''C-shaped'' morphology with a minimum located in the morning sector. The precipitation proton auroral power is on the order of 2.2 GW for an average Kp value of 2, also in close agreement with the values of the DMSP empirical model. The FUV data also reveal the presence of seasonal effects in the proton precipitation. Specifically, the latitudinal width of the proton oval is larger in summer than in winter so that the globally precipitated proton power is 1.5 times higher in summer than in winter. The occurrence probability of intense proton auroras (with energy flux >0.5 mW m À2 ) is also shown to be nearly three times higher in summer than in winter. This seasonal effect in the proton precipitation contrasts with those observed for electrons, where intense electron events occur more often in winter than in summer. We discuss a mechanism that may account for these results based on the presence of field-aligned potential drops which accelerate auroral electrons downward in regions of upward directed field-aligned current, while suppressing the precipitating magnetospheric proton flux. The presence of such field-aligned potentials is dependent on the differing solar illumination in winter and summer.

[1] The brightness of proton aurora observed near solar maximum at summer and winter solstices with the FUV-SI12 global imager on board the IMAGE satellite has been correlated with the solar wind and the interplanetary magnetic field characteristics measured by ACE satellite instruments. By contrast to the electron aurora, we find a strong correlation both on nightside and dayside between the proton precipitated power and the solar wind dynamic pressure calculated with 1-hour averaged solar wind data. For both southward and northward IMF, the proton power increases with jB z j, but much more rapidly on the nightside for southward IMF orientation. Correlations for the nightside aurora were also calculated with a series of solar wind-magnetosphere coupling functions. We find highest correlation coefficients for expressions containing the dynamic pressure or involving the solar wind electric field in the Y-Z plane. The influence of the solar wind dynamic pressure on the proton aurora is tentatively explained by the effect of the pressure on the shape of the magnetosphere, generating stretching of the magnetotail and proton precipitation but also by other coupling processes between the solar wind and the magnetosphere. Adding FUV-WIC and SI13 electron aurora images in the study, we determine how proton and electron precipitations simultaneously react to solar wind and IMF characteristics and Kp. Results shows that protons are more reactive to dynamic pressure variations than electrons when B z is positive, while the influence on of both types of particles is similar for negative B z . The precipitating proton flux is found proportionally larger compared with the electron flux when the total auroral flux increases for low activity level. Instead, for high activity level, the proportion of the proton and the electron powers are similar when auroral power increases. Consequently, it is suggested that similar mechanisms cause proton and electron auroral precipitation for high activity levels, while they appear somewhat decoupled for lower activity conditions. Citation: Coumans, V., J.-C. Gérard, B. Hubert, and M. Meurant (2006), Global auroral proton precipitation observed by IMAGE-FUV: Noon and midnight brightness dependence on solar wind characteristics and IMF orientation,

Diminished growth rates around the infesting organism demonstrate a negative influence on the host, similar to that seen in the modern demosponge-polychaete association of Verongia-Haplosyllis. This is demonstrated by changes in growth bands. As in the above-mentioned association, the endosymbiont might have been feeding directly upon the tissues of the host. The Torquaysalpinx organisms were gaining habitat and possibly also food resources - for them this interaction was clearly positive. This long-term association can therefore be classified as parasitism. This is the first evidence for parasitism in Palaeozoic sponges.

Detailed petrographic and geochemical studies of pore-filling cements and replaced (epigenic) membranes of some organic-walled microorganisms preserved in the Neoproterozoic Doushantuo Lagerstätte (China) are based on an energy dispersive system (EDS) of elemental mapping attached to backscattered MEB. Their microcrystalline apatite (collophane) occurs predominantly as phosphatized microbial pseudomorphs: phosphatic crusts of chasmolithic biofilms (or microstromatolites) and globular clusters occur lining intraparticular porosities. Three major pre-compactional cement types are identified on algal thalli, embryos and vase-shaped microfossils: epigenic collophane (by replacement of membranes), polyphasic filling of collophane and crystalline apatite and fluorapatite within intraparticular porosities (some of them microbially mediated), and latest carbonate precipitation filling the remaining intraparticular porosities (preserved at present as dedolomitized calcite). P 2 O 5 concentration has a clear peak in the microbial pseudomorphs and uniformly low concentrations elsewhere, whereas MgO, Na 2 O, K 2 O and SiO 2 show a slight increase in concentration through successive cements. These geochemical trends evidence a slight change of pore fluids accompanied by a final rise in pH, presumably following the main interval of decay, which favoured precipitation of CaCO 3 postdating that of apatite. Phosphatisation microbienne dans le Lagerstätte néoprotérozoïque de Doushantuo, Chine méridionaleMots clés. -Colonies microbiennes, Diagenèse, Apatite, Lagerstätte, Néoprotérozoïque, Chine.Résumé. -Ce travail présente une étude pétrographique et géochimique des remplacements de membranes (épigénie) et des ciments qui remplissent la porosité interne de certains microorganismes à paroi organique conservés dans le Lagerstätte néoprotérozoïque de Doushantuo (Chine). L'analyse géochimique, réalisée à partir d'un système EDS de cartographie d'éléments attaché au MEB retrodiffusé, montre que l'apatite microcristalline (collophane) apparaît souvent sous forme de pseudomorphes microbiens. Les croûtes phosphatiques des tapis (ou microstromatolites) et des associations grumeleuses microbiennes de type chasmolithique tapissent les parois des porosités intraparticulaires des microfossiles. Trois stages de ciments précipités avant la phase de compaction sont identifiés dans les algues thalloïdes, les embryons et les microfossiles énigmatiques en forme de vase : un apatite épigénique (qui remplace les membranes), un remplissage polyphasé de colophane des porosités intraparticulaires (certains contrôlés par l'activité microbienne), et une précipitation tardive carbonatée qui a comblée la porosité (actuellement conservée comme calcite dédolomitisée). Les variations géochimiques du P 2 O 5 possèdent une anomalie positive dans les pseudomorphes microbiennes ce qui permet d'envisager leur rôle actif dans la concentration d'apatite, tandis que les concentrations en MgO, Na 2 O, K 2 O et SiO 2 diminuent graduellement dans les deux stages restants d...