The Calcium Isotope Composition of Modern Seawater Determined by Thermal Ionisation Mass Spectrometry

The Ca isotopic composition of modern seawater has been determined using a ⁴³Ca-⁴⁸Ca double spike, which was calibrated using a ⁴²Ca/⁴⁴Ca seawater ratio of 0.30587 ± 0.00026. This ratio was determined from a total evaporation experiment in which the ion beam was measured from the beginning to the end of the emission. With integration of the peak intensities, the fractionation effects can be minimised, since total evaporation of the reservoir cancels out the effect of vapour enrichment in the light isotopes. This experiment avoids the gravimetric uncertainty inherent in the double spike calibration. This calibration allows the precise redetermination of the seawater isotopic composition of Ca. A mean ⁴⁰Ca/⁴⁴Ca ratio for two Atlantic water samples of 45.143 (2s_mean= 0.003) was found. The good reproducibility of the Ca isotope ratios in present seawater and the very strong isotopic homogeneity of Ca in the oceans illustrate the advantage of using seawater as the common standard, with the advantage of decreasing interlaboratory bias.     

Open Problems and Recent Advances in Volcanic Hazard Evaluation

The long prism/needle‐shaped polycrystalline quartz aggregates and square/parallelogram‐shaped singlephase quartz inclusions in omphacite and garnet of ultrahigh pressure eclogite were first discovered from the Jiangalesayi area, South Altyn UHP belt. Based on their morphology, these quartz inclusions are quartz paramorphs after stishovite. The minimum peak pressure of the eclogite is estimated to be >8–9 GPa at 800– 1000 °C based on the stability field of stishovite. This new evidence, together with previous stishovite exsolution microstructure in the gneiss from the same region, suggests an ultra‐deep subduction and exhumation of the South Altyn continental rocks to/from mantle depths in stishovite stability field. Evidence of ultra‐deep subduction of continental materials might be more common and diverse than previous thought. Exhumation of subducted continental rocks from≥300 km has been considered impossible because they are denser than mantle at these depths. How did the stishovite bearing continental rocks of the South Altyn exhumated? As we all know, the densities of stishovite (4.3 g/cm³) are much higher than coesite (2.9 g/cm³), and stishovite transforms into coesite with temperature increases. Density calculations were performed for subducted continental rocks along phase transition of stishovite to coesite, using the third‐order Birch‐Murnaghan equation of state based on mineral fractions obtained from experiments and Perple_X. The results show that the density of Siliceous rocks decrease remarkably, lower than the surrounding mantle in coesite stability field, whereas the density of Oligosiliceous and Silicon unsaturated rocks is higher than surrounding mantle. Thus, we propose that the thermal induced transformation could provide an initial driven force for the exhumation of ultra‐deep subducted silica‐enriched felsic continental rocks. Temperature increase could be derived from an increased geothermal gradient from convective mantle or mantle plume. Mafic to ultra‐mafic rocks and silica‐deficient rocks may be captured by the upwelling subducted continental rocks and exhumated together.     

Modelling the atmospheric CO2 10-μm non-thermal emission in Mars and Venus at high spectral resolution

A study of the CO₂ atmospheric emissions at 10-μm in the upper atmospheres of Mars and Venus is performed in order to explain a number of ground-based measurements of these emissions recently taken at very high spectral resolution in both planets. The measurements are normally used to derive atmospheric temperatures and winds, but uncertainties on the actual emission layers were so far a serious drawback for their correct interpretation. The non-LTE models used for Mars and Venus in the present analysis are entirely similar in order to perform consistent comparisons between the two planets. In particular, the same scheme of CO₂ states and ro-vibrational bands are used, with similar assumptions on collisional routes and rate coef?cients, and also the same radiative transfer approximations. The emissions at 10-μm are produced in both atmospheres by the same excitation mechanism: radiative pumping of the CO₂(00⁰1) vibrational state by direct solar absorption(at 4.3 μm) and indirect absorption (at 2.7 μm, followed by collisional quenching). The computed radiances are specially strong in the upper mesosphere and lower thermosphere of the two planets during maximum solar illumination, producing a population inversion in such conditions with the lower states of the bands, the CO₂ (10⁰0) and CO₂(02⁰0). We obtained that other population inversions are also possible, involving higher energy CO₂ states. The larger solar ?ux available on Venus is found to produce larger vibrational populations and stronger emissions than equivalent atmospheric layers on Mars, in agreement with the observations. A number of perturbation studies were used to determine the exact emission altitudes, or weighting function peaks, for usual nadir sounding. The sensitivity of the emission to non-LTE model uncertainties and to atmospheric variations in temperature and CO₂ density is also presented. The dependence with the solar zenith angle and with the emission angle, as obtained with this model, could also be useful for guiding future observations.     

Fault geometries from the space distribution of the 1990–1997 Sannio–Benevento earthquakes: inferences on the active deformation in Southern Apennines

In this study, we analyze the recent (1990–1997) seismicity that affected the northern sector (Sannio–Benevento area) of the Southern Apennines chain. We applied the Best Estimate Method (BEM), which collapses hypocentral clouds, to the events of low energy (M_{d max}=4.1) seismic sequences in order to constrain the location and geometry of the seismogenetic structures. The results indicate that earthquakes aligned along three main structures: two sub-parallel structures striking NW–SE (1990–1992, Benevento sequence) and one structure striking NE–SW (1997, Sannio sequence). The southernmost NW–SE structure, which dips towards NE, overlies the fault that is likely to be responsible for a larger historical earthquake (I_{o max}=XI MCS, 1688 earthquake). The northernmost NW–SE striking structure dips towards SW. The NE–SW striking structure is sub-vertical and it is located at the northern tip of the fault segment supposed to be responsible for the 1688 earthquake. The spatio-temporal evolution of the 1990–1997 seismicity indicates a progressive migration from SE (Benevento) to NW (Sannio) associated to a deepening of hypocenters (i.e., from about 5 to 12 km). Hypocenters cluster at the interface between the major structural discontinuities (e.g., pre-existing thrust surfaces) or within higher rigidity layers (e.g., the Apulia carbonates). Available focal mechanisms from earthquakes occurred on the recognized NW–SE and NE–SW faults are consistent with dip-slip normal solutions. This evidences the occurrence of coexisting NW–SE and NE–SW extensions in Southern Apennines.     

GRIDA3—a shared resources manager for environmental data analysis and applications

GRIDA3 (Shared Resources Manager for Environmental Data Analysis and Applications) is a multidisciplinary project designed to deliver an integrated system to forge solutions to some environmental challenges such as the constant increase of polluted sites, the sustainability of natural resources usage and the forecast of extreme meteorological events. The GRIDA3 portal is mainly based on Web 2.0 technologies and EnginFrame framework. The portal, now at an advanced stage of development, provides end-users with intuitive Web-interfaces and tools that simplify job submission to the underneath computing resources. The framework manages the user authentication and authorization, then controls the action and job execution into the grid computing environment, collects the results and transforms them into an useful format on the client side. The GRIDA3 Portal framework will provide a problem-solving platform allowing, through appropriate access policies, the integration and the sharing of skills, resources and tools located at multiple sites across federated domains.     

Is there a possibility to correct fossil n-alkane data for postsedimentary alteration effects?

The long chain n-alkane composition of plant material can significantly differ between plant groups e.g. trees and grasses. Due to their relative recalcitrance, they have been employed in paleoecological research as molecular proxies for different types of vegetation. Most of those paleoenvironmental studies rely on the assumption that characteristic molecular fingerprints of plant material are preserved in the fossil organic material without significant alteration. However, there exists evidence that n-alkane distributions may change in the course of plant litter degradation. Here, the authors propose and discuss a conceptual approach to the correction of n-alkane patterns in paleosols and terrestrial sediments for postsedimentary alteration effects. This might have potential to improve paleoenvironmental reconstructions derived from these molecular fossils. In soil depth profiles typically a correlation between the OEP (odd over even predominance) and paleoecological valuable long-chain n-alkane ratios (LARs) can be found. Similar relationships have been also obtained from n-alkane records in paleosols. With the OEP serving as a proxy of microbial reworking, the correction procedure applies OEP vs. LAR regression functions to correct fossil LARs for degradation effects. The regression functions have been derived from modern soils. The application of the procedure and its significance for paleoecological interpretations is demonstrated on a case study of a loess-paleosol sequence (∼400–700 ka) in Romania. It is shown that changes in the C27/C31 n-alkane ratio at this site are closely related to degradation effects rather than to changes in the paleovegetation (e.g. tree vs. grass abundance). However, it was found that the C29/C31 ratio is a more suitable paleoenvironmental proxy at the Mircea Voda site. The results indicate that there is a future potential to correct fossil n-alkane ratios via the OEP/LAR relationship, however at the moment a general straight forward application of this approach might be critical due to lack of extended and diverse n-alkane records from modern soils. The need of more systematic n-alkane studies on soil profiles is highlighted to improve knowledge concerning dynamics and actual mechanisms of postsedimentary LAR and OEP changes.