Trace element partitioning between carbonatitic melts and mantle transition zone minerals: Implications for the source of carbonatites

The occurrence of CO₂-rich lavas (carbonatites, kimberlites) and carbonate-rich xenoliths provide evidence for the existence of carbonatitic melts in the mantle. To model the chemical composition of such melts in the deep mantle, we experimentally determined partition coefficients for 23 trace elements (including REE, U-Th, HFSE, LILE) between deep mantle minerals and carbonatite liquids at 20 and 25 GPa and 1600 °C. Under these conditions, majoritic garnet and CaSiO₃ perovskite are the main reservoirs for trace elements. This study used both femtosecond LA-ICP-MS and SIMS techniques to measure reliable trace element concentrations. Comparison of the two techniques shows a general agreement, except for Sc and Ba. Our experimentally determined partition coefficients are consistent with the lattice strain model. The data suggest an effect of melt structure on partition coefficients in this pressure range. For instance, strain-free partition coefficient (D₀) for majorite-carbonatite melts do not follow the order of cation valence, , observed for majorite-CO₂-free silicate melts. The newly determined partition coefficients were combined with trace element composition of majoritic garnets found as inclusions in diamond to model trace element patterns of deep-seated carbonatites. The result compares favorably with natural carbonatites. This suggests that carbonatites can originate from the mantle transition zone.     

Modelling larval dispersal and settlement of the reef-building polychaete Sabellaria alveolata: Role of hydroclimatic processes on the sustainability of biogenic reefs

The honeycomb worm Sabellaria alveolata forms biogenic reefs which constitute diversity hotspots on tidal flats. The largest known reefs in Europe, located in the Bay of Mont-Saint-Michel (English Channel), are suffering increasing anthropogenic disturbances which raise the question of their sustainability. As the ability to recover depends partly on the recolonization of damaged reefs by larval supply, evaluating larval dispersal and the connectivity between distant reefs is a major challenge for their conservation. In the present study, we used a 3D biophysical model to simulate larval dispersal under realistic hydroclimatic conditions and estimate larval retention and exchanges among the two reefs of different sizes within the bay. The model takes into account fine-scale hydrodynamic circulation (800×800 m²), advection–diffusion larval transport, and gregarious settlement behaviour. According to the field data, larval dispersal was simulated for a minimal planktonic larval duration ranging from 4 to 8 weeks and the larval mortality was set to 0.09 d⁻¹. The results highlighted the role played by a coastal eddy on larval retention within the bay, as suggested by previous in situ observations. Very different dispersal patterns were revealed depending on the spawning reef location, although the two reefs were located only 15 km apart. The settlement success of the larvae released from the smallest reef was mainly related to tidal conditions at spawning, with the highest settlement success for releases at neap tide. The settlement success of the larvae from the biggest reef was more dependent on meteorological conditions: favourable W and SW winds may promote a ten-fold increase in settlement success. Strong year-to-year variability was observed in settlers’ numbers, with favourable environmental windows not always coinciding with the main reproductive periods of Sabellaria. Settlement kinetics indicated that the ability to delay metamorphosis could significantly improve the settlement success. Although bidirectional exchanges occurred between the two reefs, the highest settlers’ numbers originated from the biggest reef because of its stronger reproductive output. Because of the recent decline of this reef due to increasing anthropogenic disturbances larval supply in the bay may not be sufficient enough to ensure the sustainability of the remarkable habitat formed by Sabellaria alveolata reefs.     

Tvashtar awakening detected in April 2006 with OSIRIS at the W.M. Keck Observatory

We detected a volcanic outburst in Io's northern hemisphere on 17 April 2006 with the OSIRIS imaging spectrometer at Keck, and confirmed it was still erupting on 2 June 2006. The eruption, which we name 060417A, was located in Tvashtar Paterae, ∼100 km southeast of the February 2000 eruption. The observed temperature was , over a surface area of , providing a total thermal output of .     

A catalog of tsunamis in New Caledonia from 28 March 1875 to 30 September 2009

In order to establish a tsunami alert system in New Caledonia in April 2008, the French Secretary of State for Overseas Affairs, with the aid of the UNESCO French Commission, mandated an investigation to build a more complete record of the most recent tsunamis. To complete this task, a call for witnesses was broadcast through various media and in public locations. These witnesses were then interviewed onsite about the phenomenon they had observed. Previous witness reports that had been obtained in the last few years were also used. For the most recent events, various archives were consulted. In total, 18 events were documented, of which 12 had not been previously mentioned in past work. These results confirm an exposure to a hazard of: (1) local origin (the southern part of the Vanuatu arc) with a very short post-seismic delay (< 30 min) before the arrival of wave trains; (2) regional origin (Solomon Islands arc, northern part of the Vanuatu arc) with a delay of several hours; and (3) an exposure to trans-oceanic tsunamis (Kamchatka 1952, South Chile 1960, Kuril Islands 2006, North Tonga 2009), unknown until today. These results highlight the necessity for New Caledonia to adopt an alert system, coupled with ocean tide gauges, that liaises with the main alert system for the Pacific (Pacific Tsunami Warning Center), and brings to light the importance of establishing a prevention campaign.     

A source study of PM in Saxony by Size-Segregated Characterisation

Airborne particulate matter in Saxony (Germany) was investigated at three different sites (central urban, urban outskirts, rural) during a winter (1999/2000) and a summer (2000) campaign. PM was collected simultaneously at all three sites using five-stage Berner impactors. Besides size-segregated chemical particle characterisation and mass closure source apportionment of the particle components, especially of the carbonaceous fraction was an aim of the study. Source apportionment was performed exclusively on the basis of experimental data without support of models considering a set of basic assumptions and logical deductions. The derived simple equations permit to differentiate the carbonaceous fraction in traffic, domestic heating (winter) and biogenic (summer) contributions.The total carbon (TC) in the smallest particle size range (Dp_aer = 0.05-0.14μm) at the urban site, contributing 88% to the mass in that class, was completely attributed to traffic emissions. For the particle size range Dp_aer = 0.42-1.2 μm (50-60% of the total mass) TC was attributed to traffic (67%) and domestic heating (33%) in winter and to traffic (82%) and biogenic origin (18%) in summer.Size-segregated determination of alkanes revealed that these compounds were mainly of biogenic origin in summer and of anthropogenic origin in winter considering the carbon preference index (CPI_odd). Particulate PAHs found in winter samples originated mainly from domestic heating and not from traffic emissions.The method described cannot provide complete results, but the demonstrated source apportionment can be helpful to assess a given situation with regard to possible steps against the exceeding of the EU limit of the PM₁₀ mass concentration of 50 μg m⁻³.     

Impact of recent climate change on the hydrology of coastal Mediterranean rivers in Southern France

The purpose of this paper is to analyse the regional impact of recent climate change on the water resources in southern France. We produced spatial reconstructions of the monthly evolutions of temperature, precipitation and water discharge in 15 watersheds of six coastal river basins and examined the major changes based on trend analysis for the last 40 years. In this part of the Mediterranean, the general warming trend was strongly enhanced by changes in the atmospheric circulation patterns, characterized by a northward extension of the subtropical high pressure domain during spring and summer. During these seasons, monthly warming rates could achieve almost twice the mean annual warming rates. Although annual precipitation did not follow clear trends, water discharge significantly decreased in one third of the watersheds and accounted for an estimated 20% reduction of the water resources in this region. This concerns both the highest and lowest watersheds. In the former, the reduction is likely the result of a temperature induced switch of snowfall to rainfall at high altitudes. In the latter, the reduction of discharge seems to come from lower groundwater levels, which may be related to the temperature increase too, but also have other origins. The recent climatic evolution is consistent with most modelling simulations for the future, indicating that the reduction of the water resources will hold on, probably still enhanced by decreases in precipitation.     

Comparison of HIPWAC and Mars Express SPICAM observations of ozone on Mars 2006-2008 and variation from 1993 IRHS observations

Ozone is a tracer of photochemistry in the atmosphere of Mars and an observable used to test predictions of photochemical models. We present a comparison of retrieved ozone abundances on Mars using ground-based infrared heterodyne measurements by NASA Goddard Space Flight Center’s Heterodyne Instrument for Planetary Wind And Composition (HIPWAC) and space-based Mars Express Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) ultraviolet measurements. Ozone retrievals from simultaneous measurements in February 2008 were very consistent (0.8 μm-atm), as were measurements made close in time (ranging from <1 to >8 μm-atm) during this period and during opportunities in October 2006 and February 2007. The consistency of retrievals from the two different observational techniques supports combining the measurements for testing photochemistry-coupled general circulation models and for investigating variability over the long-term between spacecraft missions. Quantitative comparison with ground-based measurements by NASA/GSFC’s Infrared Heterodyne Spectrometer (IRHS) in 1993 reveals 2-4 times more ozone at low latitudes than in 2008 at the same season, and such variability was not evident over the shorter period of the Mars Express mission. This variability may be due to cloud activity.     

Detecting stratigraphical issues using direct radiocarbon dating from small-mammal remains

Frequently preserved in archaeological and palaeontological sites, the tiny size of small-mammal remains favours percolations into underlying layers along stratigraphic sequences. This is one of the various post-depositional processes that may affect the integrity of the original deposits and therefore the subsequent scientific interpretations. Recent developments in sample preparation offer the possibility of detecting intrusive episodes through the absolute dating of minute amounts of bone (down to 10 mg), meaning that isolated elements (such as mandibles in this case) are sufficient to obtain reliable radiocarbon dates if collagen is moderately to well preserved. The radiocarbon dates obtained here for small-mammal bones (recovered from pre-Bølling to recent deposits) and their comparison with previous dates obtained from other sources (large-mammal bones, charcoal, botanical samples, etc.), with different protocols and instruments, illustrate the potential of small-mammal dating to reveal (and eventually contribute a solution to) stratigraphical issues in different archaeological contexts.     

Impact of the Eastern Mediterranean Transient on the distribution of anthropogenic CO2 and first estimate of acidification for the Mediterranean Sea

In the Mediterranean Sea the carbon chemistry is poorly known. However, the impact of the regional and large-scale anthropogenic pressures on this fragile environment rapidly modifies the distribution of the carbonate system key properties like C_T (total dissolved inorganic carbon), A_T (total alkalinity), C_ANT (anthropogenic CO₂), and pH. This leads inexorably to the acidification of its waters. In order to improve our knowledge, we first develop interpolation procedures to estimate C_T and A_T from oxygen, salinity, and temperature data using all available data from the EU/MEDAR/MEDATLAS II database. The acceptable levels of precision obtained for these estimates (6.11 ??mol-kg⁻¹ for C_T and 6.08 ??mol kg⁻¹ for A_T) allow us to draw the distribution of C_ANT (with an uncertainty of 6.75 ??mol kg⁻¹) using the Tracer combining Oxygen, inorganic Carbon, and total Alkalinity (TrOCA) approach. The results indicate that: 1) all Mediterranean water bodies are contaminated by anthropogenic carbon; 2) the lowest concentration of C_ANT is 37.5 ??mol kg⁻¹; and 3) the western basin is more contaminated than the Eastern basin. After reconstructing the distribution of key properties (C_T, A_T, C_ANT) for four periods of time (between 1986 and 2001) along a west-east section throughout the whole Mediterranean Sea, we analyze the impact of the Eastern Mediterranean Transient (EMT). Not only has the concentration of C_ANT increased (especially in the intermediate and the bottom layers of the eastern basin, during and after the EMT), but also the distribution of all properties has been considerably perturbed. This is discussed in detail. For the first time, the level of acidification is estimated for the Mediterranean Sea. Our results indicate that for the year 2001 all waters (even the deepest) have been acidified by values ranging from −0.14 to −0.05 pH unit since the beginning of the industrial era, which is clearly higher than elsewhere in the open ocean. Given that the pH of seawater may affect a very large number of chemical and biological processes, our results stress the necessity to develop new programs of research to understand and then predict the evolution of the carbonate system properties in the Mediterranean Sea.     

Keck AO observations of Io in and out of eclipse

We present adaptive optics (AO) observations of Io taken with the W.M. Keck II telescope on 18 December 2001 (UT) before the satellite went into eclipse, and while it was in Jupiter's shadow. Making these kind of Io-in-eclipse observations, as well as the associated data reduction and analysis are challenging; hence one focus of the paper is to explain the methods and tools used for these data sets. For the sunlit images Io itself was used as the wavefront reference source, while nearby Ganymede was used as reference ‘star’ when Io was in eclipse. Observations were obtained in K′-, L′-, and M-bands. The sunlit images have been deconvolved using MISTRAL. The Io-in-eclipse data were deconvolved with IDAC and MISTRAL. The former gives better results, both in absolute photometry and in matching the original images. We determined the flux densities of the hot spots from the original Io-in-eclipse data with StarFinder, as well as from the deconvolved images by integrating the intensity over the relevant areas. We determined the highly anisoplanatic PSF via a FFT method from the original data, and used this in StarFinder and as a starting PSF for IDAC and MISTRAL. We derived temperatures and areal coverage of all 19 spots detected in both K′- and L′-band images of Io-in-eclipse. We also determined temperatures and areal coverage of the hot spots visible on the L′- and M-band images of sunlit Io. Most volcanoes contain a compact hot ‘core’ (?10 km² at 600-800 K) within a larger area at lower temperatures (e.g., ∼10²-10⁴ km² at 300-500 K). The total heat flow contributed by these active volcanoes is 0.2 W m⁻², ∼8% of the average global heat flow measured at 5-20 μm by Veeder et al. [J. Geophys. Res. 99 (1994) 17095].