Response of hurricane-type vortices to global warming as simulated by ARPEGE-Climat at high resolution

Atlantic hurricanes and their sensitivity to anthropogenic warming are investigated using very high (0.5°×0.5° over the Atlantic domain) resolution global simulations. The ARPEGE-Climat variable resolution grid demonstrates its usefulness in regional climate studies since resolution can be multiplied by a factor of 2.5 over the domain of interest compared to a uniform grid, for a similar computer cost. The question of hurricane characteristics dependence on anthropogenic warming is tackled trough the implementation of a tracking method. Changes in the total number, as well as locations, of hurricanes appear to depend more on sea surface temperature (SST) spatial patterns anomaly than Atlantic mean intensity, essentially through the change in large scale vertical wind shear. A uniform SST anomaly forcing produces increased and eastward shifted systems while a spatially contrasted anomaly leads to a decrease. Comparison between cyclogenesis density calculated from tracking or large scale combined variables (as a modified Gray parameter) brings some confidence in the use of the latter to investigate low resolution simulations. Mean hurricane dynamical characteristics are weakly changed by the warming but precipitation core and latent heat flux are enhanced in all scenarios.     

Effect of organic solvent type on the removal of nitrate ion using liquid membrane technique

In this study, the removal of nitrate ions from aqueous solutions with liquid membrane technique has been investigated for different organic solvent types in which solubilized tetradecyl trimethyl ammonium bromide (TDTMABr) as carrier. n-butyl alcohol, chloroform, and mixture of chloroform + n-hexane (n-hexane 85% + chloroform 15%) were used as organic solvent. Kinetic parameters (k _1d, k _2m, k _2a, t _max, R _m^max, J _m^max, J _a^max) were calculated from obtained data. time R _a values of mixture, butyl alcohol, and chloroform are 0.81, 0.78, and 0.55, respectively. Similarly R _d, R _m, and t _max values of the mixture equal to 0.14, 0.04, and 87.92 min, respectively. This behavior of the system shows the organic solvent type is an effective parameter on separation yield. It can be concluded that the mixture is the most effective organic solvent type among the investigated ones, because liquid membrane systems should be operated within the range of having the R _m, R _d, and t _max values are minimum while R _a values are maximum.     

Direct evidence of imbalanced seagrass (Posidonia oceanica) shoot population dynamics in the Spanish Mediterranean

Direct census of shoots tagged in permanent plots was used to assess the present (2000–2002)Posidonia oceanica population dynamics in 25 meadows along the Spanish Mediterranean Coast. Shoot density ranged from 154±8 to 1,551±454 shoots m⁻², absolute shoot mortality from 5±0 to 249±53 shoots m⁻² yr⁻¹, and absolute shoot recruitment from <5 ±1 to 62±42 shoots m⁻²yr⁻¹. Specific shoot mortality and recruitment rates, which are mathematically and statistically (p>0.05) independent of shoot density, varied from 0.015±0.006 to 0.282±0.138 yr⁻¹ and 0.018±0.005 to 0.302±0.093 yr⁻¹, respectively. Absolute shoot mortality rate was scaled to shoot density (Pearson correlation, r=0.78, p<0.0001), and variability in specific shoot recruitment rate was partially due to differences in the percentage of growing apexes, which produce most of the recruits within the population (Pearson correlation, r=0.50, p<0.001), demonstrating the existence of structural constraints on shoot demography. Shoot half-life was estimated to range from 2.5 to 60.4 yr and meadow turnover times between 6.7 yr and more than a century, provided current estimates of shoot mortality, recruitment rates, and density remain uniform. There were differences in shoot mortality and recruitment at the regional scale, with the meadows developing along the coast of the Spanish mainland experiencing the highest shoot mortality (Tukey test, p<0.05) and tending to exhibit the highest shoot recruitment. The low shoot recruitment did not balance shoot mortality in most (60%) of the meadows, showing a prevalence of declining populations among the 25 meadows studied (Wilcoxon ranked sign test, p<0.0005). This study demonstrates the power of direct census of seagrass shoots in permanent plots to evaluate the present status of seagrass meadows, to detect on-going population decline, and to provide some insight onto the possible factors involved. The incorporation of direct census of seagrass meadows to monitoring programs will help provide the early-warning signals necessary to support management decisions to conserve seagrass meadows.     

Nouveaux éléments sur la structure et le fonctionnement hydrogéologique du plateau basaltique de l'Aubrac (Massif central,France). Première évaluation des potentialités en eau souterraine

In volcanic areas, the quality of the geological data at the various scales is of paramount importance for the estimation of aquifer potentialities and thus for groundwater exploitation. Geological and hydrogeological investigation (synthesis of existing data, field geological observations, reconstruction of the infra-volcanic morphology, stream gauging, field hydrogeology, etc.) have been performed on the 450-km² Aubrac basaltic plateau (Massif Central, France). These results allow us to specify the hydrological structure and functioning of this volcanic plateau that were quite unknown before. It is mainly constituted by the piling up of lava flows resting on a plutonic and metamorphic substratum. This volcanic unit constitutes an aquifer of regional importance whose groundwater resources are currently underexploited. These results allow us to delineate zones and strategies for priority hydrogeological prospecting. To cite this article: P.-Y. Bourlier et al., C. R. Geoscience 337 (2005).     

Titanite and zircon fission-track dating resolves successive igneous episodes in the formation of the composite Kaçkar batholith in the Turkish eastern Pontides

The Kaçkar batholith in the Turkish eastern Pontides comprises several intrusive units with distinctive textural, mineralogical and geochemical characteristics. Their titanite and zircon fission-track ages confirm that the different lithodem units result from consecutive igneous episodes, establish their emplacement sequence and, together with geochemical data, help to relate them to their geodynamic context. The Çaml?kaya granitoid (112.4 ± 1.6 Ma) was emplaced during an immature-arc magmatic episode of early Cretaceous age. The S?rtyayla (57.1 ± 1.2 Ma) and Marselevat (52.9 ± 1.3 Ma) granitoids are late products of a late-Palaeocene mature-arc episode. The Ayder granitoid (46.4 ± 1.0 Ma) is the result of middle- to late-Eocene post-collisional magmatism related to slab break-off. The Halkal?ta? quartz diorite (43.7 ± 2.3 Ma) and the Güllüba? monzonite (38.1 ± 0.9 Ma) document a middle- to late-Eocene episode related to post-collisional extension. The data reveal the advantages of dense sampling, spanning a maximum range of elevations. Apart from the increased precision on the mean, redundant sampling allows to shift the basis for interpretation from a priori assumptions to a posteriori numerical criteria when using geochronometers with low to moderate closure temperatures, including apatite, titanite and zircon fission-tracks but also K–Ar (Ar–Ar) biotite, muscovite and K-feldspar.     

Leaf breakdown in two tropical streams: Differences between single and mixed species packs

We assessed leaf breakdown of five native riparian species from Brazilian Cerrado (Myrcia guyanensis, Ocotea sp., Miconia chartacea, Protium brasiliense, and Protium heptaphyllum), incubated in single and mixed species packs in two headwater streams with different physico-chemical properties in the Espinhaço Mountain range (Southeastern Brazil). Leaves were placed in plastic litter bags (15 cm×20 cm, 10 mm mesh size) and the experiments were carried out during the dry seasons of 2003 and 2004. Leaf nitrogen and phosphorus contents were similar in all species, but polyphenolic contents were different (P<0.001). M. guyanensis showed higher polyphenolics content (8.48% g⁻¹ dry mass) and leaf toughness. Individually, higher breakdown rates were found in M. guyanensis at Indaiá stream (k=0.0063±0.0005 d⁻¹) and in Ocotea sp. at Garcia stream (k=0.0088±0.0006 d⁻¹). However, P. brasiliense and P. heptaphyllum showed lower breakdown rates at Indaiá and Garcia streams (Indaiá: k=0.0020±0.0002 and 0.0019±0.0001 d⁻¹; Garcia: k=0.0042±0.0001 and 0.0040±0.0002 d⁻¹). Single and mixed breakdown processes of each species were not statistically different on both streams. However, all species showed higher breakdown rates at Garcia stream (P<0.01). These results suggest that leaf breakdown is not altered when litter benthic patches are composed by a mixture of species in the same proportions that they occur on riparian leaf falls.     

An assessment of changes in properties of steppe kurgan paleosoils in relation to prevailing climates over recent millennia

Comparative analysis of morphological and chemical properties of the soil chronosequence on Kastanozems soils in the steppe zone of the Russian Plain, which included paleosoils buried beneath kurgans erected ca. 2000 BC, AD 50, AD 200, and AD 1250 was performed to reconstruct the paleoenvironmental conditions in this archeologically important region. Paleoenvironmental dynamics were traced using the state of microbial communities of paleo and modern soils (including the dynamics of total and glucose-reactive biomass, and the abundance of microorganisms grown on selected media). We demonstrate that the share of the glucose-reactive microorganisms in the microbial community, the ecological–trophic structure, and oligotrophicity index might serve as indicators of the state of microbial communities and be used for paleoenvironmental reconstructions. The morphological–chemical and microbial properties confirm an arid period ca. 2000 BC, slightly wetter conditions ca. AD 50, and more humid conditions ca. AD 1250.     

Food and habitat partitioning in grazing snails (<Emphasis Type="Italic">Turbo smaragdus</Emphasis>), Northern New Zealand

Gut content analyses and fatty acid profiles were used to identity food consumption and assimilation in a dominant grazing snail (Turbo smaragdus) in rocky shore and estuarine habitats, at Waiwera Estuary, northern New Zealand. Gut contents of freshly collected individuals indicated that snails utilize a wide range of food sources within their habitats, including microalgae and foliose-corticated macrophytes (rocky intertidal), and mangrove tissue and filamentous algae (mangrove stand). Laboratory feeding experiments revealed thatT. smaragdus prefers microalgae and possibly filamentous epiphytes, regardless of snail size or habitat of origination. The fatty acid profiles of snails fed different diets (brown algae [Hormosira banksii], diatoms, mangrove pneumatophores, and filamentous green algae [Chaetomorpha sp.]) confirmed the assimilation of the given foods, except for the mangrove treatment, which resulted in a low, long chain, fatty acid (LCFA) signature. Incongruities between the gut content analyses (high number of mangrove particles) and fatty acid profiles (low LCFA signature) of field and laboratory snails exposed to a mangrove diet suggest that snails target microalgal and filamentous epiphyte food sources on the pneumatophores and inadvertently ingest mangrove particles. Snails within all food treatments, except diatoms, had a relatively strong bacterial signature (18∶1n–7, Σ15+Σ17). Bacteria may have readily accumulated in the experimental tanks and been selected by snails as an alternative food source. In the field, snails and other grazers may ingest detritus and biofilms to access dense populations of bacteria. This research highlights the need for a comprehensive and multianalytical approach to elucidate the role of grazers in algal-plant dominated ecosystems.     

Climate simulation of the twenty-first century with interactive land-use changes

To include land-use dynamics in a general circulation model (GCM), the physical system has to be linked to a system that represents socio-economy. This issue is addressed by coupling an integrated assessment model, IMAGE2.2, to an ocean–atmosphere GCM, CNRM-CM3. In the new system, IMAGE2.2 provides CNRM-CM3 with all the external forcings that are scenario dependent: greenhouse gas (GHGs) concentrations, sulfate aerosols charge and land cover. Conversely, the GCM gives IMAGE changes in mean temperature and precipitation. With this new system, we have run an adapted scenario of the IPCC SRES scenario family. We have chosen a single scenario with maximum land-use changes (SRES A2), to illustrate some important feedback issues. Even in this two-way coupled model set-up, land use in this scenario is mainly driven by demographic and agricultural practices, which overpowers a potential influence of climate feedbacks on land-use patterns. This suggests that for scenarios in which socio-economically driven land-use change is very large, land-use changes can be incorporated in GCM simulations as a one-way driving force, without taking into account climate feedbacks. The dynamics of natural vegetation is more closely linked to climate but the time-scale of changes is of the order of a century. Thus, the coupling between natural vegetation and climate could generate important feedbacks but these effects are relevant mainly for multi-centennial simulations.