Retrieval of the boundary layer height from active and passive remote sensors. Comparison with a NWP model

In this study, we used boundary layer heights derived from lidar in Romania to validate the Weather Research Forecast (WRF) model improved by ARIA Technologies SA in the framework of ROMAIR LIFE project. Lidar retrievals were also compared to the retrievals from meteorological data, both modeled (Global Data Assimilation System; GDAS) and measured (microwave radiometry). Both the gradient and the wavelet covariance methods were used to compute the boundary layer height (BLH) from the range corrected lidar signal, and their equivalence was shown. The analysis was performed on 102 datasets, spread over all seasons and 3 years (2009–2011). A good agreement was found for the remote sensors (lidar and microwave radiometer) which are co-located and measure simultaneously. The correlation of the measured boundary layer height and the modelled one was 0.66 for the entire dataset, and 0.73 when considering daytime data, i.e., for a well defined boundary layer. A systematic underestimation of the boundary layer height by the WRF during non-convective periods (nocturne, stable atmosphere) was found.     

Assessment of the ecological quality status of soft-bottoms in Reunion Island (tropical Southwest Indian Ocean) using AZTI marine biotic indices

The ability of the two synthetic marine biotic indices, AMBI and M-AMBI, to account for changes in the ecological quality of coastal soft bottoms of Reunion Island according to disturbances was assessed from macrobenthic samples collected in five sectors between 1994 and 2004. Samples were collected under non-perturbed conditions and at two sites subjected to heavy organic enrichment. Both indices are based on a classification of macrofauna into ecological groups (EG), and their transfer to tropical waters required some adaptations. These indices proved efficient in detecting a degradation of habitat quality. Their use resulted in the classification of all sites sampled between 1996 and 1998 as "good" or "high". M-AMBI nevertheless tended to result in the attribution of a slightly worse ecological quality status than AMBI. Together with an update of the EG species list for the Indian Ocean area, our results support the extension of both indices for the assessment of tropical soft bottoms.     

Effets combinés de la pêche et de l'eutrophisation sur la perche (Perca fluviatilis L.) dans les eaux vaudoises du Léman

Catches of perch have strongly decreased in Lake of Geneva from 1975 to 1981. This decrease was attributed to the impact of overfishing, enhanced by the accelerated growth of perch. Therefore, too many perches were captured before their first reproduction and the stocks of reproducers were strongly reduced. Furthermore, adverse meteorological conditions occurred probably during several periods of reproduction. The accelerated growth of perch was attributed to the combined effects of increasing eutrophication (more food available) and of overfishing (decreased perch density in the shoals).      

The effects of alteration and the interpretation of heat flow and radioactivity data—a reply to R.U.M. Rao

The first²²⁴Ra (t_1/2 = 3.64days) measurements from mixing zones of estuarine systems are presented for the Pee Dee River-Winyah Bay and Delaware Bay Estuaries. High-resolution gamma-ray spectrometry was used to determine²²⁴Ra,²²⁸Ra (t_1/2 = 5.7years), and²²⁶Ra (t_1/2 = 1622years) activity ratios. Desorption and diffusion from suspended and bottom sediments contributes to the non-conservative increases of the three isotopes in each systems. In Delaware Bay²²⁴Ra concentrations were nearly constant over the 2.5‰ to 15‰ salinity range where two turbidity maximum zones are located.²²⁸Th scavenging onto the suspended particles in the turbid zones may supply a regenerative source of²²⁴Ra in this system. Samples collected on the ebb and flood tide from a salt marsh along Delaware Bay have a 5-fold increase in²²⁴Ra from flood to ebb and 3- and 2-fold increases for²²⁸Ra and²²⁶Ra respectively, indicating salt marshes are another source of radium to estuarine waters.     

Description de deux nouvelles Cyclotelles (Bacillariophyceae) de milieux alcalins et eutrophes:Cyclotella costei nov. sp. etCyclotella wuethrichiana nov. sp.

Two new species of the genus Cyclotella are presented which have been discovered during ecological and paleoecological research studies in the littoral zone of two small alkaline eutrophic lakes in France (Lake Paladru) and in Switzerland (Lake Le Loclat). These new species are namedCyclotella costei nov. sp. andCyclotella wuethrichiana nov. sp.     

Neodymium and strontium isotope study of ophiolite and orogenic lherzolite petrogenesis

Neodymium isotopic analyses have been measured on nine ophiolites and four orogenic lherzolites. ε_Nd varies from +12 to +3 in the ophiolites and from +18 to +2 in the orogenic lherzolites. The majority of the analyses plot on a ε_Nd-ε_Sr correlation line as defined by Nd and Sr isotopic analyses of oceanic basalts. However, certain ophiolitic and lherzolitic samples exhibit high⁸⁷Sr/⁸⁶Sr ratios and as such lie to the right of the correlation line towards seawater compositions.From these data one can postulate several origins for ophiolites including that of mid-ocean ridges and ocean islands. If the orogenic lherzolites are interpreted as representative of the mantle occurring below active ridges a more complex model is required involving mantle heterogeneity and multi-episodic chemical fractionation starting prior to 2 Ga ago.     

Effects of compressibility on the flow of lava

Lava contains gas bubbles and hence is a compressible liquid whose density increases as a function of pressure. After eruption at the Earth's surface, it spreads at a rate which is a function of its thickness and it is compressed under its own weight. Therefore, both thickness and spreading rate are determined by a balance between viscous and compressible effects. Theoretical equations are derived for the shape and velocity of a compressible liquid spreading on a horizontal surface. Solutions are obtained for a fixed eruption rate Q. The radial extent of the flow increases proportional to t ^1/2. A dimensionless number C is defined which characterizes the importance of flow compression: , where ₀ is bubbly lava density at atmospheric pressure, compressibility, viscosity and g the acceleration of gravity. C can be thought of as the ratio of two characteristic length-scales, one for compression effects and one for viscous effects. The larger C is, the more important compressibility effects are. As C is increased, the flow becomes thinner because the liquid is compressed more and more efficiently. Compressibility acts to smooth out variations of flow thickness, which provide the driving force. Thus, all else being equal, a compressible liquid flows less rapidly than an incompressible one. When trying to infer the effective viscosity of a flow from its spreading rate, the neglect of compressibility leads to an overestimate. The various factors which act to determine the distribution of gas bubbles in lava flows are reviewed and discussed quantitatively. Comparison with data from Obsidian Dome (Eastern California) shows that disequilibrium effects are important and that bubble resorption during burial in a thick flow is not a pervasive phenomenon. The analysis is applied to the 1979 dome of Soufrière de Saint Vincent (W.I.). An effective value of compressibility for this 100-m-thick dome is 1.5x10^–6 Pa^–1. This implies that, all else being equal, the viscosity of this lava may be overestimated by a factor of 5 if no account is taken of the compressible nature of the flow.     

Evolution of the late Pleistocene Mojanda–Fuya Fuya volcanic complex (Ecuador), by progressive adakitic involvement in mantle magma sources

The Mojanda–Fuya Fuya Volcanic Complex consists of two nearby volcanoes, Mojanda and Fuya Fuya. The older one, Mojanda volcano (0.6 to 0.2 Ma), was first constructed by andesites and high-silica andesites forming a large stratovolcano (Lower Mojanda). This edifice was capped by a basaltic andesite and andesitic cone (Upper Mojanda), which collapsed later to form a 3-km-wide summit caldera, after large phreatomagmatic eruptions. The Lower Fuya Fuya edifice was constructed by the extrusion of viscous Si-rich andesitic lavas and dacitic domes, and the emission of a thick sequence of pyroclastic-flow and fallout deposits which include two voluminous rhyolitic layers. An intermediate construction phase at Fuya Fuya is represented by a mainly effusive cone, andesitic in composition (San Bartolo edifice), the construction of which was interrupted by a major sector collapse in the Late Pleistocene. Finally, a complex of thick siliceous lavas and domes was emplaced within the avalanche amphitheatre, forming the Upper Fuya Fuya volcanic centre. This paper shows that the general evolution from an effusive to an explosive eruptive style is related to a progressive adakitic contribution to the magma source. Although all the rocks of the complex are included in the medium-K field of continental arcs, the Fuya Fuya suite (61–75 wt.% SiO₂) shows depletion in Y and HREE and high Sr/Y and La/Yb values, compared to the less silicic Mojanda suite (55–66.5 wt.% SiO₂). The Mojanda calc-alkaline suite was generated by partial melting of an adakite-metasomatised mantle source that left a residue with 2% garnet, followed by fractional crystallization of dominant plagioclase + pyroxene + olivine at shallow, intra-crustal depths. For Fuya Fuya, geochemical and mineralogical data suggest either (1) partial melting of a similar metasomatised mantle with more garnet in the residue (4%), followed by fractional crystallization involving plagioclase, amphibole and pyroxene, or (2) mixing of mafic mantle-derived magma from the Mojanda suite and slab melts, followed by the same fractional crystallization process.     

Isotopic and geochemical characterization of salinization in the shallow aquifers of a reclaimed subsiding zone: The southern Venice Lagoon coastland

The coastal plain bordering the southern Venice Lagoon is a reclaimed lowland characterized by high subsidence rate, and ground level and water-table depth below sea level. In this agricultural region, where the surface hydrologic network is entirely artificially controlled by irrigation/drainage canals, salinization problems have long been encountered in soils and groundwaters. Here we use isotopic and geochemical tracers to improve our understanding of the origin of salinization and mineralization of the semi-confined aquifer (0–40 m), and the freshwater inputs to this hydrological system. Water samples have been collected at different seasons in the coastal Adriatic Sea, lagoon, rivers and irrigation canals, as well as in the semi-confined aquifer at depths between 12 and 35 m (14 boreholes), and in the first confined aquifer (three boreholes drilled between 40 and 80 m depth). Stable isotopes (δ¹⁸O and δD) and conductivity profiles show that direct saline intrusion from the sea or the lagoon is observed only in a restricted coastal strip, while brackish groundwaters are found over the entire topographic and piezometric depression in the centre of the study area. Fresh groundwaters are found only in the most western zone. The sharp isotopic contrast between the western and central regions suggests disconnected hydrological circulations between these two parts of the shallow aquifer. The border between these two regions also corresponds to the limits of the most strongly subsiding zone.Our results can be interpreted in terms of a four end-member mixing scheme, involving (1) marine water from the lagoon or the open sea, (2) alpine and pre-alpine regional recharge waters carried either by the main rivers Adige, Bacchiglione and Brenta (irrigation waters) or by the regional groundwater circulation, (3) local precipitation, and (4) evaporated waters infiltrated from the surface. Infiltration from the surface is also revealed by the stratification of the electrical conductivity profiles, showing that the brackish groundwaters are overlain by a shallow layer of less saline water all over the central depression. In the first confined aquifer, the groundwaters have isotopic compositions similar to the deep groundwaters of the Venetian confined aquifers (40–400 m depth). The isotopic data and the Br/Cl ratio show that the origin of the salinization of the phreatic aquifer can be ascribed to seawater intrusion alone, with no indication of the involvement of deep brines (identified at 450 m depth) in the process.The chemical composition of the saline and brackish groundwaters is characterized by an excess of sodium and a deficit of calcium compared to conservative mixing between fresh groundwaters and seawater. This suggests that the phreatic aquifer is progressively freshening, as a consequence of the beneficial influence of the extensive irrigation/drainage network, including raised canals acting as a hydraulic barrier along the coast. This freshening tendency may have been lasting since the reclamation in the mid-twentieth century, and has probably been accelerated by the ban on groundwater abstraction since the 1970s.