Hf isotope compositions of northern Luzon arc lavas suggest involvement of pelagic sediments in their source

New Hf isotopic compositions for island arc basalts from the Luzon arc (Philippines) define a remarkable sub-horizontal trend in Hf–Nd isotopic space with a small range of _Hf (+5 to +17) associated with a large variation in _Nd (–7 to +8). The data plot above and barely overlap the terrestrial array defined by oceanic basalts and continental crust. Mixing hyperbolas passing through the data intersect fields for depleted mantle and pelagic sediments suggesting that these two components formed the source of the Luzon arc lavas. An exception is the Batan Island where the low _Nd ratios are associated with low _Hf values. A mixing hyperbola fitting the Batan samples suggests that their mantle source was modified by subducted material prior to contamination by terrigenous clays. More generally, the geochemical relationships in Luzon lavas show that the mixing endmembers are source components rather than melts. The relationship between Nd and Hf isotopic compositions in the Luzon volcanics show that the type of sediment subducted under an island arc is a determining factor in the control of the two isotopic systems in island arc environments.Electronic Supplementary Material Supplementary material is available for this article at     

Wind in Ireland: long memory or seasonal effect?

Since Haslett and Raftery’s paper Space-Time Modelling with Long-Memory Dependence: Assessing Ireland’s Wind Power Resource (1989), modelling meteorological time series with long memory processes, in particular the ARFIMA model has become very common. Haslett and Raftery fitted an ARFIMA model on Irish daily wind speeds. In this paper, we try to reproduce Haslett and Raftery’s results (focusing on the dynamic of the wind process, and not on cross-correlation and space dependencies), and show that an ARFIMA model does not properly capture the behaviour of the series (in Modelling daily windspeed in Ireland section). Indeed, the series show a periodic behaviour, that is not taken into account by the ARFIMA model. Removing this periodic behaviour yields no results either, we therefore try to fit a GARMA model that takes into account both seasonality and long memory (in Seasonality and long memory using GARMA models section). If a GARMA process can be fitted to the data to model Irish daily data, we will show that these models could also be used to model Dutch hourly data.

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Evaluation of the Weather Research and Forecast/Urban Model Over Greater Paris

Meteorological modelling in the planetary boundary layer (PBL) over Greater Paris is performed using the Weather Research and Forecast (WRF) numerical model. The simulated meteorological fields are evaluated by comparison with mean diurnal observational data or mean vertical profiles of temperature, wind speed, humidity and boundary-layer height from 6 to 27 May 2005. Different PBL schemes, which parametrize the atmospheric turbulence in the PBL using different turbulence closure schemes, may be used in the WRF model. The sensitivity of the results to four PBL schemes (two non-local closure schemes and two local closure schemes) is estimated. Uncertainties in the PBL schemes are compared to the influence of the urban canopy model (UCM) and the updated Coordination of Information on the Environment (CORINE) land-use data. Using the UCM and the CORINE land-use data produces more realistic modelled meteorological fields. The wind speed, which is overestimated in the simulations without the UCM, is improved below 1,000 m height. Furthermore, the modelled PBL heights during nighttime are strongly modified, with an increase that may be as high as 200 %. At night, the impact of changing the PBL scheme is lower than the impact of using the UCM and the CORINE land-use data.     

Hydrothermal alteration in andesitic volcanoes: Trace element redistribution in active and ancient hydrothermal systems of Guadeloupe (Lesser Antilles)

The mineralogy and the trace element compositions of hydrothermally-altered volcanic materials collected from ash fall deposits and in four debris-avalanche deposits (DADs) at La Soufrière volcano in Guadeloupe have been determined. Phreatic explosions of the 1976 eruption and flank collapse events have sampled various parts of the active and ancient hydrothermal systems of the volcano. Hydrothermal mineral assemblages (smectite + silica polymorphs ± pyrite/jarosite ± gypsum) are typical of rock alteration by low-temperature acid-sulphate fluids. High-temperature mineral assemblages are rare, indicating that phreatic explosions and flank collapse events have sampled mainly the upper parts of the volcanic edifice.Andesitic eruptive products affected by shallow hydrothermal alteration are complex assemblages of volcanic materials (glass, phenocrysts and xenocrysts with complex magmatic histories) of different ages and compositions. The use of incompatible element ratios and REE compositions normalised to an unaltered reference material overcomes the interpretation difficulties related to mass balance effects of alteration processes and the petrologic heterogeneity of the initial material.REE and other incompatible elements (Th, U, Hf, Zr) are mainly concentrated in the glassy matrix of unaltered andesitic rocks. Secondary S-bearing mineral phases (e.g., gypsum, jarosite) that have precipitated from acid-sulphate fluids do not contain substantial incompatible elements (REE, U, Th, Hf, Zr). Compositional variations of incompatible elements in hydrothermally-altered andesitic materials reflect mainly volcanic glass–smectite transformation, which is characterised by (i) strong depletion of alkalis and alkaline earths (Ba, Sr) and first transition series elements (Zn, Cu, Cr, Co, Ni), (ii) immobility of highly incompatible elements (Th, Zr, Hf, LREE) and (iii) strong depletion of MREE and HREE. The sigmoid shape of normalised REE pattern is characteristic of glass–smectite transformation by low-temperature acid-sulphate fluids. This transformation also produces significant variations in U/Th values, which offer the opportunity to date the cessation of hydrothermal alteration and to reconstruct the evolution in space and time of hydrothermal activity in a volcanic edifice.     

Bathymay : la structure sous-marine de Mayotte révélée par l'imagerie multifaisceaux

The BATHYMAY marine survey was carried out in January 2004 around the French volcanic island of Mayotte, onboard the research vessel Marion Dufresne 2. Multibeam bathymetry revealed for the first time the morphology of the whole outer slope. Preliminary interpretations show broad canyons that deeply incise the slope, numerous volcanoes and huge landslides. Large submarine plateaus are also highlighted, bounded by steep cliffs and active normal faults. A model for Mayotte is suggested, in which eruptive activity, sometimes influenced by normal faulting, was concentrated along a N140° regional line (the Comoros archipelago axis), with landslide activity concentrated on the northeastern and southwestern flanks of this line. To cite this article: J.-C. Audru et al., C. R. Geoscience 338 (2006).     

13C/12C composition, a novel parameter to study the downward migration of paper sludge in soils?

δ ¹³C values of crop and forest soils were measured 8 years after disposal of paper sewage sludge. The carbon transfer from paper sludge downward to the first humic layer is evidenced by a ¹³C-enrichnient of up to + 5.6‰ due to the input of ¹³C-enriched sludge carbonates. ¹³C/¹²C composition is thus a novel, sensitive parameter to follow the downward transfer of paper sludge carbon.     

The Multiscale TROPIcal CatchmentS critical zone observatory M-TROPICS dataset I: The Nyong River Basin,Cameroon

Simultaneously acquiring time series of climate, hydrology and hydrochemical data over decades on river systems is pivotal to understand the complex interactions involving rock, soil water, air and biota in the Critical Zone, to build integrated modelling and to propose predictive scenarios. Among the Critical Zone Observatories (CZOs) implemented in the past 25 years, only a few are located in the humid Tropics despite the importance of these regions in terms of population density, fast-changing land use, biodiversity hotspots, biomass stock on continents, size of river systems, etc. Since 1994, weathering and erosion processes and fluxes have been investigated at both local (experimental watershed) and regional scales in the Nyong River Basin (Cameroon) which belongs to the Critical Zone Observatories network named Multiscale TROPIcal CatchmentS (M-TROPICS). The data shared by M-TROPICS in Cameroon are: (1) rainfall; (2) air temperature, air relative humidity, wind speed and direction, and global radiation; (3) stream and river water level; (4) pH, electrical conductivity, water temperature and suspended particulate matter (SPM) concentration; (5) major ion, alkalinity and dissolved organic carbon (DOC) concentrations. The dataset already contributed to describe the water partitioning in these tropical humid watersheds, to better understand the factors controlling chemical weathering and physical erosion in tropical ecosystems, particularly the role of organic matter. The dataset also contributed to calculate elemental weathering fluxes and saprolite production rate and to propose denudation rates on tropical cratonic landscapes. Hydrological modelling allowed quantification of the geographical water sources contributing to streamflow. DOC data were used to determine greenhouse-gas emissions and carbon budgets from African inland waters. However, long-term solute concentrations at the outlet of a small tributary of the Nyong River exhibit non-stationary behaviour over the last 26 years. The processes governing those fluctuations are not yet fully understood and might be related to changes in the hydrological regime, land-cover and land-use. The latter highlights the need for longer time-series and continued support for CZOs particularly in the humid tropics.     

Expansion of an invasive coral species over Abrolhos Bank,Southwestern Atlantic

Invasive coral species of the genus Tubastraea have been increasingly recorded in Southwestern Atlantic waters since the 1980s. Their invasion and infestation are mainly related to port and oil exploration activities. For the first time the presence of Tubastraea tagusensis colonies is reported in Espírito Santo State, colonizing a port shore area, and incrusting oil/gas platform structures situated in the southern Abrolhos Bank, which is part of the most important coral reef system of the South Atlantic Ocean. Tubastraea colonies exhibit fast growth and high recruitment rates, and colonized 40% of the analyzed structures in just four years. The projection of port and oil/gas industry growth for the Espírito Santo State (more than 300%) highlights an alert to the dispersal of this alien species to natural areas.     

Environmental flows in hydro-economic models

The protection of environmental flows, as a management objective for a regulating agency, needs to be consistent with the aquifer water balance and the degree of resource renewability. A stylized hydro-economic model is used where natural recharge, which sustains environmental flows, is considered both in the aquifer water budget and in the welfare function as ecosystem damage. Groundwater recharge and the associated natural drainage may be neglected for aquifers containing fossil water, where the groundwater is mined. However, when dealing with an aquifer that constitutes a renewable resource, for which recharge is not negligible, natural drainage should explicitly appear in the water budget. In doing so, the optimum path of net extraction rate does not necessarily converge to the recharge rate, but depends on the costs associated with ecosystem damages. The optimal paths and equilibrium values for the water volume and water extraction are analytically derived, and numerical simulations based on the Western La Mancha aquifer (southwest Spain) illustrate the theoretical results of the study.