Role of stochastic forcing in ENSO in observations and a coupled GCM

A procedure is presented to estimate the role of atmospheric stochastic forcing (SF) in El Ni?o–Southern Oscillation (ENSO) simulated by a coupled ocean–atmosphere general circulation model (CGCM), in direct comparison to observations represented by a global reanalysis product. SF is extracted from the CGCM and reanalysis as surface wind anomalies linearly independent of the sea-surface temperature anomalies. Madden–Julian Oscillation (MJO) is isolated from SF to quantify its role in ENSO. A coupled ocean–atmosphere model of intermediate complexity is forced with SF, as well as its MJO and non-MJO components, from the reanalysis and CGCM. The role of SF is estimated by comparing the original ENSO in observations and the CGCM with that reproduced by the intermediate model. ENSO statistics in both reanalysis and CGCM are better reproduced when the intermediate model is tuned to be weakly stable than unstable. The intermediate model driven by SF from the reanalysis reproduces most characteristics of observed ENSO, such as its spectrum, seasonal phase-locking, fast decorrelation of ENSO SST during boreal spring, and its lag-correlation with SF. In contrast, not all characteristics of ENSO in the CGCM are reproduced by the intermediate model when SF from the CGCM is used. The seasonal phase-locking of ENSO in the CGCM is not reproduced at all. ENSO, therefore, appears to be driven by SF to a lesser degree in the CGCM than in observations. Characteristics of observed ENSO reproduced by the intermediate model (driven by SF) can be largely attributed to the MJO; which, for instance, is responsible for the fast decorrelation of ENSO SST during boreal spring in both reanalysis and CGCM. The non-MJO component seems to be more responsible than the MJO for erroneous features of ENSO in the CGCM.     

Evaluation of mineral precipitation potential in a spent nuclear fuel repository

In this study, the potential for mineral precipitation reactions to occur during the excavation, disposal, backfilling and closure of a deep geological repository for the final disposal of spent nuclear fuel was evaluated with the assistance of hydrogeochemical modelling. Four modelling exercises, corresponding to the main expectable geochemical scenarios in the Excavation Damaged Zone (EDZ) throughout repository evolution, were carried out and the times for sealing of the discontinuities owing to mineral precipitation in each of them were evaluated and discussed. The simulations show that mineral precipitation reactions are thermodynamically feasible in most of the studied cases. The main mineral phases potentially responsible for the hydraulic sealing of the EDZ are calcite and ferric oxyhydroxides, being the estimated volumes occupied by the precipitation of calcite between one and three orders of magnitude larger than the volume of precipitating ferric phases. The estimated times for complete sealing of the EDZ may vary between several hundreds to more than 1 million years. The shortest sealing times (less than 3,000 years) are obtained for the mixture of groundwaters from the repository depth with dilute infiltration waters.     

Hydrochemistry of Lakes of the Patagonian Province of Tierra del Fuego (Argentina)

Chemical studies on 19 lakes of the Argentine sector of the Patagonian Tierra del Fuego Island were performed. These lakes are placed in two geological provinces, Extra Andine (northern) and Fueguian Cordillera (southern). Range of the results obtained, pH (5.80–8.60), TDS (29.5–10,232 mg/l), ionic composition (from calcium bicarbonate to sodium chloride type), Secchi disc depth (0.05–12 m), total inorganic nitrogen (20–237 μg N/l), orthophosphate (5–498 μg P/l), total phosphorus (5–3,800 μg P/l) and chlorophyll a (0.1–63.0 μg/l), indicated the presence of a wide variety of aquatic ecosystems. According to Gibbs model, the mechanisms that control the water chemistry are mainly rock dominance and evaporation–crystallization processes.     

Monitoring study of the mine pond reclamation of Mina Concepción, Iberian Pyrite Belt (Spain)

Mining of massive (Cu, Pb and Zn) sulphide bodies in the Iberian Pyrite Belt (SW Spain) has generated a great number of abandoned waste deposits such as mine ponds. These represent large accumulations of reactive minerals and subsequently, emission sources of trace elements and formation of acid drainage. Even if they have been restored, monitoring studies are required to evaluate the corrective effects and how they may change over time. This work presents the results of a monitoring study carried out at Mine Concepción mine pond, based on mineralogical (XRD), geochemical (INAA, X-ray fluorescence, ICP-MS) and geophysical (electrical resistivity tomography) techniques. In it, a series of relevant parameters have been well delimited, such as the infilling thickness and its variation and, the position, geometry and absence of water leakages through the base of the mine pond. Additionally, the existence of an internal, remnant flow of acid waters that tends to come out through the pond dyke has been identified. Chemistry of these waters indicates that oxidation processes affecting the Mina Concepción mine tailings are generating acid drainage waters which could potentially release substantial amounts of trace elements to the river Odiel. Thus, giving that not complete sealing is accomplished by the restoration capping and rainfall water infiltrates into the pond materials, at least the sealing of the dyke through which leakages occur should be revised.     

The effect of recent climatic trends on Urticaceae pollination in two bioclimatically different areas in the Iberian Peninsula: Malaga and Vigo

Malaga (Mediterranean coast) and Vigo (Atlantic coast) are representative of two bioclimatically different areas belonging to the Mediterranean and the Eurosiberian region, respectively. This contribution represents a study on recent trends in the principal meteorological parameters in these areas and their influence on the phenology of Urticaceae (nettle family) atmospheric pollen, one of the main causes of pollinosis in Spain. The study covers the period 1991–2006 for Malaga and 1995–2005 for Vigo, and compares the differences in climate and phenological behaviour observed at both localities. The sampling of atmospheric pollen was performed with Hirst volumetric pollen traps. The two localities present different tendencies as far as temperature is concerned: while the mean annual temperature in the Mediterranean region has increased by 0.06°C/year, the same parameter has decreased in the Atlantic area by 0.1°C/year. This tendency is even more pronounced as far as the minimum temperatures are concerned, especially during spring in Malaga and autumn in Vigo. On the other hand, wind speed has tended to increase, periods of calm have diminished and winds blowing off the sea have increased in both places. These changes in meteorological parameters have advanced the end of the pollen season in Malaga and delayed its start in Vigo. Total annual pollen counts have decreased in Vigo, while the number of pollen-free days has increased in both areas.     

Oxygen isotope fractionation in synthetic magnesian calcite

Mg-bearing calcite was precipitated at 25°C in closed system free-drift experiments from solutions containing NaHCO₃, CaCl₂ and MgCl₂. The chemical and isotope composition of the solution and precipitate were investigated during time course experiments of 24-h duration. Monohydrocalcite and calcite precipitated early in the experiments (<8 h), while Mg-calcite was the predominant precipitate (>95%) thereafter. Solid collected at the end of the experiments displayed compositional zoning from pure calcite in crystal cores to up to 23 mol% MgCO₃ in the rims. Smaller excursions in Mg were superimposed on this chemical record, which is characteristic of oscillatory zoning observed in synthetic and natural solid-solution carbonates of differing solubility. Magnesium also altered the predominant morphology of crystals over time from the {104} to {100} and {110} growth forms.The oxygen isotope fractionation factor for the magnesian-calcite-water system (as 10³lnα_Mg-cl-H2O) displayed a strong dependence on the mol% MgCO₃ in the solid phase, but quantification of the relationship was difficult due to the heterogeneous nature of the precipitate. Considering only the Mg-content and δ¹⁸O values for the bulk solid, 10³lnα_Mg-cl-H2O increased at a rate of 0.17 ± 0.02 per mol% MgCO₃; this value is a factor of three higher than the single previous estimate (Tarutani T., Clayton R.N., and Mayeda T. K. (1969) The effect of polymorphims and magnesium substitution on oxygen isotope fractionation between calcium carbonate and water. Geochim. Cosmochim. Acta 33, 987-996). Nevertheless, extrapolation of our relationship to the pure calcite end member yielded a value of 27.9 ± 0.02, which is similar in magnitude to published values for the calcite-water system. Although no kinetic effect was observed on 10³lnα_Mg-cl-H2O for precipitation rates that ranged from 10^3.21 to 10^4.60 μmol · m⁻² · h⁻¹, it was impossible to disentangle the potential effect(s) of precipitation rate and Mg-content on 10³lnα_Mg-cl-H2O due to the heterogeneous nature of the solid.The results of this study suggest that paleotemperatures inferred from the δ¹⁸O values of high magnesian calcite (>10 mol% MgCO₃) may be significantly underestimated. Also, the results underscore the need for additional experiments to accurately characterize the effect of Mg coprecipitation on the isotope systematics of calcite from a chemically homogeneous precipitate or a heterogeneous material that is analyzed at the scale of chemical and isotopic zonation.     

A Sustainability Framework for Enhancing the Long-Term Success of Lulucf Projects

Collateral impacts of land use and land-use change and forestry (LULUCF) projects, especially those concerning social and environmental aspects, have been recognized as important by the Marrakech Accords. The same applies to the necessity of assessing and, if possible, of quantifying the magnitude of these impacts. This article aims to define, clarify and structure the relevant social, economic and environmental issues to be addressed and to give examples of indicators that ought to be included in the planning, design, implementation, monitoring, and ex post evaluation of LULUCF projects. This is being done by providing a conceptual framework for the assessment of the sustainability of such projects that can be used as a checklist when dealing with concrete projects, and that in principle is applicable to both Annex I and non-Annex I countries. Finally, a set of recommendations is provided to further develop and promote the proposed framework.     

Stratified sampling of satellite images with a systematic grid of points

Sampling satellite images presents some specific characteristics: images overlap and many of them fall partially outside the studied region. A careless sampling may introduce an important bias. This paper illustrates the risk of bias and the efficiency improvements of systematic, pps (probability proportional to size) and stratified sampling.A sampling method is proposed with the following criteria: (a) unbiased estimators are easy to compute; (b) it can be combined with stratification; (c) within each stratum, sampling probability is proportional to the area of the sampling unit; and (d) the geographic distribution of the sample is reasonably homogeneous. Thiessen polygons computed on image centres are sampled through a systematic grid of points. The sampling rates in different strata are tuned by dividing the systematic grid into subgrids or replicates and taking for each stratum a certain number of replicates.The approach is illustrated with an application to the estimation of the geometric accuracy of Image2000, a Landsat ETM+ mosaic of the European Union.     

The Cretaceous iron belt of northern Chile: role of oceanic plates,a superplume event,and a major shear zone

The Cretaceous constitutes a turning point in the tectonic, magmatic, and metallogenic history of Chile. The geological evidence indicates that a major change occurred in late Neocomian time when superplume emplacement (Mid-Pacific Superplume) and plate reorganization processes took place in the Pacific. The superplume event resulted in a major ridge-push force resulting in increased coupling between the subducting and overriding plates. This completely changed the tectonic setting of Chile ending the Early Cretaceous extensional period (aborted rifting in the back-arc basin), and increasing stress at a crustal scale. As a consequence, overpressurized dioritic magmas were pushed up mainly along the best possible structural path in northern Chile, i.e., the Atacama Fault Zone, eventually forming a +500-km-long belt of Kiruna-type iron deposits with reserves of ~2,000 Mt (60% Fe), a unique case in Chile's geological history.