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Diaz-Hernandez J.L.,IFAPA Camino de Purchil | Sanchez-Navas A.,University of Granada | Sanchez-Navas A.,Instituto Andaluz Of Ciencias Of La Tierra Iact Csic Ugr | Reyes E.,Instituto Andaluz Of Ciencias Of La Tierra Iact Csic Ugr
Chemical Geology | Year: 2013

Dolomite formation in soils constitute a particular challenge because of: 1) scant magnesium content in continental environments as opposed to the marine medium, 2) the kinetic problem related to the incorporation of magnesium into the carbonate, and 3) the unknown role of soil dolomites in the global carbon cycle. Pedogenic dolomite formed at deeper soil levels (subsoil) before the development of petrocalcic horizon barriers was investigated in a semiarid region of SE Spain (Guadix-Baza basin). Mineralogical characterization, textural relationships and isotopic data concerning soil dolomite, together with the results of a precipitation experiment, provided fuller knowledge of the processes and conditions governing neoformation of dolomite in these soils. In the study case, dolomite enrichment occurs beyond the limit of major biological activity, which coincides with the rooting depth of native perennial plants in the semiarid soils studied. Textural studies reveal the corrosion of inherited dolomite crystals in the upper soil horizons and the formation of dolomite in depth in relation to a clayey material, composed mainly of smectites. Stable isotope distribution in dolomites throughout the profiles indicates a fractionation with depth. This is explained by the formation of dolomites after the dissolution of the pedogenic calcite. The calcite detected in the subsoil is interpreted here as a precursor of the neoformed dolomites that transport the isotopic signal associated with biological activity of soils to deeper layers. Dolomite formation appears to be favoured by the presence of clay minerals in the precipitation media. Clays retain water during evapotranspiration stages, which drastically change the transport properties of the media and promote the incorporation of Mg into the structure of the neoformed Ca,Mg-carbonate. As confirmed by laboratory experiments, diffusion-controlled crystal-growth processes lead to the formation a precursory "protodolomite" with disordered Ca,Mg distribution from a fluid locally supersaturated in dolomite. © 2013 Elsevier B.V. Source

Cardenas-Parraga J.,University of Granada | Garcia-Casco A.,University of Granada | Garcia-Casco A.,Instituto Andaluz Of Ciencias Of La Tierra Iact Csic Ugr | Harlow G.E.,American Museum of Natural History | And 3 more authors.
European Journal of Mineralogy | Year: 2012

Jadeitite (jadeite jade) from Sierra del Convento (eastern Cuba) occurs in a subduction-related serpentinite-matrix mélange associated with a variety of high-pressure tectonic blocks including garnet-amphibolites and related anatectic trondhjemites. The eastern Cuban jadeitite is massive and characterized by rare quartz inclusions and omphacite exsolution in jadeite crystals, as well as replacement or infilling by omphacite. Minor minerals include epidote, biotite, albite, phengite, titanite, rutile, zircon, and apatite. Oscillatory zoning in jadeite crystals and zircon ages suggest hydrothermal crystallization in veins formed in serpentinized peridotite, probably of the mantle wedge. Al-Na-Mg-Ca-bearing fluids of variable composition but high pH (capable of mobilizing Zr and Hf at SiO2-subsaturated conditions) deposited jadeitite in veins during episodic opening of the fractures at depth in the subduction environment. Late-stage crystallizations include omphacite, albite and epidote from fluids nearly saturated in SiO 2. The compositional gap of two coexisting pyroxenes indicates a temperature of jadeite formation higher than 500 °C. Zircon Pb/U ages of 107.4 ± 0.5 Ma and 107.8 ±1.1 Ma attest formation during the earliest stages of subduction in the region. These ages and the high temperature of formation of jadeitite suggest a genetic link between the jadeite-forming fluids and fluids derived from associated anatectic trondhjemites crystallized at depth (15 kbar). © 2012 E. Schweizerbart'sche Verlagsbuchhandlung. Source

Mladenov N.,University of Granada | Mladenov N.,University of Colorado at Boulder | Sommaruga R.,University of Innsbruck | Morales-Baquero R.,University of Granada | And 9 more authors.
Nature Communications | Year: 2011

Remote lakes are usually unaffected by direct human influence, yet they receive inputs of atmospheric pollutants, dust, and other aerosols, both inorganic and organic. In remote, alpine lakes, these atmospheric inputs may influence the pool of dissolved organic matter, a critical constituent for the biogeochemical functioning of aquatic ecosystems. Here, to assess this influence, we evaluate factors related to aerosol deposition, climate, catchment properties, and microbial constituents in a global dataset of 86 alpine and polar lakes. We show significant latitudinal trends in dissolved organic matter quantity and quality, and uncover new evidence that this geographic pattern is influenced by dust deposition, flux of incident ultraviolet radiation, and bacterial processing. Our results suggest that changes in land use and climate that result in increasing dust flux, ultraviolet radiation, and air temperature may act to shift the optical quality of dissolved organic matter in clear, alpine lakes. © 2011 Macmillan Publishers Limited. All rights reserved. Source

Moleon M.,University of Witwatersrand | Almaraz P.,Instituto Andaluz Of Ciencias Of La Tierra Iact Csic Ugr | Sanchez-Zapata J.A.,University Miguel Hernandez
European Journal of Wildlife Research | Year: 2013

In a previous study, we suggested that hyperpredation by shared predators on red-legged partridges (Alectoris rufa), once a parasite (rabbit haemorrhagic disease, RHD) had decimated populations of rabbit (Oryctolagus cuniculus), the primary prey for most of the Mediterranean predators, was a major force driving partridge population dynamics in Spain years ago (Moleón et al., PLoS One 3:e2307, 2008). Recently, however, Blanco-Aguiar et al. (Eur J Wildl Res 58:433-439, 2012) have asserted that this conclusion is poorly evidence-based and can subsequently promote raptor persecution by hunters. In response to Blanco-Aguiar and colleagues, here we provide complementary insights that favour our earlier hypothesis. After explaining several key concepts of the hyperpredation process, we use additional data and analyses to show that (1) a synchronised regime shift (i.e. a step, abrupt change in population size) to significantly lower population levels in both the rabbit and partridge populations took place coinciding with the RHD outbreak; (2) rabbit and partridge population dynamics were highly synchronised after the RHD outbreak, but not before; (3) an enhanced spatial autocorrelation at all the spatial scales emerged after RHD for partridge populations; and (4) the main shared predators' diet patterns were consistent with the hypothesis of enhanced predation pressure as a plausible mechanism behind the observed partridge dynamics. We support the idea that hunting bag data may be useful to infer realistic population dynamics and the ecological mechanisms explaining them, provided that (1) they are corrected by the number of hunting licenses; (2) appropriate statistical tools are employed; and (3) methodological constraints are adequately taken into account. Finally, we argue that the opinion of Blanco-Aguiar and colleagues that our original results can lead to raptor persecution is a misinterpretation of our study. In this sense, we make an appeal for the importance of accurately differentiating between the ultimate (e.g. infectious diseases favoured by humans) and the proximate (e.g. enhanced predation pressure) causes of the decline in prey of economic interest (e.g. game species) in order to avoid unnecessary, unfounded or presumed conflicts with lobbies of conservation concern (e.g. hunters). © 2013 Springer-Verlag Berlin Heidelberg. Source

Capaccioni B.,University of Bologna | Menichetti M.,Urbino University | Renzulli A.,Urbino University | Tassone A.,University of Buenos Aires | Huertas A.D.,Instituto Andaluz Of Ciencias Of La Tierra Iact Csic Ugr
Geofluids | Year: 2013

The geothermal area of Rio Valdez is located in the central portion of the Isla Grande de Tierra del Fuego (South Argentina), ten kilometers south of the southeastern sector of the Fagnano Lake. It consists of a series of thermal springs with low discharge rates (≤1L/s) and temperatures in the range of 20-33°C distributed in an area of <1km2. The thermal springs are characterized by alkaline, Na-HCO3 waters with low salinity (0.53÷0.58g/L), but relatively high fluoride contents (up to 19.4mg/L). Their composition is the result of a slow circulation at depth, possibly through deep tectonic discontinuities connected with the Magallanes-Fagnano Fault (MFF) system. According to geothermometric calculations, thermal waters reach temperatures in the range of 100-150°C and an almost complete chemical equilibrium with the alkali-feldspars in the metavolcanic country rocks. The relatively high fluorine contents can be explained by the slow ascent and cooling of deep groundwaters followed by a progressive re-equilibration with F-bearing, hydrated Mg-silicates, such as chlorite, which has been recognized as an abundant mineral in the metavolcanics of the Lemaire Formation and metapelites and metagraywackes of the Yahgán Formation. Finally, the isotopic composition of the investigated samples is consistent with the infiltration from local snow melting at altitudes in the range of 610-770m asl. The comparison of our data with those collected in 1991 seems to suggest a possible progressive decline of the bulk thermal output in the near future. This possibility should be seriously considered before planning a potentially onerous exploitation of the resource. Presently, the only ways to exploit this geothermal resource by the population scattered in the area are the direct use of thermal waters and/or spa structures. © 2012 Blackwell Publishing Ltd. Source

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