Graphite–sulfide deposits in Ronda and Beni Bousera peridotites (Spain and Morocco) and the origin of carbon in mantle-derived rocks     

E. Crespo  F.J. Luque  M. Rodas  H. Wada  F. Gervilla 《Gondwana Research》2006,9(3):279-290

This paper describes unusual graphite–sulfide deposits in ultramafic rocks from the Serranía de Ronda (Spain) and Beni Bousera (Morocco). These deposits occur as veins, stockworks and irregular masses, ranging in size from some centimeters to a few meters in thickness. The primary mineral assemblage mainly consists of Fe–Ni–Cu sulfides (pyrrhotite, pentlandite, chalcopyrite and cubanite), graphite and chromite. Weathering occurs in some sulfide-poor deposits that consist of graphite (up to 90%), chromite and goethite. Texturally, graphite may occur as flakes or clusters of flakes and as rounded, nodule-like aggregates. Graphite is highly crystalline and shows light carbon isotopic signatures (δ¹³C≈− 15‰ to − 21‰). Occasionally, some nodule-like graphite aggregates display large isotopic zoning with heavier cubic forms (probably graphite pseudomorphs after diamond with δ¹³C up to − 3.3‰) coated by progressively lighter flakes outwards (δ¹³C up to − 15.2‰).Asthenospheric-derived melts originated the partial melting (and melt–rock reactions) of peridotites and pyroxenites generating residual melts from which the graphite–sulfide deposits were formed. These residual melts concentrated volatile components (mainly CO₂ and H₂O), as well as S, As, and chalcophile elements. Carbon was incorporated into the melts from the melt–rock reactions of graphite-bearing (formerly diamonds) garnet pyroxenites with infiltrated asthenospheric melts. Graphite-rich garnet pyroxenites formed through the UHP transformation of subducted kerogen-rich crustal material into the mantle. Thus, graphite in most of the studied occurrences has light (biogenic) carbon signatures. Locally, reaction of the light carbon in the melts with relicts of ¹³C-enriched graphitized diamonds (probably generated from hydrothermal calcite veins in the subducting oceanic crust) reacted with the partial melts to form isotopically zoned nodule-like graphite aggregates.  相似文献   

Attitude stability of a gravity-stabilized gyrostat satellite     

Marcelo R. M. Crespo da Silva 《Celestial Mechanics and Dynamical Astronomy》1970,2(2):147-165

This paper treats analytically the problem of the stability of the attitude motions of a gravity-stabilized gyrostat satellite that is in a circular orbit around a spherical planet. The vehicle considered consists of a body with no special symmetries that has any number of rotors attached to it. The internal angular momentum vector due to these rotors is parallel to one of the principal axes of the entire satellite; this axis is aligned with (or close to) the normal to the orbit plane. Both the cases in which each rotor is driven by a motor at a constant spin rate relative to the main body of the vehicle and the one in which each rotor is rotating freely, without any friction, are treated. Stability (both infinitesimal and in the sense of Liapunov) of the attitude motions of the vehicle can be quickly predicted by using the results derived here, which are summarized in the form of a continuous, three-dimensional, stability diagram.National Research Council Post-Doctoral Research Associate at NASA-Ames Research Center, Moffett Field, Calif. Parts of this research were included in [12].  相似文献   

The historical (218 ± 14 aBP) explosive eruption of Tutupaca volcano (Southern Peru)     

Pablo Samaniego  Patricio Valderrama  Jersy Mariño  Benjamín van Wyk de Vries  Olivier Roche  Nélida Manrique  Corentin Chédeville  Céline Liorzou  Lionel Fidel  Judicaëlle Malnati 《Bulletin of Volcanology》2015,77(6):1-18

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High-frequency multi-solute calibration using an in situ UV–visible sensor     

Juan Pesántez  Christian Birkel  Giovanny M. Mosquera  Pablo Peña  Viviana Arízaga-Idrovo  Emma Mora  William H. McDowell  Patricio Crespo 《水文研究》2021,35(9):e14357

Monitoring the temporal variation of solute concentrations in streams at high temporal frequency can play an important role in understanding the hydrological and biogeochemical behaviour of catchments. UV–visible spectrometry is a relatively inexpensive and easily used tool to infer those concentrations in streams at high temporal resolution. However, it is not yet clear which solutes can be modelled with such an in-situ sensor. Here, we installed a UV–visible spectrometer probe (200–750 nm) in a high-altitude tropical Páramo stream to record the wavelength absorbance at a 5-min temporal resolution. For calibration, we simultaneously sampled stream water at a 4-h frequency from February 2018 to March 2019 for subsequent laboratory analysis. Absorbance spectra and laboratory-determined solute concentrations were used to identify the best calibration method and to determine which solute concentrations can be effectively inferred using in situ spectrometry through the evaluation of six calibration methods of different mathematical complexity. Based on the Nash – Sutcliffe efficiency (NSE) and Akaike information criterion metrics, our results suggest that multivariate methods always outperformed simpler strategies to infer solute concentrations. Eleven out of 21 studied solutes (Al, DOC, Ca, Cu, K, Mg, N, Na, Rb, Si and Sr) were successfully calibrated (NSE >0.50) and could be inferred using UV–visible spectrometry even with a reduced daily sampling frequency. It is worth noting that most calibrated solutes were correlated with wavelengths (WLs) in the low range of the spectra (i.e., UV range) and showed relatively good correlation with DOC. The latter suggests that estimation of metal concentrations could be possible in other streams with a high organic load (e.g., peat dominated catchments). In situ operation of spectrometers to monitor water quality parameters at high temporal frequency (sub-hourly) can enhance the protection of human water supplies and aquatic ecosystems as well as providing information for assessing catchment hydrological functioning.  相似文献   

Catchment scale hydrology of an irrigated cropping system under soil conservation practices          下载免费PDF全文

Patricio Cid  Helena Gómez‐Macpherson  Hakim Boulal  Luciano Mateos 《水文研究》2016,30(24):4593-4608

Soil erosion by water is a pressing environmental problem caused and suffered by agriculture in Mediterranean environments. Soil conservation practices can contribute to alleviating this problem. The aim of this study is to gain more profound knowledge of the effects of conservation practices on soil losses by linking crop management and soil status to runoff and sediment losses measured at the outlet of a catchment during seven years. The catchment has 27.42 ha and is located in a commercial farm in southern Spain, where a package of soil conservation practices is an essential component of the farming system. The catchment is devoted to irrigated annual crops with maize–cotton–wheat as the primary rotation. Mean annual rainfall‐induced runoff coefficient was 0.14 and mean annual soil loss was 2.4 Mg ha^?1 y^?1. Irrigation contributed to 40% of the crop water supply, but the amount of runoff and sediment yield that it generated was negligible. A Principal Components Analysis showed that total soil loss is determined by the magnitude of the event (rainfall and runoff depths, duration) and by factors related to the aggressiveness of the events (rainfall intensity and preceding soil moisture). A third component showed the importance of crop coverage to reduce sediment losses. Cover crops grown during autumn and early winter and crop residues protecting the soil surface enhanced soil conservation notably. The role of irrigation to facilitate growing cover crops in Mediterranean environments is discussed. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Pollen–climate reconstruction from northern South Island,New Zealand (41°S), reveals varying high‐ and low‐latitude teleconnections over the last 16 000 years          下载免费PDF全文

Ignacio A. Jara  Rewi M. Newnham  Marcus J. Vandergoes  Courtney R. Foster  David J. Lowe  Janet M. Wilmshurst  Patricio I. Moreno  James A. Renwick  Aline M. Homes 《第四纪科学杂志》2015,30(8):817-829

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Possible mixotrophy of pigmented nanoflagellates: Microbial plankton biomass, primary production and phytoplankton growth in the NW Iberian upwelling in spring     

B.G. Crespo  O. Espinoza-GonzálezI.G. Teixeira  C.G. CastroF.G. Figueiras 《Estuarine, Coastal and Shelf Science》2011,94(2):172-181

Microbial plankton biomass, primary production (PP) and phytoplankton growth rates (μ) were estimated along the NW Iberian margin during an upwelling relaxation event. Although the interaction between wind forcing and coastline singularities caused high spatial variability in PP (0.4-8.4 g C m⁻² d⁻¹), two domains (coastal and oceanic) could be distinguished regarding microbial plankton biomass and μ. At the coastal domain, with higher influence of upwelling, diatoms showed an important contribution (27 ± 17%) to total autotrophic biomass (AB). Nonetheless, AB was dominated by autotrophic nanoflagellates (ANF) at both realms, accounting for 62 ± 16% and 89 ± 6% of the integrated AB at the coastal and oceanic domain respectively. AB and heterotrophic biomass (HB) were significantly higher at the oceanic than at the coastal domain, with both biomasses covarying according to HB:AB = 0.33. Whereas the low phytoplankton carbon to chlorophyll a ratio (C_ph:chl a = 38 ± 3) and the high μ = 0.54 ± 0.09 d⁻¹ registered at the coastal stations suggest that phytoplankton was not nutrient limited at this domain, the values (C_ph:chl a = 157 ± 8; μ = 0.17 ± 0.02 d⁻¹) recorded at the oceanic domain point to severe nutrient limitation. However, the high Fv/Fm fluorescence ratios (0.56 ± 0.09) measured at the sea surface in the oceanic domain suggest that nutrient limitation did not occur. To reconcile these two apparently opposite views, it is suggested the occurrence of mixotrophic nutrition of ANF, with heterotrophic nutrition supplying about 75% of carbon requirements.  相似文献   

Extrusion vs. accretion at the frictional–viscous décollement transition in experimental thrust wedges: the role of convergence velocity     

María Lujn  Fabrizio Storti  Federico Rossetti  Ana Crespo‐Blanc 《地学学报》2006,18(4):241-247

In many cases, thrust wedges accreted at shallow crustal levels show an across‐strike rheological variability along the basal décollement, notably from brittle to ductile behaviour. In this paper, we illustrate the results of sandbox analogue modelling research devoted to studying the influence of convergence velocity on wedge architecture when laterally juxtaposed frictional and viscous materials occur along the basal décollement of accreting thrust wedges. Our results show that slow convergence favours a near symmetrical distribution of thrust vergence within wedge sectors accreted above viscous décollement material, whereas fast convergence favours vergence asymmetry. In particular, at fast convergence rates the hinterlandward extrusion of viscous décollement material at the toe of the frictional wedge is favoured and contributed to accommodate a significant amount of the total contraction. Terra Nova, 18, 241–247, 2006  相似文献   

Low-pH Freshwater Discharges Drive Spatial and Temporal Variations in Life History Traits of Neritic Copepod Acartia tonsa     

Victor M. Aguilera  Cristian A. Vargas  Patricio H. Manríquez  Jorge M. Navarro  Cristian Duarte 《Estuaries and Coasts》2013,36(5):1084-1092

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Temperate rainforest response to climate change and disturbance agents in northwestern Patagonia (41°S) over the last 2600 years     

Ignacio A. Jara  Patricio I. Moreno 《Quaternary Research》2012,77(2):235-244

We present detailed pollen and charcoal records from Lago Pichilafquén (~ 41°S) to decipher the effects of climate change and varying disturbance regimes on the composition and structure of the vegetation on the Andean foothills of northwestern Patagonia during the last 2600 yr. Here, temperate rainforests have dominated the landscape since 2600 cal yr BP with variations ranging from cool-temperate and wet north Patagonian rainforests to relatively warm and summer-drought-resistant Valdivian rainforests. We interpret relatively warm/dry conditions between 1900–2600, 690–750 and 320–430 cal yr BP, alternating with cold/wet conditions between 1500–1900, 750–1100 and 430–690 cal yr BP. Rapid deforestation and spread of plants introduced by Europeans occurred at 320 and 140 cal yr BP. The record includes five tephras with ages of 2130, 1460, 1310, 1210, and 340 cal yr BP, all of which precede local fire events and increases in trees favored by disturbance by less than 100 yr. We conclude that centennial-scale changes in the southern westerlies were the primary driver of vegetation shifts in northwestern Patagonia over the last 2600 yr. Within this interval, local disturbance regimes altered the structure, composition, and dynamics of the lowland rainforest vegetation during several discrete, short-lived episodes.  相似文献