Rare earth element geochemistry in cold-seep pore waters of Hydrate Ridge, northeast Pacific Ocean   总被引：2，自引：1，他引：1  

Tobias Himmler  Brian A. Haley  Marta E. Torres  Gary P. Klinkhammer  Gerhard Bohrmann  Jörn Peckmann 《Geo-Marine Letters》2013,33(5):369-379

The concentrations of rare earth elements (REEs), sulphate, hydrogen sulphide, total alkalinity, calcium, magnesium and phosphate were measured in shallow (<12 cm below seafloor) pore waters from cold-seep sediments on the northern and southern summits of Hydrate Ridge, offshore Oregon. Downward-decreasing sulphate and coevally increasing sulphide concentrations reveal sulphate reduction as dominant early diagenetic process from ~2 cm depth downwards. A strong increase of total dissolved REE (∑REE) concentrations is evident immediately below the sediment–water interface, which can be related to early diagenetic release of REEs into pore water resulting from the re-mineralization of particulate organic matter. The highest pore water ∑REE concentrations were measured close to the sediment–water interface at ~2 cm depth. Distinct shale-normalized REE patterns point to particulate organic matter and iron oxides as main REE sources in the upper ~2-cm depth interval. In general, the pore waters have shale-normalized patterns reflecting heavy REE (HREE) enrichment, which suggests preferential complexation of HREEs with carbonate ions. Below ~2 cm depth, a downward decrease in ∑REE correlates with a decrease in pore water calcium concentrations. At this depth, the anaerobic oxidation of methane (AOM) coupled to sulphate reduction increases carbonate alkalinity through the production of bicarbonate, which results in the precipitation of carbonate minerals. It seems therefore likely that the REEs and calcium are consumed during vast AOM-induced precipitation of carbonate in shallow Hydrate Ridge sediments. The analysis of pore waters from Hydrate Ridge shed new light on early diagenetic processes at cold seeps, corroborating the great potential of REEs to identify geochemical processes and to constrain environmental conditions.  相似文献   

A parsimonious crop-water productivity index: an application to Brazil     

Marco P Maneta  Purnendu N Singh  Marcelo Torres  Wesley W Wallender  Stephen A Vosti  Lineu N Rodrigues  Luis H Bassoi  Julie A Young 《Area》2009,41(1):94-106

Reducing poverty in rural areas of developing countries requires sustained and sustainable increases in agricultural water productivity. However, aside from traditional measures of precipitation, little is known about water available to farmers or how productively they use it. We present a crop-water productivity index (a ratio of the value of annual crop production to a dimensionless potential water availability index) for large water basins using readily available low-resolution data. The index is transferable, permits direct inter-basin comparisons, and is simple to calculate. We calculate the index for each municipality in the São Francisco river basin in Brazil. No clear patterns linking water availability and value of agricultural output are evident, even though clusters of municípios with high- and low-crop-water productivity emerge, and the former may be useful in guiding policies aimed at increasing water productivity. Finally, analyses of the effects of information uncertainty on the crop-water productivity index suggest that the returns to agricultural investments in certain places in the São Francisco river basin are more risky than others. Improvements in data quality and quantity can help refine estimates of the index and reduce their uncertainty.  相似文献   

Overview of the geography of the Monte Desert biome (Argentina)     

E. Abraham  H.F. del Valle  F. Roig  L. Torres  J.O. Ares  F. Coronato  R. Godagnone 《Journal of Arid Environments》2009,73(2):144-153

The compilation of published results on the geography of the Monte Desert biome of Argentina that we present here offers a review of its boundaries and ecotones, and of its biophysical and socio-economic characteristics. In relation to socio-ecological issues, the focus is on a case study in the province of Mendoza. An analysis is presented about the ecological-economic issues and the sustainable investment policies in rangelands of the Patagonian Monte. In addition, this biome is compared with other South American arid biomes and their North American counterparts. We identified some gaps in the current knowledge, especially at a mesoscale level, where studies on Monte borders are deemed necessary as well as explicit boundary criteria for ecosystem differentiation. Also the ecological-economic relations and feedbacks between livestock herbivory, soil erosion and market behaviour should be considered within the framework of wider socio-ecological research.  相似文献   

Sky luminance distribution in the North of Iberian Peninsula during winter     

J.L. Torres  M. de Blas  A. García  A. Gracia  A. de Francisco 《Journal of Atmospheric and Solar》2010,72(16):1147-1154

This work is based on the study of outdoor daylight conditions during the winter period in Pamplona (the Iberian Peninsula). The 15 standard sky types proposed by the Commission Internationale de l’Eclairage (CIE) are used. The selected sky type in each moment is the one exhibiting the lowest root mean standard deviation (RMSD) when the theoretical and experimental luminance distributions in the sky hemisphere are compared. The selection was derived from luminance distribution data from 145 patches of the sky hemisphere and registered every 10 min from October to March from 2007 and 2008.The most frequent sky type observed in winter in Pamplona is V.5 (cloudless polluted with a broad solar corona), with a frequency of occurrence of 21%. Notwithstanding, the group of overcast skies exhibits a slightly higher frequency (40%) than the clear skies (37%). Seven out of the 15 standard sky types, i.e.V.5, I.1, III.4, II.1, IV.4, II.2 and III.3, are practically 80% of those under study. In order to provide a possible application in daylight climates studies, the frequency of occurrence of the 15 sky types is included in eleven intervals of solar elevation on the threshold corresponding to the time period and the location considered.  相似文献   

Accurate X-ray position and multiwavelength observations of the isolated neutron star RBS 1774     

N. Rea  M. A. P. Torres  P. G. Jonker  R. P. Mignani  S. Zane  M. Burgay  D. L. Kaplan  R. Turolla  G. L. Israel  D. Steeghs 《Monthly notices of the Royal Astronomical Society》2007,379(4):1484-1490

  相似文献   

Models for Support and Information Effects: A Comparative Study   总被引：1，自引：0，他引：1  

Xavier Emery  Juan F. Soto Torres 《Mathematical Geology》2005,37(1):49-68

The recoverable reserves in an ore deposit depend on several factors, in particular the size of the selective mining units (support effect) and the misclassifications when sending these units to mill or dump according to their estimated grade (information effect). Both effects imply a loss of selectivity and have to be correctly forecasted. In this work, several models are reviewed and applied to a synthetic ore deposit characterized by a highly skewed grade histogram and a spatial connectivity of high grades. The affine correction, mosaic correction, and discrete Gaussian model are compared when assessing the global recoverable reserves, whereas local estimations are performed by indicator kriging with affine correction, bigaussian disjunctive kriging, and multigaussian conditional expectation. Despite their convenience and simplicity, distribution-free methods like affine correction or indicator kriging have a poorer accuracy than the other methods. In the global framework, the discrete Gaussian model is a better alternative and is based on mild assumptions. Local estimations are not accurate and may be improved by resorting to a more suitable parametric model or to conditional simulations.  相似文献   

Using the DPFT approach to improve flash flood forecasting models     

D. Sempere Torres  J. Y. Rodriguez  Ch. Obled 《Natural Hazards》1984,5(1):17-41

DPFT is a lumped approach for operational flash flood forecasting, based on the unit hydrograph. Using a multi-event alternating iterative algorithm, it identifies a robust and stable average transfer function and a consistent set of effective rainfall series associated with each event at the same time. This key ingredient allows an objective calibration of different loss functions, relating gauged precipitation and effective rainfall. A case study based on an operational French basin (545 km²) is presented. Three lumped production functions have been calibrated and compared. The results show that more elaborate models of loss functions must be proposed, and some possible directions for this are pointed out.Presently at the Institut de Ciences de la Terra Jaume Almera, Apartat 30102, 08080 Barcelona, Spain.Presently at EDF-DTG. Service de Ressources en Eau, BP 4348, 31029 Toulouse Cedex, France.  相似文献   

Monocolumn behavior in waves: Experimental analysis   总被引：1，自引：0，他引：1  

S.H. Sphaier  F.G.S. Torres  I.Q. Masetti  A.P. Costa  C. Levi 《Ocean Engineering》2007,34(11-12):1724-1733

A series of tests with a model of a monocolumn platform with a moonpool were performed at the LabOceano/COPPE, at the Universidade Federal do Rio de Janeiro, with the objective of determining the entrance area at the bottom of the moonpool that minimizes vertical motion in waves. The tests include measurements of monocolumn surge, pitch and heave motion, vertical motion of the water column inside the moonpool, with different mooring systems, in regular, irregular and transient waves.This paper presents experimental results of the monocolumn vertical motion and the internal water column motion in the moonpool in transient waves and results of vertical motion of the water column inside the moonpool with the model held still in transient waves. These measurements allow an analysis of the impact of the moonpool's bottom opening on the monocolumn vertical motion in waves.The theoretical analysis of a mass–spring–damper system with two degrees of freedom, similar to the studied system, has shown some analogy with den Hartog's damped vibration absorber; however, there are significant differences in terms of added mass and coupled terms of added mass and damping coefficients dependent on oscillation frequencies.  相似文献   

Cosmology after COBE     

Sergio Torres 《Astrophysics and Space Science》1995,228(1-2):313-325

The measured anisotropies in the temperature of the cosmic microwave background radiation (CMB) by the Cosmic Background Explorer (COBE) are consistent with models of gravitational collapse for the formation of large scale structure in the universe. The amplitude of cosmological fluctuations on the largest scales is fixed by COBE. From COBE's data it is also possible to test for the shape of the primordial spectrum. Statistical tests using COBE's two year data and based on the geometric characteristics of anisotropy spots taking into account cosmic variance and the relevant experimental details indicate that the primordial spectrum has a slope in the rangen = 0.8 – 1.3. Possible identification of hot and cold spots of cosmological origin is also given.Presented at the Fourth United Nations/European Space Agency Workshop on Basic Space Science. Cairo, Egypt, 27 June - 1 July 1994.  相似文献   

Migration and Development? The Gendered Costs of Migration on Mexico's Rural “Left Behind”          下载免费PDF全文

Rebecca M. Torres  Lindsey Carte 《Geographical review》2016,106(3):399-420

Governments, civil society, and policymakers assert the potential of international migration to foster development and alleviate poverty. Often such claims are rooted in macroscale geopolitical analyses of migration and development, which mask the localized, uneven, and embodied ways family members “left behind” bear the costs and subsidize the U.S./Mexico (inter)national integration project. Informed by feminist geopolitics, this article demonstrates how the left behind disproportionately bear the hidden costs of neoliberal restructuring and migration. We draw upon Mexican Migration Project (MMP) ethnosurvey data to frame the narratives of migrant family members left behind. Narratives were constructed through in‐depth interviews conducted in rural Veracruz. We conclude that in the absence of geographically specific examinations of the hidden costs associated with neoliberal development and migration it is possible that “migration for development” programs and policies may exacerbate inequities that will perpetuate migration and further weaken Mexican origin communities.  相似文献