象牙海岸Issia地区铌钽砂矿的研究(英文)

在西非的象牙海岸Issia地区分布着许多铌钽矿床,包括原生矿和砂矿。原生矿产在分带很好的伟晶岩中。这个地区发育着许多花岗岩和花岗伟晶岩。伟晶岩可分为:(1)分异不好的伟晶岩,无矿化;(2)含Be伟晶岩,分带较好,见绿柱石;(3)含Be-Nb-Ta的伟晶岩,分带很好,是矿体;(4)Be-Nb-Ta-Li伟晶岩,分带很好,是矿体。除了10多个原生矿外,还有许多砂矿。砂矿有两种类型:一种近原生矿的坡积砂矿,另一种是经河流冲刷搬运后的冲积砂矿。我们选择了Etienne-Meguhe砂矿作为近原生矿的坡积砂矿的代表,Bemadi矿作为河流冲积型的砂矿的代表,对这两种类型的砂矿的风化、搬运、沉积机理进行了比较研究。研究发现不同的搬运距离和搬运模式对铌钽砂矿的主要矿物——铌钽铁矿的化学性质没有什么影响,而其物理形态则发生了变化。坡积型砂矿的铌钽铁矿常与石英、长石等矿物连生,其颗粒大小与原生的Nb-Ta伟晶岩中的铌钽铁矿一致;经河流冲积而形成的砂矿中,铌钽铁矿颗粒变小、轮廓变得圆滑,几乎无连生矿物,但矿体集中,常在河流的冲积扇中分布,易开采。     

Coupled redox transformations of catechol and cerium at the surface of a cerium(III) phosphate mineral

Highly insoluble Ce-bearing phosphate minerals form by weathering of apatite [Ca₅(PO₄)₃.(OH,F,Cl)], and are important phosphorous repositories in soils. Although these phases can be dissolved via biologically-mediated pathways, the dissolution mechanisms are poorly understood. In this paper we report spectroscopic evidence to support coupling of redox transformations of organic carbon and cerium during the reaction of rhabdophane (CePO₄·H₂O) and catechol, a ubiquitous biogenic compound, at pH 5. Results show that the oxic–anoxic conditions influence the mineral dissolution behavior. Under anoxic conditions, the release of P and Ce occurs stoichiometrically. In contrast, under oxic conditions, the mineral dissolution behavior is incongruent, with dissolving Ce³⁺ ions oxidizing to CeO₂. Reaction product analysis shows the formation of CO₂, polymeric C, and oxalate and malate. The presence of more complex forms of organic carbon was also confirmed. Near edge X-ray absorption fine structure spectroscopy measurements at Ce-M_4,5 and C-K absorption edges on reacted CePO₄·H₂O samples in the absence or presence of catechol and dissolved oxygen confirm that (1) the mineral surface converts to the oxide during this reaction, while full oxidation is limited to the near-surface region only; (2) the Ce valence remains unchanged when the reaction between CePO₄·H₂O and O₂ but in the absence of catechol. Carbon K-edge spectra acquired from rhabdophane reacted with catechol under oxic conditions show spectral features before and after reaction that are considerably different from catechol, indicating the formation of more complex organic molecules. Decreases in intensity of characteristic catechol peaks are accompanied by the appearance of new π^* resonances due to carbon in carboxyl (ca. 288.5 eV) and carbonyl (ca. 289.3 eV) groups, and the development of broad structure in the σ^* region characteristic of aliphatic carbon. Evolution of the C K-edge spectra is consistent with aromatic-ring cleavage and polymerization. These results further substantiate that the presence of catechol, O₂ (aq) causes both the oxidation of structural Ce³⁺ and the transformation of catechol to more complex organic molecules. Scanning Transmission X-Ray Microscopy measurements at the C K and Ce M_4,5 edges indicate three dominant organic species, varying in complexity and association with the inorganic phase. Untransformed catechol is loosely associated with CeO₂, whereas more complex organic molecules that exhibit lower aromaticity and stronger CO π^* resonances of carboxyl-C and carbonyl-C groups are only found in association with the grains. These results further serve as basis to postulate that, in the presence of O₂, CeO₂ can mediate the oxidative polymerization of catechol to form higher molecular weight polymers. The present work provides evidence for a pathway of biologically-induced, non-enzymatic oxidation of cerium and formation of small CeO₂ particles at room temperature. These findings may have implications for carbon cycling in natural and cerium-contaminated soils and aqueous environments.     

Carbon isotope fractionation in phospholipid fatty acid biomarkers of bacteria and fungi native to an acid mine drainage lake

This study identifies isotope signatures associated with autotrophic and heterotrophic microbial communities that may provide a means to determine carbon cycling relationships in situ for acid mine drainage (AMD) sites. Stable carbon isotope ratios (δ¹³C) of carbon sources, bulk cells, and membrane phospholipids (PLFA) were measured for autotrophic and heterotrophic microbial enrichment cultures from a mine tailings impoundment in northern Ontario, Canada, and for pure strains of the sulfur oxidizing bacteria Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. The autotrophic enrichments had indistinguishable PLFA distributions from the pure cultures, and the PLFA cyc-C_19:0 was determined to be a unique biomarker in this system for these sulfur oxidizing bacteria. The PLFA distributions produced by the heterotrophic enrichments were distinct from the autotrophic distributions and the C_18:2 PLFA was identified as a biomarker for these heterotrophic enrichments. Genetic analysis (16S, 18S rRNA) of the heterotrophic cultures indicated that these communities were primarily composed of Acremonium fungi.Stable carbon isotope analysis revealed that bulk cellular material in all autotrophic cultures was depleted in δ¹³C by 5.6–10.9‰ relative to their atmospheric CO₂ derived carbon source, suggesting that inorganic carbon fixation in these cultures is carbon limited. Individual PLFA from these autotrophs were further depleted by 8.2–14.6‰ compared to the bulk cell δ¹³C, which are among the largest biosynthetic isotope fractionation factors between bulk cell and PLFA reported in the literature. In contrast, the heterotrophic bulk cells were not significantly fractionated in δ¹³C relative to their carbon source and heterotrophic PLFA ranged from 3‰ enriched to 4‰ depleted relative to the isotopic composition of their total biomass. These distinct PLFA biomarkers and isotopic fractionations associated with autotrophic and heterotrophic activity in this laboratory study provide potential biomarkers for delineating autotrophic and heterotrophic carbon cycling in AMD environments.     

Characteristics of carbonaceous particles in Beijing during winter and summer 2003

Campaigns were conducted to measure Organic Carbon (OC) and Elemental Carbon (EC) in PM2.5 during winter and summer 2003 in Beijing. Modest differences of PM2.5 and PM10 mean concentrations were observed between the winter and summer campaigns. The mean PM2.5/PM10 ratio in both seasons was around 60%, indicating PM2.5 contributed significantly to PM10. The mean concentrations of OC and EC in PM2.5 were 11.2±7.5 and 6.0±5.0μg m-3 for the winter campaign, and 9.4±2.1 and 4.3±3.0 μg m-3 for the summer campaign, respectively. Diurnal concentrations of OC and EC in PM2.5 were found high at night and low during the daytime in winter, and characterized by an obvious minimum in the summer afternoon. The mean OC/EC ratio was 1.87±0.09 for winter and Z39±0.49 for summer. The higher OC/EC ratio in summer indicates some formation of Secondary Organic Carbon (SOC). The estimated SOC was 2.8 μg m-3 for winter and 4.2μg m-3 for summer.     

Climate feedbacks determined using radiative kernels in a multi-thousand member ensemble of AOGCMs

The use of radiative kernels to diagnose climate feedbacks is a recent development that may be applied to existing climate change simulations. We apply the radiative kernel technique to transient simulations from a multi-thousand member perturbed physics ensemble of coupled atmosphere-ocean general circulation models, comparing distributions of model feedbacks with those taken from the CMIP-3 multi GCM ensemble. Although the range of clear sky longwave feedbacks in the perturbed physics ensemble is similar to that seen in the multi-GCM ensemble, the kernel technique underestimates the net clear-sky feedbacks (or the radiative forcing) in some perturbed models with significantly altered humidity distributions. In addition, the compensating relationship between global mean atmospheric lapse rate feedback and water vapor feedback is found to hold in the perturbed physics ensemble, but large differences in relative humidity distributions in the ensemble prevent the compensation from holding at a regional scale. Both ensembles show a similar range of response of global mean net cloud feedback, but the mean of the perturbed physics ensemble is shifted towards more positive values such that none of the perturbed models exhibit a net negative cloud feedback. The perturbed physics ensemble contains fewer models with strong negative shortwave cloud feedbacks and has stronger compensating positive longwave feedbacks. A principal component analysis used to identify dominant modes of feedback variation reveals that the perturbed physics ensemble produces very different modes of climate response to the multi-model ensemble, suggesting that one may not be used as an analog for the other in estimates of uncertainty in future response. Whereas in the multi-model ensemble, the first order variation in cloud feedbacks shows compensation between longwave and shortwave components, in the perturbed physics ensemble the shortwave feedbacks are uncompensated, possibly explaining the larger range of climate sensitivities observed in the perturbed simulations. Regression analysis suggests that the parameters governing cloud formation, convection strength and ice fall speed are the most significant in altering climate feedbacks. Perturbations of oceanic and sulfur cycle parameters have relatively little effect on the atmospheric feedbacks diagnosed by the kernel technique.     

Using Decision Analysis to Include Climate Change in Water Resources Decision Making

Is the prospect of possible climate change relevant to water resources decisions being made today? And, if so, how ought that prospect be considered? These questions can be addressed by decision analysis, which we apply to two investments in the Great Lakes region: a regulatory structure for Lake Erie, and breakwaters to protect Presque Isle State Park, PA. These two decisions have the elements that potentially make climate change relevant: long lived, "one shot" investments; benefits or costs that are affected by climate-influenced variables; and irreversibilities. The decision analyses include the option of waiting to obtain better information, using Bayesian analysis to detect whether climate change has altered water supplies. The analyses find that beliefs about climate change can indeed affect optimal decisions. Furthermore, ignoring the possibility of climate change can lead to significant opportunity losses—in the cases here, as much as 10% or more of the construction cost. Yet the consequences of climate uncertainty for Great Lakes management do not appear to be qualitatively different from those of other risks, and thus do not deserve different treatment. The methods of sensitivity analysis, scenario planning, and decision analysis, all of which are encouraged under US federal guidelines for water planning, are applicable. We recommend increased use of decision trees and Bayesian analysis to consider not only climate change risks, but also other important social and environmental uncertainties.     

Potential mechanistic causes of increased baseflow across northern Eurasia catchments underlain by permafrost

Warming in the Arctic is occurring at twice the rate of the global average, resulting in permafrost thaw and a restructuring of the Arctic hydrologic cycle as indicated by increased stream discharge during low-flow periods. In these cold regions, permafrost thaw is postulated to increase low-flow discharge, or baseflow, through either: (a) localized increases in groundwater storage and discharge to streams due to increased aquifer transmissivity from thickening of the freeze–thaw layer above permafrost known as the active layer or (b) long-term increases in regional groundwater circulation via enhancement of groundwater–surface water interactions due to extensive permafrost loss over decades. While increasing baseflow has been observed throughout northern Eurasia, the precise mechanistic causes remain elusive. In this study, we differentiate between where these two subsurface physical mechanisms of baseflow increase are occurring by performing a baseflow recession analysis using daily streamflow records from 1913 to 2003 for 139 stations in northern Eurasia underlain by varying permafrost areal extents. Results indicate that from 1913 to 2003, the majority of catchments underlain by continuous permafrost have an increasing trend in their recession flow intercepts, a proxy for increasing active layer thickness. Alternatively, the majority of catchments underlain by permafrost types that are less spatially extensive (e.g., discontinuous, sporadic, isolated, or no permafrost) have decreasing trends in their recession flow intercepts, indicating that a potential increase in active layer thickness is not the driving factor of baseflow variations in these catchments. This may indicate that in catchments underlain by continuous permafrost, active layer thickening correlates with increases in baseflow, whereas, in other catchments with less extensive permafrost, increases in baseflow may be caused by wholesale permafrost loss and vertical talik expansion that enhances regional groundwater circulation. The results of this work may inform our understanding of the subsurface mechanisms responsible for the changing Arctic hydrologic cycle.     

Ecometrics and the paleoecological implications of Pleistocene faunas from the western coastal plains of the Cape Floristic Region,South Africa

The Pleistocene ungulate communities from the western coastal plains of South Africa's Cape Floristic Region (CFR) are diverse and dominated by grazers, in contrast to the region's Holocene and historical faunas, which are relatively species-poor and dominated by small-bodied browsers and mixed feeders. An expansion of grassy habitats is clearly implied by the Pleistocene faunas, but the presence of ruminant grazers that cannot survive the summer dry season typical of the region today suggests other important paleoecological changes. Here we use dental ecometrics to explore the paleoecological implications of the region's Pleistocene faunas. We show that the dental traits (hypsodonty and occlusal topography) of the ungulates that occurred historically in the CFR track annual and summer aridity, and we use these relationships to reconstruct past aridity. Our results indicate that the Pleistocene faunas signal paleoenvironments that were on average less arid than today, including during the summer, consistent with other lines of evidence that suggest a higher water table and expansion of well-watered habitats. Greater water availability can be explained by lower temperature and reduced evapotranspiration during cooler phases of the Pleistocene, probably coupled with enhanced groundwater recharge due to increased winter precipitation.     

Dynamic adaptive pathways in downscaled climate change scenarios

The parallel scenario process enables characterization of climate-related risks and response options to climate change under different socio-economic futures and development prospects. The process is based on representative concentration pathways, shared socio-economic pathways, and shared policy assumptions. Although this scenario architecture is a powerful tool for evaluating the intersection of climate and society at the regional and global level, more specific context is needed to explore and understand risks, drivers, and enablers of change at the national and local level. We discuss the need for a stronger recognition of such national-scale characteristics to make climate change scenarios more relevant at the national and local scale, and propose ways to enrich the scenario architecture with locally relevant details that enhance salience, legitimacy, and credibility for stakeholders. Dynamic adaptive pathways are introduced as useful tools to draw out which elements of a potentially infinite scenario space connect with decision-relevant aspects of particular climate-related and non-climate-related risks and response options. Reviewing adaptation pathways for New Zealand case studies, we demonstrate how this approach could bring the global-scale scenario architecture within reach of local-scale decision-making. Such a process would enhance the utility of scenarios for mapping climate-related risks and adaptation options at the local scale, involving appropriate stakeholder involvement.     

The impact of future climate change and potential adaptation methods on Maize yields in West Africa

Using recent advances in statistical crop yield modelling and a unique dataset consisting of yield time series for Russian regions over the period from 1955 to 2012, the study investigates the potential impact of climate change (CC) on the productivity of the three most important grains. Holding current grain growing areas fixed, the aggregate productivity of the three grains is predicted to decrease by 6.7% in 2046–2065 and increase by 2.6% in 2081–2100 compared to 1971–2000 under the most optimistic representative emission concentration pathway (RCP). Based on the projections for the three other RCPs, the aggregate productivity of the three studied crops is assessed to decrease by 18.0, 7.9 and 26.0% in the medium term and by 31.2, 25.9 and 55.4% by the end of the century. Our results indicate that CC might have a positive effect on winter wheat, spring wheat and spring barley productivity in a number of regions in the Northern and Siberian parts of Russia. However, due to the highly damaging CC impact on grain production in the most productive regions located in the South of the country, the overall impact tends to be negative. Therefore, a shift of agricultural production to the Northern regions of the country could reduce the negative impact of CC on grain production only to a limited extent. More vigorous adaptation measures are required to maintain current grain production volumes in Russia under CC.