Aspects of the geology, petrology and chemistry of some Angolan carbonatites

Using published data and the results of a new study, the main characteristics of seven Angolan carbonatite complexes are here presented. With the exception of the Lupongola complex which intrudes anorthosites, the remaining complexes are hosted by Precambrian silicic rocks. The complexes are of central or dike type and are well exposed. They represent some of the seven morpholithological types present in the province and have some intermediate lithochemical features between those of Brazilian and East African examples.Sovites at Lupongola are the richest in Sr and F, and also have the highest CaO/MgO and La/Y ratios of all sovites studied. Carbonatites from Bonga and Bailundo are the richest in P₂O₅, while those from Coola and Longonjo are the richest in BaO. Ferrocarbonatites from Bailundo and Virulundo have the highest REE contents. TiO₂ contents are usually low. Only Bonga carbonatites show well-defined variation between Ba and Mn contents and the index CaO/(CaO+Fe₂O₃+FeO+MnO+MgO).The CO₂-SiO₂-(Al₂O₃+Na₂O+K₂O) diagram distinguishes silicified carbonatites, feldspar-bearing carbonatites in which the main silicate mineral is K-feldspar, carbonatites and fenites. Potassic fenitization of country rocks is well developed at Bailundo, Bonga and Virulundo, and probably it also affected cogenetic nepheline syenites at Tchivira and Monte Verde.Fluorcarbonates of Ca and REE are encountered in all chemical varieties of carbonatites, and crystallized during late stages of rock formation. They have a strong influence both on total REE contents and on the slopes of chondrite-normalized patterns. Fluorapatite and pyrochlore are other important potential REE host minerals in the rocks studied. The REE patterns usually have discrete negative Ce anomalies, and sometimes show very discrete negative Eu anomalies. Apart from these anomalies, some rocks have very near-linear patterns, but most show inflections, which may occur between light and middle, and between middle and heavy REE. The origins of these variations are still uncertain.Other aspects of rock geochemistry show that, while some features could be explained by crystal fractionation differentiation processes, late-stage or secondary chemical modifications were widespread.     

Multiple methods for estimating the bispectrum of the cosmic microwave background with application to the MAXIMA data

We describe different methods for estimating the bispectrum of cosmic microwave background data. In particular, we construct a minimum-variance estimator for the flat-sky limit and compare results with previously studied frequentist methods. Application to the MAXIMA data set shows consistency with primordial Gaussianity. Weak quadratic non-Gaussianity is characterized by a tunable parameter   f _NL  , corresponding to non-Gaussianity at a level of  ∼10⁻⁵ f _NL  (the ratio of non-Gaussian to Gaussian terms), and we find limits of   f _NL= 1500 ± 950  for the minimum-variance estimator and   f _NL= 2700 ± 1650  for the usual frequentist estimator. These are the tightest limits on primordial non-Gaussianity, which include the full effects of the radiation transfer function.     

New ICP‐MS Results for Trace Elements in Five Iron‐Formation Reference Materials

Iron formations (IFs) typically contain low mass fractions of most trace elements, including the rare earth elements (REE), and few publications describe analytical methods dedicated to this matrix. In this study, we used bomb and table‐top acid dissolution procedures and ICP‐MS to determine the mass fractions of trace elements in IF reference materials FER‐1, FER‐2, FER‐3, FER‐4 and IF‐G. The full digestion of the IF samples with the bomb procedure required the addition of a small amount of water together with the acids. The results obtained by this method mostly agreed statistically with published values. The most remarkable exception was the higher values obtained for the heavy REE in FER‐3. The recoveries of the REE obtained with the table‐top procedure were slightly higher than those of the bomb digestion, except for the values of the heavy REE in FER‐3 and FER‐4, which were up to 30% lower than published values. Sintering of the samples with sodium peroxide was performed to determine the REE, but the results tended to be lower than those derived following acid digestion. On the whole, the recoveries showed dependence on the conditions of digestion, but subtle differences in trace mineral composition between samples also exerted influence on the analytical results for trace elements.     

New constraints from the Hα line for the temperature of the transiting planet host star OGLE‐TR‐10

The spectroscopic analysis of systems with transiting planets gives strong constraints on planetary masses and radii as well as the chemical composition of the systems. The properties of the system OGLE‐TR‐10 are not well‐constrained, partly due to the discrepancy of previous measurements of the effective temperature of the host star. This work, which is fully independent from previous works in terms of data reduction and analysis, uses the Hα profile in order to get an additional constraint on the effective temperature. We take previously published UVES observations which have the highest available signal‐to‐noise ratio for OGLE‐TR‐10. A proper normalization to the relative continuum is done using intermediate data products of the reduction pipeline of the UVES spectrograph. The effective temperature then is determined by fitting synthetic Hα profiles to the observed spectrum. With a result of T_eff = 6020 ± 140 K, the Hα profile clearly favours one of the previous measurements. The Hα line is further consistent with dwarf‐like surface gravities as well as solar and super‐solar metallicities previously derived for OGLE‐TR‐10.The Hα line could not be used to its full potential, partly because of the varying shape of the UVES échelle orders after flat field correction. We suggest to improve this feature when constructing future spectrographs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Colour Hue and Texture Evaluation for 3D Symbolization of Indoor Environments Using RGB-D Data

In this work an evaluation procedure of the use of colour hue and texture for 3D symbolization of indoor environments using RGB-D data is presented. The main characteristics of the proposed method involve RGB-D cameras to collect colour and depth data and the evaluation of the visual variables colour hue and texture combined with visual aspects such as lighting and camera configuration for the symbolization of 3D indoor environments. High quality coloured point clouds of indoor environments are obtained with the Kinect sensor and then registered and processed in order to create 3D models. These sets of point clouds can be detected, recognized and classified under one of the three following main categories: ceiling, wall or floor. After classification is done, the resulting point clouds are properly treated as 3D triangular meshes in the MeshLab software. These meshes are then filtered to form complete surfaces which are then refined before being considered for visual variable application. We evaluated the proposed method on several indoor environments to show that it efficiently combines the colour and depth data obtained from RGB-D cameras with different parameters defined for the visual variables colour hue and texture for 3D symbolization of indoor environments.     

Dimensionality reduction in drought modelling

For monitoring hydrological events characterized by high spatial and temporal variability, the number and location of recording stations must be carefully selected to ensure that the necessary information is collected. Depending on the characteristics of each natural process, certain stations may be spurious or redundant, whereas others may provide most of the relevant data. With the objective of reducing the costs of the monitoring system and, at the same time, improving its operational effectiveness, three procedures were applied to identify the minimum network of rain gauge stations able to capture the characteristics of droughts in mainland Portugal. Drought severity is characterized by the standardized precipitation index applied to the timescales of 1, 3, 6 and 12 consecutive months. The three techniques used to reduce the dimensionality of the network of rain gauges were as follows: (i) artificial neural networks with sensitivity analysis, (ii) application of the mutual information criterion and (iii) K‐means cluster analysis using Euclidean distances. The results demonstrated that the best dimensionality reduction method was case dependent in the three regions of Portugal (northern, central and southern) previously identified by cluster analysis. All the reduction techniques lead to the selection of a subset of rain gauges capable of reproducing the original temporal patterns of drought. For specific severe drought events in Portugal in the past, the comparison between drought spatial patterns obtained with the original stations and the selected subset indicated that the subset produced statistically satisfactory results (correlation coefficients higher than 0.6 and efficiency coefficients higher than 0.5). Copyright © 2012 John Wiley & Sons, Ltd.     

Reply to ‘Comment on: Rainfall,fog and throughfall dynamics in a subtropical ridge top cloud forest,National Park of Garajonay (La Gomera,Canary Islands,Spain)’ by A. Ritter and C.M. Regalado

This Reply aims to clarify and address many of the errors introduced to the discussion of our original paper (García‐Santos and Bruijnzeel, 2011; referred to henceforth as GSB2011) in the comment by Ritter and Regalado (2012) (henceforth referred to as RRR2012) as explained more fully under replies nos. 1–6, 8–12 and 14–18 below. Two (largely inconsequential) shortcomings in our original paper as detected by RRR2012 are acknowledged (see replies nos. 7 and 13 below). It is concluded that the majority of the comments offered by RRR2012 are unfounded as well as unnecessary. In summary, the two errors in GSB2011 spotted by RRR2012 (see points 7 and 13 below) could easily have been addressed in an erratum. Copyright © 2013 John Wiley & Sons, Ltd.     

Land use change effects on catchment streamflow response in a humid tropical montane cloud forest region,central Veracruz,Mexico

Tropical montane cloud forests (TMCF) are recognized for their capacity to maintain high dry-season baseflow and a host of other ecosystem services. Substantial areas of TMCF have been converted to pasture and crops such as coffee, while in other areas TCMF are recovering. However, little is known about the effects of this complex dynamic on catchment hydrology. We investigated the effect of land use on rainfall-runoff response in five neighbouring headwater micro-catchments in central Veracruz, Mexico, dominated by either mature TMCF (MF), young (20 year-old) and intermediate (40 year-old) naturally regenerating TMCF (YF and IF, respectively), shaded coffee (SC), and an intensively grazed pasture (IP). We used a 4-year record of high-resolution rainfall and streamflow (10 min) data collected from 2015 to 2019. These data were analysed via comparison of hydrologic metrics that summarize streamflow responses at various time scales and magnitudes. Results showed no statistical difference in the regulation capacity of high flows in the micro-catchment with 20 years of natural regeneration, compared to the MF. In terms of baseflow sustenance, our results support the hypothesis that MF and IF better promote this hydrologic service than the other land uses. SC exhibited a high capacity to modulate peak flows comparable to that of MF, and an intermediate capacity to sustain baseflow, suggesting that the integrated functioning of this micro-catchment was largely preserved. Finally, 40 years of intense pasture management was found to have degraded the soil hydraulic properties of IP; mainly, reducing its infiltration capacity, causing a fivefold greater peak flow response and a lower baseflow compared to MF.     

Optimal filtering high-resolution seismic reflection data using a weighted-mode empirical mode decomposition operator

Gas-hydrate related processes in deep-water marine settings exist on spatial scales that challenge conventional seismic reflection profiling to successfully image them. The conventional approach to acoustic identification of buried hydrates is to use advanced, cost-prohibitive survey techniques and highly customized software to define subsurface structure wherein compositional changes may be modeled and/or interpreted. This study adopts a different approach derived from recent theoretical advancements in signal processing. The method consists in optimal filtering high resolution, single-channel seismic reflection data using the Empirical Mode Decomposition (EMD). The time series is decomposed in sub-components and the noisy portions are suppressed adopting the technique that we referred as Weighted Mode(s) EMD. The optimal filtering greatly improves the resolution and fidelity of the seismic data set.High Resolution single channel seismic profiles, acquired over a carbonate\hydrates site in the northern Gulf of Mexico, manipulated in such way, show a complex, shallow subsurface, and suggest potential evidence for buried gas hydrates.     

Isotopic composition of precipitation during strong El Niño–Southern Oscillation events in the Southeast Region of Brazil

Equatorial Pacific sea surface temperature variations interact with processes of atmospheric circulation, creating conditions for the occurrence of El Niño–Southern Oscillation (ENSO). ENSO events represent the most important interannual phenomena affecting climate patterns worldwide and causing significant socio‐economic impacts. In the Brazilian territory, ENSO leads to an increase in drought episodes in the north‐eastern region and an increase in precipitation in the southern region, whereas the effects over the south‐east region are yet not well understood. The main goal of this study is to compare variations of isotopic composition in precipitation across the south‐east portion of the Brazilian territory during two very strong ENSO events: 1997–1998 (ENSO 1) and 2014–2016 (ENSO 2). Daily isotopic records, available from the Global Network of Isotopes in Precipitation database for ENSO 1, and samples collected during ENSO 2 were used to compare the influence of both events on the isotopic composition of precipitation. Seasonal variations indicated more depleted precipitation during the wet seasons (δ¹⁸O = ?5.4 ± 4.0‰) and enriched precipitation during the dry seasons (δ¹⁸O = ?2.8 ± 2.3‰). Observed rainfall variations were associated with atmospheric large‐scale processes and moisture transport from the Amazon region, whereas extreme values (enriched or depleted) appear to be associated with particular convective and stratiform precipitation events. Overall, more depleted isotopic composition of precipitation (δ¹⁸O = ?4.60‰) and higher d‐excess (up to +15‰) were observed during the dry season of ENSO 1 when compared with ENSO 2 dry season (δ¹⁸O‰ = ?2.80‰, d‐excess lower than +14‰). The latter is explained by greater atmospheric moisture content, particularly associated with recycling of transpiration fluxes from the Amazon region, during dry season of ENSO 1. No significant differences for δ¹⁸O and δ²H were observed during the wet season; however, d‐excess from ENSO 2 was greater than ENSO 1, due to the slightly greater atmospheric moisture content and very strong upward motion observed. Our findings highlight the opportunity that environmental isotopes offer towards understanding hydrometeorological processes, particularly, the evolution of extreme climatic events of global resonance such as ENSO.