The Sahara–Sahel Dust Corridor runs from Chad to Mauritania and expels huge amounts of mineral aerosols into the Atlantic Ocean. Data on samples collected from Algeria, Chad, Niger, and Western ...Sahara illustrate how corridor dust mineralogy and chemistry relate to geological source and weathering/transport history. Dusts sourced directly from igneous and metamorphic massifs are geochemically immature, retaining soluble cations (e.g., K, Na, Rb, Sr) and accessory minerals containing HFSE (e.g., Zr, Hf, U, Th) and REE. In contrast, silicate dust chemistry in desert basins (e.g., Bodélé Depression) is influenced by a longer history of transport, physical winnowing (e.g., loss of Zr, Hf, Th), chemical leaching (e.g., loss of Na, K, Rb), and mixing with intrabasinal materials such as diatoms and evaporitic salts. Mineral aerosols blown along the corridor by the winter Harmattan winds mix these basinal and basement materials. Dusts blown into the corridor from sub-Saharan Africa during the summer monsoon source from deeply chemically weathered terrains and are therefore likely to be more kaolinitic and stripped of mobile elements (e.g., Na, K, Mg, Ca, LILE), but retain immobile and resistant elements (e.g., Zr, Hf, REE). Finally, dusts blown southwestwards into the corridor from along the Atlantic Coastal Basin will be enriched in carbonate from Mesozoic–Cenozoic marine limestones, depleted in Th, Nb, and Ta, and locally contaminated by uranium-bearing phosphate deposits.
Abstract
Daily heterothermy is a strategy employed by endothermic birds and mammals to reduce their energetic costs by lowering their metabolic rate. We recorded nocturnal and diurnal rectal ...temperatures in three Moroccan
Gerbillus
rodent species to determine the level of heterothermy. A decrease in body temperature from night to day was observed by an average (±SD) of 8.7 (±4.2) in
G. gerbillus
, 11.1 (±3.0) in
G. amoenus
, and 7.7 (±3.3)°C in
G.
sp.1, the first records of heterothermy in the three species. The findings support a prediction that daily heterothermy is found in mammals from arid and semi-arid regions, contributing to further knowledge of thermoregulation in desert rodents.
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•RAD-seq data corroborate division of Gerbillus into four subgenera with high support.•Genealogical discordance is restricted to one branch leading to the main ...lineages.•Diversification of the genus coincides with aridification of Sahara.•Species boundaries in studied species of Gerbillus are well defined.•RAD-seq data confirm usefulness of cyt-b as a barcode marker in Gerbillus.
Gerbillus is one of the most speciose genera among rodents, with ca. 51 recognized species. Previous attempts to reconstruct the evolutionary history of Gerbillus mainly relied on the mitochondrial cyt-b marker as a source of phylogenetic information. In this study, we utilize RAD-seq genomic data from 37 specimens representing 11 species to reconstruct the phylogenetic tree for Gerbillus, applying concatenation and coalescence methods. We identified four highly supported clades corresponding to the traditionally recognized subgenera: Dipodillus, Gerbillus, Hendecapleura and Monodia. Only two uncertain branches were detected in the resulting trees, with one leading to diversification of the main lineages in the genus, recognized by quartet sampling analysis as uncertain due to possible introgression. We also examined species boundaries for four pairs of sister taxa, including potentially new species from Morocco, using SNAPP. The results strongly supported a speciation model in which all taxa are treated as separate species. The dating analyses confirmed the Plio-Pleistocene diversification of the genus, with the uncertain branch coinciding with the beginning of aridification of the Sahara at the the Plio-Pleistocene boundary. This study aligns well with the earlier analyses based on the cyt-b marker, reaffirming its suitability as an adequate marker for estimating genetic diversity in Gerbillus.
Saharan dust incursions and particulates emitted from human activities degrade air quality throughout West Africa, especially in the rapidly expanding urban centers in the region. Particulate matter ...(PM) that can be inhaled is strongly associated with increased incidence of and mortality from cardiovascular and respiratory diseases and cancer. Air samples collected in the capital of a Saharan–Sahelian country (Bamako, Mali) between September 2012 and July 2013 were found to contain inhalable PM concentrations that exceeded World Health Organization (WHO) and US Environmental Protection Agency (USEPA) PM2.5 and PM10 24-h limits 58 – 98% of days and European Union (EU) PM10 24-h limit 98% of days. Mean concentrations were 1.2-to-4.5 fold greater than existing limits. Inhalable PM was enriched in transition metals, known to produce reactive oxygen species and initiate the inflammatory response, and other potentially bioactive and biotoxic metals/metalloids. Eroded mineral dust composed the bulk of inhalable PM, whereas most enriched metals/metalloids were likely emitted from oil combustion, biomass burning, refuse incineration, vehicle traffic, and mining activities. Human exposure to inhalable PM and associated metals/metalloids over 24-h was estimated. The findings indicate that inhalable PM in the Sahara–Sahel region may present a threat to human health, especially in urban areas with greater inhalable PM and transition metal exposure.
•PM2.5 and PM10 exceeded air quality limits 58–98% of days sampled in Bamako, Mali.•PM10 contains potentially biotoxic and bioactive metals and metalloids.•PM10 is predominately from crustal material; anthropogenic emissions are secondary.•Inhalable particulate levels may threaten human health in urban West Africa.
Abstract
Background matching, a common form of camouflage, is a widespread anti-predator adaptation that hinders detection or recognition by increasing the resemblance of prey to its environment. ...However, the natural environment is complex and both spatially and temporally variable, which constrains effective background matching as an anti-predator strategy. Here, using remote sensing data (publicly available satellite imagery), we investigated how variation of habitat parameters predicts background matching in 16 Sahara–Sahel rodent species across spatial and temporal scales. All fur colour parameters (hue, saturation and brightness) strongly matched the respective habitats of the different species. Background matching in terms of hue was best at the microscale, whereas results for saturation and brightness showed more variation across spatial scales among species. Camouflage across the temporal scale (from 1 to 3 years before capture) was variable among species for all colour parameters. These complex interactions suggest that, in desert rodents, colour parameters are differentially sensitive to the respective scale of the habitat, plausibly reflecting the behaviour and life history of the species and the ecological properties determining their activity patterns. Consequently, the division between habitat (camouflage) generalists and specialists might become blurred in temporally changing and spatially variable environments.
This essay addresses recurring and growing inaccurate reports from political officials as well as counter-terrorism analysts and journalists that the Sahara-Sahel group Boko Haram is a defeated ...entity. Notwithstanding concerted efforts to rout the movement, Boko Haram and its network of jihadists have expanded. Crucial misunderstandings surrounding what fostered and sustains the phenomenon—as well as a general naivety regarding the organization’s flexibility to adapt to attract combatants, financial support, and weaponry beyond Nigeria’s borders—have made performing basic adequate risk assessments overwhelmingly challenging. Policy makers and CVE (Countering Violent Extremism) practitioners would be wise to recognize that not only has Boko Haram morphed but its growing affiliates also terrorize increased territory. The threat of militant Islam in the Sahara-Sahel, therefore, has not been contained as some would have us believe. Rather, Muslim extremism has become entangled and more complex not only in Africa but across the Muslim world. When jihadists in one territory have taken a beating, surviving fighters have simply relocated to other geographies accompanied by connections for capital and munitions. In this way, Boko Haram—the fulcrum of violent Islam in the Sahara-Sahel—has become, over time, an international jihadist actor.
Este ensayo aborda informes recurrentes y cada vez más inexactos de los funcionarios políticos, así como de analistas y periodistas antiterroristas de que el grupo Sahara-Sahel Boko Haram es una entidad derrotada. A pesar de los esfuerzos concertados para frenar el movimiento, Boko Haram y su red de yihadistas se han expandido. Los malentendidos cruciales en torno a lo que fomentó y sostiene el fenómeno, así como una ingenuidad general con respecto a la flexibilidad de la organización para adaptarse a atraer combatientes, apoyo financiero y armamento más allá de las fronteras de Nigeria, han hecho que realizar evaluaciones de riesgo básicas y básicas sea un desafío abrumadoramente. Los responsables de la formulación de políticas y los profesionales de CVE deberían reconocer que no solo Boko Haram se ha transformado, sino que sus afiliados en crecimiento aterrorizan el aumento del territorio. La amenaza del Islam militante en el Sahara-Sahel, por lo tanto, no ha sido contenida como algunos nos harían creer. Más bien, el extremismo musulmán se ha enredado y se ha vuelto más complejo no solo en África sino en todo el mundo musulmán. Cuando los yihadistas en un territorio han sido golpeados, los combatientes sobrevivientes simplemente se han trasladado a otras geografías acompañadas de conexiones para el capital y las municiones. De esta manera, Boko Haram, el punto de apoyo del islam violento en el Sahara-Sahel, se ha convertido, con el tiempo, en un actor internacional yihadista.
本文指出了政治家、反恐分析人士和记者日益离谱的反复报道, 该报道认为撒哈拉-萨赫勒地区组织博科圣地 (Boko Haram) 实质已经战败。尽管各方共同致力于击溃圣战运动, 但博科圣地组织不断延伸, 圣战分子队伍不断壮大。各方对导致这一现象产生和持续的原因误解重重, 对该组织调整自身吸引战斗人士的灵活性一无所知。再加上财政支持以及尼日利亚境外的武器装备, 进行充分的基本风险评估具有极大的挑战性。决策者和CVE(打击暴力极端主义) 倡议者将会明智地意识到, 博科圣地不仅改头换面, 而且越来越多的成员组织实施恐吓, 霸占领土。因此, 伊斯兰武装分子对于撒哈拉-萨赫勒地区造成的威胁并没有如一些人想让公众相信的那样得到遏制。相反, 穆斯林极端主义不仅在非洲变得盘根错节, 错综复杂, 而且在整个穆斯林世界也是如此。当圣战分子在一个地区发生殴打时, 幸存的战斗者能够因为资本和军火的关系转移到其他地区。长此以往, 博科圣地——撒哈拉-萨赫勒地区暴力伊斯兰教的支点——已成为一股国际圣战力量。
Desert particulate samples from locations in the Sahara–Sahel dust corridor (Western Sahara, Algeria, Chad and Niger) were segregated into size fractions ranging from <1.5 to >20μm and analysed using ...inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). The size-fractionated samples contain higher concentrations of Al, Na, Mg, Fe and most trace elements in the finer, phyllosilicate-rich materials. A notable exception is provided by Zr and Hf, which concentrate in the coarser fractions due to a higher abundance of coarse detrital zircon. Equally explicable by natural processes are enrichments (relative to the average upper continental crust) in incompatible trace elements with higher ionic potential (Nb, Ce, La), these being more resistant to chemical weathering. In contrast, samples show a relative loss of large ion lithophile elements (Rb, Cs and Ba), and the more calcareous samples show relative enrichment in Sr and depletion in Nb. However, not all the geochemical variations exhibited by these samples are easily explicable by invoking “natural” geochemical processes: anomalous concentrations of several transition metals (Zn, Pb, Cd) can be attributed to anthropogenic pollution, and enrichments in Cr, Ni and Mo are due to abrasive interaction between the siliceous dust sample and the fractionation equipment.
Large quantities of African dust are carried across the Atlantic to the Caribbean Basin and southern United States where it plays an important role in the biogeochemistry of soils and waters and in ...air quality. Dusts' elemental and isotopic composition was comprehensively characterized in Barbados during the summers of 2013 and 2014, the season of maximum dust transport. Although total suspended insoluble particulate matter (TSIP) mass concentrations varied significantly daily and between the two summers, the abundances (μg element/g TSIP) of 50 elements during “high‐dust days” (HDD) were similar. Aerosols were regularly enriched in Na, Cu, Zn, As, Se, Mo, Cd, Sn, Sb, and W relative to the upper continental crust. Enrichment of these elements, many of which are anthropogenically emitted, was significantly reduced during HDD, attributed to mixing and dilution with desert dust over source regions. Generally, Ti/Al, Si/Al, Ca/Al, Ti/Fe, Si/Fe, and Ca/Fe ratios during HDD differed from their respective values in hypothesized North African source regions. Nd isotope composition was relatively invariant for “low‐dust days” (LDD) and HDD. In contrast, HDD‐aerosols were more radiogenic exhibiting higher 87Sr/86Sr, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios compared to LDD. Generally, Barbados aerosols' composition ranged within narrow limits and was much more homogeneous than that of hypothesized African source soils. Our results suggest that summertime Barbados aerosols are dominated by a mixture of particles originating from sources in the Sahara‐Sahel regions. The Bodélé Depression, long suspected as a major source, appears to be an insignificant contributor of summertime western Atlantic dust.
Key Points
Composition of Barbados summer dust was relatively uniform compared to the variability reported for hypothesized African dust sources
Contrary to expectations, the Bodélé Depression appears to make an insignificant contribution to summertime western Atlantic dust
The elemental and isotopic composition of Barbados summer dust suggests that they are predominantly derived from the Sahara‐Sahel region
Abstract
Despite growing efforts to halt biodiversity loss, knowledge of species diversity and distribution is highly geographically biased, leaving some areas unexplored. Taxa distributed in remote, ...desert areas, such as hedgehogs (Mammalia; Eulipotyphla) in North Africa, are good examples of current knowledge gaps in systematics and biogeography. Here we studied the geographical distribution and intraspecific genetic diversity of hedgehogs in North Africa. Specimens belonging to North African and Eurasian species were analysed with mitochondrial (control region, CR) and nuclear (recombination activating gene 1, RAG1) gene fragments. This revealed a broader geographical distribution of Atelerix algirus in south-western Libya and of Paraechinus aethiopicus along the Atlantic Sahara. High intraspecific genetic differentiation was found in A. algirus and A. albiventris at the mitochondrial level, with nuclear haplotype sharing across their ranges. These findings suggest that biogeographical patterns of hedgehogs in North Africa are more complex than previously suggested, highlighting a need for further investigation in this remote and poorly known area.
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