Aeolian Dust Deposition Research Articles

Derivation of an observation-based map of North African dust emission

Changes in the emission, transport and deposition of aeolian dust have profound effects on regional climate, so that characterizing the lifecycle of dust in observations and improving the representation of dust in global climate models is necessary. A fundamental aspect of characterizing the dust cycle is quantifying surface dust fluxes, yet no spatially explicit estimates of this flux exist for the World’s major source regions. Here we present a novel technique for creating a map of the annual mean emitted dust flux for North Africa based on retrievals of dust storm frequency from the Meteosat Second Generation Spinning Enhanced Visible and InfraRed Imager (SEVIRI) and the relationship between dust storm frequency and emitted mass flux derived from the output of five models that simulate dust. Our results suggest that 64 (±16)% of all dust emitted from North Africa is from the Bodele depression, and that 13 (±3)% of the North African dust flux is from a depression lying in the lee of the Air and Hoggar Mountains, making this area the second most important region of emission within North Africa.

Sources of iron and phosphate affect the distribution of diazotrophs in the North Atlantic

Biological nitrogen fixation (BNF) supplies nutrient-depleted oceanic surface waters with new biologically available fixed nitrogen. Diazotrophs are the only organisms that can fix dinitrogen, but the factors controlling their distribution patterns in the ocean are not well understood. In this study, the relative abundances of eight diazotrophic phylotypes in the subtropical North Atlantic Ocean were determined by quantitative PCR (qPCR) of the nifH gene using TaqMan probes. A total of 152 samples were collected at 27 stations during two GEOTRACES cruises; Lisbon, Portugal to Mindelo, Cape Verde Islands (USGT10) and Woods Hole, MA, USA via the Bermuda Time Series (BATS) to Praia, Cape Verde Islands (USGT11). Seven of the eight diazotrophic phylotypes tested were detected. These included free-living and symbiotic cyanobacteria (unicellular groups (UCYN) A, B and C, Trichodesmium, the diatom-associated cyanobacteria Rhizoselinia–Richelia and Hemiaulus–Richelia) and a γ-proteobacterium (Gamma A, AY896371). The nifH gene abundances were analyzed in the context of a large set of hydrographic parameters, macronutrient and trace metal concentrations measured in parallel with DNA samples using the PRIMER-E software. The environmental variables that most influenced the abundances and distribution of the diazotrophic phylotypes were determined. We observed a geographic segregation of diazotrophic phylotypes between east and west, with UCYN A, UCYN B and UCYN C and the Rhizosolenia–Richelia symbiont associated with the eastern North Atlantic (east of 40°W), and Trichodesmium and Gamma A detected across the basin. Hemiaulus–Richelia symbionts were primarily found in temperate waters near the North American coast. The highest diazotrophic phylotype abundance and diversity were associated with temperatures greater than 22°C in the surface mixed layer, a high supply of iron from North African aeolian mineral dust deposition and from remineralized nutrients upwelled at the edge of the oxygen minimum zone off the northwestern coast of Africa.

The role of climate and aeolian dust input in calcrete formation in volcanic islands (Lanzarote and Fuerteventura, Spain)

Calcretes are widely described in non-marine settings with carbonates in their catchment, or vicinity areas, but in volcanic islands without carbonates in their substrate, calcretes are not very common. In Lanzarote and Fuerteventura Canary Islands, characterized by impressive volcanic landscapes, the sedimentary carbonate rocks are rare except for some recent marine and aeolian deposits. In these settings very well-developed calcretes cover large areas of the present landscape. The source of calcium required for the formation of these calcretes has not been discussed in much detail till now, although its role is critical to an understanding of the climatic conditions in which calcium was transported and fixed and of the calcrete formation processes. The petrological and geochemical studies (87Sr/86Sr ratios, δ13C, δ18O, major, trace and REE) carried out in this paper do confirm the important role of aeolian dust input in the formation of these calcretes. Canarian calcretes were mainly generated by pedogenic processes and are composed of various irregular carbonate lamina interbedded with fine clastic deposits. Our study indicates that these interbeddings were the result of several stages in which, during dry periods, aeolian dust deposition alternated with leaching and calcite precipitation during wetter periods when plants, insects and bacteria played an important role in carbonate precipitation. The δ18O (−2.70 to +2.22‰ VPDB) and δ13C (−8.21 to +0.24‰ VPDB) values indicate that calcretes were formed by pedogenic processes. Comparison of calculated ∆18O values for the Canary calcretes with continental mid-latitude calcrete values reflects the more homogeneous temperature regimes of calcrete formation in island (oceanic) settings. Calcrete87Sr/86Sr ratios (0.706357 to 0.709208) show strong affinity with those obtained in aeolian carbonate dust and marine deposits, and are relatively different from those obtained in basalts. REE, major and trace element concentrations show that Ca-bearing minerals from volcanic host rock contributed little to calcrete formation and most of the calcium was supplied by aeolian deposits such as the aeolian dust coming from the Sahara and Sahel or sand dunes.

Gale crater and impact processes – Curiosity’s first 364 Sols on Mars

Impact processes at all scales have been involved in the formation and subsequent evolution of Gale crater. Small impact craters in the vicinity of the Curiosity MSL landing site and rover traverse during the 364 Sols after landing have been studied both from orbit and the surface. Evidence for the effect of impacts on basement outcrops may include loose blocks of sandstone and conglomerate, and disrupted (fractured) sedimentary layers, which are not obviously displaced by erosion. Impact ejecta blankets are likely to be present, but in the absence of distinct glass or impact melt phases are difficult to distinguish from sedimentary/volcaniclastic breccia and conglomerate deposits. The occurrence of individual blocks with diverse petrological characteristics, including igneous textures, have been identified across the surface of Bradbury Rise, and some of these blocks may represent distal ejecta from larger craters in the vicinity of Gale. Distal ejecta may also occur in the form of impact spherules identified in the sediments and drift material. Possible examples of impactites in the form of shatter cones, shocked rocks, and ropy textured fragments of materials that may have been molten have been observed, but cannot be uniquely confirmed. Modification by aeolian processes of craters smaller than 40m in diameter observed in this study, are indicated by erosion of crater rims, and infill of craters with aeolian and airfall dust deposits. Estimates for resurfacing suggest that craters less than 15m in diameter may represent steady state between production and destruction. The smallest candidate impact crater observed is ∼0.6m in diameter. The observed crater record and other data are consistent with a resurfacing rate of the order of 10mm/Myr; considerably greater than the rate from impact cratering alone, but remarkably lower than terrestrial erosion rates.

Dust effects on snowpack melt and related ecosystem processes are secondary to those of forest canopy structure and interannual snowpack variability

AbstractDust deposition lowers the albedo of snow and can significantly alter snowpack energy balance. Investigation of aeolian dust deposition in the mountains of the western U.S. has shown that these effects advance the timing of snowpack melt and spring runoff across much of the region. These studies have primarily focused on alpine snowpacks with little to no overstory vegetation. To evaluate the impacts of aeolian dust on ecohydrological processes in forests, we conducted a manipulative experiment in a subalpine conifer forest in Utah's Wasatch Mountains. During the spring of 2010–2012, we added dust to the snow surface in forested plots every 1 to 2 weeks, roughly doubling the natural dust loading. We then measured snowpack ablation in control and dust addition plots, along with below‐snowpack and warm season soil temperature (Tsoil), soil water content (θ), litter decomposition rate (D), soil respiration rate (Rs), and tree xylem water potential (ψ). Differences in ablation between control and dust addition plots were similar in magnitude to differences associated with the canopy structure of the forest. Seasonal patterns in Tsoil and θ were similar between dust treatments and canopy structure groups. D, Rs, and ψ varied little between dust treatments, but there were significant differences between years. During our 3‐year study, an unusual level of interannual variability in snowfall had the greatest effect on the soil environment and ecosystem processes. The effects of aeolian dust on snowpack mass and energy balance in our forest were slightly smaller than those associated with canopy structure. Copyright © 2014 John Wiley & Sons, Ltd.

Impact of water mass mixing and dust deposition on Nd concentration and εNd of the Arabian Sea water column

The concentration and isotopic composition (εNd) of dissolved Nd have been measured in the sub-oxic/denitrifying water column of the eastern Arabian Sea to explore the impact of water mass mixing and release from particles. Dissolved Nd in the north-eastern Arabian Sea is more radiogenic (εNd: −7 to −10) compared to its south-eastern part (εNd: −11 to −15) suggesting contribution of Nd from the Bay of Bengal (BoB). The vertical profile of Nd typically show higher values in surface waters (15.8–27.8pmol/kg), followed by minima (12–18pmol/kg) in the subsurface waters (200–300m) and a gradual increase with depth thereafter. The Nd concentration does not seem to show any changes in the sub-oxic layers suggesting no impact of the sub-oxic/denitrifying conditions in this oceanic region on the biogeochemistry of Nd. The enrichment of Nd in surface waters can be explained either by supply from high Nd low salinity waters from the BoB to the Arabian Sea via the East India Coastal Current (EICC) or, alternatively the Nd surface excess can be result of release from aeolian dust depositing over the sea surface. Inverse modeling computations suggest that in addition to Nd contributed from water mass mixing, some additional excess Nd (Ndxs) is required to balance the Nd inventory in the water column. There is significant Ndxs in the surface waters of the north-eastern Arabian Sea with εNd∼−6, similar to that of dust depositing over the Arabian Sea. The fractional solubility of Nd released from the aeolian dust was estimated to be varying from ∼3% to 17% (for excess Nd inventory per unit area (Ndxs∗) of 20μgm−2 with τNd ranging from 1 to 3years). This study highlights the significance of aeolian dust deposition in controlling the abundance and distribution of Nd in the Arabian Sea, the western arm of the northern Indian Ocean, lying in the proximity to the arid landmass and characterized by high lithogenic aeolian dust deposition.

Asian monsoons in a late Eocene greenhouse world.

The strong present-day Asian monsoons are thought to have originated between 25 and 22 million years (Myr) ago, driven by Tibetan-Himalayan uplift. However, the existence of older Asian monsoons and their response to enhanced greenhouse conditions such as those in the Eocene period (55-34Myr ago) are unknown because of the paucity of well-dated records. Here we show late Eocene climate records revealing marked monsoon-like patterns in rainfall and wind south and north of the Tibetan-Himalayan orogen. This is indicated by low oxygen isotope values with strong seasonality in gastropod shells and mammal teeth from Myanmar, and by aeolian dust deposition in northwest China. Our climate simulations support modern-like Eocene monsoonal rainfall and show that a reinforced hydrological cycle responding to enhanced greenhouse conditions counterbalanced the negative effect of lower Tibetan relief on precipitation. These strong monsoons later weakened with the global shift to icehouse conditions 34Myr ago.

REE geochemistry of modern eolian dust deposits in Harbin city, Heilongjiang province, China: Implications for provenance

There has long been disagreement about the provenance of sandy dust deposits in Harbin city, Heilongjiang province, China. The present paper contributes to a better understanding of the source of sandy dust deposits in Harbin by the application of REE geochemistry. The REE composition of samples from sand–dust deposit events in Harbin was compared with that of three different grain size fractions (<11μm, 11–30μm and 30–63μm) of sandy soil samples from Horqin Sandy Land and Songnen Sandy Land. The results indicate that the REE distributions of all of the Harbin sand–dust samples are remarkably similar to each other, with distinct negative Eu anomalies and slightly negative Ce anomalies, indicating a stable provenance. Grain size exerts a significant influence on REE compositions, with a negative Eu-anomaly tending to develop with decreasing grain size. However, Ce is less influenced by grain size. The large lines of evidences, such as REE contents, distribution patterns, characteristic parameters, δEu (δEu=Eu anomalies values) vs. ΣREEs diagram, δEu vs. (LREE/HREE) diagram and (LREE/HREE) vs. LaN (subscript N represents chondrite normalized values) diagram, indicate that REE composition of dust deposits in Harbin is quite similar to that of samples from Horqin Sandy Land, especially in the case of the 11–30μm grain size fraction. This indicates that the Harbin sand–dust deposits are derived from Horqin Sandy Land and not from Songnen Sandy Land, and that material contribution of Horqin Sandy Land to Harbin dust deposits was mainly 11–30μm grain-size fraction. The importance of the Horqin Sandy Land as a major source of Harbin sand–dust weather is supported by meteorological records and meteorological data.

The transition on North America from the warm humid Pliocene to the glaciated Quaternary traced by eolian dust deposition at a benchmark North Atlantic Ocean drill site

We present Plio-Pleistocene records of sediment color, %CaCO3, foraminifer fragmentation, benthic carbon isotopes (δ13C) and radiogenic isotopes (Sr, Nd, Pb) of the terrigenous component from IODP Site U1313, a reoccupation of benchmark subtropical North Atlantic Ocean DSDP Site 607. We show that (inter)glacial cycles in sediment color and %CaCO3 pre-date major northern hemisphere glaciation and are unambiguously and consistently correlated to benthic oxygen isotopes back to 3.3 million years ago (Ma) and intermittently so probably back to the Miocene/Pliocene boundary. We show these lithological cycles to be driven by enhanced glacial fluxes of terrigenous material (eolian dust), not carbonate dissolution (the classic interpretation). Our radiogenic isotope data indicate a North American source for this dust (∼3.3–2.4 Ma) in keeping with the interpreted source of terrestrial plant wax-derived biomarkers deposited at Site U1313. Yet our data indicate a mid latitude provenance regardless of (inter)glacial state, a finding that is inconsistent with the biomarker-inferred importance of glaciogenic mechanisms of dust production and transport. Moreover, we find that the relation between the biomarker and lithogenic components of dust accumulation is distinctly non-linear. Both records show a jump in glacial rates of accumulation from Marine Isotope Stage, MIS, G6 (2.72 Ma) onwards but the amplitude of this signal is about 3–8 times greater for biomarkers than for dust and particularly extreme during MIS 100 (2.52 Ma). We conclude that North America shifted abruptly to a distinctly more arid glacial regime from MIS G6, but major shifts in glacial North American vegetation biomes and regional wind fields (exacerbated by the growth of a large Laurentide Ice Sheet during MIS 100) likely explain amplification of this signal in the biomarker records. Our findings are consistent with wetter-than-modern reconstructions of North American continental climate under the warm high CO2 conditions of the Early Pliocene but contrast with most model predictions for the response of the hydrological cycle to anthropogenic warming over the coming 50 years (poleward expansion of the subtropical dry zones).

Late Pleistocene variations of the background aeolian dust concentration in the Carpathian Basin: an estimate using decomposition of grain-size distribution curves of loess deposits

AbstractAeolian dust deposits can be considered as one of the most important archives of past climatic changes. Alternating loess and paleosol strata display variations of the dust load in the Pleistocene atmosphere. By using the observations of recent dust storms, we are able to employ Late Pleistocene stratigraphic datasets (with accurate chronological framework) and detailed granulometric data for making conclusions on the atmospheric dust load in the past. Age-depths models, created from the absolute age data and stratigraphic interpretation, allow us to calculate sedimentation rates and dust fluxes, while grain-size specifies the dry-deposition velocity, i.e. the atmospheric residence time of mineral particles. Thus, the dust concentration can be expressed as the quotient of the dust flux and gravitational settling velocity. Recent observations helped to clarify the mechanisms behind aeolian sedimentation and the physical background of this process has nowadays been well established. Based on these two, main contrasting sedimentary modes of dust transport and deposition can be recognised: the short suspension episodes of the coarse (silt and very fine sand) fraction and the long-range transport of a fine (clay and fine silt) component. Using parametric curve fitting the basic statistical properties of these two sediment populations can be revealed for Pleistocene aeolian dust deposits, as it has been done for loess in Hungary. As we do not have adequate information on the magnitude and frequency of the Pleistocene dust storms, conclusions could only be made on the magnitude of continuous background dust load. The dust concentration can be set in the range between 1100 and 2750 μg/m3. These values are mostly higher than modern dust concentrations, even in arid regions. Another interesting proxy of past atmospheric conditions could be the visibility, being proportional to the dust concentration. According to the known empirical dust concentration – visibility equations, its value is around 6.5 to 26 kilometres.

Aeolian dust deposition rates in Northern French forests and inputs to their biogeochemical cycles

This study describes the Aeolian dust deposition (ADD) in 4 sites of Northern France. Between December 2009 and March 2012, we sampled (i) Aeolian dust every four weeks, and (ii) 6 episodes of forecasted high atmospheric dust load mainly from the Saharan desert, the largest source of Aeolian dust in the world. These samples were treated with oxygen peroxide to remove organic matter so as to only compare the mineral fraction of the samples in the 4 sampling sites and to analyze their mineralogy. The solid samples contained the hardly soluble part of Aeolian dust (H-ADD). Its deposition was of 1.9 ± 0.3 g m−2 year−1 with a seasonal pattern of high deposition from spring to early autumn and a low deposition in winter. H-ADD deposition during the forecasted episodes of high atmospheric load did not systematically exceed the deposition rate during the rest of the sampling period. This indicates that such episodes little contributed to the annual H-ADD rate. The mineralogy revealed a heterogeneous set of minerals dominated by silicates with a common basis of major types (quartz, feldspars, mica, chlorite, kaolinite and interlayered clay minerals in every sample) with randomly trace minerals (Fe-oxides, sulfates, amphibole, talc, gibbsite and carbonates). The chemistry of H-ADD led to a dominant input of Si (up to 4.4 kg ha−1 year−1), while the nutrients inputs of Ca, K, Mg and P from ADD and the atmospheric organics (APD) in openfield were together of 1.5 ± 0.5 kg ha−1 year−1 with a high contribution of soluble minerals and organic matter of ca. 40% for Mg and K, and of ca. 80% for Ca and P. Nutrient inputs from APD are especially an interesting source of P for forests developed on acidic soils.

Influence of sediment, soil, and micro-relief conditions on vitality of Populus euphratica stands in the lower Tarim Riparian Ecosystem

Excessive withdrawal of water for farmland irrigation, and water losses from water reservoirs and channels, have caused water deficit problems along the Tarim River in Northwestern China. Especially, the lower reaches have been severely threatened since the 1950s, and are experiencing a drastic increase in the mineralisation of the river water. Additionally, large scale deposition of aeolian sand and dust is another major threat for the Tarim Riparian Ecosystem (TaRiEc). This development reached its “climax” with the desiccation of the Taitema Lake in 1972, and the “climax” was well expressed by severe degradation of the TaRiEc, which is in turn predominately characterized by the dying of Populus euphratica stands. All these developments led to the initiation of the “Ecological Water Diversion Project” (EWDP). The main objective of this project is to ensure a constant water supply to the lower reaches of the Tarim River via the water transfer both from the Bosten Lake catchment and from Tarim's upper and middle reaches. In this study, the processes and trends of the vegetation change during this period of intermittent water transfer were examined on the basis of remote sensing data. The results show that with the water transfer only some of the P. euphratica trees reached a more vital state.Common hypotheses about factors influencing the tree vitality under stressful conditions deal with the water level in the river, the groundwater level and the distance of the trees from the river. However, soil and sediment, as well as micro-relief conditions also play an important role and take influence on the vitality of the trees. The main objective of the present study was to analyse the features of soil and sediment concerning water passage and water storage processes in near surface and subsurface positions of the lower Tarim Riparian Ecosystem. For that purpose, 2010 and 2011 field and laboratory analyses of soil and sediment profiles were performed. Laboratory results comprise grain size measurements, pore size distribution, total organic content (TOC) and data from XRD-measurements on the soil's mineral composition for all studied sites within the lower Tarim study area and for selected ecosystem types as well. These parameters allow conclusions about water storage and water passage conditions, which play a key role for water availability and water supply of P. euphratica trees. Besides single soil and sediment parameters, such as salt content and mineral composition, layer types (vertical sequence of soil horizons and sediment layers) have been identified as leading factors determining near surface and subsurface water passage and water storage features of the Tarim Riparian Ecosystem.

Dust deposits on La Graciosa Island (Canary Islands, Spain): Texture, mineralogy and a case study of recent dust plume transport

La Graciosa volcanic island evolved in the late Pleistocene–Holocene. It is situated along the northeast of the Canarian Archipelago, with a subaerial surface of 27km2. This island is located close to the Western Sahara, being 80km from the north-western African continental shelf and 145km from the coast. The island supports a very small permanent population. The climate is coastal-arid (116mm precipitation per annum). Regular occurrences of Saharan dust plumes (about 30% of the year), with a dust accumulation rate of 20g−2year−1, produce sedimentation of dust on the island of ca. 540tyear−1. Wind-blown sediments cover a large area (more than 52%) of the otherwise volcanic island, forming sandy beaches, sand sheets, nebkhas and other aeolian deposits. Re-distributed dust deposits often occur on the leeward sides of inter-volcano areas, inter-dune areas and in endorheic sediment traps. Many of these deposits are edaphized and carbonatized. Textural analysis of the dust deposit samples shows a variable proportion of silt (80–20%), clay (19–9%), and fine to very fine sand (71–4%). The general mineralogical composition of these sediments as measured by XRD and SEM-EDS is calcite (26%), illite (26%), quartz (11%), augite (10%), aragonite (6%), anorthite (8%), kaolinite (5%) and montmorillonite (3%). The mineralogy in different size fractions is very consistent; for example, quartz content decreases from 15% in the coarse silt fraction to 5% in the fine sand. A mineral and grain-size comparison with airborne dust collected on Gran Canaria Island was undertaken; close similarities were found in the two sample sets. Such closely-matched characteristics point to a similar origin for both airborne dust and dust deposits, in line with the Saharan plume dust that regularly traverses this archipelago. It is unusual to find so much quartz in the fine sand fraction of these aeolian dust deposits. Individual quartz grains with an intermediate axial length of ~160μm were identified by SEM-EDS. Previous investigators have found similar “giant” particles in long-range transported aeolian dust (Middleton et al., 2001), in contrast to the classic model for gravity settling of airborne dust particles. The debate on this subject remains open for discussion. We present evidence of long-range, wind-transported large mineral particles and a 2004 case study of uplift wind velocity vs. plume dust generation, as well as a transport efficiency model that can explain the existence of fine sand in the dust deposits on La Graciosa Island and in the airborne samplers on Gran Canaria Island. Recent Saharan dust shows that about 10% of similar coarse-grained particulate matter is also present.

The likelihood of observing dust-stimulated phytoplankton growth in waters proximal to the Australian continent

We develop a tool to assist in identifying a link between naturally occurring aeolian dust deposition and phytoplankton response in the ocean. Rather than examining a single, or small number of dust deposition events, we take a climatological approach to estimate the likelihood of observing a definitive link between dust deposition and a phytoplankton bloom for the oceans proximal to the Australian continent. We use a dust storm index (DSI) to determine dust entrainment in the Lake Eyre Basin (LEB) and an ensemble of modelled atmospheric trajectories of dust transport from the basin, the major dust source in Australia. Deposition into the ocean is computed as a function of distance from the LEB source and the local over-ocean precipitation. The upper ocean's receptivity to nutrients, including dust-borne iron, is defined in terms of time-dependent, monthly climatological fields for light, mixed layer depth and chlorophyll concentration relative to the climatological monthly maximum. The resultant likelihood of a dust-phytoplankton link being observed is then mapped as a function of space and time. Our results suggest that the Southern Ocean (north of 45°S), the North West Shelf, and Great Barrier Reef are ocean regions where a rapid biological response to dust inputs is most likely to be observed. Conversely, due to asynchrony between deposition and ocean receptivity, direct causal links appear unlikely to be observed in the Tasman Sea and Southern Ocean south of 45°S.

Iron fluxes to Talos Dome, Antarctica, over the past 200 kyr

Abstract. Atmospheric fluxes of iron (Fe) over the past 200 kyr are reported for the coastal Antarctic Talos Dome ice core, based on acid leachable Fe concentrations. Fluxes of Fe to Talos Dome were consistently greater than those at Dome C, with the greatest difference observed during interglacial climates. We observe different Fe flux trends at Dome C and Talos Dome during the deglaciation and early Holocene, attributed to a combination of deglacial activation of dust sources local to Talos Dome and the reorganisation of atmospheric transport pathways with the retreat of the Ross Sea ice shelf. This supports similar findings based on dust particle sizes and fluxes and Rare Earth Element fluxes. We show that Ca and Fe should not be used as quantitative proxies for mineral dust, as they all demonstrate different deglacial trends at Talos Dome and Dome C. Considering that a 20 ppmv decrease in atmospheric CO2 at the coldest part of the last glacial maximum occurs contemporaneously with the period of greatest Fe and dust flux to Antarctica, we confirm that the maximum contribution of aeolian dust deposition to Southern Ocean sequestration of atmospheric CO2 is approximately 20 ppmv.

The role of Volcanic vs Seismic actions in ground deformations recorded in Oceanic Volcanic Islands: Examples from the Eastern Canary Islands (Spain)

Calcretes are widely described in non-marine settings with carbonates in their catchment, or vicinity areas, but in volcanic islands without carbonates in their substrate, calcretes are not very common. In Lanzarote and Fuerteventura Canary Islands, characterized by impressive volcanic landscapes, the sedimentary carbonate rocks are rare except for some recent marine and aeolian deposits. In these settings very well-developed calcretes cover large areas of the present landscape. The source of calcium required for the formation of these calcretes has not been discussed in much detail till now, although its role is critical to an understanding of the climatic conditions in which calcium was transported and fixed and of the calcrete formation processes. The petrological and geochemical studies (87Sr/86Sr ratios, δ13C, δ18O, major, trace and REE) carried out in this paper do confirm the important role of aeolian dust input in the formation of these calcretes. Canarian calcretes were mainly generated by pedogenic processes and are composed of various irregular carbonate lamina interbedded with fine clastic deposits. Our study indicates that these interbeddings were the result of several stages in which, during dry periods, aeolian dust deposition alternated with leaching and calcite precipitation during wetter periods when plants, insects and bacteria played an important role in carbonate precipitation. The δ18O (− 2.70 to + 2.22‰ VPDB) and δ13C (− 8.21 to + 0.24‰ VPDB) values indicate that calcretes were formed by pedogenic processes. Comparison of calculated ∆18O values for the Canary calcretes with continental mid-latitude calcrete values reflects the more homogeneous temperature regimes of calcrete formation in island (oceanic) settings. Calcrete87Sr/86Sr ratios (0.706357 to 0.709208) show strong affinity with those obtained in aeolian carbonate dust and marine deposits, and are relatively different from those obtained in basalts. REE, major and trace element concentrations show that Ca-bearing minerals from volcanic host rock contributed little to calcrete formation and most of the calcium was supplied by aeolian deposits such as the aeolian dust coming from the Sahara and Sahel or sand dunes.

Delayed build-up of Arctic ice sheets during 400,000-year minima in insolation variability

Knowledge of the past variability of climate at high northern latitudes during astronomical analogues of the present interglacial may help to inform our understanding of future climate change. Unfortunately, long-term continuous records of ice-sheet variability in the Northern Hemisphere only are scarce because records of benthic (18)O content represent an integrated signal of changes in ice volume in both polar regions. However, variations in Northern Hemisphere ice sheets influence the Siberian High (an atmospheric pressure system), so variations in the East Asian winter monsoon (EAWM)--as recorded in the aeolian dust deposits on the Chinese Loess Plateau--can serve as a useful proxy of Arctic climate variability before the ice-core record begins. Here we present an EAWM proxy record using grain-size variations in two parallel loess sections representative of sequences across the whole of the Chinese Loess Plateau over the past 900,000 years. The results show that during periods of low eccentricity and precessional variability at approximately 400,000-year intervals, the grain-size-inferred intensity of the EAWM remains weak for up to 20,000 years after the end of the interglacial episode of high summer monsoon activity and strong pedogenesis. In contrast, there is a rapid increase in the EAWM after the end of most other interglacials. We conclude that, for both the 400,000-year interglacials, the weak EAWM winds maintain a mild, non-glacial climate at high northern latitudes for much longer than expected from the conventional loess and marine oxygen isotope records. During these times, the less-severe summer insolation minima at 65° N (ref. 4) would have suppressed ice and snow accumulation, leading to a weak Siberian High and, consequently, weak EAWM winds.

Distinguishing and characterising point-source mining dust and diffuse-source dust deposits in a semi-arid district of eastern Australia

Abstract The routine monitoring of dust deposition around mines does not typically distinguish between allochthonous and locally-sourced dust. In this paper, contemporary aeolian dust deposition within a semi-arid part of eastern Australia is examined to determine the contribution of an open-pit gold mine to local dust dynamics. Over a 2.5 year period, monthly deposited dust samples were obtained from 12 sites located around the Cowal Gold Mine (CGM), and analysed for inorganic and organic proportions and granulometric properties. Although there was considerable variation in deposition between the gauges and sampling periods, there was a moderate and statistically significant seasonal trend, with mineral dust deposition lowest in winter. Imprinted over this seasonal pattern was a distinct spatial pattern of dust deposition, with gauges downwind of the CGM receiving significantly more dust than those gauges upwind (20 t/km 2 /yr). This effect was most pronounced adjacent to the mine (dust deposition of 60 t/km 2 /yr), where coarse-grained particles comprised a large proportion of the deposited dust, and diminished with distance east of the mine. Such a spatial trend is typical of a point source of dust. Average dust deposition at gauges located 8 km downwind of the mine was only slightly greater than that of gauges upwind of the mine. The ‘background’ dust populations captured at the upwind locations were dominated by fine particles, with modal particle diameters of 3–5 and 13–16 μm common. The macro-organic component of dust deposits also tended to vary seasonally, but the spatial distribution of this material was quite erratic.

EFFECTS OF DUST ON THE PERFORMANCE OF PV PANELS

EFFECTS OF DUST ON THE PERFORMANCE OF PV PANELS

Dynamics on the Interaction between Vegetation Growth and Aeolian Dust Deposition

From the holistic perspective, a new dynamic model is proposed in this research to investigate the interaction between vegetation growth and aeolian dust deposition. Three cases of equilibrium distribution can be obtained and the stability of interior equilibriums is determined. When there is a stable interior equilibrium, a critical curve exists and separates the coexistent area where vegetation can survive in the environment of aeolian dust deposition, from the other area where vegetation is to be excluded. Simulation analysis further reveals the variation of the critical curve with the parameters and the anthropic influences. The critical curve and the coexistent equilibrium described by the model may be used as a theoretical basis to evaluate the feasibility of vegetation restoration in the environment of aeolian dust deposition.