Eolian deposition determined by the oxygen plasma furnace

The oxygen plasma furnace enables small samples of clastic sediment to be separated from filter papers at low temperatures without physical or chemical alteration of the sediment. This technique provides a suitable treatment for processing very small samples of alpine eolian sediment, enabling their grain size distribution, mineralogy, and origin to be determined.     

Aeolian deposition of dust over hills: the effect of dust grain size on the deposition pattern

Wind tunnel experiments were conducted to investigate the effects of topography on the grain size characteristics of aeolian dust deposits. Experiments were performed on three isolated hills having various size and aspect ratios. The longitudinal profile of the median grain diameter was investigated for each hill. The longitudinal dust deposition profile was also studied for nine grain size classes of between 10 and 104 µm, as were wind and dust concentration profiles in the atmosphere upwind of, over and downwind of a hill. The wind tunnel experiments show that the grain size characteristics of aeolian dust deposits are affected by topography. Most apparent is the occurrence of a zone of reduced grain size on the leeside of hills, which extends from just upwind of the summit to a distance of several times the height of the hill. Slightly coarser than normal dust is deposited on the concave windward hill slope and in a zone downwind of the area of reduced grain size, but the increase in grain size in these zones remains very small. Although the normalized dust deposition profile for a hill does not vary substantially as a function of grain size, systematic trends are observed. The most important tendencies are: (1) a progressive extension, in the downwind direction, of a zone of decreased dust deposition on the leeside of a hill (the coarser the grains, the further downwind the zone of reduced deposition extends); (2) a progressive increase in dust deposition immediately upwind of a hill (the finer the grains, the higher the deposition value upwind of a hill becomes). Both tendencies are explained by the difference in inertia of the grains, which is controlled by grain size. Copyright © 2005 John Wiley & Sons, Ltd.     

Eolian processes in alpine belts of the high Tatra mountains,Poland

Eolian processes were the subject of detailed studies in the high-mountain area of the Tatra Mts. The field investigations in 1975–80 attempted to determine the amount of deflation and eolian deposition and to improve understanding of their mechanism. The net rates of these processes were determined from repeated survey of deflational forms and of eolian deposits. Observations of the mechanism of material displacement were based on field experiments carried out during strong winds. All the investigations were conducted using simple methods and traps. Relationships between the course and intensity of processes and wind conditions and soil properties were obtained.     

Airborne dust deposition in the Okavango Delta,Botswana, and its impact on landforms

This study investigated the local‐scale generation and movement of dust in the seasonal swamps of the Okavango Delta, Botswana, with a view to examining possible transfer of material between ?ood plains and islands. It was found that most of the dust load was carried in the lowest 3 m of the air column, and consisted mainly of amorphous silica, indicating that dust was generated largely on the ?ood plains. Dust loads were found to be highest above the ?ood plains and lowest over the interiors of islands, probably due to the baf?ing effect of the island trees on wind velocity. The contrast in dust loads between islands and ?ood plains suggests that there is a net transfer of dust from ?ood plains to islands, but it was not possible to quantify this transfer. It is evident, however, that ?ood plains experience net erosion and islands net aggradation. A strong seasonality in dust loads was observed, with the maximum dust loads coinciding with maximum wind velocity in October. This also coincides with peak seasonal ?ooding in the delta, and only non‐inundated ?ood plains are capable of generating dust. Years of low ?ood therefore appear to be more dusty. There may also be transfer of material from higher‐lying to lower‐lying ?ood plains, which may reduce the topographic contrast on the ?ood plains. Copyright © 2004 John Wiley & Sons, Ltd.     

Effect of rock fragment embedding on the aeolian deposition of dust on stone‐covered surfaces

Many stone‐covered surfaces on Earth are subject to aeolian deposition of atmospheric dust. This study investigates how the deposition of dust is affected when rock fragments become gradually more embedded in the ground or, inversely, become more concentrated on the surface. Experiments were executed in an aeolian dust wind tunnel with eight different types of pebbles. The following parameters were measured: dust deposition on the pebbles, dust deposition between and underneath pebbles, total dust deposition (pebbles + inter‐pebble space), and the fraction, of total deposition, of dust caught by the pebbles alone. The absolute amount of dust deposition and the dust deposition density (dust deposition per unit surface) were studied for each parameter. The effects exerted by pebble size, pebble flattening, pebble elongation and wind speed were also investigated. Dust patterns on and around pebbles were also studied via flow visualization. The absolute amount of dust settling on pebbles decreases the more that the pebbles become embedded. Dust deposition density on pebbles, on the other hand, increases with embedding. The more pebbles become embedded in the soil, the more efficient the process of dust deposition on pebbles becomes. Dust deposition between and underneath pebbles increases with pebble embedding. Dust deposition density between and underneath pebbles is maximum at 50 per cent embedding, showing that in this area dust deposition is most efficient when pebbles are halfway embedded. Total deposition slightly decreases the more pebbles become embedded, but total dust deposition density increases with embedding. Aerodynamic flow separation and diverging and converging airflow play an important role in the process of dust deposition on stone‐covered surfaces. The more pebbles protrude above the soil, the more they act as an obstacle and the more they disturb the air and dust flow creating scouring zones, flow separation bubbles and shelter areas for the dust. All these effects diminish as pebbles become more embedded in the soil. However, perturbations in dust patterns remain visible until pebbles have disappeared entirely. Copyright © 2005 John Wiley & Sons, Ltd.     

High-latitude dust deposition in snow on the glaciers of James Ross Island,Antarctica

High-latitude dust (HLD) depositions on four glaciers of James Ross Island (the Ulu Peninsula) were analysed. The deposition rate on the selected glaciers varies from 11.8 to 64.0 g m⁻², which is one order of magnitude higher compared to the glaciers in Antarctica or elsewhere in the world. A strong negative relationship between the sediment amount and altitude of a sampling site was found. This is most likely caused by the higher availability of aeolian material in the atmospheric boundary layer. General southerly and south-westerly wind directions over the Ulu Peninsula – with exceptions based on local terrain configuration – help to explain the significantly lower level of sediment deposition on San Jose Glacier and the high level on Triangular Glacier. X-ray fluorescence (XRF) spectrophotometry was used to estimate the relative proportions of the main and trace (lithophile) elements in the sediment samples. Both the sediment amount and the XRF results are analysed in a depth profile at each locality and compared among the glaciers, suggesting long-range transport of fine mineral material from outside James Ross Island. The distribution of aeolian sediment among the glaciers corresponds well with the prevailing wind direction on the Ulu Peninsula. © 2020 John Wiley & Sons, Ltd.     

Aeolian dust transport and deposition over crete and adjacent parts of the mediterranean sea

Monitoring of dust deposition at several stations on Crete over a three year period has shown that the present-day depositional flux is of the order of 10-100 gm⁻² yr⁻¹. Most of the dust deposition takes place during a few annual dust [events] which typically last for 1-3 days. Dust haze episodes are usually associated with southerly or southwesterly winds which transport fine sediment from North Africa. Dust is raised by a wide variety of meteorological conditions which generate strong near-surface winds in the source areas, but major long-range transport events are often associated with cold fronts linked to the passage of deep mid-latitude depressions during winter and spring. Dust haze frequency and deposition rates are highest in western Crete and decrease towards the east, suggesting that transport from Tunisia and neighbouring parts of North Africa is particularly important. The measured rate of dust deposition is well below the minimum level required for loess formation. Deposits which have previously been identified as loess are shown to be uncemented marine marls of Tertiary age. Laboratory analysis of red soils, surface sediments, and bedrock samples has confirmed that many of the soils contain an important aeolian dust component, but it is concluded that a more important source of soil parent material is provided by weathering of local rocks. Many of the soils contain significant amounts of quartz sand which cannot have been transported across the sea from North Africa. Reworking of weathered material and deposited dust is extensive, and is accomplished by both aeolian and fluvial processes. Tectonically-controlled depressions in the mountains and parts of the coastal lowlands have acted as long-term sinks in which a thickness of several metres of sediment and soil has accumulated during the Quaternary.     

Techniques to measure the dry aeolian deposition of dust in arid and semi‐arid landscapes: a comparative study in West Niger

Seven techniques designed to measure the dry aeolian deposition of dust on a desert surface were tested during field experiments in Niger, central‐west Africa. Deposition fluxes were measured during eight periods of 3–4 days each. Experimental techniques tested were the MDCO (marble dust collector) method, the Frisbee method, the glass plate method (optical analysis of dust deposited on glass surfaces using particle imaging software), the soil surface method (deposition on a simulated desert floor) and the CAPYR (capteur pyramidal) method. Theoretical techniques tested were the inferential method and the combination method (gradient method extended with a deposition term for coarse dust particles). The results obtained by the MDCO, Frisbee, inferential and combination methods could be directly compared by converting the data to identical standard conditions (deposition on a water surface producing no resuspension). The results obtained by the other methods (glass plate, soil surface, CAPYR) were compared relatively. The study shows that the crude (unconverted) deposition fluxes of the five experimental techniques were similar, while the crude deposition fluxes calculated by the two theoretical techniques were substantially higher, of the order of four to five times as high as for the experimental techniques. Recalculation of the data to identical environmental conditions (the standard water surface) resulted in nearly identical deposition fluxes for the MDCO, Frisbee, inferential and combination techniques, although the latter two still had slightly higher values (but the differences remained small). The measurements illustrate the need to include a grain shape factor in theoretical dust deposition models. Without such a factor, theoretical models overestimate the deposition. The paper also discusses the advantages and disadvantages of the techniques tested. Copyright © 2007 John Wiley & Sons, Ltd.     

Biological response to coastal upwelling and dust deposition in the area off Northwest Africa

Nutrient supply in the area off Northwest Africa is mainly regulated by two processes, coastal upwelling and deposition of Saharan dust. In the present study, both processes were analyzed and evaluated by different methods, including cross-correlation, multiple correlation, and event statistics, using remotely sensed proxies of the period from 2000 to 2008 to investigate their influence on the marine environment. The remotely sensed chlorophyll-a concentration was used as a proxy for the phytoplankton biomass stimulated by nutrient supply into the euphotic zone from deeper water layers and from the atmosphere. Satellite-derived alongshore wind stress and sea-surface temperature were applied as proxies for the strength and reflection of coastal upwelling processes. The westward wind and the dust component of the aerosol optical depth describe the transport direction of atmospheric dust and the atmospheric dust column load.     

Gross erosion,net erosion and gross deposition of dust by wind: field data from 17 desert surfaces

Wind erosion measurements were carried out in Nellis Dunes Recreation Area, southern Nevada, USA. Gross erosion (the total mass of sediment effectively blown away from a surface), gross deposition (the total mass of sediment effectively depositing on a surface) and net erosion (the difference in sediment mass before and after an event) were measured for 1 year, on 17 different types of surfaces developed on loose dune sand, compacted sand, loose silt, compacted and/or aggregated silt, rock‐covered sands and silts, mixtures of sand, silt and clay, exposed petrocalcic horizons, gravelly substrata and bedrock. Results showed that net erosion, which is the type of erosion measured in field and laboratory experiments, strongly differs from gross erosion. Activity on a surface is much higher than classic net erosion measurements suggest. Future studies on wind erosion should better acknowledge the distinction between the two types of process. Also, a grain diameter of maximum susceptibility to wind erosion (‘optimum deflation diameter’) near 70 µm as proposed by the aeolian literature only exists for net wind erosion. No such optimum diameter was found for gross wind erosion within the particle range 0–100 µm delineating the transport modes of suspension and modified saltation. In addition, desert surfaces predominantly composed of sand did not show an optimum deflation diameter (for net erosion) around 70 µm. Instead, there was a preferential grain size around 15 µm at which particles were most vulnerable to net emission. Desert surfaces poor in sand showed the classic value of 70 µm. This suggests that interactions exist between the type of surface and the susceptibility of particles to wind erosion. This study is solely based on field data. Although results are supported by two previous wind tunnel studies, more wind tunnel experiments documenting the interactions between gross erosion and gross deposition are necessary. Copyright © 2010 John Wiley & Sons, Ltd.     

The dynamic effects of sediment availability on the relationship between wind speed and dust concentration

Where sediment supply is unlimited, previous research suggests that a strong, positive relationship between wind speed and dust concentration exists at the event scale. This relationship can break down if sediment availability is limited or changes during an event. This paper explores the dynamic effects of sediment availability on the relationship between wind speed and dust concentration using data from nine high‐latitude dust events recorded in Iceland. Of these events, six showed a strong positive relationship between wind speed and dust concentration. For the remainder, the relationship breaks down periodically during the event due to changing surface moisture conditions and atmospheric humidity. Results suggest a need to understand how spatial and temporal changes in humidity, surface soil moisture, soil texture and threshold velocity interact and control sediment availability for dust emissions in all environments, including at high latitudes. Copyright © 2018 John Wiley & Sons, Ltd.     

Properties of modern dust accumulating in the Uinta Mountains,Utah, USA,and implications for the regional dust system of the Rocky Mountains

A growing body of work is illuminating the importance of dust as a component of soil development and biogeochemical cycling in alpine environments of the Rocky Mountains. Nonetheless, important questions remain about the dust system in this region due to a paucity of focused studies and direct measurements. This project involved deployment of modified marble dust traps in the alpine zone of the Uinta Mountains of Utah to trap modern atmospheric dust over a two year period. Results indicate that dust accumulation rates are similar to values previously reported for the Wind River Range of Wyoming, but less than values for south‐western Colorado, suggesting a south‐to‐north decrease in regional dust flux. The overall mean grain size of Uinta dust is similar to values reported by prior studies in Colorado, indicating a general uniformity in grain size distribution. Uinta dust is dominated by quartz, plagioclase, K‐feldspar, and illite with trace amounts of kaolinite, chlorite, and amphibole. In contrast, only quartz and K‐feldspar are present in the Uinta bedrock, confirming an exotic origin for the dust arriving in the alpine zone. Exotic mineralogies have also been reported in dust from other mountain ranges in the western United States, indicating that eolian delivery of allochthonous minerals is a widespread process. Geochemical analysis reveals that Bi, Na, P, Zn, Sn, Cu, Cd, Ba, Ni, W, Sb, Pb, and Tl in Uinta dust are elevated 10 to > 80‐times above their abundances in local bedrock. These results support reports of anthropogenic elemental enrichment in lake sediments from Colorado and Utah. Patterns of elemental loading suggest that certain elements are delivered by winds arriving from different directions, raising the possibility that some elements could be associated with unique source areas. Copyright © 2014 John Wiley & Sons, Ltd.     

Trapping of airborne dust by mosses in the Negev Desert,Israel

Airborne silt and clay containing calcium carbonate, quartz, clays, marine nannoplankton, and aquatic diatoms are trapped among stems of mosses in the Negev Highlands Desert. The mosses were studied in an area with 70 mm mean annual rainfall. They grow over the particles covering them and trap additional dust as it comes, resulting in the accumulation of loess sediments. The mosses protect the accumulated soil from erosion by wind or water. Remnants of the moss leaves and stems were found at a depth of 15 mm and more. No particles or minerals typical to basalt were found in the moss-trapped soil. The function of cushiony mosses may be used to explain the processes of loess trapping and protection in larger areas in moister areas such as the Northern Negev. Microscopic fossils in the dust may be used as guides to the origin of the (aeolian) sediments.     

Dunes on the skeleton coast,Namibia (South West Africa): Geomorphology and grain size relationships

Simple, and locally compound, transverse and barchanoid dunes dominate the 2000 km² Skeleton Coast dunefield in northwestern Namibia/South West Africa. Dune height and spacing are closely correlated (r = 0-89) and decrease across the dunefield from southwest to northeast, with an accompanying change from transverse to barchanoid ridges and ultimately barchans. The dunes are aligned transverse to the dominant strong south and south southwest onshore winds. Alignment patterns indicate that surface roughness changes between coastal plain and dunes cause dune-forming winds to swing to the right over the dunes, but resume their original direction beyond. Grain size and sorting vary at three scales: the dune, the dune landscape and through the dunefield. Overall the sands, derived from three localities by deflation from beaches supplied by vigorous longshore drift, become progressively finer and better sorted across the dunefield paralleling changes in dune height and spacing. A statistically significant relationship (r = ?0?65) was established between dune spacing and the phi grain size of the coarser fraction of the dune sands, demonstrating the importance of the protective effects of coarse grains, and suggesting that the morphometry of simple transverse dunes may be controlled by the scale of turbulence associated with the threshold wind speed required to move the coarsest fraction of the dune sand.     

Holocene fluvial valley fill sources of atmospheric mineral dust in the Skeleton Coast,Namibia

Western Namibia is a significant global source of atmospheric mineral dust. We investigate the relationship between dust and source sediments, assessing the sustainability of dust flux. Remote sensing studies have highlighted specific ephemeral fluvial systems as important contributors to dust flux, including highlighting sections of valleys that are the origins of dust plumes in the period 2005–2008. Little is known however about the specific within‐valley dust sediment sources, particularly whether dust is derived from modern ephemeral channel floors or older valley fill sediments, many of which have been reported in the region. As part of a region‐wide analysis of aeolian dust flux, we investigate the sediment properties of atmospheric dust samples and valley sediments from the Huab valley, one of the principal regional dust sources. Trapped dust samples contain up to 88% very fine sand and silt when collected samples are disaggregated prior to analysis. Valley fill surface samples comprise 80% very fine sand and silt, and the surface of the modern ephemeral channel 30%. Valley fill sediments were sampled at depths up to 3.6 m below the present surface and reveal Holocene depositional ages from 0.6 ± 0.03 ka back to 9.79 ± 0.73 ka. These sediments contain 30% to 6% very fine sand and silt, with levels decreasing with depth and age. Aeolian bedforms in the valley system (nebkhas on the fill surface and climbing dunes on valley margins) indicate that aeolian processes under the influence of strong seasonal easterly winds likely result in dust being winnowed out of the valley fill surfaces, with sandy bedforms being constructed from the coarser component of the fill sediments. The volume of valley fill sediment suggests dust sourced from Holocene sediments is likely to continue into the future regardless of flow conditions in the modern channel system. Copyright © 2017 John Wiley & Sons, Ltd.     

Loess accumulation and soil formation in central kansas,United States,during the past 400 000 years

Based on interpolation of thermoluminescence dates and the mean accumulation rate of 0.034 mm yr^?1, four cycles of pedogenic CaCO₃ accumulation are found within the Loveland Loess: 415–325 ka, 325–250 ka, 250–195 ka and 195–95 ka. The four CaCO₃ peaks correspond chronologically to marine oxygen isotope stages 11, 9, 7 and 5, respectively. The early Wisconsin (95–70 ka) was characterized by sand dune activity. The reddish pedocomplex was formed from 70 to 35 ka under relatively warm and moist climatic conditions with a very slow rate of silt accumulation (0·016 mm yr^?1). The Gilman Canyon pedocomplex, enriched in organic matter and dated at 35–20 ka, was formed under a strong physical weathering regime and a relatively high rate of silt accumulation (0·15 mm yr^?1), indicating a windy, relatively moist, probably cool environment. It developed when the Laurentide ice sheet was advancing and dust content in Greenland ice core was low. The Peoria Loess was accumulated at a rate of 0·3 mm yr^?1 in central Kansas under cold dry conditions when the ice sheet fluctuated around its maximum position and the dust content in the Greenland ice core was the highest. Even the warm substage around 13 ka has some corresponding evidence in the central Great Plains. The well-developed Brady Soil, dated at 10·5–8·5 ka, indicates that the early Holocene was the optimal time for soil development since 20 ka. The poorly weathered Bignell Loess might have been deposited during the Altithermal Period from 8·5 to 6 ka.     

Environmental controls on blowing dust direction at lubbock,Texas, U.S.A.

Blowing dust is a common phenomenon at Lubbock, Texas, on the Southern High Plains. The directional variability of blowing dust estimated with the ‘sand rose’ technique, using wind speed and direction data, suggest that dust transport occurs from all directions. An empirical method of determining directional variability using meteorological data on visibility reductions due to blowing dust, however, indicates that most dust comes from the west and south-west. In addition to wind speed and direction, other environmental factors must be considered in explaining the spatial pattern of dust transport. Soil erodibility is variable in the region, with the most extensive area of highly erodible soils to the west and south-west of Lubbock. Rangeland dominates land use to the east, while agriculture is extensive to the north, west and south. Local farming techniques leave bare soil during the winter and spring, when most airborne dust is produced and also when strong winds are common from the west and south-west. Soil moisture is lowest to the southwest of Lubbock, which leads to a decrease in soil structure and an increase in the potential for wind erosion in that direction. Relative humidities affect threshold wind speeds and are lowest during March and April, when winds are common from the west and south-west. The spatial and seasonal variability and interactions between many factors, both natural and human-controlled, must therefore considered in explaining the directional variability of aeolian sediment transport at Lubbock.     

Quantifying the effect of geomorphology on aeolian dust emission potential in northern China

Representation of dust sources remains a key challenge in quantifying the dust cycle and its environmental and climatic impacts. Direct measurements of dust fluxes from different landform types are useful in understanding the nature of dust emission and characterizing the dynamics of soil erodibility. In this study we used the PI-SWERL® instrument over a seasonal cycle to quantify the potential for PM₁₀ (particles with diameter ≤10 μm) emission from several typical landform types across the Tengger Desert and Mu Us Sandy Land, northern China. Our results indicate that sparse grasslands and coppice dunes showed relatively high emission potentials, with emitted fluxes ranging from 10⁻¹ to 10¹ mg m⁻² s⁻¹. These values were up to five times those emitted from sand dunes, and one to two orders of magnitude greater than the emissions from dry lake beds, stone pavements and dense grasslands. Generally, PM₁₀ emission fluxes were seen to peak in the spring months, with significant reductions in summer and autumn (by up to 95%), and in winter (by up to 98%). Variations in soil moisture were likely a primary controlling factor responsible for this seasonality in PM₁₀ emission. Our data provide a relative quantification of differences in dust emission potential from several key landform types. Such data allow for the evaluation of current dust source schemes proposed by prior researchers. Moreover, our data will allow improvements in properly characterizing the erodibility of dust source regions and hence refine the parameterization of dust emission in climate models. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd.