sub basin scale dust source geomorphology detected using modis 1 the spatial and temporal variability of dust emissions from different surfaces in the lake eyre basin australia is determined using modis data for 2003 6 the sources of 529 dust plumes were classified overall 37 of plumes originated in areas of aeolian deposits 30 from alluvial deposits and floodplains and 29 from ephemeral lakes or playas at this sub basin scale the relative importance of different dust source geomorphologies varied primarily in response to sediment supply and availability and was not related to aeolian transport capacity suggesting the lake eyre basin is a supply limited system

sand dunes as a major proximal dust source for late pleistocene loess in the negev desert israel grain size analyses of three hilltop primary eolian loess sequences in the negev desert southern israel show a bimodal grain size distribution at 50 60 m and 3 8 m using analyses of mineralogy and osl ages we demonstrate that the coarse mode is composed mostly of quartz grains and its relative magnitude increases regionally with time suggesting an enhancement of a time transgressive proximal dust source compared to a distal saharan fine grain dust the only proximal dust source for large amount of coarse silt quartz grains is the sands that advanced into sinai and the negev concurrently with the loess accretion during the late pleistocene as a result of the exposure of the mediterranean shelf we therefore propose that the coarse silt quartz grains were formed through eolian abrasion within the margins of an advancing sand sea this relationship between desert sand seas as a source for proximal coarse dust and desert margin loess deposits can be applicable to other worldwide deserts such as northern africa china and australia

dust raising in the dustiest place on earth the bodele in northern chad is the dustiest place on earth it is dusty because of the co location of strong near surface winds and a large exposure of low density friable diatomite data are reported from three kinds of observation on dust generation in the bodele a two automatic weather stations and pilot balloon tracking complemented with reanalysis data measuring and estimating wind velocities b sun photometers measuring atmospheric dust concentrations c a vacuum pump dust sampler and an array of mwac sediment samplers measuring in situ sediment transport with these data we develop four hypotheses about dust generation 1 the pulsing of dust output from the bodele depends primarily on the varying strength of a low level jet llj i e at this scale dust production is transport limited 2 the most prolific mechanism of dust production is the breakdown of saltating diatomite flakes as they collide with each other and with the surface 3 disturbance of flow around the large barchans particularly turbulence and convergence on their horns is a major contributor to dust production i e the dunes are dust mills 4 in consequence dust production is localised within the main exposure of diatomite to places where there are the most dunes as on the eastern and northern fringes of the exposure

factors affecting the nature and rate of dust production from natural dune sands this paper evaluates the influence of natural sand particle characteristics on the amount and particle size distributions of dust produced by aeolian abrasion it contrasts with previous studies of aeolian abrasion by conducting experiments using i whole sand samples as opposed to selected size fractions ii natural mature dune sands rather than artificial or freshly crushed material and iii weathered sands that have acquired a superficial clay coating instead of grains with clean surfaces whilst previous research has found clear positive relationships between particle size sorting roundness and the amount of dust produced by aeolian abrasion the relationships determined in this study show some variation according to the geomorphological context from which the original samples were obtained the most important factor affecting the amount and particle size characteristics of the dust produced was the presence of a clay coating on the grain surface that is removed by the abrasion process the dust produced by this mechanism had a modal size of 2 5 m and material 10 m comprised up to 90 of the particles produced

preferential dust sources a geomorphological classification designed for use in global dust cycle models received 11 april 2011 revised 28 september 2011 accepted 4 october 2011 published 24 december 2011 1 we present a simple theoretical land surface classification that can be used to determine the location and temporal behavior of preferential sources of terrestrial dust emissions the classification also provides information about the likely nature of the sediments their erodibility and the likelihood that they will generate emissions under given conditions the scheme is based on the dual notions of geomorphic type and connectivity between geomorphic units we demonstrate that the scheme can be used to map potential modern day dust sources in the chihuahuan desert the lake eyre basin and the taklamakan through comparison with observed dust emissions we show that the scheme provides a reasonable prediction of areas of emission in the chihuahuan desert and in the lake eyre basin the classification is also applied to point source data from the western sahara to enable comparison of the relative importance of different land surfaces for dust emissions we indicate how the scheme could be used to provide an improved characterization of preferential dust sources in global dust cycle models

control of dust emissions by geomorphic conditions wind environments and land use in northern china an examination based on dust storm frequency from 1960 to 2003 the degree to which dust emissions are controlled by geomorphic conditions wind environments and land use was investigated using the dust storm frequency dsf and data from more than 300 meteorological stations throughout northern china our analysis showed that most dust emissions originated in gobi deserts that developed in piedmont alluvial fans of the kunlun qilian and helan mountains dust emissions are low from other gobi desert regions such as the northern gurbantunggut and eastern taklimakan where high vegetation coverage restrained dust emissions or where dust size particles are not abundant after a long period of strong wind erosion sandy deserts with relatively high vegetation coverage or an extensive cover by mobile sands are not a major dust source although the highest dust emissions did not appear in regions with the highest wind energy dsf trends in each region from 1960 to 2003 were closely related to local wind activity dsf was low in regions with high levels of human activity where the mean dsf from 1960 to 2003 did not exceed 4 days year even from the 1960s to the early 1970s the period with the greatest dsf frequency did not exceed 8 days year which indicates that extensive land use did not contribute to dsf the low dsf in these areas might result from the fact that although land use could produce abundant fine soil fractions vegetation coverage and soil moisture remained higher than in the gobi deserts of arid china thereby decreasing dust storm occurrence

mapping north african landforms using continental scale unmixing of modis imagery we describe the production of a landform map of north africa utilizing moderate resolution satellite imagery and a methodology that is applicable for sub continental to global scale landform mapping a mosaic of moderate resolution imaging spectroradiometer modis apparent surface reflectance imagery was compiled for africa north of 10 n landform image endmembers were chosen to characterize ten different types of vegetated and unvegetated desert surfaces alluvial complexes dunes dry and ephemeral lakes open water basaltic volcanoes and flows mountains regs stripped low angle bedrock surfaces sand sheets and sahelian vegetation multiple endmember spectral mixture analysis mesma was applied to the modis mosaic to estimate landform and vegetation endmember fractions the major landform in each modis pixel was identified based on the majority endmember fraction in two or three endmember models accuracy assessment was conducted using two data sources the historic landform map of north africa raisz e 1952 landform map of north africa environmental protection branch office of the quartermaster general and landsat thematic mapper tm data comparison with the raisz landform map gave an overall classification accuracy of 54 with significant confusion between alluvial surfaces and regs and between sandy and clayey surfaces and dunes a second validation using 20 landsat images in a stratified sampling scheme gave a classification accuracy of 70 with confusion between dunes and sand sheets both accuracy assessment schemes indicated difficulty in vegetation classification at the margin of the sahel a comparison with minimum distance and maximum likelihood supervised classifications found that the mesma approach produced significantly higher classification accuracies this digital landform map is of sufficiently high quality to form the basis for geomorphic studies including parameterization of the surface in global and regional dust models

links between topography wind deflation lakes and dust the case of the bodele depression chad the bodele depression chad is the planet s largest single source of dust deflation from the bodele could be seen as a simple coincidence of two key prerequisites strong surface winds and a large source of suitable sediment but here we hypothesise that long term links between topography winds deflation and dust ensure the maintenance of the dust source such that these two apparently coincidental key ingredients are connected by land atmosphere processes with topography acting as the overall controlling agent we use a variety of observational and numerical techniques including a regional climate model to show that 1 contemporary deflation from the bodele is delineated by topography and a surface wind stress maximum 2 the tibesti and ennedi mountains play a key role in the generation of the erosive winds in the form of the bodele low level jet llj 3 enhanced deflation from a stronger bodele llj during drier phases for example the last glacial maximum was probably sufficient to create the shallow lake in which diatoms lived during wetter phases such as the holocene pluvial winds may therefore have helped to create the depression in which erodible diatom material accumulated instead of a simple coincidence of nature dust from the world s largest source may result from the operation of long term processes on paleo timescales which have led to ideal conditions for dust generation in the world s largest dust source similar processes plausibly operate in other dust hotspots in topographic depressions

dust production and the release of iron oxides resulting from the aeolian abrasion of natural dune sands global dust trajectories indicate that significant quantities of aeolian transported iron oxides originate in contemporary dryland areas one potential source is the iron rich clay coatings that characterize many sand sized particles in desert dunefields this paper uses laboratory experiments to determine the rate at which these coatings can be removed from dune sands by aeolian abrasion the coatings impart a red colour to the grains to which previous researchers have assigned variable geomorphological significance the quantities or iron removed during a 120 hour abrasion experiment are small 99 mg kg 1 and difficult to detect by eye however high resolution spectroscopy clearly indicates that ferric oxides are released during abrasion and the reflectance of the particles alters one of the products of aeolian abrasion is fine particles 10 mum diameter with the potential for long distance transport copyright c 2004 john wiley sons ltd

saltating particles playa crusts and dust aerosols at owens dry lake california as part of the multinational lake owens dust experiment lode we have studied the generation of dust storms on the south sand sheet of owens dry lake california an anthropogenically desiccated playa reported to be the single greatest source of particulate matter in north america during march 1993 we performed an intensive field study including eight significant dust storms building on our prior work 1978 1984 and preliminary studies 1991 1992 we studied sources and magnitude of coarse saltating particles the meteorological conditions that allow them to become mobile across the flat playa of owens dry lake and how the motion of saltating particles across different types of playa surfaces results in the generation of pm10 dusts aerosol particles smaller than 10 m aerodynamic diameter saltating grains of lacustrine sand and broken crust abrade and disaggregate the playa surface into fine aerosols and the resulting pm10 concentrations recorded during major dust storms are among the highest ever recorded in north america on 23 march 1993 we measured a 2 h concentration on the playa of 40 620 g m 3 as far as we can determine the highest ambient pm10 value ever recorded in the u s a abrasion of salt silt clay crusts by saltation is shown to be responsible for all but a small part of one dust storm the quantity sand run saltating particle transport multiplied by wind run is shown to be very closely correlated with dust aerosol concentration finally we have established that on lake bed studies are essential for quantitative prediction of dust events on the owens dry lake bed despite the difficult conditions encountered

geomorphic mapping and taxonomy of fluvial landforms abstract fluvial geomorphologists use close to a 100 different terms to describe the landforms that make up riverscapes we identified 68 of these existing terms that describe truly distinctive landforms in which form is maintained under characteristic conditions and fluvial processes clear topographic definitions for these landforms to consistently identify and map them are lacking with the explosion of continuous high resolution topography and digital elevation models we have plenty of new basemaps in which these landforms are clearly visible but very few examples of manual or automated classification of fluvial landforms fluvial landforms are the building blocks of a river and are variously referred to as geomorphic units morphological units habitat units and channel units we present a tiered framework for describing geomorphic units with tier 1 differentiating units on the basis of their stage tier 2 separating shape e g concave convex or planar tier 3 using particular key attributes to narrow in on the likely specific geomorphic unit type and tier 4 differentiating those types on the basis of vegetative or roughness modifiers information on the assemblage and configuration of geomorphic units can be used to inform process based interpretations of the range of river behavior the accuracy and transferability of such analyses is fundamentally tied to the taxonomy we assign to these discrete building blocks in this paper we clarify the terminology and definitions relating to the identification and delineation of geomorphic units margins and structural elements we establish a set of procedures that can be used to manually map and identify these features the proposed framework provides a rigorous and repeatable approach to identification of topographically defined features of riverscapes we demonstrate the application of these systematic yet flexible procedures with a series of maps from rivers in differing valley settings

cenozoic basin forming processes along the northeastern margin of eurasia constraints determined from geophysical studies offshore of hokkaido japan abstract the cenozoic evolution of a sedimentary basin on a long lasting deformation zone along the northeastern eurasian margin is investigated using geophysical studies analysis of seismic reflection data with detailed age assignments reveals that an offshore paleogene and early miocene basin around northwestern hokkaido developed as a typical pull apart depression at the right stepping part of n s trending dextral faults numerical modeling estimates the total slip on the paleogene strike slip faults is ca 12 km which matches the actual shape and volume of the basin the total displacement resulted from quite active 1 4 mm year dextral motions along the fault zone during the paleogene and early miocene deformation fields around the fault step also indicate a complicated pattern of vertical axis rotation the emergence of contraction tectonics in the middle miocene is suggested from the foreland type basin configuration observed the temporal variations of sedimentation rate through the cenozoic are estimated utilizing the depth converted seismic record and they confirm an accelerated subsidence implying a forearc foreland transition upon the eurasian margin

relation of vertical flux of particles smaller than 10 μm to total aeolian horizontal mass flux at owens lake the vertical flux of particles smaller than 10 m for a saline playa surface the particle size composition of which was classified as loam textured was estimated for a highly wind erodible site on the playa of owens dry lake in california the ratio of this vertical flux to the horizontal flux of total airborne material through a surface perpendicular to the soil and to the wind fa qtot is 2 75 10 4 m 1 this is consistent with that ratio for sand textured soils and suggests that the binding energy and size of saltating particles for the tested surface material at owens lake is of the same order as that for sandier soils the horizontal mass flux of saltating grains q in the reported wind erosion event is 51 3 of the total horizontal mass flux qtot therefore the ratio of fa q is 5 4 10 4 m 1

gravel deposits on the margins of the qinghai xizang plateau and their environmental significance abstract the thick deposits of quaternary gravels found along the margins of the qinghai xizang tibet plateau have been studied for decades here we concentrate on two sediment series widely developed along the kunlun tian shan and qilian mountains the xiyu formation a molassic series of lower pleistocene age and the middle and upper pleistocene gobi gravels these two series with their contained fossil assemblages throw light on the question of the mean altitudes and uplift rates of the tibetan plateau during the quaternary and on the related problem of the vigour and penetration of advected summer monsoonal moisture into central asia the sedimentary series on the northern piedmonts of the tibetan plateau considered here challege the view that plateau uplift accelerated in the upper pleistocene they indicate that the plateau had reached mean altitudes in the range 4000 5000 m perhaps by the end of the lower pleistocene and certainly by the middle pleistocene this diminished the incursion of southerly monsoonal moisture and so imposed arid and semi arid conditions across much of a vast region north of the plateau which among other effects precluded widespread mountain glaciation in the lower pleistocene and general ice sheet glaciation of the tibetan plateau as a whole

land use land cover and point sources of the 15 december 2003 dust storm in southwestern north america abstract a major dust event occurred on 15 december 2003 in the chihuahuan desert region of texas and new mexico usa and chihuahua mexico and in the southern high plains region of texas and new mexico using a modis satellite image 146 individual small scale sources plumes of dust were identified these plumes merged to form the regional scale dust storm the point sources were characterized with respect to land use and land cover using a combination of field work and aerial photography fifty eight of the sources are on cropland mostly on the southern high plains forty nine are on rangeland from across the entire region thirty of the dust plumes originate within playa basins mostly in the chihuahuan desert point sources of dust only represent a small fraction of the total land surface at any given moment i e the period when the image was acquired because most of the land within the region was not subject to erosion during the event in general land use and soil characteristics of point sources matched those of adjacent areas that were not emitting dust at the time suggesting that microscale variations in erodibility or meteorological factors may dictate the actual emission points of dust during individual events

eolian sediments generated by anthropogenic disturbance of playas human impacts on the geomorphic system and geomorphic impacts on the human system abstract in many of the earth s arid and semiarid lands saline lakes playas and similar landforms are disturbed as a result of human activity diversion and or consumptive use of surface or groundwaters has created the effect of a climate change in numerous drainage basins resulting in the desiccation of lakes and reactivation of eolian processes at many locations playas are natural sites for extensive eolian activity because of the deposition of clastic and chemical sediments in basins by surface water via fluvial transport and groundwater via efflorescence wind erosion and deposition of playa sediments has had a major role in the development of landforms and sedimentary units in the present lunette fields worldwide simpson desert australia and geological past from the triassic mercia mudstone england to the quaternary lahontan basin and cima volcanic field usa anthropogenic disturbance or desiccation of playa systems has resulted in the eolian transport of sand e g lop nor china konya basin turkey rajasthan india kappakoola australia several sites in west africa and or dust e g aral sea kazakhstan uzbekistan old wives lake canada kara bogaz gol ex ussr lake texcoco mexico owens dry lake mono lake and other playas usa typically this is accomplished by abstraction of water and or removal of vegetation from terminal lake basins an extensive review of the literature documents many examples and or potential examples of such phenomena in numerous nations the reactivation of eolian processes from closed basins produces air pollution in the form of fugitive dust naturally occurring compounds released into the atmosphere by human actions and has significant environmental and economic impacts on human activities in the surrounding areas restoration or mitigation of degraded land on or surrounding playas has been accomplished at lake texcoco kara bogaz gol and the konya basin and is being actively implemented at mono lake owens dry lake and the aral sea

downslope winds and dust storms in the salton basin abstractthe salton basin is a closed subsea level basin located in extreme southeastern california at the center of the basin lies the salton sea the state s largest inland lake which is surrou

desert pavement development and landscape stability on the eastern libyan plateau egypt abstract desert pavement surfaces of the eastern libyan plateau in central egypt represent a stable landscape preserving middle and upper paleolithic artifacts detailed measurements of pavement clasts indicate significant variability in clast size density lithology and orientation between pavements but no spatial relationship among any of these pavement variables over the study area pavement characteristics are unrelated to local geomorphic features including slope gradient and aspect suggesting a desert pavement surface that has developed without significant influence from transporting mechanisms such as overland flow and slope failure meridional vertical cracks in surface clasts implicate thermal stresses due to diurnal solar variation as a mechanical weathering process whereas the presence of a clast free silty layer within all soil profiles indicates that these are accretionary pavement surfaces that have grown upward over time the desert pavement in this region has likely developed in situ through mechanical breakdown of surface clasts and desert pedogenesis indicating long term stability for this region and minimal taphonomic effects on artifacts 2 cm in diameter deposited on this surface over the last ca 100 ka

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

intraplate stresses and seismicity the role of topography and density heterogeneities abstract the stress induced by the topography and by density heterogeneities in the lithosphere has been computed for two different tectonic regions of the north american plate the lithosphere was assumed to consist of a two dimensional layered elastic slab over an inviscid fluid the calculations show that these stresses are locally comparable in magnitude to the regional tectonic stress 20 50 mpa two areas have been analyzed in greater detail the southeastern united states and the rio grande rift the stress in the southeastern united states is computed along a cross section perpendicular to the strike of the appalachian mountains the computed stress appears largest beneath the blue ridge and valley and ridge provinces where the appalachian seismicity is located the stress in the western united states is computed along a cross section perpendicular to the rio grande rift large stress is shown beneath the rift and the adjacent regions the stress induced by surface and internal loading is extensional in the rio grande rift and compressional in the colorado plateau and in the great plains

assessing the microped size distributions of desert soils erodible by wind the microped size distribution of erodible soils is one of the main factors controlling the emissions of mineral aerosol to date the microped size distributions of desert soils in natural field conditions are not well known and thus the existing dust source models cannot be applied to natural sites based on dry sieving and elemental analysis of 26 soil samples collected in arid and semiarid regions it is shown that the microped size distributions of these desert soil samples involve a combination of four major mass size populations these four size populations correspond to salty soils fine quartz sand coarse dune sand and aluminosilicate silt we show that the microped size distributions of the various desert soils according to their mineralogical characteristics can be calculated by a mixture involving two or three of these four populations the main field of application for this scheme is the characterization of the erodible soil size distributions for modelling the atmospheric dust cycle

dust sources in arid and semiarid china and southern mongolia impacts of geomorphological setting and surface materials abstract analysis of the geomorphological settings and surface materials in arid and semiarid china and southern mongolia revealed that the dominant dust sources are gobi deserts and alluvial fans adjacent to gobi deserts in the piedmonts of the kunlun qilian helan and gobi altai mountains these areas have persistent supplies of dust sized particles deposited by intermittent floods from the mountains and fine materials are also generated by weathering and aeolian processes acting on the coarse fractions of gobi surfaces clear spatial differences in mineral types and contents and in the salt contents of surface materials also strongly affected the intensity of dust emissions inconsistencies in monitoring simulation and calculation of dust emissions in previous studies of northern china and mongolia may have been caused by insufficiently detailed considerations of variations in the geomorphological setting where the geomorphological settings in these areas are not considered in sufficient detail deviations arise in the estimation and prediction of dust using current models although the present study did not quantify the persistence and replenishment of dust sources in the study area our conclusions about the importance of geomorphology can improve future studies of dust sources and controlling factors improve assessments of the effects of climate change on dust emissions and facilitate the interpretation of paleoclimate records

desert pavement dynamics numerical modeling and field based calibration desert pavements are widely used as a relative surface dating tool because they are progressively better developed on surfaces ranging from thousands to hundreds of thousands of years in age recent work however has highlighted the dynamic nature of pavements and undermined their use as surface age indicators quade 2001 proposed that latest pleistocene vegetation advances destroyed all mojave desert pavements above 400 m elevation making all such pavements holocene in age in an effort to reconcile young pavement evidence with their widespread use as pleistocene surface age indicators we developed a numerical model based on the classic conceptual model in which pavements co evolve with their underlying eolian epipedons over millennial timescales in this co evolutionary process fine grained eolian deposition and av horizon development within the eolian epipedon promotes surface clast motion and pavement development enhancing the eolian sediment trapping ability of the pavement in a positive feedback model results illustrate the multi scale nature of pavement dynamics pavements may require tens of thousands of years to fully develop from a newly abandoned alluvial surface but may heal over timescales of decades to centuries if a mature eolian epipedon is present as such there is no inconsistency between rapid pavement healing and a pleistocene age for the underlying alluvial surface to calibrate the model we conducted surficial geologic mapping and pavement sedimentological analysis on two desert piedmonts our study areas include both proximal and distal fan environments illustrating the role of parent material texture in controlling the mode of pavement formation using available geochronology our work provides a rigorous calibration of pavement formation rates in our study areas and provides evidence supporting the use of pavements as local relative surface age indicators over holocene to late pleistocene timescales copyright 2007 john wiley sons ltd

mapping playa evaporite minerals and associated sediments in death valley california with multispectral thermal infrared images efflorescent salt crusts and associated sediments in death valley california were studied with remote sensing data acquired by the nasa thermal infrared multispectral scanner tims nine spectral classes that represent a variety of surface materials were distinguished including several classes that reflect important aspects of the playa groundwater chemistry and hydrology evaporite crusts containing abundant thenardite sodium sulfate were mapped along the northern and eastern margins of the cottonball basin areas where the inflow waters are rich in sodium gypsum calcium sulfate crusts were more common in the badwater basin particularly near springs associated with calcic groundwaters along the western basin margin evaporite rich crusts generally marked areas where groundwater is periodically near the surface and thus able to replenish the crusts though capillary evaporation detrital silicate minerals were prevalent in other parts of the salt pan where shallow groundwater does not affect the surface composition the surface features in death valley change in response to climatic variations on several different timescales for example salt crusts on low lying mudflats form and redissolve during seasonal to interannual cycles of wetting and desiccation in contrast recent flooding and erosion of rough salt surfaces in death valley probably reflect increased regional precipitation spanning several decades remote sensing observations of playas can provide a means for monitoring changes in evaporite facies and for better understanding the associated climatic processes at present such studies are limited by the availability of suitable airborne scanner data however with the launch of the earth observing system eos am 1 platform in 1998 multispectral visible near infrared and thermal infrared remote sensing data will become globally available

southern ocean sea ice extent productivity and iron flux over the past eight glacial cycles sea ice and dust flux increased greatly in the southern ocean during the last glacial period palaeorecords provide contradictory evidence about marine productivity in this region but beyond one glacial cycle data were sparse here we present continuous chemical proxy data spanning the last eight glacial cycles 740 000 years from the dome c antarctic ice core these data constrain winter sea ice extent in the indian ocean southern ocean biogenic productivity and patagonian climatic conditions we found that maximum sea ice extent is closely tied to antarctic temperature on multi millennial timescales but less so on shorter timescales biological dimethylsulphide emissions south of the polar front seem to have changed little with climate suggesting that sulphur compounds were not active in climate regulation we observe large glacial interglacial contrasts in iron deposition which we infer reflects strongly changing patagonian conditions during glacial terminations changes in patagonia apparently preceded sea ice reduction indicating that multiple mechanisms may be responsible for different phases of co2 increase during glacial terminations we observe no changes in internal climatic feedbacks that could have caused the change in amplitude of antarctic temperature variations observed 440 000 years ago

dry cyclogenesis and dust mobilization in the intertropical discontinuity of the west african monsoon a case study three dimensional mesoscale numerical simulations were performed over niger in order to investigate dry cyclogenesis in the west african intertropical discontinuity itd during the summer when it is located over the sahel the implications of dry cyclogenesis on dust emission and transport over west africa are also addressed using the model results together with spaceborne observations from the spinning enhanced visible and infra red imager seviri and the cloud aerosol lidar with orthogonal polarization caliop the study focuses on the case of 7 8 july 2006 during the african monsoon multidisciplinary analysis amma special observing period 2a1 model results show the formation of three dry cyclones in the itd during a 24 h period simulations are used to investigate the formation and the development of one of these cyclones over niger in the lee of the hoggar air mountains they show the development of the vortex to be associated with 1 strong horizontal shear and low level convergence existing along the monsoon shearline and 2 enhanced northeasterly winds associated with orographic blocking of air masses from the mediterranean sea the dry cyclone was apparent between 0700 and 1300 utc in the simulation and it was approximately 400 km wide and 1500 m deep potential vorticity in the center of vortex reached nearly 6 pvu at the end of the cyclogenesis period 1000 utc the role of the orography on cyclogenesis along the itd was evaluated through model simulations without orography the comparison of the characteristics of the vortex in the simulations with and without orography suggests that the orography plays a secondary but still important role in the formation of the cyclone orography and related flow splitting tend to create low level jets in the lee of the hoggar and air mountains which in turn create conditions favorable for the onset of a better defined and more intense vortex in the itd region moreover orography blocking appears to favor the occurrence of a longer lived cyclone furthermore model results suggested that strong surface winds 11 m s 1 enhanced by the intensification of the vortex led to the emission of dust mass fluxes as large as 3 g m 2 s 1 the mobilized dust was mixed upward to a height of 4 5 km to be made available for long range transport this study suggests that the occurrence of dry vortices in the itd region may contribute significantly to the total dust activity over west africa during summer the distribution of dust over the sahara sahel may be affected over areas and at time scales much larger than those associated with the cyclone itself

dust source identification using modis a comparison of techniques applied to the lake eyre basin australia the impact of mineral aerosol dust in the earth s system depends on particle characteristics which are initially determined by the terrestrial sources from which the sediments are entrained remote sensing is an established method for the detection and mapping of dust events and has recently been used to identify dust source locations with varying degrees of success this paper compares and evaluates five principal methods using modis level 1b and modis level 2 aerosol data to a differentiate dust mineral aerosol from non dust and 2 determine the extent to which they enable the source of the dust to be discerned the five modis l1b methods used here are 1 un processed false colour composite fcc 2 brightness temperature difference 3 ackerman s 1997 j geophys res 102 17069 17080 procedure 4 miller s 2003 geophys res lett 30 20 art no 2071 dust enhancement algorithm and 5 roskovensky and liou s 2005 geophys res lett 32 l12809 dust differentiation algorithm the aerosol product is modis deep blue hsu et al 2004 ieee trans geosci rem sensing 42 557 569 which is optimised for use over bright surfaces i e deserts these are applied to four significant dust events from the lake eyre basin australia omi ai was also examined for each event to provide an independent assessment of dust presence and plume location all of the techniques were successful in detecting dust when compared to fccs but the most effective technique for source determination varied from event to event depending on factors such as cloud cover dust plume mineralogy and surface reflectance significantly to optimise dust detection using the modis l1b approaches the recommended dust non dust thresholds had to be considerably adjusted on an event by event basis modis l2 aerosol data retrievals were also found to vary in quality significantly between events being affected in particular by cloud masking difficulties in general we find that omi ai and modis aqua l1b and l2 data are complementary the former are ideal for initial dust detection the latter can be used to both identify plumes and sources at high spatial resolution overall approaches using brightness temperature difference bt10 11 are the most consistently reliable technique for dust source identification in the lake eyre basin one reason for this is that this enclosed basin contains multiple dust sources with contrasting geochemical signatures in this instance btd data are not affected significantly by perturbations in dust mineralogy however the other algorithms tested including modis deep blue were all influenced by ground surface reflectance or dust mineralogy making it impossible to use one single modis l1b or l2 data type for all events or even for a single multiple plume event there is however considerable potential to exploit this anomaly and to use dust detection algorithms to obtain information about dust mineralogy

the australian desert dunefields formation and evolution in an old flat dry continent a new map the first based on interpretation of satellite imagery reveals both the complexityofaustralia sdunefieldsandtheirrelationshipswithtopography climateandsubstrate of the five main sand seas the mallee strzelecki and simpson in eastern australia cover quaternary sedimentary basins whereas the great victoria and great sandy dunefields in the west are formed by reworking of valley and piedmont sediments in a non basinal landscape of low relief ridge and valley topography these dunefields cover large areas of the arid zone and semi arid zone and small areas of dunes in sub humid areas around the margins of the continent reflecting past expansion of arid climates during glacial stages of the last several glacial cycles several areas of low relief stand out as being largely dune free the limestone nullarbor plain clay plains of the georgina basin and floodplains of rivers in the carpentaria lake eyre and murray darling drainage basins where sand is rare or not transported by diminished late quaternary rivers the yilgarn block of southwestern australia is also surprisingly free of dunes possibly as a result of long deep weathering everywhere the history of climate change is evident in dune morphology and distribution including large areas where the sand dune orientations are markedly divergent from modern sand moving wind directions

a late quaternary record of eolian silt deposition in a maar lake st michael island western alaska abstract recent stratigraphic studies in central alaska have yielded the unexpected finding that there is little evidence for full glacial late wisconsin loess deposition because the loess record of western alaska is poorly exposed and not well known we analyzed a core from zagoskin lake a maar lake on st michael island to determine if a full glacial eolian record could be found in that region particle size and geochemical data indicate that the mineral fraction of the lake sediments is not derived from the local basalt and is probably eolian silt deposition took place from at least the latter part of the mid wisconsin interstadial period through the holocene based on radiocarbon dating based on the locations of likely loess sources eolian silt in western alaska was probably deflated by northeasterly winds from glaciofluvial sediments if last glacial winds that deposited loess were indeed from the northeast this reconstruction is in conflict with a model derived reconstruction of paleowinds in alaska mass accumulation rates in zagoskin lake were higher during the pleistocene than during the holocene in addition more eolian sediment is recorded in the lake sediments than as loess on the adjacent landscape the thinner loess record on land may be due to the sparse herb tundra vegetation that dominated the landscape in full glacial time herb tundra would have been an inefficient loess trap compared to forest or even shrub tundra due to its low roughness height the lack of abundant full glacial eolian silt deposition in the loess stratigraphic record of central alaska may be due therefore to a mimimal ability of the landscape to trap loess rather than a lack of available eolian sediment

surface sediment dynamics in a dust source from spaceborne multispectral thermal infrared data abstract this study utilized spaceborne multispectral thermal infrared tir data to document spatial relationships of surface sediments over time in a modern depositional environment associated with dust emissions soda lake playa mojave desert united states the approach employed here involved time series tir data acquired from advanced spaceborne thermal emission and reflection radiometer aster and a linear spectral mixture analysis an automated algorithm was applied to derive emissivity image endmembers evaluation of the chosen endmembers revealed that they can be categorized into five major spectra classes based on diagnostic absorption features each spectrum has been identified in relation to mineral abundance and soil arrangement that are common in playa settings a clayey silt rich crust b intermediate salt crust c quartz rich deposit d salt rich rough crust e sulfate rich crust spectral classes a b c d yielded the lowest rms errors 0 0 025 over time in the iterative deconvolution algorithm between the measured and modeled spectra the produced fractional abundance images show high areal concentrations for clayey silt rich crust salt rich rough crust and quartz rich deposit as the first surficial mapping of soda lake significant changes in the spatial relationships of the major surface sediments in soda lake were observed after a flooding event 2005 and a relatively dry period 2006 the approach utilized in this study can be advantageous for continuous monitoring of environments characterized by a small area and a complex surface which may enable a better understanding of their responses to climate changes and potential for dust emissions

sedimentology and evaporite genesis in a holocene continental sabkha playa basin bristol dry lake california bristol dry lake a 155 km2 continental sabkha playa basin in the mojave desert of south eastern california is filled with at least 300 m of interbedded terrigenous clastics gypsum anhydrite and halite evaporite facies conform approximately to a bull s eye pattern with gypsum and anhydrite surrounding a basin centre accumulation of halite transects through bristol dry lake from the alluvial fan to the centre of the playa reveal 1 crudely bedded alluvial fan clastics interfingering with 2 playa margin sand flat and wadi sand and silt followed by 3 gypsum anhydrite chaotic mud halite and clay of the saline mud flat and 4 salt pan halite beds terrigenous clastics were deposited in bristol dry lake by sheetflow and by suspension settling from ponded floodwater some sediment has been reworked by aeolian processes to form barchan dunes around the playa margin thin nodular like beds of anhydrite and several types of gypsum occur across most of the playa giant hopper shaped halite cubes are suspended in saline mud flat facies suggesting that they grew displacively in brine soaked sediment just below the surface thick beds 4 m of halite in the playa centre may have formed through a complex alternating history of subaqueous and intrasedimentary precipitation under the influence of periodic floods intense evaporation and brine level lowering and capillary discharge of brines the stratigraphy in the playa centre is cyclic an ideal cycle consists of 1 chaotic mud halite at the base overlain by 2 green to red clay with abundant giant hoppers and at the top 3 red clay gypsum and anhydrite with flaser to wavy bedded sand and silt this type of cycle probably records a gradual progradation of mud flat facies over salt pans bristol dry lake sediments are nearly identical to some of the permian evaporites of the permian basin region u s a and they can serve as modern analogues for ancient sabkha facies analysis

late pleistocene and holocene dune activity and wind regimes in the western sahara desert of mauritania the western sahara desert in mauritania is dominated by extensive sand seas consisting largely of linear dunes analyses of landsat images geomorphic and stratigraphic studies and optically stimulated luminescence dating of dunes in the azefal agneitir and akchar sand seas provide evidence that three main generations of dunes were formed during the periods 25 15 ka centered around the last glacial maximum 10 13 ka spanning the younger dryas event and after 5 ka the wind regimes that occurred during each of these periods were significantly different leading to the formation of dunes on three distinct superimposed trends northeast north northeast and north and the development of the sand seas as composite geomorphic features

dust sources and deposition during the last glacial maximum and current climate a comparison of model results with paleodata from ice cores and marine sediments mineral dust aerosols in the atmosphere have the potential to affect the global climate by influencing the radiative balance of the atmosphere and the supply of micronutrients to the ocean ice and marine sediment cores indicate that dust deposition from the atmosphere was at some locations 2 20 times greater during glacial periods raising the possibility that mineral aerosols might have contributed to climate change on glacial interglacial time scales to address this question we have used linked terrestrial biosphere dust source and atmospheric transport models to simulate the dust cycle in the atmosphere for current and last glacial maximum lgm climates we obtain a 2 5 fold higher dust loading in the entire atmosphere and a twenty fold higher loading in high latitudes in lgm relative to present comparisons to a compilation of atmospheric dust deposition flux estimates for lgm and present in marine sediment and ice cores show that the simulated flux ratios are broadly in agreement with observations differences suggest where further improvements in the simple dust model could be made the simulated increase in high latitude dustiness depends on the expansion of unvegetated areas especially in the high latitudes and in central asia caused by a combination of increased aridity and low atmospheric co2 the existence of these dust source areas at the lgm is supported by pollen data and loess distribution in the northern continents these results point to a role for vegetation feedbacks including climate effects and physiological effects of low co2 in modulating the atmospheric distribution of dust

mineralogical maturity in dunefields of north america africa and australia studies of dunefields in central and western north america show that mineralogical maturity can provide new insights into the origin and evolution of aeolian sand bodies many of the world s great sand seas in africa asia and australia are quartzdominated and thus can be considered to be mineralogically mature the algodones california and parker arizona dunes in the southwestern united states are also mature but have inherited a high degree of mineralogical maturity from quartz rich sedimentary rocks drained by the colorado river in libya sediments of the zallaf sand sea which are almost pure quartz may have originated in a similar fashion the fort morgan colorado and casper wyoming dunefields in the central great plains of north america and the namib sand sea of southern africa have an intermediate degree of mineralogical maturity because their sources are large rivers that drained both unweathered plutonic and metamorphic rocks and mature sedimentary rocks mojave desert dunefields in the southwestern united states are quite immature because they are in basins adjacent to plutonic rocks that were their sources other dunefields in the great plains of north america those in nebraska and texas are more mature than any possible source sediments and therefore reflect mineralogical evolution over time such changes in composition can occur because of either of two opposing long term states of the dunefield in one state dunes are stable for long periods of time and chemical weathering depletes feldspars and other weatherable minerals in the sediment body in the other state which is most likely for the great plains abrasion and ballistic impacts deplete the carbonate minerals and feldspars because the dunes are active for longer periods than they are stable d 2003 elsevier b v all rights reserved

supply limited horizontal sand drift at an ephemerally crusted unvegetated saline playa a site at owens dry lake was observed for more than 4 years the site was a vegetation free saline playa where the surface formed ephemeral crusts crusts that form after rainfall sometimes these crusts were destroyed and often a layer of particles on the crust would engage in vigorous aeolian activity three phases of active sand drifting are defined as almost no movement extreme supply limitation loose particles on crust with some degree of sand drift moderate supply limitation and unlimited source movement corresponding to a destroyed surface crust unlimited supply these phases occurred 45 49 and 6 of the time respectively the accumulation of loose particles on the crust was mostly the result of in situ formation crusted sediments with loose particles on top can exhibit mass flux rates about the same as for noncrusted sediments crusted sediments limit or eliminate sand drift in two conditions for rough crusts that effect a sufficiently high threshold friction velocity above the wind friction velocity and for limited amounts of loose particles on the crust where particle supply is less than would be transported in normal saltation for a thick sandy surface these supply limited cases are similar to wind erosion of limited spilled material on a hard concrete surface we quantified supply limitation by defining a potential or supply unlimited sand drift function q ag where a represents supply limitation that decreases as the particle source is depleted here q is the mass of sand transported through a surface perpendicular to the ground and to the wind and having unit width during time period t and g u u2 u2 t dt for u u t g is integrated for the same time period t as for q u is the friction velocity of the wind and u t is the threshold friction velocity of the wind hard crusts usually formed in the summer tended to show almost no change of threshold friction velocity with time and often gave total protection from wind erosion rough crusts provided sufficient protection expressed as high threshold friction velocities for these high threshold friction velocities aeolian activity was greatly reduced or practically prevented the softest crusts usually formed in the winter provided much less protection and sometimes were destroyed by the wind following this destruction the potential or supply unlimited sand drift would be observed

influences of eolian and pedogenic processes on the origin and evolution of desert pavements well developed desert pavements are present above eolian deposits that mantle flows of the cima volcanic field located in the mojave desert california soil stratigraphic data and geochemical data demonstrate that eolian and pedogenic processes play major roles in the evolution of these pavements eolian dust 1 accelerates mechanical fragmentation of flow rock providing the source material for pavements and 2 accumulates slowly below basaltic colluvium in flow depressions eventually promoting development of cumulate soils below the evolving stone pavement an increase in dust flux during the holocene has raised ancient pleistocene pavements as much as 20 cm above the former land surface the results of our studies demonstrate for the first time that most desert pavements do not form by deflation by overland flow or by upward migration of stones through a slowly formed clayey argillic horizon desert pavements are born and maintained at the surface

change in atmospheric mineral aerosols in response to climate last glacial period preindustrial modern and doubled carbon dioxide climates desert dust simulations generated by the national center for atmospheric research s community climate system model for the current climate are shown to be consistent with present day satellite and deposition data the response of the dust cycle to last glacial maximum preindustrial modern and doubled carbon dioxide climates is analyzed only natural non land use related dust sources are included in this simulation similar to some previous studies dust production mainly responds to changes in the source areas from vegetation changes not from winds or soil moisture changes alone this model simulates a 92 33 and 60 change in dust loading for the last glacial maximum preindustrial and doubled carbon dioxide climate respectively when impacts of carbon dioxide fertilization on vegetation are included in the model terrestrial sediment records from the last glacial maximum compiled here indicate a large underestimate of deposition in continental regions probably due to the lack of simulation of glaciogenic dust sources in order to include the glaciogenic dust sources as a first approximation we designate the location of these sources and infer the size of the sources using an inversion method that best matches the available data the inclusion of these inferred glaciogenic dust sources increases our dust flux in the last glacial maximum from 2 1 to 3 3 times current deposition

rapid salt weathering in the coastal namib desert implications for landscape development data on the rate and style of breakdown on naturally occurring rock types are important to improving geomorphological understanding of landscape development in arid environments two years exposure of rock blocks cut from an english limestone bath stone as well as locally relevant namibian rocks karibib marble and damara granite within four distinctive microenvironments in and around a coastal salt pan environment reveals high rates of breakdown in the bath stone blocks observable breakdown in the marble blocks and weight gains and strength increases in the granite blocks breakdown is associated with high conductivities and large amounts of halite and gypsum within the surface sediments frequency of wetting and drying appears to be a major control on the resultant breakdown rates these findings can be compared with recent data from further inland in the namib desert which suggest very slow rates of breakdown of similar blocks of damara granite and karibib marble even where salts are readily available high rates of rock breakdown within coastal salt pans appear to contribute to dust production and the effective flattening of relief along the coastal strip

dust emission from wet and dry playas in the mojave desert usa the interactions between playa hydrology and playa surface sediments are important factors that control the type and amount of dust emitted from playas as a result of wind erosion the production of evaporite minerals during evaporative loss of near surface ground water results in both the creation and maintenance of several centimeters or more of loose sediment on and near the surfaces of wet playas observations that characterize the texture mineralogic composition and hardness of playa surfaces at franklin lake soda lake and west cronese lake playas in the mojave desert california along with imaging of dust emission using automated digital photography indicate that these kinds of surface sediment are highly susceptible to dust emission the surfaces of wet playas are dynamic surface texture and sediment availability to wind erosion change rapidly primarily in response to fluctuations in water table depth rainfall and rates of evaporation in contrast dry playas are characterized by ground water at depth consequently dry playas commonly have hard surfaces that produce little or no dust if undisturbed except for transient silt and clay deposited on surfaces by wind and water although not the dominant type of global dust salt rich dusts from wet playas may be important with respect to radiative properties of dust plumes atmospheric chemistry windborne nutrients and human health published in 2007 by john wiley sons ltd

contemporary glacigenic inputs to the dust cycle the importance of glacigenic dust in the earth s system during glacial periods is widely acknowledged under contemporary conditions the world s largest dust sources are in low lying hot arid regions and this is where most aeolian research is focused however the processes of dust production and emissions are still operating in cold climate regions particularly in proglacial areas this paper assesses current understanding of the relationship between glacierised landscapes and dust emissions and inputs to the global dust cycle it focuses on how elements in the glacial and aeolian geomorphic sub systems interact to determine the magnitude frequency and timing of aeolian dust emissions and on feedback mechanisms between the systems where they have been measured dust emission intensity and deposition rates in glacierised catchments are very high in some cases far exceeding those in lower latitudes however few studies span long time scales the impact of future glacier retreat on the balance between sediment supply availability and aeolian transport capacity and implications for glacigenic dust emissions is also considered this balance depends on relative spatial and temporal changes in meltwater suspended sediment concentration and wind strengths which promote dust emissions and patterns and rates of soil development and vegetation succession on recently deglaciated terrain which protect sediments from deflation retreat of the antarctic ice sheet could mean that in future glacigenic contributions to the dust cycle exceed those of non glacigenic sources in the southern hemisphere copyright 2012 john wiley sons ltd

dust model intercomparison dmip study over asia overview 1 an intercomparison study involving eight dust emission transport models over asia dmip has been completed participating dust models utilize a variety of dust emission schemes horizontal and vertical resolutions numerical methods and different meteorological models two huge dust episodes occurred in spring 2002 and were used for the dmip study meteorological parameters dust emission flux and dust concentration diameter 20 m are compared within the same domain on the basis of pm and nies lidar measurements we found that modeled dust concentrations between the 25 and 75 percentiles generally agreed with the pm observations the model results correctly captured the major dust onset and cessation timing at each observation site however the maximum concentration of each model was 2 4 times different dust emission fluxes from the taklimakan desert and mongolia differ immensely among the models indicating that the dust source allocation scheme over these regions differs greatly among the various modeling groups this suggests the measurements of dust flux and accurate updated land use information are important to improve the models over these regions the dust vertical concentration profile at beijing china and nagasaki japan has a large scatter more than two times different among the models for beijing the scaled dust profile has a quite similar vertical profile and shows relatively good agreement with the lidar extinction profile however for nagasaki the scaled dust profiles do not agree these results indicate that modeling of dust transport and removal processes between china and japan is another important issue in improving dust modeling

characterization of dust emission from alluvial sources using aircraft observations and high resolution modeling 1 we investigate mineral dust emission from alluvial sediments within the upland region in northern mauritania in the vicinity of a decaying nocturnal low level jet llj for the first time the impact of valleys that are embedded in a rather homogeneous surrounding is investigated with regard to their role as dust source measures for local atmospheric dust burden were retrieved from airborne observations satellite observations and model simulations and analyzed in order to provide complementary information at different horizontal scales observations by the leandre nouvelle generation backscatter lidar system flying aboard the french falcon 20 aircraft were taken along five parallel flight legs perpendicular to the orientation of the main valley system dominating the topography of the study area results from a comparison of lidar derived extinction coefficients with topography and aerial photographs confirm the relevance of 1 alluvial sediments at the valley bottoms as a dust source and 2 the break down of the nocturnal llj as a trigger for dust emission in this region an evaluation of the arome regional model forecasting dust at high resolution 5 km grid points toward an under representation of alluvial dust sources in this region this is also evident from simulations by the mesonh research model although mesonh simulations show higher dust loadings than arome which are more comparable to the observations both models underestimate the dust concentrations within the boundary layer compared to lidar observations a sensitivity study on the impact of horizontal grid spacing 5 km versus 1 km highlights the importance of spatial resolution on simulated dust loadings

ephemeral lakes and desert dust sources 1 the processes that determine which areas are strong sources of mineral aerosols are not well known in this study we consider the role of ephemeral lakes in modulating emissions of atmospheric mineral aerosols we focus on two ephemeral lake regions that have been identified as source regions the zone of chotts in tunisia and algeria and etosha pan in namibia comparisons of satellite retrieved inundation data and the toms absorbing aerosol index suggest that during some periods of inundation desert dust loadings are reduced there is some indication that after flooded areas have dried there is increased dust loading however the role of the inundated ephemeral lake compared with nearby regions in modulating desert dust sources is unclear in addition problems with interpreting the toms ai make conclusions difficult more research is required to understand the small scale sources of atmospheric desert dust in dry unvegetated topographic lows index terms 0305 atmospheric composition and structure aerosols and particles 0345 4801 0315 atmospheric composition and structure biosphere atmosphere interactions 1615 global change biogeochemical processes 4805 1655 global change water cycles 1836 3360 meteorology and atmospheric dynamics remote sensing citation mahowald n m r g bryant j del corral and l steinberger ephemeral lakes and desert dust sources geophys res lett 30 2 1074 doi 10 1029 2002gl016041 2003

geochemical evidence for african dust inputs to soils of western atlantic islands barbados the bahamas and florida 1 we studied soils on high purity limestones of quaternary age on the western atlantic ocean islands of barbados the florida keys and the bahamas potential soil parent materials in this region external to the carbonate substrate include volcanic ash from the island of st vincent near barbados volcanic ash from the islands of dominica and st lucia somewhat farther from barbados the fine grained component of distal loess from the lower mississippi river valley and wind transported dust from africa these four parent materials can be differentiated using trace elements sc cr th and zr and rare earth elements that have minimal mobility in the soil forming environment barbados soils have compositions that indicate a complex derivation volcanic ash from the island of st vincent appears to have been the most important influence but african dust is a significant contributor and even mississippi river valley loess may be a very minor contributor to barbados soils soils on the florida keys and islands in the bahamas appear to have developed mostly from african dust but mississippi river valley loess may be a significant contributor our results indicate that inputs of african dust are more important to the genesis of soils on islands in the western atlantic ocean than previously supposed we hypothesize that african dust may also be a major contributor to soils on other islands of the caribbean and to soils in northern south america central america mexico and the southeastern united states dust inputs to subtropical and tropical soils in this region increase both nutrient holding capacity and nutrient status and thus may be critical in sustaining vegetation

horizontal wind erosion flux and potential dust emission in arid and semiarid regions of china a major source area for east asia dust storms abstract arid and semiarid regions of china are important sources of dust for storms that affect east asia and the western pacific ocean however little is known about the process spatial variation and quantity of the emission and transportation of windblown sand dust from such areas in 2009 a large number of passive sand traps were set on different landscape surfaces across the arid and semiarid regions of china to monitor the horizontal wind erosion flux and establish the potential of dust emission the monitoring data suggest that the taklamakan desert has the greatest wind erosion flux the mean wind erosion flux of the marginal sand seas hinterland sand seas gobi type desert and degraded land of oases in this area is 45 07 32 37 31 11 and 19 83 kg day 1 m 2 respectively during the aeolian transport process the mean limit of a suspended load particle size is 0 066 mm aeolian sediment mean grain size and sorting are 0 11 mm and 1 40 respectively and potential pm10 dust emission rate is 0 969 kg day 1 m 2 the qaidam basin and dunhuang areas and the hexi corridor and alax areas also have strong wind erosion flux the mean wind erosion flux for the gobi type deserts in these areas is 11 57 and 39 16 kg day 1 m 2 respectively while for the degraded land of oases it is 14 78 and 12 68 kg day 1 m 2 respectively during the aeolian sediment transport process the mean limit of a suspended load particle size is 0 083 mm aeolian sediment mean grain size and sorting are 0 18 mm and 1 82 respectively and potential pm10 dust emission rate is 1 011 kg day 1 m 2 the mu us sandy land steppes of the northern yinshan mountains hunshandake sandy land and its surrounding steppes and horqin sandy land have the weakest wind erosion flux the mean value of which is 10 53 5 43 2 88 and 1 94 kg day 1 m 2 respectively during the aeolian sediment transport process the mean limit of a suspended load particle size is 0 12 mm aeolian sediment mean grain size and sorting are 0 25 mm and 2 1 respectively and potential pm10 dust emission rate is 0 103 kg day 1 m 2

influence of patagonian glaciers on antarctic dust deposition during the last glacial period dust deposition over antarctica was much higher during the last glacial period but the causes of this flux remain unclear an analysis of the composition and age of glacial outwash sediments indicates that growth and decay of glaciers in patagonia may have influenced dust transport to antarctica at that time

the role of aeolian dust in ecosystems abstract the recent upsurge in research attention to aeolian dust has shown that dust transport systems operate on very large spatial and temporal scales and involve much larger quantities of sediment than was previously realized an inevitable consequence of this is that researchers from a range of neighbouring disciplines including ecology are beginning to realize that this new knowledge has important implications for their study areas in the present paper we examine the ecological implications real and potential of this expanding knowledge of dust transport systems with a particular emphasis upon the australian dust transport system we track these ecological effects from source to sink at source wind erosion soil vegetation relationships are often dominated by temporal changes in rainfall nine years of measurements in the channel country of the lake eyre basin australia show that vegetation and soils in dune fields can recover from drought whereas on inter fluve grasslands uni directional and negative successional vegetation changes can result from wind erosion during drought on floodplains both wind erosion and vegetation responses are complicated by flood frequency up to 1999 flooding of saline claypans did not increase vegetation but did increase wind erosion through the supply of alluvial fines however after three floods within as many months vegetation became established and wind erosion rates were dramatically reduced wind erosion research attention is now gradually turning from the physical to the organic content of eroded dusts in australia organic matter content can reach 65 by mass but this cannot be explained by removal of soil organic matter alone biological soil crusts not only stabilize soils against wind erosion but contribute to some of the organic dusts the role of dust as a vector for pathogens is an area which deserves greater research attention in the future downwind from source we show that dust contributions to soils are more widespread and more variable in time and space than earlier work on dust derived loess soils has suggested recent studies also show positive dust impacts upon nutrient budgets within distant forest ecosystems and significant contributions to river nutrient loads especially in the arid sectors of internally draining river basins the number of studies of dust impacts upon marine ecosystems is increasing dramatically studies of dust within antarctic ice cores combined with dust modelling provide compelling evidence that increased soluble iron rich dust inputs to the southern ocean have stimulated phytoplankton populations modern process studies are however yet to clearly demonstrate these relationships finally we examine the potential for major dust impacts upon global climates using its positive and negative effects upon solar radiation and precipitation as examples of the complexity and importance of this new research area