modeling the mineralogy of atmospheric dust sources the variability of atmospheric dust mineralogy influences the impact of desert dust on the earth s radiative budget and biogeochemical cycles until now atmospheric transport models have assumed that dust was a constant homogeneous mixture hence neglecting this variability the lack of mineralogical data in arid areas prevented a better description of the atmospheric dust composition and we propose here a new formulation to estimate the mineral content of arid surfaces on a global scale first we collect a database of arid soil surface mineralogy for eight major minerals quartz feldspar calcite gypsum illite kaolinite smectite and hematite both for the clay and silt fraction on the basis of this we formulate a mean mineralogical table that relates classical soil types to surface mineralogy we use this table and the geographical distribution of soil types given in the food and agriculture organization soil map of the world to obtain the mineralogy of arid surfaces globally in order to validate these results we present a compilation of measured mineralogical composition of dust samples with identified sources the correlation between observed dust mineralogy and those inferred from soil types in corresponding areas is between 0 70 and 0 94 we then calculate the maps of the single scattering albedo and of the ratio of infrared extinction to visible extinction for the erodible fraction of arid areas mineralogical maps presented here will be used in future studies with an emission scheme in a global transport model

late glacial stage and holocene tropical ice core records from huascaran peru two ice cores from the col of huascaran in the north central andes of peru contain a paleoclimatic history extending well into the wisconsinan wurm glacial stage and include evidence of the younger dryas cool phase glacial stage conditions at high elevations in the tropics appear to have been as much as 8 to 12 c cooler than today the atmosphere contained about 200 times as much dust and the amazon basin forest cover may have been much less extensive differences in both the oxygen isotope ratio 18o 8 per mil and the deuterium excess 4 5 per mil from the late glacial stage to the holocene are comparable with polar ice core records these data imply that the tropical atlantic was possibly 5 to 6 c cooler during the late glacial stage that the climate was warmest from 8400 to 5200 years before present and that it cooled gradually culminating with the little ice age 200 to 500 years before present a strong warming has dominated the last two centuries

estimates of atmospheric processed soluble iron from observations and a global mineral aerosol model biogeochemical implications 1 desert dust deposition to the ocean may be a significant source of biogeochemically important elements specifically iron the bioavailability of iron in the oceans requires it to be in a soluble form and because atmospheric iron in desert dust is typically insoluble understanding the atmospheric processes that convert insoluble iron to more soluble forms is essential understanding these relationships is especially important in remote ocean regions where iron may be the limiting nutrient observations of soluble iron from 2001 cruise based aerosol measurements over the atlantic and pacific oceans ranged from 0 to 45 mean of 4 9 in the fine mode 2 5 m in diameter and 0 to 87 mean of 2 10 in the coarse mode we test two simple hypotheses of soluble iron enhancement in the atmosphere using a global model of mineral aerosols the first method assumes that iron solubility increases as iron is exposed to solar radiation approximating photoreduction reactions that are important pathways for enhancement of soluble iron in the presence of acidic solutions the second process imitates cloud processing of iron by increasing the amount of soluble iron when the mineral aerosol comes into contact with a cloud both methods resulted in similar average magnitudes of percent soluble iron compared to observations but did not capture specific events or have sufficient variability perhaps because the model does not include aerosol interactions between species other than mineral dust or other processes that may be important

airborne dust and its significance to soils abstract movement of mineral dust by the atmosphere has been underway for ages but efforts to assess its magnitude and significance have come largely in the last century attempts to identify and understand effects of the dust on soils are even more recent mostly in the last 30 years airborne movements have several forms dust is transported by large storms that can be spectacular dust is also moved by smaller pulses and in a rather continuous flux most movement is within continents or from continents to nearby oceans but fine dust fine silt and clay is carried from one continent to another prime sources of the dust are the deserts and semi arid regions of the world for example large quantities of dust are carried out of the sahara every year quantities of dust carried by individual pulses from the small ones to the massive storms extend from a few thousand to 150 million metric tons during the course of a year the total quantities can be large one example is an estimate that on the average 770 million metric tons originating in the western united states are carried 2300 km each year that amount would add roughly 3000 kg ha 1 yr 1 to soils between the rocky mountains and the mississippi river small pulses and the near continuous flux add between 100 and 200 kg ha 1 yr 1 to soils of the eastern united states on the average comparable quantities are being added to soils in other parts of the world as well airborne accessions of dust have a variety of effects in soil development and on soils after they have been formed dust dominates processes of genesis in a few soils affects horizon differentiation appreciably in many more is a primary source of constituents essential to some horizons and layers in a number of soils provides the bulk of the material for silty surface horizons in many soils and can contribute supplies of nutrient elements for plants examples of all such effects are covered in this review first among these effects to be recognized even though not understood were the silty surface layers that failed to match underlying horizons later recognized was airborne dust as a source of calcium carbonate for calcic horizons that the dust could add significant quantities of nutrient elements as for example south of the sahara came into the picture even later the beneficial effects of airborne dust to many soils raises an interesting question is the dust more or less useful in its new location than it was in its source area an adequate answer to that question would provide an improved basis for assessing the effects of wind erosion

atmospherically transported elements and deposition in the southeastern united states local or transoceanic abstract saharan dust is persistently transported and deposited in ecosystems of the western atlantic ocean this dust is an aggregate of clay and quartz particles cemented with fe oxides samples collected and analyzed from mali central africa the azores the caribbean and the eastern united states document the levels of minor and trace metals in the dust metal loadings particularly the toxic elements hg and as are significantly higher than average crustal rocks over the past decade the focus has been to understand the cycling of hg in south florida but as has received very little attention arsenic in the sediment deposited in the past decade in south florida averages 14 mg kg and appears to be correlated with al a proxy for dust the largest available aerosol data set containing as is the improve interagency monitoring of protected visual environments data set the average concentrations in aerosols collected during this program range from 17 mg kg in the virgin islands to 79 mg kg at chassahowitzka florida at chassahowitzka most of the as appears to be associated with organic c if it is assumed that the concentrations in mali dust and in the aerosols in the virgin islands are indicative of soil dust then the higher values at chassahowitzka may be derived from local or regional sources a simple calculation indicates that african dust supplies about 25 of the as deposited from aerosols in the southeastern united states comparison of the average yearly as concentrations measured in the virgin islands and everglades shows a negative relationship with the north atlantic oscillation nao this relationship demonstrates the influence of climate on the transport and deposition of aerosols to the southeastern united states

seasonal variability in the origin of recent atmospheric mineral dust at northgrip greenland abstract isotopic sr and nd and mineralogical analyses of dust extracted from snow deposits from the last decade at the northgrip greenland ice camp 75 1 n 042 3 w confirm the eastern asian source for greenland dust and extend it to the present day the 1998 and 1999 samples which represent a 2 4 month resolution of dust deposition show that there are at least two east asian sources for the greenland dust that vary seasonally the provenance of dust during the major spring summer deposition is the takla makan desert of northwest china

tracing dust sources and transport patterns using sr nd and pb isotopes continental dust transported through the atmosphere can be a tracer of atmospheric circulation and transport as well as being a source of information about climate in the dust s source area this information about the provenance of dust transported from desert areas and deposited elsewhere on the oceans and continents can be evaluated using several observational techniques satellite imagery has been used to this end in recent decades and air mass back trajectories have been calculated to trace dust deposits back to their source area another method consists of analysis of the concentration and composition of certain tracers in the dust itself and comparing them to soils and sediments from possible source areas this method has the advantage of being useable for paleo atmospheric circulation and paleo dust transport studies whereas satellite imagery and air mass back trajectories are restricted to relatively recent times we review here different kinds of isotopic tracers that have been used to trace dust provenance but special attention is focused on the use of sr nd and pb isotopes we evaluate their use in studies of both spatially as well as temporally varying continental dust source and transport

dust rains in mallorca western mediterranean their occurrence and role in some recent geological processes abstract dust rains were observed in palma de mallorca island of mallorca western mediterranean on 253 days in the 22 year period from 1982 to 2003 these and other data from the western mediterranean show that dust rains are on the increase most occur in the warmest season of the year meteorological conditions associated with this phenomenon combine hot advection from the south at low tropospheric levels with southwest winds associated with a depression in the middle troposphere dry deposition of dust often in aggregates 40 300 m across is occasionally observed analysed samples are silty and mainly composed of quartz and kaolinite they also contain minor proportions of feldspars and palygorskite which do not occur as rock forming minerals in the balearic islands comparisons of the dusty rainwater samples with soils and recent marine and karstic sediments suggest that dust deposition is an important sedimentary process in the balearic islands

tectonic evolution of the antarctic phoenix plate system since 15 ma abstract joint inversion of magnetic isochron and fracture zone data from the extinct antarctic phoenix spreading system in sw drake passage yields seven new finite reconstruction poles the inversion results are very well constrained for such a short length of plate boundary although this is partly because the finite poles are located close to the reconstructed region the optimum use of fracture zone identifications from satellite derived free air gravity data is also important as the stability of stage poles throughout the short intervals in the model affirms the model results describe a well organised spreading system since magnetic anomaly chron c5ad 15 ma in which the phoenix plate rotated about stage poles nearby to the southwest stage pole locations are broadly consistent with a hypothesis of pivoting subduction as the driving force of phoenix plate movement and there is some evidence in the progression of stage poles for late stage movement of the subduction pivot in response to the changing azimuth of the subduction zone at which the phoenix plate was being consumed the model kinematics alone provide no unequivocal support for previous interpretations of disruption of the subducted part of the phoenix plate the very latest stages of spreading saw falling spreading rates between magnetic anomaly chrons c4 8 1 ma and c2a 3 3 ma when the antarctic phoenix ridge became extinct this is consistent with an increase in shear stress across the plate bounding shackleton fracture zone due to a plate reorganisation in the neighbouring scotia sea following the cessation of spreading on the west scotia ridge

calibration of the mdco dust collector and of four versions of the inverted frisbee dust deposition sampler abstract wind tunnel experiments were conducted to determine the efficiency of sediment samplers designed to measure the deposition of aeolian dust efficiency was ascertained relative to a water surface which was considered the best alternative for simulating a perfectly absorbent surface two types of samplers were studied the marble dust collector mdco and the inverted frisbee sampler four versions of the latter catcher were tested an empty frisbee an empty frisbee surrounded by an aerodynamic flow deflector ring a frisbee filled with glass marbles and a frisbee filled with glass marbles and surrounded by a flow deflector ring efficiency was ascertained for five wind velocities range 1 5 m s 1 and eight grain size classes range 10 89 m the efficiency of dust deposition catchers diminishes rapidly as the wind speed increases it also diminishes as the particles caught become coarser adding a flow deflector ring to a catcher substantially improves the catcher s efficiency by up to 100 in some cases the addition of glass marbles to a catcher on the other hand does not seem to increase the efficiency at least not at wind velocities inferior to the deflation threshold for higher velocities the marbles protect the settled particles from resuspension keeping them in the catcher the following five parameters determine the accumulation of aeolian dust in a catcher the horizontal dust flux the weight of the particles atmospheric turbulence resuspension and the dust shadow effect created by the catcher the final accumulation flux depends on the combination of these parameters the catchers tested in this study belong to the best catchers currently in use in earth science and have been the subject of various aerodynamic studies to improve their efficiency nevertheless the catching efficiency remains low in the order of 20 40 for wind speeds above 2 m s 1 other catchers suffer from the same low efficiencies there is thus evidence to believe that dust deposition rates published in the aeolian literature and obtained by collecting the sediment in a catcher largely underestimate the true deposition the errors are considerable of the order of 100 and more a reconsideration of the literature data on aeolian dust deposition measured by catchers is therefore required

the effect of surface curvature on the deposition of loess a physical model summary a physical model for the deposition of fine dusty material loess on curved surfaces is presented the model is tested in a sedimentation experiment with a symmetrical hill with length axis perpendicular to the flow direction in a wind tunnel it appears both from the model and the experiment that loess deposition will occur preferably on windward slopes and not on leeward ones in contrast to the widespread wind shadow concept below the deflation threshold loess deposition increases as wind speed increases above the deflation threshold an effective accumulation of the loess layer on the surface will occur within a well defined wind speed interval the loess layer on the surface will erode away only if wind speed has exceeded this interval for flat and dry surfaces free of roughness elements the upper limit of the interval is 7 m s free stream velocity for wet surfaces however it may be considerably higher 15 m s and more

geochemistry of aerosols of northwestern part of india adjoining the thar desert abstract the northwestern part of india which includes the thar desert on its western side is a hot and arid region with intense aeolian activity and transport of aerosols by the prevailing sw w summer winds different size fractions of aerosols free fall ff suspended particulate matter spm pm 10 10 m from air were sampled simultaneously at four locations along the dominant wind trajectory for 600 km these aerosols and deposited surface sediments were characterized for their texture mineralogy and geochemistry including ree and sr isotopes within each size fraction a bimodal distribution of grain size was observed quartz is the dominant mineral followed by k feldspar mica calcite chlorite and plagioclase garnet amphibole titanite and zircon are some of the identified heavy minerals all samples particularly those collected during summer are compositionally homogeneous including in their ree geochemistry and are similar to average upper continental crust ucc however in the winter aerosol samples large deviations from the ucc composition are observed this is attributed to meteorological parameters such as low wind velocity and temperature inversions in the winter season during winter secondary non silicate and anthropogenic materials become important sources to ca na mg k ba and ni budget also reduction in the uptake and transport of heavy minerals lowered the concentration of ti zr y cr and ree in the aerosols geochemical coherence among aerosols deposited surface sediments and the thar sands and the limited sr isotopic data indicate that the thar sediments and certain lithotectonic units of the himalayan orogen are the proximal and distal crustal sources respectively for the aerosols in this region prevailing aridity and strong summer winds and the presence of river alluvium in the thar act together to transport silt rich dust the removal of which could be a possible mechanism of ongoing desertification

a threshold in soil formation at earth s arid hyperarid transition the soils of the atacama desert in northern chile have long been known to contain large quantities of unusual salts yet the processes that form these soils are not yet fully understood we examined the morphology and geochemistry of soils on post miocene fans and stream terraces along a south to north 27 to 24 s rainfall transect that spans the arid to hyperarid transition 21 to 2 mm rain y 1 landform ages are 2 my based on cosmogenic radionuclide concentrations in surface boulders and ar isotopes in interbedded volcanic ash deposits near the driest site indicate a maximum age of 2 1 my a chemical mass balance analysis that explicitly accounts for atmospheric additions was used to quantify net changes in mass and volume as a function of rainfall in the arid 21 mm rain y 1 soil total mass loss to weathering of silicate alluvium and dust 1030 kg m 2 is offset by net addition of salts 170 kg m 2 the most hyperarid soil has accumulated 830 kg m 2 of atmospheric salts including 260 kg sulfate m 2 and 90 kg chloride m 2 resulting in unusually high volumetric expansion 120 for a soil of this age the composition of both airborne particles and atmospheric deposition in passive traps indicates that the geochemistry of the driest soil reflects accumulated atmospheric influxes coupled with limited in soil chemical transformation and loss long term rates of atmospheric solute addition were derived from the ion inventories in the driest soil divided by the landform age and compared to measured contemporary rates with decreasing rainfall the soil salt inventories increase and the retained salts are both more soluble and present at shallower depths all soils generally exhibit vertical variation in their chemistry suggesting slow and stochastic downward water movement and greater climate variability over the past 2 my than is reflected in recent 100 y rainfall averages the geochemistry of these soils shows that the transition from arid to hyperarid rainfall levels marks a fundamental geochemical threshold in wetter soils the rate and character of chemical weathering results in net mass loss and associated volumetric collapse after 105 to 106 years while continuous accumulation of atmospheric solutes in hyperarid soils over similar timescales results in dramatic volumetric expansion the specific geochemistry of hyperarid soils is a function of atmospheric sources and is expected to vary accordingly at other hyperarid sites this work identifies key processes in hyperarid soil formation that are likely to be independent of location and suggests that analogous processes may occur on mars

chemical weathering mass loss and dust inputs across a climate by time matrix in the hawaiian islands we determined the total mass loss and rate of chemical weathering from three minimally eroded hawaiian lava flows that are 10 170 and 350 ka old using a backhoe we sampled the entire weathering zone at 28 sites and measured the depletion or enrichment of each major element in each soil horizon relative to parent material we were able to assess the influence of both climate and substrate age on chemical weathering because each flow crosses a precipitation gradient from 600 to 2500 mm yr 1 mass loss rates were highest for the 0 10 ka interval under the wettest climatic conditions 54 t km 2 yr 1 and decreased to near zero in the wet sites during the 10 170 and 170 350 ka intervals not surprisingly weathering rates were lower in drier sites 24 t km 2 yr 1 from 0 10 ka to b 2tk m 2 yr 1 thereafter however the effects of precipitation were non linear there was a precipitation threshold below which mass loss was relatively small and above which mass loss was substantial but insensitive to increased rainfall chemical weathering rates depend on tectonic uplift erosion climate rock type or some combination thereof by working on stable uneroded surfaces of a single rock type across a well constrained precipitation gradient we were able to identify another potential driver the rate of dust deposition although hawai i is one of the least dusty places in the northern hemisphere dust inputs reached 82 of the total mass loss from the weathering zone at some sites and averaged 30 on the 170 ka flow this highlights the potential importance of dust as a component of observed weathering fluxes from catchments worldwide

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

saharan dust inputs to the western mediterranean sea depositional patterns geochemistry and sedimentological implications data are presented for a number of parameters for aerosols and rainwaters collected at a station on sardinia the findings are interpreted with special reference to saharan dusts and are compared to other data on these dusts obtained from a variety of sites around the mediterranean sea at the sardinia site the particle size distribution of the saharan outbreaks exhibits a bimodal structure the two modes being between 2 and 4 m and 15 and 30 m the presence of giant particles strongly affects the deposition velocities of the saharan aerosols source markers for the saharan dusts are palygorskite kaolinite calcite dolomite and rounded quartz grains the input of saharan dust has important effects on the chemistry of the mediterranean aerosols these include i increases in the atmospheric concentrations and sea surface fluxes of crust controlled trace metals e g al fe ii decreases in the efcrust values of non crust controlled trace metals e g cu zn and pb in the aerosols and iii changes in the solid state speciation of cu zn and pb which decrease their solubilities in seawater the saharan dusts also affect the composition of rainwater by raising the ph following the dissolution of calcium and by decreasing the solubility of trace metals such as cu zn and pb wet deposition controls the flux of saharan dust to the mediterranean sea but dry deposition can also be important the dust transport occurs in the form of pulses and the annual dust flux can be controlled by a few episodes of saharan outbreaks e g sometimes a single outbreak can account for 40 80 of the flux saharan dust deposition fluxes range from 2 to 25 g m 2 average 10 in the west mediterranean between 39 and 42 n from 6 to 46 g m 2 average 20 in the east mediterranean and from 0 4 to 1 0 g m 2 over the alps on continental europe the present day saharan dust fluxes 1 mg cm 2 year 1 account for about 10 20 of the recent deep sea sedimentation in the western mediterranean 3 15 mg cm 2 year 1

factors controlling threshold friction velocity in semiarid and arid areas of the united states a physical model was developed to explain threshold friction velocities u t for particles of the size 60 120 m lying on a rough surface in loose soils for semiarid and arid parts of the united states the model corrected for the effect of momentum absorption by the nonerodible roughness for loose or disturbed soils the most important parameter that controls u t is the aerodynamic roughness height z0 for physical crusts damaged by wind the size of erodible crust pieces is important along with the roughness the presence of cyanobacteriallichen soil crusts roughens the surface and the biological fibrous growth aggregates soil particles only undisturbed sandy soils and disturbed soils of all types would be expected to be erodible in normal wind storms therefore disturbance of soils by both cattle and humans is very important in predicting wind erosion as confirmed by our measurements

quantitative estimates of the effect of climate change on dust storm activity in australia during the last glacial maximum quantitative estimates are made of the effect of climate change upon dust activity during the last glacial maximum lgm which peaked 18 000 years ago using present day measurements of the occurrence of dust storms recalculated in the light of information on lgm climatic change dust activity was increased by 57 in northeast australia and by 52 in the southeast in relation to present day dust storm seasons were lengthened and dust paths were modified estimates based upon climate alone without considering the increased supplies of sediment to dust source areas during the lgm however probably underestimate lgm dust activity

the contemporary physical and chemical flux of aeolian dust a synthesis of direct measurements of dust deposition abstract the deposition of aeolian or windblown dust is widely recognized as an important physical and chemical flux to ecosystems dust deposition adds exogenous mineral and organic material to terrestrial surfaces and can be important for the biogeochemical cycling of nutrients there have been many studies that characterize the physical and chemical composition of dust however few studies have synthesized these observations in order to examine patterns geochemical fluxes we have compiled observations of dust deposition rates particle size distributions psd mineralogy and bulk elemental and organic chemistry the rates of dust deposition observed across the globe vary from almost 0 to greater than 450 g m 2 yr 1 sites receiving dust deposition can be partitioned into broad categories based on there distance from dust source regions when compared to global dust models our results suggest some models may underestimate dust deposition rates at the regional and local scales the distance from the source region that dust is deposited also influences the particle size distributions mineralogy and chemical composition of dust however more consistent dust sampling and geochemical analyses are needed to better constrain these spatial patterns on average the concentrations of most major elements si al fe mg ca k in aeolian dust tend to be similar 20 to the composition of the upper continental crust ucc but there is substantial variability from sample to sample in contrast some elements tend to be depleted na or enriched ti in dust likely as a result of soil weathering processes prior to dust emissions trace elements especially heavy metals are consistently enriched in dust relative to the ucc ecologically important nutrients such as n and p are also present in dust deposition the geochemical flux attributable to dust deposition can be substantial in ecosystems located proximal to dust source regions we calculate estimates of elemental flux rates based on the average chemical composition of aeolian dust and varying rates of deposition these estimated flux rates are useful as a rough gauge of the degree to which dust deposition may influence biogeochemical cycling in terrestrial ecosystems and should be utilized to better constrain deposition estimates of global dust models

characteristics and constituent composition of harmattan dust falling in northern nigeria abstract during the 1984 1985 harmattan season dustfall was collected at six locations in the zaria kano area of northern nigeria from the beginning of november 1984 to late march 1985 the average dustfall at six locations was 580 kg ha the total dustfall during that season may have been of the order of 700 1000 kg ha clay less than 2 m constituted 25 and silt 2 50 m 57 of the dust the rest was very fine sand the dust had higher ph and cation exchange capacity and contained more extractable phosphorus organic matter and exchangeable ca mg k and na but had less extractable a1 and exchangeable acidity than the samples from eight soil profiles with which it was compared the dust also had a higher content of 2 1 layer silicate clay minerals and lower amounts of 1 1 layer silicate clay minerals and fe oxyhydroxides than the soil samples this difference in chemical and physical properties and in constituent composition of the harmattan dust may be expected to have an impact on the characteristics and development of the soils upon which it is falling

atmospheric dust in modern soil on aeolian sandstone colorado plateau usa variation with landscape position and contribution to potential plant nutrients rock derived nutrients in soils originate from both local bedrock and atmospheric dust including dust from fardistant sources distinction between fine particles derived from local bedrock and from dust provides better understanding of the landscape scale distribution and abundance of soil nutrients sandy surficial deposits over dominantly sandstone substrates covering vast upland areas of the central colorado plateau typically contain 5 40 silt plus clay depending on geomorphic setting and slope excluding drainages and depressions aeolian dust in these deposits is indicated by the presence of titanium bearing magnetite grains that are absent in the sedimentary rocks of the region thus contents of far traveled aeolian dust can be estimated from magnetic properties that primarily reflect magnetite content such as isothermal remanent magnetization irm isothermal remanent magnetization was measured on bulk sediment samples taken along two transects in surficial sediment down gentle slopes away from sandstone headwalls one transect was in undisturbed surficial sediment the other in a setting that was grazed by domestic livestock until 1974 calculation of far traveled dust contents of the surficial deposits is based on measurements of the magnetic properties of rock surficial deposits and modern dust using a binary mixing model at the undisturbed site irm based calculations show a systematic down slope increase in aeolian dust ranging from 2 to 18 of the surface soil mass similar to the down slope increase in total fines 18 39 of surface soil mass a combination of winnowing by wind during the past and down slope movement of sediment likely accounts for the modern distribution of aeolian dust and associated nutrients at the previously grazed site dust also increases down slope 5 11 in sediment with corresponding abundances of 13 25 fines estimates of the contributions of aeolian dust to the total soil nutrients range widely depending on assumptions about grain size partitioning of potential nutrients in weathered bedrock nevertheless aeolian dust is important for this setting contributing roughly 40 80 of the rock derived nutrient stocks p k na mn zn and

calcite dust and the atmospheric supply of nd to the japan sea abstract we report neodymium concentrations and isotope ratios e nd measured in the carbonate and silicate fractions of chinese loess the goal of the study is to investigate if the atmospheric supply of dissolved calcite dust to the oceans influences the cycling of nd in seawater we primarily focus on the japan sea because it receives large quantities of dust from eastern asia and it has a known nd isotope composition and a simple hydrologic budget a steady state atmospheric transport model is used to calculate the flux of soluble nd delivered to the japan sea surface by the wet deposition of dissolved calcite dust this information is then incorporated in a steady state two box model in order to evaluate controls on dissolved e nd values as well as to calculate the residence time of nd in seawater on average calcite in fresh chinese loess contains 150 nmol of nd g 1 with an e nd of 8 6 the atmospheric input of dissolved calcite to the japan sea surface is 7 4 10 12 g yr 1 which corresponds to a dissolved nd flux of 1 1 10 18 pmol yr 1 this flux represents the largest input of nd to the basin and it is required to produce the e nd composition of japan sea waters approximately 65 of the nd flowing from the japan sea surface into the western north pacific originates directly from the input of dissolved calcite dust downwelling surface water and the remineralization of settling particles containing nd scavenged from surface water contribute 77 of the nd in the japan sea deep which indicates that 50 of the deep nd originates from calcite dust the e nd composition of deep water is balanced by a benthic flux but the input is a factor of 10 lower than the calcite dust flux and accounts for only 23 of the deep nd surface and deep waters in the japan sea have nd residence times with respect to particle scavenging of 14 and 530 yr respectively these findings reveal that the atmospheric supply of dissolved calcite dust to the japan sea is a more important component of the marine nd cycle in this basin than previously recognized

asian dustfall in the st elias mountains yukon canada in april 2001 a major atmospheric dustfall event occurred in the st elias mountains yukon territory canada field samples were collected and analyzed for particle size mineralogy chemical composition and sr nd and pb isotopes dusts found above 3000 m had their source in the gobi desert region of northern china and inner mongolia and were transported to the yukon following a series of major dust storms that took place in early april dusts found below 3000 m had local yukon or mixed source s the asian dusts had a modal volume diameter of 4 m typical of far traveled mineral aerosols however larger 10 m particles were also found at 5000 m suggesting a very rapid trans pacific transport in the mid troposphere we estimate that the april 2001 event deposited from 5500 to 6335 tons of dust over an area of 21 000 km2 in the southwestern yukon most of which probably fell within a week our findings are consistent with instrumental observations and model simulations of the april 2001 event while the dust cloud was reportedly mixed with volatile pollutants from asia we found no evidence of metal pollution associated with the dustfall in the yukon our findings contribute to clarify the dynamics and the geochemical impact of asian dust long range transport events and to better estimate eolian fluxes of dustborne elements e g fe to the ocean associated with such events they may also assist in identifying past asian dust events in ice cores drilled from the st elias mountains icefields to develop a long term record of their frequency magnitude and source s

provenance of aeolian sediment in the taklamakan desert of western china inferred from ree and major elemental data abstract to identify the provenance of aeolian deposits in the extensive dune field in the taklamakan desert is of great importance for understanding the formation of this the largest sand sea in china the opinions from earlier studies are quite dipolar and are as follows a local origin of the dune sands in different parts of the desert on the basis of various heavy mineral assemblages and b strong homogenization of the sands in the entire taklamakan on the basis of geochemical data from whole rock samples by separately examining the ree characteristics and major elemental composition in coarse and fine fractions of the samples from aeolian deposits this paper provides new data for interpreting sources of aeolian deposits in the taklamakan the sampling sites are distributed in four different fluvial systems i e the areas of the keriya river niya river and cele river in the southern part and the northern margin near the tarim river fig 1 our results show that there are some significant differences in concentrations of trace elements and in ree features between the coarse and the fine fractions of the aeolian sediment the major elemental and ree data suggest that the coarser sand is different from area to area in the desert rather than a homogenization of the entire basin the fine fractions mainly silts are more homogenized the regional difference of coarse fractions in the study areas is consistent with the fluvial and wind systems in the basin this confirms that the sands are often mixed between the northern and southern parts but there is much less mixing along the east west direction it should be emphasized that not only glacial and aeolian processes but also fluvial and lacustrine processes have jointly contributed to the formation of the huge sand sea in addition little variation is found between old and young sands in two sediment sequences in the central part of the desert indicating consistency of sand sources in a given site during the last 40 ka

significance of atmospheric inputs of calcium over the southwestern mediterranean region high mountain lakes as tools for detection 1 we quantified dry and wet atmospheric deposition of calcium over the southwest mediterranean region and we assessed its impact on calcium dynamics of two high mountain lakes differing in morphometry and catchment characteristics atmospheric deposition of ca averaged 40 mmol m 2 yr 1 and it showed a seasonal pattern similar to that reported for saharan dust export to the mediterranean region with maxima during spring and summer ca enrichment from nonmarine sources was significantly related to the toms total ozone mapping spectrometer aerosol index atmospheric inputs significantly affected ca concentration of the selected lakes which do not presumably receive significant ca inputs from weathering the intensity of the effect depended on their corresponding sensitivities to evaporation total atmospheric inputs of ca to each study lake catchment 11300 and 3100 moles were enough to explain the lake ca content 5400 and 111 moles respectively the results obtained in this study reveal that atmospheric inputs particularly saharan dust deposition may be a significant source of calcium to remote mountain lakes

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

deposition of playa windblown dust over geologic time scales thick eolian deposits are commonly observed beneath desert pavements downwind of dust emitting playas these deposits play an important role in piedmont surface evolution controlling surface hydrologic conductivity and rates of pedogenesis to better understand the factors controlling the spatial distribution of eolian deposition we developed a numerical model that treats deposition from spatially distributed playa sources using analytic point source solutions for deposition from a gaussian plume the model also accounts for complex downwind topography as a test case model predictions were compared to eolian deposit thicknesses on eagle mountain piedmont southern amargosa valley california which receives dust from nearby franklin lake playa the close relationship between the model predictions and mapped thicknesses suggests that eolian transport and deposition can be modeled from basin to regional scales within this framework these results have important implications for hydrologic pedogenic and air quality problems

mineralogy of aeolian dust reaching the north pacific ocean 2 relationship of mineral assemblages to atmospheric transport patterns atmospheric dust particles actually comprise a small number of mineral assemblages we determined the composition of these assemblages and their geographic distribution by statistical analysis of mineralogy data air mass trajectory analysis was used to identify transport paths and possible source regions for these samples three types of trajectories are most common and each displays different proportions of four mineral assemblages the first indicates outflow of air from central asia and is associated with an illite rich mineralogy the second type comprises trajectories which include low altitude transport over the japanese islands for mixed mineralogies which contained a small amount of the illite rich end member the third type is made up of trajectories crossing the north american continent and is present exclusively in the eastern north pacific area there is a mixed mineralogy associated with these trajectories our results suggest that both source area mineralogy and transport pathway contribute to the compositional variability of the mineral aerosol at a given location the results presented here show that event specific meteorological data can be useful in understanding spatial patterns of eolian transport

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 m 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

the nature origin and accumulation of loess abstract loess can be defined simply as a terrestrial clastic sediment composed predominantly of silt size particles which is formed essentially by the accumulation of wind blown dust there are three fundamental requirements for its formation 1 a sustained source of dust 2 adequate wind energy to transport the dust and 3 a suitable accumulation site most loess has been modified to some degree by local reworking bioturbation and syn depositional weathering but a process of loessification is not necessary for a dust deposit to qualify as loess the terms primary loess and secondary loess have previously been used to described wind deposited loess and redeposited loess respectively but it is more accurate to describe material reworked and redeposited by non aeolian processes as loess derived colluvium or loess derived alluvium during the quaternary loess formed in three main situations 1 mid continental shield areas beyond the limits of ice sheets periglacial loess 2 on the margins of high mountain ranges perimontane loess and 3 on the semi arid margins of some lowland deserts peridesert loess peridesert loess is relatively poorly developed partly due to the limited efficiency of silt generating mechanisms in low land deserts compared with glaciation but also important is the tendency in arid areas for dust to be dispersed over a wide area and to be rapidly reworked after deposition particularly in areas which experience frequent climatic changes the remarkably thick loess of china and central asia results from an unusual combination of conditions which has persisted for much of the last 2 3 million years namely rapid uplift of the tibetan plateau and surrounding mountain ranges high rates of sediment production and supply to adjacent basins a strong northwesterly and westerly wind regime and the existence of effective dust traps downwind of the source regions

aeolian dust transport and deposition by foehn winds in an alpine environment lake tekapo new zealand abstract observations from an automatic weather station and anemograph network are used in conjunction with recorded dust deposition rates to identify principle sources of wind blown dust within an alpine lake basin meteorological observations made throughout the study indicate that foehn windstorms provide ideal conditions for the initiation of aeolian processes including dust storm genesis a mean wind speed during foehn windstorms of 7 5 m s 1 at 2 65 m above the surface was observed to initiate entrainment of dust particles from geomorphically active areas within the lake basin particularly from the dry braid channels of glacier fed rivers exposed lacustrine deltas and degraded tussock grasslands this threshold entrainment velocity is similar to others presented within the international literature for such surface types a diurnal modulation of meteorological parameters monitored during foehn wind events suggests that aeolian processes such as dust entrainment are most likely to occur from late morning to early evening however where topography enhances wind speeds for example by channelling airflow down river valleys favourable conditions for dust entrainment may prevail throughout the night in the absence of precipitation potential dust roses were determined for two sites within the lake basin the dust roses supported anecdotal and observational evidence of principle dust sources within the study area and appear to be an effective tool for identifying the potential hazard to a particular location from blowing dust once the physical trigger conditions for dust entrainment are known this requires detailed and concurrent monitoring of meterological variables in association with dust transportation and deposition rates especially in complex terrain where many micro climates often exist

location of natural trace elements in silty soils using particle size fractionation abstract in silty material 80 of the particles range from 2 to 50 m particle size fractionation within this size range allows determination of the main mineral bearers of natural trace elements te in silty soil three silty soils were studied at ch teau thierry in the paris basin at muret in the aquitaine basin and at thann in the alsace plain these soils mainly consist of quartz alkaline feldspars plagioclase micas and chlorite the quantities of which vary with particle size as shown by xrd and chemical analyses of major elements quartz content increases with increasing particle size whereas feldspars micas and chlorites occur mainly in the 2 10 0 2 2 and

accretion of asian dust to hawaiian soils isotopic elemental and mineral mass balances hawaiian soils contain a mixture of material derived from in situ weathering of parent material plus atmospheric inputs including sea salt aerosols and asian dust we use soil mineralogy and radiogenic isotope geochemistry sr and nd to evaluate the impact of asian dust on a chronosequence of hawaiian soils dust becomes an important constituent of soils 20 ky and older near surface 50 cm depth horizons contain as much as 30 quartz a mineral absent from local parent material basaltic sr and nd isotope signatures in these horizons have been completely overprinted by asian dust signatures with 87sr 86sr ratios as high as 0 723 and end values as low as 7 ree patterns in these soils are indistinguishable from that of average upper continental crust quartz abundance and nd isotopes provide two independent tracers of long term dust additions to the chronosequence soils the two tracers indicate a minimum long term average dust accretion rate of 125 mg cm 2 ky 1 at the 150 ka chronosequence site roughly a factor of three higher than holocene dust accumulation rates estimated from north pacific sediment cores we find that the mass of dust preserved in these soil profiles does not increase with age in soils 150 ka and older requiring a loss mechanism for accreted dust on the basis of the geomorphic stability of these sites observed preferential loss of dust derived mica relative to quartz and estimates of soil si leaching rates we argue that chemical weathering is the dominant loss mechanism for dust from these soils dust has a profound effect on the budgets of elements that are susceptible to leaching losses dust becomes the dominant source of soil nutrients si and p in the oldest most intensely weathered soils we calculate a dust derived p input flux of 0 8 mg cm 2 ky 1 and a dust derived si input flux of 35 mg cm 2 ky 1 si leaching fluxes are high 1400 mg cm 2 ky 1 in the youngest 2 ka soils and drop systematically with soil age to a value that closely balances the dust derived si input flux by 4100 ka extremely refractory elements such as nb which are concentrated in soils by residual enrichment processes are much less readily impacted by dust addition although dust has had a pronounced impact on sr and nd isotopic budgets and on soil mineral composition at the 150 ka site dust cannot have contributed 4 of the total nb contained in this soil profile

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

strontium 87 strontium 86 as a tracer of mineral weathering reactions and calcium sources in an alpine subalpine watershed loch vale colorado sr isotopic ratios of atmospheric deposition surface and subsurface water and geologic materials were measured in an alpine subalpine watershed to characterize weathering reactions and identify sources of dissolved ca in stream water previous studies have noted an excess of ca in stream water above that expected from stoichiometric weathering of the dominant bedrock minerals mixing calculations based on 87 sr 86 sr indicate that on an annual basis 26 67 of ca export in streams is atmospherically derived 23 61 is from weathering of plagioclase and the remainder is from weathering of calcite present in trace amounts in the bedrock a potential source of error when applying sr isotopes in catchment studies is determination of the 87 sr 86 sr of sr released by mineral weathering which is complicated by the wide range of mineral isotopic compositions particularly in older rocks and the variable rates at which the minerals weather in this study base flow stream chemistry was used to represent the 87 sr 86 sr of sr derived from mineral weathering because it effectively integrates the potentially variable isotopic composition of sr released by weathering in the alpine environment

mineralogy of aeolian dust reaching the north pacific ocean 1 sampling and analysis the mineral composition of the 2 m clay and 2 to 20 m silt size fractions of aerosol particles collected near the margins of the north pacific ocean was determined by x ray diffraction analysis although the same mineral phases are present in the two size fractions there are significant differences in the quartz plagioclase and kaolinite concentrations north pacific aerosols are primarily composed of illite in both size fractions in addition to kaolinite in the 2 m size class and quartz and plagioclase in the 2 to 20 m size class quartz and plagioclase are present in significantly higher amounts in the 2 to 20 m size fraction while kaolinite is greater in the 2 size class western north pacific aerosol particles contain significantly higher 2 m quartz than samples collected in the east and eastern north pacific aerosols have significantly higher concentrations of 2 m smectite than those from the west

asian provenance of glacial dust stage 2 in the greenland ice sheet project 2 ice core summit greenland samples of dust from the greenland ice sheet project 2 gisp2 ice core summit greenland dated within marine isotope stage 2 between 23 340 and 26 180 calendar years b p around the time of the coldest local last glacial temperatures have been analyzed to determine their provenance to accomplish this we have compared them with approximately coeval aeolian sediments mostly loesses sampled in possible source areas psas from around the northern hemisphere the 5 m grain size fraction of these samples was analyzed on the basis that it corresponds to the atmospheric dust component of that time and locale which was sufficiently fine grained to be transported over long distances on the basis of comparison of the clay mineralogy and sr nd and pb isotope composition with ice dust and psas and assuming that we have sampled the most important psas we have determined that the probable source area of these gisp2 dusts was in eastern asia the dust was not derived from either the midcontinental united states or the sahara two more proximal areas that have been suggested as potential sources based on atmospheric circulation modeling except for a brief period during an interstadial when dust transport was exceptionally low for glacial times and had a mineralogical composition indicative of a slightly more southern provenance the source area of the dust did not change significantly during times of variably higher fluxes of dust with larger mean grain size or lower fluxes of dust with smaller mean grain size this includes the high dust period that correlates with the heinrich 2 period of major iceberg discharge into the north atlantic variable wind strengths must therefore be invoked to account for these abrupt and significant changes in dust flux and grain size

asian continental aerosol persistence above the marine boundary layer over the eastern north pacific continuous aerosol measurements from intercontinental transport and chemical transformation 2002 itct 2k2 1 we report analyses of aerosols collected for the 2002 intercontinental transport and chemical transformation experiment itct 2k2 sampling was conducted 15 april to 25 may 2002 data are from three sites a sea level site at trinidad head california a coastal mountain site 1 km altitude trinity alps and an inland mountain site near 2 km altitude mount lassen aerosols were continuously collected in eight size bins 0 09 to 10 micrometers aerodynamic diameter using eight stage rotating drum impactors samples were analyzed in 3 hour time steps by synchrotron x ray fluorescence we find the following 1 aerosol chemical composition at trinidad head was generally dominated by marine aerosols with varying minor contributions from local sources despite the presence of asian continental aerosol above the marine boundary layer significant concentrations of asian aerosols were observed at sea level only during a strong frontal passage between 22 and 25 april 2 at the elevated sites aerosol elemental composition was predominantly asian despite wide swings in concentration analysis of soil forming elements shows that asian continental dust and associated combustion products overwhelmed local source aerosols through the first half of the sampling period in the latter half asian aerosols present in the free troposphere were regularly delivered to the mountain sampling sites by nocturnal subsidence 3 asian aerosols in the lower free troposphere although highly variable were very persistent not arriving only in discrete transport events we conclude that throughout the experiment the aerosols in the lower free troposphere over the northeastern pacific ocean and western north america were dominated by continental outflow from asia with little marine or north american continental influence viewed in the context of previously published analyses of the long term aerosol history for mount lassen that showed frequent strong asian influence throughout spring summer and fall the asian impact appears likely to be quasi continuous for much of the year

dust transportation and deposition in a superhumid environment west coast south island new zealand contemporary rates of dust deposition monitored along a 300 km section of the superhumid west coast of new zealand s south island are presented in this setting dust is entrained primarily from the dry channels of braided glaciofluvial rivers that drain the western slopes of the southern alps measured dust deposition ranged between 0 21 and 118 9 kg 1 ha 1 month 1 which is similar to dust deposition rates monitored in arid and semiarid environments however these are not considered to be sufficient for present day loess genesis dust deposition was highest in summer because of the greater frequency of favourable dust transporting winds and the effect of rainfall was secondary dust transportation occurred mainly during the passage of nonprecipitating cold fronts or postfrontal southwesterlies transportation also occurred during prefrontal conditions and in winter fohn southeasterlies were the predominant dust transporting winds to affect the west coast

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

the role of atmospheric deposition in the biogeochemistry of the mediterranean sea abstract estimates of atmospheric inputs to the mediterranean and some coastal areas are reviewed and uncertainities in these estimates considered both the magnitude and the mineralogical composition of atmospheric dust inputs indicate that eolian deposition is an important 50 or even dominant 80 contribution to sediments in the offshore waters of the entire mediterranean basin model data for trace metals and nutrients indicate that the atmosphere delivers more than half the lead and nitrogen one third of total phosphorus and 10 of the zinc entering the entire basin measured data in sub basins such as the north western mediterranean and northern adriatic indicate an even greater proportions of atmospheric versus riverine inputs when dissolved fluxes are compared the form most likely to impinge on surface water biogeochemical cycles the atmosphere is found to be 5 to 50 times more important than rivers for dissolved zinc and 15 to 30 times more important for lead fluxes neglecting co limitation by other nutrients new production supported by atmospheric nitrogen deposition ranges from 2 4 g c m 2 yr 1 whereas atmospheric phosphorus deposition appears to support less than 1 g c m 2 yr 1 in spite of the apparently small contribution of atmospheric deposition to overall production in the basin it has been suggested that certain episodic phytoplankton blooms are triggered by atmospheric deposition of n p or fe future studies are needed to clarify the extent and causal links between these episodic blooms and atmospheric oceanographic forcing functions a scientific program aimed at elucidating the possible biogeochemical effects of saharan outbreaks in the mediterranean through direct sampling of the ocean and atmosphere before and after such events is therefore highly recommended

bulk and single particle mineralogy of asian dust and a comparison with its source soils 1 the mineralogical properties of asian dust have been examined in detail and the results have been compared with the chinese source soils using high resolution scanning electron microscopy transmission electron microscopy x ray diffraction and chemical analysis mineralogical classification of asian dust particles showed that the most common single particles were clay aggregates 48 that were often mixed with nanosized calcite followed by particles of quartz 22 plagioclase 11 coarse calcite 6 k feldspar 5 muscovite chlorite kaolinite amphibole gypsum fe and ti oxides which were either partly or entirely attached with clay size mineral grains the clay minerals in asian dust were mostly illite and interstratified illite smectite the average mineral composition of the bulk dust samples by x ray diffraction was quartz 28 plagioclase 11 k feldspar 8 calcite 8 illite 19 interstratified illite smectite 22 chlorite 2 smectite 1 and kaolinite 1 in the silty soils from the source regions the clay minerals and nanosized pedogenic calcite aggregated and covered silt size minerals while the sands were mostly composed of quartz and feldspars and were lined with clay minerals the mineralogy of asian dust was similar to that of the silty soil from the loess plateau but the total phyllosilicate content increased from desert sands 7 silty soil 23 to asian dust 45 fining eastward the optical properties of asian dust and its interaction with atmospheric gases and cloud are probably affected by the clay rich mineral composition the aggregation and attachment of the clay minerals on the coarser minerals and the nanosized calcite

aeolian dust contributions to soil of the namoi valley northern nsw australia abstract aeolian processes have been regarded as having little relevance to pedogenesis in the subhumid regions of eastern australia due perhaps to a perceived paucity of clear evidence of dust deposition and to difficulties of measuring an aeolian dust component within soils contrary to earlier opinions an aeolian soil component may occur in eastern australia as appreciable amounts of dust are deposited annually we report dust deposition rates and some dust characteristics at gunnedah and measured granulometric mineralogical and geochemical attributes of four soil profiles found in different physiographic areas of the namoi valley estimates of dust deposition rates indicate that a deposit at least 20 cm thick could have formed over the last 13 000 years the soil profile which most clearly indicates the presence of dust overlies basalt at bald hill here the topsoil contains a conspicuous population of particles with a modal diameter of 40 50 m and has been enriched in si by the addition of quartz which cannot have originated from the basalt or from colluvial or alluvial processes a clayey floodplain soil profile boonawa also contained a large dust particle population and also illite and moderate concentrations of k of possible aeolian origin two sandy profiles at round swamp displayed the same conspicuous dust particle populations and one exhibited an interstratified illite smectite component suggesting dust additions local aeolian processes were also indicated by the well sorted coarse sand sized particles of the round swamp east profile located on a low lunette adjacent to the swamp these fine grained quartz rich aeolian dust deposits differ considerably from the benchmark australian aeolian dust mantles which form the clay aggregated calcareous parna soils of southern new south wales

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

dry aeolian dust accumulation in rocky deserts a medium term field experiment based on short term wind tunnel simulations the spatial pattern of medium term a few months dry aeolian dust accumulation in rocky deserts is predicted using short term deposition and erosion experiments in a wind tunnel the predictions are tested in a field experiment set up in the northern negev desert of israel the results show that superimposing wind tunnel deposition and erosion maps usually leads to correct predictions of medium term dust accumulation the predictions are somewhat less confident near the inflection lines of windward hillslopes where small scale irregularities in the local topography make it difficult to locate the exact position of the areas of little accumulation elsewhere in the topography predictions are good and the method works satisfactorily highest accumulation occurs on concave windward slopes and to a lesser extent on slopes parallel to the wind little accumulation occurs on the convex windward slopes and in dust separation bubbles the smallest accumulation rates are observed immediately upwind of the top of pronounced hills and on leeslopes the rate of dry dust accumulation measured during the field experiment varied from 17 to 93 g m 2 a 1 depending on the topographic position of the accumulation plots for most plots it was of the order of 30 60 g m 2 a 1

grain size distribution and depositional processes of the mineral component of abyssal sediments lessons from the north pacific grain size analyses of the mineral component of abyssal pacific surface sediments show two distinctly different size distributions that can be associated with sediments that are dominantly eolian and dominantly hemipelagic respectively in the range of 1 to 30 m eolian grains show a distinct size mode at about 2 m 9 and little material coarser than about 16 m 6 hemipelagic grains are characterized by a much flatter size distribution that has a broad size mode near 2 m 9 and important amounts of material coarser than 16 m 6 this ability to distinguish between hemipelagic and eolian grains will obviate some long standing concerns in the interpretation of deep sea sediments examples of the utility of this technique are given for the north pacific and south atlantic

changing sources of base cations during ecosystem development hawaiian islands 87 sr 86 sr evidence from a soil chronosequence in the hawaiian islands demonstrates that the atmosphere supplies 85 of putatively rock derived sr in older sites initially bedrock is the dominant source for sr and other lithophile elements such as ca but high rates of weathering and leaching of the substrate by 20 ka lead to a shift to atmospheric sources the loss of weathering inputs coincides with other physio chemical changes in the soil and results in a steep decline of base cations in the soil pool while these patterns imply the potential for limitation of biological productivity by low base cation supply the atmosphere provides a supply of base cations in excess of nutritional needs even after nearly all rock derived base cations have been leached from the soil this raises the possibility that p limitation in terrestrial ecosystems may develop at least as much because of low rates of atmospheric deposition of p relative to ca k and other rock derived elements as because of its chemical interaction in soil

glacial interglacial changes in dust deposition on the chinese loess plateau the chinese loess plateau clp contains an extensive record of aeolian deposition through multiple glacial interglacial cycles independent chronologies based on pedostratigraphy magnetic susceptibility radiocarbon and luminescence dating were developed for 79 sites and used to estimate aeolian mass accumulation rates mars for marine isotope stages 1 5 the regional median value of mar for stage 2 is 310 g m2 yr compared to an estimate of 65 g m2 yr for stage 5 estimated mars from individual sites for stage 2 are approximately 4 3 times greater than mars for stage 5 and 2 1 times greater than for stage 1 mar values at individual sites are consistently highest in the northwest and lowest in the southwest of the clp during all marine isotope stages mars estimated on sections through loess terraces are consistently higher than mar estimates at other sites indicating that local recycling of loess material from exposed river valley deposits has been significant throughout the last 130 kyr although the spatial and temporal patterns in mar are robust there are uncertainties about the magnitude of these changes due to a lack of bulk density measurements and uncertainties in the chronologies for individual sites b site and chronological biases in the sampling used to derive regional estimates and c the unquantified nature of human impact on accumulation rates during the late holocene nevertheless the records from the clp pose a number of challenges which could be addressed by numerical models of the palaeo dust cycle

mineralogical composition of african dust delivered by red rains over northeastern spain the african dust deposition mineralogy source regions and influence on rain chemistry were analyzed for a site in the montseny mountains catalonia northeastern spain for the period august 1 1983 through august 1 1994 dust deposition was highly variable two events collected on november 9 11 1984 and march 22 25 1991 accounted for 62 of the total dust input in the 38 red rain events recorded in the period the average annual dust deposition was 5 3 g m 2 se 2 6 three source regions in the african continent were identified with back trajectory analysis 1 western sahara 2 moroccan atlas and 3 central algeria events from the moroccan atlas predominated in terms of number of events amount of rainfall and dust deposition the meteorological situations during red rains were identified western sahara events occurred principally with a depression at high latitudes 50 n forming a trough in the north atlantic moroccan atlas events occurred with a depression in front of portugal and events from central algeria were associated with a depression over spain or north africa by order of abundance median of n 13 the minerals identified in the dust by x ray diffraction were as follows illite quartz smectite palygorskite kaolinite calcite dolomite feldspars differences in mineralogy between source regions were significant for smectite kaolinite quartz and dolomite smectite and kaolinite content was highest in the algerian events while quartz and dolomite content was lowest events from the moroccan atlas had the lowest smectite and kaolinite the red rain soluble chemistry was clearly influenced by the dissolution of calcite high alkalinity calcium concentration and basic ph and by marine components high na cl arid mg 2 concentrations because of the very alkaline character of red rains they had a strong weight on the annual mean ph of rainwater this was reflected by the significant relationship r 0 71 p 0 01 between the percentage of annual precipitation as red rain and annual mean precipitation ph red rains provided 25 45 of the annual dissolved input of the major ions in precipitation and 34 of the calcium required for holm oak quercus ilex l forest growth at the study site

metal emissions from kilauea and a suggested revision of the estimated worldwide metal output by quiescent degassing of volcanoes abstract measurements of a large suite of metals pb cd cu zn and several others and sulfur at kilauea volcano over an extended period of time has yielded a detailed record of the atmospheric injection of ordinarily rare metals from this quiescently degassing volcano representative of an important type we have combined the kilauea data with data of recent studies by others emissions from volcanoes in the indonesian arc the large laki eruption of two centuries ago etna estimates of total volcanic emissions of sulfur to form the basis for a new working estimate of the rate of worldwide injection of metals to the atmosphere by volcanoes the new estimate is that volcanoes inject a substantially smaller mass of ordinarily rare metals into the atmosphere than was stated in a widely cited previous estimate j o nriagu a global assessment of natural sources of atmospheric trace metals nature 338 1989 47 49 our estimate which is an upper limit is an annual injection mass of about 10 000 tons of the metals considered versus the earlier estimate of about 23 000 tons also the proportions of the metals are substantially different in our new estimate