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

major features and forcing of high latitude northern hemisphere atmospheric circulation using a 110 000 year long glaciochemical series the greenland ice sheet project 2 glaciochemical series sodium potassium ammonium calcium magnesium sulfate nitrate and chloride provides a unique view of the chemistry of the atmosphere and the history of atmospheric circulation over both the high latitudes and mid low latitudes of the northern hemisphere interpretation of this record reveals a diverse array of environmental signatures that include the documentation of anthropogenically derived pollutants volcanic and biomass burning events storminess over marine surfaces continental aridity and biogenic source strength plus information related to the controls on both high and low frequency climate events of the last 110 000 years climate forcings investigated include changes in insolation of the order of the major orbital cycles that control the long term behavior of atmospheric circulation patterns through changes in ice volume sea level events such as the heinrich events massive discharges of icebergs first identified in the marine record that are found to operate on a 6100 year cycle due largely to the lagged response of ice sheets to changes in insolation and consequent glacier dynamics and rapid climate change events massive reorganizations of atmospheric circulation that are demonstrated to operate on 1450 year cycles changes in insolation and associated positive feedbacks related to ice sheets may assist in explaining favorable time periods and controls on the amplitude of massive rapid climate change events explanation for the exact timing and global synchroneity of these events is however more complicated preliminary evidence points to possible solar variability climate associations for these events and perhaps others that are embedded in our ice core derived atmospheric circulation records

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

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

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

the size distribution of microparticles from selected segments of the greenland ice core project ice core representing different climatic periods the size distribution of insoluble microparticles dust in the particle size interval 0 4 6 0 m radius has been measured in more than 1400 samples from the greenland ice core project grip deep ice core from summit greenland the samples were taken from ice core segments representing 32 climatic periods including ice from the eem interglacial and ice from below the eemian ice the mean dust volume distributions from the climatic periods are compared and the relationship of total dust mass to the concentration of ca2 and to the stable isotopic composition 18o is investigated the dust volume distributions are found to be lognormal in the size interval 0 4 2 0 m with nearly identical shapes changes of the lognormal part of the volume distributions are found to be connected to the total dust mass in a systematic way the total dust mass is correlated to the ca2 concentration and data do not show any enrichment in ca2 from exposed continental shelves due to lower sea levels during the last glacial maximum the total dust mass is strongly connected to 18o the volume distribution of the particles in the size interval 2 0 6 0 m is found to be almost the same in most periods the exceptions are the cold periods in the last part of the last glacial period where the volume of these particles is higher than in most periods and the periods from the eemian and just above the eemian where the volume of these particles is lower the volume distributions of both the eemian warm periods and the cold eemian events are different from the distributions in ice from both below and above the eemian ice climate changes appear to have modified the processes of production transport modification and deposition of the dust aerosol in the same way over the last 120 000 years or more

using laser light scattering to measure impurities bubbles and imperfections in ice cores 1 laser light scattering lls on polar ice or on polar ice meltwater is an accepted method for measuring the concentration of water insoluble aerosol deposits dust in the ice lls on polar ice can also be used to measure water soluble aerosols as well as imperfections air bubbles and cavities in the ice lls was originally used for measuring the dust concentration in polar ice meltwater but was later also applied to solid ice for measuring the dust concentration profile along the deep bubble free sections of the greenland ice sheet project 2 gisp2 ice core from central greenland in this paper we extend the usability of lls on ice into the realm of the nontransparent bubbly polar ice and put previous empirical findings on a theoretical footing for lls on clear bubble free polar ice we studied numerically the scattering of light by soluble and insoluble aerosol particles embedded in the ice to complement previous experimental studies for air bubbles in polar ice we calculated the effects of multiple light scattering using mie theory and monte carlo simulations and found a method for determining the bubble size and number concentration using lls on bubbly ice we also demonstrated that lls can be used on bubbly ice to rapidly measure annual layers

air clathrate crystals from the grip deep ice core greenland a number size and shape distribution study we performed microscopic observations and a statistical study of the number size and shape distribution of clathrates in the grip greenland ice core project deep ice core using 185 samples from a depth range of 1016 3014m spanning a period of 6 to 110 ka sp and encompassing the holocene wisconsin and eemian periods the number concentration of the clathrates varied considerably with climatic changes it was possible to detect the rapid climatic oscillations in the last glacial between 13 and 110 ka bp the dansgaard oeschger cycles in the number concentration profile of clathrates the mean volume of clathrates is less clearly influenced by climatic factors with a tendency towards greater volumes in warmer periods but also a growth of clathrates with depth could be detected this growth rate was calculated to be 3 1 x 10 12 cm 3 a 1 the amount of gases captured in the clathrates is estimated to be significantly smaller than the total amount of air determined by gas concentration measurements this points to diffusion processes of atmospheric gases within the ice matrix

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

possible solar influences on the dust profile of the gisp2 ice core from central greenland the greenland ice sheet project 2 gisp2 ice core dust profile in glacial wisconsinan ice from central greenland has been measured using laser light scattering lls from ice this data exhibits considerable high frequency variability by applying appropriate running averages to the data certain regularities emerge thus for example when the data was smoothed with rectangular 4 and 5 year running averages 11 year dust modulations of considerable amplitude were revealed in this paper we show how further smoothing of the data causes very large longer period dust modulations centered at 91 years in a gaussian distribution to emerge we believe that this corresponds to the 80 90 year modulation of the 11 year sunspot cycle first suggested by gleissberg we also show how adjacent 11 year dust periods can combine in a unique way to generate a 22 year hale period of dust modulation the way this occurs is similar to that by which a 22 year modulation of the measured terrestrial neutron flux is generated from two 11 year periods taken together with our observation of a 200 year suess dust modulation period these observations strengthen our claim that the dust modulations we measured in gisp2 ice are solar induced and suggest a mechanism for their production

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

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

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

calibration of laser light scattering measurements of dust concentration for wisconsinan gisp2 ice using instrumental neutron activation analysis of aluminum results and discussion in past work we used laser light scattering lls from bubble free ice to measure how the dust concentration varied along the wisconsinan glacial section of the greenland ice sheet project 2 gisp2 ice core from central greenland in this paper we show how we calibrated this dust profile using instrumental neutron activation analysis inaa of aluminum in the course of the calibration we found that excluding no3 all the major impurities soluble and insoluble present in the ice covaried linearly with respect to the dust concentration we find that the lls signal from ice below a depth of 2600 m follows a different linear trend than the lls signal from shallow ice we attribute this to the presence of numerous microbubbles diameter 0 3 mm that emerged in the deeper ice following core extraction

continuous dust concentration profile of pre holocene ice from the greenland ice sheet project 2 ice core dust stadials interstadials and the eemian in this paper we present and discuss the pre holocene dust profile of the greenland ice sheet project 2 gisp2 ice core retrieved from central greenland measured using laser light scattering lls from ice and compare it with the electrical conductivity method and oxygen isotope profiles we describe how we dated the pre holocene ice using the annual dust peaks observed with lls starting from the accepted chronology to 2250 m and obtained a chronology in substantial accord with the gas age dating of the ice we also show that the gisp2 ice core penetrated the eemian and that a record of a 10 2 kyr penultimate glaciation is present in the gisp2 core

the greenland ice sheet project 2 depth age scale methods and results the greenland ice sheet project 2 gisp2 depth age scale is presented based on a multiparameter continuous count approach to a depth of 2800 m using a systematic combination of parameters that have never been used to this extent before the ice at 2800 m is dated at 110 000 years b p with an estimated error ranging from 1 to 10 in the top 2500 m of the core and averaging 20 between 2500 and 2800 m parameters used to date the core include visual stratigraphy oxygen isotopic ratios of the ice electrical conductivity measurements laser light scattering from dust volcanic signals and major ion chemistry gisp2 ages for major climatic events agree with independent ages based on varve chronologies calibrated radiocarbon dates and other techniques within the combined uncertainties good agreement also is obtained with greenland ice core project ice core dates and with the specmap marine timescale after correlation through the 18 o of o 2 although the core is deformed below 2800 m and the continuity of the record is unclear we attempted to date this section of the core on the basis of the laser light scattering of dust in the ice

cenozoic exhumation and deformation of northeastern tibet and the qinling is tibetan lower crustal flow diverging around the sichuan basin apatite fission track thermochronology data elucidate the cooling exhumation history of the qinling qin mountains which contain a paleozoic mesozoic orogenic collage north of the sichuan basin and northeast of the tibetan plateau in particular we examine the extent to which the qinling were affected by the rising plateau the northern and eastern qinling show continuous cooling and slow exhumation since the cretaceous in contrast in the southwestern qinling rapid cooling initiated at 9 4 ma a few million years later than in the eastern tibetan plateau a compilation of major cenozoic faults in the eastern tibetan plateau and the qinling and their kinematic and dynamic characterization shows that deformation in the qinling has predominantly been strike slip active sinistral and dextral strike slip faults delineate an area of eastward rock flow and bound the area of rapid late cenozoic cooling outlined by apatite fission track thermochronology these data can be interpreted to indicate that lower crustal flow has been diverted around the longmen shan and beneath the southwestern qinling causing active plateau uplift in this area alternatively northeastern tibet may be growing eastward faster in the western qinling than the entire south china block is extruding to the east

physical and structural properties of the greenland ice sheet project 2 ice core a review substantial data sets have been collected on the relaxation characteristics density grain size c axis fabrics and ultrasonic velocities of the greenland ice sheet project 2 gisp2 core to its contact with bedrock at 3053 4 m changes in all these properties paralleled closely those found in cores from byrd station antarctica and dye 3 greenland density increased progressively with depth to a maximum of 0 921 mg m3 at about 1400 m at which depth the ice became bubble free below about 2000 m in situ densities began to decrease in response to increasing ice sheet temperatures since drilling much of the ice core has undergone significant volume expansion relaxation due to microcracking and the exsolving of enclathratized gases especially in the brittle ice zone between 650 and 1400 m grain size increased linearly to about 1000 m thereafter remaining fairly constant until the younger dryas event at 1678 m where a twofold to threefold decrease in grain size occurred these grain size changes were accompanied by a progressive clustering of crystal c axes toward the vertical including a small increase in c axis concentration across the younger dryas holocene boundary increased dust levels in the wisconsin ice have contributed to the maintenance of a fine grained texture which with its strong vertical c axis fabric persisted to nearly 3000 m however beginning at about 2800 m layers of coarse grained ice intermixed with the much finer grained matrix ice are observed below 3000 m the ice became very coarse grained this change attributed to annealing recrystallization at elevated temperatures in the ice sheet was accompanied by a dispersed or ring like redistribution of the c axes about the vertical ultrasonic measurements of vertical and horizontal p wave velocities made at 10 m intervals along the entire length of the gisp2 core fully confirmed the results of the crystallo optical observations a return to fine grained ice coincided with the first appearance of brown silty ice 13 m above bedrock bedrock material consisted of 48 cm of till including boulders and cobbles overlying gray biotite granite comprising the true bedrock there is evidence that disturbed structure in the gisp2 cores begins little more than 70 of the way through the ice sheet this disturbance increases with depth until it becomes large enough to cast suspicion on features lasting centuries or more in the bottom 10 of the ice sheet

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

electrical measurements on the greenland ice sheet project 2 core the greenland ice sheet project 2 gisp2 electrical conductivity measurement ecm record is an indication of the concentration of h in the core the ecm detected seasonal variations in the nitrate concentration of the core which were used to assist in dating the core by annual layer counting volcanic eruptions that produce acidic aerosols are recorded in the ecm record evidence of biomass burning is detected by the ecm because fire related ammonium emissions neutralize the acids in the core rapid climate transitions associated with the younger dryas and dansgaard oeschger interstadial events alter the concentration of alkaline dust and are detected by the ecm the ecm has been used to develop stratigraphic ties between the gisp2 and the greenland ice core project cores users of the data should be aware of some instrument related artifacts in the ecm record

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

polar ice stratigraphy from laser light scattering scattering from ice we demonstrate that laser light scattering lls off glacial pre holocene polar ice can be used to measure variations in dust concentration along sections of bubble free ice core we have used this technique with considerable success on the gisp2 ice core that was retrieved from central greenland down to bedrock the technique is fast non destructive and has a very high resolution 1 mm or less

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

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

conditions for bubble elongation in cold ice sheet ice highly elongated bubbles are sometimes observed in ice sheet ice elongation is favored by rapid ice deformation and opposed by diffusive processes we use simple models to show that vapor transport dominates diffusion except possibly very close to the melting point and that latent heat effects are insignificant elongation is favored by larger bubbles at pore close off but is nearly independent of bubble compression below close off the simple presence of highly elongated bubbles indicates only that a critical ice strain rate has been exceeded for significant time and provides no information on possible disruption of stratigraphic continuity by ice deformation

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

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

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