intersections between wind regimes topography and sediment supply perspectives from aeolian landforms in central asia abstract the widespread aeolian deposits of the central asian steppes and piedmonts offer potential to better understand the dynamics of the major eurasian climate subsystems over quaternary timescales however current assumptions linking climate processes with aeolian activity remain poorly substantiated and potentially problematic emerging datasets suggest that loess accumulation rates and the timing of peak dust flux along the tien shan piedmont are highly variable between sites the degree to which desert dunes reflect wind regimes and therefore provide records of climate circulation is unknown and the presumed genetic link between the region s desert dunes and piedmont loess deposits remains hypothetical these uncertainties raise questions as to the nature of the relationship between aeolian flux deposition and palaeo climate here we investigate the relationship between wind regimes and the distribution morphology and timing of two aeolian landform types dunes and loess in the topographically diverse ili basin of southeast kazakhstan and western china we establish late holocene ages for three dune sites and one loess profile and infer that the location and morphology of these landforms can be used to test their genetic link with recent wind regimes we assess the morphologic characteristics of linear dunes at four sites using a semi automated mapping approach and analyse the variability in dune orientations with respect to sand shifting wind trajectories identified from meteorological reanalysis data for each site the most frequently occurring wind direction appears to be responsible for sediment supply while the strongest winds drive dune orientation wind orientations are strongly influenced by topography back trajectories incorporating dust transport and deposition potential to the loess site suggest both westerly and northerly delivery of fine grained material to the piedmont and that the most common source areas lie in regions where surface sediment contains a mixture of coarse and fine grained material to facilitate entrainment into suspension

penetration of atlantic westerly winds into central and east asia abstract the geographical position of the convergence zone where the western atlantic climate system meets the asian winter monsoonal system depends on their relative strength these individual strengths are determined by the intensities of the air pressure gradients over the north atlantic and the siberian high pressure cell respectively since the factors that forced those gradients varied throughout glacial interglacial cycles the location of the convergence zone should have moved accordingly both the grain size characteristics of wind blown sediments and climate modelling prove that the atlantic influence extended remarkably far eastward at times the northeastern tibetan plateau was at the cross road of western and monsoonal influences during the last glacial this region was dominated by an atlantic signal with millennial scale climatic oscillations that are similar to the north atlantic marine and greenland ice core records in contrast that same region was only under monsoonal influence during the last interglacial it implies that the atlantic winds penetrated more vigorously eastward in full glacial conditions than in interglacial conditions

long time evolution of models of aeolian sand dune fields influence of dune formation and collision abstract theoretical models which approximate individual sand dunes as particles that move and interact via simple rules are currently the only viable method for examining whether large dune fields will evolve into a patterned structure we find that these types of simulations are sensitive to the influx condition and interaction function and are not necessarily robust under common assumptions in this paper we review continuum dune models and how they connect to models of dune fields that approximate dunes as interacting particles with collision and coalescence dynamics this type of simple dune field model is examined under different boundary and initial conditions we identify different long term behaviors depending on model parameters as well as the way in which dunes are initialized and collide a rule for predicting the end state of a modelled dune field is derived based on the statistics of a uniform influx dune size distribution and the interaction function possible future adjustments to the multiscale model such as the use of a gaussian influx dune size distribution and their effect on the prediction rule are also discussed

mapping the interactions between rivers and sand dunes implications for fluvial and aeolian geomorphology article i nfo the interaction between fluvial and aeolian processes can significantly change earth surface morphology when riversandsanddunes meet theinteractionofsedimenttransportbetweenthetwosystemscanleadtochangein eitherorboth systems however these two systemsare usuallystudied independently which leavesmanyques tions unresolved in terms of how they interact this paper carries out a global inventory using satellite imagery to identify 230 sites where there are significant fluvial aeolian interactions at each location key attributes such as wind river direction net sand transport direction fluvial aeolian meeting angle dune type and river channel pattern were identifiedand relationshipsbetween each factorwere analysed from thesedata six different types of interaction were classified that reflect a shift in dominance between the fluvial and aeolian systems results from this classification confirm that only certain types of interaction were significant the meeting angle and dunetype themeeting angle and interaction type and finally thechannel pattern andinteraction type however the findings also indicate the difficulties of classifying dynamic geomorphic systems from snapshot satellite images

multi spatial analysis of aeolian dune field patterns abstract aeolian dune fields are composed of different spatial scales of bedform patterns that respond to changes in environmental boundary conditions over a wide range of time scales this study examines how variations in spatial scales of dune and ripple patterns found within dune fields are used in environmental reconstructions on earth mars and titan within a single bedform type different spatial scales of bedforms emerge as a pattern evolves from an initial state into a well organized pattern such as with the transition from protodunes to dunes additionally different types of bedforms such as ripples coarse grained ripples and dunes coexist at different spatial scales within a dune field analysis of dune field patterns at the intersection of different scales and types of bedforms at different stages of development provides a more comprehensive record of sediment supply and wind regime than analysis of a single scale and type of bedform interpretations of environmental conditions from any scale of bedform however are limited to environmental signals associated with the response time of that bedform large scale dune field patterns integrate signals over long term climate cycles and reveal little about short term variations in wind or sediment supply wind ripples respond instantly to changing conditions but reveal little about longer term variations in wind or sediment supply recognizing the response time scales across different spatial scales of bedforms maximizes environmental interpretations from dune field patterns

factors determining desert dune type while most observers recognize four elemental types of desert dunes longitudinal transverse barchan and star1 3 there is little agreement about which factors determine these types the angular relationships between the resultant of sand shifting winds and both the crest and principal slipfaces of the elemental types have been discussed qualitatively for many decades these relationships have been quantified but the wide range of dune types that combine the elemental forms and the juxtaposition of different dune types show that wind regime is not the only determinant for example sand availability has been considered important we have now quantified the importance of both wind regime and sand availability as determinants of dune type we show here that the four elemental types occur in areas uniquely defined by both the equivalent sand thickness of sediments held in the dunes and a measure of directional variability of sand moving winds wind strength does not appear to be important vegetation has an ambiguous role and the particle size of dune sediments is unimportant

elongation and migration of sand dunes two distinct processes are known to act on dynamic dunes the process of migration by erosion on the windward side and deposition on the lee side typical for transverse dunes and the process of elongation typical for linear dunes these two processes are determined by wind direction relative to the dune alignment this article reviews the assertion that linear dunes experience lateral displacement in addition to elongation fieldwork on vegetated linear dunes vlds and gis work on seif dunes indicates no lateral migration for these dunes linear dunes can shift laterally only when a slip face formed on the lee side reaches the plinth of the dune the winds from both sides of the seif dune are never symmetric usually winds from one direction are more dominant and effective the outcome is the formation of peaks and saddles along the dune the strongest winds create a slip face on the lee side of the peak segments of the dune oblique to the dune alignment which reaches the base of the dune and displaces the peak downwind along the dune alignment the internal structure of the seif dune is formed mostly by this dominant wind direction and gives the impression that the dune has shifted laterally on the other hand there are cases in which the wind directions relative to dune alignment fall between those of transverse and seif dunes in such cases both processes act on the dune which subsequently experiences migration as well as elongation

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

aeolian dust dynamics in central asia during the pleistocene driven by the long term migration seasonality and permanency of the asiatic polar front loess paleosol sequences preserve detailed archives of climate change reflecting the dynamics of aeolian dust sedimentation and the paleodust content of the atmosphere the detailed investigation of particle size distributions psds of windblown sediments is an increasingly used approach to assess the paleorecord of aeolian dust dynamics the central asian loess belt offers the potential to reconstruct pleistocene atmospheric circulation patterns along an adjacent west east transect within interior eurasia through granulometric studies in this study we present the aeolian dust record of the loess sequence at remisowka se kazakhstan which reflects a detailed signal of glacial interglacial climate and atmospheric dynamics in central asia on the basis of radiocarbon and amino acid geochronologic data long term semicontinuous trends in the aeolian dust record of the last glacial cycle are observed and interpreted to reveal their paleoclimate signal in consideration of the modern synoptical atmospheric circulation patterns and aeolian dust transport in central asia it is likely that the observed trends reflect the long term migration seasonal duration and permanency of the polar front during the late pleistocene previously published models which focused on the reciprocal glacial interglacial influence of the zonal westerlies and the asiatic high on the aeolian dust transport in central asia were overly simplified and should be modified to include the major influence of the asiatic polar front as the polar front activity is intimately connected with the development and position of the interhemispherically active high level planetary frontal zone hpfz the presented data give insight to long term aeolian dust dynamics and climate variability of interior eurasia which are linked with interhemispheric climates

late oligocene to early miocene humidity change recorded in terrestrial sequences in the ili basin south eastern kazakhstan central asia enhanced aridification of central asia driven by the combined effects of orogenic surface uplift paratethys retreat changes in atmospheric moisture transport and global cooling is one of the most prominent cenozoic climate change events of the northern hemisphere deciphering regional long term patterns of central asian hydrology is therefore a key element in understanding the role of northern hemisphere mid latitude drying in the global hydrological system this study characterizes long term palaeoenvironmental conditions between the late oligocene and early miocene in south eastern kazakhstan based on stable isotopes elemental geochemistry and laser ablation uranium lead geochronology from alluvial fluvial and pedogenic deposits sedimentary facies and geochemical weathering indices suggest an increased surface and ground water discharge fed by orographically enhanced precipitation in the tien shan hinterland in contrast pedogenic stable isotope data and elevated rates of magnesium fixation in clay minerals mirror enhanced rates of evaporation in the vadose zone due to protracted aridification this study posits that pronounced surface uplift of the tien shan mountains during the oligocene miocene transition promoted regionally increased orographic precipitation and the development of fluvial discharge systems this article is protected by copyright all rights reserved

holocene lowering of the laurentide ice sheet affects north atlantic gyre circulation and climate the laurentide ice sheet which covered canada during glacial periods had a major influence on atmospheric circulation and surface climate but its role in climate during the early holocene 9 7 ka when it was thinner and confined around hudson bay is unclear it has been suggested that the demise of the ice sheet played a role in the 8 2 ka event an abrupt 1 3 c northern hemisphere cooling lasting 160 years through the influence of changing topography on atmospheric circulation to test this hypothesis and to investigate the broader implications of changing ice sheet topography for climate we analyse a set of equilibrium climate simulations with ice sheet topographies taken at 500 year intervals from 9 5 to 8 0 ka between 9 5 and 8 0 ka our simulations show a 2 c cooling south of iceland and a 1 c warming between 40 and 50 n in the north atlantic these surface temperature changes are associated with a weakening of the subtropical and subpolar gyres caused by a decreasing wind stress curl over the mid north atlantic as the ice sheet lowers the climate response is strongest during the period of peak ice volume change 9 5 8 5 ka but becomes negligible after 8 5 ka the climatic effects of the laurentide ice sheet lowering during the holocene are restricted to the north atlantic sector thus topographic forcing is unlikely to have played a major role in the 8 2 ka event and had only a small effect on holocene climate change compared to the effects of changes in greenhouse gases insolation and ice sheet meltwater

assessing the activity of faults in continental interiors palaeoseismic insights from se kazakhstan this study was financed by nerc and esrc earthquakes without frontiers project grant code ewf ne j02001x 1 1 and the centre for observation and modelling of earthquakes and tectonics comet kompsat 2 imagery was obtained through a category 1 award to rtw ejc thanks st edmund hall for travel support rtw was supported during this research by a university research fellowship from the royal society of london

moisture dynamics in central asia for the last 15 kyr new evidence from yili valley xinjiang nw china based on high resolution palynological investigations and ams 14 c dating the continuous lacustrine sediments contained in yili valley xinjiang provide an opportunity to reconstruct the effective moisture changes for the last 15 kyr in central asia the relatively warm and humid climate of the bolling allerod 15 12 9 cal kyr bp is a generalization but it seems to show some fluctuations the time of the younger dryas yd interrupted the increasing trend of effective moisture in the study region the climate was cold and relatively dry in the early yd period 12 9 12 0 cal kyr bp whereas the desert vegetation community appeared around 11 8 cal kyr bp almost the driest time since the 15 cal kyr br a sharp increase in effective moisture marked the beginning of the holocene in the yili valley the early holocene 10 6 7 6 cal kyr bp was the wettest time with a developed temperate steppe a dry climate with desert vegetation arose in the early mid holocene 7 6 6 5 cal kyr bp spanning 1100 years a second humid phase emerged between 6 5 and 5 2 cal kyr bp whose vegetation community was represented by temperate steppe moisture was reduced again and the climate became drier between 5 2 and 3 3 cal kyr bp when vegetation was dominated by desert steppe in the yili valley regional comparisons indicate that the moisture changes in yili valley were mainly influenced by the north atlantic ocean ssts through the westerlies the mean position of the siberian high pressure cell probably made a great contribution to the drought between 7 6 and 6 5 cal kyr bp the climate changes were generally consistent between the westerly dominant central asia and asian monsoon regions since the last deglaciation possibly forced by summer insolation conditions in the northern hemisphere c 2011 elsevier ltd all rights reserved

taphonomic implications of shell surface textures in bahia la choya northern gulf of california abstract the author collected shell samples of the bivalve chione from the extensive tidal flat system of bahia la choya northern gulf of california and examined their surfaces under the binocular and scanning electron microscopes samples were collected from environments ranging in degree of tidal exposure energy level and substrate inner tidal flats sandy outer flats rocky outer flats tidal channel estero channel salt marsh beach spit and subtidal surfaces were compared with those of shells experimentally subjected to bioerosion dissolution and abrasion in all more than 1100 shells were examined and described bioerosion by microborers is by far the dominant process attacking shell material in bahia la choya microbored textures dominated shell surfaces from all sedimentary environments with the exception of the beach where abrasion dominated chemical dissolution is important only in the fine grained salt marsh and inner flat environments many shells show composite textures which reflect the concurrent action of more than one taphonomic agent shells from the salt marsh for example frequently show the effects of both microboring and dissolution overprinted textures can document transport among environments

relatively recent construction of the tien shan inferred from gps measurements of present day crustal deformation rates the tien shan a high seismically active intracontinental mountain belt 1 000 2 000 km north of the himalaya has grown as a result of india s collision with asia1 the crustal shortening 200 50 km refs 2 3 and thickening that gave rise to the tien shan accommodates only a small fraction of india s total penetration into asia 2 000 3 000km and the temporal relationship of deformation in this belt to the india asia collision remains unclear here we report geodetic measurements of the tien shan using the global positioning system gps that indicate that the current crustal shortening rate is nearly half of india s convergence rate with eurasia in this area4 we infer a total shortening rate for the tien shan of 20 mm yr 1 which is approximately twice that inferred previously from the extrapolation of slip rates in the holocene3 and earthquake induced displacements during this century5 suggesting that the rate of mountain building in this region has accelerated several fold since the onset of collision 50 55 myr ago6 7 if as we argue the current shortening rate can be extrapolated to geological timescales then our results suggest that most of the tien shan has been constructed during the past 10 myr perhaps in response to an increased horizontal force following an abrupt rise of the tibetan plateau8 9

morphological variability in the linear dunefields of the strzelecki and tirari deserts australia linear dunefields dominate the arid centre of the australian continent the morphological variability of linear dunes in the strzelecki and tirari deserts of australia was assessed using a dune classification scheme based on quantifiable variables of substrate spacing and junction frequency the use of high spatial resolution aster satellite imagery enabled detailed analysis including spectral characterisation of substrate at both local and regional scales the classification of the linear dunes revealed close relationships between substrate type and dune spacing reflecting local sediment availability increasing dunefield organisation downwind is reflected in reduced numbers of dune junctions and may suggest the attainment of dynamic morphological and sedimentological equilibrium both downwind evolution and sediment nourishment from local sources play a role in linear dune formation maps illustrating the spatial distribution of planimetric variables provide a useful tool for investigating linear dune behaviour although additional variables such as height and dunefield age add to the complexity of dune formation and must also be considered

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

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

palaeotemperature reconstruction during the last glacial from δ18o of earthworm calcite granules from nussloch loess sequence germany abstract the nussloch loess palaeosol sequence rhine valley germany is considered to be one of the most complete records of the last glacial period in western europe due to its very high sedimentation rate and its good chronological control this sequence is therefore a good framework in which to develop new proxies for palaeoenvironmental reconstructions in this study we explore for the first time the potential of earthworm calcite granules as a new bio indicator and climatic proxy of absolute air and soil temperature in the context of last glacial loess these granules are composed of rhomboedric calcite crystals organized in a radial crystalline structure as these granules are individually generated by earthworms at a relative fast rate they are expected to record intra annual variations in the available sources of oxygen percolating waters of meteoric origin we extracted thirty earthworm calcite granules from 11 of 5 cm layers thick from tundra gley and brown soil horizons previously dated at 45 to 23 ka oxygen isotope ratios were measured on each individual granule the 18o of calcite granules and interlinked transfer functions between water cycle air and soil temperatures allowed us to estimate air temperatures ranging from 10 to 12 4 c which most likely reflect the warm periods of the year when earthworms were the most active

paleoenvironmental changes recorded in a luminescence dated loess paleosol sequence from the tianshan mountains arid central asia since the penultimate glaciation abstract mid latitude arid central asia aca is one of the driest regions in the world and is a key source area of global atmospheric dust loess records of paleoclimatic changes in aca are complex and interpretations are problematic due primarily to the lack of robust chronologies quartz osl and k feldspar pirir dating methods were employed to date 8 quartz and 30 k feldspar samples from a 30 m loess sequence byh10 section on the northern slope of the tianshan mountains central aca northwest china the reliability of quartz and k feldspar ages was monitored by internal checks of luminescence characteristics and by comparison of the quartz and k feldspar ages the section lithology proxy indexes of grain size and magnetic susceptibility and the high resolution osl chronology together indicate 1 quartz osl dating can be used to date aca loess samples less than 40 ka while k feldspar pirir dating is reliable for loess samples at least as old as 150 ka from aca 2 aeolian loess began to be deposited on the northern slope of tianshan mountains beginning at least 145 ka ago and was deposited primarily during the penultimate and last glaciation periods 3 rapid loess deposition occurred during mis 6 mis 4 to early mid mis 3 and mis 2 but little or no loess deposition occurred during mis 5 mis 3a and mis 1 4 this loess depositional sequence is comparable to previously published stalagmite growth records in the region on glacial interglacial cycles rapid dust deposition and lack of stalagmite growth during glacials and lack of loess deposition and stalagmite growth during interglacials indicate a climatic pattern of wet warm interglacial and dry cold glacial climatic regimes on orbital cycles in aca 5 variation in the loess deposition rates in aca was much larger than in the central loess plateau during the last glaciation 6 depositional hiatuses of 50 kyr occur in aca loess sequences and high resolution chronologies are needed when reconstructing past climatic changes

relationships between desert dunes during the late quaternary in the lake frome region strzelecki desert australia transverse and linear dunes near the ephemeral lake frome in the strzelecki desert of australia provide evidence for a genetic geomorphic relationship between desert dune types transverse dunes overlying palaeoshorelines lie upwind from linear dunes the sedimentology of both dune types is similar suggesting reworking or downwind transport of the same source material over time clay pellets from several horizons within the linear and transverse dunes provide evidence for fluctuating water tables and high evaporation rates during those periods of aeolian activity along with saltinflux associatedwith thedeflation oflakefrome weconclude thatthe nature andinitiation of dune activity is controlled not only by aridity but by local hydrology osl ages from both transverse and linear dunes indicate aeolian activity at 66 57ka and 22 11ka transverse dune building took place around 106 111ka linear dune activity initiated at least 66ka ago with reactivation around 43 28ka followed by pedogenesis in response to humid conditions widespread dune reactivation from around 22ka correlates broadly with the last glacial maximum and late glacial period consistent with evidence of cold arid conditions and dune activity in australia copyright 2007 john wiley sons ltd

seasonal stable isotope evidence for a strong asian monsoon throughout the past 10 7 m y o of wet season rainfall was signi cantly morenegative 29 5 smow prior to 7 5 ma than after 26 5 smow if this change is attributable to a lessening of the amounteffect in rainfall this agrees with oral and soil geochemical datathat indicate increasing aridity beginning at 7 5 ma keywords tibetan plateau monsoon stable isotopes paleohydrology seasonality introductionthe tibetan plateau is the engine that drives the modern asianmonsoon by generating a high altitude region of low pressure in thesummer as the plateau heats and a region of high pressure in the winteras the plateau cools hastenrath 1991 during the summer warm airrises from the plateau pulling moist air off the ocean across the indiansubcontinent and into the highlands this results in heavy summer rain fall on the subcontinent the opposite occurs in the winter resultingin cold dry air spilling off the plateau and effectively excluding rainfrom the subcontinent thus the presence of a strong wet season dry season alternation implies the presence of a plateau broad and highenough to drive the monsoon the timing of the uplift of the plateau remains a matter of con siderable debate because there are few direct indicators of paleotopog raphy in the geologic record consequently past workers in tibet re lying on indirect indicators of uplift have proposed dates ranging from40 to 3 4 ma on the basis of initiation of potassic volcanism chunget al 1998 turner et al 1993 or extension on the plateau harrisonet al 1995 coleman and hodges 1995 changes in marine sedimen tation rates burbank et al 1993 sediment types rea et al 1998 or biota nigrini and caulet 1992 kroon et al 1991 and changesin stable carbon isotope and palynological patterns on the indian sub continent quade et al 1989 chen 1981 although different areasof the plateau may have risen at different times many workers haveinferred rapid simultaneous uplift of large areas of the plateau at 7 8ma by a process such as lithospheric delamination molnar et al 1993 this inference was based on the following approximately coevalphenomena a major change in plant communities of the indian sub continent quade et al 1989 and shifts in marine upwelling patternsthat are linked to an intense monsoon kroon et al 1991 althoughthere is strong evidence for signi cant climate change at 7 8 ma it isunclear whether this is the onset of the monsoon the oral transitionseems to have been a global rather than local phenomenon cerling etal 1997 and monsoonally driven upwelling may have already beenpresent by 10 12 ma nigrini and caulet 1992 kroon et al 1991 because there is an intimate association between the intense sea sonality of the modern monsoon and a high tibetan plateau and be cause evaporation can be unambiguously recognized in the d

how do longitudinal dunes respond to climate forcing insights from 25 years of luminescence dating of the australian desert dunefields abstract this paper presents a meta analysis of 689 luminescence age estimates of australian desert sand dunes this analysis had two aims to examine the hypothesis that quaternary climate changes have forced dune accumulation and to understand longitudinal dune behaviour from the age architecture of sand dunes for which stratigraphic information is often absent or poorly known a novel approach to the analysis of probability density curves of dune age frequency shows that in the mallee dunefield of southeastern australia only the period leading up to and including the last glacial maximum lgm 18 34 ka experienced marked dune growth which cannot be explained by random stochastic activity during the lgm most but not all mallee longitudinal dunes were accumulating more rapidly than before and after in the strzelecki dunefield source bordering sbd longitudinal dune tl n 61 and osl n 40 ages are more frequent at the pleistocene holocene transition but nearby non sbd longitudinal dunes n 21 ages were only active above background levels during the lgm however the strzelecki dune age data set suffers from being drawn from a small number of individual dunes 10 sbd dated using tl 12 sbd dated by osl 7 non sbd dated by osl with a marked bias away from surficial young and basal old depths even during the lgm many dunes do not record active growth and the dunefield was most likely a mosaic of stable dune surfaces and bare mobile patches supported by the scant pollen data from the arid zone hyper aridity has not been experienced in these dunefields these vegetated dunes exhibit conservative behaviour with limited response to the range of climate forcing experienced in the late pleistocene a more complete understanding of dunefield response to quaternary climates would require an intensive and structured dating program to overcome the noise from stochastic processes leading to small scale activity in these dunes and the simultaneous removal of parts of the sedimentary record

aeolian dune field self organization implications for the formation of simple versus complex dune field patterns abstract the interpretation of aeolian dune field patterns as self organizing complex systems is a new paradigm in which pattern evolution may be addressed computer simulations supported by field and experimental data indicate that a given wind regime produces a simple dune field pattern dune type and crest orientation are determined by wind regime and pattern ordering occurs through dune dune interactions over time because dunes reorient only at their crest terminations with a change in wind regime the rate of formation of a new pattern of small dunes is typically faster than the rate of reorientation of the existing pattern resulting in the superposition of simple patterns to give rise to complex patterns complex patterns are distinct from spatial changes in a simple pattern and from the type of superposition that characterizes compound complex dunes complex patterns necessarily indicate a rate of pattern formation that is rapid compared to the rate of sediment accumulation on the depositional surface

earthworm calcite granules a new tracker of millennial timescale environmental changes in last glacial loess deposits earthworm calcite granules ecg are secreted by several earthworm species mostly lumbricus terrestris and lumbricus rubellus which release them at the surface and in the upper part of soil horizons for a long time they have been found in various calcareous quaternary deposits but more recently in western european loess sequences where they can be abundant in specific layers in this study we present the first continuous record of ecg abundance variations from two loess sequences in northern france dating from the last glacial period the aim of this research is to evaluate the reliability of ecg as a new palaeoenvironmental proxy for the study of loess environments ecg counts reveal a link between their abundance and the nature of stratigraphic units i e very high abundances in tundra gley and boreal brown soil horizons and almost none in typical calcareous loess these abundance variations are similar to those of terrestrial molluscs the ecg signal thus suggests along with sedimentological parameters grain size index calcium carbonate total organic carbon that milder climatic conditions occurred during the development of tundra gleys during the upper pleniglacial 20 35 ka and of boreal brown soils during the middle pleniglacial 35 40 ka

distribution and composition of loess sediments in the ili basin central asia loess deposits in central asia provide an important record of regional climate and environmental change however in contrast to the intensively investigated loess deposits on the chinese loess plateau clp loess sediments in the ili basin of eastern central asia are poorly understood based on field investigation and existing literature this paper presents a preliminary study of the distribution strata and composition of the ili loess the distribution of the ili loess is clearly controlled by topographic and geomorphic conditions mainly in the river terraces low uplands and slopes of the tianshan mountains the thickness of the loess varies from several meters to over two hundred meters to characterize the ili loess composition the authors analyzed its grain size geochemistry x ray diffraction pattern and heavy mineral assemblage grain size analyses reveal that the ili loess consists predominantly of silt 4 63 mu m with a minor proportion of sand which is coarser than the loess of the clp and suggests a nearby provenance the bulk mineral components of the ili loess are dominated by quartz and feldspar with minor amounts of calcite chlorite mica dolomite and hornblende more than 20 types of heavy minerals were observed with major components of amphibole magnetite and epidote the major elements of the ili loess are characterized by high abundance of sio2 al2o3 and cao and minor amounts of fe2o3 mgo na2o and k2o compared to the clp loess the ili loess is relatively rich in na2o and displays higher na2o al2o3 ratios suggesting weak weathering the distribution patterns of rees indicate that both the ili loess and clp loess are of typical upper crustal composition with enrichment in lree negative eu anomalies and depletion of hree both the heavy mineral assemblage and geochemistry indicate that the local bedrock of the ili basin may have contributed only a little to the loess sediments c 2014 elsevier ltd and inqua all rights reserved

loess accumulation in the tian shan piedmont implications for palaeoenvironmental change in arid central asia whilst correlations have been made between the loess of europe and china deposits in central asia have remained largely overlooked by scientific investigation the nature of the relationship between loess accumulation and palaeoclimate at the core of the eurasian loess belt is particularly poorly understood here we reconstruct palaeoenvironmental change in central asia over the last 40 ky based on data from the remizovka loess profile in the northern foothills of the tian shan in southern kazakhstan our interpretations are based on synthesis of chronostratigraphic colour and magnetic susceptibility data supported by chronostratigraphies from two additional sites nearby maibulak and valikhanova all three sites record substantially increased loess accumulation during late mis 3 into the global last glacial maximum glgm at remizovka increased loess flux occurred in two pulses at c 38 25 ka and 22 18 ka with the intervening period involving incipient pedogenesis at maibulak two loess pulses at c 40 30 ka and c 28 22 ka are separated by a weakly developed paleosol which may date to the same time as pedogenesis at remizovka there is additional possible periglacial influence at maibulak from c 40 33 5 ka at valikhanova there is some age overlap between paleosol and loess samples but overall loess accumulation appears to have increased at c 42 35 ka c 30 ka and the glgm with pedogenesis occurring 40 ka and c 32 ka at all three sites holocene loess accumulation is minimal this period is characterised by pedogenesis the chronostratigraphic variability between our sites highlights a need to interrogate climate driven models for loess formation in piedmont environments we interpret our data in the context of regional palaeoenvironmental archives to indicate that loess accumulation increased coeval with mis 3 glacial advance in the tian shan which was facilitated by northward expansion of the asian monsoon and associated increase in precipitation we hypothesise that increased ice volume impeded teleconnections with the temperate zone westerlies to the north these were compressed against the piedmont resulting in increased wind strength and facilitating increased loess flux peak loess accumulation during the glgm occurred under colder drier climatic conditions with reduced but sustained glacial ice volume and persistent influence of the westerlies in the arid central asian piedmont loess belt in the absence of more widespread reliably dated palaeoenvironmental records from the region our data become of critical importance for understanding past environmental conditions in central asia relative to elsewhere in eurasia and globally

late pleistocene climate evolution in southeastern europe recorded by soil bacterial membrane lipids in serbian loess abstract loess paleosol sequences in the vojvodina region in the southeastern carpathian basin have been intensively studied to obtain a high resolution stratigraphical framework for the upper pleistocene in this part of europe in these studies millennial scale sedimentation variations in the upper pleniglacial have been coupled to the greenland ice dust record indicating that the rapid climate variability characterizing the north atlantic and greenland areas is reflected in the loess deposits at the southern edge of the european loess belt rapid variations were recently also reported for the stable isotopic composition of organic matter in the surduk loess paleosol sequence located in the vojvodina region and were interpreted as episodes of increased c4 vegetation over the last glacial period based on potential coinciding changes in oceanic and atmospheric circulation patterns these episodes were attributed to plant moisture stress rather than by fluctuations in temperature although exclusive proof has not yet been provided here we report a high resolution record of continental air temperature and precipitation over the past 40 000 years based on soil bacterial lipid signatures preserved in the surduk loess paleosol sequence our temperature record shows a gradual warming trend suggesting that moisture availability indeed seems to be the main factor driving the excursions to c4 vegetation around surduk we also find that continental air temperature changes in this region may be seasonally biased and were driven by regional influences rather than by northern hemisphere climate forcings likely as a result of the inland isolation of the carpathian basin by surrounding mountains support for a regional climate driver comes from comparison of our lipid based temperature and precipitation records with similar records from the near by crvenka loess paleosol sequence which resemble the climatic trends recorded at surduk

morphodynamics boundary conditions and pattern evolution within a vegetated linear dunefield abstract the controls on the evolution of linear dunefields are poorly understood despite the potential for reactivation of dunefields which are currently stabilized by vegetation under the influence of 21st century climate change the relative roles of local influences i e boundary conditions and morphodynamic influences i e emergent properties remain unclear chronostratigraphic and sedimentological analyses were conducted on two pairs of linear dunes exhibiting different spatial patterning in the strzelecki desert of central australia it was hypothesized that morphodynamic influences via pattern coarsening would mean that dunes from the simpler pattern defined in terms of the frequency of defects i e junctions and terminations would be more mature older landforms optically stimulated luminescence osl dating of full depth regularly sampled profiles was used to establish accumulation histories for the four dunes and supported by sedimentological analysis to investigate possible compositional differences and similarities between the dunes whilst three of the dunes the two more simply patterned dunes and one of the more complex dunes have accumulation histories beginning between 100 ka and 150 ka and document sporadic net accumulation throughout the last interglacial glacial cycle to the late holocene one of the dunes with relatively complex patterning reveals that the majority of the dune accumulation 7 m at that site occurred during a relatively short window at 50 ka there is no clear sedimentological reason for the different behaviour of the younger dune the data suggest that small scale and essentially stochastic nature of the aeolian depositional erosional system can overprint any large scale morphodynamic controls the concept of dating landscape change by pattern analysis is thus not supported by this study and would require very careful interpretation of the scales being considered this further suggests caution when interpreting dune chronostratigraphies palaeoenvironmentally as different dunes are able to respond very differently to the same external stimulus e g climate in the case studied here a mechanism is proposed to account for the rapid accumulation of the anomalous dune by avulsion of the local aeolian accumulation from one dune ridge to another

denudation outpaced by crustal thickening in the eastern tianshan the modern high topography of the tianshan resulted from the reactivation of a paleozoic orogenic belt by the india asia collision today the range exhibits tectonically active forelands and intermontane basins based on quantitative morphotectonic observations and age constraints derived from cosmogenic 10be dating single grain post infrared infrared stimulated luminescence p ir irsl dating and modeling of fault scarp degradation we quantify the deformation in the nalati and bayanbulak intermontane basins in the central eastern tianshan our results indicate that at least 1 4 mm yr of horizontal crustal shortening is accommodated within these two basins this shortening represents over 15 of the 8 5 0 5 mm yr total shortening rate across the entire range at this longitude this shortening rate implies that the eastern central tianshan is thickening at a mean rate of 1 4 mm yr a rate that is significantly higher than the average denudation rate of 0 14 mm yr derived from our cosmogenic analysis this discrepancy suggests that the tianshan range has not yet reached a steady state topography and remains in a transient state of topographic growth most likely due to limited denudation rates driven by the arid climate of central asia

molecular records of continental air temperature and monsoon precipitation variability in east asia spanning the past 130 000 years our current understanding of past changes in east asian summer monsoon easm precipitation intensity derives from several loess paleosol sequences and oxygen isotope 18o records of well dated stalagmites although temperature is generally presumed to have had minimal impact on easm records past air temperature dynamics over east asia are so far relatively poorly understood mainly due to the lack of tools to reconstruct continental paleotemperatures here we report a high resolution record of east asian air temperature over the past 130 000 years based on soil bacterial lipid signatures preserved in a loess paleosol sequence from the mangshan loess plateau in china we find that maximum local insolation is the main driver of air temperature although greenhouse gas concentrations and southern hemisphere climate may influence temperature at times when insolation is weak causing a decoupling with easm precipitation intensity direct comparison of our temperature record with precipitation induced changes in past soil ph derived from the same suite of lipids confirms this decoupling subsequent cross spectral analysis of the two molecular proxy records reveals that variations in monsoon precipitation consistently lag those in air temperature throughout the whole record at the dominant precession band the length of this lag is variable however and increases as glaciation develops this observation is consistent with an increasing influence of northern hemisphere ice sheets on the modulation of easm response to insolation forcing during ice ages

the neogene de greening of central asia there remains substantial debate concerning the relative roles of tectonics and global climate in driving the evolution of climate in central asia today interior asia including the taklamakan gobi and ordos deserts is exceptionally arid and is surrounded by distinct rainfall boundaries such as those generated by the asian monsoon systems to the east and south and those generated by high topography to the north and west determining how and why these boundaries have varied over the neogene is hindered by the lack of a single proxy that can be broadly applied through space and time we construct isoscapes of pedogenic carbonate 13 c 13 c c over the neogene in asia by combining a compilation of 2236 published measurements with new data from three localities in northern central asia pedogenic carbonate 13 c records local aridity excepting localities impacted by c 4 grasslands and during large changes in atmospheric p co 2 through variations in soil respiration depth of carbonate formation and the effect of water stress on plant 13 c together these effects reflect changes in both primary productivity and mean annual precipitation throughout the neogene we find consistent and exceptionally high 13 c c in interior asia with a ring of lower 13 c c that demarcates higher precipitation this persistent ring of lower 13 c c corresponds in the south and east with the influence of the asian monsoon systems in the west and north it reflects both orographic rainfall due to uplift of the tian shan and to moisture delivery by the mid latitude westerlies finally 13 c c and hence aridity increases regionally in the latest neogene reflecting the effects of northern hemisphere glaciation and cooling this widespread de greening would have increased regional albedo and modified basin scale water balances resulting in greater dust fluxes due to reduced vegetative cover and precipitation

depositional history and archaeology of the central lake mungo lunette willandra lakes southeast australia abstract lake mungo presently a dry lake in the semi arid zone of southeastern australia preserves a unique record of human settlement and past environmental change within the transverse lunette that built up on its downwind margin the lunette is 30 km long and the variable morphology along its length suggests spatial variability in deposition over time consequently this presents differential potential for the preservation of past activity traces of different ages along the lunette earlier work at lake mungo focused primarily on the southern section of the lunette where two ritual burials of considerable antiquity were found here we describe the depositional history of the central section of the lake mungo lunette together with the first single grain optically stimulated luminescence osl chronology of the full stratigraphic sequence and of three hearths we thereby lay the foundation for systematic investigation of the distribution of archaeological traces through the sedimentary record the older depositional units lower and upper mungo were deposited ca 50 40 ka and 34 ka respectively and are substantially thinner in the central section of the lunette compared with the south by contrast the overlying unit of interbedded sands and clayey sands arumpo zanci units deposited ca 25 14 ka is markedly thicker and dominates the stratigraphic sequence in the central portion of the lunette although the sequence broadly reflects previous models of the lunette s depositional history and changing hydrological conditions our results indicate spatially variable deposition of sediments possibly as a result of changes in prevailing wind regimes archaeological traces are exposed in all stratigraphic units deposited after ca 50 ka including sediments deposited after the final lake drying ca 15 ka indicating human occupation of the area under a range of palaeoenvironmental conditions dating and stratigraphical examination of individual hearth features demonstrates that even within individual stratigraphic units human occupation persisted under variable conditions mid holocene occupation of the area following the final lake retreat took place during a period of relatively humid climate

aeolian dune field pattern boundary conditions aeolian dune field patterns reflect the complex external environment within which the pattern evolves these external environmental controls are the boundary conditions on aeolian dune field pattern formation the influences of boundary conditions such as wind regime and sediment supply are well known however boundary conditions represent a relatively unexplored area of dune field pattern formation source area geometry and areal limits are two newly recognized boundary conditions measurements of crest spacing and crest length from satellite images of dune field patterns with point and line source area geometries show an increase in spacing and crest length over distance whereas spacing and crest length in plane sourced patterns emerge equally across the dune field the impact of the size and shape of a dune field on crest spacing is tested using a previously established analytical model model results indicate that the area of a dune field limits the maximum spacing that can occur within a given area and that dune fields that are five times longer in the direction of dune migration than in the crest parallel direction can achieve the greatest spacing within a given area empirical measurements of spacing defect density and dune field area from ten different dune fields ranging over four orders of magnitude in size show that spacing increases and defect density decreases as dune field area increases because the formation of all dune fields involves a wind regime and sediment supply there must be interplay of boundary conditions within the same dune field at different stages of pattern development one boundary condition may dominate over others and with changing climatic eustatic or tectonic parameters boundary conditions may change to modify an existing pattern recognizing boundary condition controls on aeolian dune field pattern formation provides a framework for recognizing the signature of the external environment in which a pattern developed and can be used for reconstructing past dune constructional events and climatic change

the formation of loess deposits in the tashkent region and parts of central asia and problems with irrigation hydrocollapse and soil erosion abstract there are large problems of irrigation hydrocollapse and soil erosion associated with the loess deposits of central asia to get to grips with these we need a clear view of the nature and formation of the loess and in this region there are still disputes and disagreements and controversies important events in the loess deposit formation process can be identified and studied and relative significances assigned there are large loess deposits in the vicinity of tashkent in the north east of uzbekistan these were mapped and studied for many years by g a mavlyanov and associates they used a terminology which appears to be based on pavlov s nineteenth century usage and developed a polygenetic formation theory for loess deposits this was a formation theory very much associated with central asia and essentially favouring a proluvial mechanism a speculative look at the deposits near tashkent allows alternative terminologies and formation mechanisms to be considered in particular the widespread soviet antipathy to aeolian deposition can be examined the deposits associated with the chirchik river upstream of tashkent might be affected by the pavlov mechanisms but could be topped by aeolian deposits the collapse of loess when wetted is controlled by the nature of the ground and is a very significant interaction of soil and water in particular in central asia hydrocollapse and water erosion are closely related and are controlled by the complex nature of loess ground dust clouds in eastern uzbekistan are largely loess related but in the west dust material is raised from the drying aral sea bed this is often clay mineral agglomerate material and can carry dangerous pollutants