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

the transition of the monsoonal and the n atlantic climate system off nw africa during the holocene 1 the northward extent of the influence of the w african monsoon during humid periods of interglacials is subject to investigations highlighting feedback mechanisms such as vegetation to detect this regional variation and the climate system acting farther to the north will be the aim of this paper focussing on the holocene we present two very high resolution holocene sediment records off nw africa located at 31 n and 27 n the well known mid holocene climate change from the african humid period to present arid conditions is well reflected by the terrigenous input in the southern core in contrast in the northern core spectral and wavelet analyses indicate a periodic oscillation of about 900 years of the terrigenous input throughout the last 9000 years b p we conclude that the w african monsoonal influence characterized by the abrupt climatic change at 5000 years b p can be separated from the influence of the n atlantic climate system reflected by a periodic oscillation throughout the holocene

eolian quartz flux to lake biwa central japan over the past 145 000 years abstract eolian quartz flux eqf g cm 2 103yr 1 to lake biwa central japan provides direct information on variations of the east asian winter monsoon lake biwa sediments spanning the past ca 145 000 yr are characterized by two main periods when eqf values were significantly greater than 5 50 g cm 2 103yr 1 and two main intervals during which eqf values were lower two periods with eqf values 5 50 g cm 2 103yr 1occurred from ca 145 000 to 125 000 and 73 000 to 13 000 yr b p while times of lower eqf values occurred from ca 125 000 to 73 000 yr b p and around ca 5500 yr b p between ca 125 000 and 73 000 yr b p three minimum eqf values and two intervening peaks of slightly higher eqf values are recorded eqf increased markedly from ca 73 000 to 13 000 yr b p whereas between ca 53 000 and 20 000 yr b p the values recorded were relatively lower than those recorded during either the preceding or the subsequent episodes the data imply that the east asian winter monsoon strengthened during the periods when eqf values were high and weakened during the intervals with low eqf values the eqf record of lake biwa can be correlated with the grain size record of the quartz fraction in chinese loess and with the specmap marine 18o record however the eqf record apparently lags ca 5000 yr behind the loess and 18o records during stage 6 5 and 2 1 transitions and ca 10 000 yr during stage 5 4 transition these apparent lags could be due to problems with the chronology alternatively they may imply that the eolian quartz flux depended more on the extent of dust source regions than on wind intensity during these transitions

holocene vegetation and climate of the alashan plateau nw china reconstructed from pollen data a set of 55 recent pollen spectra from the alashan plateau and the qilian mountains qilianshan northwestern china has been analyzed the established relationships between the pollen spectra and modern vegetation and precipitation patterns of the studied area have been applied to 65 fossil pollen spectra from a 825 cm long sediment record collected in the topographic depression formerly occupied by eastern juyan palaeolake 41 89 n 101 85 e 892 m a s l several qualitative approaches e g indicator plant species artemisia chenopodiaceae and ephedra fragilis type s l ephedra distachya type pollen ratios and quantitative methods of vegetation and climate reconstruction have been tested with the surface pollen and then applied to the eastern juyan pollen record fossil pollen data reveal pronounced environmental changes in the studied area of the alashan plateau between ca 10 700 and 1700 cal yr b p desert taxa as chenopodiaceae nitraria calligonum reaumuria were abundant in the vegetation cover around the study site through the whole record pollen spectra dated to ca 10 700 5400 cal yr b p are characterised by highest values of chenopodiaceae e fragilis type and other desert indicating taxa suggesting rather dry climate most favourable conditions are reconstructed between 5400 and 3900 cal year b p on the basis of relative increase in abundance of artemisia pollen a return to dry conditions occurred at about 3900 cal yr b p the lake finally desiccated after 1700 cal yr b p reconstructed dry climate oscillations between 5900 and 5400 and 3100 cal yr b p correlate well with similar events found in the published records from northern and western china and central mongolia however eastern juyan record does not show the early holocene humidity maximum as suggested by the sedimentary data from monsoon influenced areas of china

palaeoclimate in the saharan and arabian deserts during the middle palaeolithic and the potential for hominin dispersals to disperse out of sub saharan africa it was necessary for hominins to cross the deserts of either the sahara and or arabia thus understanding the palaeoclimate of the saharo arabian region is central to determining the role these deserts played in the peopling of the planet when did they act as barriers and when were they more humid opening dispersal routes across them to address these questions we have conducted a temporal and spatial evaluation of dated sites from 20 to 350 ka using combined probability density function pdf and geographical information system gis analyses of all sites dated using uranium thorium u th or optically stimulated luminescence osl methods radiocarbon dates were not considered because of contamination problems in this time range the results show that during mis 2 there is little evidence for humidity in arabia as would be expected during the height of the last glacial maximum however the sahara shows a sharp rise in probability at the beginning of mis 2 peaking near the boundary with mis 3 at 29 ka there appear to be brief periods of humidity in mis 3 and 6 though at different times in the sahara ca 37 44 138 154 and 180 ka and arabia ca 40 54 and 163 ka during mis 5 both regions show much evidence for humidity with pdf peaks corresponding to insolation maxima though not all maxima are represented in either the saharan or arabian record this situation can be explained by eccentricity modulated precession when eccentricity is strong insolation is enhanced but also more variable and the desert climate is generally more humid particularly at times of high insolation the opposite happens when eccentricity is low and deserts tend to be more arid but local factors exert more of an influence on climate affecting the timing and strength of the brief humid periods experienced so that they no longer coincide with insolation maxima the spatial distribution of humid sites is compatible with a number of different modern human dispersal theories southern arabia experienced humid periods centred on 54 ka and 125 ka and this could have facilitated dispersal from east africa to southern arabia and beyond via the bab el mandab the sahara shows considerable evidence for humidity during mis 5 and may have had dispersal across its expanse at this time

holocene millennial scale vegetation changes in the yugu floodplain kongju area central south korea abstract to understand vegetation responses to past climate change on millennial timescales the holocene record of floodplain vegetation change in central south korea was reconstructed using the stable isotopic composition 13 c and pollen in buried soils low volume overbank deposition of fine grained alluvium by yugu stream over the past 10 000 years has produced a sequence that is well suited for 13 c analysis of soil organic matter the 13 c values varied between 25 and 20 during the holocene showing significant millennial scale fluctuations in five stages 11 000 8900 cal bp 8900 6100 cal bp 6100 3300 cal bp 3300 1200 cal bp and 1200 cal bp to present the abundance of c 4 plants estimated from a binary mixing model changed from approximately 17 57 during the stages from 3300 to 1200 cal bp and from 8900 to 6100 cal bp c 4 plant abundance and the percentage of arboreal pollen were high but the percentage of spores mainly moss and the freshwater algal sum were low indicating more arid environments temporal comparison of c 4 plant abundance change during the holocene with other reconstructed climate data from east asia suggests that millennial scale vegetation change or aridity change in central south korea was generally more synchronous with regional climate change during the late holocene than during the early to mid holocene this study suggests that the past vegetation in the yugu area has evolved in response to summer monsoon intensity in a non linear manner

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

the magnitude timing and abruptness of changes in north african dust deposition over the last 20 000 yr reconstructions of eolian dust accumulation in northwest african margin sediments provide important continuous records of past changes in atmospheric circulation and aridity in the region existing records indicate dramatic changes in north african dust emissions over the last 20 ka but the limited spatial extent of these records and the lack of high resolution flux data do not allow us to determine whether changes in dust deposition occurred with similar timing magnitude and abruptness throughout northwest africa here we present new records from a meridional transect of cores stretching from 311 nt o 191n along the northwest african margin by combining grain size endmember modeling with 230 th normalized fluxes for the first time we are able to document spatial and temporal changes in dust deposition under the north african dust plume throughout the last 20 ka our results provide quantitative estimates of the magnitude of dust flux changes associated with heinrich stadial 1 the younger dryas and the african humid period ahp 11 7 5 ka offering robust targets for model based estimates of the climatic and biogeochemical impacts of past changes in north african dust emissions our data suggest that dust fluxes between 8 and 6 ka were a factor of 5 lower than average fluxes during the last 2 ka using a simple model to estimate the effects of bioturbation on dust input signals we find that our data are consistent with abrupt synchronous changes in dust fluxes in all cores at the beginning and end of the ahp the mean ages of these transitions are 11 870 2 ka 1s and 4 970 2 ka respectively

late pleistocene continental climate and oceanic variability recorded in northwest pacific sediments core v21 146 provides a continuous record of northwest pacific pelagic sedimentation spanning the past 530 000 years downcore variations of 18o from benthic foraminiferal calcite were correlated to the specmap record to provide an age model for late pleistocene paleoclimatic and paleoceanographic variation fluxes of caco3 and eolian material have been determined by combining information about linear sedimentation rates bulk densities and component percentages the mass accumulation rate mar of caco3 varies from 58 to 1435 mg cm kyr 1 and exhibits the pacific ocean pattern of higher accumulation associated with glacial periods for the younger portion of the record however the pattern of caco3 accumulation appears to shift during the mid brunhes so that prior to 350 000 years ago it exhibits an opposite pattern of greater accumulation during interglacial periods the flux of eolian dust is a proxy measure of the source area aridity and correlates well to the loess soil stratigraphy in china dust fluxes range from 43 to 718 mg cm kyr 1 and are greater by a factor of about 4 during glacial times cross spectral analysis of the eolian flux and oxygen isotope records shows an inphase and coherent relationship at each of the major orbital periodicities of 100 41 and 19 kyr eolian grain sizes generally used as a proxy record of wind intensity range from 8 4 2 9 m to 6 2 13 6 m a change in grain size variability occurs near about 300 ka such that the older portion is characterized by lower frequency and higher amplitude fluctuations than the younger portion power spectra for the eolian grain size record show dominant peaks at 100 and 50 kyr and a broad 25 35 kyr peak but coherency to the oxygen isotope curve at only the 100 and 33 kyr periodicities the phase relationship for eccentricity between the eolian grain size and 18o records suggests that at the 100 kyr frequency the smallest grain sizes are associated with glacial conditions

remote sensing and gis techniques for reconstructing arabian palaeohydrology and identifying archaeological sites freshwater availability is critical for human survival and in the saharo arabian desert belt repeated fluctuations between aridity and humidity over the quaternary mean the distribution of freshwater was likely a primary control upon routes and opportunities for hominin dispersals however our knowledge of the spatio temporal distribution of palaeohydrological resources within arabia during mid late pleistocene episodes of climatic amelioration remains limited in this paper we outline a combined method for remotely mapping the location of palaeodrainage and palaeolakes in currently arid regions that were formerly subject to more humid conditions we demonstrate the potential of this approach by mapping palaeochannels across the whole arabian peninsula and palaeolakes and marshes for select regions covering c 10 of its surface our palaeodrainage mapping is based upon quantitative thresholding of hydrosheds data which applies flow routing to digital elevation model dem data while our palaeolake mapping uses an innovative method where spectral classification of landsat thematic mapper tm imagery is used to detect palaeolake deposits within endorheic closed basins before modelling maximum lake extents by flooding the basin to the level of the elevation of the highest detected deposit field survey in the nefud desert and the dawadmi and shuwaymis regions of saudi arabia indicates accuracies of 86 for palaeodrainage mapping and 96 for identifying former palaeolake basins 73 accuracy of classification of individual deposits the palaeolake mapping method has also demonstrated potential for identifying surface and stratified archaeological site locations with 76 of the surveyed palaeolake basins containing archaeological material including stratified palaeolithic archaeology initial examination of palaeodrainage in relation to archaeological sites indicates a relationship between mapped features and previously recorded palaeolithic sites an example of the application of these data for period specific regional palaeohydrological and archaeological reconstructions is presented for a region of northern saudi arabia covering the southern nefud desert and adjacent lava fields

origin and weathering properties of loess paleosol sequence in the goseong area on the east coast of south korea abstract this study aims to investigate the origin and weathering properties of the loess paleosol sequence in the goseong area on the east coast of south korea and to discuss the local sediment inputs and their paleoclimatic implications the geochemical properties suggest that the largest proportion of the sequence originated from the chinese loess plateau and or its source areas with a smaller quantity originating from the weathering products of the bedrock around the section although its origin can be regarded as the chinese loess plateau and or its source areas the sequence shows more weathered features than the chinese loess plateau moreover the weathering environments in south korea were different from those in the chinese loess plateau the difference in weathering properties may be attributed to the more humid climatic conditions in south korea the abundance of local sediment input to the sequence was controlled by sea level fluctuations in the east sea of korea and the global ice sheet developments during the glacial and interglacial cycles in the quaternary because local sediment occupies only minor proportions in the sequence the monsoon and westerly circulations in northeast asia played an important role in the loess formations in south korea as well as in the chinese loess plateau

toward the autojuggie planting 72 geophones in 2 sec this is the publisher s version also available electronically from http onlinelibrary wiley com

abrupt onset and termination of the african humid period rapid climate responses to gradual insolation forcing a detailed ca 100 yr resolution and well dated 18 ams 14 c dates to 23 cal ka bp record of latest pleistocene holocene variations in terrigenous eolian sediment deposition at odp site 658c off cap blanc mauritania documents very abrupt large scale changes in subtropical north african climate the terrigenous record exhibits a well defined period of low influx between 14 8 and 5 5 cal ka bp associated with the african humid period when the sahara was nearly completely vegetated and supported numerous perennial lakes an arid interval corresponding to the younger dryas chronozone punctuates this humid period the african humid period has been attributed to a strengthening of the african monsoon due to gradual orbital increases in summer season insolation however the onset and termination of this humid period were very abrupt occurring within decades to centuries both transitions occurred when summer season insolation crossed a nearly identical threshold value which was 4 2 greater than present these abrupt climate responses to gradual insolation forcing require strongly non linear feedback processes and current coupled climate model studies invoke vegetation and ocean temperature feedbacks as candidate mechanisms for the non linear climate sensitivity the african monsoon climate system is thus a low latitude corollary to the bi stable behavior of high latitude deep ocean thermohaline circulation which is similarly capable of rapid and large amplitude climate transitions

grain size and accumulation rate records from late cenozoic aeolian sequences in northern china implications for variations in the east asian winter monsoon and westerly atmospheric circulation we attempt to reconstruct the history of westerly and monsoonal circulations in northern china using variations in sediment grain size and accumulation rate at four loess sections in the central chinese loess plateau the initiation of aeolian accumulation at about 7 6 ma in the main part of the chinese loess plateau probably marked the onset of the monsoonal circulation both the monsoonal and westerly circulations weakened from 7 6 to 5 2 ma subsequently the monsoonal circulation strengthened progressively from 5 2 ma to the present in addition the westerly circulation strengthened from 5 2 to 0 6 ma but then weakened thereafter and especially during the last 0 6 ma comparison of our aeolian records and the deep sea sediment record suggests that the strengthening trends of the monsoonal and westerly circulations were associated with the progressive development of global ice sheets during the late cenozoic abrupt changes of both the monsoon and westerly circulations occurred at 7 6 3 4 and 1 2 0 9 ma together with a weakening trend of the westerly circulation in the last 0 6 ma and are interpreted as the consequence of the episodic uplift of the tibetan plateau spatial differences in the grain size characteristics amongst the four sections suggest that the circulation intensity and variability decreased from west to east across the loess plateau due to the topographic effect of the tibetan plateau in addition some spatial differences may have been the result of local topographic effects c 2008 elsevier b v all rights reserved

palaeohydrology of the fazzan basin and surrounding regions the last 7 million years abstract we have integrated information on topography geology and geomorphology with the results of targeted fieldwork in order to develop a chronology for the development of lake megafazzan a giant lake that has periodically existed in the fazzan basin since the late miocene the development of the basin can be best understood by considering the main geological and geomorphological events that occurred thought libya during this period and thus an overview of the palaeohydrology of all libya is also presented the origin of the fazzan basin appears to lie in the late miocene at this time libya was dominated by two large rivers systems that flowed into the mediterranean sea the sahabi river draining central and eastern libya and the wadi nashu river draining much of western libya as the miocene progressed the region become increasingly affected by volcanic activity on its northern and eastern margin that appears to have blocked the river nashu in late miocene or early messinian times forming a sizeable closed basin in the fazzan within which proto lake megafazzan would have developed during humid periods the fall in base level associated with the messinian desiccation of the mediterranean sea promoted down cutting and extension of river systems throughout much of libya to the south of the proto fazzan basin the sahabi river tributary know as wadi barjuj appears to have expanded its headwaters westwards the channel now terminates at al haruj al aswad we interpret this as a suggestion that wadi barjuj was blocked by the progressive development of al haruj al aswad k ar dating of lava flows suggests that this occurred between 4 and 2 ma this event would have increased the size of the closed basin in the fazzan by about half producing a catchment close to its current size 350 000 km2 the fazzan basin contains a wealth of pleistocene to recent palaeolake sediment outcrops and shorelines dating of these features demonstrates evidence of lacustrine conditions during numerous interglacials spanning a period greater than 420 ka the middle to late pleistocene interglacials were humid enough to produce a giant lake of about 135 000 km2 that we have called lake megafazzan later lake phases were smaller the interglacials less humid developing lakes of a few thousand square kilometres in parallel with these palaeohydrological developments in the fazzan basin change was occurring in other parts of libya the lower pliocene sea level rise caused sediments to infill much of the messinian channel system as this was occurring subsidence in the al kufrah basin caused expansion of the al kufrah river system at the expense of the river sahabi by the pleistocene the al kufrah river dominated the palaeohydrology of eastern libya and had developed a very large inland delta in its northern reaches that exhibited a complex distributary channel network which at times fed substantial lakes in the sirt basin at this time libya was a veritable lake district during humid periods with about 10 of the country underwater

groundwater discharge to a gobi desert lake during mid and late holocene dry periods abstract high levels of lake eastern juyanze and a wetter climate in the gobi desert nw china were recorded between 5100 and 4100 cal year bp from ostracod distribution shell geochemistry sedimentology and palynological data after about 4100 cal year bp lake levels decreased and groundwater discharge became dominant source of water during short term regressive events at about 4000 3800 and 3500 cal year bp as suggested by a significant difference in modern river water and groundwater chemistry and the geochemical signal of fossil ostracod shells the overall trend towards lower lake levels culminated in repeated episodes of desiccation of lake eastern juyanze between 3200 and 2900 cal year bp individual regressive events as well as the rapid environmental fluctuations of lake eastern juyanze at about 3000 cal year bp were likely caused by mid to late holocene temperature fluctuations recorded by the dunde ice core yao t thompson l g 1992 trends and features of climatic changes in the past 5000 years recorded by the dunde ice core annals of glaciology 16 21 24 and shifts of the southeastern asian monsoon

wet phases in the sahara sahel region and human migration patterns in north africa the carbon isotopic composition of individual plant leaf waxes a proxy for c3 vs c4 vegetation in a marine sediment core collected from beneath the plume of sahara derived dust in northwest africa reveals three periods during the past 192 000 years when the central sahara sahel contained c3 plants likely trees indicating substantially wetter conditions than at present our data suggest that variability in the strength of atlantic meridional overturning circulation amoc is a main control on vegetation distribution in central north africa and we note expansions of c3 vegetation during the african humid period early holocene and within marine isotope stage mis 3 50 45 ka and mis 5 120 110 ka the wet periods within mis 3 and 5 coincide with major human migration events out of sub saharan africa our results thus suggest that changes in amoc influenced north african climate and at times contributed to amenable conditions in the central sahara sahel allowing humans to cross this otherwise inhospitable region

reconstructing dust storm frequency in china since 1617 ce using coral based estimates of sea surface temperature abstract dust storms occur frequently in arid and semi arid regions of china and other parts of the world exerting a considerable influence on air quality in densely populated areas instrumental observations of dust storms are only available over the past 50 to 60 years limiting our ability to understand dust storm variability over longer timescales however tropical sea surface temperatures have been reconstructed over the past four centuries using geochemical records from corals here we show that tropical pacific sea surface temperatures as recorded by corals can be used to reconstruct dust storm frequency at one year resolution based on the coral reconstructed annual sea surface temperature anomaly data from two regions the western pacific 25 n 25 s 110 155 e and the eastern pacific 10 n 10 s 175 e 85 w published by tierney et al 2015 we reconstructed the frequency of dust storms in northern china dsfcn for the period from 1617 to 1953 ce the reconstructed dsfcn variation can be divided into several distinct periods 1 dsfcn increased from 1617 to 1650 then 2 decreased from 1650 to 1675 3 remained unchanged from 1675 to 1755 4 increased again from 1755 to 1860 5 remained unchanged from 1860 to 1925 and finally 6 decreased rapidly from 1925 to 1995 we propose the following causal chain to explain the observed relationship between dsfcn and sst as tropical pacific ocean sst increases the siberian high weakens and the eastern asian trough strengthens as the air pressure difference weakens the east asian winter monsoon weakens and strong wind frequency decreases causing dsfcn to decrease as well the statistical results support this interpretation of the causal chain

desert wetlands in the geologic record abstract desert wetlands support flora and fauna in a variety of hydrologic settings including seeps springs marshes wet meadows ponds and spring pools over time eolian alluvial and fluvial sediments become trapped in these settings by a combination of wet ground conditions and dense plant cover the result is a unique combination of clastic sediments chemical precipitates and organic matter that is preserved in the geologic record as ground water discharge gwd deposits gwd deposits contain information on the timing and magnitude of past changes in water table levels and therefore are a potential source of paleohydrologic and paleoclimatic information in addition they can be important archeological and paleontological archives because desert wetlands provide reliable sources of fresh water and thus act as focal points for human and faunal activities in some of the world s harshest and driest lands here we review some of the physical sedimentological and geochemical characteristics common to gwd deposits and provide a contextual framework that researchers can use to identify and interpret geologic deposits associated with desert wetlands we discuss several lines of evidence used to differentiate gwd deposits from lake deposits they are commonly confused and examine how various types of microbiota and depositional facies aid in reconstructing past environmental and hydrologic conditions we also review how late quaternary gwd deposits are dated as well as methods used to investigate desert wetlands deeper in geologic time we end by evaluating the strengths and limitations of hydrologic and climatic records derived from gwd deposits and suggest several avenues of potential future research to further develop and utilize these unique and complex systems

holocene african droughts relate to eastern equatorial atlantic cooling here we present evidence that the holocene african monsoon system ams varied in response to the eastern equatorial atlantic sea surface temperature sst several short term episodes of decreased moisture availability as a result of low eastern equatorial atlantic sst are suggested by planktonic foraminiferal mg ca ratios these episodes promoted a weakening of the ams and thus determined the timing and intensity of arid periods local sea surface salinities also reveal regional patterns of precipitation in equatorial western africa the high eastern equatorial atlantic ssts occur in concert with seasonally increased insolation at low latitudes suggesting a strong response of african monsoonal precipitation to oceanic conditions at low latitudes

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

hydroclimate variability in the nile river basin during the past 28 000 years it has long been known that extreme changes in north african hydroclimate occurred during the late pleistocene yet many discrepancies exist between sites regarding the timing duration and abruptness of events such as heinrich stadial hs 1 and the african humid period ahp the hydroclimate history of the nile river is of particular interest due to its lengthy human occupation history yet there are presently few continuous archives from the nile river corridor and pre holocene studies are rare here we present new organic and inorganic geochemical records of nile basin hydroclimate from an eastern mediterranean em sea sediment core spanning the past 28 ka bp our multi proxy records reflect the fluctuating inputs of blue nile versus white nile material to the em sea in response to gradual changes in local insolation and also capture abrupt hydroclimate events driven by remote climate forcings such as hs1 we find strong evidence for extreme aridity within the nile basin evolving in two distinct phases during hs1 from 17 5 to 16 ka bp and from 16 to 14 5 ka bp whereas peak wet conditions during the ahp are observed from 9 to 7 ka bp we find that zonal movements of the congo air boundary cab and associated shifts in the dominant moisture source atlantic versus indian ocean moisture to the nile basin likely contributed to abrupt hydroclimate variability in northern east africa during hs1 and the ahp as well as to non linear behavior of hydroclimate proxies we note that different proxies show variable gradual and abrupt responses to individual hydroclimate events and thus might have different inherent sensitivities which may be a factor contributing to the controversy surrounding the abruptness of past events such as the ahp during the late pleistocene the nile basin experienced extreme hydroclimate fluctuations which presumably impacted paleolithic cultures residing along the nile corridor

fine aeolian quartz records in cheju island korea during the last 6500 years and pathway change of the westerlies over east asia 1 we investigated the fine component of aeolian dust deposited on a maar of cheju island korea during the last 6500 years to specify the variability of fine aeolian dust transported by the westerlies and its main controlling factor from the viewpoint of global atmospheric circulation as a proxy for the fine aeolian dust we used the fine component of chemically isolated aeolian quartz from bulk sediments the fine quartz flux fqf varies from 0 1 to 1 4 mg cm2 a with periodicities of 1620 810 400 325 and 210 years mainly providing information on the aridity change in the dust source region the taklimakan desert the median grain size of the fine quartz mfq representing the pathway of the dust transporting westerlies fluctuates between 2 and 6 m with significant cycles of 1030 390 280 220 and 195 years and shows similar variation pattern to the fqf on the basis of visual and spectral analyses the high low fqf and the large small mfq correspond to the warm cold atmospheric temperature record from greenland ice cores with significant coherent cycles indicating that the aridity in the dust source areas and the pathway of the westerlies in east asia were linked to climatic and atmospheric conditions in greenland through the pathway change of the westerlies during the middle to late holocene the pathway change of the westerlies mainly responsible for the variability of the fine aeolian dust in east asia was probably controlled by a climatic response to initial solar activity and resulting atmospheric reorganization in polar and high latitude regions

middle holocene environmental change in central korea and its linkage to summer and winter monsoon changes to trace the surficial responses of lowlands to past climate change we investigated 13c in total organic carbon toc c n ratios magnetic susceptibility ms and silicon si intensity directly proportional to concentration in wetland sediments collected from the gimpo area of central korea covering 6600 4600 cal yr bp two organic layers with high toc negatively depleted 13ctoc values 27 to 29 low ms values and low si intensities were found at 6200 5900 and 5200 4800 cal yr bp respectively these middle holocene wet periods corresponded to relatively intensified summer monsoon and solar activity periods the intervening dry period 5900 5200 cal yr bp with high ms high si and low toc corresponded to an intensified dust activity interval and stronger winter monsoon this multi centennial climatic fluctuation of wet periods 6200 5900 cal yr bp and 5200 4800 cal yr bp and an intervening dry period 5900 5200 cal yr bp in central korea was more synchronous with climate change in the arid inner part of china than with that in south china suggesting possible strong high latitude driven climatic influences e g north atlantic cooling events during the middle holocene

provenance of loess material and formation of loess deposits on the chinese loess plateau abstract results of a multiple isotopic chemical and mineralogical analysis of loess from the three northwestern inland basins the junggar basin the tarim basin and the qaidam basin and the loess plateau region of china are summarized they suggest a qualification of the conventional views that the three northwestern basins were the important source areas of the loess plateau and that the sand deserts were the primary single source of the chinese loess it is argued that the gobi stony desert in southern mongolia and the adjoining gobi and sand deserts the badain jaran desert tengger desert ulan buh desert hobq desert and mu us desert in china rather than the three inland basins are the dominant source areas of the loess plateau however although these gobi and sand deserts are regarded as the main source regions they serve as dust and silt holding areas rather than dominant producers the mountain processes including glacial grinding frost weathering salt weathering tectonic processes and some fluvial comminution in the gobi altay mts hangayn mts and the qilian mts have played an important role in producing the vast amounts of loess sized material for forming the loess plateau

miocene humid intervals and establishment of drainage networks by 23 ma in the central sahara southern libya terrestrial and lacustrine neogene and quaternary sediments in the libyan fezzan provide key evidence for paleoclimate changes in the central sahara associated with lake megafezzan understanding of holocene and late pleistocene deposits is resolved but the age of older sediments is not we provide the first high resolution chronology and stratigraphy of the neogene deposits in the fezzan basin and so also the central sahara the sediments are divided into three unconformity bounded units the oldest unit comprising the shabirinah and brak formations is dated using magnetostratigraphy the shabirinah formation is a succession of lacustrine and fluvial units locally with humid and arid paleosols which progressively show evidence of increasing aridity up through the succession the overlying brak formation is a pedogenically modified palustrine limestone at basin margin locations all these units are dated to the early aquitanian to late serravallian in the early to mid miocene having formed prior to major volcanic fields to the east during the mid late aquitanian widespread stromatolitic lake sediments developed in se fezzan in the late burdigalian palustrine carbonate units developed that typically pass laterally into mixed clastic paleosol carbonate units that characterise basin margin situations the serravallian aged brak formation is a highstand deposit developed during maximum lake extent which formed due to restriction of basin drainage to the north and east due to growth of the jabal as sawda volcanic centre and uplift of the sw shoulder of the sirte basin gradual aridification of the central sahara occurred from the early miocene but this trend was periodically interrupted by humid phases during which lake megafezzan developed the hyperaridity of the central sahara must have developed after 11 ma and the main drainage networks from the fezzan basin were established before 23 ma in the oligocene indicating the great antiquity of major central saharan river basins

dust records from varved lacustrine sediments of two neighboring lakes in northeastern china over the last 1400 years dust storms are natural phenomena described in chinese historical documents as early as 1150 bc these documents provide a way to evaluate proxy data from different natural records the minerogenic clastic content and grain size from two closed maar lakes located a short distance apart in northeastern china were analyzed the area is located in the path of dust storms the minerogenic clastics in the studied maar lakes originate mainly from dust deposition general variations of the minerogenic clastic content in these two neighboring lakes show a good coincidence with dust concentration in a tibet ice core and dust events as recorded in historical documents the minerogenic clastic content in the lake sediments is linked with the climate conditions in the dust source regions and wind strength three periods of intensive dust events ad 1050 1330 ad 1590 1690 and the last 200 years have been identified during the past 1500 years the recent increasing pattern of clastic content could be linked to human activity in the dust source regions significantly most of the medieval warm period mwp was marked by a high frequency of dust storms

holocene dust deposition in the ili basin and its implications for climate variations in westerlies dominated central asia abstract understanding holocene paleoclimate in arid central asia aca is helpful for predicting future climate however holocene climate patterns and their forcing mechanisms across aca are vigorously debated in the context of global climate change here we present a holocene loess profile sgx from the ili basin in the westerlies dominated central asia based on high resolution medium grained 38 63 m quartz optically stimulated luminescence osl dating and grain size and color measurements we reconstruct the holocene paleoclimate osl geochronology indicate that this sgx loess profile covers the last 11 5 ka and grain size analyses reveal that the sediments are sandy loess and the environmentally sensitive fractions are

reactivation of the pleistocene trans arabian wadi ad dawasir fluvial system saudi arabia during the holocene humid phase the wadi ad dawasir fluvial system in central saudi arabia is investigated using remote sensing and sedimentology in combination with bio proxy analyses molluscs and ostracods age control is provided by radiocarbon as well as luminescence dating using both quartz and feldspar grains it is shown that the fluvial system was active from the asir mountains across the partially sand covered interior of the arabian peninsula to the arabian gulf during the holocene humid period sedimentology and faunal analysis reveal the presence of perennial streams and a permanent freshwater lake in the distal reach of the dawasir system that are synchronous with fluvial accumulation in the headwaters of its major tributary wadi tathlith the increased runoff during the holocene led to a re activation of streams that largely followed pre existing late pleistocene courses and eroded into older sediments the absence of holocene lakes in most of the rub al khali implies that trans arabian rivers were mainly fed by precipitation in the asir mountains monsoonal rainfall was apparently stronger there as well as in the northern south eastern and southern part of the arabian peninsula southern yemen and oman but it apparently did not directly affect the interior during the holocene the palaeoenvironmental reconstruction shows a narrow trans arabian green freshwater corridor as the result of phases of sustained flow lasting up to several centuries the permanent availability of water and subsistence for wildlife provided a favourable environment for human occupation as documented by neolithic stone tools that are found all along wadi ad dawasir

holocene atmosphere ocean interactions records from greenland and the aegean sea we compare paleoclimate proxy records from central greenland and the aegean sea to offer new insights into the causes timing and mechanisms of holocene atmosphere ocean interactions a direct atmospheric link is revealed between aegean sea surface temperature sst and high latitude climate the major holocene events in our proxies of aegean sst and winter spring intensity of the siberian high gisp2 k record follow an 2300 year spacing recognised also in the 14c record and in worldwide holocene glacier advance phases suggesting a solar modulation of climate we argue that the primary atmospheric response involved decadal centennial fluctuations in the meridional pressure gradient driving aegean sst events via changes in the strength duration and or frequency of northerly polar continental air outbreaks over the basin the observed natural variability should be accounted for in predictions of future climate change and our timeframe for the aegean climate events in addition provides an independent chronostratigraphic argument to middle eastern archaeological studies

holocene vegetation zonation in the eastern sahara recent discoveries of fossil bearing holocene lake sediments from the eastern sahara have brought further confirmation and detail to earlier indirect evidence that a major pluvial episode occurred between 9 500 and 4 500 yr bp1 3 the botanical results mainly palynological show that savanna and desert grassland occupied regions that today are plantless hyperarid deserts we present here the first evidence from the entire saharan region of a latitudinal zonation of holocene vegetation extending across a 500 km wide belt in north west sudan we have completed detailed pollen analyses of three of the several sites discovered so far and the salient features from two the northernmost and the southernmost are presented here to demonstrate a steep gradient of past vegetative cover

the use of total lake surface area as an indicator of climatic change examples from the lahontan basin abstract variation in the size of lakes in the lahontan basin is topographically constrained river diversion also has played a major role in regulating lake size in lahontan subbasins the proper gage of lake response to change in the hydrologic balance is neither lake depth level nor lake volume but instead lake surface area normalization of surface area is necessary when comparing surface areas of lakes in basins having different topographies to a first approximation normalization can be accomplished by dividing the paleosurface area of a lake by its mean historical reconstructed surface area

a lacustrine record of east asian summer monsoon and atmospheric dust loading since the last interglaciation from lake xingkai northeast china a 336 cm long sediment core spanning the last 130 ka was recovered from lake xingkai on the northeastern margin of the east asian summer monsoon domain to reveal the linkage between lacustrine depositional processes and environmental changes bayesian end member modeling analysis was conducted to partition and interpret the grain size distributions of lake xingkai sediments our results suggest that the sedimentary system is characterized by three end members ems em1 and em2 with a modal value of 13 and 10 m respectively indicate the variation of local hydraulic conditions em3 with a modal value of 5 m reflects the background atmospheric dust loading high atmospheric dust concentration generally occurred during marine isotope stage mis 5d mis 4 and early mis 3 when the climate in the asian dust source region was cold and dry in contrast low dust concentration prevailed during mis 2 likely due to the southward shift of the westerlies driven by maximum ice volume in the high latitudes

precipitation source inferred from stable isotopic composition of pleistocene groundwater and carbonate deposits in the western desert of egypt an atlantic source of precipitation can be inferred from stable isotopic data h and o for fossil groundwaters and uranium series dated carbonate spring deposits from oases in the western desert of egypt in the context of available stable isotopic data for fossil groundwaters throughout north africa the observed isotopic depletions delta d 72 to 81 per thousand delta sup 18 o 10 6 to 11 5 per thousand of fossil ge 32 000 yr b p groundwaters from the nubian aquifer are best explained by progressive condensation of water vapor from paleowesterly wet oceanic air masses that traveled across north africa and operated at least as far back as 450 000 yr before the present the values of delta sup 18 o 17 1 to 25 9 per thousand for 45 000 to 450 000 yr old tufas and vein filling calcite deposits from the kharga and farafra oases are consistent with deposition from groundwaters having oxygen isotopic compositions similar to those of fossil groundwaters sampled recently at these locations

reconstructing palaeoclimate and hydrological fluctuations in the fezzan basin southern libya since 130 ka a catchment based approach abstract we propose a novel method to evaluate regional palaeoclimate that can be used to alleviate the problems caused by the discontinuous nature of palaeoenvironmental data found in deserts the technique involves processing satellite imagery and dem s to map past rivers catchments and evaluate the areas and volumes of palaeolakes this information is used to determine the new lake evaluation index lei that allows a qualitative estimate of the amount of sediment received by lakes and how long lived those lakes are lakes with considerable longevity and large sediment stores are selected for study validation is performed using image interpretation of remote sensing data ultragpr surveys and fieldwork these techniques are also used to identify and study spring deposits and fluvial landforms that provide valuable palaeoclimate information the method is applied to the fezzan basin in southern libya focusing on the wadi ash shati and wadi el agial catchments results indicate that the palaeohydrology is accurately mapped except within dune fields we analysed the sedimentology of the key deposits identified by this methodology developing a chronology using optically stimulated luminescence osl and radiocarbon dating we find evidence for relatively humid conditions during mis 5c d and e as well as during the early to middle holocene larger lakes and more extensive river systems were present during mis 5 than are found during the holocene suggestive of greater humidity the holocene humid period started at 11 ka and continued until 5 ka being interrupted by abrupt periods of aridity at 8 2 ka and 6 ka that coincide with north atlantic cooling after each of these arid events the climate was less humid than previously suggesting that they were superimposed upon an overall drying trend the termination of the holocene humid period in the sahara has received much scrutiny in recent years and sediments of palaeolake shati provide a continuous record of this we do not find evidence to support the hypothesis of either sudden or gradual aridification of the sahara at 5 ka instead we find that that aridity started to develop at 6 5 ka whereupon the lake levels oscillated until finally drying up by 5 3 ka most of the other lakes in the fezzan also dried up at 5ka we suggest that thousands of years of aridification prior to 5 ka shrunk these lakes so that additional aridity at this time led to their final desiccation because lakes are prodigious dust sources this mechanism potentially explains the rapid rise in dust flux to the atlantic at 5 ka with this final drying being the culmination of longer term aridity albeit overprinted with considerable climate variability

gypsum nucleation and crystal morphology in analog saline terrestrial environments abstract gypsum crystals were grown in experimental conditions analogous to saline terrestrial environments within bentonite clay gels by diffusion control at three different temperatures four brine salinities and four tannic acid a model terrestrial humic substance concentrations the resulting crystals correspond to natural gypsum formed in terrestrial environments prismatic gypsum typically grew at both high and low temperatures in the absence of the organic additive with increasing organic acid concentrations the prismatic crystals progressively became flattened perpendicular to 001 and two temperature dependent trends developed at low temperatures a hemi bipyramidal habit dominated by 1111 faces developed whereas the lenticular e103 dominated habit forme at higher temperatures with progressively greater concentrations of organic material a 100 penetration twinning developed secondary complex nucleation occurred near the twin interfaces and finally rosette and rosette like aggregates formed higher temperatures generally favored better formed and larger rosettes the presence of 5 and 15 nacl greatly decreased nucleation density and resulted in larger single crystals and crystal aggregates the a 100 penetation twins appear to be diagnostic of gypsum growth in natural terrestrial sediments at a ph greater than 7 5

abrupt changes in the asian southwest monsoon during the holocene and their links to the north atlantic ocean during the last ice age the indian ocean southwest monsoon exhibited abrupt changes that were closely correlated with millennial scale climate events in the north atlantic region1 2 3 suggesting a mechanistic link in the holocene epoch which had a more stable climate the amplitude of abrupt changes in north atlantic climate was much smaller and it has been unclear whether these changes are related to monsoon variability here we present a continuous record of centennial scale monsoon variability throughout the holocene from rapidly accumulating and minimally bioturbated sediments in the anoxic arabian sea our monsoon proxy record reveals several intervals of weak summer monsoon that coincide with cold periods documented in the north atlantic region4 including the most recent climate changes from the medieval warm period to the little ice age and then to the present we therefore suggest that the link between north atlantic climate and the asian monsoon is a persistent aspect of global climate

late quaternary dust flow on the chinese loess plateau abstract the dust flux of over 25 g cm2 103yr was reached in the central part of the chinese loess plateau during the last glacial maximum this is more than three times higher than during the last interglacial and early glacial time the grain size of the pleniglacial dust reached a peak shortly after 20 000 years ago and testifies to the occurrence of strong winds and frequent dust storms

grain size of quartz as an indicator of winter monsoon strength on the loess plateau of central china during the last 130 000 yr the chinese loess paleosol sequence constitutes an important record of variations in asian monsoon climate over the past 2 4 myr magnetic susceptibility of loess and paleosols has been used as a proxy for summer monsoon intensity while median grain size has been regarded as a measure of the strength of winter monsoon winds that were responsible for most of the dust transport however median grain size is only an approximate index of winter monsoon strength because both paleosols and loess have been modified to various degrees by weathering processes that have produced pedogenic clay the quartz component of loess and paleosols is largely unaffected by weathering processes and therefore constitutes a more reliable proxy index of monsoon wind strength median grain size qmd and maximum grain size qmax values of monomineralic quartz isolated from the loess paleosol section at luochuan in the central loess plateau are characterized by two main intervals during the last ca 130 000 yr when these parameters were significantly greater than 9 and 85 m respectively and three main intervals when they were lower the data imply that the winter monsoon weakened during the intervals with low qmd and qmax values which coincide with marine oxygen isotope stages 5 3 and 1 and was strongest ca 67 000 and 20 000 yr ago during isotope stages 4 and 2 however both quartz grainsize records display second order high frequency high amplitude variations which are lacking in the magnetic susceptibility record that imply rapid and significant changes in atmospheric conditions that affect dust transport and deposition

cupressus dupreziana a dendroclimatic record for the middle late holocene in the central sahara dendroclimatology of cupressus dupreziana the tassili cypress has been attempted on samples obtained from the door beams of the old cities of ghat and barkat located at the foot of the tassili where the cypress still lives the tree rings of 20 samples were measured and dated by 24 ams 14c dates a mean ring width chronology has thus been obtained spanning though discontinuously 5220 to 100 14c bp 5990 65 cal bp as the tree ring width in dry lands depends mainly on water availability the mean ring width chronology represents a detailed record of changes in rainfall on a decade scale for the middle and late holocene of the central sahara it indicates main drought spells at 5200 5000 14c bp 5900 5760 cal bp and at 4350 bp 5120 cal bp followed by phases of enhanced precipitation and by the onset of extreme arid conditions at 1550 14c bp 1500 cal bp

bimodal grain size distribution of aeolian quartz in a maar of cheju island korea during the last 6500 years its flux variation and controlling factor 1 aeolian quartz chemically isolated from maar sediments in cheju island korea showed bimodal grain size distributions after partitioning into fine and coarse components fine and coarse quartz fluxes fqf and cqf were calculated the average median grain size of fine quartz was 3 m and the average fqf was 0 5 mg cm2 yr with a range of 0 1 1 6 mg cm2 yr during the last 6500 years the average cqf was 3 mg cm2 yr with a range of 1 5 5 mg cm2 yr and its average median grain size was 15 m comparisons of our results with the present aeolian dust activities and climate changes in dust source areas suggest that fqf was influenced by the pathway of the westerlies between taklimakan desert and cheju island while cqf was affected by the aridity in the source regions including the gobi desert in southern mongolia and the adjoining gobi and sand deserts in china during the last 6500 years

holocene climate variability although the dramatic climate disruptions of the last glacial period have received considerable attention relatively little has been directed toward climate variability in the holocene 11 500 cal yr b p to the present examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000 8000 6000 5000 4200 3800 3500 2500 1200 1000 and 600 150 cal yr b p most of the climate change events in these globally distributed records are characterized by polar cooling tropical aridity and major atmospheric circulation changes although in the most recent interval 600 150 cal yr b p polar cooling was accompanied by increased moisture in some parts of the tropics several intervals coincide with major disruptions of civilization illustrating the human significance of holocene climate variability c 2004 university of washington all rights reserved

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

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

asian dust transport during the last century recorded in lake suigetsu sediments asian dust has a significant impact on the natural environment its variability on multiple timescales modulates the ocean biogeochemistry and climate we demonstrate that temporal changes in the deposition flux of aeolian dust recorded in sediments from lake suigetsu central japan during the last century exhibit a continuous decreasing trend and a decadal scale decrease in 1952 1974 the former decreasing trend can be explained by a decrease in the dust storm frequency at source regions due to the warming of mongolia in the twentieth century suggesting future decrease of asian dust transport with further warming in mongolia decadal scale decrease of aeolian dust is explained by weaker westerlies in lower latitudes in central japan reflecting a weaker aleutian low during the corresponding period decadal scale westerly change probably causes north south shifts of the dominant dust transport path which affects subarctic northern pacific ocean biogeochemistry by changing the micronutrient iron supply

late pleistocene vegetation change in korea and its possible link to east asian monsoon and dansgaard oeschger d o cycles abstract late pleistocene carbon isotope 13c records from a paleolithic sedimentary sequence collected from baeki hongcheon central korea show long term changes with superimposed short term isotopic excursions the 13c value of the sedimentary organic matter a proxy for past vegetation change varied from 26 to 23 for the period between 30 and 90 ka with a long term variation similar to insolation changes high amplitude 1 to approximately 1 5 fluctuations superimposed on the long term changes in the 13c values decreased during stronger summer monsoon intervals but increased during the weakened summer monsoon this millennial scale pattern is generally similar to greenland dansgaard oeschger d o cycles the possible connection between the hongcheon area korea and high latitudes may be explained by atmospheric circulation changing in response to the d o oscillations in the northern hemisphere

late pleistocene and holocene aeolian dust deposition in north china and the northwest pacific ocean abstract rates of dust deposition in the north pacific and the central loess plateau of china show a poor correlation during the last 30 000 yr although in both cases the dust was derived from deserts in northern china loess accumulation rates were high at the time of the last glacial maximum while dust flux to the north pacific was low at this time maximum dust flux to the north pacific is recorded in the mid holocene but holocene rates of loess accumulation have been low these differences are shown to reflect the different nature of the wind conditions responsible for dust transport to the loess plateau and the north pacific dust transport responsible for formation of the loess occurred mainly in the lower 1 5 km of the atmosphere and was accomplished by cold low level northwesterly winds associated with cold waves emanating from the mongolian anticyclone at present such conditions occur quite frequently in winter but during the coldest phases of the pleistocene they probably also occurred in the spring and summer long range dust transport from northern china to the north pacific requires that the dust is lifted to high levels above 3 km where it can be incorporated into the strong mid latitude westerlies strong vertical motions of the atmosphere occur most frequently in the spring when the mongolian anticyclone begins to weaken and frontal depressions move across the deserts of northern china such frontal depressions were probably more frequent during the climatic optimum of the mid holocene and during previous interglacials changes in continental aridity have probably played a minor role in controlling the magnitude of the dust flux to the north pacific

paleoclimatic variations in west africa from a record of late pleistocene and holocene lake level stands of lake bosumtwi ghana abstract a detailed investigation of geomorphological evidence of paleoshorelines and exposed stratigraphic sections of lake deposits combined with a chronology based on radiocarbon dated charcoal and in situ 14c dating of wave polished bedrock provide important new constraints on lake level changes of lake bosumtwi ghana thick sequences of laminated silts alternating with transgressive sands and deltaic gravels attest to a long history of climatically controlled lake level variations the post glacial rise in lake level began sometime after 16 3 ka reached stable levels first at 14 5 0 6 ka and then rose again after ca 14 3 ka a significant lake level regression spanned the interval from 12 6 0 3 to 11 6 0 5 ka synchronous with the younger dryas deep lake conditions were reestablished after ca 11 ka at which time the lake overtopped the crater overflow continued until 8 8 0 5 ka when another significant but short lived regression occurred deep but probably not overflowing conditions were again reestablished by 7 2 0 3 ka and continued until around 3 2 0 1 ka when lake level dropped precipitously multicentury late holocene highstands occurred at 2 2 0 1 and 1 7 0 2 ka although these were significantly lower than those registered in the late glacial and early holocene the timing of late glacial events is similar to those recorded elsewhere in africa and the higher latitudes and likely reflects the dominant control of high latitude northern hemisphere conditions on the african tropics during the times of large northern hemisphere ice sheets mid to late holocene variations appear to be less coupled with changes across africa and elsewhere suggesting that regional forcing may be more important during warmer periods

grain size partitioning in loess paleosol sequence on the west coast of south korea using the weibull function abstract this study aims to partition the grain size of the loess paleosol sequence on the west coast of south korea and investigates the limitations and applicability with the partitioning method through the help of a laser diffraction grain size analyzer two to four components depending on the samples and theories employed to convert the laser diffraction data to grain size data are identified through the partitioning process however the identification of one component is thought to be contingent upon the theories employed rather than natural processes the partitioning results reveal that the sequence consists mostly of fine and coarse components transported by the same mechanisms as in the chinese loess plateau and shares common source areas with the chinese loess plateau the sequence also contains a small quantity of material from the local sources and this component is expected to provide crucial information about paleoclimatic variations in korea this study suggests that considerations of the theories are essential in modeling processes of grain size because the theories greatly influence the results of grain size analysis and the number of components and that conversions using the fraunhofer approximation seem to provide more reliable results than those using the mie theory

the middle pleistocene al mahruqah formation in the murzuq basin northern sahara libya evidence for orbitally forced humid episodes during the last 500 000 years abstract geological and geomorphological work in the endorheic murzuq basin fezzan in the northern sahara desert sw libya has revealed that the middle pleistocene al mahruqah formation consists of at least four limestone beds at four distinct elevations the corresponding limestone beds are named from oldest to youngest the antalkhata member the brak member the bi r az zallaf member and the aqar member the four members are interpreted as lacustrine deposits and they are well distinguished by their spatial extent and lithology twenty five radiometric and thermal ionisation mass spectrometric tims 230th u ages ranging from about 490 130 ka have been determined on these lacustrine limestones according to these radiometric 230th u ages the accumulation of the four limestone members of the al mahruqah formation followed the orbitally forced milankovitch eccentricity cycle of 100 ka during at least the last 400 ka the four members formed in humid episodes of several tens of thousands of years duration when large lakes might have existed the 13c and 18o values from samples of the four members of the al mahruqah formation provide independent genetic evidence on the lacustrine origin of the deposits in the murzuq basin the spatial extent of the limestone deposits and thus the intensity of the humid episodes decreases at least from the brak member to the aqar member from about 52 000 km2 to 1400 km2 respectively in spite of the limited precision and reliability of the new 230th u ages it seems possible that short humid episodes interrupted the intervening arid episodes other long term palaeohydrological records from northern and southern africa as well as the mediterranean region support the palaeoclimatic results from the murzuq basin

last glacial aeolian landforms and deposits in the rhone valley se france spatial distribution and grain size characterization abstract in the rhone valley a north south oriented cenozoic rift in southeast france thick pleistocene loess deposits have been recognized since the beginning of the last century these loess records which are disconnected from the north european loess belt nelb are of significant interest to document the evolution of perimediterranean landscapes and environments during the last glacial to overcome the poor precision of available aeolian distribution maps aeolian deposits were mapped using the topsoil textural database provided by the land use and cover area frame statistical survey project lucas the grain size distribution of aeolian sand and loess was first determined using 116 samples taken from surveyed outcrops then the areas showing a similar grain size composition were extracted from the lucas rasters the resulting map reproduces the conventional maps correctly but suggests a more significant extension of loess in better agreement with the known distribution of outcrops the map shows that the distinctive morphology of the valley dominantly controls the distribution of aeolian deposits the deflation related landforms i e yardangs closed depressions pans and desert pavements are widespread south of narrowings of the rhone valley between latitudes 44 n and 45 n they indicate palaeowinds blowing from the north northwest aeolian sand loessic sand sandy loess and loess deposits successively spread on both sides of the rhone river the loess is characterized by a coarse texture main mode around 60 m strong local thickness 5 m limited extension and abundant bioturbation this preservation results from the persistence of a shrub vegetal cover during the coldest and driest phases of the last glacial that allowed for trapping the saltating and suspended particles close to the alluvial sources

a pleistocene lacustrine episode in southeastern libya fossiliferous lacustrine deposits of middle pleistocene age have been found in central fezzan libya 1 on each side of the east west depressions of the wadi shati south of the precambrian qarqaf anticline1 8 they represent the shoreline of a former brackish water lake fig 1 which some 130 000 yr bp covered an area about 100km long and 10 20 km wide at present the area may be classified as hyperarid since 1978 a collaborative study of the fossil assemblages has been undertaken it included macro and micropalaeontological determination th u dating stable isotope and chemical analyses in parallel with sedimentological and archaeological studies of the sites here we consider the th u dating and the isotopic palaeohydrology of the lacustrine episode

eolian quartz flux variations in cheju island korea during the last 6500 yr and a possible sun monsoon linkage we have obtained a high resolution sedimentary record covering the last 6500 yr from a maar in cheju island korea in order to reconstruct the history of variations in the eolian quartz flux eqf and hence asian dust the long term variation of eqf reveals three intervals a period of high eqf 4000 2000 cal yr b p and two periods of low eqf 6500 4000 cal yr b p and 2000 cal yr b p to present which have been affected by the east asian monsoon due to insolation change and the cold air activity in high latitudes correlated with polar high pressure systems this long term variation is superimposed by millennial and centennial scale fluctuations with periodicities of 1137 739 214 162 137 127 and 111 yr implying drier conditions in the source areas in china the detrended eqf record correlates visually and statistically cross spectral analysis with the atmospheric d 14 c record solar proxy the centennial scale variability in eqf may be affected

holocene climate variability and cultural evolution in the near east from the dead sea sedimentary record abstract a comprehensive record of lake level changes in the dead sea has been reconstructed using multiple well dated sediment cores recovered from the dead sea shore interpreting the lake level changes as monitors of precipitation in the dead sea drainage area and the regional eastern mediterranean palaeoclimate we document the presence of two major wet phases 10 8 6 and 5 6 3 5 cal kyr bp and multiple abrupt arid events during the holocene the arid events in the holocene dead sea appear to coincide with major breaks in the near east cultural evolution at 8 6 8 2 4 2 3 5 cal kyr bp wetter periods are marked by the enlargement of smaller settlements and growth of farming communities in desert regions suggesting a parallelism between climate and near east cultural development

the eolian origin of silty mantle in sedentary soils from korea and japan abstract the concentration particle size distribution and oxygen isotope composition 18 o smow of quartz were examined in order to determine the extent to which the accretion of long distance eolian dusts from the interior of china had formed the sedentary soils overlying diverse parent materials in korea and japan the quartz content of the surface soils developed on quartz free basaltic materials varies from 8 9 to 47 7 generally the soil quartz found in surface horizons is finer than of the subsurface horizons and or substrata the particle size of the soil quartz decreases from the west coast to eastern coastal margins of korea and to the japanese islands this follows the major trajectory of westerly winds which carry the eolian dusts from the interior of china to mid latitude regions of the north pacific the oxygen isotope composition of the fine quartz 1 10 m in diameter when separated from surface and subsurface horizons is found in a relatively narrow range of 15 9 to 17 7 the values are indiscernible from those of recent eolian dusts from the interior desert and loess plateau of china the 18 o values from the same sized quartz found in c horizons 10 4 and 19 2 consisting of saprolitic andesites and shales respectively differ from those of the overlying soils the 18 o values of soil quartz developed on igneous materials systematically decrease with increasing particle size to 53 m 14 they abruptly decrease to 8 to 12 for fractions larger than 53 m a large apparent oxygen isotope fractionation up to 10 between fine 17 and coarse 8 to 12 grained quartz observed in the samples does not represent an equilibrium oxygen isotope fractionation for normal magmatic processes the data provide evidence for an eolian origin of the fine quartz incorporated during soil development

holocene forcing of the indian monsoon recorded in a stalagmite from southern oman a high resolution oxygen isotope record from a thorium uranium dated stalagmite from southern oman reflects variations in the amount of monsoon precipitation for the periods from 10 3 to 2 7 and 1 4 to 0 4 thousand years before the present ky b p between 10 3 and 8 ky b p decadal to centennial variations in monsoon precipitation are in phase with temperature fluctuations recorded in greenland ice cores indicating that early holocene monsoon intensity is largely controlled by glacial boundary conditions after approximately 8 ky b p monsoon precipitation decreases gradually in response to changing northern hemisphere summer solar insolation with decadal to multidecadal variations in monsoon precipitation being linked to solar activity

flood frequency of the mojave river and the formation of late holocene playa lakes southern california usa perennial lakes lasting several decades occupied silver lake playa the terminus of the mojave river as recently as 390 90 and 3620 70 bp flood routings from the mojave river headwaters to its terminal playa and water balance calculations for the resulting lakes indicate that floods comparable in magnitude to the largest floods in the modern record must occur almost annually to generate and maintain perennial lakes in contrast the modern floods of this magnitude have recurrence intervals greater than 18 years such an increase in flood frequency is required even if lake evaporation is reduced by as much as 50 modern extreme floods of the mojave river are related to meridional atmospheric circulation and a southeastward shift in the winter low pressure center over the north pacific ocean causing vigorous storms over the headwaters in the san bernardino mountains of southern california this winter pattern probably occurred more frequently to induce the large number of storms and floods needed

hydrogeologic processes in saline systems playas sabkhas and saline lakes abstract pans playas sabkhas salinas saline lakes and salt flats are hydrologically similar varying only in their boundary conditions thus in evaluating geochemical processes in these systems a generic water and solute mass balance approach can be utilized a conceptual model of a coastal sabkha near the arabian gulf is used as an example to illustrate the various water and solute fluxes analysis of this model suggests that upward flux of ground water from underlying formations could be a major source of solutes in the sabkha but contribute only a small volume of the water local rainfall is the main source of water in the modeled sabkha system with a surprisingly large recharge to rainfall ratio of more than 50 the contribution of seawater to the solute budget depends on the ratio of the width of the supratidal zone to the total width and is generally confined to a narrow zone near the shoreline of a typical coastal sabkha because of a short residence time of water steady state flow is expected within a short time 50 000 years the solute composition of the brine in a closed saline system depends largely on the original composition of the input water the high total ion content in the brine limits the efficiency of water rock interaction and absorption because most natural systems are hydrologically open the chemistry of the brines and the associated evaporite deposits may be significantly different than that predicted for hydrologically closed systems seasonal changes in temperature of the unsaturated zone cause precipitation of minerals in saline systems undergoing evaporation thus during the hot dry season months minerals exhibit retrograde solubility so that gypsum anhydrite and calcite precipitate evaporation near the surface is also a major process that causes mineral precipitation in the upper portion of the unsaturated zone e g halite and carnallite provided that the relative humidity of the atmosphere is less than the activity of water the slope of the fresh brine water interface in saline lake systems is shallower than in fresh seawater interface because of the greater density difference between the fresh brine water bodies the interface between sabkha brines and seawater slopes seaward unlike normal marine fresh water systems that slope landward moreover the brine seawater interface does not achieve steady state because it is pushed toward the sea by the sabkha s brine

the calcareous tufa in the tadrart acacus mt sw fezzan libya an early holocene palaeoclimate archive in the central sahara article i nfo the palaeoclimatic signi cance of calcareous tufa deposits found in the presently hyperarid tadrart acacus massif central sahara sw libya is discussed on the basis of u th datings stable isotope analyses and the regional hydrogeological context these deposits formed mostly between c 9600 and 8100 yr bp the isotopic signature 18 o and 13 c of this tufa indicates that the water forming these carbonates originated as isotopically depleted rainwater as a result of the northward expansion of the sw african monsoon system during the early holocene carbonate sedimentation in the tadrart acacus decreased shortly before c 8000 yr bp attributed to a drop in precipitation in the course of the well known 8 2 kyr event a correlation between tufa development and climate change in n and e africa and in the mediterranean basin during the early holocene is discussed the effect of early holocene climate change on both the landscape and the dwellers living in the tadrart acacus region is also evaluated

palaeoenvironmental reconstruction of kathu pan south africa based on sedimentological data abstract several studies have highlighted the importance of collecting well dated records of palaeoenvironmental changes on desert margins particularly in the semi arid interior of southern africa here we describe sediments at three sites in kathu pan a pan complex overlying karstic bedrock at the southern edge of the kalahari basin sinkholes have exposed sedimentary sequences dating back to the pleistocene making it possible to document multiple palaeoenvironmental regimes in this landscape using a multi analytical sedimentological approach including micromorphology energy dispersive x ray spectrometry electron microprobe loss on ignition laser diffractometry and luminescence dating we demonstrate that the sediments at kathu pan represent an environment fluctuating among a number of thresholds for accumulation of different kinds of transported and authigenic sediments within the pleistocene sands at the base of our studied sedimentary sequence the presence of palygorskite indicative of less extreme evaporative control represents a semi arid environment from 156 11 ka to 32 2 ka marine isotope stages 6 3 increased moisture availability at 84 4 ka and at 96 5 ka possibly during marine isotope stages 5a and 5c respectively is reflected in the sands by the formation of palygorskite in concert with the deposition and oxidation of organic material as the climate became increasingly arid possibly in response to global cooling during the last glacial maximum 21 2 ka kathu pan crossed a threshold and deposition of caco3 dominated over that of palygorskite in the holocene beds within our studied unit alternating caco3 and organic dominated deposits sometimes in very fine laminae reflect an increase in the amplitude of either seasonal or annual changes in water availability

enso like modulated tropical pacific climate changes since 2 36 myr and its implication for the middle pleistocene transition el nino southern oscillation enso activity and the pacific walker circulation are controlled by the zonal sea surface temperature sst gradient between the western and eastern equatorial pacific eep and the corresponding barometric difference variations in the zonal sst gradient since the early pleistocene have primarily been triggered by changes in the sst in the eastern equatorial pacific however the response of the enso like long term state to the cooling of the eep and its coupling role with tropical pacific climate changes are still not well established here we present a high resolution grain size record spanning the last 2 36 myr obtained from marine core sediment located in the west philippine sea in order to decipher the tropical pacific climate changes and reveal its controlling mechanism by combining our data with other long term climatic records from the equatorial pacific we demonstrate that the cooling of sst and enhanced upwelling in the eep resulted in the development of the walker circulation and increased monsoon precipitation in luzon from 2 2 to 1 6 myr from 1 2 to 0 8 myr and since 0 2 myr ago the progressive cooling of the high latitudes in the quaternary may be responsible for our observation here a newly identified 100 kyr dominant period between 2 2 and 1 6 myr in the enso like modulated pacific climate records indicates that the enso like system may play a key role in facilitating or responding to the global climate changes

human occupation of the northern arabian interior during early marine isotope stage 3 the early part of marine isotope stage mis 3 ca 60 50 ka is a crucial period for studying human demography and behaviour in south west asia and how these relate to climatic changes however the archaeological and palaeoenvironmental records for mis 3 in critical areas such as the arabian peninsula remain poorly developed here we present findings from the al marrat basin in the nefud desert which provides the first clear evidence for both increased humidity and human occupation of the interior of northern arabia during early mis 3 a middle palaeolithic assemblage dated by optically stimulated luminescence to ca 55 ka was found stratified within a sequence of relict palustrine deposits indicative of shallow water body formation in the al marrat basin hominin presence in northern arabia at this time coincides with the intensification and northward displacement of monsoon rainfall systems during a period of maximum insolation these findings add to a growing corpus of palaeoenvironmental evidence which indicates that the arabian interior was neither arid nor unpopulated during early mis 3 and that hydrodynamic responses to enhanced moisture availability facilitated demographic expansions into the arabian interior

coherent high and low latitude control of the northwest african hydrological balance variability in northwest african humidity has been documented for the holocene period but less is known about the development of the hydrological balance during the pleistocene period sedimentary records and numerical simulations for the past 120 000 years show abrupt millennial scale changes in humidity which may be related to changes in the strength of the north atlantic meridional overturning circulation

recent environmental change and prehistoric human activity in egypt and northern sudan abstract this paper reviews the various late quaternary records that are available from western egypt and northern sudan which includes more than 500 published radiocarbon dates and various sedimentary archives from local landscape components including palaeolakes soils drainages wadis and archaeological sites this palaeoenvironmental compilation frames the spatial and temporal context of local cultural activities when the region was most hospitable 9000 6000 bp at this time monsoonal weather influenced the portion of the african continental interior creating enough convective rainfall for occasional surface water storage in this part of the modern sahara rapid hydroclimatic changes play a key role in geomorphic evolution and resource availability as watering holes formed and dried up in the early to middle holocene neolithic people developed various subsistence strategies including opportunistic hunting of small animals e g gazelle and hare and food related e g wild sorghum millet and legumes activities gathering plant cultivation and livestock rearing during its wettest phases during the monsoonal maximum the area was drought prone sustaining a meager steppe shrub desert flora further desertification and aeolian deflation during the middle and late holocene fostered technological innovation migration and settlement as well as the further development of agrarian communities and complex culture

grain size distribution function of polymodal sediments in hydraulic and aeolian environments and numerical partitioning of the sedimentary components most continental sediments are polymodal composed of overlapping components of which the grain size generally obeys some type of natural distribution the grain size components and their function types can be determined from frequency and cumulative curve plots in order to define the function formula of the grain size distribution the function parameters can be estimated by fitting a defined function formula to the measured grain size data of the sample which simultaneously achieves numerical partitioning of the sedimentary components genetic analysis of grain size components of hydraulic and aeolian sediments demonstrates the following environmental implications fluvial sediment is composed of isolated saltation and suspension components the sediments in closed lake basins are dominated by a suspension silt clay component with a small proportion of saltation sand the fine sand component makes up the majority of desert sand overlapping with a small proportion of fine dust aeolian loess is composed of two overlapping components a short suspension time silt component and a long suspension time fine component aeolian material in the north pacific deep sea sediments is dominated by long suspension time fine dust the fine component in aeolian sediments shows a consistent grain size distribution and genetic connection from the desert sand loess of northern china to the north pacific ocean which is mainly transported by westerly winds and is dispersed in the atmosphere forming a background dust c 2002 elsevier science b v all rights reserved

sahara and sahel vulnerability to climate changes lessons from holocene hydrological data abstract the examination of more than 1500 paleohydrological dated records collected between 10 and 28 n during the last 50 years have been used to improve our knowledge and understanding of the sahara and sahel vulnerability to the atlantic monsoon changes in the long term we have analyzed the distribution of water bodies mainly lakes and wetlands over time and space the central saharan massifs played a major role in favoring water supply to the lowlands throughout the whole african humid period in addition distinct east west dynamics is recorded with humidity starting and stopping several millennia earlier to the east than to the west of the sahara a series of time lags are discussed 1 between the maximum of deep fresh water lake formation during the early holocene and the maximum of water body extensions during the mid holocene which highlight the primary role of aquifer water level in lake response to climate change 2 between the hydrological history of the sahara and the sahel and the forcings mainly insolation changes during the early and mid holocene which involves complex interactions between remnant ice sheet in the northern hemisphere open water bodies in the sahara and sahel and the atlantic monsoon system

correlation between climate events in the north atlantic and china during the last glaciation episodes of massive iceberg release heinrich events 1 3 into the north atlantic ocean during the last glaciation were associated with recurring episodes of unusually cold north atlantic surface water bond cycles 4 and cold air temperatures over greenland dansgaard oeschger events 5 6 four of the youngest of these cold events have also been reported in climate records from sites outside the north atlantic region7 but until now the entire suite has been identified only in north atlantic marine sediments greenland ice core records and tentatively in french lake sediments8 here we examine grain size data from chinese loess and intercalated accretionary palaeosols of last glacial age for evidence of similar climate signals remote from the north atlantic region we see grain size maxima with ages that match those of the last six heinrich events which we interpret as an indication of the changing strength of the east asian winter monsoon which largely controls the transport and deposition of central asian aeolian dust thus it seems that these heinrich events have left their signature in the chinese loess record this is consistent with simulations of the glacial climate9 which imply that the climates of the north atlantic and china were linked by the effect of westerly winds