growth by extension and reworking of a south western kalahari linear dune optically stimulated luminescence osl dating studies of linear longitudinal dunes have been used extensively to elucidate late quaternary environments and climates in arid or formerly arid regions yet understanding of the development of such dunes is incomplete in particular conflicting opinions have been presented regarding the propensity of linear dunes to migrate laterally the degree to which they rework their own sediment during accumulation and whether they form primarily by extension as opposed to lateral sand movement from adjacent interdunes this study focuses on this last point although the importance of the other controversies is discussed in context a simple linear dune in the south western kalahari which has a prominent termination on a pan playa surface provides an opportunity to directly test hypotheses of dune extension chronostratigraphy along a 600 m transect along the crest of the dune constrained by 42 osl ages reveals that the dune grew by extension on occasions in the late pleistocene and early holocene but has also been subject to reworking along its length which has continued until recent times dune development by extensional growth is suggested to operate under environmental conditions more conducive to net accumulation whereas reworking is largely independent of conditions throughout the last 18 ka and may represent seasonal fluctuations in the position of the dune crest the relative significance of these two modes of development is suggested to be a key control on the efficacy of linear dunes as archives of environmental and climatic change copyright 2011 john wiley sons ltd

palaeoenvironmental change recorded in the palaeodunefields of the western murray basin south australia new data from single grain osl dating this study is concerned with the reconstruction of the palaeoenvironmental history of southeastern australia for the last 300 ka by establishing a luminescence chronology of dune sand deposition in the western murray basin south australia in the study area vast fields of palaeodunes stabilised by vegetation provide evidence of past environmental change in total 98 samples were collected from dune sand layers at 13 different dune sections the time of their deposition was determined using optically stimulated luminescence dating of single quartz grains accounting for the impact of post depositional mixing by the use of a finite mixture model the oldest depositional phase demonstrates that dune sand layers of great antiquity are preserved in the western murray basin ranging up to at least 380 ka phases of substantial dune sand deposition were identified for the periods 18 38 ka and 63 72 ka older depositional phases also exist but are poorly resolved due to relatively large errors of the luminescence ages aeolian deposition during the last termination and the holocene is relatively limited with a slight clustering of ages at the time of the antarctic cold reversal and from 5 8 ka two modern ages give evidence of very recent dune sand deposition comparison with other palaeoclimate records from the region suggests that phases with high aeolian sedimentation coincide with more arid conditions and breaks in the dune record with more humid phases thus although dune records are often discontinuous and their interpretation in palaeoclimatic terms is not always straightforward the palaeodunes of the western murray basin show a good preservation of phases of aeolian activity and provide useful information for palaeoenvironmental reconstruction

temporal spatial and textural variation in the mineralogy of mississippi river suspended sediment abstract it has long been known that as a result of frequent deposition the mineralogy of mississippi river sands remains constant in time and space along the river there has never been a comparable detailed mineralogical study of the vastly more abundant muddy sediment of the river to evaluate the magnitude of variation in mississippi river fine fraction mineralogy suspended sediment was collected at 3 stations across the river during july and november 1980 samples were disaggregated and without pretreatment separated into 4 sizes 62 5 7 8 m 7 8 2 0 m 2 0 0 49 m and 0 49 m using calibration curves prepared from pure minerals with an internal standard xrd determinations of the mineralogy were obtained with a high precision minerals quantified were in order of decreasing abundance smectite illite kaolinite quartz plagioclase alkali feldspar chlorite and amphibole the largest source of variation in suspensate mineral abundance was sediment size smectite for example comprised 50 of the fine clay but was not present as silt anova revealed significant temporal variation in the abundance of smectite and illite within the finest sizes and lateral variation in quartz and feldspar abundance in coarser sizes discriminant function analysis determined that the total mineralogy of river suspended sediment varied significantly with time this temporal variation in mineralogy apparently results from differences in soil mineralogy in drainage basins of the major tributaries of the river coupled with t e time varying contributions of the tributaries

the sedimentary structure of linear sand dunes linear sand dunes dunes that extend parallel to each other rather than in star like or crescentic forms are the most abundant type of desert sand dune1 but because their development and their internal structure are poorly understood they are rarely recognized in the rock record2 models of linear dune development2 3 4 5 6 have not been able to take into account the sub surface structure of existing dunes but have relied instead either on the extrapolation of short term measurements of winds and sediment transport or on observations of near surface internal sedimentary structures from such studies it has not been clear if linear dunes can migrate laterally2 7 8 here we present images produced by ground penetrating radar showing the three dimensional sedimentary structure of a linear dune in the namib sand sea where some of the world s largest linear dunes are situated these profiles show clear evidence for lateral migration in a linear dune moreover the migration of a sinuous crest line along the dune produces divergent sets of cross stratification which can become stacked as the dune height increases and large linear dunes can support superimposed dunes that produce stacked sets of trough cross stratification these clear structural signatures of linear dunes should facilitate their recognition in geological records

holocene climate variations from zhuyeze terminal lake records in east asian monsoon margin in arid northern china zhuyeze palaeolake is a terminal lake situated in the arid northern china in the east asian monsoon margin in order to examine the holocene palaeoclimatic change in the east asian monsoon margin qingtu lake section qtl from zhuyeze palaeolake is sampled in high resolution palaeoclimatic proxies such as grain size carbonate toc c n and delta 13 c of organic matter were analyzed eleven 14 c samples and six optically stimulated luminescence osl samples were dated to provide chronological control we also investigated the geomorphic features of lake shorelines in this area the results show that the climate was warm and dry in early holocene 9 5 7 0 cal ka bp cool and humid in mid holocene 7 0 4 8 cal ka bp and increasingly drier in late holocene since 4 8 cal ka bp comparisons of our records with other records in adjacent areas as well as with the records in the asian monsoon areas suggested that changes in effective moisture was synchronous in east asian monsoon marginal zone i e the pattern of dry early holocene humid mid holocene and aridity increasing late holocene and that the moisture optimum during the holocene was out of phase between asian monsoon margin and asian monsoonal dominated region possibly due to the high temperature at that time c 2010 university of washington published by elsevier inc all rights reserved zhuyeze palaeolake is a terminal lake situated in the arid northern china in the east asian monsoon margin in order to examine the holocene palaeoclimatic change in the east asian monsoon margin qingtu lake section qtl from zhuyeze palaeolake is sampled in high resolution palaeoclimatic proxies such as grain size carbonate toc c n and delta 13 c of organic matter were analyzed eleven 14 c samples and six optically stimulated luminescence osl samples were dated to provide chronological control we also investigated the geomorphic features of lake shorelines in this area the results show that the climate was warm and dry in early holocene 9 5 7 0 cal ka bp cool and humid in mid holocene 7 0 4 8 cal ka bp and increasingly drier in late holocene since 4 8 cal ka bp comparisons of our records with other records in adjacent areas as well as with the records in the asian monsoon areas suggested that changes in effective moisture was synchronous in east asian monsoon marginal zone i e the pattern of dry early holocene humid mid holocene and aridity increasing late holocene and that the moisture optimum during the holocene was out of phase between asian monsoon margin and asian monsoonal dominated region possibly due to the high temperature at that time c 2010 university of washington published by elsevier inc all rights reserved

hydroclimatic interpretation of quaternary shorelines on south australian playas abstract the catchment of lake eyre is one of the world s largest internally drained basins the playas near its depocentre the driest region of australia contain a partial record of quaternary climatic and hydrologic events for the last full glacial cycle and probably beyond ancient beach ridges marginal to lakes eyre frome callabonna and blanche have been dated using thermoluminescence tl to provide evidence for major changes in the hydrological regime of the basin beach ridges around lake eyre provide evidence of high lake stands up to 27 m above the present lake floor during what probably corresponds to the middle to latter part of marine oxygen isotope stage 5 there is evidence also for even higher lake stands associated with earlier isotope stages three tl dates identify a period of aeolian activity during stage 4 and a further 5 tl dates from lakes eyre and frome indicate that high lake stands occurred between about 55 and 40 ka corresponding with stage 3 the stage 5 and stage 3 high stands both relate to periods of enhanced fluvial activity previously identified in the lake eyre basin and elsewhere in australia in contradiction with other work a few tl dates from some playas suggest a possible major episode of high lake levels immediately preceding or at the start of the last glacial maximum lgm 26 22 ka this may relate to a sharp temperature suppression and an increase in runoff by rivers fed from monsoons in the north while a set of relatively low elevation late holocene beaches have been dated on two of the playas a period of enhanced precipitation and stream flow in the early to mid holocene appears not to have formed higher beaches possibly due to high temperatures and evaporation rates at that time the filling of lake eyre during and since stage 5 appears to have been to no more than to a level of 12 m australian height datum ahd possibly due a spillway at about this elevation in the form of the warrawoocara channel connecting lake eyre with playas to the southeast lakes gregory blanche callabonna and frome such overflows from one large basin to another would have had a major impact on the hydrology of the region in addition to enhanced runoff essential for the maintenance of high lake levels must have been local temperatures and evaporation rates significantly reduced from present day levels

aeolian system responses to global change challenges of scale process and temporal integration aeolian sediment systems are extensive components of the earth s surface not just in today s active desert environments but in coastal locations and as presently stable loess and peri desert ergs all these systems are subject to potentially significant 21st century changes in dynamics due to global warming impacts on atmospheric circulation sediment moisture and vegetation cover but do we know enough in the critical areas of science to allow robust models of likely future dynamics to be developed since the establishment of modern aeolian science research has largely taken two divergent routes 1 small scale investigations of the processes of wind shear sediment entrainment and transportation and 2 landform and landscape analyses with bedform systems described and relationships to circulation explained an intermediate sedimentological route has generated attempts towards a more integrated understanding of system behaviour at a range of scales four recent developments provide the potential for more robust multiscale integrations of aeolian system behaviour these are 1 advances in empirical measurement that allow wind power and sediment flux relations to be better described 2 modelling of dune and dust dynamics and interactions with key controls 3 monitoring systems that allow high resolution observations of sediment flux variations to be recognized and aeolian deposit structures to be understood and 4 chronometric advances that permit the assessment of the frequency and drivers of dune system activity in the past we explore and analyse these methodological advances and their potential contribution to the multiscale integrations that are essential for better informed predictions of future global aeolian system dynamics considering whether the integration of these advances in reductionist and holistic elements of aeolian science represent an example of the effective application of the principles of earth system science copyright 2008 john wiley sons ltd

optical dating of aeolian dynamism on the west african sahelian margin abstract the sahelian margin of west africa is widely recognised as an area of recent environmental catastrophe and human suffering arising from food shortage and land degradation associated with prolonged drought the propensity of this region to suffer drought has been related using environmental data collected during the period of instrumental records to a combination of low mean annual rainfall levels and a high degree of rainfall variability which relates to sea surface temperature anomalies in the adjacent tropical atlantic ocean despite the significant environmental and human consequences of such droughts there is a paucity of long term environmental data for the west african sahel aeolian dune reactivations in this area are a potentially highly useful environmental archive of past periods of extended drought conditions which may have resulted in localised or widespread dune reactivation here we describe the initial results from an ongoing programme of research which seeks to develop a detailed record of past dune reactivations in mali we find evidence for repeated holocene dune reactivation events and a significant number of reactivations which commenced at the time of onset of the last major drought cycle in the early 1970s we obtain ages as young as 20 30 years for some significant dune units thickness up to 1 m and describe the results of experiments which test the performance of our dating exercise we specifically test for the significance of preheat temperature on single aliquot regeneration sar equivalent dose determinations and recycling ratios neither are found vary significantly as a function of preheating optical dating of sand sized quartz could provide a useful tool for palaeogeographical mapping of ancient and historical dune reactivations in this region and elsewhere

last glacial maximum dune activity in the kalahari desert of southern africa observations and simulations abstract it has long been understood that as ephemeral landscape features sand dunes are highly sensitive to environmental change and thus their distribution and the timing of their development may provide clues to past climate dynamics the relationship between climate and dune activity however is neither simple nor straightforward with a range of controls affecting the balance between erodibility the availability of sediment for deflation and erosivity the potential for sediment transport to explore such complex systems over large spatial and temporal scales a number of dune activity indices dai have been created that incorporate wind speed and moisture balances to calculate the potential for and degree of dune mobilisation using modern weather station data these indices have generally been shown to provide reasonable indications of dune activity potential until recently however the detailed quantitative data required to inform these equations has not been available for past climate scenarios and attempts to determine the relative importance of the various controls of dune activity have relied on rough estimations of climatic parameters this paper combines data from monthly general circulation model gcm outputs from the coupled ocean atmosphere gcms for 21 ka with the most detailed dai equation presently available to calculate the potential for dune reactivation in southern africa during the last glacial maximum lgm 18 24 ka based on these data and calculations it is indicated that there was significantly less potential for dune activity across southern africa at 21 ka when compared to the aeolian sediment records from the region this study poses serious and fundamental questions about 1 the reliability of the model outputs 2 the degree to which dais are able to account for the complexity and dynamics of aeolian systems and or 3 the interpretation of dune records as palaeoclimatic proxies at millennial time scales

thermoluminescence dating of sand dunes in rajasthan india we report here a new application of thermoluminescence tl for dating sand dunes this application assumes that exposure to sunlight causes bleaching of the geological tl of a sediment to a residual value and that tl accumulation starts again when the sediment is buried under fresh deposit and is thus shielded from the sun although the tl method has been applied to loess1 2 and ocean sediments3 4 the application of this technique to sand dunes provides the first reliable dating control for dune dynamics palaeoclimatology and spread of deserts

reconstructing paleoenvironments and palaeoclimates in drylands what can landform analysis contribute quaternary period palaeoenvironmental and palaeoclimatic reconstructions are based on a wide and diverse array of proxy data sets some of which are geomorphological in nature in drylands where organic proxies may be limited the use of landforms is particularly important but challenging the capacity to establish the age of depositional forms particularly through the use of luminescence dating has advanced the use of landforms in dryland palaeo research though interpretation of these geoproxy records can be complex especially at the nexus of palaeoclimate and palaeoenvironmental interpretations of past conditions in this paper the use of aeolian and lacustrine forms in quaternary research is considered focusing on the relationships between dynamics form and climate and on the essential linkage between process research and palaeoenvironmental research it is concluded that landform analysis is a critical part of dryland palaeoenvironmental climate reconstruction contributing a different set of data compared to other data sources in terms of the elements of past conditions that are revealed five principles are identified to improve the use of geoproxy records in quaternary research 1 greater use of geomorphic process studies by quaternary scientists to better inform palaeolandform interpretation 2 further development of the use of chronometric data especially in terms of interpreting large data 3 interpret landform records in location specific contexts not in general terms 4 capitalise of the complexity of spatially extensive landform records which may offer better representations of real quaternary environmental complexity than at a point proxies 5 establish ways of integrating spatially extensive geoproxy records with other palaeoenvironmental records these challenges are major but not insurmountable and should represent goals for geomorphologists chronologists and quaternary scientists alike copyright 2011 john wiley sons ltd

mega lake in the kalahari a late pleistocene record of the palaeolake makgadikgadi system abstract a distinct series of beach ridges marking the former shorelines of large inter connected lacustrine basins in the kalahari can be clearly identified from landsat imagery and shuttle radar topography mission srtm data these basins which form the terminal sump of the okavango system in northern botswana are now almost completely dry during the quaternary they were intermittently occupied by large stable lake bodies and are thought to have periodically filled to a point of coalescence inundating an area that at its largest extent encompassed 66 000 km 2 poor chronological control has previously limited the utility of this important palaeo archive as part of a region wide lake palaeo shoreline research programme a systematic optically stimulated luminescence osl dating programme has utilised a lightweight hydraulic auger to take samples at depth from relict shoreline features twenty drill sites have generated 140 samples for dating establishing a firm chronology for multiple lake full phases in all three component basins ngami mababe and makgadikgadi of this mega lake this paper presents the final set of ages in the programme derived from four cores from the western and north eastern shorelines of makgadikgadi and uses these ages to establish a chronology of mega lake high stands during the last 300 ka providing a rare directly dated long terrestrial record of positive hydrological excursions within the southern hemisphere

the hydrology of lake bosumtwi a climate sensitive lake in ghana west africa abstract lake bosumtwi lying in a million year old meteor crater is hydrologically closed in spite of the wet humid climate in this part of ghana to understand this geographical enigma a water balance model that describes both the historical lake level record and the full range of lake levels observed in terrace deposits around the lake was developed the water balance model shows that the reception of rainfall by and evaporation from the lake surface are the dominant constituents of the water balance prior to 1969 the average rainfall of 1550 mm year 1 was generally equal to lake evaporation and the average annual rise of 30 cm year 1 was produced mostly by runoff from the small watershed around the lake since 1969 with a decreased rainfall of 1380 mm year 1 the combination of rainfall and runoff has nearly equaled lake evaporation resulting in a nearly steady lake level long term simulations show that stochastic climatic variations very similar to those observed in this century could produce the full range of lake levels observed in terrace deposits the low salinity of about 1 suggests that dissolved solutes were removed by lake overflow in the recent geological past

paleoenvironmental implications of fixed dune systems in southern africa extensive systems of fixed linear dunes occur in the kalahari region of southern africa from 28 s to 16 30 s they provide evidence for large scale expansion of arid climates in the subcontinent during the quaternary on the basis of differing dune morphologies and alignments three periods of upper pleistocene aridity are recognised patterns of dune alignments reflect paleosand flow regimes and permit deduction of past winds and circulation patterns leading to the conclusion that arid episodes were associated with and probably caused by greater strength and persistence of the south african anticyclone a tentative chronology of the arid periods tends to support the hypothesis that subtropical aridity was contemporaneous with glacial conditions in high latitudes

pattern analysis of dune field parameters as a basic form of pattern analysis the parameters of dune spacing defect density crest orientation and crest length are measured from remote images and treated statistically for dunes at white sands in new mexico the algodones in california the agneitir in mauritania and the namib in namibia statistical populations are identified from frequency plots of dune spacing and crest length field scale calculations of defect density and rose diagrams of crest orientation single populations characterize simple dune fields white sands whereas multiple populations characterize compound complex dunes algodones namib and complex dune fields agneitir as time increases dune fields show an increase in dune spacing and crest length a decrease in defect density more tightly clustered crest orientation and a reduction in the variance associated with measurements of these parameters the results are consistent with models of dune fields as self organizing complex systems in which a characteristic pattern emerges as a function of constructional time because pattern evolution is a function of time it may be possible to use pattern analysis to augment current methods of age determination statistically defined populations can be used in geomorphic backstripping to unstack generations of simple patterns that give rise to complex patterns and to reconstruct each generation in terms of construction time and palaeo wind regime copyright 2006 john wiley sons ltd

challenges of calculating dunefield mobility over the 21st century attention has been directed towards both the impacts of future climate change on environmental systems and dunefield activity in the past but there has been relatively little consideration of potential dune mobility in a future and possibly warmer world this paper considers the use and limitations of four global circulation models gcms hadcm3 hadcm2 csiro mk2b and cgcm1 in combination with simple dune mobility indices to predict the activity of the kalahari dunefield it is clear that uncertainties surround gcm resolution and accuracy mobility index robustness for the calculation of intra annual dune mobility and data collection for mobility index calibration macro scale studies that look at large areas of the world over long time scales are well suited to gcm and mobility index use but dune mobility can be variable within a dunefield and it is the extreme sand transporting events occurring at high temporal resolutions that are the most important for short term studies to investigate intra annual changes in dune mobility over a specific dunefield techniques such as downscaling weather generators and probability curve fitting can help provide climate predictions for smaller areas over shorter time frames however these methods introduce uncertainty of their own and they often rely on the accuracy of original gcm predictions or the climate parameter relationships observed at present analysis of intra annual changes also requires mobility indices that can model monthly mobility patterns well although existing indices have only been used for calculating annual dune mobility potential when they are used for intra annual predictions the lack of lag response between precipitation decreases and the assumed vegetation dieback leads to an exaggerated amplitude pattern of dune mobility throughout the year calibration of dune mobility indices to dune mobility observed on the ground is therefore important but is hampered by a lack of observed measurements for individual months solutions are available to overcome some of the outlined problems but they can provide their own set of uncertainties which combine to further reduce the confidence given to future dune mobility predictions

lake size variations in the lahontan and bonneville basins between 13 000 and 9000 14c yr b p abstract recessions of lakes lahontan and bonneville that commenced 13 500 14 c yr b p were interrupted at 11 500 14 c yr b p in the lahontan basin and 12 200 14 c yr b p in the bonneville basin by relatively large perturbations in lake level that persisted for 2000 years minor glacial readvances in the sierra nevada and white mountains of california nevada occurred during the latter half of this interval between 11 000 and 9700 14 c yr b p the hydrologic response of lakes lahontan and bonneville and the mountain glacial advances were concurrent with the allerod younger dryas climatic intervals recorded in vegetational and glacial records of western and central europe

spatial variability and hydrologic evolution of australian lake basins analogue for pleistocene hydrologic change and evaporite formation abstract processes evident in basins across hydrologic gradients from humid to arid regions today provide analogues for systems that may have operated in some individual basins during periods of past hydrologic change thus lakes in humid regions today with low salinity sedimentary facies and with morphology controlled largely by wave action may closely resemble past lacustral pluvial phases experienced in zones which today are relatively arid and saline conversely playas controlled today by groundwater and in some cases subject to defletion may resemble those arid and dune building stages experienced by basins in sub humid regions today as they underwent glacial age desiccation in any such sequence of spatial or temporal gradients from humid to more arid conditions the frequency of basin filling and drying modulates the rate of evaporitive loss of interstitial waters from the exposed basin surface this in turn controls the salinity evolution of the interstitial and local groundwaters the notion of closed systems for terminal lakes while satisfactory for analysis of surface water budgets is quite inapplicable to the evolution of brines where surfacewater groundwater exchange during the high salinity drying stages becomes a controlling factor affecting all salt budgets in these systems evaporites may only be preserved when the sub surface waters have evolved to salinites near saturation for the salts concerned if sub surface waters are frequently diluted by surfacewater groundwater exchange evaporites will not be preserved in the record even though the surface system appears hydrologically closed the process of interstitial water evolution which controls efflorescence deflation and salt weathering exerts a dominating influence on basin geomorphic expression as well as on hydrochemical fractionation

the palaeoenvironmental significance of dune size hierarchies the size of a dune is a function of many factors one of which is the length of the period of consistent wind regime under which it grew ephemeral dunes are defined as those that are adjusted to diurnal wind regimes meso dunes to annual wind regimes and mega dunes to wind regimes that persist for longer periods these longer periods could be major climatic cycles but there seem to be no dunes whose size reaches that allowed by the length of some of these periods there may therefore be a maximum size beyond which mega dunes cannot grow dictated by sand supply aerodynamic processes such as speed up or by the scale of the atmospheric boundary layer these concepts are tested on dunes in the wahiba sands in oman analysed from a landsat image it is hypothesised that a large set of megadunes here formed in the lgm that a smaller set of mega dunes may be of younger dryas age and that there is a meso dune series of holocene age

multiple episodes of aridity in southern africa since the last interglacial period there is generally a dearth of evidence of the nature of quaternary climate change within desert systems which has limited previous interpretations of past environmental change at low latitudes the last glacial maximum has previously been identified as the peak of late quaternary aridity when desert systems expanded to five times their present extent1 2 3 and low latitude aridity has been described for previous glaciations4 but little evidence has been derived directly for large desert basins particularly southern africa here we report new chronological optical dating evidence of arid episodes recorded in aeolian sediments from the mega kalahari sand sea episodic aeolian activity is recorded at the northeastern desert margin whereas more sustained activity is evident from the southwestern desert core several significant arid events are apparent since the last interglacial period with dune building arid phases at 95 115 41 46 20 26 and 9 16 kyr before present existing atmospheric general circulation model simulations and independent palaeoclimate data indicate that the changes in aridity are related to changes in the northeast southwest summer rainfall gradient which are in turn related to sea surface temperatures in the southeastern atlantic ocean

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

use of the geochemical and biological sedimentary record in establishing palaeo environments and climate change in the lake ngami basin nw botswana sediment samples from a continuous 4 6 m profile in the dry bed of lake ngami in nw botswana were analysed for geochemistry and dated using both 14c and tl methods certain units in the profile were found to be diatom rich and these with the geochemical results were used as indicators of high and low lake levels within the basin the lake ngami sediments contain a high proportion of sio2 51 92 5 wt avg 72 4 wt and variable levels of al2o3 2 04 17 2 wt avg 8 88 wt based on elevated al2o3 and organic matter loiorgc results lacustrine conditions occurred at ca 42 ka until 40 ka and diatom results suggest that relatively deep but brackish conditions prevailed at 40 ka the lacustrine sedimentary record was terminated abruptly possibly by tectonic activity at ca 19 ka shallow aerobic turbulent conditions were prevalent but lake levels were at this time increasing to deeper water conditions up until ca 17 ka this period coincides with the late glacial maximum a period of increased aridity in the central southern africa region generally increasing sr ca ratios and decreasing loiorgc and al2o3 from ca 16 to 5 ka suggest decreasing inflow into the basin and declining lake levels based on the enrichment of lree results slightly alkaline conditions prevailed at ca 12 ka diatom results also support shallow alkaline conditions around this time these lake conditions were maintained primarily by local rainfall input as the region experienced a warmer wetter phase between 16 and 11 ka lake levels rose rapidly by 4 ka probably in response to enhanced rainfall in the angolan catchment these results indicate that lake levels in the lake ngami basin are responding to rainfall changes in the angolan catchment area and local rainfall the results confirm that the present day anti phase rainfall relationship between southern africa and regions of equatorial africa was extant during the late quaternary over the angolan highlands and nw botswana

late pleistocene wetting and drying in the nw kalahari an integrated study from the tsodilo hills botswana abstract the sediments and landforms at the tsodilo hills in the northwestern kalahari desert provide an opportunity to directly investigate the late quaternary wetting and drying of the region from evidence at a single site lacustrine carbonates including incorporated molluscs and diatoms a lake shoreline feature and stabalised linear dunes were investigated for their constituent palaeoenvironmental signals chronometric control is provided by calibrated 14 c ams and osl dating the evidence suggests that linear dune construction has not occurred since the last glacial maximum with particular development from 36 to 28 ka lake stands indicating wetter regional conditions than present occurred at 40 32 ka with more seasonal conditions from 36 ka and at 27 12 ka with a possible drying out at 22 19 ka data are consistent with other independent studies from the region and with recent evidence obtained from atlantic cores off the coast of namibia it is concluded that careful consideration of multi proxy data from a single location can assist in resolving discrepancies that arise from independent studies of lake cave and dune records in the kalahari

hydrodynamics in holocene lake mega chad holocene lake mega chad lmc was the largest late quaternary water body in africa the development of this giant paleo lake is related to a northward shift of the isohyetes interpreted as evidence for an enhanced monsoon african humid period numerous preserved coastal features have been described all around the lmc shore such features reveal the main paleo hydrodynamical tendencies in the context of a closed water body like lmc hydrodynamics are forced mainly by winds we use a three dimensional numerical model symphonie to simulate the mean hydrodynamics in lmc under both harmattan like northeasterly trade winds and monsoon like southwesterly winds forcings the northern part of lmc displays coastal features such as sand spits that are consistent with the simulations forced by harmattan like winds geomorphic features related to monsoon driven hydrodynamics are not clearly expressed they could have developed during the early stage of lmc but subsequently reworked at the time of sand spit building harmattan like driven hydrodynamics prevailed and related coastal features were preferentially preserved in the sedimentary record

aeolian and fluvial evidence of changing climate and wind patterns during the past 100 ka in the western simpson desert australia abstract sediments near finke in central australia provide evidence of late quaternary evolution and the interaction of aeolian and fluvial systems in response to changing climate in the western simpson desert thermoluminescence tl dating is used to develop a chronology of aeolian and alluvial activity and to identify differences in sand provenance quaternary alluviation in the finke valley at this location occurred at or prior to c 90 ka and with no surviving evidence of subsequent activity until the holocene in contrast to rivers in the eastern part of the lake eyre basin substantial alluviation took place here in the early to mid holocene probably due to reactivation of the northern monsoon and its partial penetration into central australia the regional dunefield near finke consists of linear dunes largely reworked and aligned during the last glacial 30 12 ka as part of the great anticlockwise whorl of dunes in central australia the oldest dated source bordering dunes from the finke river are bright red in colour were deposited at c 100 ka and are now buried beneath paler source bordering dunes the latter consist of two exposed units a lower one of unknown orientation that dates at 17 9 ka and an upper unit aligned to the northwest and parallel to the prevailing winds that dates at 5 0 ka the tl signature and sediment texture of the oldest source bordering dunes show them to have probably been derived from weathered alluvial red beds of similar or greater age nearby and to have contributed abundant sand to the regional dunefield immediately north of the river in contrast sand from the younger paler source bordering dunes appears to be from a different source and to have only recently extended into the regional field the finke region would seem to be in a pivotal position for the study of palaeowind patterns that have created and modified australia s whorl of continental dunes the 30 18 ka regional linear dunes near finke are oriented almost due north their cross sectional asymmetry steeper eastern slopes suggests a response to southwesterly or westerly sand transporting winds between 18 and 10 ka these winds appear to have shifted to their present southeast orientation during the past 5 ka from dune ages alignments and asymmetry it is proposed here that there was a northward shift in the wind pattern at finke by about 100 150 km 1 1 5 of latitude during the last glacial but that through this period the regional dune pattern has remained remarkably stable

temporal patterns of arid humid transitions in the south eastern arabian peninsula based on optical dating abstract the rub al khali aeolian system of the arabian peninsula is the world s largest erg while the region is presently hyper arid evidence for multiple past humid periods has been documented in previous studies radiocarbon dating of lacustrine travertine and palaeogroundwater deposits suggests that the climate was humid at 10 6 and 35 25 ka these phases have been associated with summer rainfall increases occurring in tandem with an intensification and northward migration of the monsoon system during northern hemisphere precessional maxima published optical dating studies have focused on preserved sand dune and aeolianite deposits to establish ages for the intervening arid phases here we present a summary of this work and additional optical dating results for samples of aeolian sediment from a deep drill core which provides insights into the style of barchan dune accretion in the liwa region of the united arab emirates the large dune accreted rapidly during the mid late holocene the results suggest that the transitions from humid to arid conditions and resulting accumulation of aeolian sediment in the form of large bedforms occurred abruptly at around 6 ka further aeolian sedimentation has not been constant since that time with initial gradual dune growth followed by rapid vertical accretion and possible termination of accumulation around c 2 ka

cenozoic deep sea benthic foraminifers tracers for changes in oceanic productivity from late middle eocene through earliest oligocene high latitude regions cooled and by the end of the period continental ice sheets existed in antarctica diversity of planktonic microorganisms declined and modern groups of terrestrial vertebrates originated coeval faunal changes in deep sea benthic foraminifers have been related to cooling of deep waters and increased oxygenation cooling however occurred globally whereas species richness declined at high latitudes and not in the tropics the late eocene and younger lower diversity high latitude faunas typically contain common epistominella exigua and alabaminella weddellensis opportunistic phytodetritus exploiting species that indicate a seasonally fluctuating input of organic matter to the sea floor we speculate that the species richness gradient and increase in abundance of phytodetritus exploiting species resulted largely from the onset of a more unpredictable and seasonally fluctuating food supply especially at high latitudes

evaluating the use of dune sediments as a proxy for palaeo aridity a southern african case study abstract the dominance of dryland environments in the southern hemisphere makes the study of these regions of critical importance for the development of regional hemispheric and global models of environmental change unfortunately the wetting and drying cycles associated with semi hyperarid climates are not conducive to the preservation of traditional organic proxy data sources the last decade however has seen the development of a number of alternative archives including the application of luminescence dating techniques to dunes and other aeolian deposits in continental situations the existence of relict dune fields has long been thought to be evidence of drier conditions during the pleistocene and direct ages from these features have been interpreted almost exclusively as indicating phases of aridity however an increasing number of ages from a broader range of environments are calling into question the assumption that aeolian activity can be simply equated with aridity presented here is a comparison of dune ages that have been obtained from across southern africa with a range of proxies from both terrestrial and marine records taken as a whole three primary phases of activity can be identified at 60 40 35 20 and 17 4 ka the frequent discordance with other terrestrial records indicating coeval increases in humidity and the close correlation of these phases with wind strength proxies suggest that aridity is unlikely to be the sole or even primary forcing mechanism for aeolian activity in the region and the palaeoclimatic significance of these sedimentary archives needs to be reassessed

late quaternary chronology of major dune ridge development in the northeast rub al khali united arab emirates the northeastern sector of the rub al khali desert in the eastern united arab emirates uae is dominated by large ne sw trending dune ridges orientated perpendicular to the currently prevailing northwesterly wind regime in this study extensive use has been made of artificially exposed sections through these major dune ridges that reveal internal sedimentary structures and allow an intensive high resolution sampling programme to be carried out here we present the optical dating results for samples from 7 sections the results indicate that dune activity and preservation occurred within the periods 7 3 ka 16 10 ka and 22 20 ka with evidence of earlier preservation during marine oxygen isotope stages mis 3 and 5 with net accumulation rates in the range 2 2 25 m ka 1 in several instances hiatuses in the preserved record of dune accumulation coincide with stratigraphic bounding surfaces visible in the exposed section profiles with associated truncation of internal sedimentary structures caution must be exercised when interpreting such gaps in the recorded accumulation chronologies of these dunes since these may simply constitute phases of low preservation potential rather than phases of low aeolian activity other factors such as sediment supply and availability in relation to sea level dynamics may be significant and are also considered

glaciers and climate in pacific far ne russia during the last glacial maximum a combined geomorphological physical model approach is used to generate three dimensional reconstructions of glaciers in pacific far ne russia during the global last glacial maximum glgm the horizontal dimensions of these ice masses are delineated by moraines their surface elevations are estimated using an iterative flowline model and temporal constraints upon their margins are derived from published age estimates the equilibrium line altitudes elas of these ice masses are estimated and glgm climate is reconstructed using a simple degree day melt model the results indicate that during the glgm ice masses occupying the pekulney kankaren and sredinny mountains of pacific far ne russia were of valley glacier and ice field type these glaciers were between 7 and 80 km in length and were considerably less extensive than during pre lgm phases of advance glgm ice masses in these regions had elas of between 575 22 m and 1035 41 m above sea level corresponding to an ela depression of 350 740 m relative to present data indicate that in the pekulney mountains this ela depression occurred because of a 6 48c reduction in mean july temperature and 200 mm a 1 reduction in precipitation relative to present thus reconstructions support a restricted view of glgm glaciation in pacific far ne russia and indicate that the region s aridity precluded the development of large continental ice sheets copyright 2011 john wiley sons ltd

deflation in the dustiest place on earth the bodele depression chad the bodele depression in chad is the largest single source of dust on earth because of a combination of strong near surface winds and a large reservoir of readily eroded and easily entrained low density sediment during the holocene and late pleistocene the bodele depression was host to a great lake palaeolake megachad that is now completely desiccated leaving the lake bed sediments exposed to deflation deflation in the bodele depression is revealed in erosional remnants of lake bed deposits exposed as yardangs on the lake floor erosional remnants indicate that locally up to 4 m of sediment has been removed by deflation optically stimulated luminescence dating shows that this occurred in less than 2400 years giving a rate of deflation of at least 1 6 mm yr 1 a range of other geomorphological features indicate that in some areas rates of deflation may be greater than or equal to 10 mm yr 1 deflation appears to be greatest in an arc around the northeastern margins of the lake basin where the diatomite deposits have been removed and revealed an underlying network of distributary channels preserved as gravel capped ridges the ridges which are part of an inverted topography are interpreted as deltaic distributary channels from an inland delta similar to the okavango delta examples of barchan dunes exist that were flooded by the palaeolake and which have now been exhumed from beneath layers of diatomite the distribution of extensive deflation around the northeasterly upwind end of the bodele depression probably results from a combination of large wind velocities an upwind source of abrasive sand and thinner diatomite deposits around the lake margin satellite image analysis shows that outcropping diatomite covers 24 049 km2 of the bodele depression furthermore the area from which diatomite has been removed by deflation is around 14 000 km2 combining this information with the ages and rates of deflation mentioned above indicates that some 61 000 km3 of diatomite has been eroded from the bodele depression during the past 1000 years

white sands dune field new mexico age dune dynamics and recent accumulations abstract the white sands dune field situated within the tularosa basin in southern new mexico is thought to have been largely derived by a stepwise progressive deflation of pleistocene lake otero strata with the onset of regional aridity optically stimulated luminescence osl dating of samples from a core that penetrated the gypsum accumulation of the dune field confirm a time of origin at 7000 yr dune sediment is characterized as lagged influx from previously stored lake otero sediment and contemporaneous influx derived from subsequent playas sediment became available for aeolian transport and dune field construction because of a falling water table driven by the regional aridity the current dune field is primarily a wet aeolian system in which the behavior of the accumulation surface over time is a function of the water table although surface cementation by gypsum also imparts aspects of a stabilizing system dune crests are oriented borderline transverse to the annual transport resultant and a monitored dune and its cross strata show that transverse winds from the sw during the late winter and spring account for most of the crest normal migration but a significant along crest component of migration of dune sinuosity occurs with fall and winter winds from the nw and n that strike the crests obliquely trenches across three interdune areas show dune sets and interdune strata climbing at about 0 1 depth of interdune scour increases with interdune streamwise length which acts to enhance the probability of dune cross strata deflation during arid years but also increases the probability of interdune accumulation because the water table shows a net rise over time within the trenches dune sets show a bundling of foresets between reactivation surfaces interpreted as annual cycles that reveal lee face reworking by the oblique nw and n winds and slipface progradation fostered by transverse winds from the sw a progression from grainflow dominated to wind ripple dominated cross strata within a single set revealed in the longest trench is consistent with along crest migration of dune sinuosity interdune laminations show light dark couplets interpreted as annual varves reflecting dry wet portions of the year the number of laminations preserved in vertical sections across an interdune area shows that the record is incomplete and endorses the interpretation of periods of interdune deflation a calculation of the current accumulation rate as based upon the climbing strata within the trenches is significantly greater than the long term accumulation rate determined by osl dates taken from the core in addition to compaction and possible dissolution of gypsum as partial explanations the long term accumulation rate may reflect significant variation in the accumulation rate over time short term deflation of accumulations on a regular basis and or the presence of unconformities within the gypsum body

aeolian fluvial interaction evidence for late quaternary channel change and wind rift linear dune formation in the northwestern simpson desert australia in central australia the most easterly extent of the macdonnell ranges border the simpson desert dunefield where widely spaced strike ridges intercept and isolate pockets of broad crested linear dunes that reflect regional changes in late quaternary climate flow regime and channel avulsion an energetic todd river reworked the eastern part of camel flat basin from 75 65 ka until the last glacial maximum lgm when it shifted eastwards but with some flows persisting through the basin until about 10 ka resulting desert surfaces of different age facilitate temporal comparisons of linear dune formation fine grained red dunes 75 65 ka in age occur on the western floor of the basin and are ramped against the foot slopes of the range after the lgm and especially during the holocene the river s departure enabled small pale coloured closely spaced coarser textured linear dunes to form on the abandoned floodplain in the eastern basin their orientation 20 farther west than the larger and older red dunes this realignment indicates that the australian wind whorl shifted southwards some 160 km or 1 5 after the lgm linear dunes in the northwestern simpson desert were formed by wind rifting involving vertical accretion of sand from a proximal source not by long distance sand transport with linear extension the blocking ranges have caused negligible downwind sediment accumulation over the past 75 ka

dunes in southeastern namibia evidence for holocene environmental changes in the southwestern kalahari based on thermoluminescence data abstract linear dunes in the southwestern kalahari provide evidence of the nature of paleoclimates they have special significance because their alignments indicate a previous circulation pattern with prevailing northwesterly winds at present the bases of the dunes are fixed by vegetation and only the dune crests are active in contrast to previous suggestions final dune stabilization took place before about 9 8 ka this corresponds to reduced wind velocities accompanied by more humid conditions this seems to be the last important environmental change recorded by significant landforms in the southwestern kalahari since about 8 ka the region remained more or less semi arid the long distance to seasonal south shifting humid tropic air masses innertropical convergence zone itcz and the climatic barrier of the namib and the karas mountains against atlantic influences allowed only minor fluctuations the holocene is a period of reduced pan development the pans are partly buried by the early holocene linear dunes as well as by young sand fields at pan 1073 southeast of grootpan intra pan dunes have formed during the last 1000 years

understanding the impacts of late quaternary climate change in tropical and sub tropical regions abstract the understanding of climate impacts on tropical rivers and catchments has developed in part from models developed for temperate landscapes and a common rhythm is often apparent when millennial scale studies are compared at this level issues arising from the complex response of rivers to internal and external factors appear less important than the climate driven signal understanding the fluvial record however depends on the availability and interpretation of other sources of proxy data such as pollen spectra lake levels and ocean cores in many rainforest areas few pollen records exist and many of these reveal a hiatus at the time of the last glacial maximum examples of fluvial archives from africa indonesia and tropical queensland australia are discussed in relation to independent records of vegetation change and inferences are made concerning critical episodes in fluvial history focusing on the transitions from oxygen isotope stage ois 3 towards glacial conditions in ois2 and the pleistocene holocene transition to modern climates links between climate vegetation change and fluvial activity are presented as descriptive models

development of spatially diverse and complex dune field patterns gran desierto dune field sonora mexico the pattern of dunes within the gran desierto of sonora mexico is both spatially diverse and complex identification of the pattern components from remote sensing images combined with statistical analysis of their measured parameters demonstrate that the composite pattern consists of separate populations of simple dune patterns age bracketing by optically stimulated luminescence osl indicates that the simple patterns represent relatively short lived aeolian constructional events since 25 ka the simple dune patterns consist of i late pleistocene relict linear dunes ii degraded crescentic dunes formed at 12 ka iii early holocene western crescentic dunes iv eastern crescentic dunes emplaced at 7 ka and v star dunes formed during the last 3 ka recognition of the simple patterns and their ages allows for the geomorphic backstripping of the composite pattern palaeowind reconstructions based upon the rule of gross bedform normal transport are largely in agreement with regional proxy data the sediment state over time for the gran desierto is one in which the sediment supply for aeolian constructional events is derived from previously stored sediment ancestral colorado river sediment and contemporaneous influx from the lower colorado river valley and coastal influx from the bahia del adair inlet aeolian constructional events are triggered by climatic shifts to greater aridity changes in the wind regime and the development of a sediment supply the rate of geomorphic change within the gran desierto is significantly greater than the rate of subsidence and burial of the accumulation surface upon which it rests

late quaternary lacustrine groundwater aeolian and pedogenic gypsum in the prungle lakes southeastern australia abstract detailed petrographic studies of recent or sub recent evaporites where many critical environmental parameters are defined can help in the analysis of ancient deposits and in the establishment of chemical and environmental models for evaporite formation the prungle lakes are part of the now dry willandra lakes system in semi arid southwestern new south wales the willandra lakes have been a site of cyclic quaternary sedimentation in response to the well documented global climatic fluctuations associated with the glacial interglacial cycle at times of hydrologic stress low lake levels are associated with high salt volumes inherited from evaporative concentration in large shallow lakes upstream and the inflow of saline groundwaters thus at prungle a complex array of concentric shorelines lake floor terraces and lunettes has developed as basin within basin landforms which formed in response to filling and drying cycles sediments associated with these geomorphic units include 1 1 freshwater littoral nearshore and deep water deposited laminated sands and muds with biogenic carbonates chiefly of ostracodal and algal origin 2 2 evaporites comprising interbedded clay and laminated gypsum clay couplets which consist of discrete thin laminae of sugary white euhedral prismatic gypsum separated by detrital clay layers with a high degree of optical orientation primary accessory celestite srso4 occurs as discrete patches within the gypsum laminae 3 3 groundwater pyramidal discoidal or lenticular gypsum crystals grown from supersaturation produced by evaporation at the capillary fringe of the water table these have formed displacively within the sediments and caused considerable disruption of the sediment matrix 4 4 aeolian deposition in irregular transverse ridges of sand sized reworked groundwater gypsum and disrupted lacustrine clays the gypsum crystals are predominantly discoidal pyramidal forms which are conspicuously oriented parallel to bedding well sorted and extensively corroded the clay pellets are well sorted and moderately well rounded higher in the profile bedding is indistinct due to pedogenic processes which include modification of detrital grains and secondary crystallization of gypsum and carbonate a thin gypcrete horizon occurs at the surface the last cycle of sedimentation in the prungle lakes is believed from correlation with lakes higher in the willandra system to have occurred during the period 50 000 16 000 yr b p since then groundwaters have dropped below the zone of interaction with the lake floor and surface water no longer reaches the lakes sedimentation has ceased and soil formation with secondary carbonate and gypsum has continued to the present a range of sedimentary environments is identified which depend on strong seasonal oscillations these environments are virtually absent from the australian continent today and their occurrence during the pleistocene supports the contention of enhanced climatic seasonality at that time the array of sediment types and mineralogies is almost identical to that characteristic of coastal sabkha sequences highlighting the difficulty of relying on unusual evaporative mineralogy to differentiate marine and non marine environments detailed petrographic analyses of the prungle sequence have been made in association with a review of theoretical experimental and observational studies of the environmental controls of calcium sulfate mineralogy and crystal habit this has enabled the correlation at prungle of depositional environment with gypsum petrofacies and associated compositional fabric or structural features these observations are more generally applicable to other evaporite deposits many gypsum evaporites reported in the literature have been compared with this scheme developed at prungle

lake eyre palaeohydrology from 60 ka to the present beach ridges and glacial maximum aridity lake eyre is presently an ephemeral playa lake in an extremely large 1 3 million km2 internal drainage basin with most of its inflow derived from monsoon watered northern australia the hydrologic state of the lake has varied in the past in response to climate change from a perennial lake up to 25 metres deep to a groundwater controlled playa marked by substantial sediment deflation this paper is concerned with the stratigraphic record of the last 60 ka of that hydrologic history particularly the character and age of a playa marginal unit formed by deflation from the playa and of stranded high beach ridges a major deflation episode between 60 and 50 ka excavated the present lake eyre basin and deposited a gypsum and clay rich aeolian phase the williams point aeolian unit at a number of sites around the lake after deflation ceased a thick secondary gypsum profile developed on the dune early in oxygen isotope stage 3 evidence for the state of lake eyre at this time is equivocal preliminary results from a substantial suite of amino acid racemization aar analyses of mollusc shell and bird eggshell samples from beach ridges at 5 and 10 m australian height datum ahd suggest that they are oxygen isotope stage 5 in age sedimentologic evidence suggests that it is unlikely that the shells are reworked from older deposits these aar results apparently conflict with early oxygen isotope stage 3 thermoluminescence tl dates from the 5 m ahd beach ridge nanson et al this volume however the age difference is not substantial the calibration of the aar is still at a preliminary stage and only one site was sampled for both techniques further stratigraphic and chronologic work is required to fully assess the apparent discrepancy between about 30 000 and 12 000 yr b p lake eyre was at least as dry as it is today at many sites around madigan gulf a lunette like playa marginal aeolian unit the shelly island unit was deposited during this period formed by material deflated from the playa floor forty ams radiocarbon dates span the period 35 000 to 10 000 yr b p from the shelly island unit 11 and from aeolian sediment close to playa level 29 indicating that the lake was dry during this period this evidence conflicts strongly with 2 tl dates from latest oxygen isotope stage 3 and oxygen isotope stage 2 from the 5 and 10 m ahd beach ridges nanson et al this volume additionally the aar results from the high beach ridges cannot be reconciled with these tl dates after 10 000 yr b p a minor lacustral phase occurred until the modern ephemeral playa regime became established at 3000 4000 yr b p