middle to late holocene moisture changes in the desert of northwest namibia derived from fossil hyrax dung pollen new pollen results and radiocarbon dating from fossil hyrax middens derived from the edge of the northern namib desert address the shortage of continental palaeobotanical evidence in arid namibia by providing evidence for the environmental conditions during the mid to late holocene in the region the results obtained reflect long term stability in the area throughout most of the sequence higher than modern moisture availability is suggested between c 6 and 1 ka bp by the increased abundance of poaceae cyperaceae or chenopodiaceae which respond rapidly by flowering after modest quantities of rainfall around 1 ka and recently arid conditions seem to have prevailed with a decrease in poaceae and an increase in acanthaceae other palaeoecological evidence from the local and regional surroundings that focused on fluvial deposits marine palynology and mineralogy confirms this mid holocene increase in more effective rainfall

vegetation history and climate in the savanna biome south africa since 190 000 ka a comparison of pollen data from the tswaing crater the pretoria saltpan and wonderkrater abstract the long term quaternary vegetation and climate history in south africa s savanna biome since ca 190 000 yr bp is elucidated by the palynological record of lake sediments in the tswaing crater the pretoria saltpan and spring deposits from wonderkrater despite hiatuses in both sequences palaeotemperature trends from the two places are presented by means of principal components analysis pca of pollen data allowing a new regional palaeoenvironmental reconstruction correlation in the older sections of the sequences beyond radiocarbon dating is tentative suggesting that the wonderkrater sequence is roughly 4 times younger than the tswaing sequence combined temperature indications from the two sites suggest cooling at ca 14 000 yr bp and slight warming at ca 15 000 yr bp although no data are available between ca 15 000 and 21 000 and 25 000 and 31 000 yr bp generally cool conditions are suggested between ca 11 000 and 33 000 yr bp between ca 33 000 and an extrapolated age of ca 80 000 yr bp at least three warmer pulses of varying intensity occurred no data are available between ca 80 000 and 150 000 yr but between 150 000 and ca 190 000 yr bp two cool and two moderately warm phases are suggested

controls on sand ramp formation in southern namibia sand ramps have the potential to provide rich palaeoenvironmental information in dryland regions wherein proxy records are typically scarce however current knowledge of the geomorphic controls and processes of sand ramp formation is limited this study provides a data rich examination of the key factors controlling sand ramp formation the location and morphology of 75 sand ramps in southern namibia are examined the sediments and chronologies of 10 sand ramps are studied in detail using 51 osl dates and 83 grain size and loi samples heavy mineral assemblages are used to determine the provenance of 10 samples and osl sensitivity is used to explore geomorphic processes of 8 samples sand ramp morphology can be grouped into one of four classes of increasing size and complexity and is closely linked to the available accommodation space heavy mineral assemblages indicate local sediment sources and all 75 studied sand ramps are within 4 km of a large ephemeral river channel or within 5 5 km of a dune field therefore accommodation space and sediment supply are identified as the primary controls of sand ramp formation sedimentology and osl sensitivity suggest a complex interplay of aeolian fluvial and colluvial processes contribute to sand ramp formation with large variability observed between ramps three of the ten dated sand ramps have been present in the namibian landscape for 100 ka eight sand ramps show episodic deposition between 75 12 ka and five show evidence of surface reworking over the past 2 ka environmental sensitivity is likely to be linked to the size and availability of the accommodation space therefore individual sand ramps are expected to reflect local environmental conditions recording when an abundant sediment supply coincided with available accommodation space whilst a regional analysis of multiple sand ramps with chronometric data offers the potential to identify larger scale palaeoenvironmental controls of sediment supply

late quaternary paleotemperatures derived from a speleothem from cango caves cape province south africa abstract an oxygen isotope temperature record over a large part of the past 30 000 yr has been obtained for the southern cape province of south africa by combining data on the isotopic composition of a stalagmite from a deep cave with that of a confined groundwater aquifer in the same region results show that temperatures during the last glacial maximum were on average about 6 c lower than those today with peaks up to 7 c lower a detailed analysis of the past 5000 yr suggests multiple fluctuations with generally lower temperatures 1 2 c around 4500 and 3000 yr b p the carbon isotopic composition of the stalagmite indicates significant vegetation changes between the late pleistocene and today and also during the second half of the holocene

palynology of hyrax middens 2000 years of palaeoenvironmental history in namibia abstract well preserved and dateable faunal middens in rock shelters of dry areas in southern africa occur as desiccated urine rich masses under local conditions which exclude microbial decomposition and oxidation urine cements together faecal pellets and other inclusions nine radiocarbon dated hyrax procavia capensis dung middens from the kuiseb river basin of the namib desert were sub sampled and analysed for fossil pollen some contain small proportions of rat droppings but not many macro fossils comparative modern pollen in faecal samples were also studied most plant macro fossils are severely digested but seeds are well preserved some insect inclusions were identified small scale changes in vegetation over the last two millennia were observed representing environmental fluctuations in cycles of ca 100 200 years the fluctuations partly agree with other palynological data from southern africa and with geomorphologic evidence for environmental changes in the desert region

holocene aeolian activity in the southwestern kalahari desert southern africa significance and relationships to late pleistocene dune building events little is known about the timing of dune building episodes in the southwestern kalahari desert previously arid phases when dune activity occurred have been inferred from gaps in chronologies derived from information that attests to former humid periods to redress this optically stimulated luminescence osl dating was applied to sediment samples taken from a range of aeolian landforms in the sw kalahari four periods of dune building are identified in the late pleistocene and holocene holocene aeolian activity at 6 ka and 1 2 ka led to the construction of localised dune forms in contrast to late pleistocene times when the extensive field of linear dunes that dominates the region was emplaced late holocene aridity was however sufficient to allow rapid emplacement of the lunette dune at witpan the record of aeolian activity is evaluated in the context of humid chronologies and an ocean atmosphere model of holocene climate change with good agreement obtained it is concluded that the application of

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

the leaf wax biomarker record of a namibian salt pan reveals enhanced summer rainfall during the last glacial interglacial transition abstract conventional continental geoarchives are rarely available in arid southern africa therefore palaeoclimate data in this area are still patchy and late quaternary climate development is only poorly understood in the western kalahari salt pans playas ephemeral lakes are common and can feature quasi continuous sedimentation this study presents the first climate related biomarker record using sediments from the omongwa pan a kalahari salt pan located in eastern namibia our approach to reconstruct vegetation and hydrology focuses on biogeochemical bulk parameters and plant wax derived lipid biomarkers n alkanes n alkanols and fatty acids and their compound specific carbon and hydrogen isotopic compositions the presented record reaches back to 27 ka during the glacial rather low 2h values of n alkanes and low sediment input exclude a strong influence of winter rainfall n alkane and n alkanol distributions and 13c values of n hentriacontane n c31 indicate a shift to a vegetation with a higher proportion of c4 plants at the end of the last glacial maximum until the end of heinrich stadial i ca 18 14 8 ka which we interpret to indicate an abrupt excursion to a short wetter period likely to be caused by a temporary southward shift of the intertropical convergence zone shifts in 2h values of n c31 and plant wax parameters give evidence for changes to drier conditions during early holocene comparison of this dataset with representative continental records from the region points to a major influence of summer rainfall at omongwa pan during the regarded time span and demonstrates the potential of southern african salt pans as archives for biomarker based climate proxies

interpreting geoproxies of late quaternary climate change in african drylands implications for understanding environmental change and early human behaviour abstract climate and environmental change in the late quaternary are widely regarded as key drivers of early human development and dispersal in africa robust records of change are required to assess the nature of potential impacts today s late quaternary palaeoenvironmental palaeoclimate reconstructions from the interior southern african basin kalahari are more spatially detailed have a stronger chronometric underpinning and span a longer time range than those of 10 20 years ago but are no less controversial reconstructions for the last 150 ka are usually interpreted in terms of changes in hydrological balance from conditions more humid or more arid than today and expressed in climatological terms as the changing latitudinal interplay between monsoon easterlies and tropical and mid latitude westerlies with more data than ever before why then is the record not yet delivering a more coherent picture of regional climate change this paper deliberately addresses current challenges and controversies including issues often ignored or neglected with the view that it is essential to do so if more robust interpretations of the past are to be generated in the future sources of palaeo data from the interior are predominantly geoproxies reconstructions not based on highly resolved organic or isotope records but on interpretation of spatially extensive geomorphological proxies of past environments despite being increasingly datable using osl their inclusion in syntheses has proved complex not least when interpretations appear to conflict with records from other sources consequently they are sometimes removed from regional syntheses of climate change these omissions are often replaced by spatially exaggerated interpretations of higher quality local records allowing more spatially coherent timeslice interpretations to be presented yet this is counter intuitive to the spatial complexity of conditions present in the palaeoenvironmental proxies or in climatic and environmental systems today in addition the quest to link regional records to master records from ice and ocean cores can force interpretation within a temporal scale that may be inappropriate for their analysis underplaying the reality of complexity within the environmental system there are not necessarily good or bad records of terrestrial palaeoenvironments in interior southern africa rather there are records that contain different suites of information about past land surface hydrological and climate conditions preserved at temporal scales which can sometimes be incomparable consideration of these factors may resolve apparent conflicts between datasets resulting in a better understanding of past environmental dynamics and revealing the nature of environmental variability which may be a key facet to which human development has responded

interdune deposits of the namib sand sea abstract the namib sand sea of southwestern africa is dominated by large north south trending linear dunes interdune areas however comprise about 50 of the area of the sand sea and may consist of exposures of the pre dune surface or sediments deposited between the dunes four major types of interdune deposits are identified and described 1 1 coarse poorly sorted aeolian sands 2 2 localized calcareous lacustrine deposits 3 3 silty deposits of ephemeral rivers that have flooded into the sand sea margins 4 4 sabkhas and salt marshes near the coast the preservation potential of these sediments is poor except where they are buried and protected by dunes or stabilised by high groundwater levels in coastal areas

a paleohydrologic reinterpretation of the homeb silts kuiseb river central namib desert namibia and paleoclimatic implications abstract slack water deposits are usually fine grained fine sand and coarse silt flood sediments deposited in areas of the floodplain that are sheltered from high velocity flood flows slack water deposits have been recognized by many investigators in a wide variety of physiographic and climatic settings late quaternary slack water deposits have not been described from the extremely arid namib desert of southwestern africa fine grained flood sediments in the kuiseb valley near homeb accumulated between 23 000 and 19 000 14c years bp have been interpreted by previous workers as i sediments deposited behind dune dams ii river endpoint accumulations and iii flood deposits of an aggrading river controlled either by a base level change in the lower reaches or a change in the hydrological regime in the catchment area furthermore the so called homeb silts could document more arid climatic conditions in the kuiseb catchment area during the last glacial maximum lgm our research shows that the homeb silts are slack water deposits and that in many valleys of the namib desert slack water sediments are observed most commonly at the junctions of major rivers and minor tributaries in bedrock canyon settings here we present evidence that these slack water deposits accumulated as a result of more humid conditions and or more intense precipitation events in the upper reaches of the river they do not document climatic changes in the desert itself as postulated by many researchers

how dry was dry late pleistocene palaeoclimates in the namib desert abstract evidence for late quaternary changes in climate in the namib desert is geographically scattered and often poorly dated the available evidence suggests periods of increased river discharge and groundwater flow centered on 8 12 20 24 and 26 32 ka bp based on modern analogues these palaeohydrologic changes likely involved increased rainfall and runoff in the escarpment zone east of the desert there is little evidence to suggest significantly increased rainfall within the desert during these periods except perhaps during the interval prior to 26 ka bp these data reinforce earlier conclusions that the namib has experienced mostly arid to hyperarid conditions throughout the quaternary

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

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

rapid palaeoceanographic changes in the benguela upwelling system for the last 160 000 years as indicated by abundances of planktonic foraminifera abstract two sediment cores retrieved from the continental slope in the benguela upwelling system geob 1706 19 33 7 s 11 10 5 e and geob 1711 23 18 9 s 12 22 6 e reveal striking variations in planktonic foraminiferal abundances during the last 160 000 years these fluctuations are investigated to assess changes in the intensity and position of the upwelling centres off namibia four species make up over 95 of the variation within the core and enable the record to be divided into episodes characterized by particular planktonic foraminiferal assemblages the fossil assemblages have meaningful ecological significance when compared to those of the modern day and the relationship to their environment the cold water planktonic foraminifer neogloboquadrina pachyderma sinistral n pachyderma s dominates the modern day coastal upwelling centres and neogloboquadrina pachyderma dextral and globigerina bulloides characterize the fringes of the upwelling cells globorotalia inflata is representative of the offshore boundary between newly upwelled waters and the transitional reduced nutrient levels of the subtropical waters in the fossil record episodes of high n pachyderma s abundances are interpreted as evidence of increased upwelling intensity and the associated increase in nutrients the n pachyderma s record suggests temporal shifts in the intensity of upwelling and corresponding trophic domains that do not follow the typical glacial interglacial pattern periods of high n pachyderma s abundance describe rapid discrete events dominating isotope stages 3 and 2 the timing of these events correlates to the temporal shifts of the angola benguela front jansen et al 1997 situated to the north of the walvis ridge absence of high abundances of n pachyderma s from the continental slope of the southern cape basin indicates that southern ocean surface water advection has not exerted a major influence on the benguela current system the coincidence of increased upwelling intensity with the movement of the angola benguela front can be interpreted mainly by changes in strength and zonality of the trade wind system

late holocene environmental change in the northwestern namib desert margin new fossil pollen evidence from hyrax middens abstract the lack of anoxic environments in arid lands makes well preserved fossil pollen difficult to find the scarcity of continental palaeobotanical data in tropical arid zones restricts the understanding of aridification processes in these endangered ecosystems it is essential to improve the knowledge about their environmental histories during the holocene and therefore we attempt to investigate the causes and describe the patterns of vegetation change in northern namibia with that aim we analyzed pollen from fossil hyrax dung that accumulated over long periods of time by sampling stratigraphically coherent sequences in five radiocarbon dated middens the fossil hyrax middens were found in rock shelters on the eastern desert edge in the northwestern kaokoveld within the so called nama karoo biome this is an ecotonal area between the namib desert and the savanna biomes which reflects features from both systems and its life form composition largely depends on an erratic rainfall pattern thirty three samples were analyzed for pollen and the pollen record reflects a non continuous vegetation history over the last 5200 yr with a hiatus between ca 4200 and 1690 yr bp the pollen spectra reflect arid savanna vegetation with a marked increase in the tree grass ratio from ca 1300 cal yr bp the most likely cause for this change is a decline in moisture that we relate to intrinsic savanna dynamics with early pastoralism megahervibore migration and changes in the hyrax diet playing a minor role

50 000 years of vegetation and climate change in the southern namib desert pella south africa abstract this paper presents the first continuous pollen record from the southern namib desert spanning the last 50 000 years obtained from rock hyrax middens found near the town of pella south africa these data are used to reconstruct vegetation change and quantitative estimates of temperature and aridity results indicate that the last glacial period was characterised by increased water availability at the site relative to the holocene changes in temperature and potential evapotranspiration appear to have played a significant role in determining the hydrologic balance the record can be considered in two sections 1 the last glacial period when low temperatures favoured the development of more mesic nama karoo vegetation at the site with periods of increased humidity concurrent with increased coastal upwelling both responding to lower global regional temperatures and 2 the holocene during which time high temperatures and potential evapotranspiration resulted in increased aridity and an expansion of the desert biome during this latter period increases in upwelling intensity created drier conditions at the site considered in the context of discussions of forcing mechanisms of regional climate change and environmental dynamics the results from pella stand in clear contrast with many inferences of terrestrial environmental change derived from regional marine records observations of a strong precessional signal and interpretations of increased humidity during phases of high local summer insolation in the marine records are not consistent with the data from pella similarly while high percentages of restionaceae pollen has been observed in marine sediments during the last glacial period they do not exceed 1 of the assemblage from pella indicating that no significant expansion of the fynbos biome has occurred during the last 50 000 years these findings pose interesting questions regarding the nature of environmental change in southwestern africa and the significance of the diverse records that have been obtained from the region

reconstruction of se trade wind intensity based on sea surface temperature gradients in the southeast atlantic over the last 25 kyr 1 a prominent feature in the southeast atlantic is the angola benguela front abf the convergence between warm tropical and cold subtropical upwelled waters at present the sea surface temperature sst gradient across the abf and its position are influenced by the strength of southeasterly se trade winds here we present a record of changes in the abf sst gradient over the last 25 kyr variations in this sst contrast indicate that periods of strengthened se trade wind intensity occurred during the last glacial maximum the younger dryas and the mid to late holocene while heinrich event 1 the early part of the bolling allerod and the early holocene were periods of weakened se trade winds

southeast african records reveal a coherent shift from high to low latitude forcing mechanisms along the east african margin across last glacial interglacial transition abstract late quaternary climate variability in the southern african subtropics is still only poorly resolved with significant complexity and apparent contradictions in the regional dataset to more effectively interpret and synthesize key regional records we reanalysed the data from 13 pollen sequences from the summer rainfall zone of south africa spanning the last 45 000 years obtaining directly comparable quantitative reconstructions of mean annual temperature and summer rainfall temperature reconstructions from across the region provide consistent results with all sites reflecting trends observed in southwest indian ocean sea surface temperatures in the adjacent mozambique channel precipitation reconstructions are more heterogeneous with two distinct subregions being identified in the northeast long term trends in precipitation are determined by sea surface and continental temperature trends revealing a positive relationship between temperature and rainfall this long term pattern appears to be primarily driven by high northern latitude mechanisms with direct local insolation being subordinate their relative impact reversed during terminal glacial period early holocene at which time direct insolation forcing became the main driver of rainfall variability further south in central south africa precipitation variability appears also to be influenced by the latitudinal position of the southern hemisphere westerlies which combine with tropical flow to create tropical temperate trough advecting moisture into the interior in this region periods of maximum precipitation coincide with periods of elevated ssts and equatorward expansions of the westerly storm track this study allows for a fully constrained understanding of climate dynamics along the eastern african margin for the last 45 000 years linking dynamics to drivers and describing how the climate systems evolved across the last glacial interglacial transition

climatic forcing of cyclic carbonate sedimentation during the last 5 4 million years along the west florida continental margin abstract ocean drilling project odp hole 625b from 890 m water on the west florida carbonate ramp slope provides a continuous 235 m long record of cyclic sedimentation responding to global climatic change and regional tectonics over the past 5 4 ma relatively rapid sedimentation rates 5 cm 1000 yr and a 30 cm sampling interval 6 10 000 yr permit a high resolution investigation of milankovitch influenced carbonate sedimentation on a continental margin total carbonate percent coarse 63 m and oxygen isotope data exhibit good correlation with established mid and late pleistocene composite records indicating that the climate signal recorded on the west florida slope closely parallels the global climate signal obtained from deep sea sediments a high amplitude low frequency 100k yr eccentricity signal of the past 800k yr is unique within the 5 4 ma record of total carbonate and percent coarse prior to this the data are characterized by lower amplitude variations and less regular periodicities the interval from 0 8 to 2 8 ma consists of low amplitude fluctuations with periodicities widely distributed in the obliquity band 30 60k yr from 2 8 to 5 4 ma the data show larger amplitude aperiodic variations sedimentation from the present to 2 8 ma was controlled primarily by sea level fluctuations associated with changing global ice volumes during periods of lowered sea level fine grained terrigenous sediments from the mississippi and other rivers diluted the end page 1070 indigenous pelagic carbonate sediments of the west florida slope the interval from 0 8 to 2 8 ma differs from the late quaternary in that smaller sea level oscillations and less extensive north american ice sheets resulted in smaller amplitude sediment cycles sediments older than 2 8 ma record aperiodic fluctuations caused perhaps by loop current circulation responding to the final closing of the isthmus of panama between 3 5 and 4 0 ma intensified circulation may have transported and redeposited terrigenous sediments from the mississippi delta fan to the west florida carbonate ramp creating high amplitude but aperiodic sediment cycles this study demonstrates that milankovitch orbital variations can create well developed primary pelagic sedimentary cycles on continental margins and that such cycles are not restricted to the very deep sea the data from odp 625b in conjunction with other contemporaneous cores from contrasting settings provide the opportunity to obtain a quantitative understanding of the interactions between external orbital forcing climate and continental margin sedimentation

a north to south transect of holocene southeast atlantic continental margin sediments relationship between aerosol transport and compound specific δ13c land plant biomarker and pollen records 1 we examined near surface late holocene deep sea sediments at nine sites on a north south transect from the congo fan 4 s to the cape basin 30 s along the southwest african continental margin contents distribution patterns and molecular stable carbon isotope signatures of long chain n alkanes c27 c33 and n alkanols c22 c32 are indicators of land plant vegetation of different biosynthetic types which can be correlated with concentrations and distributions of pollen taxa in the same sediments calculated clusters of wind trajectories and satellite aerosol index imagery afford information on the source areas for the lipids and pollen on land and their transport pathways to the ocean sites this multidisciplinary approach on an almost continental scale provides clear evidence of latitudinal differences in lipid and pollen composition paralleling the major phytogeographic zonations on the adjacent continent dust and smoke aerosols are mainly derived from the western and central south african hinterland dominated by deserts semi deserts and savannah regions rich in c4 and cam plants the northern sites congo fan area and northern angola basin which get most of their terrestrial material from the congo basin and the angolan highlands may also receive some material from the chad region very little aerosol from the african continent is transported to the most southerly sites in the cape basin as can be expected from the present position of the phytogeographic zones the carbon isotopic signatures of the n alkanes and n alkanols both become isotopically more enriched in 13c from north to south the results of the study suggest that this combination of pollen data and compound specific isotope geochemical proxies can be effectively applied in the reconstruction of past continental phytogeographic developments

forcing of wet phases in southeast africa over the past 17 000 years a continuous record of hydrologic variability for the past 17 000 years at the mouth of the zambezi river shows that hydrologic conditions in southeast africa were controlled by variations in local insolation and migrations of the intertropical convergence zone rather than by indian ocean temperature records of hydroclimatological variability in southern africa since the last glacial maximum have produced a conflicting picture of the relative influences of events in the remote northern hemisphere and the more local indian ocean this paper presents a continuous record of hydrological variability for the past 17 000 years from marine sediment core drilled off the mouth of the zambezi river the record shows that hydrological conditions in the region were influenced by variations in local insolation and migrations of the intertropical convergence zone which were probably driven by events in the northern hemisphere rather than the indian ocean intense debate persists about the climatic mechanisms governing hydrologic changes in tropical and subtropical southeast africa since the last glacial maximum about 20 000 years ago in particular the relative importance of atmospheric and oceanic processes is not firmly established1 2 3 4 5 southward shifts of the intertropical convergence zone itcz driven by high latitude climate changes have been suggested as a primary forcing2 3 whereas other studies infer a predominant influence of indian ocean sea surface temperatures on regional rainfall changes4 5 to address this question a continuous record representing an integrated signal of regional climate variability is required but has until now been missing here we show that remote atmospheric forcing by cold events in the northern high latitudes appears to have been the main driver of hydro climatology in southeast africa during rapid climate changes over the past 17 000 years our results are based on a reconstruction of precipitation and river discharge changes as recorded in a marine sediment core off the mouth of the zambezi river near the southern boundary of the modern seasonal itcz migration indian ocean sea surface temperatures did not exert a primary control over southeast african hydrologic variability instead phases of high precipitation and terrestrial discharge occurred when the itcz was forced southwards during northern hemisphere cold events such as heinrich stadial 1 around 16 000 years ago and the younger dryas around 12 000 years ago or when local summer insolation was high in the late holocene that is during the past 4 000 years

fossil hyrax dung and evidence of late pleistocene and holocene vegetation types in the namib desert abstract pollen was derived from fossil dung of herbivorous hyraxes deposited in a rock shelteron the highest mountain in namibia da ures or brandberg situated on the namib desert margin radiocarbon dating ranging in age between modern times and 30000yrbp showed it representsthe rst empirical pollen evidence of continental palaeovegetation during the late pleistocene alongthe western escarpment of southern africa the initial results indicate last glacial maximum vegeta tion differed totally from the current pattern as vegetation types were dominated by small asteraceaeshrubs in contrast to those of the holocene and modern times which show more succulents grassandwoody elements arboreal pollen the resultssuggest that cape oral communities didnot reachinto thetropics along thewestern escarpment ofafrica despite such pollentypes occurring inmarinecores copyright 2004 john wiley sons ltd keywords palynology namibia restionaceae late pleistocene last glacial maximum

rock hyrax middens a palaeoenvironmental archive for southern african drylands abstract like many of the world s subtropical regions southern africa is highly sensitive to changes in the earth s climate system but a dearth of reliable palaeoenvironmental records means that relatively little is known about how regional environments have been affected over centennial to multi millennial timescales to a large extent this sensitivity is a function of the position of these regions at the interface between temperate and tropical circulation systems the resulting seasonality and irregularity of rainfall have limited the development of suitable archives such as lakes and wetlands for the preservation of palaeoenvironmental proxies this paper reviews and evaluates the value of rock hyrax middens as novel palaeoenvironmental archives in southern africa considered are 1 the contemporary taxonomy distribution and ecology of hyraxes 2 the mechanisms of hyrax midden development their physical and chemical structure rates of accumulation and age and 3 the palaeoenvironmental proxies preserved within hyrax middens including fossil pollen stable isotopes and biomarkers the interpretive constraints and opportunities offered by these various midden characteristics are assessed with a view to demonstrating the potential of these deposits widespread as they are through arid and semi arid southern africa in providing a more detailed and chronologically resolved view of late quaternary palaeoenvironments across the subcontinent

palaeoenvironmental conditions in south africa at the pleistocene holocene transition abstract palaeoenvironmental records which include the interval between 11 000 and 10 000 bp have been investigated for 15 sites in south africa less than half of them are well dated and have a resolution adequate for elucidating climatic conditions during the time of the younger dryas a sea surface temperature record from a marine mollusc sequence provides the only unequivocal evidence of cooling during this time none of the palynological sequences from the interior of the subcontinent suggest consistent deviations in temperature or moisture attributable to a younger dryas equivalent based on the available evidence therefore it seems that if global younger dryas conditions influenced the climate of south africa the effect was too small to register a spatially consistent pattern in the pollen sequences of the interior of the country

multiphase late quaternary aeolian sediment accumulation in western south africa timing and relationship to palaeoclimatic changes inferred from the marine record abstract extensive aeolian deposits exist along the western margin of south africa from cape town through to the namib sand sea and represent a significant palaeoenvironmental archive recording millennial scale patterns of regional and hemispheric environmental change to establish the timing of dune development this study applies optically stimulated luminescence osl dating techniques to the aeolian features of the west coast in total 35 samples were obtained from six dune cores along a north south transect extending from elands bay 32 26 s 18 14 e to kleinsee 29 14 s 16 59 e ages from these dunes exhibit five distinct peaks suggesting phases of activity deposition at 4 5 16 24 30 33 43 49 and 63 73 ka the spatial and temporal extent of the data have allowed for correlations to be made with evidence from marine cores from the southeast atlantic and a more coherent regional environmental history to be developed results suggest that 1 environmental changes in this region are strongly linked to variations in wind strength and atmospheric circulation systems during the late quaternary and 2 luminescence ages from aeolian deposits cannot necessarily be equated with periods of increased aridity with other factors such as wind strength and sediment supply being of critical importance

orbital forcing of climate over south africa a 200 000 year rainfall record from the pretoria saltpan late pleistocene variations in rainfall in subtropical southern african are estimated from sediments preserved in the pretoria saltpan a 200000 year old closed basin crater lake on the interior plateau of south africa we show that south african summer rainfall covaried with changes in southern hemisphere summer insolation resulting from orbital precession as predicted by orbital precession geometry berger 1978 this south african record is out of phase with north african palaeomonsoon indices street and grove 1979 rossignol strick 1983 mcintyre et al 1989 the amplitude of the rainfall response to insolation forcing agrees with climate model estimates prell and kutzbach 1987 these results document the importance of direct orbital insolation forcing on both subtropical north and south african climate as well as the predicted antiphase sensitivity to precessional insolation forcing

orbital and millennial antarctic climate variability over the past 800 000 years a high resolution deuterium profile is now available along the entire european project for ice coring in antarctica dome c ice core extending this climate record back to marine isotope stage 20 2 800 000 years ago experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation we assessed the general correspondence between dansgaard oeschger events and their smoothed antarctic counterparts for this dome c record which reveals the presence of such features with similar amplitudes during previous glacial periods we suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records

late quaternary dynamics of southern africa s winter rainfall zone abstract variations in the nature and extent of southern africa s winter rainfall zone wrz have the potential to provide important information concerning the nature of long term climate change at both regional and hemispheric scales positioned at the interface between tropical and temperate systems southern africa s climate is influenced by shifts in the intertropical convergence zone the westerlies and the development and position of continental and oceanic anticyclones over the last glacial interglacial cycle substantial changes in the amount and seasonality of precipitation across the subcontinent have been linked to the relative dominance of these systems central to this discussion has been the extent to which the region s glacial climates would have been affected by expansions of antarctic sea ice equatorward migrations of the westerlies more frequent intense winter storms and an expanded wrz this paper reviews the developing body of evidence pertaining to shifts in the wrz and the evolution of ideas that have been presented to explain the patterns observed dividing the region into three separate axes along the western and southern margins of the continent and across the interior into the karoo and the kalahari a range of evidence from both terrestrial sites and marine cores is considered and potential expansions of the wrz expansions are explored despite the limitations of many of the region s proxy records a coherent pattern has begun to develop of a significantly expanded wrz during phases of the last glacial period with the best documented being between 32 17 ka while more detailed inferences will require the recovery and analysis of longer and better dated records this synthesis provides a new baseline for further research in this key region

new chronological evidence for the nature and timing of linear dune development in the southwest kalahari desert abstract the age of the linear dunes in the southwest kalahari desert has not previously been directly established by applying the optical dating method to samples from the dunefield a number of questions relating to the timing and nature of linear dune development are addressed the last major period of simple linear dune development occurred 17 000 10 000 years ago probably from the reworking of earlier aeolian sediments dune emplacement occurred under more arid probably windier conditions than those prevailing today which are only responsible for episodic surficial dune sand movement as well as simple linear dunes the dunefield also contains more complex linear dune patterns samples from one area in the eastern dunefield demonstrate that multi phase development is more probable for complex dune patterns as opposed to single phase evolution under a complex wind regime

late quaternary highstands at lake chilwa malawi frequency timing and possible forcing mechanisms in the last 44 ka the extensive shoreline deposits of lake chilwa southern malawi a shallow water body today covering 600 km2 of a basin of 7500 km2 are investigated for their record of late quaternary highstands osl dating applied to 36 samples from five sediment cores from the northern and western marginal sand ridges reveal a highstand record spanning 44 ka using two different grouping methods highstand phases are identified at 43 7 33 3 ka 26 2 21 0 ka and 17 9 12 0 ka total error method or 38 4 35 5 ka 24 3 22 3 ka 16 2 15 1 ka and 13 5 12 7 ka finite mixture model age components with two further discrete events recorded at 11 01 0 76 ka and 8 52 0 56 ka highstands are comparable to the timing of wet phases from other basins in east and southern africa demonstrating wet conditions in the region before the lgm which was dry and a wet lateglacial which commenced earlier in the southern compared to northern hemisphere in east africa we find no evidence that wet phases are insolation driven but analysis of the dataset and gcm modelling experiments suggest that heinrich events may be associated with enhanced monsoon activity in east africa in both timing and as a possible causal mechanism

late quaternary linear dune accumulation and chronostratigraphy of the southwestern kalahari implications for aeolian palaeoclimatic reconstructions and predictions of future dynamics abstract the linear dunes of the kalahari now largely inactive have long been identified as having potential palaeoenvironmental significance the application of optically stimulated luminescence osl dating to these dunes in the 1990s provided the first chronology of aeolian accumulation in this region though field methodologies and time consuming multiple aliquot laboratory protocols limited both the depth of sampling in dune bodies and the total number of samples dated in order to permit a more thorough investigation of the potential of these dunes to preserve long chronological records this intensive study presents 71 osl ages from the linear dunes of the southwestern kalahari at witpan south africa sampled with coring equipment at regular and frequent intervals down to bedrock the earliest sand accumulation recorded at witpan is at 104 ka and in spatially discrete locations other evidence of dune activity is recorded at 77 76 57 52 and 35 27 ka although an inherently discontinuous archive the linear dunes of the southwestern kalahari have the potential to record multiple phases of dune construction following the last glacial maximum there is near continuous evidence of dune building with a peak of accumulation recorded from 15 to 9 ka at five individual sites this latter period is generally recognised from other proxy evidence as being unusually arid in this region and such periods of dune activity are likely to be related to intensification of the continental anticyclone during the holocene accumulation has continued at most sites sampled albeit at a lesser intensity this may imply that these dunes are presently not far from thresholds of activation

late quaternary dune accumulation along the western margin of south africa distinguishing forcing mechanisms through the analysis of migratory dune forms abstract the west coast of south africa is situated at a critical location between temperate and subtropical oceanic and atmospheric circulation systems and palaeoenvironmental proxies from this region have the potential to elucidate issues concerning variations within these systems over glacial interglacical cycles while semi arid climates have hindered the preservations of organic proxies a variety of aeolian bedforms have been analysed in an effort to improve our understanding of environmental change in the region optically stimulated luminescence measurements of 51 samples from 15 reticulate dune sites along the west coast have enabled the identification of phases of aeolian activity as well as periods of relative geomorphic stability combined with data derived from previous studies of the region s sediment accumulating deposits and other palaeoenvironmental proxies periods of increased windiness are identified at 16 24 30 33 43 49 and 63 73 ka from approximately 17 12 ka decreasing transport capacity resulted in the stabilisation of the west coast s dune fields during the holocene altithermal 4 8 ka despite reduced wind strength increased aridity resulting from higher temperatures and a reduced influence of moisture bearing westerly systems appears to have trigged widespread remobilisation of the region s dune fields the combination of ages from a variety of dune forms with different development mechanisms and comparisons with a range of proxy data sources have allowed for an enhanced interpretation of the region s aeolian archives moving beyond simple correlations between dune activity and aridity

sources transport and deposition of terrestrial organic material a case study from southwestern africa abstract southwestern africa s coastal marine mudbelt a prominent holocene sediment package provides a valuable archive for reconstructing terrestrial palaeoclimates on the adjacent continent while the origin of terrestrial inorganic material has been intensively studied the sources of terrigenous organic material deposited in the mudbelt are yet unclear in this study plant wax derived n alkanes and their compound specific 13c in soils flood deposits and suspension loads from regional fluvial systems and marine sediments are analysed to characterize the origin of terrestrial organic material in the southwest african mudbelt soils from different biomes in the catchments of the orange river and small west coast rivers show on average distinct n alkane distributions and compound specific 13c values reflecting biome specific vegetation types most notably the winter rainfall associated fynbos biome of the southwestern cape in the fluvial sediment samples from the orange river changes in the n alkane distributions and compound specific 13c compositions reveal an overprint by local vegetation along the river s course the smaller west coast rivers show distinct signals reflecting their small catchment areas and particular vegetation communities marine surface sediments spanning a transect from the northern mudbelt 29 s to st helena bay 33 s reveal subtle but spatially coherent changes in n alkane distributions and compound specific 13c indicating the influence of orange river sediments in the northern mudbelt the increasing importance of terrigenous input from the adjacent western coastal biomes in the central mudbelt and contributions from the fynbos biome to the southern mudbelt these findings indicate the different sources of terrestrial organic material deposited in the mudbelt and highlight the potential the mudbelt has to preserve evidence of environmental change from the adjacent continent

linear dune accumulation chronologies from the southwest kalahari namibia challenges of reconstructing late quaternary palaeoenvironments from aeolian landforms abstract the linear dunes of the southern kalahari dunefield constitute one of the major palaeoenvironmental proxies in the region the application of optically stimulated luminescence osl dating since the1990s and advancements in the depth of sampling using augering equipment over the past few years have permitted the reconstruction of linear dune accumulation chronostratigraphies for entire dune profiles from base to crest these methods are applied to four dunes in the mariental stampriet region of the southern kalahari dunefield sampled at predominantly 0 5 m intervals individual dunes record multiple phases of dune construction but with only a few phases recorded consistently between two or more of the dunes results from the 48 osl ages produced here extend the aeolian accumulation record for the southern kalahari dunefield through the last three glacial interglacial cycles with two ages from the early part of mis6 a synthesis of all existing luminescence ages for the southern kalahari reveals that the dunefield has been partially active throughout much of the past 120 ka there are no clear clusters of ages within osl age errors this is in contrast to previous syntheses of ages for this region in addition these new data from mariental stampriet dunes show that clusters in grouped dune osl ages can be spuriously produced as a function of reducing the sampling frequency with depth within the dunes from 0 5 to 1 mintervals this has significant implications for previous conclusions regarding discrete phases of aeolian accumulation based on sampling at 1 m intervals and less vertically intensive sampling techniques the total luminescence data set of 136 ages for the southern kalahari implies that this dunefield has been close to the threshold of reactivation throughout much of the late quaternary

stratigraphic charcoal analysis on petrographic thin sections application to fire history in northwestern minnesota results of stratigraphic charcoal analysis from thin sections of varved lake sediments have been compared with fire scars on red pine trees in northwestern minnesota to determine if charcoal data accurately reflect fire regimes pollen and opaque spherule analyses were completed from a short core to confirm that laminations were annual over the last 350 yr a good correspondence was found between fossil charcoal and fire scar data individual fires could be identified as specific peaks in the charcoal curves and times of reduced fire frequency were reflected in the charcoal data charcoal was absent during the fire suppression era from 1920 a d to the present distinct charcoal maxima from 1864 to 1920 occurred at times of fire within the lake catchment fire was less frequent during the 19th century and charcoal was substantially less abundant fire was frequent from 1760 to 1815 and charcoal was abundant continuously fire scars and fossil charcoal indicate that fires did not occur during 1730 1750 and 1670 1700 several fires occurred from 1640 to 1670 and 1700 to 1730 charcoal counted from pollen preparations in the area generally do not show this changing fire regime simulated sampling of the thin section data in a fashion comparable to pollen slide methods suggests that sampling alone is not sufficient to account for differences between the two methods integrating annual charcoal values in this fashion still produced much higher resolution than the pollen slide method and the postfire suppression decline of charcoal characteristic of my method but not of pollen slides is still evident consideration of the differences in size of fragments counted by the two methods is necessary to explain charcoal representation in lake sediments

pollen in fossil hyrax dung from marine isotope stages 2 and 3 reveals past environments in namibia abstract in view of a scarcity of terrestrial quaternary pollen records relating to climate change in desert areas we present new terrestrial sequences from hyrax middens in namibia while the few previously available pollen records are mainly holocene we present climate time series for marine isotope stages 2 and 3 mis 2 and mis 3 the data are from two sites in central namibia that are surrounded by desert plains and close to the namibian escarpment viz the d ures massif brandberg and 200 km further south the mirabib shelter located in a small inselberg in the studied material grass rich pollen assemblages were more common at mirabib where the vegetation is desert grassland than at brandberg with its mountain vegetation hyrax radiocarbon ages range from 21 ka to 50 ka with inconsistencies in ages near the limit of effective radiocarbon dating however correlation of overlapping sequences supports the chronology we present despite chronological gaps in the available deposits pollen assemblages from different middens indicate marked climate cycles starting with moderately cool dry conditions with grassy karroid vegetation at mirabib c 50 ka after a gap in the record warmer conditions with savanna woodland are indicated at both mirabib and brandberg around 40 ka eventually cool conditions supporting shrubby grassland with wild olives developed at brandberg during mis 2 c 21 ka comparison with marine pollen data confirms earlier findings that terrestrial pollen assemblages differ markedly from south atlantic ocean marine pollen assemblages of the same age presumably due to mixing of pollen from wide source areas at the marine localities versus the more locally restricted terrestrial pollen sources trapped in hyrax dung the results therefore add information for the interpretation of local vegetation shifts on land during the interval between 50 ka and 21 ka in namibia

climate variability in the botswana kalahari from the late pleistocene to the present day 1 noble gas concentrations and oxygen isotopes in groundwaters from the kalahari desert in botswana contain a 45 ka paleotemperature record indicating that mean annual temperatures during the period from 24 ka bp to 45 ka bp were 5 2 1 5 c cooler than from 16 ka to the present day in addition to enrichments in oxygen 18 groundwaters recharged after 16 ka bp also contain higher concentrations of excess air entrained air bubbles taken together the noble gas oxygen isotope and excess air based paleoclimate archives provide evidence that the high interior desert of southern africa was both cooler and dryer prior to the last glacial maximum lgm cool dry conditions also suggest a weaker hydrological cycle in southern africa this is contrary to the predicted enhancement of monsoon strength by increased summer insolation in the southern tropics induced by orbital precession during the lgm

quantification of climate change for the last 20 000 years from wonderkrater south africa implications for the long term dynamics of the intertropical convergence zone abstract in southeast africa a region for which few palaeoenvironmental records are available the fossil pollen record from the wonderkrater spring mound has contributed substantially to our understanding of past vegetation change since the last glacial maximum lgm 21 ka multivariate analysis of the pollen data by scott and thackeray 1987 provided environmental reconstructions suggesting relatively mesic lgm conditions with warm and dry conditions during the early holocene 11 6 cal kbp this conforms to predicted patterns of precipitation change in the southern african tropics in response to northern hemisphere cooling and orbital forcing subsequent data from the cold air cave speleothems and a sea surface temperature record from the mozambique channel however indicate that conditions during the early to mid holocene may have been wetter than present in the wonderkrater region to explore this question further we have created a series of botanical climatological transfer functions based on a combination of modern climate and plant distribution data from southern africa applying these to the wonderkrater fossil pollen sequence we have derived quantitative estimates for temperatures during the cold and warm quarters as well as precipitation during the wet and dry quarters in addition a species selection method based on bayesian statistics is outlined which provided a parsimonious choice of likely plant species from what are otherwise taxonomically broad pollen types we do not propose that our findings invalidate the previous principal component analyses but they do have the advantage of being based more clearly on the relationship between modern plant distributions and individual climatic variables results indicate that temperatures during both the warm and cold seasons were 6 2 c colder during the lgm and younger dryas and that rainy season precipitation during the last glacial maximum was 50 of that during the mid holocene our results also imply that changes in precipitation at wonderkrater generally track changes in mozambique channel sea surface temperatures with a steady increase following the younger dryas to a period of maximum water availability at wonderkrater 3 7 ka these findings argue against a dominant role of a shifting intertropical convergence zone in determining long term environmental trends and indicate that the northern and southern tropics experienced similar climatic trends during the last 20 kyr

a record of rapid holocene climate change preserved in hyrax middens from southwestern africa the discovery of sensitive paleoenvironmental proxies contained within fossilized rock hyrax middens from the margin of the central namib desert africa is providing unprecedented insight into the region s environmental history high resolution stable carbon and nitrogen isotope records spanning 0 11 700 cal calibrated yr b p indicate phases of relatively humid conditions from 8700 7500 6900 6700 5600 4900 and 4200 3500 cal yr b p with a period of marked aridity occurring from 3500 until ca 300 cal yr b p transitions between these phases appear to have occurred very rapidly often within 200 years of particular importance are 1 the observed relationship between regional aridifi cation and the decline in northern hemisphere insolation across the holocene and 2 the signifi cance of suborbital scale variations in climate that covary strongly with fl uctuations in solar forcing together these elements call for a fundamental reexamination of the role of orbital forcing on tropical african systems and a reconsideration of what factors drive climate change in the region the quality and resolution of these data far surpass any other evidence available from the region and the continued development of this unique archive promises to revolutionize paleoenvironmental studies in southern africa

holocene environmental changes in namibia inferred from pollen analysis of swamp and lake deposits spring deposits exposed during building operations in downtown windhoek and lake sediments retrieved from underneath 50 m of water in a sinkhole lake otjikoto contain pollen profiles which reflect environmental changes in namibia during the holocene at windhoek moist local conditions are reflected by pollen in the spring deposits which were radiocarbon dated to between ca 7000 and 6000 bp they remained relatively favourable until 5630 bp despite signs of drying weedy compositae lactucoideae or liguliflorae increased until the end of this record ca 2410 bp indicating local disturbance deposits from lake otjikoto were dated to the late holocene although an accurate chronology could not be estabiished for the sequence due to unexpected results with radiocarbon measurements pollen accumulation values and composition indicate relatively dry conditions after 3500 bp which were followed temporarily by a wetter climate during more recent times

paleolimnology of a shrub tundra lake and response of aquatic and terrestrial indicators to climatic change in arctic quebec canada to better understand past aquatic ecosystems and their development a 99 cm sediment core was extracted from a shrub tundra lake in northern quebec fossil chironomids diatoms and pollen were analysed at 1 0 cm intervals several inference models based on chironomids and diatoms were used to reconstruct lake water conditions surface water temperature dissolved organic carbon doc alkalinity and water colour for the last 6700 cal yr reconstructed water temperatures varied between 10 3 and 17 6 8c with a cooling trend since at least 1500 cal yr bp doc concentrations increased with the establishment of terrestrial vegetation in the lake s catchment and decreased with the onset of the late holocene cooling trend lake water alkalinity was higher during the lake s early history and decreased throughout its postglacial development whereas water colour remained at fairly low levels throughout the entire record our results suggest that aquatic organisms directly influenced by temperature chironomids reacted most rapidly to climatic changes whereas terrestrial vegetation pollen reacted with a slight lag the vegetation succession in the catchment had subsequent impacts on the composition of runoff waters and hence on other aquatic organisms diatoms d 2004 elsevier b v all rights reserved

depositional environment and osl chronology of the homeb silt deposits kuiseb river namibia previous studies suggest that the homeb silts of the kuiseb valley namibia i accumulated in a dune dammed lake ii are end point deposits iii represent an aggrading river bed and iv are slackwater deposits thus they have been used alternatively as evidence of past drier conditions or past wetter conditions lithostratigraphic analysis of two sediment sequences at homeb indicates sedimentation by aggradation of the kuiseb river triggered by a transition from an arid to humid climate osl ages for the sequences were obtained by the sar protocol on aliquots of 9 6 mm and 4 0 mm diameter and on single grains four millimeter aliquot minimum ages closely approximate the single grain minimum ages and are younger than 9 6 mm aliquot minimum and central ages based on these results the small aliquot 4 mm approach appears to provide ages comparable to those obtained by the more laborious and time consuming single grain method minimum ages indicate rapid deposition of the homeb silts in at least two episodes centered at 15 ka and 6 ka during climate transitions from arid to humid flash floods eroded the valley fills during slightly more arid conditions

lacustrine sediments at narabeb in the central namib desert namibia abstract deep within the hyper arid namib desert at narabeb which is today isolated by 100 m high linear dunes is a 36 m section of lacustrine mudstones and interbedded sands the slightly calcareous and laminated sands of this sequence are composed mainly of rounded to subrounded lightly stained quartz that is similar to the sands of the underlying tertiary tsondab sandstone formation and the surrounding dunes of the namib sand sea the six calcareous mudstone units in this sequence are variably laminated and sandy contain halite filled fractures and have been radiocarbon dated at 20 000 26 000 yr b p the interrelationship of sediments at this site with middle to early stone age implements suggests an age of more than 20 000 years whereas 234u 230th dating of the basal mudstone gave an age of 210 000 260 000 yr b p the calcareous mudstones were deposited in a lake at the former end point of the tsondab river which was prevented from reaching the atlantic ocean by n s trending linear dunes of the namib sand sea the interbedded sands were deposited during low water or dry stages of the lake sometime before 14 000 yr b p the terminus of the tsondab river shifted eastward from narabeb in response to the northward encroachment of linear dunes and the present end point was eventually established at tsondab vlei 38 km to the east lacustrine deposition at narabeb just as at tsondab vlei today probably occurred mainly in response to precipitation in the headwaters of the tsondab river although no major climatic change is necessary to explain the sequence at narabeb the clustering of radiocarbon dates on carbonate from the namib desert in the periods 20 000 35 000 yr b p and 10 000 14 000 yr b p suggests an increase in precipitation during those times

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

age and dynamics of linear dunes in the namib desert bristow c s duller g a t lancaster n 2007 age and dynamics of linear dunes in the namib desert geology 35 6 555 558 sponsorship american chemical society

optical age estimates for hyper arid fluvial deposits at homeb namibia abstract two 25 m sequences of slack water facies sediments have been dated in the kuiseb river in namibia by optical dating of sand sized quartz grains the eight samples indicate the sediments were deposited between 6 3 and 9 8 ka this revises previous age estimates for the homeb silts according to our criteria six out of eight samples displayed characteristics of partial bleaching this result was not unexpected as arid fluvial systems have high suspended sediment concentrations short flow durations and a tendency for flow peaks to occur at night

evidence for progressive holocene aridification in southern africa recorded in namibian hyrax middens implications for african monsoon dynamics and the african humid period abstract presented here are stable nitrogen isotope data from a rock hyrax procavia capensis middens from northwestern namibia that record a series of rapid aridification events beginning at ca 3800 cal yr bp and which mark a progressive decrease in regional humidity across the holocene strong correlations exist between this record and other terrestrial and marine archives from southern africa indicating that the observed pattern of climate change is regionally coherent combined these data indicate hemispheric synchrony in tropical african climate change during the holocene with similar trends characterising the termination of the african humid period ahp in both the northern and southern tropics these findings run counter to the widely accepted model of direct low latitude insolation forcing which requires an anti phase relationship to exist between the hemispheres the combined dataset highlights 1 the importance of forcing mechanisms influencing the high northern latitudes in effecting low latitude climate change in africa and 2 the potential importance of solar forcing and variations in the earth s geomagnetic shield in determining both long term and rapid centennial scale climate changes identifying a possible mechanism for the variations marking the ahp termination in both the southern and northern tropics

evolving southwest african response to abrupt deglacial north atlantic climate change events abstract climate change during the last deglaciation was strongly influenced by the bipolar seesaw producing antiphase climate responses between the north and south atlantic however mounting evidence demands refinements of this model with the occurrence of abrupt events in southern low to mid latitudes occurring in phase with north atlantic climate improved constraints on the north south phasing and spatial extent of these events are therefore critical to understanding the mechanisms that propagate abrupt events within the climate system we present a 19 400 year multi proxy record of climate change obtained from a rock hyrax midden in southernmost africa arid anomalies in phase with the younger dryas and 8 2 ka events are apparent indicating a clear shift in the influence of the bipolar seesaw which diminished as the earth warmed and was succeeded after 14 6 ka by the emergence of a dominant interhemispheric atmospheric teleconnection

insolation and glacial interglacial control on southwestern african hydroclimate over the past 140 000 years available online xxxx editor g m henderson keywords leaf wax n alkane hydrogen and carbon isotopes african palaeoclimate monsoonal precipitation namibia the past climate evolution of southwestern africa is poorly understood and interpretations of past hydrological changes are sometimes contradictory here we present a record of leaf wax d and 13 c taken from a marine sediment core at 23 s off the coast of namibia to reconstruct the hydrology and c 3 versus c 4 vegetation of southwestern africa over the last 140 000 years 140 ka we find lower leaf wax d and higher 13 c more c 4 grasses which we interpret to indicate wetter southern hemisphere sh summer conditions and increased seasonality during sh insolation maxima relative to minima and during the last glacial period relative to the holocene and the last interglacial period nonetheless the dominance of c 4 grasses throughout the record indicates that the wet season remained brief and that this region has remained semi arid our data suggest that past precipitation increases were derived from the tropics rather than from the winter westerlies comparison with a record from the congo basin indicates that hydroclimate in southwestern africa has evolved in antiphase with that of central africa over the last 140 ka

holocene hydrologic and vegetation developments in the orange river catchment south africa and their controls the summer rainfall zone srz in the south african interior experienced pronounced hydrological and vegetation changes during the holocene inferred to be driven mainly by shifts in atmospheric and

late pleistocene holocene vegetation and climate change in the middle kalahari lake ngami botswana abstract pollen spores and microscopic charcoal from a sediment core from lake ngami in the middle kalahari reflect paleovegetation and paleoclimatic conditions over the last 16 600 cal years bp the location of lake ngami allows for the receipt of moisture sourced from the indian and or atlantic oceans which may have influenced local rainfall or long distance water transport via the okavango system we interpret results of statistical analyses of the pollen data as showing a complex dynamic system wherein variability in tropical convective systems and local forcing mechanisms influence hydrological changes our reconstructions show three primary phases in the regional precipitation regime 1 an early period of high but fluctuating summer rainfall under relatively cool conditions from 16 600 12 500 cal bp with reduced tree to herb and shrub ratio 2 an episode of significantly reduced rainfall centered around c 11 400 cal bp characterized by an increase in xeric asteraceae pollen but persistent aquatic elements suggesting less rainfall but cool conditions and lower evaporation that maintained water in the basin and 3 a longer phase of high but fluctuating rainfall from 9000 cal bp to present with more woody savanna vegetation vachellia acacia and combretaceae we propose a model to relate these changes to increased indian ocean sourced moisture in the late pleistocene due to a southerly position of the african rain belt a northerly contraction of tropical systems that immediately followed the younger dryas and a subsequent dominance of local insolation forcing modulated by changes in the se atlantic basin

extending the aridity record of the southwest kalahari current problems and future perspectives an extensive luminescence based chronological framework has allowed the reconstruction of expansions and contractions of the kalahari desert over the last 50 ka however this chronology is largely based on near surface pits and sediment exposures these are the points on the landscape most prone to reactivation and resetting of the luminescence dating clock this is proving to be a limiting feature for extending palaeoenvironmental reconstructions further back in time one way to obviate this is to sample desert marginal areas that only become active during significant arid phases an alternative is to find and sample deep stratigraphic exposures the mamatwan manganese mine at hotazel in the sw kalahari meets both these criteria luminescence dating of this site shows the upper sedimentary unit to span at least the last 60 ka with tentative age estimates from underlying cemented aeolian units dating back to the last interglacial and beyond results from mamatwan are comparable to new and previously published data from linear dunes in the sw kalahari but extend back much further analysis of the entire data set of luminescence ages for the sw kalahari brings out important inferences that suggest that different aeolian forms 1 have been active over different time scales in the past 2 have different sensitivities to environmental changes and 3 have different time scales over which they record and preserve the palaeoenvironmental record this implies that future optically stimulated luminescence work and palaeoenvironmental reconstructions must consider both site location and its relationship to desert margins and sediment depositional styles so that the resolution and duration of the aridity record can be optimally understood

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

late quaternary palaeohydrological changes in the northern namib sand sea new chronologies using osl dating of interdigitated aeolian and water lain interdune deposits abstract ephemeral rivers today terminate in playas adjacent to the eastern part of the namib sand sea although there is evidence that these fluvial systems penetrated further west in the past there are water lain sediments exposed in interdune areas of the northern namib sand sea associated with the former course of the tsondab river which are central to palaeoenvironmental reconstruction in the region these deposits indicate that there was increased moisture availability in this presently hyper arid region and or the catchments of the rivers to the east of the sand sea in the great escarpment until now the chronology for the deposition of these sediments has been based on radiocarbon 14 c dates on carbonate materials the validity of these ages is problematic and 14 c limits the timescale to which these sediments can be dated the water lain units are bracketed by aeolian sand units which are highly suitable for optically stimulated luminescence osl dating here 24 osl ages from three sites associated with the former course of the tsondab river are presented allowing a reassessment of the timing of sediment deposits and the west to east progression of the terminus of the tsondab river during the late quaternary narabeb which is 60 km north west of the current end point of the tsondab river at tsondab vlei contains eight mud units six of which are shown to be of marine oxygen isotope stage mis 5 128 75 ka age water lain units at hartmut pan 55 km north west of tsondab vlei are dated by osl to between 16 9 0 9 ka and 12 7 0 1 ka at ancient tracks closest to the tsondab vlei 6 km west mud units are younger and placed between 12 0 0 7 and 12 8 0 8 ka 11 5 0 5 10 5 0 5 ka and after 10 5 0 5 ka this new chronology is compared with other key regional records to identify potential regional relationships and forcing factors there is greatest correspondence with the records in the north of the summer rainfall zone a revision of both old and young 14 c ages on carbonate materials calls for revision of other 14 c chronologies in the region and highlights the problems with the continued used of histograms of 14 c ages to indicate periods of increased humidity in southern africa

climatic conditions in southern africa since the last glacial maximum inferred from pollen analysis abstract a review of late quaternary palaeoclimatic data derived from several pollen sequences between ca 22 and 34 s in southern africa shows a degree of similarity in temperature and moisture variations between the various site pollen data from sites such as wonderkrater and rietvlei transvaal tate vondo venda elim orange free state equus cave southern kalahari and boomplaas cape province suggest relative dryness during the last glacial maximum wet conditions during the late glacial and dry conditions during the early holocene ca 8000 yr b p followed by progressively moister conditions peaking soon after the development of a temperature optimum ca 6500 yr b p problems with radiocarbon dating of polleniferous spring deposits however prevent precise correlations of especially late pleistocene sequences different seasonal patterns in the late glacial and early holocene may explain palaeobotanical data and are partly compatible with simulations of past climates of kutzbach and guetter 1986

a 190 ky record of lithogenic grain size on the namibian slope forging a tight link between past wind strength and coastal upwelling dynamics abstract we inferred wind strength variations at the namibian coast and its effect on upwelling intensity over the last 190 ky by comparing grain size data and alkenone based sea surface temperatures ssts from one sediment core located on the upper slope off luderitz 25 6 s 13 38 e the wind strength proxy was defined by partitioning terrigenous grain size distributions gsds into two sub populations owing to a simple statistical model the fine poorly sorted component is assumed to include both fine aeolian dust and hemipelagic mud carried by rivers or winnowed from the shelf those two fractions are assumed to have been identically sorted during settling in the water column and are not distinguished by our approach the mode of the coarse well sorted sub population displays rapid high amplitude variations through time we ascribe a strictly aeolian origin to this component and consider that low altitude winds are able to carry coarse grained particles to the ocean as shown by grain size measurements of present dust material from the adjacent continent stuut j b w prins m a schneider r r weltje g j jansen j h f postma g 2002 a 300 kyr record of aridity and wind strength in southwestern africa inferences from grain size distributions of sediments on walvis ridge se atlantic mar geol 180 221 233 variations in the coarse grained dust diameter are closely correlated with sst changes past ssts records from the namibian upper slope have been previously hypothesized as reflecting upwelling intensity combined with occasional injection of warm water from the angola dome we challenge this view in considering that past long term ssts variations are primarily induced by the wind strength and witness coastal upwelling intensity early mis 6 is the only period with evidences of warm poleward water intrusion at the core site the windiest conditions occurred during isotopic stages 3 and 4 the wind strength proxy defined in this study can be used confidently as an independent proxy for past upwelling intensity over the last two climatic cycles

a 300 kyr record of aridity and wind strength in southwestern africa inferences from grain size distributions of sediments on walvis ridge se atlantic abstract the terrigenous fraction of sediments recovered from walvis ridge se atlantic ocean reveals a history of southwestern african climate of the last 300 kyr end member modelling of a data set of grain size distributions n 428 results in three end members the two coarsest end members are interpreted as eolian dust the third end member as hemipelagic mud the ratio of the two eolian end members reflects the eolian grain size and is attributed to the intensity of the se trade winds trade winds were intensified during glacials compared to interglacials changes in the ratio of the two eolian end members over the hemipelagic one are interpreted as variations in southwestern african aridity late quaternary southwestern african climate was relatively arid during the interglacial stages and relatively humid during the glacial stages owing to meridional shifts in the atmospheric circulation system during glacials the polar front shifted equatorward resulting in a northward displacement of the zone of westerlies causing increased rainfall in southwestern africa the equatorward shift of the polar front is coupled with an increase of the meridional pressure gradient leading to enhanced atmospheric circulation and increased trade wind intensity

sedimentology and paleohydrology of late quaternary lake deposits in the northern namib sand sea namibia abstract the namib sand sea is the largest active desert dunefield in southern africa and is comprised mainly of large north south linear dunes in the interdune areas of the northern sand sea eleven small areas of calcareous lacustrine sediment have been studied these beds are typically less than a metre thick and are dominantly comprised of calcareous sandstones to mudstones and sandy limestones the carbonates are mainly magnesian calcites 1 14 mgco 3 with some protodolomite and aragonite calcified reed casts and fresh to brackish water gastropods diatoms and ostracods are present in some beds 18 o values indicate a hot and dry climate a number of enriched 13 c values may reflect high salinity low organic populations or carbonate recrystallization these carbonate rich lacustrine deposits are indicative of increased periods of moisture availability in this normally hyperarid region during the late quaternary the origin of the water responsible for depositing these sediments may be 1 ponding at the end point of the tsondab river which at one time extended farther west into the sand sea 2 flooding into interdune corridors when water levels rose in rivers such as the kuiseb 3 groundwater seepage into depressions either through dunes that border rivers or from the underlying tsondab sandstone and 4 increased rainfall we do not believe that there is evidence to support a major increase in precipitation over the region however even a small increase in precipitation in the headwaters of valleys that drain toward the sand sea might 1 generate enough additional runoff to extend the terminal point of rivers such as the tsondab farther into the dunes 2 cause lateral flooding from major valleys into interdune corridors and 3 recharge aquifers the sedimentary records at narabeb ancient tracks and west pan which lie along the old course of the tsondab river favor a ponded river origin for them whereas groundwater seepage is favored at other sites the chronology of deposition based on radiocarbon dates suggests that ponding and recharge occurred earlier in the lower western part of the area and later in the east this is in harmony with the view that the end point of the tsondab river progressively retreated eastward between about 30 and 14 ka bp as dunes blocked its route

holocene and deglacial ocean temperature variability in the benguela upwelling region implications for low latitude atmospheric circulation 1 mg ca analyses of g bulloides and abundances of n pachyderma left coiling from ocean drilling program odp leg 175 hole 1084b in the benguela coastal upwelling system document lower sea surface temperatures during the last glacial maximum lgm younger dryas mid holocene and little ice age in the southeastern atlantic taking into consideration the possible effects of differential carbonate dissolution the mg ca data indicate younger dryas temperatures 2 3 c cooler than those of the early holocene and lgm temperatures 4 5 c cooler than those of the early holocene the cool interval during the deglacial period at hole 1084b matches the timing of younger dryas shifts in cariaco basin and greenland ice sheet records and that of a nearby alkenone record comparison of mid holocene cooling at hole odp1084b with other high resolution records of holocene and last deglacial sea surface temperatures from the tropical atlantic implies consistent basin wide changes in atmospheric circulation a brief period of 1 5 2 c cooling between 17 8 and 17 2 ka if related to heinrich event 1 is consistent with a previously hypothesized tropical origin of all heinrich climate change events

holocene climatic optimum in southwest africa evidence from the marine clay mineral record abstract sediment composition grain size and clay mineral record of a high resolution sediment core from the continental slope off namibia was investigated to gain information on the deposition of terrigenous matter in this part of the southwest african continental margin during the last 18 k y the depositional processes involved are fluvial input by the kunene river and eolian input from the namib and kalahari deserts each supplying characteristic mineral suites during low sea level erosion of the exposed shelf yields additional material the amount of eolian or fluvial matter depends on the strength of the transport process which is a function of aridity or humidity of the source area thus allowing paleoclimatic interpretations arid conditions prevailed during a low sea level from 18 to 15 ka and unconsolidated shelf sediment was mobilized and supplied to the slope by short distance transport by southerly winds a dramatic increase in the accumulation of terrigenous sediment is recorded from 15 to 10 ka without major changes in sediment composition which is attributed to increased runoff of the kunene river and fluvial erosion of shelf sediments this period coincides with a strengthening of the monsoonal system during a precessional minimum which is observed in numerous sites in central africa and indicates an intensified influence of the monsoon at the kunene headwaters a distinct shift in clay mineralogy towards river derived material marks a second period of increased river runoff during high sea level from 9 to 5 ka indicating maximum humidity in the source area from 6 to 5 ka this corresponds to the holocene climatic optimum observed in the arid belts of northern africa the present balance between fluvial and eolian input was reached approximately at 4 ka