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

the amspoort silts northern namib desert namibia formation age and palaeoclimatic evidence of river end deposits abstract detailed geomorphological and chronological investigations of the nw namibian amspoort silt formation show that the sediments are typical river end deposits this type of endoreic sediment occuring only in desert margin areas provides valuable information about the palaeo environment in the hoanib valley the fine grained deposits have buried riverine trees radiocarbon dating of the wood and luminescence dating of the sediments allow a detailed reconstruction of the aggradation processes accumulation started 10 km downstream of amspoort around the beginning of the 15th century and ended in the 19th century some kilometres upstream of amspoort this upstream shift of sedimentation during the little ice age was caused by gradually decreasing runoff resulting from aridification of the upper part of the hoanib river catchment lying east of the namib desert margin 1 200 m a s l the amspoort silt terrace is evidence of palaeo hydrological fluctuations in nw namibia at present the hoanib river erodes deeply into the silty deposits indicating that nw namibia receives more monsoonal rainfall today than during the little ice age however this contradicts the hypothesis of a continual natural aridification of nw namibia damaraland kaokoveld since the mid 19th century in the course of global climatic change rather deposition and erosion of the amspoort silts indicate that landscape degradation in nw namibia is primarily anthropogenically induced and most probably not accelerated by a decrease in precipitation

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

palynological evidence for late quaternary warming episodes in southern africa abstract polleniferous sediments from southern africa associated with past warm episodes before the last glacial maximum are rare interpretation of environmental conditions during these phases are complicated by difficulties of dating in sediments from the northern areas north of 28 s the prominence of tropical woodland pollen suggests that the period between 7000 and 6500 yr b p was associated with optimal temperatures during the holocene identifying the warmest phase in the southern high lying grasslands and semi arid karoo shrublands south of 28 s is difficult because unlike the savanna areas of the north they do not yield good pollen indicators for changes in temperature such as those of frost sensitive trees however some pollen sequences from further south along the southern coast of africa 34 s and at marion island in the southern ocean 47 s suggest that the holocene temperature optimum occurred at about the same time in the sub antarctic area in the south and the subtropical regions in the north the advent of moister conditions in southern africa during the early to middle holocene is generally recorded earlier ca 7500 6500 yr b p in the north at ca 26 s than around 31 s ca 5000 yr b p this change is provisionally associated with a relative shift in seasonality from a predominance of all season precipitation to a greater proportion of summer rainfall which apparently reached the southern karoo areas two thousand years later than the northern bushveld region

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

detecting holocene movements of the woodland steppe ecotone in northern china using discriminant analysis discriminant functions link vegetation zones and surface pollen along the woodland steppe ecotone in northern china these links were utilised to reconstruct palaeovegetation using fossil pollen data from four lake sediment sites within the ecotone holocene movements of the vegetation zones were derived from the above results and were interpreted as the results of climatic topographic and edaphic factors this study shows that climatic change was the driving factor for ecotonal movement but that the positions of vegetational zones were nevertheless controlled by topographical and edaphic conditions and consequently boundaries between different vegetational zones responded individualistically copyright 2001 john wiley sons ltd

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

the origin of fluvial valleys and early geologic history aeolis quadrangle mars in southern aeolis quadrangle in eastern mars parallel slope valleys flat floored branching valleys v shaped branching valleys and flat floored straight canyons dissect the heavily cratered plateau sequence associated knife like ridges are interpreted as fissure eruption vents and thin dark stratiform outcrops are interpreted as exhumed igneous sills or lava flows ridged lava plains are also common but are not themselves modified by fluvial processes i mapped 56 asymmetric scarps or ridges that are probable thrust faults these faults exhibit an orientation vector mean of n63 w 11 95 confidence interval and they transect the lava plains and the older plateau sequence units by comparison the vector mean for the 264 valleys mapped is n48 w 12 with a larger dispersion about the mean the similar orientations displayed by thrust fault and valley axes suggest that valley locations are partly controlled by preexisting thrust faults and related fracture systems most valleys are also arranged orthogonally to and along the perimeter of the ridged plains a possible model for valley development is 1 freshly outgassed water became entombed as frost snow and ice within the cratered terrains during heavy bombardment and the accompanying deposition of impact ejecta volcanic ash and eolian materials 2 effusive volcanism and lava sill emplacement heated subsurface ice in the vicinity of the ridged plains and faults and fractures provided zones of increased permeability for water transport to the surface and 3 headward sapping at thermal springs thermokarst subsidence and limited downvalley fluid flows then carved and modified the valleys

reassessment of carbonate ages by dating both carbonate and organic material from an etosha pan namibia stromatolite evidence of humid phases during the last 20ka abstract previous research on lacustrine stromatolites from etosha pan in namibia obtained ages on carbonate close to or beyond the limits of radiocarbon dating these ages suggested that the basin was likely not subject to extensive flooding during the last ca 40 ka this study shows that ams radiocarbon ages for the carbonate of a stromatolite from poacher s point are 15 21 ka older than ages for organic material in the stromatolite structure calibrated ages range from 30 to 40 ka for carbonate and 3 19 ka for the organic residue the new ages together with petrographic and isotopic data for the stromatolite have provided important new information on past flooding of etosha pan including evidence of prolonged lacustrine conditions during the holocene climatic optimum

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

palynological analysis of hyrax middens from southern africa abstract hyrax middens in relatively dry parts of africa preserve plant material which includes pollen the bottoms of two stratified hyrax dung middens from blydefontein basin in the karoo shrubland of south africa were dated by radiocarbon to ca 300 yr b p and ca 1130 yr b p comparison of midden pollen spectra with pollen from alluvial sediments near one of the hyrax middens and in modern surface samples indicates that middens contain pollen which reflects local vegetation and that diet probably does not have a major influence on pollen spectra changes in pollen composition probably reflect climatic conditions during the early history of the older midden profile grass dominated spectra suggest moist conditions existed between 1200 and 300 yr b p and an interval of slightly more shrubby karoid vegetation possibly points to a minor dry spell at 1000 yr b p a sharp increase of karoid shrub vegetation and a decrease of grass since 300 yr b p is reflected in both middens the change was apparently triggered by relatively dry conditions and later during the last 150 years it was enhanced by overgrazing from european domestic stock

eddy induced diapycnal fluxes and their role in the maintenance of the thermocline abstract high resolution numerical experiments are diagnosed to study the integral effects of geostrophic eddy fluxes on the large scale ocean circulation three characteristic large scale flows are considered 1 an anticyclonic single gyre 2 a double gyre and 3 an unblocked zonal flow a simple analog of the antarctic circumpolar current it is found that buoyancy and potential vorticity budgets in the presence of eddies are dominated by a balance between vertical advection into the control volume by ekman pumping and eddy transfer across the density surfaces achieved by diapycnal eddy fluxes with small scale mixing making only a minor contribution possible oceanographic implications of the results are discussed

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

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

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

comments on rainfall variability in equatorial and southern africa relationships with sea surface temperatures along the southwestern coast of africa abstract this article presents the results of an analysis of sea surface temperature sst fluctuations in the upwelling region along the benguela coat and its relationship to rainfall variability both along the coast and throughout equatorial and southern africa the analysis incorporates compositing and time series analysis coastal rainfall is markedly enhanced during warm water years and suppressed during cold water years the effects are strongest in march and april at some stations march totals of 50 mm in cold water years contrast with 200 to 400 mm in march of warm water years spectral analysis shows the variability of ssts to be more pronounced on time scales of 5 to 6 years and strong relationships with rainfall throughout equatorial and southern africa are evident on this time scale in coastal regions there may be some degree of direct local forcing of rainfall anomalies via sst anomalies but the temporal and geographical patterns of the relationships suggest that in general both ssts an

evidence of past climatic change in the namib desert abstract a preliminary survey of some areas of the central and northern namib desert was undertaken in order to identify geomorphic and sedimentary features that could potentially provide information on past climatic change in the region wherever possible samples were collected for radiocarbon dating the visits to the skeleton coast area were especially revealing practically every river valley in this tract shows a sequence of terraces and deposits that would warrant a detailed study in all about 120 new radiocarbon dates were obtained for the region these have supplied a wealth of individual results and collectively have enabled the construction of a tentative chronological sequence of the changes in climate for the past 40 000 yr three periods of increased aridity in the hinterland but with decreasing intensity are postulated during the last glacial maximum the early holocene and between a d 1200 and a d 1600 the inter pleniglacial up to 23 000 yr b p the late glacial and the period between about 4000 yr b p and 1200 yr b p on the other hand were more humid than today also with decreasing intensity other indicators of past climate were also identified but since they lie beyond the range of radiocarbon dating they cannot as yet be placed in a chronological context of significance is the fact that convincing evidence was obtained for climatic change within the last millennium and especially the rainfall is found to have been increasing since the 16th century

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

vegetation history inferred from pollen in late quaternary faecal deposits hyraceum in the cape winter rain region and its bearing on past climates in south africa abstract pollen analysis shed light on vegetation community structure over the last 23 000 year in the western cape the pollen from dated hyrax faecal accumulations hyraceum relates to the evolution of climate and contributes to proxy records in southern africa principal components analyses of the pollen data and 13c values of the hyrax dung samples show millennial and shorter scale temperature moisture and seasonality variations in the winter rain region the moisture availability at times do not parallel that in previously studied proxy records in the summer rain region showing an asynchronous moist event in the early holocene and drier conditions in the middle holocene anomalies in climate between the two regions may depend on the degree of northward or southward shifting of winter and summer rain circulation systems scenarios with winter rain or cool growing seasons mostly typify the dung sequence but do not exclude the possibility of southward displacement of the westerly belt under precessional strength with slight summer rain increases during the last glacial maximum limited southward displacement is also possible during the mid holocene

timing of lake level changes in etosha pan namibia since the middle holocene from osl ages of relict shorelines in the okondeka region abstract in 2003 examination of aerial photographs revealed a series of previously unknown relict shorelines on the arcuate ridge possibly a clay lunette dune that marks the western boundary of etosha pan in namibia the shorelines are 120 600 m wide and the most prominent extend for tens of km around the lunette dune the shorelines were examined on the ground in 2004 and an attempt was made to date the three lowest levels at ca 5 2 5 and 1 m above the present pan surface the osl ages obtained indicate higher and more prolonged lake conditions than today at ca 6 4 4 0 and 2 1 ka with the youngest shoreline sediments resting on an ancient pan surface dating to ca 13 ka the evidence indicates dry conditions in the pan at ca 13 ka wetter conditions and higher lake levels in the middle holocene followed by a decline in lake levels to the present periods of inundation were of sufficient duration to produce shorelines at the southwestern end of the pan due to the prevailing northeasterly winds that would have maximized wave action along this section of the pan margin the etosha findings together with other regional paleoclimate data suggest four periods of increased wetness in sw africa during the holocene at 7 5 4 5 3 5 2 5 1 7 and ca 1 0 ka there is widespread evidence for the oldest of these periods suggesting that it was a prominent and widespread interval of wetness prior to ca 8 0 ka the climate may have been drier than today

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

southwest african climate independent of atlantic sea surface temperatures during the younger dryas abstract to investigate land sea interactions during deglaciation we compared proxies for continental pollen percentages and accumulation rates and marine conditions dinoflagellate cyst percentages and alkenone derived sea surface temperatures the proxies were from published data from an ams radiocarbon dated sedimentary record of core geob 1023 5 encompassing the past 21 000 years the site is located at ca 2000 m water depth just north of the walvis ridge and in the vicinity of the cunene river mouth we infer that the parallelism between increasing sea surface temperatures and a southward shift of the savanna occurred only during the earliest part of the deglaciation after the antarctic cold reversal southeast atlantic sea surface temperatures no longer influenced the vegetation development in the kalahari stronger trade winds during the antarctic cold reversal and the younger dryas period probably caused increased upwelling off the coast of angola a southward shift of the atlantic anti cyclone could have resulted in both stronger trade winds and reduced impact of the westerlies on the climate of southwestern africa