the late quaternary palaeoecology of a floristic kingdom the southwestern cape south africa abstract the southwestern cape province of south africa is the core region of the cape floristic kingdom one of six such large scale phytogeographical units and by far the smallest the region possesses one of the richest plant communities in the world when measured in terms of plant species numbers per unit area and many different hypotheses have been advanced in order to explain this prolific diversity historical processes and evolutionary development through time are frequently invoked as explanations but remarkably little is known of the historical biogeography of the region and fossil bearing sediments have yielded only a fragmented picture of the temporal development of the flora late quaternary terrestrial sediments offer an opportunity to investigate the more recent history of the flora although here too there exist several constraints which limit the precision of palaeoecological and palaeoenvironmental reconstructions for the moment knowledge of late quaternary vegetation history is restricted to upland sites of organic sediment accumulation although an increasingly detailed picture of vegetation development against a backdrop of environmental changes is emerging this paper reviews the evidence from several fossil pollen bearing sediments in the mountains of the southwestern cape and presents a vegetation history for the last 14 500 years we draw the somewhat surprising conclusion of relative vegetation stability during the time of marked climatic and environmental dynamism elsewhere the hypothesis that assumed limited vegetation change could be a consequence of high species richness coupled with low pollen identification resolution is tested using multiple discriminant analysis it is argued that apparently subtle shifts in vegetation community patterns did indeed prevail during the late quaternary this possibly has some important implications for the evolution and maintenance of high plant species diversity in the cape floristic region

persistent millennial scale climatic variability over the past 25 000 years in southern africa abstract data from stalagmites in the makapansgat valley south africa document regional climatic change in southern africa in the late pleistocene and holocene a new tims u series dated stalagmite indicates speleothem growth from 24 4 to 12 7 ka and from 10 2 to 0 ka interrupted by a 2 5 ka hiatus high resolution oxygen and carbon stable isotope data suggest that postglacial warming was first initiated 17 ka was interrupted by cooling probably associated with the antarctic cold reversal and was followed by strong warming after 13 5 ka the early holocene experienced warm evaporative conditions with fewer c4 grasses cooling is evident from 6 to 2 5 ka followed by warming between 1 5 and 2 5 ka and briefly at ad 1200 maximum holocene cooling occurred at ad 1700 the new stalagmite largely confirms results from shorter holocene stalagmites reported earlier the strongest variability superimposed on more general trends has a quasi periodicity between 2 5 and 4 0 ka also present are weaker 1 0 ka and 100 year oscillations the latter probably solar induced given similarities to the antarctic records the proximate driving force producing millennial and centennial scale changes in the makapansgat record is postulated to be atmospheric circulation changes associated with change in the southern hemisphere circumpolar westerly wind vortex

last interglacial and holocene altithermal environments in south africa and namibia micromammalian evidence abstract climatic interpretations are derived indirectly from evidence for vegetation changes based on the remains of micromammals small rodents and shrews from archaeological sites thus far only border cave has provided evidence apparently referable to the earlier altithermal in oxygen isotope substage 5e vegetation zones and by implication climatic zones apparently extended 3 and more south of their present southern limits rainfall may have been up to 100 more than it is today and much more seasonal with drier winters mean annual temperatures were perhaps about 1 c higher on other evidence eight other sites provide evidence concerning conditions during the holocene altithermal 7000 6000 yr b p the evidence seems to indicate relatively low annual precipitation in the main summer rainfall region and an extended rainfall season in the southwestern winter rainfall region it is less clear whether or not annual rainfall was relatively high at this time in the latter region although in the namib desert conditions were apparently wetter this tends to agree with the dry period analogue of cockcroft et al 1987 and would imply reduced seasonality of precipitation throughout the region in contrast to the situation during the earlier altithermal apparent conflict with palynological evidence may be explainable but requires further examination

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

climatic and sea level controls on late quaternary eolian activity on the agulhas plain south africa abstract located at the interface between the temperate westerly and sub tropical climate systems south africa s winter rainfall zone wrz is a key location in understanding late quaternary atmospheric circulation dynamics inactive eolian deposits in the wrz comprising pan fringing lunette and coastal dunes were investigated to establish their depositional ages and utility as paleoenvironmental indicators the resulting optical luminescence chronology reveals episodic lunette accretion at 60 000 45 000 yr 12 000 13 000 yr 2800 2600 yr 1200 yr and episodes of lunette and coastal dune accretion on the agulhas plain are temporally distinct reflecting differing fundamental controls on their activity comparisons to previously published data also reveal that the lunettes differ in age from more ancient coastal eolianites lunette deposition is asynchronous between locations reflecting the topographic and hydrological setting of the individual pans in near coastal settings with limited surface recharge lunette accretion appears to be at least partially controlled by sea level induced changes in groundwater levels those pans with more significant surface recharge particularly from fluvial systems may produce less ambiguous paleoenvironmental records with pan status more strongly reflecting regional hydrological conditions lunette orientation is indicative of strong westerly winds during both the pleistocene and holocene lunette accretion would have been promoted by reduced on shore moisture transport during the summer months enhancing rainfall seasonality such conditions would have been promoted by increased continentality as the agulhas bank was exposed during low sea level stands

dune activity as a record of late quaternary aridity in the northern kalahari new evidence from northern namibia interpreted in the context of regional arid and humid chronologies abstract sediments from presently vegetated linear dune ridges in the caprivi strip of northern namibia are optically dated to assess the timing of dune building phases and aridity in the late quaternary the dunes have been constructed from sediments likely to have been initially transported into the area by fluvial processes dune sediments do not preserve obvious evidence of hiatuses in deposition in the dated period 48 121 ka but continuous deposition and therefore continuous aridity is considered unlikely given differences in dated phases compared with chronologies from western zimbabwe to the southeast and western zambia to the north that include ages derived from the same equivalent sampling depths laboratory experiments provide evidence that dune sediments have not been bioturbated since deposition such that sample palaeodoses determined from different sampling depths are a true reflection of the duration of sediment burial independent chronologies from cave sediments provide evidence that humid episodes have occurred in the region within the dated range of dune construction it is concluded that dune construction in the late quaternary has been punctuated that the preserved record reflects the attributes of the aeolian processes that affect linear dune development and that the late quaternary record of dune building in the middle and northern kalahari was spatially complex

late quaternary sea ice history in the indian sector of the southern ocean as recorded by diatom assemblages abstract a modern analog technique mat5201 31 has been applied to fossil diatom assemblages to provide down core estimates of february sea surface temperatures ssts and of sea ice duration over the past 220 000 years at 56 40 s 160 14 e at the core location sea ice progression lagged the sst drop by 1 ka at interglacial glacial transitions and sea ice retreat was almost synchronous to the sst increase at glacial interglacial terminations sea ice increased continuously during glacial periods to reach its maximum extent at the end of glacial times although ssts were almost constant during glacials this indicates that ssts are the major parameter determining the advance and retreat of sea ice at transitions but that the sea ice advance during glacial conditions may be related to positive feedbacks of the ice on albedo air temperature and meridional wind stress the strong correlation r 0 75 between sea ice duration at the core location and the vostok co2 record argues for a control of antarctic sea ice extent on atmospheric co2 concentration via the modification of the ocean to atmosphere gas balance

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

reconstructing pathways of aeolian pollen transport to the marine sediments along the coastline of sw africa the distribution of pollen in marine sediments is used to reconstruct pathways of terrigenous input to the oceans and provides a record of vegetation change on adjacent continents the wind transport routes of aeolian pollen is comprehensively illustrated by clusters of trajectories isobaric 4 day backward trajectories are calculated using the modelled wind field of echam3 and are clustered on a seasonal basis to estimate the main pathways of aeolian particles to sites of marine cores in the south eastern atlantic trajectories and clusters based on the modelled wind field of the last glacial maximum hardly differ from those of the present day trajectory clusters show three regional and two seasonal patterns determining the pathways of aeolian pollen transport into the south eastern atlantic ocean mainly transport out of the continent occurs during austral fall and winter when easterly and south easterly winds prevail south of 25 s winds blow mostly from the west and southwest and aeolian terrestrial input is very low generally a good latitudinal correspondence exists between the distribution patterns of pollen in marine surface sediments and the occurrence of the source plants on the adjacent continent the northern angola basin receives pollen and spores from the congolian and zambezian forests mainly through river discharge the zambezian vegetation zone is the main source area for wind blown pollen in sediments of the angola basin while the semi desert and desert areas are the main sources for pollen in sediments of the walvis basin and on the walvis ridge a transect of six marine pollen records along the south western african coast indicates considerable changes in the vegetation of southern africa between glacial and interglacial periods important changes in the vegetation are the decline of forests in equatorial africa and the north of southern africa and a northward shift of winter rain vegetation along the western escarpment

vegetation and seasonality shifts during the late quaternary deduced from 13c 12c ratios of grazers at equus cave south africa abstract season of rainfall can be a major influence on the relative proportions of c3 and c4 grasses in a landscape since their relative distribution is essentially constrained by temperatures during the growing season cool growing seasons favor c3 grasses whereas warm ones favor c4 grasses 13c 12c ratios in tooth enamel carbonate of grazers from the site of equus cave northern cape province south africa were used to determine vegetation and rainfall seasonality shifts during the late quaternary the results show shifts in the relative proportion of c3 and c4 grasses during the latter stages of the pleistocene and domination by c4 grasses in the holocene the data show that the northwestern cape did not fall within a winter rainfall zone during this period as has been postulated in recent climate models instead a more complex situation is suggested in which at least two periods of enhanced winter rainfall occurred within a predominantly summer rainfall regime

the record of continental dust from australia in tasman sea sediments abstract the flux of aeolian dust from australia to sediments of the tasman sea has increased during glacial stages of the last four glacial cycles low fluxes of dust from australia before 350 ka were followed by an increase in stage 10 and high fluxes in peak glacial periods thereafter the initiation of higher dust fluxes in stage 10 is consisten with previous estimates of the age of onset of aridity in the source area dust flux to the tasman sea is thought to record the intensity of deflation from the source area in interior southeastern australia which was marked by arid conditions and possibly greater windiness during the last glacial a transect of five cores from the central tasman sea revealed consistently low dust fluxes north of 33 s increasing southward to approximately 40 s glacial to interglacial movement of the northern boundary of the dust plume governed by the position of the subtropical ridge was less than 6 latitude probably closer to 3 350 km the position of the dust plume determined in this study and its response to climate change are significantly different from a previous reconstruction based on the measurement of quartz content of the non biogenic sediment fraction

assessment of sidoarjo mud flow embankment stability using very low frequency electromagnetic method the earth on lusi embankment has a high failure potential due to several factors such as seepage leakage vertical and horizontal deformation cracking and fault discontinuity overtopping mud slide and swelling very low frequency electromagnetic method was carried out at lusi embankment in order to delineate fracture and potential pathway of seepage occurring through the subsurface structure the embankment body to reach these objectives several methods were carried out in the selected area such as direct current resistivity total station and rayleigh wave dispersion to provide information on the mechanical properties lusi embankment subsurface this study indicates that seepage and fracture through the lusi embankment is presented by a set of lines which are possibly caused by deformation in the lusi area furthermore based on the fracture and seepage positions and mud or fluid flow direction the unstable lusi embankment is determined as located around the northwest and northern parts of the area

magnitude scaling of the near fault rupture directivity pulse abstract current ground motion models all assume monotonically increasing spectral amplitude at all periods with increasing magnitude however near fault recordings from recent earthquakes confirm that the near fault fault normal forward rupture directivity velocity pulse is a narrow band pulse whose period increases with magnitude this magnitude dependence of the period of the near fault pulse is expected from theory because the period of the pulse is related to source parameters such as the rise time duration of slip at a point on the fault and the fault dimensions which generally increase with magnitude this magnitude dependence of the pulse period causes the response spectrum to have a peak whose period increases with magnitude such that the near fault ground motions from smaller earthquakes may exceed those of larger earthquakes at intermediate periods around 1 s this paper presents preliminary equations relating the period of the fault normal component of the forward rupture directivity velocity pulse to the earthquake magnitude and a preliminary model for the acceleration response spectra of near fault fault normal ground motions that includes the magnitude dependence of the period of the response spectral peak

synthetic reconstructions of southern african environments during the last glacial maximum 21 18kyr and the holocene altithermal 8 6kyr abstract the pash database has been assembling palaeoclimatic data from the southern hemisphere for a number of years the southern african sector now contains more than 100 records spanning the last 200 000 years a number of these relate to the last glacial maximum and holocene altithermal which represent the two most recent extremes in global temperatures syntheses of these records have permitted the preparation of preliminary palaeoenvironmental maps for the two intervals the results provide insights into probable changes in atmospheric circulation as temperatures across the subcontinent rose by 6 7 c these changes are in agreement with a present day model which has been developed to explain short term variations in southern african climate the results presented here should assist in calibrating models developed to predict future climate change

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

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

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

seismic response of embankment dams under near fault and far field ground motion excitation the characteristics of near fault and far field earthquakes differ records suggest that a near fault ground motion is characterized by a large high energy pulse and a distinctive pulse shape for the velocity time history the present study compared near fault and far field ground motion effects and investigates the consequence of well known characteristics of near fault ground motion on the nonlinear dynamic response of an embankment dam it was shown that median maximum demands such as crest settlement and critical slip surface displacement of the embankment dam were higher for near fault ground motion than far field motion for pulse type near fault input the maximum demand was a function of spectral shape and the ratio of the pulse period to the fundamental period of the embankment dam near fault ground motion with a period pulse 1 5 to 4 times greater than the natural period of the dam created a larger seismic demand than when the pulse period was equal to or smaller than the natural period of dam this difference increased up to 1 85 times as the ground motion intensity increased velocity related ground motion intensity indices such as peak ground velocity were much more effective than peak ground acceleration to correlate with seismic demand this was because shear stress level has a direct relation with the velocity time history of ground motion

evidence of younger dryas and neoglacial cooling in a late quaternary palaeotemperature record from a speleothem in eastern victoria australia a calcitic stalagmite collected from a limestone cave in the buchan area of eastern victoria has been dated by three mass spectrometric uranium series analyses two growth phases are represented the older from 13 4 to 10 6 ka and the younger from 3 2 to 2 1 ka oxygen isotope analysis reveals that temperatures were below present day values at all times but particularly cool conditions are indicated between 12 3 and 11 4 ka and neoglacial conditions occurred at about 3 ka the older cold climate event is clearly synchronous with the younger dryas in europe and this is the first time that strong evidence for this event has been found in australia carbon isotope variations are interpreted as indicating changes in plant productivity on the surface and are most likely controlled by variations in summer rainfall they indicate particularly high levels of plant productivity from 11 5 to 11 0 ka 1996 john wiley sons ltd

relationship between antarctic sea ice and southwest african climate during the late quaternary here we compare late quaternary southwest african climate records from the west coast of southern africa published winter rainfall and trade wind intensity records from a core off the coast of namibia to records of antarctic sea ice extent this comparison reveals coherent changes between antarctic sea ice extent and the southwest african winter rain region since 45 k y b p with enhanced winter rainfall and trade wind vigor during periods of increased sea ice presence we propose an oceanic and atmospheric coupling between antarctic sea ice and the winter rainfall zone of southwest africa that may lead to increased desertification in the region if global warming persists

effects of near fault ground shaking on sliding systems a numerical study is presented for a rigid block supported through a frictional contact surface on a horizontal or an inclined plane and subjected to horizontal or slope parallel excitation the latter is described with idealized pulses and near fault seismic records strongly influenced by forward directivity or fling step effects from northridge kobe kocaeli chi chi aegion in addition to the well known dependence of the resulting block slippage on variables such as the peak base velocity the peak base acceleration and the critical acceleration ratio our study has consistently and repeatedly revealed a profound sensitivity of both maximum and residual slippage 1 on the sequence and even the details of the pulses contained in the excitation and 2 on the direction or in which the shaking of the inclined plane is imposed by contrast the slippage is not affected to any measurable degree by even the strongest vertical components of the accelerograms moreover the slippage from a specific record may often be poorly correlated with its arias intensity these findings may contradict some of the prevailing beliefs that emanate from statistical correlation studies the upper bound sliding displacements from near fault excitations may substantially exceed the values obtained from some of the currently available design charts

estimates of in situ gas hydrate concentration from resistivity monitoring of gas hydrate bearing sediments during temperature equilibration as part of ocean drilling program leg 204 at southern hydrate ridge off oregon we have monitored changes in sediment electrical resistivity during controlled gas hydrate dissociation experiments two cores were used each filled with gas hydrate bearing sediments predominantly mud silty mud one core was from site 1249 1249f 9h3 42 1 m below seafloor mbsf and the other from site 1248 1248c 4x1 28 8 mbsf at site 1247 a third experiment was conducted on a core without gas hydrate 1247b 2h1 3 6 mbsf first the cores were imaged using an infra red ir camera upon recovery to map the gas hydrate occurrence through dissociation cooling over a period of several hours successive runs on the multi sensor track includes sensors for p wave velocity resistivity magnetic susceptibility and gamma ray density were carried out complemented by x ray imaging on core 1249f 9h3 after complete equilibration to room temperature 17 18 c and complete gas hydrate dissociation the final measurement of electrical resistivity was used to calculate pore water resistivity and salinities the calculated pore water freshening after dissociation is equivalent to a gas hydrate concentration in situ of 35 70 along core 1249f 9h3 and 20 35 for core 1248c 4x1 assuming seawater salinity of in situ pore fluid detailed analysis of the ir scan x ray images and split core photographs showed the hydrate mainly occurred disseminated throughout the core additionally in core 1249f 9h3 a single hydrate filled vein approximately 10 cm long and dipping at about 65 was identified analyses of the logging while drilling lwd resistivity data revealed a structural dip of 40 80 in the interval between 40 and 44 mbsf we further analyzed all resistivity data measured on the recovered core during leg 204 generally poor data quality due to gas cracks allowed analyses to be carried out only at selected intervals at sites 1244 1245 1246 1247 1248 1249 and 1252 with a few exceptions data from these intervals yield low to no gas hydrate concentration which corresponds to estimates from downhole resistivity logs however since the gas cracking may be the result of gas hydrate dissociation this is a biased sampling cores that had contained some gas hydrate may have been excluded

punctuated aridity in southern africa during the last glacial cycle the chronology of linear dune construction in the northeastern kalahari abstract the mega kalahari of central southern africa is one of the most extensive quaternary desert basins on a regional scale present day aeolian activity is restricted to episodic dune crest reactivation in the most arid southwestern desert core there is however abundant evidence of former periods of both more arid and more humid conditions many of which have little or no chronological control we have employed optical dating of quartz sand grains to develop a chronology of arid intervals as recorded by phases of linear dune construction in the northeastern sector of the mega kalahari we identify repeated phases of aeolian deposition during the last interglacial glacial cycle at ca 95 115 41 46 20 26 and post 20 ka which are separated by depositional hiatuses that we infer to correspond to more humid periods these aeolian depositional events correlate with and are inferred to relate to millennial scale cold sea surface temperature events in the southeast atlantic which have been linked to sub milankovitch climate changes recognised in northern hemisphere oceanic and cryospheric environmental archives covering the same time period while the present landscape is the product of either post 20 ka hwange national park dune field or 20 30 ka victoria falls dune field aeolian activity and subsequent erosion and reworking much of the vertical expression of the larger dune forms corresponds to the earlier periods of activity the linear ridges of the area are rich archives of late quaternary terrestrial climate change

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

sliding displacement of flexible earth slopes subject to near fault ground motions abstracta fully coupled simplified method that incorporates soil nonlinearity is used to conduct sliding block analysis of slopes subjected to near fault pulse like and nonpulse like ground motions the effects of the ground motion pulse on the computed sliding displacements are investigated and the efficiency of various ground motion intensity measures for predicting the sliding displacement of slopes is evaluated it is shown that the slope is expected to have larger displacements over shorter time intervals when near fault ground motions have pulse like characteristics results also indicate that for cases in which the natural period of a slope is close to the period of the pulse of a recorded ground motion an equivalent wavelet pulse appropriately represents the displacement response of slopes predictive models are developed for the sliding displacement of near fault ground motions using spectral acceleration and peak ground velocity as predictive variables in addition it is shown that for certai

late quaternary palaeoenvironments of the winter rainfall zone of southern africa palynological and sedimentological evidence from the agulhas plain abstract south africa s winter rainfall zone is a climatically sensitive region lying at the interface of the earth s temperate and sub tropical climatic systems its seasonally arid climate has generally prevented the preservation of long and organic rich sedimentary deposits producing a spatially limited and temporally biased quaternary record this paper seeks to address this issue further and develop a fuller understanding of the wider climatic changes in this region during the late quaternary modern climatic data does not support the definitions of the winter rainfall zone presented in previous syntheses and this factor amongst others may explain difficulties in resolving the palaeoenvironmental record in this region we present palaeoenvironmental evidence from the agulhas plain an area marginal to the modern winter rainfall zone cored sedimentological and palynological records from two pans are integrated with previously reported records of aeolian activity providing evidence for phases of enhanced aridity and humidity during the late quaternary the record is fragmentary which may reflect the cycling of sediment between the pans and their accompanying lunette dunes lacustrine sedimentary sequences dating to c 33 ka 47 ka provide evidence for enhanced humidity consistent with evidence in the winter and year round rainfall zones increased humidity is also recorded from c 2 ka following drier conditions than the present c 2 7 2 5 ka palynological evidence supports the sedimentological interpretations of pan water status and offers rare insights into the nature of the region s unique fynbos vegetation during the late pleistocene

seismic performance evaluation of high cfrd slopes subjected to near fault ground motions based on generalized probability density evolution method abstract this research mainly addresses evaluating the seismic reliability and analyzing the random dynamic response of high concrete faced rockfill dam cfrd slopes suffering from the near fault earthquakes by establishing a novel method of generating the representative acceleration time histories coupled with the recently proposed generalized probability density evolution method gpdem a probability evaluation is performed after generating two groups of near fault ground motions pulse like and non pulse like earthquakes coupling a series of statistical stochastic parameters with the spectral representation random function method a 242 m high cfrd is selected as an example for finite element stochastic dynamic time series analysis and second order statistical values including mean and standard deviation and probability information of three indices the safety factor the cumulative time of safety factor 1 0 fs 1 0 and the maximum cumulative slippage of the dam slopes are determined respectively the effective non stationary near fault earthquakes will be adopted to determine the stochastic earthquake loading for the dynamic response evaluation of dam slopes the statistical and probabilistic results demonstrate that the seismic characteristics make a great difference to the seismic response of slope stability as well as the pulse properties the stochastic near fault earthquakes combined with the gpdem can evaluate seismic performance and reliability effectively from the perspective of randomness and the failure probability can be obtained directly

late quaternary palaeoenvironments of the southwestern cape south africa a regional synthesis the contemporary uniqueness of the southwestern cape environemnt suggests that its response to the environmental perturbations of the late quaternary may have been correspondingly distinctive despite the wide variety of palaeoenvironmental evidence which has accumulated from within the region a coherent picture of the evolution and development of its environments has remained elusive since the publication of several regional reviews over the last decade or so a considerable body of palynological and other palaeoecological evidence has emerged which prompts a fresh synthesis as to the nature of late quaternary environmental changes in the southwestern cape s fynbos biome although there are few sediments which date to the appropriate period the last glacial maximum in contrast to the situation evident in the summer rainfall region is suggested to be a period characterised by considerably cooler and wetter conditions in certain parts of the biome the first half of the holocene appears to have been somewhat drier than much of the second half and the warmer temperatures of the holocene hypsithermal are associated with reduced moisture availability intra regional contrasts are evident in the response to late quaternary environmental changes furthermore it transpires that for much of the later quaternary and for large areas of the region precipitation may have fluctuated out of phase with changes in the interior of the subcontinent a situation which has great relevance to the prediction of future environmental changes and their impacts in the southwestern cape

using peak ground velocity to characterize the response of soil pile system in liquefying ground abstract performance of a soil pile system can be significantly influenced by many characteristics of an earthquake ground motion and it is vitally important to identify the ground motion parameters that have the most significant effects on the response when predicting the level of movement or damage in the pile in this paper three dimensional finite element fe analysis was conducted to simulate a centrifuge experiment on the nonlinear behavior of a pile founded in liquefiable soil subjected to strong earthquake motions the result of the fe analysis was found to be in reasonable agreement with the experimental data as such the calibrated fe model was used to investigate the influence of ground motion parameters on the pile soil response in both liquefied and non liquefied soils it was found that peak ground velocity pgv is an appropriate ground motion parameter to characterize the response of the soil pile system in liquefying ground the maximum pile bending moment pile lateral displacement and soil lateral displacement increased with increasing pgv moreover near fault ground motions could result in more severe damage to the pile compared to far fault grounds motions this study provided a new insight on the influence of ground motion parameters in particular pgv on the dynamic performance of a pile foundation

holocene vegetation history and palaeoenvironments at klaarfontein springs western cape south africa several sedimenit cores ai ounid the coastal lake of verlorenvlei westem cape have thus far revealed important details of the development of this semi arid winter rainfall environment during the late quatemary complex interplay between climate change sea level fluctuation and human activities have characterized the verlorenvlei record and suggests that these environments have been subject to high degrees of disturbance over time however due to the discontiniuous nature of the sedimentary record the holocene record has remained fragmentary investigation of a 6 in vibracore sequence at klaarfontein 32 25 26 s 18 29 40 e an artesian spring site some 18 km inland of eland s bay facilitates a more complete holocene palaeoenivironmental reconstruction pollen concentrations in 37 spectra distributed through the 6 m core vary with organic content but at all depths are stufficient to facilitate interpretation of vegetation history and reveal a high degree of dynamism in the local and regional enviro

relict periglacial slope deposits in the hex river mountains south africa observations and palaeoenvironmental implications abstract shattered bedrock near the summit of matroosberg western cape mountains is closely associated with several blockstreams which grade downslope into broad terraces with an increase in slope angles the regolith grades into broad bands of coarse but sorted material parallel to the maximum gradient the width of the coarse stripes increases in the downslope direction where they merge into openwork block deposits several tens of metres long and wide whereas the terraces near the summit plateau closely resemble gelifluction sheets the large sorted stripes and coarse debris mantles are analogous to the stone banked terraces described for the colorado front range the landforms are primarily related to seasonal frost creep at the last glacial maximum lgm when mean annual temperatures are estimated to have been around 0 c i e winter temperatures 7 8 c lower than present snowcover must have been limited to allow deep frost penetration

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