links between southwestern tropical indian ocean sst and precipitation over southeastern africa over the last 17 kyr abstract time series of mg ca ba ca and 18o analyzed in tests of surface dwelling planktonic foraminifer globigerinoides ruber from two marine sediment cores recovered in the mozambique channel off the zambezi river southwestern tropical indian ocean reveal climate variability over the last 17 kyr analysis of samples collected from the water column of the mozambique channel validates that mg ca in g ruber reflects calcification temperatures at 0 30 m water depth and that the surface water of the southwestern indian ocean is very sensitive to dissolved ba input from adjacent rivers foraminiferal ba ca and mg ca time series are used to reconstruct hydrological and thermal changes over southeastern african and southwestern tropical oceans the mg ca based sea surface temperature sst estimates indicate that the thermal evolution of the tropical southwestern indian ocean followed within age model uncertainties climate changes over antarctica the trend of the sst record is marked by a gradual warming from 24 7 0 6 c at 17 0 0 2 kyr bp to 26 4 0 3 c at 10 11 kyr bp interrupted by two prominent coolings of 1 5 0 2 c and 1 c centered at 15 0 1 kyr bp and 13 4 0 2 kyr bp respectively declining ssts in the early holocene reach their minimum 25 c at 8 7 0 2 kyr bp and give way to stable thermal conditions over the middle and late holocene the ba ca record indicates that the zambezi basin experienced relatively wet conditions during the early phase of the last deglaciation bolling allerod and the early holocene these wet phases coincide with an increase of sst in the mozambique channel in contrast relatively dry conditions throughout the middle and late holocene epoch are accompanied by relatively cold mozambique channel surface water these shifts likely reflect a response to meridional shifts of the austral westerlies and subtropical front these hypothesized shifts would have modulated the advection of cold southern ocean water into the mozambique channel changes in sst in the mozambique channel and possible resultant changes in the zonal gradient in the tropical indian ocean in turn had a strong impact on the precipitation over southeastern africa

a high resolution 15 600 year pollen and microcharcoal record from the cederberg mountains south africa abstract the cederberg mountains western cape province south africa are located within the fynbos biome which exhibits some of the highest levels of species richness and endemism in the world the region s post glacial vegetation history however remains largely unknown presented here are high resolution pollen and microcharcoal records spanning the last 15 600 years obtained from the de rif rock hyrax midden from the driehoek valley of the central cederberg in this region previous pollen studies have shown muted variability in vegetation community composition during periods of globally marked climatic variability e g the last glacial interglacial transition in our record however significant changes in vegetation composition are apparent most notably they indicate a shift from ericaceous restioid fynbos present from 15 600 to 13 300 cal yr bp to a brief but prominent development of proteoid fynbos at the beginning of the holocene around 11 200 cal yr bp this vegetation shift is associated with increased moisture at the site and coincides with reduced fire frequency as indicated by the microcharcoal record at 10 400 cal yr bp there is a marked reduction in protea type pollen which is replaced by thicket characterised by dodonaea which became the dominant arboreal pollen type this shift was likely the result of a long relatively fire free period coupled with warmer and wetter climates spanning much of the early holocene a brief but marked decrease in water availability around 8500 8000 cal yr bp resulted in the strong decrease of dodonaea pollen the vegetation of the mid to late holocene is characterised by the increased occurrence of asteraceae and succulent taxa suggesting substantially drier conditions these data give unprecedented insight into the vegetation dynamics across a period of substantial rapid climate change and while they confirm the presence of fynbos elements throughout the last 15 600 years the results highlight significant fluctuations in the vegetation that were triggered by changes in both climate and fire regimes

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

a unified approach to orbital solar and lunar forcing based on the earth s latitudinal insolation temperature gradient widespread empirical evidence suggests that extraterrestrial forcing influences the earth s climate but how this could occur remains unclear here we describe a new approach to this problem that unifies orbital solar and lunar forcing based on their common control of the earth s latitudinal insolation gradient lig the lig influences the climate system through differential solar heating between the tropics and the poles that gives rise to the latitudinal temperature gradient ltg which drives the earth s atmospheric and wind driven ocean circulation we use spectral analysis of recent changes in the earth s ltg to support earlier work on orbital timescales davis and brewer 2009 that suggests the climate system may be unusually sensitive to changes in the lig identification of lig forcing of the ltg is possible because the lig varies according to seasonally specific periodicities based on obliquity in summer 41 kyr orbital and 18 6 yr lunar cycle and precession 21 kyr orbital cycle and total solar irradiance 11 yr solar cycle in winter we analyse changes in the northern hemisphere ltg over the last 120 years and find significant 99 peaks in spectral frequencies corresponding to 11 years in winter and 18 6 years in summer consistent with lig forcing the cross seasonal and multi frequency nature of the lig signal and the diffuse effect of the ltg driver on the climate system may account for the complexity of the response to extraterrestrial forcing as seen throughout the climatic record this hypersensitivity of the ltg to the lig appears poorly reproduced in climate models but would be consistent with the controversial theory that the ltg is finely balanced to maximise entropy c 2011 elsevier ltd all rights reserved

late quaternary vegetation dynamics and hydro climate in the drakensberg south africa abstract a multi proxy study of a sediment sequence from braamhoek wetland covering the last c 16 000 years reveals a record of regional climate and vegetation dynamics in the drakensberg region south africa including signals from both the organic sediment fraction fossil pollen charcoal n alkane abundance n alkane 13c toc and the inorganic fraction mineral magnetic properties the reconstruction supported by a robust chronology indicates two major periods of increased regional wetness during the late pleistocene to early holocene phase c 13 800 12 600 cal yr bp c 10 200 8500 cal yr bp and one during the late holocene c 2000 cal yr bp to present drier conditions are recorded during the younger dryas c 12 600 11 300 cal yr bp and mid holocene c 7000 2000 cal yr bp a major decline in fynbos vegetation during the early holocene suggests a shift towards warmer temperatures and possibly towards less pronounced winter rains in eastern south africa from c 8500 cal yr bp comparison with records from interior of south africa show relatively high inter site variability however the braamhoek moisture proxies do co vary with the speleothem isotope records from makapansgat suggesting a similar hydro climate evolution in eastern and interior parts of the summer rainfall region during the studied period on multi millennial time scales an inverse hydro climatological pattern is evident between these two south african records and reconstructions from tropical locations in southeast africa such a rainfall dipole between eastern tropical and southern africa has previously been identified on shorter time scales i e on inter annual to millennial scales the braamhoek study suggests that a similar dipole pattern is acting also on a multi millennial perspective these long term precipitation anomalies are tentatively coupled to teleconnections from multi millennial changes in the dynamics of the indian ocean dipole iod and el nino southern oscillation enso

empirical relationship between leaf wax n alkane δd and altitude in the wuyi shennongjia and tianshan mountains china implications for paleoaltimetry article i nfo estimating past elevation not only provides evidence for vertical movements of the earth s lithosphere but also increases our understanding of interactions between tectonics relief and climate in geological history development of biomarker hydrogen isotope based paleoaltimetry techniques that can be applied to a wide range of sample types is therefore of continuing importance here we present leaf wax derived n alkane d dwax values along three soil altitudinal transects at different latitudes in the wuyi shennongjia and tianshan mountains in china to investigate dwax gradients and the apparent fractionation between leaf wax and precipitation ewax p we findthatsoil dwax trackaltitudinal variationsof precipitation d along the three transects that span variable environment conditions and vertical vegetation spectra an empirical dwax altitude relation is therefore established in which the average dwax lapse rate of 2 27 0 38 100 m is suitable for predicting relative paleoelevation change relative uplift the application of this empirical gradient is restricted to phases in the mountain uplift stage whenthe atmospheric circulation had not distinctly changed and to when the climate was notarid anempirical dwax latitude altitudeformulaisalsocalculated dwax 3 483lat 0 0227alt 261 5 which gives the preliminary spatial distribution pattern of dwax in modern china meanvalue of ewax p intheextreme humid wuyimountainsisquite negative 154 compared to the humid shennongjia 129 and the arid but with abundant summer precipitation tianshan mountains 130 which suggests aridity or water availability in the growing season is the primary factor controlling soil sediment ewax p along the tianshan transects values of ewax p are speculated to be constant with altitude while along the wuyi and shennongjia transects ewax p are also constant at the low mid altitudes but become slightly more negative at high altitudes which could be attributed to overestimates of precipitation d or the vegetation shift to grass conifer additionally a reversal of altitude effect in the vertical variation of dwax was found in the alpine zone of the tianshan mountains which might be caused by atmospheric circulation change with altitude this implies that the paleo circulation pattern and its changes should alsobe evaluated whenstable isotope based paleoaltimetry is applied

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

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

holocene rainfall variability in southern chile a marine record of latitudinal shifts of the southern westerlies geochemical and clay mineral parameters of a high accumulation marine sediment core from the chilean continental slope 41 s provide a 7700 yr record of rainfall variability in southern chile related to the position of the southern westerlies we especially use the iron content measured with a time resolution of ca 10 yr on average of 14 caccelerator mass spectrometry dated marine sediments as a proxy for the relative input of iron poor coastal range and iron rich andean source rocks variations in this input are most likely induced by rainfall changes in the continental hinterland of the core position based on these interpretations we find a pronounced rainfall variability on multicentennial to millennial time scales superimposed on generally more arid conditions during the middle holocene 7700 to 4000 cal yr b p compared to the late holocene 4000 to present this variability and thus changes in the position of the southern westerlies are first compared to regional terrestrial paleoclimate data sets from central and southern chile in order to derive possible wider implications and forcing mechanisms of the holocene latitudinal shifts of the southern westerlies we then compare our data to ice core records from both tropical south america and coastal antarctica these records show similar bands of variability centered at ca 900 and 1500 yr comparisons of band pass filters suggest a close connection of shifts of the southern westerlies to changes within the tropical climate system the correlation to climate conditions in coastal antarctica shows a more complicated picture with a phase shift at the beginning of the late holocene coinciding with the onset of the modern state of el nin o southern oscillation system the presented data provide further evidence that the well known millennial scale climate variability during the last glacial continued throughout the holocene fl 2001 elsevier science b v all rights reserved

effects of aridity and vegetation on plant wax δd in modern lake sediments we analyzed the deuterium composition of individual plant waxes in lake sediments from 28 watersheds that span a range of precipitation d h vegetation types and climates the apparent isotopic fractionation ea between plant wax n alkanes and precipitation differs with watershed ecosystem type and structure and decreases with increasing regional aridity as measured by enrichment of 2 h and 18 o associated with evaporation of lake waters the most negative ea values represent signatures least affected by aridity these values were 125 5 for tropical evergreen and dry forests 130 for a temperate broadleaf

sea ice and wind variability during the holocene in east antarctica insight on middle high latitude coupling abstract micropaleontological and biomarker data from two high accumulation marine sites from the coastal and continental shelf zone ccsz off east antarctica adelie land at 140 e and eastern prydz bay at 77 e are used to reconstruct holocene changes in sea ice and wind stress at the basin wide scale these data demonstrate congruent increase in sea ice concentration persistence and wind stress related sea surface turbulence in the two regions since 7 cal ka bp with a particularly strong signal since 4 5 3 5 cal ka bp comparison of these high latitude records with sea ice and turbulence records from the southern mid latitudes highlights distinctive climatic evolutions according to the different latitudinal bands sea ice persistence and turbulence increase in east antarctica ccsz are opposite to sea surface warming and sea ice retreat recorded after 4 5 3 5 cal ka bp in the east atlantic and indian sector between 55 and 45 s at the same period paleodata suggest sst cooling in all major coastal upwelling systems of the southern hemisphere caused by the northward transport of subpolar surface waters as a response to southern westerlies reinforcement we therefore propose as suggested for the northern hemisphere that holocene changes in the latitudinal insolation gradient primarily forced by obliquity and precession and amplified by sea ice and glacial ice expansions in the antarctic realm are responsible for the observed contrasted latitudinal patterns of southern latitudes

late holocene covariability of the southern westerlies and sea surface temperature in northern chilean patagonia abstract the climate of chilean patagonia is strongly influenced by the southern westerlies which control the amount and latitudinal distribution of precipitation in the southern andes in austral summer the southern westerly wind belt swwb is restricted to the high latitudes it expands northward in winter which results in a strong precipitation seasonality between 35 and 45 s here we present a new precipitation seasonality proxy record from quitralco fjord 46 s where relatively small latitudinal shifts of the swwb result in large changes in precipitation seasonality our 1400 yr record is based on sedimentological and geochemical data obtained on a sediment core collected in front of a small river that drains the patagonian andes which makes this site particularly sensitive to changes in river discharge our results indicate fe al and ti al values that are low between 600 and 1200 ce increasing at 1200 1500 ce and high between 1500 and 1950 ce increasing fe al and ti al values reflect a decrease in mean sediment grain size from 30 to 20 m which is interpreted as a decrease in seasonal floods resulting from an equatorward shift of the swwb our results suggest that compared to present day conditions the swwb was located in a more poleward position before 1200 ce it gradually shifted towards the equator in 1200 1500 ce where it remained in a sustained position until 1950 ce this pattern is consistent with most precipitation records from central and southern chile the comparison of our record with published regional sea surface temperature sst reconstructions for the late holocene shows that equatorward shifts of the swwb are systematically coeval with decreasing ssts and vice versa which resembles fluctuations over glacial interglacial timescales we argue that the synchronicity between sst and swwb changes during the last 1400 years represents the response of the swwb to temperature changes in the southern hemisphere

isotopic analysis of equid teeth from wonderwerk cave northern cape province south africa abstract stable carbon and nitrogen isotope ratios have been determined from equid teeth from a well dated sequence of holocene deposits at wonderwerk cave situated in a summer rainfall area of the northern cape province of south africa stable carbon isotope ratios confirm the existence of a c 4 grassland habitat throughout the holocene nitrogen isotope ratios are assessed in relation to data from modern equid samples from southern africa temporal variability in both carbon and nitrogen isotope ratios of holocene equid samples from wonderwerk appears to be analogous to spatial variability of such ratios determined for faunal samples from modern environments relationships between isotope ratios and data from modern environments are used to obtain rainfall indices

reconstruction of holocene sea surface salinity in the skagerrak kattegat a climatic and environmental record of scandinavia holocene sea surface salinity in the skagerrak kattegat is reconstructed using weighted averaging regression and calibration wa of diatom data from core skagen 3 diatom data from surface sediments together with 10 yr mean values of salinity and water temperature were used as a modern training set canonical correspondence analysis cca was used to identify statistically significant directions of variation within the training set the results of forward selection of the environmental variables and associated monte carlo permutation tests of the statistical significance of each variable the canonical coefficients and the intraset correlations of the environmental variables with the cca axes suggest that summer and winter sea surface salinities sss wss are potentially reconstructable from fossil diatom assemblages the changes in sea surface salinity during the holocene can be correlated with changes in climate of the circum baltic area the current patterns of the skagerrak kattegat and the development of the baltic sea generally low sss and large differences between wss and sss dsw s during 9000 6000 yr bp might have resulted from a climate with higher precipitation than today in the circum baltic area and its catchment or a climate with maximum precipitation in late spring or early summer the mechanism behind these patterns may be the combination of the northward shift of the jet stream and a stronger surface westerly penetration into the continent caused by a reduced latitudinal insolation gradient and enhanced land sea contrast in the early to middle holocene it was however complicated by local events such as changes in the strength of various currents in the skagerrak kattegat successions of baltic brackish and freshwater phases and hydrodynamic conditions in the circum baltic area 1998 john wiley sons ltd

inception of the northern european ice sheet due to contrasting ocean and insolation forcing about 115 000 yr ago the last interglacial reached its terminus and nucleation of new ice sheet growth was initiated evidence from the northernmost nordic seas indicate that the inception of the last glacial was related to an intensification of the atlantic meridional overturning circulation amoc in its northern limb the enhanced amoc combined with minimum northern hemisphere insolation introduced a strong sea land thermal gradient that together with a strong wintertime latitudinal insolation gradient increased the storminess and moisture transport to the high northern european latitudes at a time when the northern hemisphere summer insolation approached its minimum

hydrological response of a dryland ephemeral river to southern african climatic variability during the last millennium a long term flood record from the buffels river the largest ephemeral river of nw south africa 9250 km2 was reconstructed based on interpretation of palaeoflood documentary and instrumental rainfall data palaeoflood data were obtained at three study reaches with preserved sedimentary evidence indicating at least 25 large floods during the last 700 yr geochronological control for the palaeoflood record was provided by radiocarbon and optically stimulated luminescence osl dating annual resolution was obtained since the 19th century using the overlapping documentary and instrumental records large floods coincided in the past within three main hydroclimatic settings 1 periods of regular large flood occurrence 1 large flood 30 yr under wetter and cooler prevailing climatic conditions ad 1600 1800 2 decreasing occurrence of large floods 1 large flood 100 yr during warmer conditions e g ad 1425 1600 and after 1925 and 3 periods of high frequency of large floods 4 5 large floods in 20 30 yr coinciding with wetter conditions of decadal duration namely at ad 1390 1425 1800 1825 and 1915 1925 these decadal scale periods of the highest flood frequency seem to correspond in time with changes in atmospheric circulation patterns as inferred when comparing their onset and distribution with temperature proxies in southern africa

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

does mean annual insolation have the potential to change the climate long term climatic changes such as glacial interglacial cycles are usually explained in term of changes in solar energy received at the top of the atmosphere in particular daily insolation in the high northern hemisphere latitudes during summer is widely used in interpreting palaeoclimate records this insolation forcing is strongly marked by changes in precession however some climate variations are much more imprinted by changes in obliquity this was the case for sea surface temperature in the north atlantic during the eemian period as well as for the vostok ice core deuterium excess history over the last 250 ka therefore we investigate the insolation forcing in order to identify characteristics that could explain the observed climate response this is mainly the case for annual mean insolation variations simple hypotheses for how this forcing could act on climate are also suggested these being mainly related to changes in the moisture transport induced by the annual insolation gradient between low and high latitudes along these lines a simple conceptual model of annual mean temperature variations illustrates the role of annual mean insolation on climate c 2004 elsevier b v all rights reserved

orbital forcing and role of the latitudinal insolation temperature gradient orbital forcing of the climate system is clearly shown in the earths record of glacial interglacial cycles but the mechanism underlying this forcing is poorly understood traditional milankovitch theory suggests that these cycles are driven by changes in high latitude summer insolation yet this forcing is dominated by precession and cannot account for the importance of obliquity in the ice age record here we investigate an alternative forcing based on the latitudinal insolation gradient lig which is dominated by both obliquity in summer and precession in winter the insolation gradient acts on the climate system through differential solar heating which creates the earths latitudinal temperature gradient ltg that drives the atmospheric and ocean circulation a new pollen based reconstruction of the ltg during the holocene is used to demonstrate that the ltg may be much more sensitive to changes in the lig than previously thought from this it is shown how lig forcing of the ltg may help explain the propagation of orbital signatures throughout the climate system including the monsoon arctic oscillation and ocean circulation these relationships are validated over the last eemian interglacial which occurred under a different orbital configuration to the holocene we conclude that lig forcing of the ltg explains many criticisms of classic milankovitch theory while being poorly represented in climate models

abrupt cooling of antarctic surface waters and sea ice expansion in the south atlantic sector of the southern ocean at 5000 cal yr b p antarctic surface waters were warm and ice free between 10 000 and 5000 cal yr b p as judged from ice rafted debris and microfossils in a piston core at 53 s in the south atlantic this evidence shows that about 5000 cal yr b p sea surface temperatures cooled sea ice advanced and the delivery of ice rafted detritus ird to the subantarctic south atlantic increased abruptly these changes mark the end of the hypsithermal and onset of neoglacial conditions they coincide with an early neoglacial advance of mountain glaciers in south america and new zealand between 5400 and 4900 cal yr b p rapid middle holocene climate changes inferred from the taylor dome ice core antarctica cooling and increased ird in the north atlantic and the end of the african humid period the near synchrony and abruptness of all these climate changes suggest links among the tropics and both poles that involved nonlinear response to gradual changes in northern hemisphere insolation sea ice expansion in the southern ocean may have provided positive feedback that hastened the end of the hypsithermal and african humid periods in the middle holocene

a late quaternary pollen sequence from mfabeni peatland south africa reconstructing forest history in maputaland abstract this paper documents a continuous 44 000 yr pollen record derived from the mfabeni peatland on the maputaland coastal plain a detailed fossil pollen analysis indicates the existence of extensive podocarpus abundant coastal forests before 33 000 cal yr bp the onset of wetter local conditions after this time is inferred from forest retreat and the development of swampy conditions conditions during the last glacial maximum 21 000 cal yr bp are inferred to have been colder and drier than the present as evidenced by forest retreat and replacement of swampy reed sedge communities by dry grassland forest growth and expansion during the holocene altithermal 8000 6000 cal yr bp indicates warm relatively moist conditions previous records from maputaland have suggested a northward migration of podocarpus forest during the late holocene however we interpret a mid holocene decline in podocarpus at mfabeni as evidence of deforestation forest clearance during the mid holocene is supported by the appearance of morella serrata suggesting a shift towards more open grassland savanna possibly due to burning these signals of human impact are coupled with an increase in acacia indicative of the development of secondary forest and hence disturbance

hydrogen isotope ratios of recent lacustrine sedimentary n alkanes record modern climate variability abstract hydrogen isotope ratios were measured on n alkanes n c12 to n c31 extracted from recent lake surface sediments along a n s european transect to test if modern climate variability is recorded in these biomarkers d values of the n alkanes are compared to d values of meteoric water from the iaea gnip database spanning a range from 119 in northern sweden to 41 in southern italy to lake water d values and to mean annual temperatures varying between 2 0 c in the north and 13 7 c in the south d values of the short chained n alkanes n c12 to n c20 excluding algal derived n c17 and n c19 are higher in the north and lower in the south the isotopic fractionation e for hydrogen between meteoric water and the short chained n alkanes is increasing from n to s by more than 100 and is significantly correlated to mean annual temperature for n c16 and n c18 this suggests that these n alkanes may originate from a different source in the northern lakes possibly due to petroleum contamination or are synthesized using a different biochemical pathway the n c17 and n c19 alkanes of algal origin the n c21 and n c23 alkanes originating from water plants and the long chain n alkanes n c25 n c27 n c29 and n c31 of terrestrial origin clearly correlate with d values of meteoric water lake water and mean annual temperature indicating that they excellently record the d value of meteoric water the mean hydrogen isotope fractionation ec17 w of 157 sd 13 between n c17 and meteoric water is fairly constant over the wide range of different climates and lake environments suggesting only minor influence of environmental factors on this biochemical fractionation this suggests that d values of n c17 are suitable to reconstruct the isotopic composition of source water the mean fractionation between the long chain n alkanes and water is 128 sd 12 the mean difference of 31 between both e values is likely due to evaporative enrichment of deuterium in the leaf water if this is the only influence on the enrichment the difference between the d values of terrestrial and aquatic compounds might be suitable to reconstruct terrestrial evapotranspiration of the lake environment

grip deuterium excess reveals rapid and orbital scale changes in greenland moisture origin the northern hemisphere hydrological cycle is a key factor coupling ice sheets ocean circulation and polar amplification of climate change here we present a northern hemisphere deuterium excess profile covering one climatic cycle constructed with the use of 18 o and d greenland ice core project grip records past changes in greenland source and site temperatures are quantified with precipitation seasonality taken into account the imprint of obliquity is evidenced in the site to source temperature gradient at orbital scale at the millennial time scale grip source temperature changes reflect southward shifts of the geographical locations of moisture sources during cold events and these rapid shifts are associated with large scale changes in atmospheric circulation

high frequency holocene glacier fluctuations in new zealand differ from the northern signature understanding the timings of interhemispheric climate changes during the holocene along with their causes remains a major problem of climate science here we present a high resolution 10be chronology of glacier fluctuations in new zealand s southern alps over the past 7000 years including at least five events during the last millennium the extents of glacier advances decreased from the middle to the late holocene in contrast with the northern hemisphere pattern several glacier advances occurred in new zealand during classic northern warm periods these findings point to the importance of regional driving and or amplifying mechanisms we suggest that atmospheric circulation changes in the southwest pacific were one important factor in forcing high frequency holocene glacier fluctuations in new zealand

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

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

holocene palynology and palaeoenvironments in the savanna biome at tswaing crater central south africa abstract a radiocarbon dated pollen and microscopic charred particle record from the holocene section of the tswaing crater in the savanna biome of south africa give new evidence for environmental changes during the period c 9400 1800 cal years bp pollen grains are scarce or absent in layers dating from before 9400 cal years bp but deposits rich in pollen occur in overlying layers the section dated between 9400 cal years bp and c 7200 cal years bp contains grass asteraceae and dry savanna pollen types that suggest fluctuating but generally dry moisture conditions later between c 7200 and 1800 cal years bp broad leaved savanna woodland elements and local swamp pollen indicate relatively stable vegetation and wetter mildly fluctuating climatic conditions which is consistent with previously published biomarker analysis between c 6200 and 5500 cal years bp the numbers of charred particles increased slightly this indicates burning activity which can probably be attributed to dry season ignition of denser fuel under relatively moist conditions a decrease of local swamp pollen between c 3600 and 3500 cal years bp suggests that conditions became briefly drier again as pollen of woody elements declined in favour of open grassland pollen a comparison between the tswaing pollen profile and various other sequences within the central interior of south africa suggests generally similar conditions over the central interior of the sub continent during the holocene deviating from sequences further afield along the coastal areas of southern africa between 9400 cal years bp and ca 7200 cal years bp the western and southern coasts were probably controlled by different atmospheric and oceanic circulation regimes under the influence of a strong westerly winter rain system while the north eastern area where tswaing is situated experienced weaker precession and less summer rain from the intertropical convergence zone

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

pollen distribution in the marine surface sediments of the mudbelt along the west coast of south africa abstract the distribution of pollen in marine surface sediments offshore of the west coast of south africa has been investigated to aid in the interpretation of marine pollen records of onshore vegetation changes a transect of sediment surface pollen samples retrieved from the namaqualand mudbelt from just south of the orange river mouth 29 s to st helena bay 33 s indicates distinctive pollen spectra reflecting vegetation communities on the adjacent continent pollen concentration increases southwards partly in relation to greater pollen productivity due to higher biomass and density of fynbos vegetation and of sedimentary processes and low pollen concentrations consequent to dilution with silt and clay from the orange river the distribution of specific pollen taxa suggests that the orange river is a major contributor of pollen to the northern mudbelt declining southwards while the pollen distribution in the central mudbelt is largely attributable to seasonal inputs of pollen from offshore berg winds and local ephemeral namaqualand rivers the typical fynbos elements dominate in the southern mudbelt indicating a pollen source mainly in the fynbos vegetation types these conclusions support a companion analysis of fossil pollen records of two marine sediment cores from the northern and southern mudbelt respectively this study demonstrates that pollen records from marine sediment cores in the namaqualand mudbelt have the potential to be a tool to reconstruct palaeovegetation on the adjacent continent however to better reconstruct the palaeoclimate of south africa and fully understand the relations between terrestrial and marine deposits more marine surface sediments along the western coast of south africa as well as more terrestrial surface sediments need to be studied

late quaternary climatic changes revealed by luminescence dating mineral magnetism and diffuse reflectance spectroscopy of river terrace palaeosols a new form of geoproxy data for the southern african interior lyons j r tooth s duller g 2014 late quaternary climatic changes revealed by luminescence dating mineral magnetism and diffuse reflectance spectroscopy of river terrace palaeosols a new form of geoproxy data for the southern african interior quaternary science reviews 95 43 59

holocene glaciations in the ema glacier valley monte sarmiento massif tierra del fuego abstract investigations carried out in the ema glacier valley tierra del fuego on the eastern side of monte sarmiento massif enable the recognition of five holocene glacial events the oldest glacial advance deposited the so called external moraines of ema glacier with a probable occurrence between 6000 and 5000 14 c y bp without discarding the potential for these deposits to be from lateglacial time the remaining four readvances built up a complex inner moraine system named informally internal moraines of ema glacier the oldest recognized till unit that constitutes this proximal moraine system was deposited shortly before 3135 14 c y bp when glaciolacustrine sedimentation took place during glacier recession subsequent glacial advances accumulated till at about 1288 14 c y shortly after 695 14 c y and between 379 14 c y and 60 y bp this chronology of holocene glacier events coincides with and is well complemented by the one established by other authors for fiordo pia at cordillera darwin 75 km to the east the ema pia chronology is used to calibrate tentatively a series of moraine belts previously identified in the mountain ranges adjacent to ushuaia 150 km se of the surveyed region a comparative chart shows that the chronological data obtained for the neoglacial readvances in tierra del fuego are in accordance with those for the southern patagonian andes further north it follows that the holocene behavior of the glaciers in the andean region of tierra del fuego and southern patagonia is essentially a response to the same regional climate change

holocene pollen from swamp cave and hyrax dung deposits at blydefontein kikvorsberge karoo south africa abstract pollen analysis of material from a variety of sediment types including those from ponds streams a rock shelter and hyrax dung accumulations in the blydefontein basin 31 09 s 25 05 e fig 1b provide a record of vegetation change in the eastern karoo over the last 10 000 years the pollen composition fluctuated as a result of different taphonomic processes inherent in the various sampled deposits results further demonstrate that long term vegetation changes alternated between karoo shrub and grassland plant communities karoo shrubs suggesting relatively dry conditions were generally prominent in the early holocene until ca 5400 yr bp when more grassy vegetation began to flourish presumably in response to increased summer rain conditions pollen representation of the early holocene is not detailed enough to trace millennial scale variations during this period but more detailed middle to late holocene data show millennial or shorter scale shifts between grassland and drier karroid veld

pollen indications of holocene palaeoenvironments at florisbad spring in the central free state south africa mid to late holocene pollen data from florisbad in the central free state south africa reveal a number of moisture fluctuations commencing at c 6500 bp the pollen sequence indicates an arid climate but shows more availability of moisture under grassy conditions from summer rain at c 6300 bp and again at c 4420 bp the interval between these dates is characterized by a dry episode with karroid shrubs some time between 5500 and 4500 bp possibly as a result of less marked summer seasonality after 4220 bp moisture conditions gradually fluctuated in intensity or seasonal availability until c 2100 1700 bp when strong summer evaporation is indicated at the upper end of the sequence the data are complemented by previously published results on environmental change from the nearby deelpan site to the west although some distinct events correlate regionally over south africa summer rains appear to have been significant at florisbad at an earlier stage in the mid holocene than in the karoo to the south

contrasting evolution of sea surface temperature in the benguela upwelling system under natural and anthropogenic climate forcings we present alkenone derived sea surface temperature sst records from three marine cores collected within the southern benguela upwelling system bus spanning the last 3 ka the sst evolution over the last 3 millennia is marked by aperiodic millennial scale oscillations that broadly correspond to climatic anomalies identified over the north atlantic region the bus sst data further suggest cooling and warming trends opposite to the temperature evolution in the moroccan upwelling region and in antarctica in contrast the last decades are marked by a cooling of unprecedented magnitude in both the benguela and moroccan upwelling systems which is not observed in the antarctic record these contrasted responses in atlantic upwelling systems triggered by natural and anthropogenic forcings shed light on how different climatic mechanisms are mediated by ocean atmosphere interactions and transmitted to the geological records of past and present climate changes citation leduc g c t herbert t blanz p martinez and r schneider 2010 contrasting evolution of sea surface temperature in the benguela upwelling system under natural and anthropogenic climate forcings geophys res lett 37 l20705 doi 10 1029 2010gl044353

a late holocene climate record from a stalagmite cold air cave northern province south africa abstract stable isotope analyses of a uranium series dated stalagmite from south africa provide a record of climate changes for the periods 4400 4000 years and 800 years ago to recent interrupted by a prolonged growth hiatus generally enriched stable oxygen isotope values interpreted here to indicate more humid conditions occurred around 800 years ago subsequently a marked depletion in oxygen and carbon isotope values occurred about 600 years ago reflecting we believe shifts toward drier cooler conditions as the regional indication of the little ice age this period with depleted yet oscillating isotope values is replaced by a period with enriched isotopes until recent times the record is notable for sharp shifts in isotopic values on the scale of decades which reflect rapid oscillations in local climate conditions

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

half precessional dynamics of monsoon rainfall near the east african equator extensive records exist with which to assess the relationship between external climate forcings such as changes in insolation and climate variability for middle and high latitudes but records from equatorial regions are relatively few especially from regions experiencing the passage of the intertropical convergence zone a continuous and well resolved climate proxy record of hydrological variability during the past 25 000 years from equatorial east africa is now presented and analysed

some aspects of the tectonics of subduction zones abstract the main structures of a subduction zone are as follows 1 1 on the outer wall faults formed either by reactivation of the structural grain of the oceanic plate when the latter is slightly oblique to the trench or by a new fault network parallel to the trench or both the width of the faulted zone is about 50 miles 2 2 on the inner wall either an accretionary prism or an extensional fault network or both collapsed structures and slumps are often associated sometimes creating confusion with the accretionary structures 3 3 the overall structure of the trench itself is determined by the shape of the edge of the continental crust or of the island arc its detailed structure however is related to the oceanic plate namely when the structural grain of the latter is slightly oblique to the trench which then takes an en echelon form collapsed units can fill up the trench which is in that case restricted to an irregular narrow depression the tectonic framework of the trench can be buried under a sedimentary blanket when the sedimentation rate is high and the trench bottom is a large flat area two extreme types of active margins can be distinguished convergent compressive margins when the accretionary mechanism is strongly active and convergent extensional margins where the accretionary mechanism is absent or only weakly active the status of a given margin between these two extreme types is related to the convergence rate of the plates the dip of the subduction zone the sedimentation activity and the presence of a continental obstacle because oceanic seamounts and aseismic ridges are easily subducted examples are taken from the barbados middle america peru kuril japan nankai marianna manila new hebredes and tonga trenches

a 22 kyr bp sedimentological record of lake rukwa 8 s sw tanzania environmental chronostratigraphic and climatic implications abstract the sedimentological study of a 12 8 m long core r96 i from lake rukwa tanzania 8 s provides a new record of past lake level fluctuations that took place in response to changes of the regional climate since the last glacial period from 21 to 15 cal kyr bp nearshore and swamp marsh environments are evidenced from clastic deposition macrophytes debris and ca mg carbonate enrichments a transgressive sequence starting around 15 cal kyr bp lead to the humid lacustrine optimum between 15 and 7 cal kyr bp from 12 to 10 cal kyr bp anoxic lake bottom environments were favored by the concomitant effects of high primary productivity increased subsidence and inputs of volcanic ash in the lake the middle holocene 7 3 cal kyr bp is characterized by high concentrations of silt carbonates and low organic content which indicate the occurrence of relatively oxic shallow and saline depositional environments especially around 7 and 3 4 cal kyr bp although grainsize and toc profiles suggest that shallow environments likely persisted in the upper holocene low mg concentration values for the last 3 kyr may indicate a trend toward relatively more dilute environments the two main lake rukwa low stand periods at 21 15 and 7 3 cal kyr bp correspond remarkably well with the insolation maximum at the equator which occurred at 17 kyr bp for the spring equinox and at 6 kyr bp for the autumn equinox respectively we suggest that during these periods of minimum inter hemispheric insolation gradients monsoon circulation weakened in south equatorial regions and the itcz was located north of 8 s in east africa

north atlantic holocene climate evolution recorded by high resolution terrestrial and marine biomarker records abstract holocene climatic change is driven by a plethora of forcing mechanisms acting on different time scales including insolation internal ocean e g atlantic meridional overturning circulation amoc and atmospheric e g north atlantic oscillation nao variability however it is unclear how these driving mechanisms interact with each other here we present five biomarker based paleoclimate records air sea surface temperature and precipitation from a fjordic sediment core revealing north atlantic terrestrial and marine climate in unprecedented detail the early holocene 10 7 7 8 kyrs bp is characterised by relatively high air temperatures while ssts are dampened by melt water events and relatively low precipitation the middle holocene 7 8 3 2 kyrs bp is characterised by peak ssts declining air temperatures and high precipitation a pronounced marine thermal maximum occurs between 7 5 5 kyrs bp 3000 years after the terrestrial thermal maximum driven by melt water cessation and an accelerating amoc the neoglacial cooling between 5 8 and 3 2 kyrs bp leads into the late holocene we demonstrate that an observed modern link between icelandic precipitation variability during different nao phases may have existed from 7 5 kyrs bp a simultaneous decoupling of both air and sea surface temperature records from declining insolation at 3 2 kyrs bp may indicate a threshold after which internal feedback mechanisms namely the nao evolved to be the primary drivers of icelandic climate on centennial time scales

hydrogen isotope ratios of lacustrine sedimentary n alkanes as proxies of tropical african hydrology insights from a calibration transect across cameroon abstract hydrogen isotope values d of sedimentary aquatic and terrestrial lipid biomarkers originating from algae bacteria and leaf wax have been used to record isotopic properties of ancient source water i e precipitation and or lake water in several mid and high latitude lacustrine environments in the tropics however where both processes associated with isotope fractionation in the hydrologic system and vegetation strongly differ from those at higher latitudes calibration studies for this proxy are not yet available to close this gap of knowledge we sampled surface sediments from 11 lakes in cameroon to identify those hydro climatological processes and physiological factors that determine the hydrogen isotopic composition of aquatic and terrestrial lipid biomarkers here we present a robust framework for the application of compound specific hydrogen isotopes in tropical africa our results show that the d values of the aquatic lipid biomarker n c17 alkane were not correlated with the d values of lake water carbon isotope measurements indicate that the n c17 alkane was derived from multiple source organisms that used different hydrogen pools for biosynthesis we demonstrate that the d values of the n c29 alkane were correlated with the d values of surface water i e river water and groundwater which on large spatial scales reflect the isotopic composition of mean annual precipitation such a relationship has been observed at higher latitudes supporting the robustness of the leaf wax lipid d proxy on a hemispheric spatial scale in contrast the d values of the n c31 alkane did not show such a relationship but instead were correlated with the evaporative lake water d values this result suggests distinct water sources for both leaf wax lipids most likely originating from two different groups of plants these new findings have important implications for the interpretation of long chain n alkane d records from ancient lake sediments in particular a robust interpretation of palaeohydrological data requires knowledge of the vegetation in the catchment area as different plants may utilise different water sources our results also suggest that the combination of carbon and hydrogen isotopes does help to differentiate between the metabolic pathway and or growth form of organisms and therefore the source of hydrogen used during lipid biosynthesis

influence of late pleistocene and holocene climate on vegetation distributions in southwest africa elucidated from sedimentary n alkanes differences between 12 s and 20 s abstract global and local climatic forcing e g concentration of atmospheric co2 or insolation influence the distribution of c3 and c4 plants in southwest africa c4 plants dominate in more arid and warmer areas and are favoured by lower pco2 levels several studies have assessed past and present continental vegetation by the analysis of terrestrial n alkanes in near coastal deep sea sediments using single samples or a small number of samples from a given climatic stage the objectives of this study were to evaluate vegetation changes in southwest africa with regard to climatic changes during the late pleistocene and the holocene and to elucidate the potential of single sample simplifications we analysed two sediment cores at high resolution altogether ca 240 samples from the southeast atlantic ocean 20 s and 12 s covering the time spans of 18 to 1 ka and 56 to 2 ka respectively our results for 20 s showed marginally decreasing c4 plant domination of ca 5 during deglaciation based on average chain length acl27 33 values and carbon isotopic composition of the c31 and c33n alkanes values for single samples from 18 ka and the holocene overlap and thus are not significantly representative of the climatic stages they derive from in contrast at 12 s the n alkane parameters show a clear difference of plant type for the late pleistocene c4 plant domination 66 c4 on average and the holocene c3 plant domination 40 c4 on average during deglaciation vegetation change highly correlates with the increase in pco2 r 0 91 short term climatic events such as heinrich stadials or antarctic warming periods are not reflected by vegetation changes in the catchment area instead smaller vegetation fluctuations during the late pleistocene occur in accordance with local variations of insolation

bursting the bubble of ballooning plutons a return to nested diapirs emplaced by multiple processes a popular model for the emplacement of roughly spherical plutons is that of ballooning or in situ inflation of a magma chamber in a common version of this model magma ascends until loss of heat or buoyancy causes the outermost magma to crystallize and cease ascent while the hotter tail of magma continues to rise and expand the already crystallized outer margin this expansion forms a concentric gneissic to mylonitic foliation and flattening type strain in the outer margin of the pluton by means of subsolidus deformation and pushes aside the surrounding country rock to form a dynamothermal aureole that postdates regional structures our reexamination of three supposedly ballooned plutons ardara ireland cannibal creek australia papoose flat california and evaluation of published descriptions of many others indicate that this model is largely incorrect deflections of country rock structures strains and porphyroblast matrix relationships indicate that only minor to moderate expansion usually 30 or less occurred during emplacement that other emplacement mechanisms must have occurred and that regional deformation continued during and after emplacement internal structures indicate that when magma chamber expansion did occur it did so by flow of magma that magmatic foliations and lineations formed late in the magma chamber evolution that enclave shapes are neither good strain markers nor indicators of the magnitude of expansion and that only minor internal subsolidus deformation results from emplacement this study indicates that many plutons previously interpreted as post tectonic ballooning plutons are better viewed as syntectonic nested diapirs emplaced by a variety of country rock material transfer processes this nested diapir model implies that magma ascent may occur by rise of large magma batches instead of transport in dikes followed by ballooning that magma chamber dynamics differ from that in the ballooning model and that normally zoned plutons may form by intrusion of several pulses of magma rather than by in situ crystal fractionation from a single parent melt

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

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

reconstruction of environmental and climate changes at braamhoek wetland eastern escarpment south africa during the last 16 000 years with emphasis on the pleistocene holocene transition abstract a paleo environmental record covering the last 16 ka 16 000 cal yrs bp from the eastern areas of the summer rainfall region in south africa is presented this area is until now sparsely investigated due to the lack of well preserved natural archives for this study we used a peat section from a wetland situated close to the drakensberg escarpment where the high annual rainfall amounts supported a continuous peat accumulation since c 16 ka one peat core was analysed in terms of fossil pollen composition carbon and nitrogen content isotope composition 13c 15n and microscopic charcoal concentration the greatest degree of temporal resolution was achieved from the late pleistocene and early holocene section where proxy records indicate relatively dry conditions between ca 16 13 7 ka 12 8 10 5 ka 9 5 8 2 ka and wet conditions between c 13 7 12 8 ka and 10 5 9 5 ka a weak moisture signal is also evident at c 8 2 7 5 ka the late pleistocene to early holocene period was relatively cool while conditions became generally warmer after 11 8 ka the interpretation of the mid and late holocene sequence is limited due to a slow accumulation and low sample resolution but the available data suggest relatively dry conditions until c 1 5 ka followed by more humid conditions until c 0 5 ka we suggest that the millennial scale variability within the record can be attributed to shifts in the circulation systems dominating the region i e the latitudinal movements of the inter tropical convergence zone itcz and the dynamics of the mid latitude low pressure belts

expansion of the hadley cell under global warming 1 a consistent weakening and poleward expansion of the hadley circulation is diagnosed in the climate change simulations of the ipcc ar4 project associated with this widening is a poleward expansion of the subtropical dry zone simple scaling analysis supports the notion that the poleward extent of the hadley cell is set by the location where the thermally driven jet first becomes baroclinically unstable the expansion of the hadley cell is caused by an increase in the subtropical static stability which pushes poleward the baroclinic instability zone and hence the outer boundary of the hadley cell

links between the antarctic oscillation and winter rainfall over western south africa 1 relationships between the antarctic oscillation aao and winter rainfall over western south africa are investigated this region receives most of its annual rainfall during austral winter and often experiences severe drought it is found that 6 6 of the 7 8 wettest driest winters jja during 1948 2004 occur during negative positive aao phase i e positive negative pressure anomalies over antarctica and negative positive anomalies over the midlatitudes the mechanisms by which the aao appears to influence winter rainfall involve shifts in the subtropical jet and changes in the low level moisture flux upstream over the south atlantic and in the mid level uplift low level convergence and relative vorticity over the region the anomalous circulation patterns extend into spring thus the springs following the identified winters also show similar rainfall anomalies

interhemispheric dynamics of the african rainbelt during the late quaternary abstract the spatial pattern of precipitation variability in tropical and subtropical africa over the late quaternary has long been debated prevailing hypotheses variously infer 1 insolation controlled asymmetry of wet phases between hemispheres 2 symmetric contraction and expansion of the tropical rainbelt and 3 independent control on moisture available in southern africa via sea surface temperatures in the indian ocean in this study we use climate model simulations covering the last glacial cycle 120 kyr with hadcm3 and the multi model ensembles from pmip3 the palaeoclimate model intercomparison project to investigate the long term behaviour of the african rainbelt and test these simulations against existing empirical palaeohydrological records through regional model data comparisons we find evidence for the validity of several hypotheses with various proposed processes occurring concurrently but with different regional emphasis e g asymmetric shifts at the seasonal extremes and symmetric expansions contractions towards west equatorial regions crucially variations in rainfall are associated with multiple forcing mechanisms that vary in their dominance both spatially and temporally over the glacial cycle an important consideration when interpreting and extrapolating from often relatively short palaeoenvironmental records

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

mid to late holocene climate change an overview the last 6000 years are of particular interest to the understanding of the earth system because the boundary conditions of the climate system did not change dramatically in comparison to larger glacial interglacial changes and because abundant detailed regional palaeoclimatic proxy records cover this period we use selected proxy based reconstructions of different climate variables together with state of the art time series of natural forcings orbital variations solar activity variations large tropical volcanic eruptions land cover and greenhouse gases underpinned by results from general circulation models gcms and earth system models of intermediate complexity emics to establish a comprehensive explanatory framework for climate changes from the mid holocene mh to pre industrial time the redistribution of solar energy due to orbital forcing on a millennial timescale was the cause of a progressive southward shift of the northern hemisphere nh summer position of the intertropical convergence zone itcz this was accompanied by a pronounced weakening of the monsoon systems in africa and asia and increasing dryness and desertification on both continents the associated summertime cooling of the nh combined with changing temperature gradients in the world oceans likely led to an increasing amplitude of the el nin o southern oscillation enso and possibly increasingly negative north atlantic oscillation nao indices up to the beginning of the last millennium on decadal to multi century timescales a worldwide coincidence between solar irradiance minima tropical volcanic eruptions and decadal to multi century scale cooling events was not found however reconstructions show that widespread decadal to multi century scale cooling events accompanied by advances of mountain glaciers occurred in the nh e g in scandinavia and the european alps this occurred namely during the little ice age lia between ad w1350 and 1850 when the lower summer insolation in the nh due to orbital forcing coincided with solar activity minima and several strong tropical volcanic eruptions the role of orbital forcing in the nh cooling the southward itcz shift and the desertifi cation of the sahara are supported by numerous model simulations other simulations have suggested that the fingerprint of solar activity variations should be strongest in the tropics but there is also evidence that changes in the ocean heat transport took place during the lia at high northern latitudes with possible additional implications for climates of the southern hemisphere sh

continental scale temperature variability during the past two millennia past global climate changes had strong regional expression to elucidate their spatio temporal pattern we reconstructed past temperatures for seven continental scale regions during the past one to two millennia the most coherent feature in nearly all of the regional temperature reconstructions is a long term cooling trend which ended late in the nineteenth century at multi decadal to centennial scales temperature variability shows distinctly different regional patterns with more similarity within each hemisphere than between them there were no globally synchronous multi decadal warm or cold intervals that define a worldwide medieval warm period or little ice age but all reconstructions show generally cold conditions between ad 1580 and 1880 punctuated in some regions by warm decades during the eighteenth century the transition to these colder conditions occurred earlier in the arctic europe and asia than in north america or the southern hemisphere regions recent warming reversed the long term cooling during the period ad 1971 2000 the area weighted average reconstructed temperature was higher than any other time in nearly 1 400 years

a tenfold increase in the orange river mean holocene mud flux implications for soil erosion in south africa soil erosion poses a major threat to sustainable agriculture in southern africa but is difficult to quantify one measure of soil erosion is the sediment flux of rivers the orange river is the principal source of sediment to the western margin of south africa with an estimated mean mud flux over the last 11 500 years the holocene epoch of 5 1 3 2 7 4 million metric tons year mt yr a total of 43 gigatons gt 10 15 g representing 72 of the holocene mud flux has accumulated on the shelf in the orange river prodelta and mudbelt a clayey fine silt deposit focused on the inner to middle shelf only 8 5 gt of the mud flux occurs in holocene calcareous ooze on the slope comparison of the clay to mud ratio of offshore deposits with orange river suspended sediment and catchment soils indicates that 20 11 gt of the holocene mud flux has been lost as clay beyond the margin the orange river mud flux prior to the building of large dams 1930 1969 is ten times greater than the mean holocene mud flux and is reconciled with estimates of soil erosion within the catchment a tenfold increase in the orange river mud flux implies up to a hundredfold increase in total soil erosion depending on the extent of mud storage over periods of decades to centuries within the catchment erosion has shifted from areas of high relief and rainfall of the drakensberg escarpment during the holocene to intensely cultivated lands of low relief having moderate to high rainfall in the eastern catchment and to a lesser extent grazing areas of the southern orange river catchment

climatic patterns in equatorial and southern africa from 30 000 to 10 000 years ago reconstructed from terrestrial and near shore proxy data abstract as part of a wider study of last glacial and deglacial climates in the southern hemisphere continents we here review terrestrial and near shore marine records from equatorial and southern africa between 30 000 and 10 000 years ago 30 10 ka this time interval covers the lead up to the last glacial maximum lgm 21 2 ka the lgm proper and the ensuing deglacial records selected for review needed to meet three requirements continuity or near continuity over the period a well established chronology and at least one but preferably several unambiguous proxy ies we aim to show how regional climates of the sub continent have responded to orbital forcing as opposed to other global glacial interglacial boundary conditions and how they are related to high latitude climates sea and land surface conditions positions of the intertropical convergence zone itcz and of the westerly belt evidence of past climates derived from many independent proxies is given from west to southwest africa moisture from the atlantic ocean then from equatorial east africa to the southern subtropical summer rainfall domain moisture mainly from the indian ocean the lgm was cooler than today and generally drier in the tropics north of 8 9 s glacial to holocene increase in monsoonal precipitation primarily related to orbitally induced summer insolation in the northern hemisphere occurred by steps of increasing amplitude 17 16 14 5 11 5 ka major wet dry spells coincide with abrupt warm cold events in high northern latitudes and related itcz migrations in the southern tropics the main post glacial increase in tropical rainfall generally appears more gradual and in phase with antarctic warming data suggest a restricted northward migration of the itcz and concentration of tropical rainfall well south of the equator during the lgm and the younger dryas drier glacial conditions prevailed in southeastern africa while parts of southwestern africa point to enhanced humidity during the lgm suggesting that the winter westerly belt was either stronger than today or displaced further north possibly as a result of more extensive antarctic sea ice inferred african climatic fluctuations show the competing influences of tropical and high latitude climates of both hemispheres and suggest changes in both meridional and zonal circulation modes this review also reveals major geographical and methodological gaps and a number of unresolved issues providing pointers for future research

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

holocene geochronology of a continentalshelf mudbelt off southwestern africa the holocene lithostratigraphy and geochronology of sediments on an inner continental shelf mud belt off the west coast of southern africa is presented based on a study of seven large gravity cores numerous grab samples and two vibracores two distinctive sections of the mudbelt have been identie ed the northern section is associated with the orange river prodelta and is dominated by laminated clay rich sediments while the southern section off namaqualand is associated with more homogeneous muds ams radiocarbon ages of 31 samples from these cores are problematic due to the absence of expected modern material at the sediment ocean interface and numerous age reversals and inconsistencies in some of the cores possible mechanisms to explain the apparently anomalously old surface and near surface samples are suggested most likely expla nations appear to lie in a combination of sediment retrieval problems the periodic loss of e ne particulate organic carbon from within the water column the sampling of possible relic sediments and most likely of all the incorporation into the sediments of 14 c depleted terrigenous organic matter the age reversals are especially evident in the laminated sediments and the entrainment of old carbon from the terrestrial source of these sediments is offered as the most parsimonious explanation stable carbon isotope analyses and a single lumi nescence age support the contention that radiocarbon date inconsistencies are a consequence of terrestrial inputs of carbon which is non contemporaneous with the actual time of sedimentation in studies of offshore accumulations of terrigenous material the marine derived organic fraction may therefore prove a more reliable measure of radiocarbon chronology

decadal rainfall dipole oscillation over southern africa modulated by variation of austral summer land sea contrast along the east coast of africa abstracta rainfall dipole mode characterized by negative correlation between subtropical southern africa and equatorial eastern africa is identified in instrumental observation data in the recent 100 years the dipole mode shows a pronounced oscillation signal at a time scale of about 18 years this study investigates the underlying dynamical mechanisms responsible for this dipole pattern it is found that the southern african rainfall dipole index is highly correlated to the land sea contrast along the east coast of africa when the land sea thermal contrast strengthens the easterly flow toward the continent becomes stronger the stronger easterly flow via its response to east coast topography and surface heating leads to a low pressure circulation anomaly over land south of the maximum easterly flow anomalies and thus causes more rainfall in the south on a decadal time scale an enso like sst pattern acts to modulate this land sea contrast and the consequent rainfall dipole during a wet in the south

influence of tropical easterlies in southern africa s winter rainfall zone during the holocene abstract south africa s southwestern cape occupies a critical transition zone between southern hemisphere temperate winter and tropical summer moisture bearing systems in the recent geological past it has been proposed that the relative influence of these systems may have changed substantially but little reliable evidence regarding regional hydroclimates and rainfall seasonality exists to refine or substantiate the understanding of long term dynamics in this paper we present a mid to late holocene multi proxy record of environmental change from a rock hyrax midden from katbakkies pass located along the modern boundary between the winter and summer rainfall zones derived from stable carbon and nitrogen isotopes fossil pollen and microcharcoal these data provide a high resolution record of changes in humidity and insight into changes in rainfall seasonality whereas previous work concluded that the site had generally experienced only subtle environmental change during the holocene our records indicate that significant abrupt changes have occurred in the region over the last 7000 years contrary to expectations based on the site s location these data indicate that the primary determinant of changes in humidity is summer rather than winter rainfall variability and its influence on drought season intensity and or length these findings are consistent with independent records of upwelling along the southern and western coasts which indicate that periods of increased humidity are related to increased tropical easterly flow this substantially refines our understanding of the nature of temperate and tropical circulation system dynamics in sw africa and how changes in their relative dominance have impacted regional environments during the holocene