geochemical cycling of redox sensitive metals in sediments from lake malawi a diagnostic paleotracer for episodic changes in mixing depth changes in heat balance wind stress and lake level can affect the efficiency of mixing and depth of oxygen penetration in deep tropical lakes this study examines how transient changes in these parameters as reflected by the redox state of bottom waters are recorded in the sedimentary record of lake malawi we measured concentration profiles of redox sensitive metals across a layer of oxidized sediment deposited within a sequence composed of reduced sediments in a core taken at 298 m water depth 100 m below the present day chemocline by examining a range of metals that exhibit different geochemical behaviors mobilization under reducing fe mn versus oxidizing u conditions formation of insoluble sulfides cd mo pb zn susceptibility to scavenging onto fe or mn oxyhydroxide precipitates co mo pb v zn we are able to outline a sequence of events consistent with the formation of this feature 1 at some time before 11 ky bp there was an episode of penetration of oxygenated waters to depths close to or greater than that of this core i e substantially deeper in the lake basin than at present at this time diagenetically remobilized fe and mn were oxidized and precipitated in a near surface sediment horizon 2 fe and mn oxyhydroxides that precipitated from the water column as metal rich anoxic waters were mixed upward into oxygenated waters were deposited in an immediately overlying layer of the sediment such material continued to accumulate in surface sediments for a few hundred years until oxic conditions no longer prevailed in overlying waters 3 as the depth of the chemocline rose relative to the present day lake surface this authigenic material was in turn overlain by reducing sediments 4 subsequent diagenetic remobilization at the top and bottom of this redox sandwich resulted in formation of horizons enriched in u mo and sulfide forming metals notably cd along the redox gradients both above and to a lesser extent below the layer of oxidized sediment these enrichments immobilized under reducing conditions will remain as permanent markers of the episode of deepening of the chemocline even after reduction and remobilization of the oxidized fe and mn solids in addition such markers may be useful in determining whether observed episodic interruptions in deposition of varved sediments in the deep anoxic basins of lake malawi are due to bioturbation brought on by episodes of deeper oxygen penetration in the water column

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

abrupt climate change in southeast tropical africa influenced by indian monsoon variability and itcz migration 1 the timing and magnitude of abrupt climate change in tropical africa during the last glacial termination remains poorly understood high resolution paleolimnological data from lake tanganyika southeast africa show that wind driven seasonal mixing in the lake was reduced during the younger dryas inter allerod cool period older dryas and heinrich event 1 suggesting a weakened southwest indian monsoon and a more southerly position of the inter tropical convergence zone over africa during these intervals these events in lake tanganyika coeval with millennial and centennial scale climate shifts in the high latitudes suggest that changes in itcz location and indian monsoon strength are important components of abrupt global climate change and that their effects are felt south of the equator in africa however we observe additional events in lake tanganyika of equal magnitude that are not correlated with high latitude changes indicating the potential for abrupt climate change to originate from within tropical systems

late pleistocene and holocene vegetation history of the bale mountains ethiopia abstract a sediment core recovered from garba guracha a glacial lake at 3950 m altitude in the bale mountains of ethiopia at the boundary of the ericaceous and afroalpine vegetation belts provides a 16 700 year pollen record of vegetation response to climatic change the earliest vegetation recorded was sparse and composed mainly of grasses amaranthaceae chenopodiaceae and artemisia indicating an arid climate at 13 400 cal bp amaranthaceae chenopodiaceae pollen declined sharply and cyperaceae increased suggesting a change to moister conditions the younger dryas interval is represented by a small increase in artemisia and reduced cyperaceae indicating aridity just after the start of the holocene 11 200 cal bp the upper altitudinal limit of the ericaceous belt rose and woody ericaceous vegetation extended across the sanetti plateau in response to increased moisture and temperature the marked change from clastic to organic lake sedimentation at this time reflects the increase in woody vegetation cover in the lake catchment accompanied by soil stabilisation and increased leaf litter and soil humus content from about 6000 cal bp and especially after 4500 cal bp mid altitude dry afromontane juniper podocarpus forests developed on the northern slopes of the mountains in response to reduced rainfall in a shortened wet season erica shrub and forest decreased in area and altitude and the afroalpine ecosystem expanded on the plateau podocarpus declined from about 2000 cal bp as juniperus increased to its present dominance at 2500 3300 m altitude human impact on the high altitude afroalpine and ericaceous vegetation has been relatively minor confirming that the endemic biodiversity of the ethiopian mountains is a legacy of natural holocene vegetation change following repeated expansion and contraction of the upland ecosystems during the quaternary

hydroclimatic and geothermal controls on the salinity of mbaka lakes sw tanzania limnological and paleolimnological implications summary the hydroclimatic and geothermal controls on the salinity of small tropical crater lakes masoko katubwi kyambangunguru ilamba and kingiri aligned with the mbaka fault line north of lake malawi are investigated by water stable isotopes which are used to trace evaporative processes as to establish lake water balances and by chloride concentrations allowing to identify the main salinity sources this region shows positive excess in the exchanges between atmosphere and lake surfaces p e 0 with the exception of lake ilamba the lakes are closed surface basins and their levels are relatively stable as catchment inflows cannot be neglected groundwater outflows have to compensate for this excess the isotopic budgets show that these lakes constitute a series of windows on the local shallow aquifer in addition the estimated losses by evaporation cannot solely account for the lake salinity observed as the most saline lake differs from not the most evaporated lake salinity is then investigated from chloride concentrations and seems to be controlled by inflows which results from the mixing between i fresh and ii hydrothermal ground waters the contrasts in lake salinity almost one order of magnitude are first related to the hydrothermal contribution which increases with the proximity of the mbaka fault second due to positive exchange with the atmosphere the lake salinity appears systematically diluted in regard to the respective inflows this dilution effect increases as the fraction of total inputs lost by evaporation or the lake water residence time increases this current hydrological study shows that local wetter conditions are not inconsistent with higher lake salinity and allows to conciliate the questioned and apparent contradictory lake masoko wetter and salty paleoenvironmental and paleoclimatic records for the last glacial maximum and younger dryas time intervals further in a general manner this work addresses the case of lake submitted to wet environment and highlights the potential contribution of hydrothermal water on lakes salinization occurring in active regions such as the east african rift system

an abrupt change in the african monsoon at the end of the younger dryas 1 high resolution studies of variations in the elemental and stable carbon and nitrogen isotope composition of organic matter in cores from lakes malawi tanganyika and bosumtwi tropical africa indicate an abrupt change in the wind driven circulation of these lakes that within the limits of available chronologies was contemporaneous with the end of the younger dryas in the northern hemisphere the change was also coincident with shifts in surface winds recorded in cores from off the west and northeast coasts of africa a range of other proxies indicate that these changes in wind regime were accompanied by a marked increase in precipitation in the northern tropics africa south of 5 10 s on the other hand initially suffered drought conditions together the evidence suggests an abrupt northward translation of the african monsoon system at circa 11 5 0 25 ka b p the data assembled here contribute to a growing body of work showing that the younger dryas was a major climatic excursion in tropical africa furthermore they add substance to recent suggestions that climatic events in the southern hemisphere may have played a significant role in the abrupt demise of the younger dryas

influence of climate change on algal community structure and primary productivity of lake malawi east africa from the last glacial maximum to present biomarkers of aquatic algae and compound specific carbon isotopes are used to examine past variations in algal community composition and primary productivity in lake malawi we note major changes at the pleistocene holocene boundary from the last glacial maximum until 11 8 calendar years before present kyr b p lake malawi was characterized by either low rates of primary productivity or algal productivity that was dominated by a group other than diatoms at the onset of the holocene conditions similar to those of modern lake malawi were initiated with diatoms and nitrogen fixing cyanobacteria becoming more important contributors to primary productivity the transition at 11 8 kyr b p is likely related to a shift in the dominant wind direction over lake malawi resulting from a southward shift in the mean latitudinal position of the intertropical convergence zone during the last glacial throughout the 23 kyr b p record the effects of windinduced upwelling are important and may be the main control on the carbon isotopic composition of algal lipids through delivery of 13c depleted co2 derived from organic matter decomposition in deeper waters to the photic zone relationships are also suggested between thermal stratification and primary productivity with cool conditions at 12 and 8 kyr b p resulting in weaker thermal stratification and increased primary productivity the opposite situation occurs at 4 9 kyr b p when significantly warmer temperatures and decreased algal productivity are observed thus in lentic systems such as lake malawi the major influence of climate on algal ecology appears to be through feedbacks in physical circulation mechanisms

holocene paleo climatic record from the south african namaqualand mudbelt a source to sink approach variations in the sediment input to the namaqualand mudbelt during the holocene are assessed using an integrative terrestrial to marine source to sink approach geochemical and sr and nd isotopic

biogenic silica deposition in lake malawi east africa over the past 150 000years abstract we report a 150 000 year record of the abundance of biogenic silica bsi in drill cores from the northern and central basins of lake malawi the periods of highest diatom burial at both sites occurred around 65 69 and 51 60 thousand years ago ka after the termination of prolonged intense drought in the region these peaks are believed to reflect elevated delivery of dissolved silica to the lake due to acceleration of chemical weathering in the drainage basin the droughts that preceded these bsi depositional episodes occurred at precessional frequency corresponding to times of minimum austral spring or summer insolation in the region prior to 60 ka subsequent arid spells have not been as severe due to the reduced amplitude of precessional forcing as a result of the superimposed effect of eccentricity however biogenic silica records do not show significant sensitivity to precessional forcing the bsi burial flux in the north basin displays strong millennial scale variability since 50 ka with peak values occurring during cold times in the northern hemisphere as reflected in the greenland ice core records we observe no relationship between bsi and deposition of volcanic tephras in this system the central basin core also displays millennial scale variability in bsi abundance during the past 50 ky of comparable magnitude to that in the north basin but without systematic correlation to the north basin bsi or greenland ice core records in general we conclude that bsi profiles from the north and probably south basins are more readily interpreted in terms of regional climate dynamics than are bsi profiles from more central locations in long narrow tropical rift lakes diatom burial rates are suspected to be too influenced by silica limitations imposed by diatom production and burial in the upwelling systems at either end of these low latitude lacustrine systems

sedimentary environment evolution and biogenic silica records over 33 000 years in the liaohe delta china the burial efficiency of biogenic silica bsi in deltaic sediments is associated both with the nutrient balance in estuarine ecosystems and with the carbon cycle and climate change to explore these relationships foraminifera data physical and chemical parameters and ages determined by accelerator mass spectrometry 14c and optically stimulated luminescence from a core drilled at the southwestern edge of the lower liaohe plain in may 2012 were presented the sedimentary environments since 33 000 cal yr bp were divided into four depositional units namely a fluvial deposit u1 lacustrine deposit u2 marine related deposit u3 and upper delta plain deposit u4 environmentally mediated differences in apparent mass accumulation rates amars of bsi and organic carbon corg were significant the bsi amar in the later parts of u1 and u2 occurred mainly in the pleistocene and averaged 11 34 0 22 and 16 69 0 91 g m 2 yr 1 which is lower than the analogues for u3 23 59 2 89 41 74 6 37 g m 2 yr 1 and u4 37 25 9 96 g m 2 yr 1 that occurred during the holocene the bsi record responded more coherently and was more sensitive than corg to northern hemisphere paleoclimatic variations on a long timescale and to abrupt periodic winter monsoon winds or warming forcings on a short timescale there was a negative correlation between the concentration of bioavailable fe2o3 and the ratio of bsi corg the implication being that fe availability may have modulated silicic acid uptake on a very short timescale and in turn impacted the dynamics of carbon burial

bipolar modulation of millennial scale west african monsoon variability during the last glacial 75 000 25 000 years ago abstract time series of planktonic foraminiferal 18 o and ba ca based sea surface salinity sss estimates from the eastern gulf of guinea eastern equatorial atlantic indicate changes in runoff that reflect variability of spatially integrated precipitation over the equatorial west african monsoon area millennial scale and recurring runoff induced sss rises and declines in the range of 1 5 and 2 psu practical salinity unit reveal rapid oscillation between dry and wet phases the timing of decreased runoff coincides with oscillation of dansgaard oeschger stadials and heinrich events the most severe monsoon weakening correlating with the latter 18 o residual time series derived by removing temperature ice volume and salinity components from the foraminiferal 18 o record suggest that weak monsoon precipitation during stadials and heinrich events was accompanied by significant shifts in 18 o precipitation toward higher values furthermore 18 o analysis of individual tests of globigerinoides ruber pink 18 o indiv during dry episodes show a total range and variance of 2 3 and 0 25 n 121 indicating that seasonal contrast of sea surface freshening was significantly reduced during heinrich events relative to that of interstadials which show a total range and variance of 3 35 and 0 42 n 140 on the basis of the timing and magnitude of changes in the monsoon record it is evident that northern high latitude climate was the most dominant control on the west african monsoon variability however a southern high latitude imprint is also apparent during some episodes this centennially resolved climate record demonstrates that the equatorial west african monsoon experienced profound changes in the amount seasonal contrast and moisture source of summer monsoon precipitation during the last glacial the most plausible mechanism is a large scale southward displacement of the monsoon trough most likely initiated by large scale reorganization of atmospheric circulation in response to northern high cooling and southern high latitude warmth

high resolution 14c dating of a 25 000 year lake sediment record from equatorial east africa abstract we dated a continuous 22 m long sediment sequence from lake challa mt kilimanjaro area kenya tanzania to produce a solid chronological framework for multi proxy reconstructions of climate and environmental change in equatorial east africa over the past 25 000 years the age model is based on a total of 168 ams 14 c dates on bulk organic matter combined with a 210 pb chronology for recent sediments and corrected for a variable old carbon age offset this offset was estimated by i pairing bulk organic 14 c dates with either 210 pb derived time markers or 14 c dates on grass charcoal and ii wiggle matching high density series of bulk organic 14 c dates variation in the old carbon age offset through time is relatively modest ranging from 450 yr during glacial and late glacial time to 200 yr during the early and mid holocene and increasing again to 250 yr today the screened and corrected 14 c dates were calibrated sequentially statistically constrained by their stratigraphical order as a result their constrained calendar age distributions are much narrower and the calibrated dates more precise than if each 14 c date had been calibrated on its own the smooth spline age depth model has 95 age uncertainty ranges of 50 230 yr during the holocene and 250 550 yr in the glacial section of the record the 13 c values of paired bulk organic and grass charcoal samples and additional 14 c dating on selected turbidite horizons indicates that the old carbon age offset in lake challa is caused by a variable contribution of old terrestrial organic matter eroded from soils and controlled mainly by changes in vegetation cover within the crater basin

climate drying and associated forest decline in the lowlands of northern guatemala during the late holocene abstract palynological studies document forest disappearance during the late holocene in the tropical maya lowlands of northern guatemala the question remains as to whether this vegetation change was driven exclusively by anthropogenic deforestation as previously suggested or whether it was partly attributable to climate changes we report multiple palaeoclimate and palaeoenvironment proxies pollen geochemical sedimentological from sediment cores collected in lake peten itza northern guatemala our data indicate that the earliest phase of late holocene tropical forest reduction in this area started at 4500 cal yr bp simultaneous with the onset of a circum caribbean drying trend that lasted for 1500 yr this forest decline preceded the appearance of anthropogenically associated zea mays pollen we conclude that vegetation changes in peten during the period from 4500 to 3000 cal yr bp were largely a consequence of dry climate conditions furthermore palaeoclimate data from low latitudes in north africa point to teleconnective linkages of this drying trend on both sides of the atlantic ocean

vegetation history in western uganda during the last 1200 years a sedimentbased reconstruction from two crater lakes pollen plant macrofossil and charcoal records from two neighbouring crater lakes lake wandakara and lake kasenda in lower montane altitude 1200m western uganda 0 5dn 30 reveal major changes in local and regional vegetation over the last 1200 years which can be related to regional variations in climate especially effective precipitation and human impact the biological signals are supplemented by evidence from physical sedimentary analyses magnetic susceptibility loss on ignition dry mass accumulation rate for major catchment changes in a wider regional context from ad 750 to 900 medium altitude moist forest existed around lake kasenda which was largely replaced by grassland by ad 1000 coincident e with evidence for increased catchment erosion and fire events linked to human impact during a brief arid phase despite wetter conditions from ad 1000 to 1200 and in the 1400s grassland prevailed around both sites until c ad 1700 1750 with increased catchment disturbance from ad 1600 t

fish fossils as paleo indicators of ichthyofauna composition and climatic change in lake malawi africa abstract numerous biological and chemical paleorecords have been used to infer paleoclimate lake level fluctuation and faunal composition from the drill cores obtained from lake malawi africa however fish fossils have never been used to examine changes in african great lake vertebrate aquatic communities nor as indicators of changing paleolimnological conditions here we present results of analyses of a lake malawi core dating back 144 ka that describe and quantify the composition and abundance of fish fossils and report on stable carbon isotopic data 13c from fish scale bone and tooth fossils we compared the fossil 13c values to 13c values from extant fish communities to determine whether carbon isotope ratios can be used as indicators of inshore versus offshore pelagic fish assemblages fossil buccal teeth pharyngeal teeth and mills vertebra and scales from the fish families cichlidae and cyprinidae occur in variable abundance throughout the core carbon isotopic ratios from numerous fish fossils throughout the core range between 7 2 and 27 5 similar to those found in contemporary lake malawi benthic and pelagic fish faunas these results are the first paleo record of fish fossils from a lake malawi sediment core and the first reported 13c values from lake malawi fish fossils this approach provides a new methodology and framework for interpreting pelagic versus inshore fish faunas lake level fluctuations and the evolution of the lake malawi fish assemblages

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

seasonal and interannual particle export in an african rift valley lake a 5 yr record from lake malawi southern east africa a time sequencing sediment trap was deployed at 300 350 m in lake malawi east africa from 1987 to 1992 to measure particulate export to the deep anoxic hypolimnion in the northern and central lake regions the monthly settling particulate samples provide a data set of seasonal and interannual export fluxes of organic carbon biogenic opal calcium carbonate and lithogenic material maximum total particle fluxes 50 400 mg m 2 d 1 occurred primarily during the dry windy season april through october when algal productivity is high because of wind induced upwelling of nutrient enriched metalimnion and hypolimnion waters peak flux particulates contained an abundance of aulacoseira and stephanodiscus diatom valves and chains the total particle mass flux during the wet austral summer months november through march was consistently one to three orders of magnitude less than that measured during the dry months and consisted of mineral shards terrestrial plant debris and scattered diatom tests the 5 yr trap data provide support for the claim that the light dark lamination couplets abundant in northern and central lake cores reflect seasonal delivery to the sediments of diatom rich particulates during the windy months and diatom poor material during the wet season however interannual and spatial variability in upwelling and productivity patterns as well as el nino southern oscillation enso related rainfall and drought cycles appears to exert a strong influence over the magnitude and geochemical composition of particle export to the deep hypolimnion of lake malawi

wet phases in tropical southern africa during the last glacial period 1 a 45 000 year high resolution sedimentary record from lake masoko in tanzania shows the climate in this part of east africa to have been characterized by a short and less severe dry season during the last glacial maximum moisture and lake level proxies pollen assemblages and magnetic susceptibility indicate that rainfall in the masoko area was strongly controlled by low latitude insolation i e precessional forcing such observations contrast with the climatic patterns previously reconstructed in east africa for the last glacial indeed widespread dry conditions are generally observed and are attributed to the predominant control of high latitude glacial forcing over insolation forcing on the tropical hydrology however during the younger dryas cold event out of phase with regional insolation behaviour wetter conditions prevailed in this area suggesting that the rainfall belt over africa was probably shifted to the south bringing moisture to the southernmost tropics

sedimentation in lake malawi east africa during the past 10 000 years a continuous paleoclimatic record from the southern tropics a suite of piston cores recovered from lake malawi 9 14 s 34 35 e east africa in 1986 has been analyzed for major and minor elements organic c and n calcium carbonate and diatoms an internally consistent stratigraphy was constructed from calcium carbonate abundance and variations in the two most abundant diatom genera stephanodiscus and melosira with age control obtained primarily from 14c dating of the carbonate differences with time in fe abundance in a transect of cores from different water depths have been interpreted to reflect changes in chemocline depth the depth to the chemocline was on the order of 100 m shallower than present prior to 3500 yr b p indicating less seasonality carbonate production and preservation appears to be related to climatically induced changes in both salinity and chemical distributions in the water column the carbonate which precipitates from surface waters is most abundant during the interval from about 10 000 to 6000 yr b p this micrite most likely represents periods of low lake level when salinity increased and carbonate precipitation was enhanced sedimentary evidence suggests that lake levels were 100 150 m lower than present during this period this record is different from climatic trends in northern intertropical africa but appears to also be related to changes in insolation and monsoon circulation this is the northernmost basin in africa reported to exhibit a southern hemisphere response to the early holocene northern hemisphere summer insolation maximum the climatic hingeline north of lake malawi 9 s implied by our results is significantly south of that indicated by general circulation model simulations however the cores show evidence for periods of abrupt climate change during the interval of generally arid climate

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

climate variability at the southern boundaries of the namib southwestern africa and atacama northern chile coastal deserts during the last 120 000 yr abstract in this study we present grain size distributions of the terrigenous fraction of two deep sea sediment cores from the se atlantic offshore namibia and from the se pacific offshore northern chile which we unmix into subpopulations and which are interpreted as coarse eolian dust fine eolian dust and fluvial mud the downcore ratios of the proportions of eolian dust and fluvial mud subsequently represent paleocontinental aridity records of southwestern africa and northern chile for the last 120 000 yr the two records show a relatively wet last glacial maximum lgm compared to a relatively dry holocene but different orbital variability on longer time scales generally the northern chilean aridity record shows higher frequency changes which are closely related to precessional variation in solar insolation compared to the southwestern african aridity record which shows a remarkable resemblance to the global ice volume record we relate the changes in continental aridity in southwestern africa and northern chile to changes in the latitudinal position of the moisture bearing southern westerlies potentially driven by the sea ice extent around antarctica and overprinted by tropical forcing in the equatorial pacific ocean

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

geomorphological contributions to palaeolimnology on the african continent abstract article history received 19 december 2007received in revised form 5 july 2008accepted 22 july 2008available online 3 august 2008keywords quaternarybeach ridgeshorelinelakemultiproxyosl lakes are highly informative repositories of information of the terrestrial response to regional and global climatedrivers in quaternary studies lake oor records are now frequently used to establish the magnitude timing andgeographicalextentofhumid aridtransitionsovertimescalesof10 2 10 4 years whiletheresolutionof thisrecordisunparalleled much of the geochemical and sedimentary da ta is challenging to interpret and highly basin speci c geomorphologicalproxies particularlyshorelines offeranadditionaloralternativerecordoflakehistory withrecenttechnological advances facilitating both access to and the utility of this proxy record recent advances in opticallystimulated luminescence osl dating allow the determination of the age of beach ridge emplacement in theabsence of organic material while the availabilityof shuttle radar topography mission srtm data in conjunctionwith digital elevation models dem aids in the identi cation of shoreline features and the topographicreconstruction of the former extent of palaeolakes here we highlight and illustrate the use of lacustrine shorelinefeatures for unravelling a quaternary climate signal wit hin africa from otherwise inaccessible and undatablepalaeolake records in the semi arid and arid subtropics an d identify their contribution towards high resolutionmultiproxy reconstructions of tropical low latitude quaternary environments and climates 2008 elsevier b v all rights reserved

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

a 2000 year atmospheric history of methyl chloride from a south pole ice core evidence for climate controlled variability methyl chloride ch3cl is a naturally occurring ozone depleting gas with a complex biogeochemical cycle involving tropical vegetation soils biomass burning and the oceans this study presents ch3cl measurements in air extracted from a 300 m ice core from south pole antarctica covering the time period from 160 bc to 1860 ad the data exhibit an increasing trend of 3 ppt parts per trillion over 100 years and higher frequency variations that appear to be climate related ch3cl levels were elevated from 900 1300 ad by about 50 ppt relative to the previous 1000 years coincident with the warm medieval climate anomaly mca ch3cl levels decreased to a minimum during the little ice age cooling 1650 1800 ad before rising again to the modern atmospheric level of 550 ppt these variations most likely reflect changes in tropical and subtropical conditions and raise the possibility that a warmer future climate may result in higher tropospheric ch3cl levels

facies architecture of flexural margin lowstand delta deposits in lake edward east african rift constraints from seismic reflection imaging abstract lake edward is single half graben rift basin unique in the east african rift system as a result of its connection to lake george via the kazinga channel a paleo river valley which is incised into the flexural margin of the lake using recently acquired normal incidence seismic reflection data and thirty three lake bottom sediment samples we examine the consequences of this hydrologic connection for understanding depositional processes and facies development along the flexural margin of lake edward three depositional sequences were defined in the study area based on top and bottom discordances of seismic reflections climatically induced changes in lake level appear to have forced sequence development sequence i deposits indicate that highstand conditions prevailed earlier in the pleistocene evidence for high frequency lake level change comes from lowstand delta clinoforms in two separate stratigraphic intervals on the flexural margin an older lowstand event occurred during sequence ii time and reduced lake level by at least 37 m a younger lowstand event occurred during the deposition of sequence iii and reduced lake level by 18 m clastic sedimentation on the flexural margin of lake edward is strongly modified by inflow from the kazinga channel and lake george during periods of lowered lake level we suggest that the presence of an incised valley at the margin of the rift controls the stratigraphic development of clinoforms diagnostic of lowstand deltaic sedimentation the morphology and orientation of these clinoforms suggest that discharge from lake george during arid periods utilized the kazinga channel to transport sediment toward the exposed flexural margin of lake edward dipping reflections in sigmoid oblique clinoforms suggest that these flows were capable of transporting sediment loads that included coarse grain sizes deposition by this process occurred several times during the late quaternary history of lake edward and represents an important modern analogue for linked incised valley lacustrine delta sequences in the stratigraphic record

paleolimnological evidence for the onset and termination of glacial aridity from lake tanganyika tropical east africa geochemical and sedimentological data in a continuous 60 000 year sediment core record from the kalya horst region of central lake tanganyika provide a detailed history of paleoclimate mediated weathering and overflow events from upstream lake kivu univariate elemental profiles bivariate elemental ratios and multivariate analyses of chemical trends show variations between the dry late pleistocene 32 18 ka cal yr bp and the wetter conditions that both preceded and post date that interval this record places important new constraints on the timing of aridity in east africa during the high latitude last glacial maximum lgm based on significant decreases in magnetic susceptibility and soluble cation concentrations coinciding with biogenic silica elemental indicatorsintheoldestportionofthesedimentaryrecord 60 50kacalyrbp characterizethisintervalasacomparatively wetperiod similar to modern conditions our record demonstrates that the ensuing transition toward arid conditions in tropical africa during high latitude glaciation was a two staged event with intermediate levels of aridity occurring from 50 32 ka cal yr bp followed by intense aridity from 32 18 ka cal yr bp the initiation of inflow from upstream lake kivu into lake tanganyika is evidenced at 10 6 ka cal yr bp through its influence on both elemental profiles mg ca and through its effect on 87 sr 86 sr increases in elemental mg ca sr concentrations coincide with the timing of the lake kivu overflow metal geochemistry suggests that the overflow from lake kivu into lake tanganyika may have ceased between 8 and 6 ka cal yr bp suggesting a period of middle holocene aridity in east africa 2007 elsevier b v all rights reserved

century to millennial scale climatic variability in lake malawi revealed by isotope records diatom based oxygen isotope data 18odiatom from lake malawi show multi centennial scale wet dry intervals spaced approximately every 2 3 ka throughout a 25 ka sequence the 18odiatom record is supported by a lower resolution deuterium dpa isotope curve derived from palmitic acid we interpret these isotope data in terms of major shifts in precipitation and evaporation moderated by seasonal controls on the host organisms dry periods marked by relatively positive isotope values represent the extension of abrupt holocene events noted from northern and equatorial africa to 10 15 s these events in lake malawi correspond to cool episodes in greenland thereby demonstrating teleconnections generated by meridional temperature gradients sea surface temperatures are likely to be the primary transmitter of deglacial climate changes although trade wind strength and direction is critical in controlling precipitation patterns in tropical regions conversely the global hydrological cycle driven by low latitude regions represents an important positive feedback amplifying deglacial processes

biomarker records of palaeoenvironmental variations in subtropical southern africa since the late pleistocene evidences from a coastal peatland abstract southern africa s unique global position has given rise to a dynamic climate influenced by large sea surface temperature gradients and seasonal fluctuations in the inter tropical convergence zone due to the semi arid climate of the region terrestrial palaeorecords are rare and our understanding of the long term sensitivity of southern african terrestrial ecosystems to climatic drivers is ambiguous a 810 cm continuous peat core was extracted from the mfabeni peatland with a 14 c basal age of c 47 thousand years calibrated before present kcal yr bp positioning it as one of the oldest known sub tropical coastal peatlands in southern africa this peat core provides an opportunity to investigate palaeoenvironmental changes in subtropical southern africa since the late pleistocene biomarker n alkane n alkanoic acid and n alkanol analysis in conjunction with previously published bulk geochemical data was employed to reconstruct organic matter om sources rates of om remineralisation and peatland hydrology our results showed that the principal om source into the peatland was emergent and terrestrial plants with exception of shallow lake conditions when submerged macrophytes dominated c 44 5 42 6 29 7 26 1 23 1 16 7 7 1 and 2 2 kcal yr bp n alkane proxies suggest that local plant assemblages were predominantly influenced by peatland hydrology by incorporating temperature sensitive n alkanoic acid and n alkanol proxies it was possible to disentangle the local temperature and precipitation changes we report large variations in precipitation intensities but subdued temperature fluctuations during the late pleistocene the holocene period was characterised by overall elevated temperatures and precipitation compared to the preceding glacial period interspersed with a millennial scale cooling event a close link between the mfabeni archive and adjacent indian ocean marine core records was observed suggesting the regional ocean surface temperatures to be the dominant climate driver in this region since the late pleistocene

lithostratigraphy physical properties and organic matter variability in lake malawi drillcore sediments over the past 145 000years abstract scientific drill cores recovered from lake malawi exhibit a remarkable down core lithologic variability and are indicative of radically changing environmental conditions forced by large amplitude lake level shifts over the past 150 kyr here we present detailed lithologic and sedimentary fabric descriptions of the key sedimentary units along with down core physical properties data down core organic matter geochemistry toc c n and 13c data sets and images and descriptions from core sections and from sediment smear slide microscopy these data reveal a fundamental change in lake malawi s limnology and regional climate at ca 60 70 ka prior to this time the lake was characterized by large amplitude variations in lake level and water chemistry but after 60 ka the lake remained comparatively high and the central basin drill site accumulated mainly organic rich laminated sediments organic matter sources changed dramatically during the different lake stages during major lake high stands a mixed assemblage of algal diatom dominated woodland and aquatic macrophyte c4 pathway and grassland c3 pathway organic matter was deposited whereas during extreme low lake stages water depths

a high resolution paleoclimate record spanning the past 25 000 years in southern east africa high resolution profiles of the mass accumulation rate of biogenic silica and other geochemical proxies in two piston cores from northern lake malawi provide a climate signal for this part of tropical africa spanning the past 25 000 years the biogenic silica mass accumulation rate was low during the relatively dry late pleistocene when the river flux of silica to the lake was suppressed millennial scale fluctuations due to upwelling intensity in the late pleistocene climate of the lake malawi basin appear to have been closely linked to the northern hemisphere climate until 11 thousand years ago relatively cold conditions in the northern hemisphere coincided with more frequent north winds over the malawi basin perhaps resulting from a more southward migration of the intertropical convergence zone

diatomaceous sediments and environmental change in the pleistocene olorgesailie formation southern kenya rift valley abstract the olorgesailie formation is comprised of lacustrine volcaniclastic and alluvial sediments that formed in the southern kenya rift between about 1 2 million and 490 000 years ago diatoms are common in much of the sequence and preserve a record of environmental change within the basin a high resolution diatom stratigraphy has been developed for these deposits the data document the presence of freshwater and saline lakes as well as wetlands transfer functions indicate that these water bodies ranged in conductivity between about 200 20 000 s cm 1 with ph varying between about 7 5 and 10 3 pedogenesis affected multiple horizons within the succession reflecting periods of emergence that encompass much of the time represented by the olorgesailie formation a variety of other sedimentological indicators carbonates rhizoliths mudcracks erosional channels also record periods when the sampled portions of the basin were dominated by terrestrial conditions stone tools are common at several levels indicating the use of the area by hominins lakes and wetlands were potentially usable as sources of potable water by hominins for part of the basin history but at other times were undrinkable other water sources springs rivers would have been necessary during these periods paleoenvironments in the basin were complex and changed frequently with time such shifts in resources and habitat distribution during olorgesailie formation time seem likely to have influenced the behavior and evolution of local plant and animal populations including homo

spatial and temporal variation in cores from lake titicaca bolivia peru during the last 13 000yrs we compared the stratigraphy of sediment cores that span the last 13 000 yrs from three sites in the main basin of lake titicaca boliva peru as indicators of regional paleoclimate the cores show similar patterns of change after 6400 calendar yrs before present cal yr bp but differ before that time site ne98 pc2 which is near the rio illave and its delta shows differences in diatom species composition and in calcium carbonate concentrations relative to cores from the other two sites particularly during times of inferred high precipitation in contrast the carbon isotopic stratigraphy of the three sites is relatively similar the magnetic susceptibility data suggest that the proximity of site ne98 pc2 to the river and delta resulted in higher loads of detrital sediment prior to 6400 yr bp whereas pelagic sources contributed most of the sediment at the other sites these differences highlight the potential for spatial heterogeneity of sediment records in large lake systems and the importance of evaluating multiple cores for robust interpretation of paleoenvironmental history

atmospheric circulation patterns during late pleistocene climate changes at lake malawi africa abstract the climate of tropical africa transitioned from an interval of pronounced orbitally paced megadroughts to more humid and stable conditions approximately 70 000 years ago scholz et al 2007 the regional atmospheric circulation patterns that accompanied these climatic changes however are unclear due to a paucity of continental paleoclimate records from tropical africa extending into the last interglacial we present a new 140 kyr record of the deuterium hydrogen isotopic ratio of terrestrial leaf waxes d wax from drill cores from lake malawi southeast africa that spans this important climatic transition d wax shifts from highly variable and relatively d depleted to more stable and d enriched around 56 ka contemporary with the onset of more humid conditions in the region moisture source and transport history dominate the d wax signal at lake malawi with local rainfall amount playing a secondary role for much of the paleorecord analysis of modern moisture sources for lake malawi suggests that d depletion of waxes during the megadroughts may have been caused by an enhanced contribution of the drier d depleted air mass currently located in central southern africa to the lake malawi catchment this d depleted air mass is associated with the descending limb of the hadley cell which implies significant changes in the hadley circulation during the megadroughts and related changes in the position of the intertropical convergence zone over africa these findings demonstrate the ability of d wax to serve as an atmospheric tracer when used in conjunction with additional proxy records for moisture balance and elucidate potential mechanisms for pronounced hydrological change in southeast africa during the late pleistocene

biogenic silica a neglected component of the coupled global continental biogeochemical cycles of carbon and silicon on geological time scales 106 years the global geochemical cycles of carbon and silicon are coupled by the drawdown of atmospheric co2 through chemical weathering of ca and mg silicate minerals in continental rocks rivers transport the soluble products of weathering cations alkalinity and silicic acid to the oceans where they are utilized by marine ecosystems on decadal to glacial interglacial time scales however large biotic fluxes and storages of si within terrestrial and freshwater ecosystems need to be taken into account recent studies have emphasized the importance of si accumulating plants which deposit significant amounts of amorphous hydrated silica in their tissues as opal phytoliths these include grasses sedges palms some temperate deciduous trees and conifers and many tropical hardwoods landscapes dominated by accumulator plants such as tropical rainforests grasslands herbaceous wetlands and bamboo forests act as silica factories important silica bioengineers in freshwater ecosystems comprise diatoms sponges and chrysophytes this paper reviews the biological role of si in higher plants the impact of vegetation on rates of chemical weathering the fluxes of si through catchment ecosystems lakes and rivers and the potential contribution of new geochemical and isotopic tracers to si biogeochemistry multiproxy investigations of lake sediments will provide novel insights into past variations in si biocycling from terrestrial to aquatic realms on 10 106 year time scales copyright 2008 john wiley sons ltd

orbital forcing of glacial interglacial variations in chemical weathering and silicon cycling within the upper white nile basin east africa stable isotope and biomarker evidence from lakes victoria and edward on quaternary time scales the global biogeochemical cycle of silicon is interlocked with the carbon cycle through biotic enhancement of silicate weathering and uptake of dissolved silica by vascular plants and aquatic microalgae notably diatoms for which si is an essential nutrient large tropical river systems dominate the export of si from the continents to the oceans here we investigate variations in si cycling in the upper white nile basin over the last 15 ka using sediment cores from lakes victoria and edward coupled measurements of stable o and si isotopes on diatom separates were used to reconstruct past changes in lake hydrology and si cycling while the abundances of lipid biomarkers characteristic of terrestrial emergent higher plants submerged floating aquatic macrophytes and freshwater algae document past ecosystem changes during the late glacial to mid holocene 15 5 5 ka bp orbital forcing greatly enhanced monsoon rainfall forest cover and chemical weathering riverine inputs of dissolved silica from the lake catchments exceeded aquatic demand and may also have had lower si isotope values since 5 5 ka bp increasingly dry climates and more open vegetation reinforced by the spread of agricultural cropland over the last 3 4 ka have reduced dissolved silica inputs into the lakes centennial to millennial scale dry episodes are also evident in the isotopic records and merit further investigation

tropical east african climate change and its relation to global climate a record from lake tanganyika tropical east africa over the past 90 kyr abstract forcing mechanisms of tropical climate in continental areas remain poorly understood due in large part to a lack of continuous long term high fidelity records sediment core t97 52v from lake tanganyika provides new insight into the timing and mechanisms behind east african climate change over the past 90 kyr this record is particularly important because other than a recently recovered scientific drill core from lake malawi there are no other continuous well dated records from east africa prior to 60 ka the high resolution age model presented here provides a large degree of age certainty for the past 45 kyr and our suite of proxies allows a thorough examination of lake tanganyika s dynamics from core stratigraphy and chemical analyses we present evidence of a lake level drop greater than 400 m sometime prior to 90 ka much greater than that inferred for the lgm suggesting a period of intense aridity sometime around 100 ka additionally core t97 52 v preserves evidence of worm burrows detected by x radiographic imagery as indicated by burrow shaped deposits of iron oxide indicating a shallow lake at the time of deposition of that material intermittently high lake levels between 78 ka and 72 ka developed at the same time as a weakened asian monsoon and a pluvial phase in northeast brazil suggesting a global reorganization of climate possibly forced by a reduction in orbital eccentricity over the past 60 ka this core preserves the same events recorded in a core collected 100 km away in the southern basin of lake tanganyika including an unexplained increase in biogenic silica at 37 ka suggesting that this vast lake is responding coherently across both major bathymetric basins to regional and global climate forcing

climatic and volcanic forcing revealed in a 50 000 year diatom record from lake massoko tanzania the interactions between climatic and volcanic forcing on diatom communities contained in a 50 000 year sedimentary sequence from lake massoko tanzania were examined at the century scale 19 discrete tephra inputs to the lake isolated the sedimentary nutrient supply and shifted the diatom communities to those tolerant of low phosphorus levels whereas at the millennial scale diatom inferred shifts in precipitation evaporation based on conductivity optima and diatom life form ratios were broadly similar to lake level reconstructions from lake rukwa lake malawi and others in the region some fluctuations of lake massoko are consistent with the precession driven changes in insolation but the major climate shifts do not relate directly to orbital forcing of summer insolation south of the equator and show more consistency with records from the equatorial and northern tropics that receive rainfall from the passing of the intertropical convergence zone sea surface temperatures are strongly correlated to multimillennial scale climate patterns over this region of africa

effect of aridity and rainfall seasonality on vegetation in the southern tropics of east africa during the pleistocene holocene transition fossil pollen analyses from northern lake malawi southeast africa provide a high resolution record of vegetation change during the pleistocene holocene transition 18 9 ka recent studies of local vegetation from lowland sites have reported contrasting rainfall signals during the younger dryas yd the lake malawi record tracks regional vegetation changes and allows comparison with other tropical african records identifying vegetation opening and local forest maintenance during the yd our record shows a gradual decline of afromontane vegetation at 18 ka around 14 5 ka tropical seasonal forest and zambezian miombo woodland became established at 13 ka drier more open formations gradually became prevalent although tropical seasonal forest taxa were still present in the watershed during the yd this drought intolerant forest type was likely restricted to areas of favorable edaphic conditions along permanent waterways the establishment of drought tolerant vegetation followed the reinforcement of southeasterly tradewinds resulting in a more pronounced dry winter season after 11 8 ka the onset of the driest most open vegetation type was coincident with a lake low stand at the beginning of the holocene this study demonstrates the importance of global climate forcing and local geomorphological conditions in controlling vegetation distribution

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

a window into africa s past hydroclimates the sisal_v1 database contribution africa spans the hemispheres from temperate region to temperate region and has a long history of hominin evolution although the number of quaternary palaeoclimatic records from the continent is increasing much of the history of spatial and temporal climatic variability is still debated speleothems as archives of terrestrial hydroclimate variability can help reveal this history here we review the progress made to date with a focus on the first version of the speleothem isotopes synthesis and analysis sisal database the geology of africa has limited development of large karst regions to four areas along the northern coast bordering the mediterranean eastern africa and the horn of africa southwestern africa and southern africa exploitation of the speleothem palaeoclimate archives in these regions is uneven with long histories of research e g in south africa but large areas with no investigations such as west africa consequently the evidence of past climate change reviewed here is irregularly sampled in both time and space nevertheless we show evidence of migration of the monsoon belt with enhanced rainfall during interglacials observed in northeast africa southern arabia and the northern part of southern africa evidence from eastern africa indicates significant decadal and centennial scale rainfall variability in northwestern and southern africa precession and eccentricity influence speleothem growth largely through changing synoptic storm activity

groundwater residence time and paleorecharge conditions in the deep confined aquifers of the coastal watershed south east tanzania summary analysis of radiocarbon and stable isotopes of c h and o in groundwater samples from the coastal watershed of southeastern tanzania is used to decipher the age of groundwater and the climatic conditions at the time of recharge radiocarbon dating was corrected on the basis of stable carbon isotope ratios and hydrochemical data two main recharge periods are recognised 1 a recent recharge period with residence times dated to younger than 1 3 ka bp for the shallow aquifer and some deep groundwater aquifers and 2 a paleorecharge occurring during the late pleistocene to holocene transition between 6 and 13 ka bp for the lower confined aquifer the climatic excursions arid and humid phases identified in this study match well with those identified from studies of paleo climatic records in tanzania and east africa the oxygen 18 and radiocarbon results show that there is a potential mixing of groundwater of varying ages along flow paths in the coastal aquifer system this has also been shown by redox parameters in some of the deeper aquifer samples the data also revealed that there is relatively simple pattern of lateral groundwater flow in the deeper confined aquifer isotopic evidence from this study and related studies in paleolimnology improves our knowledge of the past climates the data suggests that the paleorecharge to the confined aquifer was from inland under wetter climatic conditions than present therefore paleorecharge from the adjacent mountain regions to coastal area like ifakara morogoro and udzungwa mountains could be important parts of recharge area of the kimbiji aquifer however the hinterland mountains of dar es salaam mainly pugu mkuranga ruvu and kisarawe could also play an important role in replenishing the kimbiji coastal aquifers in contrast recharge in the shallow unconfined aquifer is characterized by local rainfall and river water infiltration this study is the first of its kind assessing fingerprinting of paleoclimates in southeastern coastal tanzania using the isotopic composition of deep groundwater aquifers the freshwater resources in the neogene aquifer contain paleo groundwater aquifers that have been mixed with recently recharged flow systems hence the resources may be sustainable this study also provides information that may be useful for designing optimum strategies for a sustainable management of groundwater resources in the coastal aquifer and it testifies to the importance of groundwater as a paleoclimatic archive such information is also essential for consideration by modellers in their attempts to simulate the hydrogeological processes in confined aquifers over very long time spans

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

effects of climate and landscape development on the terrestrial phosphorus cycle past variations in the terrestrial cycle of phosphorus p a biolimiting nutrient are poorly understood detailed geochemical analysis of p in lake sediment cores spanning the late pleistocene to the present from the western appalachian plateau the coast mountains of british columbia and the san bernardino mountains of southern california reveal large changes in terrestrial p cycling p is transformed from a mineralized form to more bioavailable forms with increased soil development and landscape stability in the catchments this process occurs relatively rapidly i e within 3 000 5 000 yr and can be reset quickly the degree of transformation depends on local climate and the starting point of the soil system the release of solid phase p from these landscapes follows modeled patterns of high rates during the initial stages of soil development and low rates upon soil and landscape stabilization changes in weathering style were confirmed for the southern california catchment by analysis of ge si ratios of lake diatoms which revealed substantially higher values during an interval of high p release and low values at present these records point to significant variability in the terrestrial p mass balance on glacial time scales a feature that needs to be incorporated into models of nutrient andmore carbon cycling in the past less

spatial reconstruction of semi quantitative precipitation fields over africa during the nineteenth century from documentary evidence and gauge data the article presents a newly created precipitation data set for the african continent and describes the methodology used in its creation it is based on a combination of proxy data and rain gauge records the data set is semi quantitative with a wetness index of 3 to 3 to describe the quality of the rainy season it covers the period ad 1801 to 1900 and includes data for 90 geographical regions of the continent the results underscore a multi decadal period of aridity early in the nineteenth century

little ice age drought in equatorial africa intertropical convergence zone migrations and el nino southern oscillation variability high resolution analyses of the mg concentration in authigenic calcite in five cores from lake edward provide a water balance history of central equatorial africa spanning the past 1400 yr a high ratio of mg to ca mg indicates strong droughts in central africa during the little ice age a d 1400 1750 in contrast to records from lake naivasha kenya which suggest a wet little ice age this spatial pattern in africa likely arose due to coupled changes in the high latitudes the position of the intertropical convergence zone and the el nino southern oscillation enso system our results further suggest that the patterns and variability of twentieth century rainfall in central africa have been unusually conducive to human welfare in the context of the past 1400 yr

climate and seismicity in the higher central himalaya during 20 10 ka evidence from the garbayang basin uttaranchal india abstract in the trans himalaya the trans himadri fault thf controlled the extent of past glaciers the rivers were impounded by glacial debris resulting in the formation of lakes that recorded regional climatic and seismic events one such lake formed at garbayang where the upper 28 m lacustrine succession spanned an age range of 20 10 ka magnetic susceptibility and sedimentological data suggest that the region experienced high amplitude low frequency millennial scale climate changes during the period 20 3 and 13 2 ka followed by low amplitude high frequency changes from 13 2 11 1 ka a sudden drop in magnetic susceptibility and elemental concentration of layers dated at 11 12 ka suggests cooling associated with the younger dryas occurrence of faulted strata seismites during 20 17 and 14 13 ka suggests recent activation of the thf this is noteworthy as the thf has been considered dormant since its last reactivation at 11 ma further the luminescence dates suggest that radiocarbon ages on organic carbon are grossly overestimated due to a hard water effect caused by the dominance of limestone in the lake catchment this implies that earlier radiocarbon based palaeoenvironmental reconstruction in the region will need revalidation

evidence for global teleconnections in a late pleistocene speleothem record of water balance and vegetation change at sudwala cave south africa abstract understanding the global response to millennial scale climatic events is essential to our comprehension of climatic teleconnections and projection of future change however the extent and nature of their expression in areas of the southern hemisphere is often viewed as equivocal here we report uranium thorium dating of speleothem formations sampled at sudwala cave in the north eastern lowveld region of south africa s summer rainfall zone srz the growth intervals of multiple formations alongside a detailed chronology and multi proxy analysis of two periods of growth 40 35 ka and 13 8 12 8 ka in a stalagmite sc1 provide information regarding key fluctuations in the palaeoclimatic and palaeoenvironmental conditions during the late pleistocene high resolution stable isotope trace element and micro raman analysis are used alongside petrographic investigation to provide a detailed assessment of the climatic conditions associated with the onset and termination of growth in sc1 the combined raman and petrographic analysis represents a rare approach enabling the identification of aragonite calcite shifts both within and across growth intervals and diagenetic events potentially significantly influencing the recorded signal and often resulting in the major loss of chemical information consequently the identification of this post depositional chemical alteration could become a crucial prerequisite in speleothem palaeoclimatology particularly in areas prone to aragonite speleothem deposition susceptible to calcite conversion such as cave sites hosted by dolomitic karst systems the multiple proxies used in this study highlight the complex forcing relationships between climatically related environmental change and local cave conditions on speleothem precipitation contesting a common paradigm by associating drier conditions at sudwala with the initiation of speleothem growth the growth interval identified in stalagmite sc1 during the late deglaciation 13 85 12 79 ka coincides convincingly with both the southern hemispherically forced antarctic cold reversal 14 1 12 8 ka and the younger dryas 12 9 11 5 ka of northern hemispheric origin identifying southern africa as a vital location for the investigation of the hemispheric to global expression of the millennial scale fluctuations of the last deglaciation

coherent changes of southeastern equatorial and northern african rainfall during the last deglaciation during the last deglaciation wetter conditions developed abruptly 14 700 years ago in southeastern equatorial and northern africa and continued into the holocene explaining the abrupt onset and hemispheric coherence of this early african humid period is challenging due to opposing seasonal insolation patterns in this work we use a transient simulation with a climate model that provides a mechanistic understanding of deglacial tropical african precipitation changes our results show that meltwater induced reduction in the atlantic meridional overturning circulation amoc during the early deglaciation suppressed precipitation in both regions once the amoc reestablished wetter conditions developed north of the equator in response to high summer insolation and increasing greenhouse gas ghg concentrations whereas wetter conditions south of the equator were a response primarily to the ghg increase

decadal record of climate variability spanning the past 700 yr in the southern tropics of east africa biogenic silica profiles in varved sediments from northern lake malawi nyasa east africa span the past 700 yr and reflect past primary productivity in the overlying waters on a centennial scale this has been influenced by lake level and a consequent shift in the location of high diatom productivity within the lake basin primary production was higher during the little ice age an arid period from about a d 1570 to 1850 when lake level was about 120 m lower than during the previous three centuries or the past 150 yr

hydrological changes and paleoproductivity in the gulf of california during middle and late holocene and their relationship with itcz and north american monsoon variability abstract this study investigates changes in precipitation patterns and variations in paleoproductivity in the tropical pacific region associated with the north american monsoon intertropical convergence zone itcz latitudinal migration and changes in insolation during the middle and late holocene major and trace element records al ba c k si and ti and zr al and ba al ratios in a core from alfonso basin southern gulf of california are used as proxies of terrigenous input and bio productivity records reveal an increase in precipitation and low bio productivity ca 6200 to 2400 cal yr bp associated with the strengthening of monsoonal precipitation and northward shift of the itcz mean position in the eastern tropical pacific a multi centennial drought from ca 2400 to 1900 cal yr bp and a dry and cold interval ca 700 and 500 cal yr bp are characterized by strong aeolian input and enhanced productivity associated with diminution of the summer monsoonal precipitation and reduced insolation in the northern hemisphere and more southerly itcz position correlation of alfonso basin records with other records in the gulf of california and the pigmy and cariaco basins in the gulf of mexico and central atlantic provides constraints on nam itcz migration and insolation driven changes

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

geochronology and paleoclimatic implications of the last deglaciation of the mauna kea ice cap hawaii we present new 3he surface exposure ages on moraines and bedrock near the summit of mauna kea hawaii which refine the age of the mauna kea ice cap during the local last glacial maximum llgm and identify a subsequent fluctuation of the ice margin the 3he ages when combined with those reported previously indicate that the local ice cap margin began to retreat from its llgm extent at 20 5 2 5 ka in agreement with the age of deglaciation determined from llgm moraines elsewhere in the tropics the ice cap margin receded to a position at least 3 km upslope for 4 5 5 0 kyr before readvancing nearly to its llgm extent the timing of this readvance at 15 4 ka corresponds to a large reduction of the atlantic meridional overturning circulation amoc following heinrich event 1 subsequent ice margin retreat began at 14 6 1 9 ka corresponding to a rapid resumption of the amoc and onset of the bolling warm interval with the ice cap melting rapidly to complete deglaciation additional 3he ages obtained from a flood deposit date the catastrophic outburst of a moraine dammed lake roughly coeval with the younger dryas cold interval suggesting a more active hydrological cycle on mauna kea at this time a coupled mass balance and ice dynamics model is used to constrain the climate required to generate ice caps of llgm and readvance sizes the depression of the llgm equilibrium line altitude requires atmospheric cooling of 4 5 1 c whereas the mass balance modeling indicates an accompanying increase in precipitation of as much as three times that of present we hypothesize 1 that the llgm temperature depression was associated with global cooling 2 that the temperature depression that contributed to the readvance occurred in response to an atmospheric teleconnection to the north atlantic and 3 that the precipitation enhancement associated with both events occurred in response to a southward shift in the position of the inter tropical convergence zone itcz such a shift in the itcz would have allowed midlatitude cyclones to reach mauna kea more frequently which would have increased precipitation at high elevations and caused additional cooling

modern seasonality in lake challa kenya tanzania and its sedimentary documentation in recent lake sediments from november 2006 to january 2010 a sediment trap that was cleared monthly was deployed in lake challa a deep stratified freshwater lake on the eastern slope of mt kilimanjaro in southern kenya geochemical data from sediment trap samples were compared with a broad range of limnological and meteorological parameters to characterize the effect of single parameters on productivity and sedimentation processes in the crater basin during the southern hemisphere summer november march when the water temperature is high and the lake is biologically productive nondiatom algae calcite predominated in the sediment trap samples during the long rain season march may a small amount of organic matter and lithogenic material caused by rainfall appeared this was followed by the cool and windy months of the southern hemisphere winter june october when diatoms were the main component indicating a diatom bloom initiated by improvement of nutrient availability related to upwelling processes the sediment trap data support the hypothesis that the light dark lamination couplets which are abundant in lake challa cores reflect seasonal delivery to the sediments of diatom rich particulates during the windy months and diatom poor material during the wet season however interannual and spatial variability in upwelling and productivity patterns as well as el nino southern oscillation enso related rainfall and drought cycles exert a strong influence on the magnitude and geochemical composition of particle export to the hypolimnion of lake challa

linking active margin dynamics to overriding plate deformation synthesizing geophysical images with geological data from the norfolk basin the tonga kermadec subduction system in the southwest pacific preserves a series of crustal elements and sediments which have recorded subduction initiation rift and back arc basin formation the norfolk basin is the farthest landward of all back arc basins formed in the tonga kermadec region and may preserve the earliest record of subduction initiation regionally for the norfolk basin we use a set of multibeam bathymetry magnetic and seismic reflection and refraction data to constrain basin structure and the mode and timing of formation a structural interpretation reveals a two stage tectonic evolution 1 a convergent tectonic regime until 38 34 ma alternatively related to island arc collision or subduction initiation and 2 lithospheric extension after 34 ma these observations may help to constrain mechanical models that predict rapid extension following convergence of the overriding plate during subduction initiation or arc reversals

rapid climate change from north andean lake fuquene pollen records driven by obliquity implications for a basin wide biostratigraphic zonation for the last 284 ka this paper compares a new super high resolution pollen record from a central location in lake fuquene 4 n with 3 pollen records from marginal sites from the same lake basin located at 2540 m elevation in the eastern cordillera of colombia we harmonized the pollen sum of all records and provided previously published records of climate change with an improved age model using a new approach for long continental pollen records we dissociated from subjective curve matching and applied a more objective procedure including radiocarbon ages cyclostratigraphy and orbital tuning using the new 284 ka long fuquene basin composite record fq bc as the backbone groot et al 2011 we showed that a common 9 m cycle in the arboreal pollen percentage ap records reflects obliquity forcing and drives vegetational and climatic change the ap records were tuned to the 41 kyr component filtered from standard benthic 18o lr04 record changes in sediment supply to the lake are reflected in concert by the four records making frequency analysis in the depth domain an adequate method to compare records from the same basin we calibrated the original 14c ages and used where necessary biostratigraphic correlation i e for records shorter than one obliquity cycle pollen records from the periphery of the lake showed changes in the abundance of alnus and weinmannia forests more clearly while centrally located record fq 9c shows a more integrated signal of regional vegetation change the revised age models show that core fq 2 reflects the last 44 ka and composite record fq 7c the last 85 5 ka marginally located core fq 3 has an age of 133 ka at 32 m core depth and the lowermost 11 m of sediments appear of older but unknown age the longest record fq bc shows 60 yr resolution over the period of 284 27 ka all pollen records are in support of a common regional vegetation development leading to a robust reconstruction of long series of submillennial climate oscillations reflecting dansgaard oeschger do cycles reconstructed climate variability in the tropical andes since marine isotope stage mis 8 compares well with ngrip 18o based epica dome c d based and the mediterranean sea surface temperature record md01 2443 44 uk 37 based underpinning the global significance of the climate record from this tropical andean lake a basin wide biostratigraphy is presented and we concluded although with varying robustness that each core is representative of regional vegetational and climatic change

late quaternary vegetation history of southeast africa the molecular isotopic record from lake malawi abstract accurate reconstructions of past hydrological variability are essential for understanding the climate history of the tropics in tropical africa the relative proportion of vegetation utilizing the c3 vs c4 photosynthetic pathway is mainly controlled by precipitation and thus past hydrological changes can be inferred from the vegetation record in this study biomarkers of terrestrial plants lignin phenols and plant leaf wax carbon isotopes are examined from a well dated sedimentary record from lake malawi to provide a vegetation aridity record of the past 23 cal ka from southeast africa we suggest that the ratio of cinammyl to vanillyl c v lignin phenols in lake malawi sediments mainly reflects inputs of c3 trees woody tissue vs c4 grasses non woody tissue and find that changes in the c v ratio generally support variability noted in the n alkane carbon isotope record together these records provide evidence for increased c4 vegetation grasses surrounding lake malawi during last glacial maximum lgm the younger dryas in the early holocene and from 2 cal ka to the present suggesting drier conditions at these times elevated inputs of c3 vegetation are noted in the intervals from 17 13 6 cal ka and 7 7 2 cal ka indicating wet conditions in southeast africa a relationship is noted between the n alkane average chain length acl and temperature with longer acls associated with higher temperatures higher n alkane carbon preference index cpi values correlate with higher mass accumulation rates of biogenic silica and may result from periodic increased northerly winds over lake malawi which enhance upwelling and diatom productivity while simultaneously increasing erosion and transport of plant leaf waxes to the lake the molecular data produced in this study suggest that the carbon isotopic signature of bulk sediment 13ctoc in lake malawi is primarily a reflection of terrestrial inputs c3 vs c4 vegetation and may not mainly reflect changes in algal productivity as previously thought

oceanic atmospheric and ice sheet forcing of south east atlantic ocean productivity and south african monsoon intensity during mis 12 to 10 variations in the strength of coastal upwelling in the south east atlantic ocean and summer monsoonal rains over south africa are controlled by the regional atmospheric circulation regime although information about these parameters exists for the last glacial period little detailed information exists for older time periods new information from odp site 1085 for marine isotope stages mis 12 10 shows that glacial interglacial productivity trends linked to upwelling variability followed a pattern similar to the last glacial cycle with maximums shortly before glacial maxima and minimums shortly before glacial terminations during the mis 11 10 transition several periodic oscillations in productivity and monsoonal proxies are best explained by southwards shifts in the southern sub tropical high pressure cells followed by abrupt northwards shifts comparison to coeval sea surface temperature measurements suggests that these monsoonal cycles were tightly coupled to anti phased hemispheric climate change with an intensified summer monsoon during periods of northern southern hemisphere cooling warming the timing of these events suggests a pacing by insolation over precession periods a lack of similar regional circulation shifts during the mis 13 12 transition is likely due to the large equatorwards shift in the tropical convection zone that occurred during this extreme glaciation

new evidence for a reduced water balance in east africa during the last glacial maximum implication for model data comparison some syntheses of lake level data for the last glacial maximum lgm in east africa 10 n and 30 s east of 25 e show apparently wetter conditions than present for some basins whereas palaeovegetation reconstruction indicates a generally dry climate pmip gcm simulations for the lgm support both scenarios for this region when run under different boundary conditions here we compare three new records from lakes in the data poor southern part of east africa lake malawi lake massoko and lake rukwa we also re assess previously published lake level data and apply a salinity transfer function to the diatom record from lake manyara our results show that in contrast to previous interpretations these lakes were at least as low as today at the lgm and are thus in agreement with the palaeovegetation data relative drought across east africa is best simulated by gcms that use computed ssts rather than the higher climap values lower ssts and the presence of the northern hemisphere ice sheets must have been dominant over any monsoon precipitation rise caused by astronomically induced summer insolation enhancement in the southern african tropics

large temperature variability in the southern african tropics since the last glacial maximum 1 the role of the tropics in global climate change is actively debated particularly in regard to the timing and magnitude of thermal and hydrological response continuous high resolution temperature records through the last glacial maximum lgm from tropical oceans have provided much insight but surface temperature reconstructions do not exist from tropical continental environments here we used the tex86 paleotemperature proxy to reconstruct mean annual lake surface temperatures through the last glacial maximum lgm in lake malawi east africa 9 14 s we find a 3 5 c overall warming since the lgm with temperature reversals of 2 c during the younger dryas 12 5 ka bp and at 8 2 ka bp maximum holocene temperatures of 29 c were found at 5 ka bp a period preceding severe drought in africa these results suggest a substantial thermal response of southeastern tropical africa to deglaciation and to varying conditions during the holocene

centennial to millennial changes in maar lake deposition during the last 45 000 years in tropical southern africa lake masoko tanzania abstract the masoko maar southern tanzania provides one of the most continuous late quaternary lacustrine sedimentary records from africa a detailed chronostratigraphic framework coupled with sedimentological and magnetic measurements allows us to construct a 30 year resolution continuous sedimentary sequence covering the last 45 000 years and to address local depositional environment and climate variability in the tropical southern africa based on present day observations and measurements our results indicate that the low field magnetic susceptibility of the sediment is highly controlled by climate driven processes wind stress and or lake level amplitude changes acting on the titanomagnetite rich shoreline reservoir the tephra and turbidite free magnetic susceptibility record is strongly modulated by a persistent multi decadal to centennial variability 80 to 200 years probably linked to the gleissberg and suess cycles of solar activity at lower frequency the variability of deposition is controlled by the precessional cycle and its harmonics suggesting a dominant multi millennial forcing of low latitude insolation on climatic changes in tropical southern africa inferred wetter conditions during the last glacial maximum and the younger dryas at masoko 9 s indicate southward shifts of the intertropical convergence zone associated with the north atlantic glacial dynamics and or contrasted hydrological changes in the rungwe highlands compared to the neighbouring areas finally former regional transfer function between diatom assemblages and water chemistry suggested drier conditions during the last glacial maximum at lake masoko barker p williamson d gasse f gibert e 2003 climatic and volcanic forcing revealed in a 50 000 year diatom record from lake massoko tanzania quaternary research 60 368 376 in this context further climate proxy data such as pollen and hydrobiological studies in small deep lakes are needed to support our alternative interpretation of the masoko record

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