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Late Quaternary Environmental Change and Human Occupation of the Southern African Interior

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The interior southern African basin (Kalahari) is a remarkable region, with a complex and dynamic environmental history and a long record of utilization by human populations during the late Quaternary. Paleoenvironmental reconstructions are beginning to provide a spatially detailed record of landscape and hydrological dynamics in the Kalahari, with a strong chronometric underpinning for records of environmental extremes. Theories concerning the distribution of early people in the landscape place great importance on the temporal dynamics of water availability, and may be particularly relevant in the Kalahari where there is significant evidence of hydrologic/climatic-driven landscape change. High amplitude environmental variability during MIS 6-2 is evidenced by periods of dune building within currently stabilized dunefields and the intermittent existence of large lacustrine systems such as Megalake Makgadikgadi that remain all but ephemerally dry under present-day conditions. That the wider Kalahari was, at times, a key resource for Stone Age populations is evident from the extensive occurrence of stone tools, most notably in association with the fluvial networks and lake basins of the Okavango-Chobe-Zambezi system. Today, these riparian corridors link the semiarid desert region to the southern subtropics and, in the past, drove environmental change in the Kalahari, potentially impacting the occupation and dispersal of hominins within the interior southern African basin.

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... True desert biomes include the Sahara (Drake and Breeze 2016;Cancellieri et al. 2016;Jones et al. 2016;Van Peer 2016) and Namib Deserts. Semi-arid regions include the Kalahari (Burrough 2016;Robbins et al. 2016) and Namaqualand, a semi-arid southward extension of the Namib . By far the most expansive arid zone of all is the Sahara, the Earth's largest tropical desert, stretching from the Atlantic Ocean to the Red Sea and bordered by semi-desert and Mediterranean biomes to the north and the grasslands of the Sahel to the south. ...
... Dunefields, mountain massifs, coastlines, river systems, oases, and paleolakes within deserts presented hunter-gatherer populations with very varied opportunities and constraints. Although aridity is frequently emphasized as a driver of cultural change and innovation (e.g., Clark 1960), arguments for climatic variability as more influential are gaining traction (Burrough 2016;Jones et al. 2016;Stewart et al. 2016). For example, Burrough (2016) states that "In the context of past population dynamics, overarching climatic theories remain largely irrelevant, since it is regional environmental (rather than climatic) variability to which hominins are likely to have responded," where the spatial complexities of landscape and regional climate dynamics should be taken into greater account. ...
... Although aridity is frequently emphasized as a driver of cultural change and innovation (e.g., Clark 1960), arguments for climatic variability as more influential are gaining traction (Burrough 2016;Jones et al. 2016;Stewart et al. 2016). For example, Burrough (2016) states that "In the context of past population dynamics, overarching climatic theories remain largely irrelevant, since it is regional environmental (rather than climatic) variability to which hominins are likely to have responded," where the spatial complexities of landscape and regional climate dynamics should be taken into greater account. For the Sahara, Cancellieri et al. make two important points of relevance. ...
Chapter
Africa from Marine Isotope Stages (MIS) 6-2 saw the crystallization of long-term evolutionary processes that culminated in our species' anatomical form, behavioral florescence, and global dispersion. Over this *200 kyr period, Africa experienced environmental changes on a variety of spatiotemporal scales, from the long-term disappearance of whole deserts and forests to much higher frequency, localized shifts. The archaeological, fossil, and genetic records increasingly suggest that environmental variability profoundly affected early human population sizes, densities, interconnectedness, and distribution across the African landscape – that is, population dynamics. At the same time, recent advances in anthropological theory predict that such paleodemographic changes were central to struc-turing the very records we are attempting to comprehend. The book introduced by this chapter represents a first concerted effort to assess modern human population dynamics throughout Africa, whether these changed with environmental fluctuations, and how they contributed to our species' evolutionary trajectory.
... One of the earliest known fossils of the H. sapiens clade was found at Florisbad, 112 Kalahari Basin is key for understanding the evolution of early human behavioral evolution in Africa over the long term, and others have highlighted its significance. 26,63,95,102,105,127,128 However, a comprehensive review that brings together evidence from these diverse research programs across the whole of the Kalahari Basin has not previously been published. ...
... Low precipitation and high evaporation in the Middle and Southern Kalahari results in arid and semi-arid conditions with a notable rarity of surface water today. 95 These kinds of conditions have led to a general perception that much of the interior of Africa was not suitable for early human occupation. ...
... 129 Through the Pleistocene and Holocene in the Middle Kalahari, there is extensive evidence for the intermittent existence of large lacustrine systems that are today ephemerally dry. 95,130,131 In the Southern Kalahari, Pleistocene wet periods have been identified at pan and spring sites based on sedimentary analysis. 33 archeological sites, provides a unique opportunity to reframe the narratives about the evolution of our species. ...
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The Kalahari Basin, southern Africa preserves a rich archeological record of human origins and evolution spanning the Early, Middle and Late Pleistocene. Since the 1930s, several stratified and dated archeological sites have been identified and investigated, together with numerous open‐air localities that provide landscape‐scale perspectives. However, next to recent discoveries from nearby coastal regions, the Kalahari Basin has remained peripheral to debates about the origins of Homo sapiens. Though the interior region of southern Africa is generally considered to be less suitable for hunter‐gatherer occupation than coastal and near‐coastal regions, especially during glacial periods, the archeological record documents human presence in the Kalahari Basin from the Early Pleistocene onwards, and the region is not abandoned during glacial phases. Furthermore, many significant behavioral innovations have an early origin in the Kalahari Basin, which adds support to poly‐centric, pan‐African models for the emergence of our species.
... The southern African interior possesses a long record of human occupation (Barham, 2000;Burrough, 2016;) that, for the most part, remains poorly investigated. This is despite the richness of available sites reported in the middle of the twentieth century by van Riet Lowe (1935), Clark (1950) Bond and Summers (1954) and others. ...
... Archaeological research has favoured sites that offer good organic preservation, with a strong focus on cave-sites along the South African coast (Backwell et al., 2014;Stewart et al., 2012) (Fig. 1). The interior Kalahari basin however possesses an abundance of Stone Age archaeological sites (see Burrough, 2016 for an overview), albeit that many are in open air contexts. While these may often lack associated organic deposits, many are situated in landscape contexts that attest to extreme and repeated water deficits and surpluses Burrough and Thomas, 2013;Thomas et al., 2003; that have potentially vital implications for human population distributions in the Quaternary and today (Brooks, 1984;Barham, 2000). ...
Article
Single grain OSL dating has been used to produce new chronologies for three previously investigated sites in the northern Kalahari basin in western Zambia containing both Middle and Later Stone Age material (Phillipson, 1975a, b). We find that Mode 3 (Middle Stone Age, MSA) assemblages in the Upper Zambezi Valley pre-date the Last Glacial Maximum. The chronology produced here is consistent with age estimates from a handful of dated sites within the wider Kalahari basin. The Mode 3 to Mode 5 (Later Stone Age, LSA) relationship at one site, Chavuma, is unlikely to be a continuous transition as previously thought. Instead we find a significant chronological hiatus between MSA material deposited at 66.5 ± 9.9 ka and LSA material deposited at 16.7 ± 2.6 ka. We consider these dated archaeological finds within the context of current archaeological and palaeoenvironmental records for the region. The results demonstrate the highly variable climate history of the region and the limitations of the existing archaeological record for modelling human responses to habitat change.
... In the African context, the specific role of the continental margins as "refugia" during periods of aridity within the continental interior has been highlighted in various studies (Walter et al. 2000;Faure et al. 2002;Hetherington et al. 2008;Compton 2011). However, with the exception of the environmental archives provided by the East African lakes (e.g., Scholz et al. 2007;Castañeda et al. 2009) the continental Quaternary paleoclimatic record is sparse and geomorphic evidence of paleo-aridity in particular has proved difficult to interpret (Chase 2009;Thomas and Burroughs 2012;Burrough 2016). Although blanket claims of "Quaternary aridity" or "glacial aridity" should be treated with caution, phases of enhanced late Quaternary aridity can be identified within the southern African interior (e.g., Chase 2009Chase , 2010Chase et al. 2009Chase et al. , 2011Chevalier and Chase 2015;Collins et al. 2014;Dupont et al. 2011;Lancaster 2002;Partridge et al. 1997;Scholz et al. 2007;Shi et al. 2001;Stager et al. 2011;Stuut et al. 2002;Thomas and Burrough 2012;Truc et al. 2013). ...
Chapter
The southern Cape of South Africa hosts a remarkably rich Middle Stone Age (MSA) archaeological record. Many of the associated caves and rock shelters are coastal sites, which contain evidence for varied occupational intensity and marine resource use, along with signs of notable landscape, environmental, and ecological change. Here, we review and synthesize evidence for Quaternary landscape and climatic change of relevance to the southern Cape MSA. We seek to highlight the available data of most relevance to the analysis and interpretation of the region’s archaeological record, as well as critical data that are lacking. The southern Cape MSA occupation spans the full range of glacial-interglacial conditions (i.e., 170–55 ka). It witnessed marked changes in coastal landscape dynamics, which although driven largely by global eustatic sea level changes, were modulated by local-scale, often inherited, geological constraints. These prevent simple extrapolations and generalizations concerning paleolandscape change. Such changes, including pulses of coastal dune activity, will have directly influenced resource availability around the region’s archaeological sites. Evidence for paleoclimatic change is apparent, but it is scarce and difficult to interpret. It is likely, however that due to the same diversity of rainfall sources influencing the region today, compared to parts of the continental interior, the southern Cape climate was relatively equable throughout the last 150 kyr. The region’s paleoecology, particularly in relation to the coastal plains exposed during sea level lowstands, is a key element missing in attempts to synthesize and model the resources available to occupants of this region. Technology, settlement, and subsistence probably changed in response to these paleoclimate/landscape adjustments, but improvements in baseline archaeological and paleoenvironmental data are required to strengthen models of ecosystem variation and human behavioral response through the MSA.
... In the African context, the specific role of the continental margins as "refugia" during periods of aridity within the continental interior has been highlighted in various studies (Walter et al. 2000;Faure et al. 2002;Hetherington et al. 2008;Compton 2011). However, with the exception of the environmental archives provided by the East African lakes (e.g., Scholz et al. 2007;Castañeda et al. 2009) the continental Quaternary paleoclimatic record is sparse and geomorphic evidence of paleo-aridity in particular has proved difficult to interpret (Chase 2009;Thomas and Burroughs 2012;Burrough 2016). Although blanket claims of "Quaternary aridity" or "glacial aridity" should be treated with caution, phases of enhanced late Quaternary aridity can be identified within the southern African interior (e.g., Chase 2009Chase , 2010Chase et al. 2009Chase et al. , 2011Chevalier and Chase 2015;Collins et al. 2014;Dupont et al. 2011;Lancaster 2002;Partridge et al. 1997;Scholz et al. 2007;Shi et al. 2001;Stager et al. 2011;Stuut et al. 2002;Thomas and Burrough 2012;Truc et al. 2013). ...
... I do so through a series of discontinuities touching on the demographic implications of major technological and climatic transitions, the introduction of pastoralism, and the limitations of the region's ethnographic record. For reasons of space, I emphasise the past 25,000 years, a span broadly http://dx.doi.org/10.1016/j.jaa.2016.07.001 0278-4165/Ó 2016 Published by Elsevier Inc. equivalent to the Later Stone Age (LSA) of traditional nomenclature, although current drylands were certainly inhabited as early as the Acheulean (Klein, 2000) and their settlement is currently a major research focus for the succeeding Middle Stone Age (Burrough, 2016;Stewart, 2012, 2016;Robbins et al., 2016;Vogelsang et al., 2010). Smith (1995), Lane et al. (1998), Campbell et al. (2010), Kinahan (2011), and papers in Jerardino et al. (2013) all provide more detailed overviews of individual dryland archaeologies. ...
... It is worth noting that the northern Kalahari formerly supported an extensive lake (i.e. Makgadikgadi) just before and after the Last Glacial Maximum, as well as the presence of the Okavango Delta and associated river systems; archeological data may suggest high population density nearby the pans, although this likely predates the genetic structure we observe today (Burrough 2016;Robbins et al. 2016). Our lack of samples outside of Botswana, Namibia and northern South Africa prevent precise inference of m in Zambia, Limpopo, and Mozambique; but Figure 2 indicates recent extensive gene flow in the east, consistent with the expansion of Bantu-speaking agriculturalists into eastern grasslands and coastal forests. ...
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Recent genetic studies have established that the KhoeSan populations of southern Africa are distinct from all other African populations and have remained largely isolated during human prehistory until about 2,000 years ago. Dozens of different KhoeSan groups exist, belonging to three different language families, but very little is known about their population history. We examine new genome-wide polymorphism data and whole mitochondrial genomes for more than one hundred South Africans from the ≠Khomani San and Nama populations of the Northern Cape, analyzed in conjunction with 19 additional southern African populations. Our analyses reveal fine-scale population structure in and around the Kalahari Desert. Surprisingly, this structure does not always correspond to linguistic or subsistence categories as previously suggested, but rather reflects the role of geographic barriers and the ecology of the greater Kalahari Basin. Regardless of subsistence strategy, the indigenous Khoe-speaking Nama pastoralists and the N|u-speaking ≠Khomani (formerly hunter-gatherers) share ancestry with other Khoe-speaking forager populations that form a rim around the Kalahari Desert. We reconstruct earlier migration patterns and estimate that the southern Kalahari populations were among the last to experience gene flow from Bantu-speakers, approximately 14 generations ago. We conclude that local adoption of pastoralism, at least by the Nama, appears to have been primarily a cultural process with limited genetic impact from eastern Africa.
... This might be countered by the fact that Lesotho is not alone in southern Africa in having produced evidence of late Pleistocene fishing activity, since Robbins et al. (1994Robbins et al. ( , 2000) have documented a pulse of fish procurement focused on cichlids, most probably Serranochromis spp. and, more especially, sharptooth catfish (Clarias gariepinus) around 36-30 ka at White Paintings Shelter in the northwestern Kalahari (Robbins et al. 2012, 2016. The same authors have also shown that there is good evidence that fishing was important in this region during the Holocene ( Robbins et al. 1998Robbins et al. , 2000Robbins et al. , 2009, while today and in the recent past Khoe-speaking Bushmen along Botswana's Botlele and Nata Rivers practice/ have practiced delayed return economies focused on fishing with heavy investment in nets, traps, and weirs (Cashdan 1986). ...
... Other regions also show varied climatic conditions. For example, lakes and archaeological sites in the central Kalahari Basin feature humid events during MIS 4 (Burrough, 2016;Burrough et al., 2009aBurrough et al., , 2009bRobbins et al., 2016), whereas the southern Kalahari appears to be drier (e.g., Lukich and Ecker, 2022;Telfer and Thomas, 2007). ...
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Marine Isotope Stage (MIS) 5 and 4 are periods of major cultural innovations in the Middle Stone Age (MSA) of southern Africa. While extensive data is available for the coast, far less is known about the interior, in particular its central plateau. This is likely due to the large geographic extent of this area and a general paucity of caves and rock shelters that can provide long stratigraphic sequences and environmental records. The lack of information and systematic research has hindered our understanding of regional variation and patterns of human dispersal within the subcontinent. Our research at the open-air MSA site of Lovedale situated on the Modder River addresses this issue. Using sediment micromorphology, infrared spectroscopy of bones and sediments, phytolith and faunal analyses, as well as luminescence dating, we have reconstructed the evolution of paleoenvironments in this region at specific points over the last ∼80,000 years. Our results help contextualize human occupation and hunting strategies associated with a pre-Howiesons Poort technology that occurred in a wetland environment during a short-lived warm, dry period dated to ∼70 ka. These results show that humans settled the grasslands of the central interior at the onset of MIS 4 and confirm the importance of wetlands in human subsistence strategies, especially in times of climatic stress.
... However, what is significant about the northwestern Kalahari-a notoriously semiarid part of southern Africa-is that these activities depend either on unearned water-that is, on the inflow of rain falling hundreds of kilometers to the north in the highlands of Angola-or on significantly wetter conditions locally. The poor preservation of bone at Melikane and the still incomplete nature of excavations of the Pleistocene sequence at Sehonghong currently preclude comparing Lesotho with Botswana for MIS 3, but there is no evidence at present that people focused on fish in the Kalahari during MIS 2, even though conditions there were significantly wetter on several occasions at this time (see Burrough 2016). ...
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The marginalization of surviving hunter-gatherer groups to Africa’s ecological and sociopolitical fringes makes it certain that very different societal forms existed in the past. In relatively recent periods, such as the late Holocene, rich, well preserved archaeological records can mitigate this issue. Much more challenging are the problems created in the temporal dimension, particularly across deep time. For example, it is now abundantly clear that Africa played host to our species’ behavioral evolution, and that this occurred during — and was at least in part fuelled by — later Pleistocene climatic and environmental change. The nature, scale, and pace of these changes have no parallels in the Holocene, including, of course, the ethnographic present. Beyond climatic flux, moreover, Africa during the bulk of the later Pleistocene experienced effective temperatures substantially lower than those of today. What forms did African hunter-gatherer societies take during periods of pronounced climatic instability or cooling, i.e. when conditions differed most from those of the ethnographic present? We address this question here by integrating later Pleistocene and Holocene paleoenvironmental and archaeological data to explore hunter-gatherer adaptive diversity in one of the continent’s most temperate regions: the Maloti-Drakensberg Mountains of Lesotho. We consider the fish assemblages from three archaeological sites: Sehonghong, Pitsaneng, and Likoaeng. Between them, they provide a history of highland fish exploitation over more than 30,000 years. We show that humans often managed to adjust to ecological pressure by transforming their dietary base, with knock-on implications for settlement, technology, and perhaps sociopolitical structures. Our analysis furthers ongoing efforts to move African hunter-gatherer archaeology beyond the shadow of the Kalahari Desert.
... In the last decades, great interest has been addressed to the study of the interaction between environmental processes and human occupation (Bridgland, 2000;Burrough, 2016;Foerster et al., 2015;Hoelzmann et al., 2001). Central-southern Italy represents an open-air laboratory to investigate this topic because of its highly dynamic landscape and associated human frequentation since Prehistoric times (Ascione et al., 2020;Bini et al., 2013;Brandolini et al., 2019;Di Donato et al., 2018;Giaccio et al., 2017;Gioia et al., 2019Gioia et al., , 2020Russo Ermolli et al., 2014). ...
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The map is aimed at illustrating the relationships between landscape evolution and human occupation in the Isernia basin since the Middle Pleistocene. We carried out a detail scale geological–geomorphological investigation integrated with archaeological data. Overall data suggest enhanced landscape modification related to the long-term evolution of the Isernia basin. Moreover, during the Middle Pleistocene an alluvial plain environment was present, as testified also by the famous Lower Palaeolithic site of Isernia La Pineta dated to ca. 600 ky. From 600 ky onwards, extensional tectonics and related valley incision reshaped the Isernia basin, with the formation of terraced surfaces and the deposition of a travertine plateau. Archaeological findings from the Lower Palaeolithic up to the Chalcolithic Age testify to pre- and protohistoric settlements on these surfaces. In historical times, Romans settled on the Isernia terrace ridge taking advantage of the outcropping travertines to support wall foundations and to extract construction material.
... Proxy data from the Kalahari Basin conflict as to whether this region was likewise arid during late MIS 5a (e.g. Brook et al., 1998;Burrough et al., 2009;Burrough, 2016;Robbins et al., 2016). Stewart et al. (2016) point out that if it was indeed dry both in the interior and on the coasts, then the wet and cool environment around Melikane may have provided a refugium for lowland populations. ...
Article
Multidisciplinary research suggests that Marine Isotope Stage 5 (~130–74 ka) was an important evolutionary stage in African deep history. Population expansion and growth spurred changes in material culture as well as the exploration of previously unoccupied regions and ecosystems. The archaeological sequence at Melikane Rockshelter (1860 masl) in the Maloti-Drakensberg Mountains of highland Lesotho, southern Africa, stretches from the late Holocene back to sub- stage 5a, ~80 ka. The site’s earliest strata represent one of the earliest known examples of a sustained human presence in high mountain systems worldwide. This paper deals with the lithic assemblages from those levels, which are currently the oldest radiometrically dated archaeology in Lesotho and one of the few stratified assemblages of Last Interglacial age in the southern African interior. The results of a typo-technological analysis of the assemblages are presented. They suggest that the afromontane foragers who resided at Melikane employed both blade-focussed and bipolar flaking systems, curated a maintainable toolkit suited to frequent residential moves, and used a hybrid provisioning system adapted to their immediate environment. Comparisons with other late Last Interglacial assemblages across the subcontinent suggest that highland populations at this time were largely disconnected from their lowland counterparts. This implies that as Last Interglacial populations in southern Africa expanded into new environments, they also fragmented, adapting to local conditions rather than adhering to a universal technological system.
... 200 ka only soon after 70 ka, the climate was humid enough for human migrations between southern and eastern Africa and subsequent out-of-Africa expansions. Outside the humid tropics, stable environments were rather the exception, however, and landscape evolution was dynamic (Burrough, 2016). Huge lakes repeatedly existed in the structural basins of the northern and central Kalahari (Fig. 2) during the last 200 ka and before, which is that lakes developed, vanished and reappeared under changing climates (e.g. ...
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Based on genetic studies, a Pleistocene Kalahari “palaeo-wetland”, which spanned the region of the Okavango Delta and the Makgadikgadi Basin, was recently considered the geographic origin of evolutionary modern humans. It was proposed that subsequent out-of-homeland migration was induced by climate shifts. The Tsodilo Hills, which are in relative proximity to the Okavango Delta, represent a site of ancient human occupation since at least 100 ka. Local hydrological dynamics were predominately controlled by climate variability and are archived in the sediments of Palaeolake Tsodilo. This study seeks to better understand the Late Pleistocene environments of the ancient Tsodilo people with a focus on palaeo-hydrological settings, which played a major role for their livelihoods. Our multidisciplinary approach included different remote sensing and geophysical methods, comprehensive application of differential GPS, and sedimentological analyses concentrating on the lake beds. Four palaeo-shorelines could be identified, three of which indicate highstands during which the Tamacha palaeo-river drained Palaeolake Tsodilo towards the Okavango Panhandle. Two highstands during MIS3b and LGM are related to periods of largely increased fish consumption by humans as has been documented by archaeologists. The palaeolake was likely most extended about 100 ka ago or earlier, when it covered ca. 70 km² and was 16 m deep. A single (neo-)tectonic fault could be detected. We assume that the Tamacha palaeo-river was a gateway for ancient humans to reach the Tsodilo Hills from these palaeo-wetlands. The people took advantage of the Tsodilo Hills as shelter from weather hazards and as a natural fortress against predators and elephants. Geologically, the Tsodilo Hills were comparatively calm. They represented a relatively safe haven where the social behaviour of early modern humans could evolve to a higher complexity, which relates to the fundamental question when and where modern human behaviour began.
... Unfortunately, the study remains unpublished in full (Partridge & Dalbey, 1986;Sampson, 2001Sampson, , 2004. However, new research from a large-scale project in the Makgadikgadi Basin, Botswana, promises the combination of survey and open-air excavated contexts, integrated with local palaeoenvironmental archives (Burrough, 2016;Burrough et al., 2021). ...
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It has been proposed that a multiregional model could describe how Homo sapiens evolved in Africa beginning 300,000 years ago. Multiregionalism would require enduring morphological or behavioral differences among African regions and morphological or behavioral continuity within each. African fossils, archeology, and genetics do not comply with either requirement and are unlikely to, because climatic change periodically disrupted continuity and reshuffled populations. As an alternative to multiregionalism, I suggest that reshuffling produced novel gene constellations, including one in which the additive or cumulative effect of newly associated genes enhanced cognitive or communicative potential. Eventual fixation of such a constellation in the lineage leading to modern H. sapiens would explain the abrupt appearance of the African Later Stone Age 50–45 thousand years ago, its nearly simultaneous expansion to Eurasia in the form of the Upper Paleolithic, and the ability of fully modern Upper Paleolithic people to swamp or replace non‐modern Eurasians.
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The Makgadikgadi–Okavango–Zambezi basin (MOZB) is a structural depression in the south-western branch of the East African Rift System of the northern and middle Kalahari, central southern Africa. In the present day, the mainly dry subbasins of the MOZB are part of a long-lived lacustrine system that has likely existed since Early Pleistocene and from which an extant freshwater fish radiation emerged seeding all major river systems of southern Africa. During hydrologically favourable periods the subbasins were connected as a single mega-lake termed Lake Palaeo-Makgadikgadi. Previous geomorphological studies and OSL dates have provided evidence for repeated mega-lake periods since approximately 300 ka. The environmental and climatic implications of such large scale late Quaternary lake-level fluctuations are controversial, with the duration of mega-lake phases poorly constrained. Here, we present the first evidence for a Marine Isotope Stage (MIS) 5 mega-lake period (about 935–940 m a.s.l.) reconstructed from a diatom-rich, 30-cm-thick lacustrine sediment section, exposed close to a palaeo-shoreline of the Makgadikgadi Basin. Based upon the environmental setting and in comparison with sedimentation rates of other similar lake environments, we tentatively estimated that the highstand lasted approximately 1 ka during MIS 5d–b. The 30-cm section was sampled in 0.5-cm steps. Diatom species diversity ranges from 19 to 30 through the section. The dominant species are Pseudostaurosira brevistriata, Rhopalodia gibberula, Cyclotella meneghiniana and Epithemia sorex. The total of 60 sediment samples provide us with a record at decadal to bi-decadal resolution. Based on diatom assemblages and their oxygen isotope composition (δ¹⁸O) we infer an alkaline and mostly oligohaline lake with shallow water conditions prevailing in MIS 5, and is potentially analogous to a Heinrich event. The climate over southern Africa during MIS 5 has been considered very arid but the hydromorphological context of our sediment section indicates that we captured a mega-lake period providing evidence that short-term excursions to significantly higher humidity existed. A hydrologically more favourable environment during MIS 5 than formerly presumed is in line with the early human occupation of the Kalahari.
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There is generally a dearth of evidence of the nature of Quaternary climate change within desert systems, which has limited previous interpretations of past environmental change at low latitudes. The Last Glacial Maximum has previously been identified as the peak of Late Quaternary aridity, when desert systems expanded to five times their present extent, and low-latitude aridity has been described for previous glaciations. But little evidence has been derived directly for large desert basins, particularly southern Africa. Here we report new chronological (optical dating) evidence of arid episodes recorded in aeolian sediments from the Mega Kalahari sand sea. Episodic aeolian activity is recorded at the northeastern desert margin, whereas more sustained activity is evident from the southwestern desert core. Several significant arid events are apparent since the last interglacial period, with dune-building (arid) phases at ~95-115, 41-46, 20-26 and 9-16kyr before present. Existing atmospheric general circulation model simulations and independent palaeoclimate data indicate that the changes in aridity are related to changes in the northeast-southwest summer rainfall gradient, which are in turn related to sea surface temperatures in the southeastern Atlantic Ocean.
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Terrestrial wildlife migrations, once common, are now rare because of ecosystem fragmentation and uncontrolled hunting. Botswana historically contained migratory populations of many species but habitat fragmentation, especially by fences, has decreased the number and size of many of these populations. During a study investigating herbivore movement patterns in north-west Botswana we recorded a long-distance zebra Equus burchelli antiquorum migration between the Okavango Delta and Makgadikgadi grasslands, a round-trip distance of 588 km; 55% of 11 animals collared in the south-eastern peripheral delta made this journey. This was unexpected as, between 1968 and 2004, the migration could not have followed its present course because of the bisection of the route by a veterinary cordon fence. As little evidence exists to suggest that large-scale movements by medium-sized herbivores can be restored, it is of significant interest that this migration was established to the present highly directed route within 4 years of the fence being removed. The success of wildlife corridors, currently being advocated as the best way to re-establish ecosystem connectivity, relies on animals utilizing novel areas by moving between the connected areas. Our findings suggest that medium-sized herbivores may be able to re-establish migrations relatively quickly once physical barriers have been removed and that the success of future system linkages could be increased by utilizing past migratory routes.
Chapter
We present a synthesis of archaeological and paleoenvironmental information for the period MIS 6-2 in the Kalahari. Discussion centers on the implications of nine new, internally consistent OSL ages obtained from White Paintings Rock Shelter. These dates provide a better understanding of the Middle Stone Age (MSA) and Late Stone Age (LSA) sequence. In addition, the revised chronology dates 11 buried soil A-horizons that were formed during wetter periods. The buried A-horizons, along with dated speleothems and high lake levels in the Kalahari correlate with Antarctic warming events (A) and North Atlantic Heinrich events (H). We also discuss the implications of the Kalahari megalake, paleolake Makgadikgadi , for human populations and compare dated changes in the archaeological sequence at WPS with dates established in Khoisan genetic evolutionary studies.
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Kalahari Group stratigraphy covers some 2.5 million km2 of southern Africa. These sediments, of which the Kalahari Sand is the most ubiquitous, are of post-Cretaceous age, and have low fossil and organic contents - characteristics that have impeded geological interpretation in the past. In the last two decades geomorphological studies, focused on the semi-arid region (the "Kalahari Desert') south of the Zambezi River, have provided contemporary and past geomorphological processes on the landscape. Research on caves, lakes, pans and fluvial links have indicated widespread humid episodes in the late Quaternary that are asynchronous with those in other sub-tropical arid regions, and which have been magnified, particularly in the Okavango Delta and adjacent parts of northern Botswana, by tectonic activity. Variations in groundwater recharge and chemistry have led to the formation of complex duricrust suites up to 100m in thickness, many of which are associated with surface landforms. The most enigmatic landforms are vast "fossil' linear dune fields, which cannot be related to present or past climatic parameters, and for which new explanations are being sought. -from Authors
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Over 600 luminescence ages have to date been published from southern Africa's continental dunefields and isolated dunes, providing a rich record of aeolian system dynamics during the Late Quaternary. The majority of records come from sites within the five linear dune-dominated dunefields of the Kalahari, with lesser representation of other major dune areas, including the Namib and West Coast dunefields, and of other dune types, including lunettes and transverse forms. Dune database records are analysed not only in terms of the evidence they provide for Late Quaternary environmental changes over the last 190 ka, the purpose for which most ages have been produced, but in terms of the analytical techniques used, data quality and data presentation, as these all impact on how dune luminescence ages have been, or should be, interpreted as a tool for palaeoenvironmental and dune development studies.
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The western part of the Makgadikgadi basin in northern Botswana displays a variety of lacustrine, fluvial and aeolian landforms in close juxtaposition. The area is divided into a number of distinct geomorphological units, whose form, relationships and evolution are described. A sequence of stages in the evolution of the landscape is put forward, and a chronology suggested on the basis of 20 new 14C dates on samples from widely separated parts of the whole basin. Correlation with adjacent parts of southern Africa is examined, and some palaeoclimatic inferences drawn.-Authors
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A model of climate change over southern Africa is presented. It includes both latitudinal changes in and in situ intensification of major atmospheric circulation features of the southern African sector of the southern hemisphere. Longitudinal changes in the position of the African cloud band and the position of the southern African trough of planetary wave four are incorporated. Likewise, changing sea-surface temperature fields in the oceans adjacent to the subcontinent and changes in primary moisture transport patterns are integrated into the conceptual framework of the model. The model posits warmer, wetter conditions being forced by changes originating in the easterly circulation of the tropics and cooler, drier conditions being brought about by an expansion equatorward of the westerlies and their associated weather disturbances. The manner in which the precessional Change component of the Milankovitch hypothesis may additionally modulate such changes is examined. The model is tested against two highly-resolved proxy climate series for the summer rainfall region, one a 200 000-year series derived from a sediment core drilled in the Tswaing Crater, north of Pretoria, the other a 3000-year decadal-scale series from a stalagmite collected in a cave in the Makapansgat Valley, southwest of Pietersburg. The directions and nature of the climatic changes postulated in the model appear to be upheld by the observations.
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The spatial pattern of precipitation variability in tropical and subtropical Africa over the late Quaternary has long been debated. Prevailing hypotheses variously infer (1) insolation-controlled asymmetry of wet phases between hemispheres, (2) symmetric contraction and expansion of the tropical rainbelt, and (3) independent control on moisture available in Southern Africa via sea surface temperatures in the Indian Ocean. In this study we use climate-model simulations covering the last glacial cycle (120. kyr) with HadCM3 and the multi-model ensembles from PMIP3 (the Palaeoclimate Model Intercomparison Project) to investigate the long-term behaviour of the African rainbelt, and test these simulations against existing empirical palaeohydrological records. Through regional model-data comparisons we find evidence for the validity of several hypotheses, with various proposed processes occurring concurrently but with different regional emphasis (e.g. asymmetric shifts at the seasonal extremes and symmetric expansions/contractions towards West equatorial regions). Crucially, variations in rainfall are associated with multiple forcing mechanisms that vary in their dominance both spatially and temporally over the glacial cycle an important consideration when interpreting and extrapolating from often relatively short palaeoenvironmental records.
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A noble gas temperature and δ18O record covering the past 30 000 years has been obtained from the Stampriet artesian aquifer in southeastern Namibia (24°S, 19.5°E). Radiocarbon ages, corrected for water-rock interactions along the flow path, increase uniformly with distance from the recharge area. Dissolved atmospheric noble gases indicate that the mean annual temperature in Namibia was about 5.3°C lower during the last glacial maximum (LGM) than today. Together with the glacial/interglacial temperature changes of the same magnitude (5.5°C to 6°C) recorded at the Uitenhage aquifer and at the Cango caves in South Africa, these data indicate a uniform cooling of southern Africa. A peak in excess air concentration suggests a transition from a dry to a wetter climate at approximately 6000 years BP. The 18O record at Stampriet is characterized by an enrichment of 1.3‰ during the LGM, in contrast to the Uitenhage aquifer, which shows a depletion of 1‰. This pattern may be explained by an increased importance of Atlantic moisture sources during the LGM.
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Present day landscapes in Zimbabwe are the resultant of uplift and erosion since Palaeozoic time. Vestiges of the Pre-Karoo landscape are particularly numerous across the resistant banded ironstones and jaspilites of the ancient Sebakwian and Bulawayan groups, and a major watershed of that age can be traced parallel to, but about l00 km south of the present Zambezi-Limpopo divide. Post-Karoo time is recorded geomorphologically by the progression of the six major erosion cycles that coincide with those seen in the adjacent countries. As a result of tilting and encroaching of younger erosion cycles along the Zambezi and Limpopo rivers and their tributaries, certain changes of drainage have occurred during Cainozoic time. Changes during the Quaternary include renewed erosion and spasmodic and patchy deposition of river alluvium. - from Author
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A topographic map of the Okavango Delta and environs has been constructed using a combination of elevation data including trigonometric beacons and spot heights from the government of Botswana, surveys of the navigable channels, U. S. Department of Defense data and measurements made during a geophysical survey of the region. The topography provides insight into the local tectonic and sedimentary history. Local tectonics are dominated by uplift and horst formation associated with the Ghanzi Ridge, and an arch to the north of the Panhandle, which appear to represent the tips of incipient rifts which are propagating from the northeast. The Delta has formed in the resulting depression between these arches. The Panhandle has developed along a fault, and may be largely an erosional feature incised into the northern uplift zone. The Delta itself is an alluvial fan of remarkably uniform gradient. There is no evidence of regional tilting of the fan surface. Local highs and lows are developed on the fan, but channel location is relatively insensitive to this local topography. Moreover, marked elevation differences exist between adjacent channels, creating hydrologically unstable conditions. These unusual features of the local hydrology arise because of the confining effect of channel-flanking vegetation. Sedimentation in the Delta appears to be causing crustal sagging of the central Delta, which has: tilted the major palaeo-shoreline of the Mababe Depression to the west; formed a local depression within the Ghanzi Ridge facing the Delta; and detached a sliver of the ridge along the Thamalakane fault. It is suggested that local seismicity also results mainly from sediment loading. The Selinda spillway occupies a marked local depression, which is a graben between the Gumare fault and an extension of the Linyanti fault. It is probable that southwesterly propagation of the uplift zone associated with the incipient rift will ultimately deflect the Okavango River into the Chobe-Zambezi river system via this graben.
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Lake Ngami and the Mababe Depression contain series of concentric shoreline features controlled by volume: area thresholds in the Okavango Delta region. Of particular interest are the 945 m (Lake Palaeo-Makgadikgadi) and the 936 m shorelines, the latter representing the amalgamation of the two lakes along the Thamakalane axis. Lower shorelines and fluvial landforms permit reconstruction of the final desiccation of the two lakes. Preliminary dating suggests the 936 m level was attained from 17 000-12 000 BP and c. 2000 BP, whilst lower levels prevailed c. 25 000 BP and 8000-6000 BP. Consideration of the palaeohydrologic budget attributes the 936 m level to increased precipitation and possibly increased inflow, whilst tectonism must have played a part in the 945 m level. The present erratic regime of the Okavango is a result of the interplay of factors such as variations in inflows and local precipitation, and hydrological changes due to minor tectonic events, siltation and vegetation blockage.
Chapter
New optically stimulated luminescence ages, in combination with detailed analysis of sediment from White Paintings rock shelter provide a basis for reconstructing palaeoenvironment and site formation processes at the longest archaeological sequence in the Kalahari. The new data resolve previous ambiguities related to the site’s chronology. A series of soil stratigraphic units documents changing conditions at the site over the past 100/120 ka. Millennialscale periods of increased moisture availability, occupation intensity, and landscape stability alternate with periods characterized by more arid conditions, aeolian sedimentation, and lower site occupation intensity. Broader trends in the sediment data suggest a general transition from greater moisture availability in the Pleistocene and Early to Mid Holocene toward more arid conditions in the Late Holocene. Wetter climates occurred at the time of Heinrich events in the North Atlantic due to slowing or cessation of the North Atlantic Deep Water flow (NADW) that resulted in warming of Southern Hemisphere oceans and the associated weakening of the South Atlantic and South African anticyclones.
Article
Attempts to reconstruct past changes in climate-related forcing of dryland landscapes are hampered by the lack of an adequate quantitative framework for understanding the production and interpretation of dated sedimentary records. In drylands, as in other environments, information on past forcing conditions is progressively modified, degraded and removed from the available stratigraphic record by a series of ‘filters’ involving changes in the primary forcing factors themselves, geomorphological processes and the sampling/dating procedures. In this paper we describe a quantitative model that includes these effects, and use the model to examine the nature of preserved dryland sedimentary records and their relationships to primary forcing conditions: thicker preserved sedimentary records reflect periods of more intense aeolian activity; localized switching between erosion and deposition results in discontinuous and highly variable stratigraphic sequences; a preservation bias towards younger deposits is observed, potentially leading to a continuum of accumulation that decays approximately in proportion to 1= ffiffiffiffiffiffiffiffi age p . Time periods not represented by deposition can in some cases be interpreted as periods of higher precipitation and/or lower wind energy. An asymmetry exists between the efficiency with which past ‘drier’ and ‘wetter’ episodes can be identified, which relates to the timeseparation of depositional periods and the correct distinction between hiatuses due to forcing conditions and those due to undersampling. Relevant to this is the effect of random dating errors (statistical uncertainty), which (increasingly with age) filter-out higher frequency events from the record. A new data treatment method (termed Accumulation Rate Variability) provides an efficient proxy for accumulation rates, and therefore the intensity of aeolian activity, with significant improvements over existing date–frequency methods. The filtering problem discussed applies to all attempts at understanding the timing and nature of past events, independent of the proxies and dating methods employed. Further explicit analysis of these issues would be beneficial.
Article
Dunefields are today often found in regions where environmental conditions are no longer conducive to widespread aeolian transport and deposition, and are thus seen as potential archives of palaeoenvironmental information. Some dune types are more suitable for this purpose than others, and linear dunes (used here synonymously with longitudinal dunes) have been most frequently employed. They are commonly found in dryland and dryland-marginal regions, and they are apparently less migratory than some other dune forms, thereby offering the potential for longer environmental histories. Most recent studies have employed optical (OSL) dating surveys, which directly date the emplacement of dune sands, to attempt to produce a representative history of aeolian accumulation at a dunefield scale; yet such studies have not always given due consideration to the geomorphology of linear dune accumulation. Although linear dunes do not rework their sand as readily as, say, barchans dunes, it is clear that sand deposited during an aeolian event is likely to have been removed from elsewhere on the dunefield's surface. For this reason, all dune archives must be assumed to be discontinuous over long timescales. The effect of sediment redistribution on dune preservation, and thus palaeoenvironmental interpretation, is difficult to observe and poorly understood.
Article
Geomorphological studies of caves and lakes in northern Botswana since 1973 have yielded a suite of 80 radiometric dates which permit palaeoenvironmental reconstruction of the landscape over the last 45, 000 years. The unique characteristics of the landforms, when interpreted with caution, yield palaeoclimatic information on both northern Botswana and the catchments of the Okavango River in the Angolan Highlands. Several major shifts in precipitation are indicated for the period 45,000–20,000 BP, with dry conditions prevailing at 25,000 BP. The Late Glacial was characterised by humid conditions, especially from 16,000–13,000 BP, whilst the early Holocene was semi-arid, with precipitation peaks circa 6,000–5,000 BP and 2,000 BP. The results contrast sharply with some southern African palaeo-climatic descriptions in print, where many of the inferences have been drawn from studies of the northern hemisphere inter-tropical zone. The implications of the study are briefly discussed in relation to palaeoclimatic models of the whole African continent.
Article
Both Atlantic and Indian Ocean climate dynamics exert influence over tropical African hydroclimate, producing complex patterns of convergence and precipitation. To isolate the Indian Ocean influence on African paleohydrology, we analyzed the deuterium/hydrogen ratio of higher plant leaf waxes (δDwax) in a 25 000-year sediment record from Lake Challa (3° S, 38° E) in the easternmost area of the African tropics. Whereas both the seismic record of inferred lake level fluctuations and the Branched and Isoprenoidal Tetraether (BIT) index proxy record changes in hydrology within the Challa basin, δDwax, as a proxy for the isotopic composition of precipitation (δDP) is interpreted as a tracer of large-scale atmospheric circulation that integrates the history of the moisture transported to the Lake Challa area. Specifically, based on modern-day isotope–rainfall relationships, we argue that Lake Challa δDwax reflects the intensity of East African monsoon circulation. The three hydrological proxy records show generally similar trends for the last 25 000 years, but there are important differences between them, primarily during the middle Holocene. We interpret this deviation of δDwax from local hydrological history as a decoupling of East African monsoon intensity – which heavily influences the isotopes of precipitation in East Africa today – from rainfall amount in the Challa basin. In combination, the hydrological proxy data from Lake Challa singularly highlight zonal gradients in tropical African climate that occur over a variety of timescales, suggesting that the Congo Air Boundary plays a fundamental role in controlling hydroclimate in the African tropics.
Article
The recovery of detailed and continuous paleoclimate records from the interior of the African continent has long been of interest for understanding climate dynamics of the tropics, and also for constraining the environmental backdrop to the evolution and spread of early Homo sapiens. In 2005 an international team of scientists collected a series of scientific drill cores from Lake Malawi, the first long and continuous, high-fidelity records of tropical climate change from interior East Africa. The paleoclimate records, which include lithostratigraphic, geochemical, geophysical and paleobiological observations documented in this special issue of Palaeo3, indicate an interval of high-amplitude climate variability between 145,000 and ~60,000years ago, when several severe arid intervals reduced Lake Malawi's volume by more than 95%. These intervals of pronounced tropical African aridity in the early Late Pleistocene around Lake Malawi were much more severe than the Last Glacial Maximum (LGM), a well-documented period of drought in equatorial and Northern Hemisphere tropical east Africa. After 70,000years ago climate shifted to more humid conditions and lake levels rose. During this latter interval however, wind patterns shifted rapidly, and perhaps synchronously with high-latitude shifts and changes in thermohaline circulation. This transition to wetter, more stable conditions coincided with diminished orbital eccentricity, and a reduction in precession-dominated climatic extremes. The observed climate mode switch to decreased environmental variability is consistent with terrestrial and marine records from in and around tropical Africa.
Article
Long, wide, but extremely low, parallel ridges of sand are believed to represent the eroded stumps of former longitudinal dunes. Lacking erosion channels of any kind, they are probably unique features. The former dunes are thought to have been degraded mainly by sheet erosion, which was effected by (1) a high-intensity rainfall, (2) a partial vegetation cover, and (3) an unconsolidated, permeable sandy terrain. Probably this combination of factors is rare. Small basins in the troughs between the sand ridges are underlain by a mixture of sand and clay that came from the ridges. These basins are maintained by deflation, together with excavation by buffalo, elephant, and other large animals. The history of the ridges implies Pleistocene climatic change. A very wet period succeeded a very dry period. Also a short, recent dry period is suggested.
Article
Luminescence dating of sediments from rockshelters is complicated by the possibility of incomplete sunlight bleaching in antiquity and uncertainties in the distribution of radioactivity. Yet such dating is important for the Middle Stone Age in southern Africa where rockshelters provide a large fraction of the known record. Sufficient bleaching is demonstrated for sediments at White Paintings Rockshelter in northwest Botswana by comparing results from slowly bleaching thermoluminescence signals and rapidly bleaching optically stimulated luminescence. Radioactive disequilibrium is also shown to be present in these sediments and believed to result from fractionation between 238U and 234U, requiring a small correction to the dose rate. Derived ages are in broad agreement with independent dating evidence and archaeological expectations.
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This article examines the struggle of various actors over the use of representations of the past to aid the development of communities in central southern Africa. It addresses the contradictions, contestations and dilemmas involved in this process through a case study of the Kuomboka, a heritage festival held annually in the heart of the Upper Zambezi Valley. Hosted by the Lozi peoples of western Zambia, the festival utilises Lozi history and heritage and is viewed as a strong symbol of identification not only for people who consider themselves Lozi but also for Zambians in general and other Africans. Significantly, Kuomboka is also a festival visited by very few non-Africans. I will argue that the struggle to extract contemporary value out of this manifestation of Lozi heritage is fought on three levels – first, over contested versions of the past; second, over the uses of heritage; and, finally, over ownership of heritage and the implications of this ownership for the distribution of the benefits of heritage development. The intensity of the struggle, which is fought across divisions of class and ethnicity, also highlights the competition over scarce resources that exists in a region suffering economic underdevelopment and social disadvantage.
Article
a b s t r a c t The Middle Kalahari is characterised by significant regional scale geomorphic activity and landscape change during the late Quaternary period. Very little however, is known about vegetation dynamics over this period due in part to the absence of well-preserved organic records. Here we test the application of phytolith analyses to sandy shoreline deposits of megalake Makgadikgadi, one of the sumps of the Okavango delta, routinely sampled and dated as part of a separate systematic geomorphological analysis. We confirm the presence of both an abundant and diverse assemblage of diagnostic phytoliths within these sand-dominated samples. The phytolith record reveals significant differences in the savanna vegetation through time with the composition of shoreline vegetation during different lake high-stand events was found to vary. Lake high stands are characterised by a coherently grassland dominated signal as well as a general trend towards more mesic and C 3 prominent taxa during lake events after w40 ka. We suggest that phytolith analyses, whilst far from a perfect proxy, provide the potential to offer an important insight into long-term changes in Kalahari savanna, critical for understanding the response of regional vegetation to climatic and hydrological change both in the past and under future climate change scenarios.
Article
Recent geomorphological research in northern Botswana has shown the existence of an extensive palaeolake system adjacent to the Okavango Delta, with links to the Zambezi via the Chobe River at altitudes of 940-945 m and 936 m. This paper investigates the Chobe-Zambezi link and presents evidence in the form of terraces and major sand ridges, for the existence of Lake Caprivi, a palaeolake of c 2000 km2 at 936 m, ponded behind the Mambova Falls at the Chobe-Zambezi confluence. -from Authors
Article
In terms of overall activity transverse dunes are migratory, linear dunes are sand-passing or extending forms and star dunes accumulate sand. These characteristics have major implications for the interpretation of relict dunes, creating a need for careful consideration of the type of dune regarded as relict and the evidence upon which such a diagnosis is based. -from Author
Article
Climate and environmental change in the Late Quaternary are widely regarded as key drivers of early human development and dispersal. In Africa, robust records of change are required to assess the nature of potential impacts. Today’s late Quaternary palaeoenvironmental/palaeoclimate reconstructions from the interior southern African basin (Kalahari) are more spatially detailed, have a stronger chronometric underpinning, and span a longer time range, than those of 10–20 years ago, but are no less controversial. Reconstructions for the last ∼150 ka are usually interpreted in terms of changes in hydrological balance from conditions more humid or more arid than today, and expressed in climatological terms as the changing latitudinal interplay between monsoon easterlies and tropical and mid-latitude westerlies. With more data than ever before, why then is the record not yet delivering a more coherent picture of regional climate change? This paper deliberately addresses current challenges and controversies, including issues often ignored or neglected, with the view that it is essential to do so if more robust interpretations of the past are to be generated in the future.
Article
Long environmental proxy records are very scarce in semi-dry continental areas and often those available present conflicting interpretations. However, more in-depth investigation of apparent contradictions, can address these problems. For example, comparison of the upper parts of pollen and sediment sequences from the Tswaing Crater and Wonderkrater spring (South Africa) and isotopes in a speleothem at Lobatse Cave (Botswana) from the Savanna Biome establishes a basis for understanding of long-term regional environmental processes in central Southern Africa over the last 60 ka. The different proxies for the vegetation can hypothetically be reconciled on condition that the chronologies on which they are based and environmental controls are firm. We discuss the ratio of woody elements, under-storey herb-cover and the vegetation's general C4/C3 status in the central savanna region, in relation to seasonal rainfall and temperature variations and long-term climate forcing.
Article
a b s t r a c t In order to define criteria for long-term climate change models in Southern Africa, an overview of the available pollen data during the Late Quaternary is needed. Here we reassess the paleo-climatic condi-tions in southern Africa by synthesising available fossil pollen data that can provide new insights in environmental change processes. The data considered here include the latest as well as previously published information that has been difficult to assess. Available calibrated pollen sequences spanning the Late Pleistocene and Holocene were subjected to Principal Components Analysis (PCA) to monitor taxa sensitive to moisture and temperature fluctuations. The PCA values are presented graphically as indicators of climate variability for the region. The results cover different biomes that include the summer-rain region in the north and east, the winter-rain area in the south and the dry zone in the west. The PCA plots directly reflect major changes of terrestrial environments due to variations in temperature and moisture. Mostly sub-humid but fluctuating conditions are indicated during the cold Marine Isotope Stage (MIS) 2, which were followed by a dry phase soon after the beginning of the Holocene but before the middle Holocene in the northern, central and eastern parts of the sub-continent. Marked but non-parallel moisture changes occurred in different subregions during the Holocene suggesting that climatic forcing was not uniform over the entire region. Some events seemed to have had a more uniform effect over the sub-continent, e.g., a relatively dry summer rain event at c. two thousand years ago, which can possibly be related to the ENSO phenomenon. The role of anthropogenic activities in some of the most recent vegetation shifts is likely.
Article
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.