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A record of rapid Holocene climate change preserved in hyrax middens from southwestern Africa
Abstract
The discovery of sensitive paleoenvironmental proxies contained within fossilized rock hyrax middens from the margin of the central Namib Desert, Africa, is providing unprecedented insight into the region's environmental history. High-resolution stable carbon and nitrogen isotope records spanning 0–11,700 cal (calibrated) yr B.P. indicate phases of relatively humid conditions from 8700–7500, 6900–6700, 5600–4900, and 4200–3500 cal yr B.P., with a period of marked aridity occurring from 3500 until ca. 300 cal yr B.P. Transitions between these phases appear to have occurred very rapidly, often within <200 years. Of particular importance are: (1) the observed relationship between regional aridification and the decline in Northern Hemisphere insolation across the Holocene, and (2) the significance of suborbital scale variations in climate that covary strongly with fluctuations in solar forcing. Together, these elements call for a fundamental reexamination of the role of orbital forcing on tropical African systems, and a reconsideration of what factors drive climate change in the region. The quality and resolution of these data far surpass any other evidence available from the region, and the continued development of this unique archive promises to revolutionize paleoenvironmental studies in southern Africa.
... Stable carbon isotope analyses of fecal pellets and hyraceum reflect the input of C 3 and C 4 vegetation, and nitrogen isotope studies can reveal changes in relative moisture (Chase et al., 2012;Ivory et al., 2021). Middens can differ in thickness and the amount of hyraceum versus fecal pellets, and thus can have varying degrees of dietary bias and represent disparate temporal scales (Scott and Cooremans, 1992;Scott et al., 2004;Gil-Romera et al., 2006;Scott and Woodborne, 2007;Chase et al., 2009Chase et al., , 2012. ...
... In southern Africa, massive middens composed primarily of hyraceum have been discovered, providing paleoenvironmental insight for the late Pleistocene and Holocene (Chase et al., 2009(Chase et al., , 2012Carr et al., 2010). These types of middens can be subsampled for isotope and pollen analyses, much like a sediment core, and the data can be interpreted as a time series (Chase et al., 2012). ...
... Modern vegetation in the Nejd is severely fuel-limited due to the sparseness of the vegetation. The presence of increased charcoal suggests that vegetation during this interval was continuous enough to be more conducive to burning (Blackford, 2000;Chase et al., 2009;Genet et al., 2021). ...
Arid regions are especially vulnerable to climate change and land use. More than one-third of Earth's population relies on these ecosystems. Modern observations lack the temporal depth to determine vegetation responses to climate and human activity, but paleoecological and archaeological records can be used to investigate these relationships. Decreasing rainfall across the Late Holocene provides a case study for vegetation response to changing hydroclimate. Rock hyrax ( Procavia capensis ) middens preserve paleoenvironmental indicators in arid environments where traditional archives are unavailable. Pollen from modern middens collected in Dhofar, Oman, demonstrates the reliability of this archive. Pollen, stable isotope (δ ¹³ C, δ ¹⁵ N), and microcharcoal data from fossil middens reveal changes in vegetation, relative moisture, and fire from 4000 cal yr BP to the present. Trees limited to moister areas (e.g., Terminalia ) today existed farther inland at ~3100 cal yr BP. After ~2900 cal yr BP, taxa with more xeric affiliations (e.g., Senegalia ) had increased. Coprophilous fungal spores ( Sporormiella ) and grazing indicator pollen revealed an amplified signal of domesticate grazing at ~1000 cal yr BP. This indicates that trees associated with semiarid environments were maintained in the interior desert during ~3000–4000 yr of decreasing rainfall and that impacts of human activity intensified after the transition to a drier environment.
... The impact of this dynamic is also evident during the glacialinterglacial cycles of the late Quaternary. Records from the Namib Desert, show that the Benguela system strongly influences climate, with a negative relationship between upwelling intensity and terrestrial humidity at centennial to multi-millennial timescales (Chase et al., 2023;Chase et al., 2010;Chase et al., 2009;Chase et al., 2019b). This blocking of tropical systems has been implicated as a driver of environmental change in the summer rainfall as far east as the Makgadikgadi basin of northern Botswana (Stokes et al., 1997), as well as in some records from the winter rainfall zone, where even modest contributions of summer rainfall may have had a significant impact on rainfall and drought season length/intensity (Chase et al., 2015a(Chase et al., , 2015b. ...
... The major oceanic circulation systems (the cold Benguela current and the warm Agulhas and Angola currents, temperatures shown in • C (data from Reynolds et al., 2007)) and atmospheric circulation systems (white arrows) are indicated. The Groenfontein hyrax midden site (4, white star) is shown in relation to key palaeoclimatic records (1 -Cango Caves Talma and Vogel, 1992) and Efflux Cave (Braun et al., 2020), 2 -Seweweekspoort (Chase et al., , 2017, 3-Katbakkies Pass (Chase et al., 2015b;Meadows et al., 2010), 5 -De Rif (Chase et al., , 2015aQuick et al., 2011;Valsecchi et al., 2013), 6 -Pakhuis Pass (Chase et al., 2019a;Woodborne, 2007a, 2007b), 7 -Elands Bay Cave (Cowling et al., 1999;Parkington et al., 2000), 8 -Pella (Chase et al., 2019b;Lim et al., 2016), 9 -Zizou (Chase et al., 2019b, 10 -Spitzkoppe (Chase et al., 2009(Chase et al., , 2019b. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.) ...
... Variations in midden δ 15 N are interpreted (as per other studies of nitrogen isotopes in hyraceum, e.g. Chase et al., 2019a;Chase et al., 2009;Chase et al., 2019b;Chase et al., 2012) to reflect changes in water availability. This is considered to be a function of a more open nitrogen cycle in arid regions, meaning that nitrogen in such regions is more prone to loss through transformation and the release of gaseous products is depleted in 15 N, and the remaining nitrogen in the soil is enriched (Austin and Vitousek, 1998). ...
... Several continuous high-resolution records from rock hyrax middens from the Namib Desert have indicated that the last glacial period was indeed relatively humid compared to the Holocene (Lim et al., 2016;Chase et al., 2019), adding significant detail to our understanding of regional climate change over the last 50,000 years. While some middens, such as those from Pella (Lim et al., 2016), are located at the margins of the Namib Desert, and may be considered to reflect conditions in the Great Escarpment, others, such those recovered from Spitzkoppe (Chase et al., 2009(Chase et al., , 2019 and, particularly, Mirabib (Scott et al., 2018), are located to the west and lie within the arid core of the desert. In contrast to the region's fluvio-lacustrine archives, it is generally considered that rock hyrax middens preserve a predominantly local signal that reflects the foraging range of the animals (less than ∼60 m from the midden/shelter site) (Sale, 1965;Chase et al., 2012) and that, accordingly, the indications of increased glacial-age humidity at Spitzkoppe and Mirabib can be interpreted to reflect conditions within the desert itself. ...
... Strong similarities are evident in the stable nitrogen isotope records (interpreted as a reflection of water availability) from middens recovered from Aba Huab/Austerlitz , Spitzkoppe (Chase et al., 2009(Chase et al., , 2019, Zizou (Chase et al., 2019), and Pella (Chase et al., 2019), indicating a generally common climate response signal across a 900-km transect of the Namib Desert (Fig. 1). Evidence of associated changes in vegetation, however, is often restricted to the Holocene (Scott et al., 1991(Scott et al., , 2022Scott, 1996;Gil-Romera et al., 2006, with the only indications of glacial-age vegetation coming from the continuous 50-kyr record from Pella (Lim et al., 2016), and shorter MIS 2-3 time slices from the Brandberg (Scott et al., 2004) and Mirabib (Scott et al., 2018). ...
... As described by Chase et al. (2012, 2019), rock hyrax δ 15 N records are interpreted as a proxy for water availability, with higher δ 15 N indicating drier conditions. As described in several previous studies, and supported by strong correlations with a diverse range of proxy climate records (Chase et al., 2009(Chase et al., , 2015a(Chase et al., , 2019, drier conditions induce more N flow to inorganic soil nitrogen pools that are subject to gaseous loss of 15 N-depleted products (Austin and Vitousek, 1998;Handley et al., 1999;Murphy and Bowman, 2009). Plants growing in the resulting 15 N-enriched soils exhibit higher δ 15 N values (Craine et al., 2009;Hartman and Danin, 2010), a signal that is transmitted to the tissues (and excreta) of animals that consume them (Murphy and Bowman, 2006;Hartman, 2011;Carr et al., 2016). ...
This paper presents the first continuous multi-proxy record of climate and vegetation change from the central Namib Desert extending over much of the last ca. 39,000 years. Derived from rock hyrax middens, evidence from stable carbon and nitrogen isotopes, pollen, and microcharcoal reveals significant differences between glacial-age and Holocene climates and vegetation types. Although still arid to semi-arid, conditions during Marine Oxygen Isotope Stages (MIS) 2–3 were significantly more humid than in the Late Holocene. Considerable associated vegetation change is apparent, with cooler temperatures and higher/more-regular rainfall promoting the westward expansion of relatively mesic shrubby karroid vegetation during MIS 2–3. With the last glacial–interglacial transition, increasing temperatures and less/less-regular rainfall resulted in marked vegetation changes and the establishment of current xeric grasslands. The inter-plant spacing of the karroid vegetation promoted by wetter conditions does not carry fire effectively, and the microcharcoal record indicates that more extensive fires may develop only with the development of grassier vegetation under drier conditions. As with other terrestrial records from the Namib Desert and environs, no Cape flora elements were found to support previously hypothesised expansion of the Fynbos Biome during the last glacial period.
... Early reconstructions of palaeoclimatic conditions during the Holocene in the Namib Desert and surroundings were based on microfaunal studies, geomorphological research and radiocarbon dating of inclusions in riverine deposits and dunes (e.g., Brain and Brain, 1977;Heine, 1982;Vogel and Rust, 1987;Lancaster and Teller, 1988;Vogel, 1989), followed by studies on Atlantic Ocean pollen from marine boreholes (Fig. 1), dust geochemistry, isotopes and micropalaeontology (Scott et al., 1991;Shi et al., 1998Shi et al., , 2000Shi et al., , 2001Stuut et al., 2002;Farmer et al., 2005;Dupont et al., 2008) and terrestrial records like stalagmites, geomorphology, and archaeology (e.g., Stokes et al., 1997;Stute and Talma, 1998;Brook et al., 1999Brook et al., , 2011Brook et al., , 2015Thomas and Shaw, 2002;Eitel et al., 2005;Heine, 2005;Srivastava et al., 2005;Chase et al., 2009Chase et al., , 2011Thomas and Burrough, 2012;Sletten et al., 2013;Marais et al., 2015;Railsback et al., 2016Railsback et al., , 2018Railsback et al., , 2019Voarintsoa et al., 2017;Kinahan, 2018;Schüller et al., 2018). These studies have added critical information on past hydrological regimes of southern Africa, especially rainfall ( Fig. 1), which is one of the major shifting climate features in the subcontinent. ...
... In particular, pollen studies have mostly used hyrax dung, a deposit type that preserves fossil pollen optimally in the drylands of Namibia and shows potential for future palaeoenvironmental studies in these areas (Scott, 1996;Scott et al., 2004Scott et al., , 2018Gil-Romera et al., 2006Lim et al., 2016). Stable light isotope studies of dung have also proved informative and have important potential for future palaeoclimatic studies (Chase et al., 2009(Chase et al., , 2012(Chase et al., , 2019a. Apart from pollen and isotopes, hyrax dung preserves other remains like cuticles, insects, aDNA, etc (Chase et al., 2012). ...
... The general climate history for the Holocene in Namibia as derived from different earlier proxy records referred to above, suggests generally wetter but varying conditions during the early Holocene peaking ca. 8 ka, and generally drier conditions in the later Holocene ca. 4 ka (Scott et al., 1991;Chase et al., 2009Chase et al., , 2011. The moisture changes accompany upwelling in the Atlantic Ocean, which relate to water temperature, and follow wide regional circulation patterns (Farmer et al., 2005). ...
Fossil pollen and geochemical sequences from a series of hyrax dung deposits from rock shelters along the eastern margin of the central Namib Desert shed light on the Holocene environmental history of Namibia. Grassy pollen assemblages suggest relatively humid conditions during the early Holocene between ca. 9.6 and 7.7 ka. A series of stepwise changes follows, including the prominence of different pioneer plant communities of which changes in ratios between grassy and shrub pollen types suggests moisture oscillations. The development of more C4 plants around ca. 4.5 ka, as indicated by isotope concentrations and persistent grass pollen percentages, point to the development of a different climatic regime than that in the early Holocene, which extended the area of subtropical savanna towards the south at c. 24°S. This transition can in part be interpreted as a vegetation response to a shift in the rainfall distribution from an early even seasonal distribution to the current late Holocene summer rainfall regime. Climate changes may have been driven by variations in austral summer and winter solar insolation with changes in total solar irradiance (TSI) superimposed upon them. Through its link to Bond events in the North Atlantic, and thus Atlantic Meridional Overturning Circulation (AMOC), TSI may have affected SSTs in the SE Atlantic and SW Indian Ocean, which influence both summer and winter rainfall in southern Africa.
... Notwithstanding, some continuous terrestrial records from the SAMR have been recovered, notably from Lake Ngami (Cordova et al., 2017), Wonderkrater (Scott, 1982) and Tswaing Crater (Kristen et al., 2010;Metwally et al., 2014;Partridge et al., 1997;Scott, 1999), cave sites such as Cold Air Cave (Holmgren et al., 2003;Lee-Thorp et al., 2001), baobabs (Woodborne et al., 2015) and rock hyrax middens from the Namib Desert and the eastern Karoo (Chase et al., 2009(Chase et al., , 2019bScott et al., 2005) (Fig. 1). The resolution of these records ranges from multi-centennial to multimillennial for the lake and wetland sites to sub-to multi-decadal for the speleothem and most rock hyrax midden records. ...
... Increasing austral summer insolation is predicted to result in progressively more humid conditions from the early to late Holocene (Chase, 2021;COHMAP, 1988;Partridge et al., 1997), and indeed in the northeastern SAMR, records do indicate such a trend (Chevalier and Chase, 2015;Holmgren et al., 2003;Partridge et al., 1997;Schefub et al., 2011). However, evidence from the distal margin of the SAMR is more ambiguous (Chevalier and Chase, 2015;Scott et al., 2022) and, in the case of the Namibian records, actually indicative of progressive aridification across the Holocene, similar to trends observed in the Northern Hemisphere (Chase et al., 2009(Chase et al., , 2019b. ...
... Aranibar et al., 2008;Carr et al., 2016;Craine et al., 2009;Hartman, 2011;Hartman and Danin, 2010;Murphy and Bowman, 2006;Newsome et al., 2011;Swap et al., 2004). Studies of 15 N in hyrax middens from a wide range of environments indicate consistently strong correlations between midden 15 N and independent climate proxy records, supporting the conclusion that environmental moisture availability is a major driver of midden 15 N records (Carr et al., 2016;Chase et al., 2009Chase et al., , 2015aChase et al., , 2017Chase et al., , 2019b. ...
Evidence for climate variability in the southern African monsoon region (SAMR) is limited by a spatially and temporally discontinuous palaeoclimatic dataset. We describe a 6680 year long, largely sub-decadal resolution δ¹⁵N record from a rock hyrax midden from southeastern Africa. The results provide a detailed reconstruction of regional hydroclimates since the beginning of the mid-Holocene. A long-term – albeit subtle – increase in humidity consistent with precessional forcing is observed, but the record is dominated by a strong ∼1750-yr cycle, a signal that is shared with other SAMR records. Considered in their regional context, these data suggest that changes coincident with the termination of the African Humid Period at ∼5500 cal BP do not express the abrupt transition observed in some records from the northern African tropics. Rather they indicate gradual changes, as observed at peri-equatorial sites. Notably, however, eastern and western subregions of the SAMR experience a rapid phase shift beginning ∼5500 cal BP, with initially in-phase hydroclimate anomalies transitioning to the establishment of a strong east-west dipole. This likely reflects a coeval strengthening of the Southeast Atlantic trade winds and decreased atmospheric pressure in southeast Africa, factors associated with increasing (decreasing) austral (boreal) summer insolation. The results highlight the distinct nature of southern African responses across this key period of African climate history.
... If it were an asymmetrical migration of the ITCZ, then in Northern Hemisphere winter one would expect it to be wetter in the south African savanna (see, Fig. S22). However, reported data (Chase et al., 2009;Railsback et al., 2018, green squares at Fig. 3) from south Africa suggest that the region was experiencing wetter conditions at this time. An asymmetrical expansion of the Hadley cells to the north in the Northern Hemisphere and to the south in the Southern Hemisphere would result in a drought over the Mediterranean and may, in turn, result in more humid conditions, over the western parts of north and south African savanna. ...
... An asymmetrical expansion of the Hadley cells to the north in the Northern Hemisphere and to the south in the Southern Hemisphere would result in a drought over the Mediterranean and may, in turn, result in more humid conditions, over the western parts of north and south African savanna. To confirm such a hypothesis, it would be desirable to gather more paleoclimate data from different sides of the spatial transect identified in this study and also to collect more African subtropical paleoclimate data, similar to those presented by Chase et al. (2009) and Railsback et al. (2018) which propose a wetter phase during our temporal period of interest (see, Fig. 3). ...
... (Carolin et al., 2019;Lemcke and Sturm, 1997;Sharifi et al., 2015;Weiss et al., 1993) that are mentioned in the main text. The green squares over Africa indicate the locations of the data (Chase et al., 2009;Railsback et al., 2018) which show a wetter period during the period of interest. The January location of the ITCZ is plotted after Yan (2005). ...
It has been proposed that there was an abrupt climatic change event around 4.2 ka BP that affected societies and even has been linked to the collapse of empires. Subsequent studies have reached conclusions that both support and contradict the proposed event yet, nevertheless, 4.2 ka BP has now been adopted as the stratigraphic boundary point between the Middle and Upper Holocene. Time series plots of paleoclimate studies that claim to support the abrupt climate change hypothesis show differing temporal patterns so, in this study, we apply the Bayesian structural time series (BSTS) approach using the CausalImpact package to test data from southeast Europe and southwest Asia for which it is claimed that they demonstrate a climatic anomaly around 4.2 ka BP. To do this, each "affected" time series is synthetically reconstructed using "unaffected" series as predictors in a fully Bayesian framework by the BSTS method and then forecast beyond the assumed starting point of the event. A Bayesian hypothesis test is then applied to differences between each synthetic and real time series to test the impact of the event against the forecast data. While our results confirm that some studies cited in support of the 4.2 ka BP event hypothesis do indeed hold true, we also show that a number of other studies fail to demonstrate any credible effect. We observe spatial and data patterning in our results, and we speculate that this climatic deterioration may have been a consequence of an asymmetrical northward expansion or migration of the Northern Hemisphere Hadley cell. Furthermore, we observe that while the signals are generally not credible, types of proxy data from the Mesopotamia region and east are consistent with aeolian dust storms.
... Variations in midden δ 15 N are interpreted (as per other studies of nitrogen isotopes in hyraceum, e.g. Chase et al., 2019a;Chase et al., 2009;Chase et al., 2019b;Chase et al., 2012) to reflect changes in aridity. This is generally attributed to a more open nitrogen cycle in arid regions. ...
... Aranibar et al., 2008;Carr et al., 2016;Craine et al., 2009;Hartman, 2011;Hartman and Danin, 2010;Murphy and Bowman, 2006;Newsome et al., 2011;Swap et al., 2004). Studies of 15 N in hyrax middens from a wide range of environments indicate consistently strong correlations between midden 15 N and independent climate proxy records, supporting the conclusion that aridity is a major driver of midden 15 N records (Carr et al., 2016;Chase et al., 2009Chase et al., , 2015aChase et al., , 2017Chase et al., , 2019b. ...
... While Holocene faunas of Namibia show similar arid-adapted species as currently, the early Holocene (10 to 8 ka) phase may have been more arid (Robbins et al., 2000(Robbins et al., : 1108. This contrasts with what would be expected during the African Humid Period (ca. 9 to 6 ka) where evidence of humid phases from 9 to 3 ka are recorded in hyrax midden deposits in Namibia (Chase et al., 2009). There may be some evidence of faunal change in response to the mid-Holocene altithermal, a warm period between 7 and 5 ka (Fitchett, 2019). ...
... In the northern Cape, there is an overall trend of increasing aridification in the later Holocene, reaching a peak around 3 to 2 ka (Ecker et al., 2018: 142). This may correspond to increasing aridity from 3 ka recorded in hyrax middens in Namibia (Chase et al., 2009). In the eastern Free State, bone taphonomic and site formation evidence from the Heelbo bonebed suggests drought conditions here at ca. 3.7 ka (Backwell et al., 2018b). ...
Analyses of faunal remains are a key means of inferring palaeoenvironmental change. In this paper, the use of faunal remains as a proxy for environmental conditions from Marine Isotope Stage 6 to the Holocene in southern Africa is reviewed. The focus of this review is on large herbivore abundance and how these fluctuate temporally and regionally in accordance with palaeo-climatic shifts. Here, southern Africa is divided into four eco-regions loosely based on climatic, biotic and zoogeographic traits: the Cape Floristic Region, the arid and semi-arid region, the savanna and grassland region, and the wetter eastern region. The relative abundance of large herbivores within these regions are noted, and temporal trends are inferred. On the whole, most eco-regions maintain similar herbivore compositions over time showing the regional ecological resilience of these taxa to local-scale environmental change. Yet some changes in faunal frequencies are apparent. The Cape Floristic Region shows evidence of significant faunal turnover from the Late Pleistocene to the Holocene. Here, grazers are significantly more abundant during glacial periods, probably linked to the terrestrial expansion of the palaeo-Agulhas coastal plain. Shifts in ungulate abundance in the currently xeric central interior, also indicate wetter periods in the Pleistocene. Holocene faunas are generally similar to historic distributions but shifts between xeric and mesic periods are also evident.
... Recent years have seen the proliferation of palaeoclimate proxy records in southern Africa and the African continent (Nash et al. 2016a). Datasets covering the late Holocene have been developed from speleothems (Holmgren et al. 1999(Holmgren et al. , 2003Sletten et al. 2013;Scroxton et al. 2017;Voarintsoa et al. 2017;Braun et al. 2019), mammalian middens (Chase et al. 2009;Scott 1996), tree rings (Woodborne et al. 2016), pollen (Ekblom et al. 2012), and lake records (Stager et al. 2013), all of which can be representative of precipitation variability. However, annually resolved palaeoclimate records remain sparse in comparison to other regions and continents, including other southern hemisphere landmasses such as South America and Australasia (Neukom and Gergis 2012). ...
... Records are therefore drawn from northeastern or central Namibia, the highest resolution of which is the DC1 record from the speleothem isotope record at 19.4°S (Voarintsoa et al. 2017). Lower resolution pollen and isotopic proxies from hyrax middens supplement these records (Scott 1996;Chase et al. 2009). In addition, hydroclimate reconstructions from Anjohibe cave in northwestern Madagascar (Scroxton et al. 2017) and eastern African lakes (Tierney et al. 2013), as well as reconstructions of southwest Indian Ocean SSTs derived from coral records (Zinke et al. 2014) and southeast Atlantic upwelling (Farmer et al. 2005), were examined for evidence of rainfall variability in neighbouring regions and drivers of rainfall. ...
Understanding of long-term climatic change prior to instrumental records necessitates reconstructions from documentary and palaeoclimate archives. In southern Africa, documentary-derived chronologies of nineteenth century rainfall variability and palaeoclimate records have permitted new insights into rainfall variability over past centuries. Rarely considered, however, is the climatic information within early colonial documentary records that emerge from the late fifteenth century onwards. This paper examines evidence for (multi-)seasonal dry and wet events within these earlier written records (c. 1550–1830 CE) from southeast Africa (Mozambique) and west-central Africa (Angola) in conjunction with palaeoclimate records from multiple proxies. Specifically, it aims to understand whether these sources agree in their signals of rainfall variability over a 280-year period covering the ‘main phase’ Little Ice Age (LIA) in southern Africa. The two source types generally, but do not always, show agreement within the two regions. This appears to reflect both the nature of rainfall variability and the context behind documentary recording. Both source types indicate that southeast and west-central Africa were distinct regions of rainfall variability over seasonal and longer timescales during the LIA, with southeast Africa being generally drier and west-central Africa generally wetter. However, the documentary records reveal considerable variability within these mean state climatic conditions, with multi-year droughts a recurrent feature in both regions. An analysis of long-term rainfall links with the El Niño–Southern Oscillation (ENSO) in southeast Africa suggests a complex and possibly non-stationary relationship. Overall, early colonial records provide valuable information for constraining hydroclimate variability where palaeoclimate records remain sparse.
... Neumann et al., 2008;Norstr€ om et al., 2009;Neumann et al., 2010). To contextualise our findings and assess spatial variability in Holocene climate across the summer rainfall region of southern Africa, we compare our data with shifts in moisture availability reflected in highly resolved and well-constrained stable isotope records from speleothems in northern South Africa (Cold Air Cave; Holmgren et al., 2003) and northern Namibia (Dante Cave; Sletten et al., 2013), as well as from hyrax middens from central Namibia (Spitzkoppe; Chase et al., 2009). We also make use of newly available biomarker data from the southeast African coast (Miller et al., 2019(Miller et al., , 2020. ...
... b) d 18 O stalagmite record from Anjohibe Cave, northwest Madagascar(Wang et al., 2019). c) d 15 N Sptizkoppe hyrax midden record, northern Namibia(Chase et al., 2009). d) d 18 O stalagmite record from ...
The magnitude and frequency of extreme events is projected to increase under future climate change and understanding the major drivers of global climate variability is dependent on the development of detailed records from critical regions. Subtropical Africa is known to have undergone phases of significant change resulting from variations in broad-scale atmospheric and oceanic circulation patterns, but the nature and cause for these variations remain intensely debated. Here we present a highly resolved sedimentary record from the eastern margin of South Africa to reconstruct hydroclimate in southeast Africa over the past 7000 years. Stratigraphic and inorganic proxies preserve a highly sensitive record that document dramatic shifts in moisture balance, with phases of severe drought recorded at 4700–4200 and 3700–2600 cal yr BP. We suggest that pronounced hydroclimate variability observed in the Mkhuze record was likely triggered by changes in the activity of El Niño-Southern Oscillation (ENSO), which acted to control the transport of moisture from the Indian Ocean across southeast Africa. We show that rapid shifts in moisture availability were a characteristic feature of mid-late Holocene climate across the summer rainfall region of southern Africa, with these events broadly anti-phased with hydroclimatic shifts in East Africa and northwest Madagascar. These findings suggest that evaluating drought frequency, ecological risk and food security within the region is likely to be closely tied to ENSO and its response to future global warming.
... Stable nitrogen isotope analysis of midden hyraceum samples were performed at the Department of Archaeology, University of Cape Town following Chase et al. (2010Chase et al. ( , 2009, with a contiguous/ overlapping samples obtained two series of offset 1 mm holes. The standard deviation derived from replicate analyses of homogeneous material was better than 0.2‰. ...
... The environmental processes relating to this recycling or loss of 15 N are not tied exclusively to rainfall amount, but in climatic terms are more accurately considered to relate to water availability (Murphy and Bowman, 2006). Studies of 15 N in hyrax middens from a wide range of environments indicate consistently strong correlations between midden 15 N, local vegetation/soil 15N, as well as independent climate proxy records, supporting the conclusion that environmental moisture availability is a major driver of midden 15 N records (Carr et al., 2016;Chase et al., 2009Chase et al., , 2010Chase et al., , 2011Chase et al., , 2013Chase et al., , 2015aChase et al., , 2015bChase et al., , 2017. ...
The Cape Floristic Region (CFR) is one of the world's major biodiversity hotspots, and much work has gone into identifying the drivers of this diversity. Considered regionally in the context of Quaternary climate change, climate stability is generally accepted as being one of the major factors promoting the abundance of species now present in the CFR. However, little direct evidence is available from the region, and responses to changes in global boundary conditions have been difficult to assess. In this paper, we present new high-resolution stable isotope data from Pakhuis Pass, in the species-rich western CFR, and contextualise our findings through comparison with other records from the region. Combined, they indicate clear, coherent changes in regional hydroclimate, which we relate to broader forcing mechanisms. However, while these climate change events share similar timings (indicating shared macro-scale drivers), the responses are distinct between sites, in some cases expressing opposing trends over very short spatial gradients (<50 km). We describe the evolution of these trends, and propose that while long-term (10 5 yr) general climatic stability may have fostered high diversity in the region through low extinction rates, the strong, abrupt changes in hydroclimate gradients observed in our records may have driven a form of allopatric speciation pump, promoting the diversification of plant lineages through the periodic isolation and recombination of plant populations.
... The upper and lower sections of DR-2 are composed primarily of hyraceum and have a relatively consistent accumulation rate. Data from other well-dated middens (Chase et al., 2009 provides support that the hyrax middens selected for this and related studies are characterised by generally consistent rates of accumulation. ...
... The low amplitude fluctuations in δ 13 C (from − 26.79 to −27.68‰) that are evident at DR-1 indicate changes in the water-use efficiency of the system over time, with less depleted δ 13 C reflecting drier conditions. The δ 15 N signal in animal tissues is primarily influenced by climate and reflects changes in water availability (further discussion found in Chase et al., 2009 andChase et al., 2010). ...
... Aside from these faecal steroids, coprolites often contain other lipid biomarkers such as alkanes, alkanols or triterpenoids, which generally represent dietary components of the animal's last meal (van Geel et al. 2008(van Geel et al. , 2011Gill et al. 2009;Carr et al. 2010). Ancient DNA analysis provides precise taxonomic identification of the source animal and the coprolite's organic content (e.g., Poinar et al. 1998Poinar et al. , 2001, while stable isotope analysis provides insights into the source animal's dietary components and trophic level (Ghosh et al. 2003;Carr et al. 2010Carr et al. , 2016, as well as palaeoclimatic issues (e.g., Chase et al. 2009;, 2012Meadows et al. 2010). ...
... Furthermore, its particular co-occurrence with faecal 5β-stanols provides unambiguous evidence for an animal latrine. Such middens have the ability to preserve well in hot and dry environments, where the urine rapidly evaporates and thereby seals in the majority of the associated organic matter (Chase et al. 2009). ...
As part of a rock art dating project at Qurta (Upper Egypt), samples were collected from an organic deposit and from an accumulation of individual faecal pellets. Radiocarbon dating of these relatively well-preserved materials indicates an unexpectedly old age of ca. 45,000 BP or older. In order to identify the biogenic nature of these deposits and to reconstruct the palaeo-environment at the time of their formation, micromorphological, palaeobotanical, and biomarker analyses were carried out. All data indicate that the organic deposit and the pellets were produced by different species. The presence of a novel biomarker, which only occurs in animal urine (hippuric acid), contributed to the conclusion that the organic deposit most likely represents the remains of a rock hyrax (Procavia capensis) latrine, whereas the pellets stem from small bovids. Plant macroremains from the pellets indicate that the animals browsed in the more vegetated areas, presumably near the Nile, although the general environment was probably mainly arid and open. Combined with the dates, this suggests that the pellets date to MIS 3 or 4. Our results demonstrate the great potential of an interdisciplinary approach to the study of Quaternary coprolite deposits, allowing for more adequate and more complete interpretation.
... This reduces to 50 mm Figure 1. Location of the study area in coastal Namibia showing isohyets (50-300 mm yr -1 inland) and location of Spitzkoppe (Chase et al., 2009). Also shown are locations of age-date sites. ...
... So between ∼1550-1700 much of the Namib desert appears to have been undergoing regional dry conditions. However, in the δ 15 N data from hyrax middens (from Spitzkoppie, Figure 1) reported in Chase et al. (2009) over central coastal Namibia (corroborated in Grodek et al., 2013) suggest brief periods of local rainfall over the Kuiseb valley, during this interval. The possibility of localised coastal rainfall during an otherwise dry period appear to have provided ideal conditions for mass flow development and provides the basis for comparisons with more humid perennial floodplain formation (cf. ...
The present work considers morphological and sedimentary evidence from floodplain island sediments in the ephemeral Kuiseb river of central coastal Namibia. Morphologically the islands constitute point bars, curvilinear ridges and composite megaforms. The island sediments consistently comprise two lithofacies – a lower relatively thick often massive silt-very fine sand which is overlain by an upper, thinner, intermittent fine sand. The structure and texture of the lower beds suggest that early island deposition took place as a series of mass flows in association with low velocity stream flow. Originating from pre-existing upstream silt and very fine sand, the mass flows appear to have entered the main Kuiseb valley under unusual conditions of relatively heavy, coastal rainfall during the generally drier conditions of the Little Ice Age. Upon desiccation the sediments were soon partially indurated due to extreme evaporation effects. The upper fine sand lithofacies are regarded as being the product of more recent major flood events. The fine sands were deposited as a result of upper catchment rainfall leading to the formation of mainly overbank and levee deposits, in addition to eroding the islands into their current morphology. Hence the Kuiseb floodplain islands are characterised as hybrid deposits reflecting changing palaeo-climatic conditions over the last 600 years or so. This type of hybridisation involving infrequent earlier mudflow deposition, the induration and retention of the deposits and their later modification by renewed flooding, might be regarded as an important characteristic of moderate to low energy hyper-arid rivers worldwide.
... Various authors have proposed solar activity changes an important driver for millennial-scale climate variability in Africa (e.g. Chase et al., 2009;Heine and Völkel, 2011;Hennekam et al., 2014;. The subject requires additional integration work to better understand temporal and spatial relationships in more detail. ...
... Rock hyrax middens have proved to be useful hydroclimate archives in southern Africa (e.g. Chase et al., 2009). Chances for preservation of the middens are best in arid regions with annual rainfall of less than 400 mm/year (Chase et al., 2012). ...
The Medieval Climate Anomaly (MCA) is a recognized period of distinct pre-industrial climate change, with a core period of 1000–1200 CE. The field of palaeoclimatology has made major progress over the past 15 years during which a great number of high- and medium-resolution case studies were published, reconstructing climate change of the past millennia. In many parts of the world, regional data coverage has now reached a point which allows compiling palaeoclimate maps for well-defined time intervals. Here we present hydroclimatic trend maps for the MCA in Africa based on 99 published study locations. Key hydroclimatic proxy curves are visualized and compared in a series of 16 correlation panels. Proxy types are described and possible issues discussed. Based on the combined MCA dataset, temporal and spatial trends are interpreted and mapped out. Three areas have been identified in Africa in which rainfall seems to have increased during the MCA, namely Tunisia, western Sahel and the majority of southern Africa. At the same time, a reduction in precipitation occurred in the rest of Africa, comprising of NW and NE Africa, West Africa, Eastern Africa and the Winter Rainfall Zone of South Africa. MCA hydroclimate change in Africa appears to have been associated with characteristic phases of ocean cycles, as also supported by modern climate observations. Aridity in Morocco typically coincides with the positive phase of the North Atlantic Oscillation (NAO), whilst increased rainfall in the western Sahel is often coupled to the positive phase of the Atlantic Multidecadal Oscillation (AMO). Reduction in rainfall in the region Gulf of Aden/southern Red Sea to Eastern Africa could be linked to a negative Indian Ocean Dipole (IOD) or a derived long-term equivalent Indian Ocean cycle parameter. The Intertropical Convergence Zone (ITCZ) appears to have been shifted pole-wards during the MCA, for both the January and July positions. MCA hydroclimate mapping revealed major data gaps in the Sahara, South Sudan, Somalia, Central African Republic, Democratic Republic of Congo, Angola, northern Mozambique, Zambia and Zimbabwe. Special efforts are needed to fill these gaps, e.g. through a dedicated structured research program in which new multiproxy datasets are created, based on the learnings from previous African MCA studies.
... A minimum pollen sum of 400 grains was counted at a magnification of Â400 under a light microscope, and identified with the help of the literature (van Zinderen Bakker, 1953, 1956van Zinderen Bakker and Coetzee, 1959;Scott, 1982), and photographic and slide reference collections at the Universities of the Free State, Cape Town, and Montpellier. The bulk stable nitrogen ( 15 N) and carbon ( 13 C) isotope contents of 767 overlapping hyraceum samples were measured at the Department of Archaeology, University of Cape Town following Chase et al. (2009Chase et al. ( , 2010Chase et al. ( , 2011Chase et al. ( , 2012, with contiguous/overlapping samples obtained from two series of offset 1 mm holes. For the stable isotope analyses, the standard deviation derived from replicate analyses of homogeneous material was better than 0.2‰ for both nitrogen and carbon. ...
... As C 3 plants are depleted in 13 C compared with most CAM and all C 4 plants, higher d 13 C values indicate more abundant warm season (C 4 ) grasses and/or succulent plants (CAM), and generally warmer/ more arid conditions. Hyraceum d 15 N is an indicator of changes in ecosystem wateravailability (Chase et al., 2009(Chase et al., , 2011(Chase et al., , 2013(Chase et al., , 2015bCarr et al., 2016a). A positive relationship exists between aridity and d 15 N in soils, plants and herbivores, with drier conditions correlating with enriched d 15 N (Carr et al., 2016a), most likely as a result of denitrification processes in arid/semi-arid soils (Heaton, 1987;Handley et al., 1994Handley et al., , 1999Bowman, 2006, 2009;Wang et al., 2010;Hartman, 2011). ...
Africa's southern Cape is a key region for the evolution of our species, with early symbolic systems, marine faunal exploitation, and episodic production of microlithic stone tools taken as evidence for the appearance of distinctively complex human behavior. However, the temporally discontinuous nature of this evidence precludes ready assumptions of intrinsic adaptive benefit, and has encouraged diverse explanations for the occurrence of these behaviors, in terms of regional demographic, social and ecological conditions. Here, we present a new high-resolution multi-proxy record of environmental change that indicates that faunal exploitation patterns and lithic technologies track climatic variation across the last 22,300 years in the southern Cape. Conditions during the Last Glacial Maximum and deglaciation were humid, and zooarchaeological data indicate high foraging returns. By contrast, the Holocene is characterized by much drier conditions and a degraded resource base. Critically, we demonstrate that systems for technological delivery e or provisioning e were responsive to changing humidity and environmental productivity. However, in contrast to prevailing models, bladelet-rich microlithic technologies were deployed under conditions of high foraging returns and abandoned in response to increased aridity and less productive subsistence environments. This suggests that posited links between microlithic technologies and subsistence risk are not universal, and the behavioral sophistication of human populations is reflected in their adaptive flexibility rather than in the use of specific technological systems.
... ditions are reported in the central, eastern, and northern regions of southern Africa's SRZ, while relatively mesic conditions are reported in the southwestern WRZ during the Early Holocene(Scott & Lee-Thorp 2004;Lewis 2008). These conditions are reversed in the MH(Scott & Lee-Thorp 2004: 81). Several forcing mechanisms are proposed for this trend.Chase et al. (2009Chase et al. ( , 2010 suggest that Northern Hemisphere forcing is responsible for these conditions, aligning with the African Humid Period from ca. 14.8 to especially in the Savanna biome, may have superseded the influence of latitudinal shifts in the ITCZ. Overall, local, regional, and global forcing mechanisms are responsible for chang ...
The adoption of Zooarchaeology by Mass Spectrometry (ZooMS) provides an alternative approach to traditional morphological and ancient DNA (aDNA) analysis, allowing previously unidentifiable and morphologically ambiguous remains to be identified. Dietary preferences are reflected in the stable carbon and nitrogen isotope ratios, with variations indicating behavioural, physiological, and/or environmental change. Together, fauna identified by ZooMS and stable carbon and nitrogen isotopes has the potential to provide more information about vegetation and palaeoenvironmental change than either dataset alone.
This study focuses on the morphologically unidentifiable faunal assemblage from
Grassridge Rockshelter (GRS), South Africa. Ten samples were selected from the late Pleistocene (LP; ca. 43–28 ka), 20 from the terminal Pleistocene (TP; ca. 13.5–11.6 ka), and 70 from the mid-Holocene (MH; ca. 7.3–6.8 ka) layers. Here, fauna identified by ZooMS and stable carbon and nitrogen isotopes from bone collagen is used to infer the palaeoenvironmental conditions at GRS during each occupation.
Eighty-five percent (n = 85) of the GRS sample was successfully identified to at least tribe using ZooMS. Success increased through time, but not significantly, suggesting that ZooMS can be used on older assemblages, up to ca. 40 ka, and in warm environments.
Faunal and stable isotope shifts are documented and are indicative of changing vegetation and palaeoenvironment through time. At GRS, results indicate a cool and dry grassland environment dominated by open-habitat grazers during the LP, transitioning to a warmer and mesic mosaic environment dominated by browsers during the MH. Broad taxonomic resolutions and the misidentification of a suni antelope (Neotragus moschatus) indicate a need for the development of novel ZooMS peptide markers, the expansion of the reference database, and emphasise the need to incorporate multiple proxies when undertaking palaeoenvironmental research. Furthermore, the identification of a blue duiker (Philantomba monticola) and ostrich (Struthio camelus) was unexpected, highlighting the potential of ZooMS to identify rare or unexpected taxa.
... Hyrax midden δ 15 N values are thought primarily to reflect water availability. In a study evaluating Holocene palaeoenvironmental change in Namibia, Chase et al. (2009) observed that δ 15 N values from hyrax middens were negatively correlated with other indicators of past precipitation, as has been observed in modern plants, soils, and vertebrate tissues (e.g. Cormie, Luz & Schwarcz, 1994;Robinson, 2001;Amundson et al., 2003;Crowley et al., 2011). ...
What can the stable isotope values of human and animal faeces tell us? This often under-appreciated waste product is gaining recognition across a variety of disciplines. Faecal isotopes provide a means of monitoring diet, resource partitioning, landscape use, tracking nutrient inputs and cycling, and reconstructing past climate and environment. Here, we review what faeces are composed of, their temporal resolution, and how these factors may be impacted by digestive physiology and efficiency. As faeces are often used to explore diet, we clarify how isotopic offsets between diet and faeces can be calculated, as well as some differences among commonly used calculations that can lead to confusion. Generally, faecal carbon isotope (δ13 C) values are lower than those of the diet, while faecal nitrogen isotope values (δ15 N) values are higher than in the diet. However, there is considerable variability both within and among species. We explore the role of study design and how limitations stemming from a variety of factors can affect both the reliability and interpretability of faecal isotope data sets. Finally, we summarise the various ways in which faecal isotopes have been applied to date and provide some suggestions for future research. Despite remaining challenges, faecal isotope data are poised to continue to contribute meaningfully to a variety of fields.
... However, the external morphological similarities between these two taxa support differentiation only at species level. This high divergence can be explained by the ancient character of this group (Heinicke et al. 2014), having persisted through extreme climatological and environmental changes and, consequently, experiencing long isolation periods in southwest Africa (Chase et al. 2009;Garzanti et al. 2018). Both species revealed notable genetic intraspecific variation between close localities, which can, in both cases, be explained by the high ecological specialisation in these geckos, promoting and maintaining isolation and by the relatively fast mtDNA evolutionary rates (Jesus et al. 2006). ...
We here describe a new species of feather-tailed leaf-toed gecko, Kolekanos, from southern Benguela Province, Angola, based on morphological and osteological evidence, supported by phylogenetic analy- sis of mitochondrial data. The new species adds to the rapidly growing and newly-recognised endemic biodiversity of Angola, doubling the number of Kolekanos species, breaking the pattern observed within other closely-related African members of a clade of circum-Indian Ocean leaf-toed geckos – Ramigekko, Cryptactites and Afrogecko – all of which are presently monotypic. The new species is easily distinguished from K. plumicaudus, based on spine-like (as opposed to feather-like) scales on the margins of the original tail. Phylogenetic analyses also recovered the new taxon as monophyletic, with a well-supported sister re- lationship to K. plumicaudus, from which it differs by a substantial 24.1% NADH-dehydrogenase subunit 2 mitochondrial gene uncorrected p-distance.
... Stable nitrogen isotope data from a rock hyrax (Procavia (Chase et al., 2010). The Spitzkoppe hyrax midden site (Chase et al., 2009), Brandberg (Scott et al., 2004), and marine core site ODP 1078 are strongly correlated with the southeast Atlantic coastal upwelling (Farmer et al., 2005). The results of the algorithm were obtained according to the weights of the indicators in the dataset, and it is known from Figure 5 that we collected more records in South America than in Africa. ...
Global paleomonsoon precipitation evolution is confined to asynchronous responses to global monsoons to shared forcings, including summer insolation, sea surface temperature, atmospheric circulation coupling, and ocean circulation. However, most studies are based on conclusions drawn from single or a few discrete records or deduced from top-down climate models, which limits our ability to understand the latitudinal effect of monsoon precipitation. In particular, precipitation is a locally constrained climate factor. Here, we present a comprehensive assessment of global monsoon precipitation over the last 12,000 cal year BP based on modern observations, paleoclimate simulations, paleoclimate records, and monsoon precipitation reconstructions over the past 12,000 cal year BP based on a bottom-up algorithm called climate field reconstruction approaches. The results show that the middle latitude monsoon precipitation is in line with the evolution of the insolation and significant long-term decreasing (increasing) trends in low latitude monsoon precipitation have not occurred over the last 12,000 years BP. For modern monsoon evolution, the monsoon precipitation also changes along the meridional direction, with overall decreasing precipitation in the global monsoon region and increasing precipitation in the monsoon margin area. Monsoon systems at different latitudes all record eight Holocene weak precipitation events, including the Younger Dryas (12,900 cal year BP to 11,700 cal year BP), which can be considered a strong effect caused by a significant reduction or collapse of a meridional ocean circulation system, namely, the Atlantic Meridional Overturning Circulation. Moreover, the low- and middle-latitude monsoon precipitation lags by approximately 2,000 years behind the onset of North Atlantic warming. Taken together, our findings provide important insights into the latitudinal effect of monsoon precipitation at different locations.
... The 4.2 ka event was first identified in the 1990s, based on evidence from geological records from Mesopotamia (Cullen et al., 2000;Bar-Matthews et al., 2003), the Nile valley (Stanley et al., 2003;Arz et al., 2006), Indus valley (Staubwasser et al., 2003;Prasad and Enzel, 2006;Dixit et al., 2014), European caves (Drysdale et al., 2006), North American peat deposits (Booth et al., 2004), North Atlantic deep-sea sediments (Bond et al., 1997), and East Asian stalagmites (Wang et al., 2005;Cai et al., 2021). The 4.2 ka event was characterized by significant aridity at low-and mid-latitudes (Thompson et al., 2002;Kröpelin et al., 2008;Liu and Feng, 2012;Zielhofer et al., 2017), whereas the climate was relatively moist at middle and high latitudes (Menounos et al., 2008;Chase et al., 2009;Jordan et al., 2017), demonstrating a significant spatial divergence in the response to the 4.2 ka event between different regions (Railsback et al., 2018;Railsback et al., 2022), as well as differences in its timing and structural characteristics. ...
The 4.2 ka event was the most abrupt climatic event during the transition between the middle and late Holocene. It had a profound influence on the regional ecological environment and human cultural development and was characterized by the rapid onset of aridification in the mid- and low-latitudes regions of the Northern Hemisphere. However, the nature, structure and spatial expression of the 4.2 ka event in the Asian summer monsoon (ASM) region are controversial. We produced a detailed record of regional vegetation change during the interval of 5000–3500 cal yr BP, based on a high-resolution (~10 yr) pollen record from Yazihai Lake, on the margin of the region influenced by the ASM. The results indicate that an interval of climatic aridification, correlative with the 4.2 ka event, occurred during 4340–3880 cal yr BP, with the duration of 460 yr. However, the structure of the event is relatively complex, with arid conditions during 4340–4280 cal yr BP, wetter conditions during 4280–4150 cal yr BP, and arid conditions during 4150–3880 cal yr BP. A comprehensive comparison of the results from Yazihai Lake with existing high-resolution and well-dated paleoclimate records from the ASM region show that the precipitation response to the 4.2 ka event was spatially and temporally synchronous, with a consistent of timing, duration, and structural characteristics in the northern and southwestern parts of the ASM region; whereas the opposite response occurred in the southeastern part, where the precipitation increased. We suggest that the driving mechanism of the 4.2 ka event was related to sea-air interactions in the low-latitude region. Sea surface temperature (SST) anomalies and the variation of the El Niño-Southern Oscillation (ENSO) in the tropical Pacific region was the main cause, which led to a weaker ASM circulation and a southward shift of the monsoon rainbelt. These changes resulted in decreased monsoonal precipitation and a dry climate in the northern and southwestern parts of the ASM region, but to increased precipitation in the southeastern part.
... Nevertheless, the Holocene climate in the southern southwestern Atlantic is still not well understood, mainly a consequence of the few detailed studies in Holocene marine sediments (Nielsen et al., 2004;Chase et al., 2009;Chiessi et al., 2014Chiessi et al., , 2015Carvahlo-Campos et al., 2016). The uncertainties surrounding present and future sea-level rise have revived the debate around sea-level changes from which arises the need for high-resolution reconstructions of regional sea level (Billeaud et al., 2009;Costas et al., 2016). ...
The Holocene shows rapid climatic changes associated with alternating intervals of glacier advances and retreats. The coastal regions, where beach ridges constitute common preserved landforms, are highly sensitive to register such changes and bring light into past littoral environments. Excellent marine Argentinean Holocene deposits associated with the last climate optimum are preserved at the Río de la Plata estuary (Argentina). In this beach ridge, fourteen detailed sedimentary logs were studied in order to generate an palaeoenvironmental model. The analysis of major hierarchy surfaces of the ridge was performed combined field work and Virtual-Outcrop analysis. The ridge presents internal clinoforms that subdivide it into eleven clinothems. The first two clinothems correspond to the development of a sand ridge as a response to the erosion and reworking of previous aeolian Late Pleistocene sediments. Subsequently, a bioclastic ridge was amalgamated with the sand ridge (clinothems III to XI). Simultaneously, in a landward position, a lagoon and washover deposits were developed. Finally, after the stabilization of the beach ridge the continuous sea level fall generated the actual coastal plain deposits. Six ¹⁴C ages were obtained at the base of selected clinothems, dated between 5,240 ± 110 cal BP and 3,900 ± 90 cal BP; meaning that in 1,340 years the beach prograded 290 m. Stable isotope analyses (δ¹³C and δ¹⁸O) allowed to infer that the temperature during the evolution of the ridge has two maximum values of 22.5 °C and a minimum of 18.5 °C. The salinity range between 32.53‰ and 33.16‰, showing short variability. The sudden change in the composition of the ridge, from sandy to carbonate sediments, may be interpreted as a combined result of an increase of carbonate productivity along with a decrease of siliciclastic supply at the coast. This stage would have been developed approximately around 5ka B.P., in coincidence with the Holocene Climatic Optimum (as recorded in Argentina) when propitious climatic conditions may have led to the proliferation of large communities of warm and warm temperate benthic organisms. We stress that, the strong activity of the Brazilian current during the Mid-Holocene thermal maximum enabled excellent conditions for the development of a carbonate warm beach similar to that occurring at tropical and subtropical areas nowadays. This study provides an example of the strong changes occurred in coastal environments as a result of climate change, particularly in the context of global warming episodes which characterized interglacial periods of the Late Quaternary in eastern South America.
... While hot and dry conditions prevailed in some regions, the opposite was the case elsewhere due to differences in weather regimes (Wanner et al. 2008). In southernmost Africa, the MHA was hot and dry in the winter-rainfall zone (primarily the entire South African west coast) (Compton 2006;Chase & Meadows 2007;Weldeab et al. 2013;Kirsten et al. 2020), but wetter overall in the summer-rainfall region which includes the Namib Desert, and the central and eastern regions of South Africa (e.g., Ramsay 1996;Lee-Thorp et al. 2001;Chase et al. 2009;Neumann et al. 2010;Quick et al. 2018). This allowed settlement opportunities for southern African hunter-gatherers in currently remote desert areas of Namibia as rainfall increased markedly in that region during the MHA (e.g., Kinahan 2018). ...
After the Last Glacial Maximum, important yet milder climatic trends continued to characterise the Holocene. None of them was more challenging to forager groups in the central west coast of South Africa than the mid-Holocene Altithermal (8200–4200 cal BP ). Hot and dry weather and 1–3 m higher sea levels were thought once to have barred local foragers from this region because of a lack of sites dating to this period. Instead, this initial scenario reflected largely a sampling problem. Steenbokfontein Cave is one of a few sites with some of the largest mid-Holocene deposits, allowing insights into forager adaptations during this period. Results show high mobility over large distances and a terrestrial diet mostly dependant on small bovids, complemented with fewer coastal resources. Stone tool kits and lithic raw materials among various sites suggest that much evidence for mid-Holocene occupation is actually found near the local riparian systems.
... Onshore traditional archives such as wetlands, peats and lake deposits are rare in this western region but a novel alternative of pollen archives of arid to semi-arid zones has been developed in the form of hyrax urine middens, or hyraceums (Scott, 1996). Primary data are provided by Scott (1996), Gil-Romero et al. (2006, Scott et al. (2004), Scott and Woodborne (2007a, b), Chase et al. (2009), Lim et al. (2016, and re-interpretation of the data and dating methods by Scott et al. (2022). ...
Although the lack of Late Quaternary pollen, phytolith and charcoal records for southern Africa has been bemoaned by many, there are a surprising number of publications by a relatively small group of researchers. Previous comprehensive reviews covered the research up to 2016 and 2018 so this paper only considers a selection of more recent studies, with a focus on the three types of botanical remains (pollen, phytoliths, micro- and macro-charcoal). The newer works use the traditional approaches of identification of vegetation and the use of modern analogues to reconstruct past climate and relate the results to other works and proxies. Sibudu Cave, with its long record and multi-proxy record is presented as a case study because the vegetation, climate and human behaviour are well integrated together. A more recent and general trend to provide emphasis on identifying climate driving forces and re-interpretation of data have a tendency to obscure the original sound research.
... The hydroclimatic shifts recorded in the composite midden (sites 6, 14 and 25) representing a 900 km long north-south transect in the Namib are conceptualised and modelled by Chase et al. (2019), with an explanation for what drives increased aridity, but the corollary mechanism for wetter intervals is perhaps less clear. Chase et al. (2009) suggest increased aridity occurs due to an intensified South Atlantic Anticyclone and related stronger upwelling in the Benguela cold current, and that this is driven by an increased intra-hemispheric temperature gradient with precession pacing which sees austral summer insolation maxima occur at the same time as boreal summer insolation maxima. The 46 to 44 cal kyr B.P wetter phase is at the opposite insolation forcing, with austral summer insolation minima (boreal summer insolation maxima), which would reduce the temperature gradient and lessen the dominance of the South Atlantic Anticylone, perhaps allowing easterly rainfall sources to reach the eastern edge of the Namib. ...
The Namib Desert and the Kalahari constitute the drylands of southern Africa, with the current relatively humid portions of the latter having experienced periodically drier conditions during the Late Quaternary. This study explores the range of dryland archives and proxies available for the past ~190 ka. These include classic dryland geomorphological proxies, such as sand dunes, as well as water-lain sediments within former lakes and ephemeral fluvial systems, lake shorelines, sand ramps, water-lain calcrete and tufa sediments at the interface of surface hydrological and hydrogeological, speleothems and groundwater hydrogeological records, and hyrax middens. Palaeoenvironmental evidence can also be contained within geoarchaeological archives in caves, overhangs and rockshelters. This integration of records is undertaken with the aim of identifying a (or a number of) terrestrial regional chronostratigraphic framework(s) for this time period within southern Africa, because this is missing from the Quaternary stratigraphy lexicon. Owing to a lack of long, near-continuous terrestrial sequences in these drylands, the correspondence between nearby terrestrial records are explored as a basis for parasequences to build this chronostratigraphy. Recognising the modern climatological diversity across the subcontinent, four broad spatial subdivisions are used to explore potential sub-regional parasequences, which capture current climatic gradients, including the hyper-arid west coast and the decrease in aridity from the southwest Kalahari toward the north and east. These are the Namib Desert, the northern Kalahari, the southern Kalahari and the eastern fringes of the southern Kalahari. Terrestrial chronostratigraphies must start from premise that climate-driven environmental shifts may have occurred independently to those in other terrestrial locations and may be diachronous compared to the marine oxygen isotope stratigraphy (MIS), which serves as a global-scale master climatostratigraphy relating to global ice volume. The fragmented nature of preserved evidence means that we are still some way from producing unambiguous parasequences. There is however, a rich record to consider, compile and compare, within which seven broad wetter intervals are identified, with breaks between these inferred to be relatively drier, and some also have proxy evidence for drying. The onset and cessation of these wetter intervals does not align with MIS: they occur with greater frequency, but not with regular periodicity. Precession-paced insolation forcing is often invoked as a key control on southern African climate, but this does not explain the pacing of all of the identified events. Overall, the pattern is complex with some corresponding wetter intervals across space and others with opposing west-east trends. The evidence for drying over the past 10 ka is pronounced in the west (Namib Desert), with ephemerally wet conditions in the south (southern Kalahari). The patterns identified here provide a framework to be scrutinised and to inspire refinements to proposed terrestrial chronostratigraphies for southern Africa. Considering changes across this large geographic area also highlights the complexity in environmental responses across space as we continue to test a range of hypotheses about the nature of climatic forcing in this region.
... The fluvial sediments are the erosion products of periodic wetter intervals in the immediate hinterland and occasionally within the desert itself (Barnard, 1989;Gingele, 1996;Eitel et al., 1999a;Blümel et al., 2000;Stanistreet and Stollhofen, 2002;Dupont, 2006, Geyh andHeine, 2014). Rains within the desert are rare (Ward et al., 1997; this paper) but have provided animals and humans with opportunities to briefly expand their range westwards (Chase et al., 2009;Kinahan, 2016). The hyperarid climate results from the combined influence of the subtropical South Atlantic Anticyclone, the cold coastal Benguela Current, the warm south-flowing inshore Angola Current, the Congo Air Boundary and the northeastern monsoonal influences of the Intertropical Convergence Zone (Tyson, 1986;Jury, 1996;Shannon et al., 1986). ...
The aeolian regime of the 100 km wide, hyperarid Namib Desert has been sporadically punctuated by the deposition of fluvial sediments generated during periods of higher humidity either further inland or well within the desert from Late Oligocene to Late Holocene. Four new Late Cenozoic formations are described from the northern Skeleton Coast and compared with formations further south: the Klein Nadas, Nadas (gravels, sands), Vulture’s Nest (silts) and Uniab Boulder Formations. The Klein Nadas Formation is a trimodal mass-flow fan consisting of thousands of huge, remobilised, end-Carboniferous Dwyka glacial boulders, many >3 m in length, set in an abundant, K-feldspar-rich and sandy matrix of fine gravel. Deluge rains over the smallest catchments deep within the northern Namib were the driving agent for the Klein Nadas Fan, the termination of which, with its contained boulders, rests on the coastal salt pans. These rains also resulted in catastrophic mass flows in several of the other northern Namib rivers. The Uniab Boulder Formation, being one, consists only of huge free-standing boulders. Gravelly fluvial deposition took place during global interglacial and glacial events. The Skeleton Coast Erg and other smaller dune trains blocked the rivers at times. The low-energy, thinly bedded silt deposits of the central and northern Namib are quite distinctive from the sands and gravels of older deposits. Their intermittent deposition is illustrated by bioturbation and pedogenesis of individual layers. Published offshore proxy climatological data (pollens, upwelling, wind, sea surface temperatures) point to expansion of the winter-rainfall regime of the southern Cape into southwestern Angola during strong glacial periods between the Upper Pleistocene and Holocene. In contrast to deposition initiated by short summer thunder storms, we contend that the silt successions are river-end accumulations within which each layer was deposited by runoff from comparatively gentle winter rains that lasted several days.
... The major oceanic circulation systems (the cold Benguela Current and the warm Agulhas and Angola Currents; temperatures shown in°C; Reynolds et al., 2007) are indicated, as well as the position of Pearly Beach (star) in relation to key palaeoclimatic records. 1, Cango Caves (Talma and Vogel, 1992); 2, Seweweekspoort (Chase et al., , 2017; 3, Katbakkies Pass (Meadows et al., 2010;Chase et al., 2015b); 4, De Rif (Chase et al., , 2015aQuick et al., 2011;Valsecchi et al., 2013); 5, Pakhuis Pass (Scott andWoodborne, 2007a, 2007b;Chase et al., 2019a); 6, Elands Bay Cave (Cowling et al., 1999;Parkington et al., 2000); 7, Pella (Lim et al., 2016;Chase et al., 2019b); 8, Stampriet Aquifer (Stute and Talma, 1998); 9, Zizou (Chase et al., 2019b); 10, Spitzkoppe (Chase et al., 2009(Chase et al., , 2019b; 11, ODP 1084B (Farmer et al., 2005); 12, GeoB 1023-5 . (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) ...
The southwestern Cape of South Africa is a particularly dynamic region in terms of long-term climate change. We analysed fossil pollen from a 25,000 year sediment core taken from a near-coastal wetland at Pearly Beach that revealed that distinct changes in vegetation composition occurred along the southwestern Cape coast. From these changes, considerable variability in temperature and moisture availability are inferred. Consistent with indications from elsewhere in southwestern Africa, variability in Atlantic Meridional Overturning Circulation (AMOC) was identified as a strong determinant of regional climate change. At Pearly Beach, this resulted in phases of relatively drier conditions (~24–22.5 cal ka BP and ~22–18 cal ka BP) demarcated by brief phases of increased humidity from ~24.5–24 cal ka BP and 22.5–22 cal ka BP. During glacial Termination I (~19–11.7 ka), a marked increase in coastal thicket pollen from ~18.5 to 15.0 cal ka BP indicates a substantial increase in moisture availability, coincident, and likely associated with, a slowing AMOC and a buildup of heat in the southern Atlantic. With clear links to glacial and deglacial Earth system dynamics and perturbations, the Pearly Beach record represents an important new contribution to a growing body of data, providing insights into the patterns and mechanisms of southwestern African climate change.
... During these Antarctic warm periods, sea ice, the circumpolar circulation and the SHW retreated. This is recorded by Southern Ocean diatom burial rates as well as paleoclimate archives at the southernmost tips of Africa and South America (Lamy et al., 2001;Anderson et al., 2009;Chase et al., 2009;Hahn et al., 2017 and references therein;Zhao et al., 2016). It has been hypothesized that southward shifts of the SHW and the South African high-pressure cell allow the SIOCZ and TTT to shift further south causing an increase in humidity in our study area. ...
We present a continuous and well-resolved record of climatic variability for
the past 100 000 years from a marine sediment core taken in Delagoa Bight,
off southeastern Africa. In addition to providing a sea surface temperature
reconstruction for the past ca. 100 000 years, this record also allows a
high-resolution continental climatic reconstruction. Climate sensitive organic
proxies, like the distribution and isotopic composition of plant-wax lipids as
well as elemental indicators of fluvial input and weathering type provide
information on climatic changes in the adjacent catchment areas (Incomati,
Matola and Lusutfu rivers). At the transition between glacials and
interglacials, shifts in vegetation correlate with changes in sea surface
temperature in the Agulhas Current. The local hydrology, however, does not
follow these orbitally paced shifts. Instead, precipitation patterns follow
millennial-scale variations with different forcing mechanisms in glacial
vs. interglacial climatic states. During glacials, southward displacement of
the Intertropical Convergence Zone facilitates a transmission of northern
hemispheric signals (e.g., Heinrich events) to the southern hemispheric
subtropics. Furthermore, the southern hemispheric westerlies become a more
direct source of precipitation as they shift northward over the study site,
especially during Antarctic cold phases. During interglacials, the observed
short-term hydrological variability is also a function of Antarctic climate
variability; however, it is driven by the indirect influence of the southern
hemispheric westerlies and the associated South African high-pressure cell
blocking the South Indian Ocean Convergence Zone related precipitation. As a
consequence of the interplay of these effects, small-scale climatic zones
exist. We propose a conceptual model describing latitudinal shifts of these
zones along the southeastern African coast as tropical and temperate climate
systems shift over glacial and interglacial cycles. The proposed model
explains some of the apparent contradictions between several paleoclimate
records in the region.
... These dates predate European settlement of South Africa which occurred during the early 17 th century. Southern African climate changes are known to have underwent significant regional fluctuations during the Holocene (Chase et al., 2009, Lee-Thorp et al., 2001, Metwally et al., 2014, Scott and Vogel, 2000 (Mayewski et al., 2004). It was suggested that this RCC event could be linked to the dry period experienced along the South African eastern coast as noted by Neumann et al. (2010). ...
The Cape Parrot (Poicephalus r. robustus) is the only endemic parrot found in South Africa. This subspecies is restricted to the mistbelt forests of the Eastern Cape, Kwa-Zulu Natal and Limpopo Provinces. Recent population census estimates suggest that there are fewer than a 1600 Cape Parrots left in the wild. Habitat loss and illegal harvesting for the pet trade are among the major drivers of these low population numbers. The current conservation status of P. robustus ssp. does not lend the Cape Parrot sufficient protection national and international conservation agencies, as it is internationally seen as a subspecies of Poicephalus robustus i.e. P. robustus robustus. A better understanding of the Cape Parrot’s taxonomic position within the genus is therefore urgently needed. The three data chapters presented in this thesis address the main aims of this study.
The taxonomic status of the Cape Parrot (Poicephalus robustus robustus) has been the focus of much debate over the years. A number of authors have suggested that the Cape Parrot should be viewed as a distinct species separate from the other two P. robustus subspecies (P. r. fuscicollis and P. r. suahelicus). These recommendations were based on previously published morphological, ecological and behavioural assessments. In this chapter the validity of these recommendations were investigated using multilocus DNA analyses. A total of 138 specimens from five Poicephalus species (P. cryptoxanthus, P. gulielmi, P. meyeri, P. robustus and P. rueppellii) were genotyped using 11 microsatellite loci. Additionally, two mitochondrial (cytochrome oxidase I gene and 16S ribosomal RNA) markers and one nuclear intron (intron 7 of the β-fibrinogen gene) marker were amplified and sequenced. Bayesian clustering analysis and pairwise FST analysis of microsatellite data identified P. r. robustus as genetically distinct from the other P. robustus subspecies. Phylogenetic analysis on sequence data also supported the microsatellite analyses, placing P. r. robustus in a distinct clade separate from the other P. robustus subspecies. Molecular clock analysis places the most recent common ancestor of P. r. robustus and P. r. fuscicollis / P. r. suahelicus at 2.13 to 2.67 million years ago. These results all support previous recommendations to elevate the Cape Parrot to species level.
In the second data chapter, an assessment of the historical and contemporary genetic structure of the Cape Parrot was performed. The effect of anthropogenic habitat fragmentation on species, which live in naturally patchy habitats, has rarely been examined in South Africa. The Cape Parrot is a habitat specialist, restricted to forest patches in the Eastern Cape, KwaZulu-Natal and Limpopo Provinces of South Africa. Although current overexploitation of forests in southern Africa is certainly an important driver of fragmentation, this is not solely
vi
responsible for the relictual nature of South African forests. In the Pliocene, periods of climate change driven aridity and increased fire frequency, contributed towards the ‘natural’ fragmentation of the forests in southern Africa. In this chapter, 85 modern samples, collected from 1951 to 2014, and 29 historical samples, collected from 1870 to 1946, were used to investigate the historical and contemporary genetic structure of Cape Parrots using 16 microsatellite loci. Bayesian clustering analysis identified three geographically correlated genetic clusters: a southern group restricted to forest patches in the Eastern Cape, a central group including birds from KwaZulu-Natal and a genetically distinct northern Limpopo cluster. Results suggest that Cape Parrots have experienced at least two major population bottlenecks. An ancient decline during the mid-Holocene (~1800-3000 years before present) linked to climate change, and a more recent bottleneck, associated with logging of forests during the early 1900’s. This chapter highlights the effects of climate change and human activities on this endangered species.
The third data chapter, deals with the use of molecular data in forensic analysis of Cape Parrots. The illicit harvesting of wild Cape Parrots for the pet trade is a significant threat faced by this endemic South African species. Illegal trade in rare wildlife species is a major threat to many parrot species around the world. Wildlife forensics plays an important role in the preservation of endangered or threatened wildlife species. Identification of illegally harvested or traded animals through DNA techniques is one of the many methods implemented during forensic investigations. In this study, 16 microsatellite markers specifically designed for the South African endemic Cape Parrot were assessed for their utility in forensic casework. In addition, this chapter evaluates the genetic diversity of the captive Cape Parrot population and compares this to the wild Cape Parrot population, using these 16 loci. The results showed that the full 16 locus panel has sufficient discriminatory power to be used in parentage analyses of suspected illegally traded Cape Parrots. It was further observed that a panel of 12 loci has sufficient power to assign confiscated birds thought to be illegally removed from the wild to their area of origin. It was recommended that the current reference data sets should be expanded to increase the accuracy of the assignment analyses. The level of genetic diversity observed within the captive data set was comparable to that observed in the wild populations. The captive Cape Parrots did, however, have double the number of private alleles compared to that observed in the most genetically diverse wild population. This was accredited to the presence of rare alleles present in the founder population, which has not been lost due to genetic drift, as many of the specimens tested in this study are F1 to F3 wild descendants.
vii
The results from this comprehensive genetic study on the South African endemic Cape Parrot will have a number of implication for the conservation of this species. The taxonomic assessment of the Cape Parrot clearly supported its elevation to full species. The phylogeographic analysis of these parrots showed that the contemporary population is strongly geographically structured, with a distinct, isolated northern population in the Limpopo Province of South Africa. These results will aid local and international conservation authorities with the planning and implementation of future conservation endeavours focusing on the Cape Parrot. The assessment of a panel of microsatellite markers for their use in forensic analysis will aid conservation and law enforcement authorities to better control legal and illegal trade of this South African endemic. Recommendations were also made with regards to the management of a captive population for possible future reintroduction purposes.
... Foden et al. [41] showed that the temperature increase in Namibia during the last two or three decades is roughly three times more than the global mean temperature increase reported for the 20th century. Several authors [42][43][44] showed that drastic temperature increases and drier conditions were present in southern Africa on a number of occasions during the last few centuries. It is further proposed that the decomposition of the dead plants altered the chemical properties of the sand which manifested in the hydrophobicity of FC soil. ...
Background:
In this multidisciplinary study we present soil chemical, phytochemical and GIS spatial patterning evidence that fairy circles studied in three separate locations of Namibia may be caused by Euphorbia species.
Results:
We show that matrix sand coated with E. damarana latex resulted in faster water-infiltration rates. GC-MS analyses revealed that soil from fairy circles and from under decomposing E. damarana plants are very similar in phytochemistry. E. damarana and E. gummifera extracts have a detrimental effect on bacteria isolated from the rhizosphere of Stipagrostis uniplumis and inhibit grass seed germination. Several compounds previously identified with antimicrobial and phytotoxic activity were also identified in E. gummifera. GIS analyses showed that perimeter sizes and spatial characteristics (Voronoi tessellations, distance to nearest neighbour ratio, pair correlation function and L-function) of fairy circles are similar to those of fairy circles co-occurring with E. damarana (northern Namibia), and with E. gummifera (southern Namibia). Historical aerial imagery showed that in a population of 406 E. gummifera plants, 134 were replaced by fairy circles over a 50-year period. And finally, by integrating rainfall, altitude and landcover in a GIS-based site suitability model, we predict where fairy circles should occur. The model largely agreed with the distribution of three Euphorbia species and resulted in the discovery of new locations of fairy circles, in the far southeast of Namibia and part of the Kalahari Desert of South Africa.
Conclusions:
It is proposed that the allelopathic, adhesive, hydrophobic and toxic latex of E. damarana, E. gummifera, and possibly other species like E. gregaria, is the cause of the fairy circles of Namibia in the areas investigated and possibly in all other areas as well.
... The evaluation of different palaeoclimate proxies all over Namibia led to the assumption of much wetter conditions during the Early Holocene, which caused significantly higher runoff than today [57]. Just after the Early to Mid-Holocene transition, the climate of southern Africa became much drier [58], resulting in a decreased discharge and a lack of flood-derived sediments in the Swakop River [42]. Accordingly, the age of the snail shell (R5) allows the determination of the stratigraphic position of the sediments below the Swakop River's youngest terrace complex. ...
The concentrations of long-lived in-situ produced cosmogenic nuclides (10Be, 21Ne, 26Al) in quartz obtained from a very recent (~200 a; based on 14C data on organic material) terrace of the Swakop River in Namibia are nearly constant throughout a 322 cm-long depth profile. These findings corroborate earlier hypotheses postulating a homogeneous distribution of these nuclides in freshly deposited river terrace sediments. An averaged nuclide concentration is a crucial and generally assumed prerequisite for the determination of numerical ages of old sediments.
... During these Antarctic warm 357 periods, sea ice, the circumpolar circulation and the SHW retracted. This is recorded by358 Southern Ocean diatom burial rates as well as paleoclimate archives at the southernmost tips of 359 Africa and South America(Lamy et al., 2001;Anderson et al., 2009;Chase et al., 2009; Hahn et 360 al 2016 and references therein;Zhao et al., 2016). It has been hypothesized that the SHW and the South African high-pressure cell, allow the SIOCZ and TTT to shift 362 further south causing an increase in humidity in our study area.Miller et al., (2019b) suggest 363 this mechanism for the region just south of our site (termed eastern central zone), which shows 364 Holocene hydroclimatic shifts similar to those recorded in GeoB20616-1. ...
Abstract. We present a continuous and well-resolved record of climatic variability for the past 100,000 yrs from a marine sediment core taken in Delagoa Bight, off southeastern Africa. In addition to providing a sea surface temperature reconstruction for the past ca. 100,000 yrs, this record also allows a high-resolution continental climatic reconstruction. Climate sensitive organic proxies, like the distribution and isotopic composition of plant-wax lipids as well as elemental indicators for fluvial input and weathering type provide information on climatic changes in the adjacent catchment areas (Incomati, Matola, and Lusutfu rivers). At the transition between glacials and interglacials, shifts in vegetation correlate with changes in sea surface temperature in the Agulhas current. The local hydrology, however, does not follow these orbital-paced shifts. Instead, precipitation patterns follow millennial scale variations with different forcing mechanisms in glacial versus interglacial climatic states. During glacials, southward displacement of the Intertropical Convergence Zone facilitates a transmission of northern hemispheric signals (e.g. Heinrich events) to the southern hemispheric subtropics. Furthermore, the southern hemispheric westerlies become a more direct source of precipitation as they shift northward over the study site, especially during Antarctic cold phases. During interglacials, the observed short-term hydrological variability is also a function of Antarctic climate variability, however, it is driven by the indirect influence of the southern hemispheric westerlies and the associated South African high-pressure cell blocking the South Indian Ocean Convergence Zone related precipitation. As a consequence of the interplay of these effects, small scale climatic zones exist. We propose a conceptual model describing latitudinal shifts of these zones along the southeastern African coast as tropical and temperate climate systems shift over glacial and interglacial cycles. The proposed model explains some of the apparent contradictions between several paleoclimate records in the region.
... With the last sea-level rise and closing of the EAST-Portal of the P-AP between 9-7 Ka BP [14,[32][33][34][35][36]94,103] (Figure 11); came the last true isolation between the bontebok and the blesbok and the last P-AP migration of large grazers. Several significant post-LGM (LGM was 20-18 Ka BP) climate and vegetation changes happened after 20 Ka BP in the south-western Cape [27,37,143]. Grazers of C 4 grasses such as bontebok and blesbok predominated in eastern and southern Africa during the LGM [17] and other similar periods of lowered sea-levels, as much as 120 m below the present level [40]. ...
Re-evaluation of bontebok following a multidisciplinary approach indicate its native habitat as the now submerged Palaeo-Agulhas Plain off the southern South African coast, and dominated by C 4 grasslands and savannah. Large grazer populations migrated across the plain and around the eastern end of the Cape Folded Belt into the Eastern Cape interior following climate oscillations and geographic-shifts of the winter-/summer-/all-year rainfall isohyets. Presently 77% of all bontebok are found on private farmland with grassland bioregions in the Eastern Cape, Free State and other. Bontebok showed enhanced performance in these grasslands if compared with poor performance on southwestern Cape Lowland Renosterveld (SWC-LRV). Renosterveld (RV) was previously perceived as the bontebok's native habitat of origin. We argue that bontebok became trapped in RV due to sea-level rises and consequent multiple species congestion. Bontebok meta-population management on private farms showed significant species improvement when compared with government conservation actions in SWC-LRV. Geographic habitat constraints appear to have been the greatest factor limiting bontebok integrity. IUCN recognizes a global population size of 1,618 as reported by the Non-Detriment Finding of the Scientific Authority of South Africa, whereas actual population size is more than 7,000. We quantify post-1930s bontebok performance against phylogeographic and palaeoclimate proxies.
... The δ 15 N signal from BK-2-2 is considered to primarily indicate changes in wateravailability. As described in previous works, and supported by strong correlations with independent climate records (Chase et al., 2015a;Chase et al., 2015b;Chase et al., 2010;Chase et al., 2009;Chase et al., 2012), this reflects aridity-driven changes in soil nitrogen pools, with drier conditions inducing more N flow to inorganic pools that are subject to gaseous loss of 15 N depleted products (Austin and Vitousek, 1998;Handley et al., 1999;Murphy and Bowman, 2009). Plants growing in the resulting 15 N-enriched soils exhibit higher δ 15 N values (Craine et al., 2009;Hartman and Danin, 2010), as do the tissuesand in the case of hyrax middens, the excretaof animals that consume them (Carr et al., 2010a(Carr et al., , 2016aHartman, 2011;Murphy and Bowman, 2006). ...
South Africa's southern Cape is a highly dynamic climatic region that is influenced by changes in both temperate and tropical atmospheric and oceanic circulation dynamics. Recent research initiatives suggest that the major elements of the regional climate system have acted both independently and in combination to establish a mosaic of distinct climate regions and potentially steep climate response gradients across the southern Cape. To consider this further, we present new high resolution δ¹³C and δ¹⁵N data from a rock hyrax (Procavia capensis) midden from Baviaanskloof, in the Cape Fold Mountains of South Africa's Eastern Cape Province. Spanning the last 7200 years, these data provide detailed information regarding environmental changes in the mid- and late Holocene, allowing us to assess the spatio-temporal nature of climate change anomalies across the wider region. Throughout the full duration of the record, a negative correlation between humidity and palaeotemperature reconstructions from nearby Cango Cave is observed. In conjunction with correlations with Southern Ocean sea-surface temperatures and sea-ice presence, we infer a dominant influence of the southern westerlies in determining multi-millennial scale hydroclimate variability. At shorter, multi-centennial to millennial timescales, the Baviaanskloof data indicate a clearer expression of tropical influences, highlighting a delicate balance between the mechanisms driving regional climate dynamics across timescales, and the sensitivity of the region to changes in global boundary conditions.
... This study provides strong support for a dramatic population decline ∼1,815 years before present (BP; North population), ∼1807 years BP (Central population) and up to ∼3,026 years BP (South population). Southern African climates are known to have undergone significant regional fluctuations during the Holocene (Scott and Vogel 2000, Lee-Thorp et al. 2001, Chase et al. 2009, Metwally et al. 2014). ...
The Cape Parrot Poicephalus robustus is a habitat specialist, restricted to forest patches in the Eastern Cape (EC), KwaZulu-Natal (KZN) and Limpopo provinces of South Africa. Recent census estimates suggest that there are less than 1,600 parrots left in the wild, although historical data suggest that the species was once more numerous. Fragmentation of the forest biome is strongly linked to climate change and exploitation of the forest by the timber industry. We examine the subpopulation structure and connectivity between fragmented populations across the distribution of the species. Differences in historical and contemporary genetic structure of Cape Parrots is examined by including both modern samples, collected from 1951 to 2014, and historical samples, collected from 1870 to 1946. A total of 114 individuals (historical = 29; contemporary = 85) were genotyped using 16 microsatellite loci. We tested for evidence of partitioning of genotypes at both a temporal and spatial scales by comparing shifts in allelic frequencies of historical (1870–1946) and contemporary (1951–2014) samples across the distribution of the species. Tests for population bottlenecks were also conducted to determine if anthropogenic causes are the main driver of population decline in this species. Analyses identified three geographically correlated genetic clusters. A southern group restricted to forest patches in the EC, a central group including birds from KZN and a genetically distinct northern Limpopo cluster. Results suggest that Cape Parrots have experienced at least two population bottlenecks. An ancient decline during the mid-Holocene (∼ 1,800-3,000 years before present) linked to climate change, and a more recent bottleneck, associated with logging of forests during the early 1900s. This study highlights the effects of climate change and human activities on an endangered species associated with the naturally fragmented forests of eastern South Africa. These results will aid conservation authorities with the planning and implementation of future conservation initiatives. In particular, this study emphasises the Eastern Cape mistbelt forests as an important source population for the species and calls for stronger conservation of forest patches in South Africa to promote connectivity of forest taxa.
... 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). Such periods of interior aridity are not necessarily restricted to, or specifically characteristic of "glacial" periods, but an emerging theme in southern African research has been the hypothesis that the coastal margins may have been of increased importance for human habitation during periods of interior aridity (e.g., Morris 2002;Hetherington 2008;Parkington 2010;Compton 2011;Blome et al. 2012). ...
... The later Holocene witnessed warm temperatures overall, punctuated by several cold reversals of variable duration and intensity. The longest such excursion was the Neoglacial, a period of widespread cooling and humidity registered across much of southern Africa, including the Maloti-Drakensberg region, between ~3.5 and 2.0 ka (Nash and Meadows 2012; but see Chase et al. 2009). A strong Neoglacial signature has been recorded at Likoaeng (1,725 masl), an open-air site near Sehonghong, the fish assemblages from which we consider below. ...
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.
... The later Holocene witnessed warm temperatures overall, punctuated by several cold reversals of variable duration and intensity. The longest such excursion was the Neoglacial, a period of widespread cooling and humidity registered across much of southern Africa, including the Maloti-Drakensberg region, between ~3.5 and 2.0 ka (Nash and Meadows 2012; but see Chase et al. 2009). A strong Neoglacial signature has been recorded at Likoaeng (1,725 masl), an open-air site near Sehonghong, the fish assemblages from which we consider below. ...
... The palaeoflood chronology shows a period of flood activity in the Fish River at 1640-1700 CE that climatically corresponds to the Little Ice Age (LIA; 1300-1800 CE; Tyson et al., 2000). Similarly, increased moisture conditions during 1550-1700 and 1825-1900 were recorded from middens of rock hyrax (Procavia capensis; Chase et al., 2009) in the Namib Desert. In the central Namib (Swakop, Kuiseb, and Tsauchab rivers), evidence is seen of flooding during the LIA, but field data suggest palaeoflood magnitudes minimally exceeded, if at all, the most recent floods (Heine, 2004;Heine and Völkel, 2011). ...
Abstract
Ephemeral rivers in dryland regions exhibit a high interannual variability of streamflow regime, mainly dominated by floods. In these environments, floods are a water resource and a potential hazard with important socioeconomic implications. The Fish River (86,600 km2) is the largest ephemeral stream in Namibia and, recently, also the focus of new development plans, including construction of the largest dam in Namibia. The hydrological analysis to support decisions implies large uncertainties owing to spatial-limited and short hydrological records (since 1962). Here we investigate the current and past patterns of extreme floods combining instrumental, historical, and palaeoflood records. Palaeoflood studies were performed at two reaches with preserved sedimentary evidence: at the upper sector (Vogelkranz) upstream of Hardap Dam (~13% catchment area) and in the lower part of the river, in the Fish River Canyon National Park (70% catchment area). In the Hardap reach, the palaeoflood record identified at least eight large floods during the last 350 years, with the largest flood reaching a minimum discharge of 4800 m3 s−1 (150-year return period). In the Fish River Canyon reach, the sedimentary record shows at least 12 large floods over the last 400 years, the largest with an estimated minimum discharge of 8700 m3 s−1. The elevation of alluvial surfaces without flood evidence provided an upper bound for flood stages, associated with discharges of 6400 m3 s−1 and 16,140 m3 s−1 for the upper and mid-lower Fish River respectively. In the upper reach, the flood frequency analysis (FFA) combining systematic and palaeoflood data provided lower discharges (~25%) of the flood quantiles than the ones using only systematic data sets. In the Fish River Canyon reach, incorporation of the palaeoflood data into the FFA results in slightly higher values in the magnitude of the higher flood quantiles (~4–7%). The FFA analysis using an upper limited lognormal distribution function (LN4) fitted with palaeoflood data shows a good performance with a slow behaviour approaching the upper limit. Our flood frequency results suggest that the Hardap Dam should increase the spillway capacity and safety check flood of the original design in order to satisfy the dam safety criteria. However, the projected reevaluation figures calculated from conventional hydrological methods results in an overestimation of the safety floods according to our estimations.
... The 20 kyr Wonderkrater spring mound record yielded a number of radiocarbon age inversions , which is likely to be a function of the carbon systematics on the site. In other applications, such as the rock hyrax midden palaeoclimate records that extend back to 20 kyr BP (Chase et al., 2009(Chase et al., , 2010(Chase et al., , 2011, radiocarbon provides a coherent chronology. Dating of the Tswaing impact crater record has also been improved by a radiocarbon chronology that extends to 50 kyr BP, but this only covers the deposit to about 18 m depth in a total sequence of 80 m, and the basal date is fixed on a single fission-track date of 220 kyr BP (Kristen et al., 2007). ...
The southern African landscape has been subject to denudation, sediment mobilisation, and deposition over the last 5 Ma. Dating the geological, geomorphological and archaeological evidence of these processes has been achieved through the application of different dating techniques (cosmogenic, luminescence, radiocarbon, electron spin resonance and uranium series disequilibrium). Dating evidence can address issues such as tectonic versus isostatic uplift, chemical versus physical weathering, water processes in the landscape, the age of hominid remains, and the archaeological trajectory of humans from early modernity to the present. Although dating methods are improving, many problems lie in user errors linked to inadequate understanding of the dating context and limitations of the dating methods. Confidence in chronologies is enhanced through reproducibility, stratigraphic consistency and cross-referencing between different techniques.
... 4.2ka Brain and Brain 1977 7.6-6.0ka nd Vogel and Visser 1981 7.6ka nd Chase et al., 2009 8.2ka 4.8-2.7ka Vogel 1989 8.3-4.3ka ...
Climatic amelioration during the mid-Holocene Optimum is associated with hunter-gatherer occupation of remote sites in the Namib Desert. Subsequent changes in late Holocene site distribution suggest there were alternative responses to increasing aridity during this period. Abandonment or episodic occupation is evident in some areas, while others show an emphasis on mountain refugia and resource anomalies. Specialized coping strategies developed during this time allowed a broad re-occupation of the desert when conditions improved briefly during the Medieval Warm Epoch. Successive patterns of settlement and subsistence in the Namib Desert Holocene sequence exemplify the four moments of Holling's adaptive cycle.
... The excursions to local minima of δ 18 O and the Type E dissolutional surface associated with them in Stalagmite DP1 indicate that the 4.2 ka event was a wetter phase, or two wetter phases, in northeastern Namibia. Other evidence for a wetter rather than drier 4.2 ka event in the summer rainfall zone of southern Africa comes from fluvial sediments suggesting exceptionally "strong flow" into Lake Ngami, in Botswana east of Dante Cave, at about 4.2 ka BP (Robbins et al., 2005) and a spike in δ 15 N in hyrax middens at Spitzkoppe, southwest of Dante, suggesting wetter conditions at about 4.2 ka BP (Chase et al., 2009). Much farther away, Marchant and Hooghiemstra (2004) compiled evidence of wetness around 4 ka BP in the South American tropics, although the individual studies' chronologies were not well constrained and/or the numbers of analyses were minimal. ...
The climatic event between 4.2 and 3.9 ka BP known as the “4.2 ka event” is commonly considered to be a synchronous global drought that happened as one pulse. However, careful comparison of records from around the world shows that synchrony is possible only if the published chronologies of the various records are shifted to the extent allowed by the uncertainties of their age data, that several records suggest a two-pulsed event, and that some records suggest a wet rather than dry event. The radiometric ages constraining those records have uncertainties of several decades if not hundreds of years, and in some records the event is represented by only one or two analyses. This paper reports a new record from Stalagmite DP1 from northeastern Namibia in which high ²³⁰Th/²³²Th activity ratios allow small age uncertainties ranging between only 10–28 years, and the event is documented by more than 35 isotopic analyses and by petrographic observation of a surface of dissolution. The ages from Stalagmite DP1 combine with results from 11 other records from around the world to suggest an event centered at about 4.07 ka BP with bracketing ages of 4.15 to 3.93 ka BP. The isotopic and petrographic results suggest a two-pulsed wet event in northeastern Namibia, which is in the Southern Hemisphere's summer rainfall zone where more rain presumably fell with southward migration of the Inter-Tropical Convergence Zone as the result of cooling in the Northern Hemisphere. Comparison with other records from outside the region of dryness from the Mediterranean to eastern Asia suggests that multiple climatic zones similarly moved southward during the event, in some cases bringing wetter conditions that contradict the notion of global drought.
The 4.2 ka Event has generally been regarded as a period of decades to at most a few centuries in which comparatively dry conditions existed in the Middle East and more broadly across the mid-latitude Northern Hemisphere. This paper presents new stable-isotopic and petrographic observations from two previously-unreported U-Th-dated stalagmites from Dante Cave in northeastern Namibia. The results are most compatible with wetter conditions during the 4.2 ka Event, and wetness during the 4.2 ka Event is the only inference supported by evidence. These new results add to observations previously reported from a third Dante Cave stalagmite suggesting a comparatively wet 4.2 ka Event in which Africa's Tropical Rain Belt migrated southward and rainfall increased along the Congo Air Boundary and/or Kalahari Discontinuity. The new results support findings from three other locations in Namibia and Botswana, from at least seven other locations in the Southern Hemisphere, and at least one in southern China, that suggest a wetter rather than drier 4.2 ka Event in those regions. The pattern emerging from these sites generally agrees with recent modeling results indicating increased moisture over broad areas (but not all) of the Southern Hemisphere. This in turn suggests a 4.2 ka Event that was not a global drought but was instead a set of latitudinally-dependent responses to global-scale southward migration of the Inter-Tropical Convergence Zone (ITCZ), and thus Africa's loosely linked Tropical Rain Belt, as a result of cooling of the Northern Hemisphere, which brought drier conditions to some areas and wetter conditions to others.
Sediments are the most important source of Late Quaternary palaeoclimate information in southern Africa, but have been little studied from a geochemical perspective. However, recent advances in analytical techniques that allow rapid and near-continuous elemental records to be obtained from sedimentary sequences has resulted in the increasing use of elemental indicators for reconstructing climate. This paper explores the diverse information that can be acquired from the inorganic component of sediments and reviews some of the progress that has been made over the last two decades in interpreting the climatic history of southern Africa using elemental records. Despite the general scarcity of elemental records, excellent examples from the region exist, which provide some of the longest and most highly resolved sequences of environmental change currently available. Records from Tswaing crater and marine deposits on the southern KwaZulu-Natal coastline have provided rare glimpses into hydroclimate variability over the last 200 000 years, suggesting that summer rainfall in the region responded predominantly to insolation forcing on glacial-interglacial timescales. Over shorter timescales, lakes and wetlands found in the Wilderness embayment on the southern Cape coast and along the Maputaland coast in north-eastern South Africa have yielded highly-resolved elemental records of Holocene environmental change, providing insight into the changing interactions between tropical (e.g., El Niño-Southern Oscillation) and temperate (e.g., mid-latitude westerlies) climate systems affecting rainfall variability in the region. The examples discussed demonstrate the multiple environmental processes that can be inferred from elemental proxies and the unique insight this can provide in advancing our understanding of past climate change on different timescales. The interpretation of geochemical data can be complicated by the complex nature of sedimentary environments, various proxy assumptions and analytical challenges, and the reliability of sediment-based climate reconstructions is substantially enhanced through multi-proxy approaches.
A comprehensive understanding of the relationship between land cover, climate change and disturbance dynamics is needed to inform scenarios of vegetation change on the African continent. Although significant advances have been made, large uncertainties exist in projections of future biodiversity and ecosystem change for the world's largest tropical landmass. To better illustrate the effects of climate–disturbance–ecosystem interactions on continental‐scale vegetation change, we apply a novel statistical multivariate envelope approach to subfossil pollen data and climate model outputs (TraCE‐21ka). We target paleoenvironmental records across continental Africa, from the African Humid Period (AHP: ca 14 700–5500 yr BP) – an interval of spatially and temporally variable hydroclimatic conditions – until recent times, to improve our understanding of overarching vegetation trends and to compare changes between forest and grassy biomes (savanna and grassland). Our results suggest that although climate variability was the dominant driver of change, forest and grassy biomes responded asymmetrically: 1) the climatic envelope of grassy biomes expanded, or persisted in increasingly diverse climatic conditions, during the second half of the AHP whilst that of forest did not; 2) forest retreat occurred much more slowly during the mid to late Holocene compared to the early AHP forest expansion; and 3) as forest and grassy biomes diverged during the second half of the AHP, their ecological relationship (envelope overlap) fundamentally changed. Based on these asymmetries and associated changes in human land use, we propose and discuss three hypotheses about the influence of anthropogenic disturbance on continental‐scale vegetation change.
Despite being one of the world’s oldest deserts, and the subject of decades of research, evidence of past climate change in the Namib Desert is extremely limited. As such, there is significant debate regarding the nature and drivers of climate change in the low-latitude drylands of southwestern Africa. Here we present data from stratified accumulations of rock hyrax urine that provide the first continuous high-resolution terrestrial climate record for the Namib Desert spanning the past 50,000 yr. These data, spanning multiple sites, show remarkably coherent variability that is clearly linked to orbital cycles and the evolution and perturbation of global boundary conditions. Contrary to some previous predictions of southwestern African climate change, we show that orbital-scale cycles of hydroclimatic variability in the Namib Desert region are in phase with those of the northern tropics, with increased local summer insolation coinciding with periods of increased aridity. Supported by climate model simulations, our analyses link this to variations in position and intensity of atmospheric pressure cells modulated by hemispheric and land-sea temperature gradients. We conclude that hydroclimatic variability at orbital time scales is driven by the combined influence of direct low-latitude insolation forcing and the influence of remote controls on the South Atlantic anticyclone, with attendant impacts on upwelling and sea-surface temperature variations.
Variations in Holocene climate are of importance in understanding the contemporary diversity found in global climates and biogeography. This is particularly true for South Africa, which spans the subtropics and midlatitudes, and is bordered to the east by the warm Indian Ocean Agulhas Current, and to the west by the cold Atlantic Ocean Benguela Current. Holocene variations in South African climate include evidence for globally synchronous warming and cooling events, and for locally discrete variations in both precipitation amount and seasonality. The study of Holocene climates relies heavily on fossil proxies. Due to the aridity of much of the region in the Holocene, poor preservation of these proxies has been a critical challenge. Key future trajectories in South African Holocene climate science include concerted efforts to better spatially and temporally resolve the climate record, for key periods of interest, and more generally to determine local-scale climatic variability and climatic drivers.
Recent and historical austral summer and winter rainfall characteristics have been widely investigated across southern Africa. However, a notable gap of knowledge remains for the Namibian region. This article presents the first extensive 19th century (1845–1900) hydro‐climate history for central Namibia, derived from documentary evidence. Unpublished and published data sources were scrutinized in various archives and libraries in Germany, Switzerland, Namibia and South Africa. Missionary Carl Hahn's detailed diaries are the most valuable source of information for the earliest period until 1859. Other important sources of information include the Rhenish Missionary Society (RMS) annual reports and monthly ‘Berichte’ (news), station chronicles, official annual reports for the colonial period (1894 onwards) and letters/diaries by traders, travellers, etc.
Climate information was transcribed, translated and organized chronologically. Using a five‐point categorization system ranging from very wet (+2) to very dry (−2), each year was classified according to overall rainfall conditions during the rain season. A portion of the chronology is compared with instrumental rainfall data for Okahandja, Windhoek and Rehoboth and confirms good agreement. Possible associations between El Niño‐Southern Oscillation (ENSO) phases and subsequent austral summer rainfall conditions are explored for central Namibia. Wetter years (42%) are over‐represented in comparison to dry years (38%) during the second half of the 19th century in central Namibia, with a high percentage (42%) constituting either extremely wet or extremely dry years. Inter‐annual rainfall variability between 1845 and 1900 seems more pronounced than elsewhere in southern Africa during this period. Extreme to very strong and prolonged El Niño (e.g. 1876–1878) and La Nina (e.g. 1865–1866) phases account for rare hydro‐climatic synchronicity between southern African sub‐regions and between continents of the Southern Hemisphere.
The mega-diverse, Mediterranean-type fynbos biome may be vulnerable to future changes in climate and associated fire regimes, in particular to increasing summer-drought intensity and associated potential expansion of adjacent semi-arid vegetation types. Studying Holocene vegetation dynamics at the fynbos–succulent karoo boundary may provide insights into the resilience or sensitivity of fynbos to climate change. In this study, fossil pollen, non-pollen palynomorphs and charcoal data spanning ~5500 to −50 cal. yr BP were generated from an accelerator mass spectrometer (AMS) radiocarbon-dated sediment core extracted directly at the present-day fynbos–succulent karoo biome boundary at Groenkloof, a site in the Kamiesberg Mountains of Namaqualand, South Africa. Contrary to expectations, during the Mid-Holocene Altithermal from 5480 to 4025 cal. yr BP, fynbos and fire thrived through summer moisture subsidies associated with enhanced sub-tropical easterly flow. Subsequent cooling from 4025 to 2005 cal. yr BP resulted in enhanced summer drought and overall fynbos biome contraction, though woody fynbos shrubs persisted through physiological adaptations to drought. Desert succulents typical of the succulent karoo, such as those of Aizoaceae and Crassulaceae, failed to colonise the emergent niche space, resulting in dominance of an ambiguous grassy, asteraceous fynbos. More recent wetting associated with the ‘Little Ice Age’ Holocene temperature minima from 695 to 100 cal. yr BP prompted a resurgence in fynbos abundance, but frequent fire driven by pastoralists appears to have reduced the fynbos community’s functional diversity. Palaeoecological data from the Kamiesberg suggest that both climatic buffering of mountain refugia and high physiological resistance among certain fynbos taxa have contributed to the biome’s long-term resilience. Summer rainfall associated with the sub-tropical easterlies has been key in maintaining eastern fynbos refugia in past interglacial temperature maxima. The data also suggest that pre-historic land use and resulting fire-regime manipulations have resulted in the development of a taxonomically and functionally simplified alternative fynbos ecosystem state.
This paper characterises predator–prey interactions amongst African mammals from C4 savanna environments using stable carbon and nitrogen isotope proxies for diet. Stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope data from hair and faeces of large African mammal carnivores and herbivores as potential prey are presented for a diverse range of taxa. Carbon isotope data imply that most carnivores from the “lowveld” savanna of South Africa form part of C4 grass-based foodwebs. Nitrogen isotope data show clear differences between trophic levels, although it appears the magnitude of these differences vary between predators feeding on invertebrates and vertebrates, respectively. While the number of carnivore samples for which data are available are relatively few and data for prey are restricted mainly to large ungulate herbivores, results clearly demonstrate the potential for future applications of this technique to predator–prey foodwebs in African savannas. In tandem with traditional approaches, stable isotopes can help elucidate patterns of predator impacts on prey populations, domestic livestock and resolving similar foodwebs in palaeoenvironmental contexts.
Palaeoecological and geological evidence for changing atmospheric circulation patterns in Chile indicates that equatorward and poleward shifts of the Southern Westerlies (Pacific precipitation source) were an important factor during Weichselian and Holocene climate change. We focus on the evidence and possible causes of considerable climate change in the Holocene at around 2700 BP, which was associated with a steep rise in atmospheric radiocarbon content, indicating an abrupt decrease in solar activity. Climate change may have been caused by the lowering of solar irradiation through two amplifying factors, namely (1) increased cosmic ray intensity, stimulating cloud formation and precipitation, and (2) reduced solar UV intensity, causing a decline of stratospheric ozone production and cooling as a result of less absorption of sunlight. A decrease in the latitudinal extent of Hadley Cell circulation may have occurred with concomitant equatorward relocation of mid-latitude storm tracks, which brought about northward movement of vegetation belts and advance of glaciers.
Spring deposits exposed during building operations in downtown Windhoek, and lake sediments retrieved from underneath 50 m of water in a sinkhole (Lake Otjikoto), contain pollen profiles which reflect environmental changes in Namibia during the Holocene. At Windhoek moist local conditions are reflected by pollen in the spring deposits which were radiocarbon-dated to between ca. 7000 and 6000 BP. They remained relatively favourable until 5630 BP despite signs of drying. Weedy Compositae (Lactucoideae or Liguliflorae) increased until the end of this record ca. 2410 BP, indicating local disturbance. Deposits from Lake Otjikoto were dated to the late Holocene although an accurate chronology could not be estabiished for the sequence due to unexpected results with radiocarbon measurements. Pollen accumulation values and composition indicate relatively dry conditions after 3500 BP which were followed temporarily by a wetter climate during more recent times.
A detailed (ca. 100yr resolution) and well-dated (18 AMS 14C dates to 23 cal. ka BP) record of latest Pleistocene–Holocene variations in terrigenous (eolian) sediment deposition at ODP Site 658C off Cap Blanc, Mauritania documents very abrupt, large-scale changes in subtropical North African climate. The terrigenous record exhibits a well-defined period of low influx between 14.8 and 5.5 cal. ka BP associated with the African Humid Period, when the Sahara was nearly completely vegetated and supported numerous perennial lakes; an arid interval corresponding to the Younger Dryas Chronozone punctuates this humid period. The African Humid Period has been attributed to a strengthening of the African monsoon due to gradual orbital increases in summer season insolation. However, the onset and termination of this humid period were very abrupt, occurring within decades to centuries. Both transitions occurred when summer season insolation crossed a nearly identical threshold value, which was 4.2% greater than present. These abrupt climate responses to gradual insolation forcing require strongly non-linear feedback processes, and current coupled climate model studies invoke vegetation and ocean temperature feedbacks as candidate mechanisms for the non-linear climate sensitivity. The African monsoon climate system is thus a low-latitude corollary to the bi-stable behavior of high-latitude deep ocean thermohaline circulation, which is similarly capable of rapid and large-amplitude climate transitions.
Nitrogen (N) cycling was analyzed in the Kalahari region of southern Africa, where a strong precipitation gradient (from 978 to 230 mm mean annual precipitation) is the main variable affecting vegetation. The region is underlain by a homogeneous soil substrate, the Kalahari sands, and provides the opportunity to analyze climate effects on nutrient cycling. Soil and plant N pools, 15N natural abundance (δ15N), and soil NO emissions were measured to indicate patterns of N cycling along a precipitation gradient. The importance of biogenic N2 fixation associated with vascular plants was estimated with foliar δ15N and the basal area of leguminous plants. Soil and plant N was more 15N enriched in arid than in humid areas, and the relation was steeper in samples collected during wet than during dry years. This indicates a strong effect of annual precipitation variability on N cycling. Soil organic carbon and C/N decreased with aridity, and soil N was influenced by plant functional types. Biogenic N2 fixation associated with vascular plants was more important in humid areas. Nitrogen fixation associated with trees and shrubs was almost absent in arid areas, even though Mimosoideae species dominate. Soil NO emissions increased with temperature and moisture and were therefore estimated to be lower in drier areas. The isotopic pattern observed in the Kalahari (15N enrichment with aridity) agrees with the lower soil organic matter, soil C/N, and N2 fixation found in arid areas. However, the estimated NO emissions would cause an opposite pattern in δ15N, suggesting that other processes, such as internal recycling and ammonia volatilization, may also affect isotopic signatures. This study indicates that spatial, and mainly temporal, variability of precipitation play a key role on N cycling and isotopic signatures in the soil–plant system.
The mean annual rainfall in southern Africa is found to explain over half of the observed variance in the stable nitrogen (N) isotopic signatures of C3 vegetation in southern Africa (r2=0.54, P<0.01). The inverse relationship between the stable N isotopic signatures of foliar samples from C3 vegetation and long-term southern African rainfall is found on a scale larger than previously observed. A modest relationship is found between stable carbon (C) isotopic signatures of C3 vegetation and rainfall across the region (r2=0.20, P<0.01). No such relationship is found between stable C and N isotopic signatures of C4 vegetation and rainfall. The explanation of the relationship between 15N in C3 vegetation and the mean annual rainfall presented here is that nutrient availability varies inversely with water availability. This suggests that water-limited systems in southern Africa are more open in terms of nutrient cycling and therefore the resulting natural abundance of foliar 15N in these systems is enriched. The use of this relationship may be of value to those researchers modeling both the dynamics of vegetation and biogeochemistry across this region. The use of the isotopic enrichment in C3 vegetation as a function of rainfall may provide an insight into nutrient cycling across the semi-arid and arid regions of southern Africa. This finding has implications for the study of global change, especially as it relates to vegetation responses to changing regional rainfall regimes over time.
This paper characterizes predator–prey interactions amongst African mammals from C4 savanna environments using stable carbon and nitrogen isotope proxies for diet. Stable carbon (δ13C) and nitrogen (δ15N) isotope data from hair and faeces of large African mammal carnivores, and herbivores as potential prey, are presented for
a diverse range of taxa. Carbon-isotope data imply that most carnivores from the “lowveld” savanna of South Africa form part
of C4 grass-based food webs. Nitrogen isotope data show clear differences between trophic levels, although it appears that the
magnitude of these differences varies between predators feeding on invertebrates and vertebrates, respectively. Whilst the
number of carnivore samples for which data are available is relatively few, and data for prey are restricted mainly to large
ungulate herbivores, results clearly demonstrate the potential for future applications of this technique to predator–prey
food webs in African savannas. In tandem with traditional approaches, stable isotopes can help elucidate patterns of predator
impacts on prey populations, domestic livestock, and resolving similar food webs in palaeoenvironmental contexts.
A detailed (ca. 100 yr resolution) and well-dated (18 AMS dates to 23 cal. ka BP) record of latest Pleistocene–Holocene variations in terrigenous (eolian) sediment deposition at ODP Site 658C off Cap Blanc, Mauritania documents very abrupt, large-scale changes in subtropical North African climate. The terrigenous record exhibits a well-defined period of low influx between 14.8 and 5.5 cal. ka BP associated with the African Humid Period, when the Sahara was nearly completely vegetated and supported numerous perennial lakes; an arid interval corresponding to the Younger Dryas Chronozone punctuates this humid period. The African Humid Period has been attributed to a strengthening of the African monsoon due to gradual orbital increases in summer season insolation. However, the onset and termination of this humid period were very abrupt, occurring within decades to centuries. Both transitions occurred when summer season insolation crossed a nearly identical threshold value, which was 4.2% greater than present. These abrupt climate responses to gradual insolation forcing require strongly non-linear feedback processes, and current coupled climate model studies invoke vegetation and ocean temperature feedbacks as candidate mechanisms for the non-linear climate sensitivity. The African monsoon climate system is thus a low-latitude corollary to the bi-stable behavior of high-latitude deep ocean thermohaline circulation, which is similarly capable of rapid and large-amplitude climate transitions.
Mg/Ca analyses of G. bulloides and abundances of N. pachyderma (left coiling) from Ocean Drilling Program (ODP) Leg 175 Hole 1084B in the Benguela coastal upwelling system document lower sea surface temperatures during the Last Glacial Maximum (LGM), Younger Dryas, mid-Holocene, and Little Ice Age in the southeastern Atlantic. Taking into consideration the possible effects of differential carbonate dissolution, the Mg/Ca data indicate Younger Dryas temperatures 2°-3°C cooler than those of the early Holocene and LGM temperatures 4°-5°C cooler than those of the early Holocene. The cool interval during the deglacial period at Hole 1084B matches the timing of Younger Dryas shifts in Cariaco Basin and Greenland Ice Sheet records and that of a nearby alkenone record. Comparison of mid-Holocene cooling at Hole ODP1084B with other high-resolution records of Holocene and last deglacial sea surface temperatures from the tropical Atlantic implies consistent basin-wide changes in atmospheric circulation. A brief period of 1.5°-2°C cooling between 17.8 and 17.2 ka, if related to Heinrich event 1, is consistent with a previously hypothesized tropical origin of all Heinrich climate change events.
ODP Site 1078 situated under the coast of Angola provides the first record of the vegetation history for Angola. The upper 11 m of the core covers the past 30 thousand years, which has been analysed palynologically in decadal to centennial resolution. Alkenone sea surface temperature estimates were analysed in centennial resolution. We studied sea surface temperatures and vegetation development during full glacial, deglacial, and interglacial conditions. During the glacial the vegetation in Angola was very open consisting of grass and heath lands, deserts and semi-deserts, which suggests a cool and dry climate. A change to warmer and more humid conditions is indicated by forest expansion starting in step with the earliest temperature rise in Antarctica, 22 thousand years ago. We infer that around the period of Heinrich Event 1 a northward excursion of the Angola Benguela Front and the Congolian Air Boundary resulted in cool sea surface temperatures and a northward extension of desert vegetation along the coast. Rain forest and dry forest returned 15 thousand years ago. During the Holocene, dry forests and Miombo woodlands expanded. Also in Angola globally recognised climate changes at 8 thousand and 4 thousand years ago had an impact on the vegetation. During the past 2 thousand years, savannah vegetation became dominant.
Fossil rodent middens and wetland deposits from the central Atacama Desert (22 degrees to 24 degrees S) indicate increasing summer precipitation, grass cover, and groundwater levels from 16.2 to 10.5 calendar kiloyears before present (ky B.P.). Higher elevation shrubs and summer-flowering grasses expanded downslope across what is now the edge of Absolute Desert, a broad expanse now largely devoid of rainfall and vegetation. Paradoxically, this pluvial period coincided with the summer insolation minimum and reduced adiabatic heating over the central Andes. Summer precipitation over the central Andes and central Atacama may depend on remote teleconnections between seasonal insolation forcing in both hemispheres, the Asian monsoon, and Pacific sea surface temperature gradients. A less pronounced episode of higher groundwater levels in the central Atacama from 8 to 3 ky B.P. conflicts with an extreme lowstand of Lake Titicaca, indicating either different climatic forcing or different response times and sensitivities to climatic change.
Titanium and iron concentration data from the anoxic Cariaco Basin, off the Venezuelan coast, can be used to infer variations in the hydrological cycle over northern South America during the past 14,000 years with subdecadal resolution. Following a dry Younger Dryas, a period of increased precipitation and riverine discharge occurred during the Holocene "thermal maximum." Since approximately 5400 years ago, a trend toward drier conditions is evident from the data, with high-amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the "Little Ice Age." These regional changes in precipitation are best explained by shifts in the mean latitude of the Atlantic Intertropical Convergence Zone (ITCZ), potentially driven by Pacific-based climate variability. The Cariaco Basin record exhibits strong correlations with climate records from distant regions, including the high-latitude Northern Hemisphere, providing evidence for global teleconnections among regional climates.
(13)C/^(12)C ratios have been determined for plant tissue from 104 species representing 60 families. Higher plants fall into two categories, those with low δ_(PDB1) ^(13)C values (-24 to -34‰) and those with high δ ^(13)C values (-6 to -19‰). Algae have δ^(13)C values of -12 to -23‰. Photosynthetic fractionation leading to such values is discussed.
(1) Semi-arid savannas, wherever they occur, have generally been overgrazed and encroached on by bush. A model is developed which accounts for the growth of woody vegetation and of grasses, and analyses the competition between them for available soil water. (2) The model is based on Walter's two layer hypothesis. Woody vegetation and grasses compete for water in the surface layers of the soil, but woody vegetation has exclusive access to a source of water relatively deep underground. Where there is only a small biomass of grass the soil surface tends to become impermeable and, in these conditions, the model shows that two different steady states may develop: with a lot of woody vegetation alone, or with a relatively large biomass of grass and rather little woody vegetation. (3) The results are discussed in terms of the concept of resilience. The continued existence of both stable states under ranching conditions seems to depend on periodic heavy, or over-, grazing which allows for the maintenance of unpalatable or unstable grass species, which thus set a minimum to grass biomass--a minimum which cannot be reduced by herbivores. (4) Comparison of the dynamics of various savanna and other natural systems leads to the conclusion that the resilience of the systems decreases as their stability (usually induced) increases.
¹³C/¹²C ratios have been determined for plant tissue from 104 species representing 60 families. Higher plants fall into two categories, those with low δPDBI¹³C values (—24 to —34‰) and those with high δ ¹³C values (—6 to —19‰). Algae have δ ¹³C values of —12 to —23‰. Photosynthetic fractionation leading to such values is discussed.
A new diatom record from Lake Victoria’s Pilkington Bay, subsampled at 21- to 25-year intervals and supported by 20 AMS dates, reveals a ∼10,000 calendar year environmental history that is supported by published diatom and pollen data from two nearby sites. With their chronologies adjusted here to account for newly documented ancient carbon effects in the lake, these three records provide a coherent, finely resolved reconstruction of Holocene climate change in equatorial East Africa. After an insolation-induced rainfall maximum ca. 8800–8300 cal yr B.P., precipitation became more seasonal and decreased abruptly ca. 8200 and 5700 yr B.P. in apparent association with northern deglaciation events. Century-scale rainfall increases occurred ca. 8500, 7000, 5800, and 4000 yr B.P. Conditions after 2700 yr B.P. were generally similar to those of today, but major droughts occurred ca. 1200–600 yr B.P. during Europe’s Medieval Warm Period.
The existing paleoenvironmental data from the Australian arid zone lack sensitivity and come from only a few sites. Macrofossils and pollen from four dated middens of the stick-nest rat (Leporillus spp.) were analyzed from two sites in Western Australia. Animal and plant macrofossil remains were well preserved and provided evidence of change in species distribution within the last 1150 yr. Brush-tail possum and golden bandicoot have contracted their ranges in the recent past, possibly since the introduction of cats into Australia. An undescribed lacewing was also a significant find. Pollen preserved in parts of the same midden and in middens from different sites indicates that records are sensitive to the composition of the local vegetation when the midden was built. Pollen spectra are quite different from playa lakes, which record largely regional vegetation. Pollen preserved in the fecal pellets, desiccated urine, and grass mat nesting material provided similar information but some differences were apparent, suggesting dietary preferences were reflected in the fecal component. The pollen record suggested a trend to less-wooded vegetation cover in central Australia between 900 and 300 yr B.P.
In 2003 examination of aerial photographs revealed a series of previously unknown relict shorelines on the arcuate ridge, possibly a clay lunette dune, that marks the western boundary of Etosha Pan in Namibia. The shorelines are 120–600m wide and the most prominent extend for tens of km around the lunette dune. The shorelines were examined on the ground in 2004 and an attempt was made to date the three lowest levels at ca. 5, 2.5 and 1m above the present pan surface. The OSL ages obtained indicate higher and more prolonged lake conditions than today at ca. 6.4, 4.0 and 2.1ka with the youngest shoreline sediments resting on an ancient pan surface dating to ca. 13ka. The evidence indicates dry conditions in the pan at ca. 13ka, wetter conditions and higher lake levels in the middle Holocene followed by a decline in lake levels to the present. Periods of inundation were of sufficient duration to produce shorelines at the southwestern end of the pan due to the prevailing northeasterly winds that would have maximized wave action along this section of the pan margin. The Etosha findings, together with other regional paleoclimate data, suggest four periods of increased wetness in SW Africa during the Holocene at 7–5, 4.5–3.5, 2.5–1.7 and ca. 1.0ka. There is widespread evidence for the oldest of these periods suggesting that it was a prominent and widespread interval of wetness. Prior to ca. 8.0ka the climate may have been drier than today.
13C/12C ratios in plants depend on factors like temperature, evaporation or seasonal moisture distribution. Fluctuations of 13C/12C in Procavia capensis (hyrax) dung samples from different vegetation zones and various ages over the last 20000 years indicate variations in the amounts of C4 and CAM, or C3 plants consumed by these herbivores. Potentially they also indicate vegetation changes that may have occurred. 13C/12C values for a series of hyrax middens of Late Pleistocene/Holocene age, from a variety of biomes across Southern Africa, show that hyraxes favour mainly C3 plants in their diets but they do incorporate CAM or C4 plants under certain circumstances. In the eastern mountainous summer-rain area around Clarens with C3 woodland and unpalatable “sour” grassland consisting mainly of C4 grasses and fewer of the C3 type, hyraxes seem to avoid at least the C4 component of grass and rely mainly on leaves of the woody plants. Isotopic data for hyrax dung in the western Cape Cederberg region indicate diets composed almost exclusively of C3 plants during the last 20000 years. Slight shifts towards more enriched values occur, e.g., around 420 and 2100 years ago, which may indicate slight increase in CAM or C4 plants. Interestingly no enrichment occurs during the Last Glacial Maximum when a shortage of atmospheric CO2 may have favoured C4 plants. During the late Holocene some CAM and/or C4-plant ingestion by hyraxes is suggested in the dry western and southern areas which receive more summer rains, probably reflecting the availability of some palatable (or “sweet”) summer grasses. Although slight, a comparable pattern of isotope change is observed in three areas viz., the Cederberg, the Karoo and the Namib Desert, suggesting that plant cover is responding to regional climate mechanism ca. 2100 years BP. This does not necessarily imply similar seasonal rainfall shifts over the whole of this wide area.
A prominent feature in the Southeast Atlantic is the Angola-Benguela Front (ABF), the convergence between warm tropical and cold subtropical upwelled waters. At present, the sea-surface temperature (SST) gradient across the ABF and its position are influenced by the strength of southeasterly (SE) trade winds. Here, we present a record of changes in the ABF SST gradient over the last 25 kyr. Variations in this SST contrast indicate that periods of strengthened SE trade-wind intensity occurred during the Last Glacial Maximum, the Younger Dryas, and the Mid to Late Holocene, while Heinrich Event 1, the early part of the Bølling-Allerød, and the Early Holocene were periods of weakened SE trade-winds.
The 13C/12C isotope ratios in animal1 and human2 bone can be used as indicators of diet, more recently it was shown that the 15N/14N ratios of animals and humans are similarly determined by the food they eat3–5. Specifically, the stable carbon isotope composition reflects the proportion of C3 and C4 plants at the base of the food chain1,2, while both 15N and 13C reveal the difference between a marine and terrestrial diet in modern as well as archaeological contexts5–7. Here we present data for human and animal bones from southern Africa which only partly conform to previously recognized patterns for 15N/14N ratios. Prehistoric human bones from a particular coastal region of South Africa show 15N/14N ratios consistent with the marine and terrestrial diets indicated by the 13C/12C ratios, but bones of both prehistoric humans and modern wild animals from a larger part of the subcontinent show variations in 15N/14N ratios which cannot be ascribed to known variations in diet. It appears that, in some environments, nitrogen isotope studies must also take into account the possible influence of the climate.
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.
1. The paper is based on field observations and studies of a captive colony.
2. A classified list of food plants is discussed under the headings of lowland habitat, drought conditions and alpine habitat. Rock hyraces are shown to have a very wide food selectivity. Water requirements and some unusual foods are mentioned briefly.
3. Feeding behaviour is shown to be of two types described as “group” and “casual” feeding. The pattern of group feeding is described and its diurnal occurrence discussed. Casual feeding is briefly considered.
4. Evolutionary changes in hyrax feeding habits have been in the direction of decreasing selectivity of food material. The relationship of hyraces to the ungulate stock is supported by a number of similarities between the feeding behaviour of modern hyraces and ungulates.
Summary • A negative relationship between water availability and the abundance of 15N relative to 14N (expressed as 15N) in the bone collagen of herbivores has been widely reported. However, the relative importance of dietary 15N and animal metabolism in producing this effect remains unclear. • To evaluate the relative importance of these two factors, we examined variation in 15N of both grass foliage and kangaroo (Macropus spp.) bone collagen. We assessed whether the offset between grass and bone collagen 15N was constant with respect to water availability. • An index of water availability (annual actual evapotranspiration/annual potential evapotranspiration) explained a considerable proportion of the variation in both grass 15N (R2 = 0·40) and bone collagen 15N (R2 = 0·57), and the slopes of these negative relationships were similar, with a near-constant 15N offset between grass foliage and bone collagen. • This finding suggests that dietary 15N is the main cause of the negative relationship between kangaroo bone collagen 15N and water availability, with metabolic factors having little discernible effect. Functional Ecology (2006) 20, 1062–1069 doi: 10.1111/j.1365-2435.2006.01186.x
Pollen was derived from fossil dung of herbivorous hyraxes, deposited in a rock shelter on the highest mountain in Namibia, Dâures or Brandberg, situated on the Namib Desert margin. Radiocarbon dating ranging in age between modern times and 30 000 yr BP showed it represents the first empirical pollen evidence of continental palaeovegetation during the Late Pleistocene along the western escarpment of southern Africa. The initial results indicate Last Glacial Maximum vegetation differed totally from the current pattern as vegetation types were dominated by small Asteraceae shrubs, in contrast to those of the Holocene and modern times which show more succulents, grass and woody elements (arboreal pollen). The results suggest that Cape floral communities did not reach into the tropics along the western escarpment of Africa, despite such pollen types occurring in marine cores. Copyright © 2004 John Wiley & Sons, Ltd.
1.
It has been reported that when the vegetarian Bush hyrax Heterohyrax and the Rock hyrax Procavia are allopatric they occupy an almost identical niche, while when sympatric they differ in feeding behaviour. To investigate whether indeed a displacement in feeding behaviour takes place where Procavia johnstoni and Heterohyrax brucei occur sympatrically, the feeding characteristics of three (two H. brucei, one P. johnstoni)allopatric family groups and four (two of each species) sympatric family groups living on five kopjes in the Serengeti were studied and compared.
2.
The vegetation of these five kopjes was surveyed. It was divided into four classes (grass, forb, bush, tree), the plant species identified and the indices of diversity and similarity calculated. The plant biomass was roughly quantified through a foliage density (f.d.) factor and the seasonal variation of vegetation recorded.
The number of plant species ranged from 65 to 95 (Fig. 4). The closer the kopjes are geographically, the greater the resemblance in their plant species composition (Fig. 6). Although bushes and trees comprise the fewest plant species (15–27%) they form the highest foliage density values (65–85%; Table 1, Fig. 5).There is a substantial variation of plant species diversity. A significant correlation exists between the diversity indices and crown cover, but there is no correlation between diversity indices and a) kopje area or b) the quotient of total number of hits per transect length.
Grasses, forbs and small bushes observe more or less the rainfall pattern, while other bushes, and trees, never completely lose their leaves (Fig. 7).
3.
The behaviour of individuals in the groups was regularly observed and recorded in the wet and dry seasons.
a)
H. brucei was observed feeding on 64 plant species (Annex A) but 2\2-11 species formed 90% of the animals' staple diet. There is a high correlation (r
s=0.90) between the comparative abundance of vegetation (measured by f.d.) and the proportions of the four vegetation classes eaten by H. brucei (Fig. 8). All four family groups fed roughly in proportion to the foliage density, yet showed preference for certain plant species. They browsed predominantly on bushes and trees in the wet (81%) and dry (92%) seasons (Fig. 11), but showed a tendency to eat more grass and browse less in the wet season. There are marked differences in feeding between the family groups, due to selective preferences and the vegetation composition in the respective kopjes (Table 2, Fig. 10).
b)
P. johnstoni was observed feeding on 79 plant species (Annex A). The animals have a high seasonal adaptability: in the wet season they showed a high preference for grasses (78%), but in the dry season when grasses became parched and poor in quality they browsed (57%) extensively (Fig. 11), and more or less in proportion to the foliage density of each vegetation class (Fig. 9).
P. johnstoni must go outside the kopje to graze. Around one kopje the cropped grass area was very marked, its size varying with rainfall (Figs. 12 and 13).
a)
Competition for food could occur especially in the dry season when both species browse. However, no evidence could be found for a competition-induced displacement here.
4.
Almost no aggressive behaviour was observed between the species.
5.
Both P. johnstoni and H. brucei have morning and evening feeding activity peaks in the wet and dry seasons, the evening one always being higher (Fig. 14). There was no indication in sympatric groups of any activity shift induced by the presence of the other species.
Evidence on the social character of group feeding and the guarding function of the territorial is presented.
6.
The results obtained are compared with those of other authors. There is no indication of niche segregation in sympatric kopjes. Possible climatic and other reasons for regional sympatry are discussed.
The advantage of selecting food items rich in protein and energy and low in fibre content are considered and food competitors listed.
The stable carbon and nitrogen isotope ratios of bone collagen have been used to trace diet and habitat selection of the larger mammals of East Africa. 238 individuals of 43 species from montane forests and grasslands in Kenya and Tanzania have been analyzed. The results show that carbon isotopes discriminate between (1) grazers and browsers in savanna grasslands, (2) forest floor and savanna grassland herbivores and (3) forest floor and forest canopy species. Nitrogen isotopes discriminate between (4) carnivores and herbivores, (5) forest and savanna grassland herbivores, and (6) water-dependent and drought-tolerant herbivores. This technique provides a quantitative approach to assessing long-term habitat and diet selection and the role of resource partitioning in animal community structure.
Data are presented for the 15N/14N ratios of 140 indigenous terrestrial plants from a wide variety of natural habitats in South Africa and Namibia. Over much of the area, from high-rainfall mountains to arid deserts, the 15N values of plants lie typically in the range -1 to +6; with no evident differences between C3 plants and C4 grasses. There is a slight correlation between 15N and aridity, but this is less marked than the correlation between the 15N values of animal bones and aridity. At coastal or saline sites, however, the mean 15N values for plants are higher than those at nearby inland or non-saline sites-e.g.: arid Namib coast (10 higher than inland Namib); wet Natal beach (5 higher than inland Natal); saline soils 500 km from coast (4 higher than non-saline soils). High values were also found at one site where there were no marked coastal or saline influences. These environmental effects on the isotopic composition of plants will extend upwards to the animals and humans they support. They therefore have important consequences for the use of nitrogen isotope data in the study of the dietary habits and trophic structures of modern and prehistoric communities.
Sediment composition, grain size and clay mineral record of a high-resolution sediment core from the continental slope off Namibia was investigated to gain information on the deposition of terrigenous matter in this part of the Southwest African continental margin during the last 18 k.y. The depositional processes involved are fluvial input by the Kunene River and eolian input from the Namib and Kalahari deserts, each supplying characteristic mineral suites. During low sea level, erosion of the exposed shelf yields additional material. The amount of eolian or fluvial matter depends on the strength of the transport process, which is a function of aridity or humidity of the source area, thus allowing paleoclimatic interpretations. Arid conditions prevailed during a low sea level from 18 to 15 ka and unconsolidated shelf sediment was mobilized and supplied to the slope by short-distance transport by southerly winds. A dramatic increase in the accumulation of terrigenous sediment is recorded from 15 to 10 ka without major changes in sediment composition, which is attributed to increased runoff of the Kunene River and fluvial erosion of shelf sediments. This period coincides with a strengthening of the monsoonal system during a precessional minimum, which is observed in numerous sites in Central Africa and indicates an intensified influence of the monsoon at the Kunene headwaters. A distinct shift in clay mineralogy towards river-derived material marks a second period of increased river runoff—during high sea level—from 9 to 5 ka, indicating maximum humidity in the source area from 6 to 5 ka. This corresponds to the Holocene climatic optimum observed in the arid belts of Northern Africa. The present balance between fluvial and eolian input was reached approximately at 4 ka.
A systematic drilling and optical dating programme on Middle Kalahari beach ridge (relict shoreline) sediments has enabled the identification of multiple episodes of lake high stands of an extensive palaeolake system at the terminus of the Okavango Delta, northern Botswana. This paper presents 23 ages from the Mababe Depression and establishes four shoreline construction phases in the late Quaternary coeval with other sub-basin lake high stands (Lake Ngami). These synchronous lake phases result from a coalescence of the sub-basins into a unified palaeolake, Lake Thamalakane, covering an area of ∼ 32,000 km2. Six additional ages are also presented from the Chobe enclave to the north of the basin where shoreline ridges were emplaced at the same time as Lake Thamalakane phases. This suggests that increased flow in the Chobe and Zambezi system significantly contributed to the Middle Kalahari lake phases in both the post-glacial and Holocene periods. The integration of these new data and their compatibility with other regional and tropical palaeo-archives is discussed in the light of understanding Quaternary climate drivers within the Kalahari.
This paper begins with an overview of the African rainfall regime, noting in particular the contrast among various regions of the continent, followed by a description of the nature of climatic (i.e., rainfall) variability over Africa on time scales of decades and centuries. The decadal scale is examined using modern data covering the twentieth century. The century scale is examined using historical reconstructions of climate, based on a combination of geologic, geographic and historical information (e.g., lake chronologies, landscape descriptions, archives and diaries).The presentation includes some results of an analysis of a new historical semi-quantitative data set for Africa covering the last two centuries. It was produced using a combination of historical information, nineteenth century rainfall records, and statistical relationships among various sectors of Africa. Presented here are reconstructions of lake level fluctuations for numerous lakes of eastern and southern Africa.This overview of climatic fluctuations is utilized to uncover inherent spatial and temporal characteristics of the rainfall variability. The dominance over time of various spatial modes is emphasized and the questions of synchroneity of the hemispheres and the abruptness of change are considered. The contrast between the two hemispheres is also surveyed, notably the different time scales of variability and potential causal factors in the variability. One of the most important contrasts is the multi-decadal persistence of anomalies over most of northern Africa. This has implications for the causes of long-term fluctuations, even those historical and paleo-time scales.
Evidence for Late Quaternary changes in climate in the Namib Desert is geographically scattered and often poorly dated. The available evidence suggests periods of increased river discharge and groundwater flow centered on 8–12, 20–24, and 26–32 ka BP. Based on modern analogues, these palaeohydrologic changes likely involved increased rainfall and runoff in the escarpment zone east of the desert. There is little evidence to suggest significantly increased rainfall within the desert during these periods, except perhaps during the interval prior to 26 ka BP. These data reinforce earlier conclusions that the Namib has experienced mostly arid to hyperarid conditions throughout the Quaternary.
This paper documents the first Holocene palaeoecological record for the Okavango Delta, northwest Botswana. Sedimentological, stable carbon isotope and palynological data, supported by conventional and AMS radiocarbon assays, are presented from coring sites at Gauxa Lagoon and the Ncamasere and Tamacha valleys along the western margin of the Okavango Panhandle. Earliest Holocene vegetation patterns are not readily distinguished at the three sites, owing to poor pollen preservation conditions. A wet phase or period of enhanced Okavango flooding is tentatively identified around 9000 BP on the basis of increased accumulation of organic matter within floodplain sediments. Palynological and sedimentological data, combined with stable carbon isotope analyses, suggest that relatively dry conditions extended from 7000 to 4000 BP (punctuated by a wet phase at around 6000 BP). This is interpreted as indicating reduced rainfall over the Okavango headwaters in Angola. Conditions from around 4000 BP became progressively wetter, initially in response to increased water throughputs via the Okavango system. Wettest conditions occurred from 2300 to 1000 BP due to a combination of increased regional rainfall and raised Okavango flood levels. Conditions approach those of the present day after this time. A major shift from grass- to sedge-dominated vegetation communities, apparent at all three sites in the past thousand years, is attributed to anthropogenic disturbance. These changes are subsequently discussed in light of regional continental and marine palaeoenvironmental records, and the implications for the future management of the Okavango River considered.
We present well-dated high-resolution Holocene records of sea-temperature (SST) and upwelling intensity off northwest (NW) Africa. We identify long-term cooling trends over the Holocene in the subtropical North Atlantic in response to boreal summer insolation. A pronounced cooling event of ∼1 °C ca. 8.5 cal ka indicates a large-scale reorganization of the ocean current system possibly induced by meltwater from the northern North Atlantic. Our alkenone SST record off Cape Ghir provides strong evidence for the impact of ocean circulation changes on subtropical North Atlantic SSTs. It is likely that cold waters were propagated to the subtropics via the Canary Current in a way similar to Heinrich events and the Younger Dryas off Cape Blanc. We find 2-3 k.y. periodic variations in SST and upwelling intensity off NW Africa superimposed on the cooling trend. Such a cycle has been documented in various paleoclimate archives in phase with solar forcing. We show that these variations on millennial time scales are linked to the North Atlantic subtropical gyre circulation and the Northern Hemisphere atmospheric circulation, and in particular to changes in the pressure gradient between the Icelandic Low and the Azores High. This suggests that oceanic circulation, in response to solar forcing, played a more important role in the generation of 2-3 k.y. cyclicity than has been previously considered.
Direct observations of sunspot numbers are available for the past four centuries, but longer time series are required, for example, for the identification of a possible solar influence on climate and for testing models of the solar dynamo. Here we report a reconstruction of the sunspot number covering the past 11,400 years, based on dendrochronologically dated radiocarbon concentrations. We combine physics-based models for each of the processes connecting the radiocarbon concentration with sunspot number. According to our reconstruction, the level of solar activity during the past 70 years is exceptional, and the previous period of equally high activity occurred more than 8,000 years ago. We find that during the past 11,400 years the Sun spent only of the order of 10% of the time at a similarly high level of magnetic activity and almost all of the earlier high-activity periods were shorter than the present episode. Although the rarity of the current episode of high average sunspot numbers may indicate that the Sun has contributed to the unusual climate change during the twentieth century, we point out that solar variability is unlikely to have been the dominant cause of the strong warming during the past three decades.
Fossil assemblages from 53 packrat middens indicate which plant species were dominant during the last 24,000 years in the eastern Grand Canyon. Past vegetational patterns show associations that cannot be attributed to simple elevational displacement of the modern zones. A model emphasizing a latitudinal shift of climatic values is proposed.
Biological diversity in Namibia: Windhoek, Namibian National Biodiversity Task Force
- P Barnard
Barnard, P., 1998, Biological diversity in Namibia:
Windhoek, Namibian National Biodiversity
Task Force, Directorate of Environmental Affairs, 332 p.
Glacial temperatures and moisture transport regimes reconstructed from noble gas and δ 18 O, Stampriet aquifer, Namibia
- M Stute
- A S Talma
Stute, M., and Talma, A.S., 1998, Glacial temperatures and moisture transport regimes reconstructed from noble gas and δ 18 O, Stampriet
aquifer, Namibia, in Proceedings, Isotope
Techniques in the Study of Past and Current
Environmental Changes in the Hydrosphere
and the Atmosphere: International Atomic Energy Agency Vienna Symposium 1997: Vienna,
International Atomic Energy Agency Volume
SM-349/53, p. 307–328.