The Middle Stone Age (MSA) of southern Africa, and in particular its Still Bay and Howiesons Poort lithic traditions, represents a period of dramatic subsistence, cultural, and technological innovation by our species, Homo sapiens. Climate change has frequently been postulated as a primary driver of the appearance of these innovative behaviours, with researchers invoking either climate instability as a reason for the development of buffering mechanisms, or environmentally stable refugia as providing a stable setting for experimentation. Testing these alternative models has proved intractable, however, as existing regional palaeoclimatic and palaeoenvironmental records remain spatially, stratigraphically, and chronologically disconnected from the archaeological record. Here we report high-resolution records of environmental shifts based on stable carbon and oxygen isotopes in ostrich eggshell (OES) fragments, faunal remains, and shellfish assemblages excavated from two key MSA archaeological sequences, Blombos Cave and Klipdrift Shelter. We compare these records with archaeological material remains in the same strata. The results from both sites, spanning the periods 98–73 ka and 72–59 ka, respectively, show significant changes in vegetation, aridity, rainfall seasonality, and sea temperature in the vicinity of the sites during periods of human occupation. While these changes clearly influenced human subsistence strategies, we find that the remarkable cultural and technological innovations seen in the sites cannot be linked directly to climate shifts. Our results demonstrate the need for scale-appropriate, on-site testing of behavioural-environmental links, rather than broader, regional comparisons.

Funding: This research would not have been possible without financial support from the Clarendon Fund, University of Oxford, and a Natural Environmental Research Council studentship to PR. Financial support for the KDS and BBC projects was provided to CSH by a National Research Foundation/Department of Science and Technology funded Chair at the University of the Witwatersrand, South Africa, and by the University of Bergen, Norway.

Data Availability: Due to permit restrictions, photographs of the OES specimens sampled are available from the authors, following a review process by the Curator of the Iziko Museum, Wendy Black. All faunal and shellfish samples listed by quadrant and layer, respectively, are available in the Supporting Information S2 File . Further information can be obtained from JR, SB and KLvN.

Oxygen isotope fractionation between body water and CaCO 3 is about 30‰ (following the standard fractionation from H 2 O to CaCO 3 [ 33 ]). Although OES δ 18 O is influenced by the δ 18 O of rainfall source, given that ostriches obtain most of their body water from plants and recycled metabolic water [ 25 ], it is primarily influenced by 18 O-enrichment in plants due to evapotranspiration [ 18 – 21 ]. Evapotranspiration in leaves leads to preferential loss of 16 O and 18 O enrichment in the leaf [ 24 ]. The magnitude of this effect is enhanced by low relative humidity [ 26 , 34 ]. As a result, OES δ 18 O strongly reflects the influence of humidity or relative humidity (RH) over and above the regional controls exerted by meteoric water δ 18 O values [ 19 – 21 ]. OES will have more positive δ 18 O under conditions of increased aridity, while lower δ 18 O reflects greater humidity [ 19 – 21 ]. In the context of southern Africa, these evaporation-linked changes will have a much greater effect than any shifts in rainfall source or influence [ 11 , 35 ]. That said, given that the winter rainfall zone is associated with summer drought [ 19 , 36 ], expansion of C 3 biomes across the southern Cape coast, reflected in lower OES δ 13 C, will likely be associated with increased aridity, and higher δ 18 O, during the ostrich breeding period, which occurs just prior to a region’s rainy season [ 37 ].

δ 13 C values from the inorganic fractions of OES reflect the ambient vegetation consumed by the ostrich in the breeding season in which the eggs were laid [ 15 – 17 ]. The apparent δ 13 C fractionation between plant diet and eggshell CaCO3 (ε* plant-CaCO3 ) is c. 15‰ [ 16 – 17 ]. Ostrich preferences for fresh palatable vegetation mean that, while OES δ 13 C will not provide a direct indicator of local plant biomass, it will provide indirect insight into the proportions of C 3 , C 4 and CAM plants available in the surrounding landscape [ 18 ]. The intersection of precipitation-controlled vegetation zones for the last several million years on the southern Cape Coast means that stable isotope analysis of OES can track rainfall dynamics in the past ( Fig 1 ) [ 19 ]. Vegetation in the winter rainfall zone comprises mainly C 3 plants, with relatively low δ 13 C values (globally -24 to -32‰), while vegetation in the year-round rainfall zone includes some C 4 plants with higher (-10 and -14‰) δ 13 C values [ 22 , 31 ]. CAM plants in the C 3 -dominated winter rainfall zone of the southern Cape coast of South Africa today have ‘C 3 ’ δ 13 C, while those in the year-round rainfall region have δ 13 C, spanning C 3 and C 4 values [ 32 ]. As a result, any increase in CAM taxa will complement the emergence of C 4 plants in this region.

The ostrich, Struthio camelus australis, has been part of Africa’s vertebrate fauna since the Pliocene. Their eggs have been valued by hunter-gatherers of the MSA and LSA, as well as by many ethnographic groups, as indicated by their abundance in southern African archaeological sites, including BBC and KDS. Ostriches are opportunistic mixed-feeders and are one of very few animals known to eat C 3 , C 4 , and CAM vegetation [ 25 , 30 ]. They also show no particular preference for any of these groups and it is instead plant tenderness that dictates ostrich vegetation choice [ 30 ]. In order to facilitate adaptation to arid conditions, ostriches are non-obligate drinkers, with limited water excretion, and can survive on green vegetation without drinking for a number of days [ 25 ].

A) The position of sites discussed in this paper (1 = BBC, 2 = KDS, 3 = Nelson’s Bay Cave, 4 = Pinnacle Point) relative to the winter (to the left of the red line), year-round (between the red and orange lines), and summer rainfall (to the right of the orange line) zones of the modern southern Cape coast of South Africa on a map of % C 3 /C 4 plant species abundances (adapted from Vogel et al. [ 22 ]). B) A close-up view of the coastline proximate to BBC and KDS.

In this paper, we undertake stable carbon and oxygen isotope analysis of OES, alongside traditional faunal and shellfish environmental proxy analysis, from the MSA occupation levels of Blombos Cave (BBC) (98-73ka) (34°25’S, 21°13’E) and Klipdrift Shelter (KDS) (72–59 ka) (34°27’S, 20°43’E) in order to produce ‘on-site’ records of vegetation, precipitation seasonality, aridity, and sea temperature for the periods of human occupation ( Fig 1 ). A total of 83 and 42 fragments of OES were analysed from BBC and KDS, respectively. In addition to high densities of OES, rich faunal and shellfish assemblages at these sites provide further insight into terrestrial and marine environments of relevance to human ecologies, technologies, and cultural behaviours [ 27 – 28 ]. The archaeological sequences from these sites include both the Still Bay (76.7 ± 4.8–73.3 ± 4.5 ka- [ 29 ]) and Howiesons Poort (64.8 ± 4.8 and 59.5 ± 4.6 ka- [ 28 ]) traditions, and associated evidence of bone tool technologies, ochre production, and personal ornamentation [ 6 , 12 , 28 ].

One means of addressing this problem is the development of high-resolution palaeoenvironmental datasets from within, or in close association with, archaeological sequences (e.g. [ 11 ]). Although such records can potentially be subject to anthropogenic influence, they are easily dated and can be directly correlated with evidence of early human behaviour. Moreover, archaeological sites offer the potential for the rich and diverse preservation of multiple, independent palaeonvironmental proxies. Stable carbon and oxygen isotope analysis of ostrich eggshell (OES), ubiquitous at MSA and Later Stone Age (LSA) southern African sites, is one such proxy. OES δ 13 C reflects the ambient vegetation consumed by an ostrich during the breeding season [ 15 – 18 ], and δ 18 O, the ostrich’s source water [ 19 – 21 ]. In the southern Cape these parameters are controlled by both seasonality and amount of rainfall as the region is dissected by winter and seasonally-bimodal year-round precipitation zones [ 22 – 23 ]. Plants, which undergo 18 O enrichment during evapotranspiration [ 24 ], are the primary source of an ostriches’ water [ 25 ]. Fractionation due to evapotranspiration is negatively correlated to relative humidity [ 26 ]. Therefore, OES δ 18 O tracks shifts in relative humidity/aridity [ 19 – 21 ].

The punctuated nature of both the Still Bay and Howiesons Poort, and their chronological overlap with the Marine Isotope Stage 5a/4 and 4/3 transitions, respectively, has made climatic variability a particularly attractive focus for researchers. It has been argued that climatic and environmental instability immediately precedes or overlaps these periods, and new behavioural repertoires emerged as buffering mechanisms [ 11 – 13 ]. In contrast, it has also been suggested that climatic and environmental instability are not in phase with human behavioural changes, and cultural innovation instead occurred in hospitable refugia [ 2 ]. However, the evidence needed to test these hypotheses rigorously has been lacking. Research in the southern Cape of South Africa, where many of the important MSA sites bearing these industries are found, is currently limited by a general lack of well-understood palaeoenvironmental records with sound chronological control [ 14 ]. Where they do exist, they tend to remain spatially and chronologically disconnected from the archaeological sequences they have been used to explain, leading to broad generalisations and untestable correlations.

The Still Bay (c. 77–73 ka) and Howiesons Poort (c. 65–59 ka) Middle Stone Age (MSA) lithic traditions of southern Africa are argued to represent major periods of cultural, technological, and subsistence innovation by early Homo sapiens [ 1 – 3 ]. Sophisticated heat-treated, pressure-flaked technologies are associated with the Still Bay [ 4 ] while the origins of complex hafting technologies and hunting strategies have been associated with the backed stone segments of the Howiesons Poort [ 5 ]. Both the Still Bay and Howiesons Poort have also been linked to the earliest examples of material culture associated with symbolically mediated behaviour [ 6 ]. However, the factors behind their apparently sudden and widespread emergence and then disappearance remain hotly debated, with demography, sea level, and climate change all argued to have played major roles [ 7 – 10 ].

The BBC shellfish data consist of an enlarged sample (from an additional 7 quadrats) to that published previously [ 38 ]. The BBC shellfish data are from 261.4kg of shell fragments– 76.6kg from layers CF to CA (M1 and Upper M2 phases), 17.8kg from the CG layers (Lower M2 phase) and 167.1kg from layers CP to CH (M3 phase). These comprise a minimum number of 16,861 specimens (MNI). The enlarged sample did not significantly change densities reported previously. The KDS shellfish data used here are from Henshilwood et al. [ 28 ] and are from a 29kg sample with a total MNI of 999. Shellfish were analysed according to the methods outlined by Henshilwood et al. [ 28 , 38 ].

The assemblages were analysed following Driver [ 60 ] and Klein and Cruz-Uribe [ 61 ] using the comparative faunal collections of the Ditsong National Museum of Natural History (formerly the Transvaal Museum) in Pretoria. Only mammals the size of, or larger than, the Cape dune molerat (Bathyergus suillus) are included in this analysis. Taxa denoted as ‘cf.’ are included in this study. We use Skinner and Chimimba [ 62 ] to categorise ungulates into grazers, browsers and mixed-feeders. In our analysis, eland (Tragelaphus oryx) are classified as mixed-feeders due to their tendency to sometimes consume grass during summer [ 63 ]. Extinct taxa such as the blue antelope (Hippotragus leucophaeus), giant buffalo (Syncerus antiquus) and Cape horse (Equus capensis) were assigned dietary categories based on previous research [ 64 – 65 ]. Due to evidence of trophic flexibility of eland [ 63 , 65 ] and Raphicerus [ 66 ]–two of the most prominent bovids at BBC and KDS–we combine browsers and mixed-feeders.

Mammalian fauna from excavations at BBC spanning 2001–2010 from layers CH to CL (Phase M3) were analysed by SB. JR analysed further specimens from the 2011 and 2013 excavation seasons at BBC from layers CF to CA (the M1 and Upper M2 phases). Layer CG (the Lower M2 phase) was not analysed. A total of 3,783 specimens from the M3 and 948 specimens from the M1 and Upper M2 phases were identified to at least the class level. We also examined fauna from the 2011 and 2012 excavation seasons at KDS from layers PDC to PAU. Of the 35,864 specimens recovered from KDS, 2,266 (6.3%) could be identified to at least the class level. Piece-plotted specimens and faunal remains recovered from coarse fraction screened through 3mm sieves were analysed at both sites. Sample sizes for both BBC and KDS were relatively small because of the fragmented nature of the assemblages. For example, at BBC only 2.9% of the 32,546 specimens recovered from the M1 and Upper M2 were identifiable.

Statistical regression analyses were undertaken to discern the statistical correlation between δ 13 C and δ 18 O at both sites. The significance of δ 13 C and δ 18 O variation by layer and site was determined by ANOVA comparative tests for each isotope. Where variance was found to be significant, this was combined with a post-hoc Tukey-corrected pair-wise comparison to determine which layers were significantly different from each other. Given that ANOVA tests, and post-hoc Tukey comparisons, work best when even samples sizes are maintained, when applying this measure by site, the BBC dataset was split in two. Data from levels CC, CD, CF and CI were treated as BBC 1 and levels CJ, CK, CL and CN/CO were treated as BBC 2. All statistical analyses were conducted using the free programme R software.

Samples were cleaned on all edges using an air abrasion system. 5 x 5 millimetre pieces of OES were then removed from each sample using a craft knife. The ‘interior’ edge of these fragments was then sampled using a diamond-tipped drill. Samples were weighed out to approximately 0.150 mg using a Sartorius CP2 P microbalance, with the resulting powder transferred into glass vials with sealed lids. These vials were then placed in a heated tray maintained at 70°C. Following reaction with 100% Phosphoric Acid, gases evolved from the samples were analysed to stable carbon and oxygen isotopic composition using a Thermo Gas Bench 2 connected to a Thermo Delta V Advantage Mass Spectrometer in the Stable Light Isotope Facility, University of Bradford. Carbon and oxygen isotope values were compared against international standards registered by the International Atomic Energy Agency. Replicate analysis of an internal OES standard suggests that analytical error is c. ± 0.1‰ for δ 13 C and ± 0.2‰ for δ 18 O.

The curation and long-distance exchange of ostrich eggshell, notably in the form of beads, has been demonstrated ethnographically [ 57 – 58 ]. However, no evidence for this so far exists in the MSA or LSA records of southern Africa. Nevertheless, only plain fragments, and no beads, with no evidence for engraving or decoration were used in this study in order to avoid potentially curated and transported artefacts (with none existing at BBC regardless). In addition, given that the southern Cape coast provides an excellent environment for ostriches, and OES frequency is correlated with frequencies of grazing animal taxa at KDS [ 28 , 59 ], it seems likely that the OES sampled is representative of local subsistence opportunities and ostrich availability in the past. The OES analysed in this study is therefore likely representative of local, or at least, regional conditions.

Concerns have been raised regarding the movement of small OES fragments through an archaeological sequence as a result of burrowing action or bioturbation [ 55 ]. However, where finely excavated sequences have been available for the MSA, protein diagenesis dates from OES have been shown to complement those from other methodologies [ 55 ]. The refined, modern excavation methodologies applied during the new excavations at BBC and KDS ensure that the OES sampled in this study are from well-understood, firm contextual settings with no evidence for stratigraphic disturbance [ 28 , 56 ]. While Johnson et al. [ 16 – 17 ] demonstrate only small shifts in δ 13 C values of the inorganic and organic fractions with heating, obviously burnt samples are avoided where possible in this study.

OES isotopic values represent a very short period of ostrich plant consumption, and values can therefore vary between eggs laid at marginally differed times of year [ 15 – 17 , 52 ]. Furthermore, a number of female ostriches can contribute to a nest in any one year [ 53 ]. Each female may have slightly different dietary habits and, therefore, δ 13 C and δ 18 O values. To take into account this variation, the maximum number of available OES fragments were measured from each stratigraphic layer sampled (at least 7 and up to 12). This is a great advance on previous studies [ 54 ] and follows Ecker et al. [ 20 ] and Lee-Thorp and Ecker [ 21 ]. The samples analysed in this study are listed in Table C and Table D in S1 File . δ 13 C and δ 18 O values from each site were also examined in bivariate plots to avoid including two samples from the same egg in statistical analysis (Figure A and Figure B in S1 File ).

356 pieces of ochreous material have been recovered from KDS. By mass, PBE has the highest concentration of red ochre in the assemblage (847.6g), although much of this consists of finely processed pieces weighing less than 0.1g. PBE also represents the highest concentration of red ochre, derived from a more limited focus on certain geological types, and is argued to represent the deliberate processing of large amounts of ochre for very specific purposes. By contrast, PBC exhibits the widest geological variability in the sequence [ 28 ]. Ninety-five fragments of deliberately engraved OES have also been recovered from layers PAY to PCA (3.8% of the total number of OES fragments), with the majority coming from PBC and PBD [ 28 ].

While the KDS tools are typical of the Howiesons Poort of southern Africa, three main technological phases can be observed within the sequence [ 28 ]. The lowermost phase (PCA, PBE) is characterised by the predominant exploitation of silcrete for blade production, the prevalence of notched tools, the presence of strangulated blades and of highly standardized truncated blades. The following phase (PBC, PBA/PBB) is marked by an increase in quartz exploitation that becomes the most common raw material, while backed tools, including typical segments constitute the main tool group. The uppermost phase (PAY) is defined by the predominance of quartzite, an increase in blade size, the emergence of an independent and structured flake production based on a Levallois concept, a decrease in backed tools, and the presence of a few unifacial points. This phase could be interpreted as a transitional layer towards the post-HP [ 28 ].

The uppermost dated layer yields an SG-OSL age of 51.7 ± 3.3 ka, the middle layers containing Howiesons Poort-type industries range from 65.5 ± 4.8 to 59.4 ± 4.6 ka and the lowermost excavated, anthropogenically sterile layers give an age of 71.6 ± 5.1 ka [ 28 ]. Although layer PDA is dated to between c. 71.6 and 63.5 ka, the remainder of the OES sequence is dated to between c. 65.5 and 59.4 ka ( Fig 3 ) (Table B in S1 File ).

The Klipdrift Cave complex is a wave cut platform located 19 metres above sea level in a steep quartzite cliff (34°27.0963’S, 20°43.4582’E) in the De Hoop Nature Reserve, 12–15 metres from the Indian Ocean and 45 kilometres west of BBC. KDS is a c. 7 metre deep shelter, separated from a larger, western cave area by a promontory. KDS was first excavated in 2011 with subsequent seasons in 2012 and 2013.

The similarity of SG-OSL ages between the different layers of phase M3 suggests that the deposits accumulated over a short time interval in the middle part of Marine Isotope Stage (MIS) 5 between about 107 and 90 ka (MIS 5c to 5b) (Table A and Table B in S1 File ). There is no support for a significant difference in timing between layers CJ and CH/CI as previously suggested by Jacobs et al. [ 51 ], following re-analysis of sample ZB5 [ 29 ]. An SG-OSL date from the CQ hiatus sand layer of 143.2 ± 4.5 ka provides a terminus post quem for initial occupation of the site. Lithics are abundant in phase M3 though no bone tools have yet been recovered from this phase [ 50 ]. Modified ochre is common, with eight slabs demonstrating deliberate engravings [ 46 ]. Finds of two Haliotis midae shells containing a pigment-rich compound and associated artefacts forming part of a toolkit has led to claims that the site was used as an ochre processing workshop during part of this phase [ 39 ].

Although Multi-grain OSL and a Thermoluminescence date on burnt silcrete exist for the lower M2 phase [ 49 ] (Table A in S1 File ), here we use a more recent SG-OSL determination of 77 ± 3 ka to date this phase (Table B in S1 File ). Bone technology, bifacial points, and shell beads are absent from the lower M2 phase. The intensity of cultural deposits is low in this phase, without any evidence for the deliberate engraving of ochre pieces, and human occupation of the site was likely of short duration and representative of small group sizes at this time [ 38 , 50 ].

More than 2,000 pieces of ochre have been recovered from the Still Bay phases. Two ochre pieces with deliberately engraved cross-hatched patterns come from the M1 phase [ 45 ]. The designs clearly result from deliberate action and have been considered among the earliest abstract representations [ 45 – 46 ]. A further six engraved ochre pieces from these phases have been recovered [ 46 ]. Microscopic analysis of a bone fragment has revealed that it was also deliberately marked with eight parallel lines [ 47 ]. The discovery of 65 Nassarius kraussianus shell beads in the Still Bay phases of BBC is synonymous with personal ornamentation, and use-wear analysis indicates they were hung on a cord or sinew [ 44 , 48 ].

The Still Bay-type bifacial points from the M1 and upper M2 phases of BBC are made from silcrete, quartzite, and quartz. A macrofracture study of these points shows that while some were used as spear points, others probably served as multifunctional tools [ 41 ]. Approximately half of the silcrete points were heat treated and finished using pressure-flaking methods [ 42 ]. More than thirty formal bone tools have also been recovered from the Still Bay levels [ 38 , 43 ]. Some of the bone tools were polished after being shaped and scraped and have been suggested to be hafted projectile points [ 44 ].

The M1 and upper M2 phases contain Still Bay-type bifacial foliate points in association with evidence for shell beads, formal bone tools, engraved bone and ochre. Thermoluminescence (TL) dates from burnt lithics, Electron-Spin Resonance (ESR) age estimates on faunal tooth enamel [ 40 ], and four Multi-Grain Optically Stimulated Luminescence (OSL) ages from the M2 phase previously indicated a range between 80 and 60 ka (39) (Table A in S1 File ). More recent Single Grain Optically Stimulated Luminescence (SG-OSL) assessments, however, now suggest that these phases began no earlier than 75.5ka and ended no later than 67.8 ka [ 29 ] (Table B in S1 File ) ( Fig 2 ).

BBC is located in Blombosfontein Nature Reserve, about 300km east of Cape Town on the southern coast of South Africa (34°25’S, 21°13’E). The cave is positioned on a south-facing cliff c. 35m above modern sea level, approximately 100 metres from the present shoreline [ 38 ]. BBC is set into the calcified sediments of the Tertiary Wankoe Formation, and the calcareous environment is at least partially responsible for the good preservation of the recovered deposits [ 38 ]. In particular, the MSA sequence of BBC represents one of the longest and richest sequences of early subsistence, technological, and cultural innovations by Homo sapiens worldwide. The MSA levels of BBC are divided into three phases: M1, M2 (upper and lower), and M3 (Table A in S1 File , Fig 2 ).

Results and Discussion

Changes in vegetation, precipitation source, and precipitation amount on the southern Cape coast of South Africa (98-59ka) Late Pleistocene δ13C records from faunal tooth enamel and speleothems on the southern Cape coast of South Africa have been used to track changes in the regional proportion of C 3 and C 4 plant taxa and, indirectly, shifts in the seasonality of rainfall [11,67]. While further East, at Nelson’s Bay Cave, Sealy showed little change in the local proportions of these taxa over the last 20,000 years [67], closer to BBC and KDS, at Pinnacle Point, Bar-Matthews et al. [11] argued that the considerable shifts in speleothem δ13C were indicative of substantial changes in seasonal rainfall influence between 90 and 53 ka. OES δ13C data from the sites of BBC and KDS show significant change over the period 98–59 ka but, compared to changes in δ13C enrichment seen in the nearby Pinnacle Point speleothem record, they are muted. This difference may be due to the fact that ostrich diets will not necessarily fully reflect shifts in C 4 plant availability at this time [21]. In addition, higher OES δ13C can record aridity-dependent changes in C 3 grass δ13C, or CAM presence, associated with changes in local aridity, rather than rainfall seasonality [19,21]. As with the OES δ18O measured here, δ18O values from the Pinnacle Point speleothem record also show fluctuations during this time that have been interpreted as being driven by changes in rainfall source [11]. Compared to the speleothem record, however, our OES data demonstrates more dramatic δ18O fluctuations between 98–59 ka that cannot be accounted for by winter and summer rainfall ‘source’ effects even at their extremes (following West et al. [35]). This is unsurprising given that while speleothem δ18O is reflective of changes in groundwater, and therefore predominantly precipitation, OES δ18O is strongly influenced by the evaporative potential of plant transpiration in the region [17–21]. Lowest OES δ13C and δ18O measurements occur at the beginning of the BBC sequence, suggestive of humid, winter rainfall conditions at this time. Between at least 90 ka to c. 73 ka the sequence demonstrates higher δ13C and δ18O, indicative of increasing aridity and, potentially also, increased year-round rainfall influence or aridity-linked CAM presence. From c. 72 to 59 ka at KDS substantial fluctuations in δ13C and δ18O values imply that this was a period of great instability in plant evapotranspiration, humidity/aridity, and seasonal rainfall dynamics.

Comparison of OES δ13C and δ18O, faunal, and shellfish records Bar-Matthews et al. [11] argue that the coincidence of change in speleothem δ13C and δ18O between 97 and 68 ka, and a substantial period of climatic instability between 68 and 60 ka, at Pinnacle Point, is illustrative of increasing aridity during times of greater summer rainfall influence on the southern Cape coast. This contrasts with suggestions that the winter rainfall zone expanded across the southern Cape coast during glacial periods [23]. Our OES record also demonstrates simultaneous changes in δ13C and δ18O between c. 100 and 59 ka. The combination of our data with faunal and shellfish environmental proxy datasets, however, enables us to tease apart the primary influences on OES δ13C on the southern Cape coast through time. At BBC, enrichment in δ13C follows increased proportions of the warm water shellfish indicator species Cymbula oculus (Fig 4). Warmer waters on the southern Cape suggest suppressed upwelling, lower influence of easterlies and concomitant increasing influence of westerly winds and winter rainfall [68]. Just prior to OES δ13C enrichment at the end of Phase M3 there is also an increase in browser/mixed feeder, rather than grazer, taxa perhaps associated with C 3 presence and winter rainfall (Fig 4) (Table M and Table N in S1 File). Increased OES δ18O indicates increased aridity at this time and, overall, it is likely that OES δ13C enrichment also documents this increased aridity, perhaps in the form of increased CAM presence, and increased summer drought strength in the winter rainfall zone, rather than an increase in C 4 vegetation and summer rainfall influence at this time. By contrast, enrichment in OES δ18O, indicative of increased aridity, at KDS during MIS 4 is associated with increased relative proportions of the cold-water shellfish taxa, Cymbula granatina (Fig 4). Colder waters suggest an increased prevalence of near-shore upwelling, easterly winds and summer rainfall at this time which could lead to increased C 4 presence in the region [68]. Furthermore, unlike BBC, enrichment in OES δ13C in layer PBC is accompanied by higher numbers of grazing taxa that dominate the faunal assemblage at this time (Fig 4) (Table O in S1 File). This indicates that in this instance OES δ13C enrichment is indicative of increased C 4 grassland resources in the region. As a result, it seems that the relationship between changing aridity and rainfall regime influence is more complex and context-specific than has previously been suggested [23].