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Journal of Arid Environments 74 (2010) 870–884

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Journal of Arid Environments

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A 35 ka pollen and isotope record of environmental change along thesouthern margin of the Kalahari from a stalagmite and animal dungdeposits in Wonderwerk Cave, South Africa

G.A. Brook a,*, L. Scott b, L.B. Railsback c, E.A. Goddard d

a Department of Geography, University of Georgia, Athens, GA 30602, USAb Department of Plant Sciences, University of the Free State, Bloemfontein, 9300, South Africac Department of Geology, University of Georgia, Athens, GA 30602, USAd College of Marine Science, University of South Florida, 140 7th Avenue South, St. Petersburg, FL 33701, USA

a r t i c l e i n f o

Article history:Received 11 June 2009Received in revised form9 November 2009Accepted 23 November 2009Available online 23 December 2009

Keywords:ArchaeologyCavesDungPaleoclimatePollenSouthern AfricaSpeleothem

* Corresponding author. Tel.: þ1 706 542 2322; faxE-mail addresses: gabrook@uga.edu (G.A. Brook),

rlsbk@gly.uga.edu (L.B. Railsback), egoddard@marine.

0140-1963/$ – see front matter � 2009 Elsevier Ltd.doi:10.1016/j.jaridenv.2009.11.006

a b s t r a c t

A 0.6-m-long horizontal core from a stalagmite in the entrance area of Wonderwerk Cave in South Africa,a National Heritage Site, has provided a 35 ka record of environmental change. A pollen sequence fromthe stalagmite, and two animal dung deposits, is longer and more detailed for the end of the Pleistocenethan previous palynological reports from the southern Kalahari region. This pollen record closelymatches information from spring peats at Wonderkrater in Northern Province indicating that speleo-them pollen can provide reliable paleovegetation data. The d18O and d13C records resemble those fromCold Air Cave in Northern Province and parallel variations in Greenland Ice Sheet GISP2 paleotemper-ature. This indicates that past climate changes in southern Africa were linked to changes in globalatmospheric and oceanic circulation patterns possibly triggered by conditions in the North Atlanticregion. The Wonderwerk data suggest wetter conditions at ca. 33 ka, from 23 to 17 ka, and from 4 ka topresent. Conditions were drier 17–13 ka, when microstromatolitic carbonate was deposited on the flankof the stalagmite, and possibly also during depositional hiatuses from 33 to 23 ka and 13 to 4 ka.

� 2009 Elsevier Ltd. All rights reserved.

1. Introduction

There are few high-resolution records of climate change forsouthern Africa and, because of the predominantly semiarid envi-ronment, few sediment types suitable for pollen analysis. However,the sub-continent has caves containing speleothems (e.g. Holmg-ren et al., 2003) and these deposits have provided high-resolutionclimate records for many other parts of the world based largely onvariations in d18O and d13C values of the speleothem carbonate (e.g.Denniston et al., 2000; Fleitmann et al., 2003; Wang et al., 2008;Webster et al., 2007). However, there have been relatively fewstudies of speleothems that have incorporated pollen analysis(Bastin, 1978; Bastin et al., 1982; Bastin and Gewelt, 1986; Brookand Nickmann, 1996; Brook et al., 1987, 1990a,b; Burney et al., 1994;Caseldine et al., 2007; Scott and Bonnefille, 1986). This is despiteresearch showing that modern pollen deposition on stalagmites is

: þ1 706 542 2388.scottl.sci@ufs.ac.za (L. Scott),usf.edu (E.A. Goddard).

All rights reserved.

a reliable indicator of the local vegetation (e.g. Burney and Burney,1993).

The objective of this research is to obtain paleoenvironmentaldata from the petrography, stable isotope geochemistry, and pollenof a massive stalagmite (W-1) in the entrance to Wonderwerk Cavein South Africa. Wonderwerk Cave is a National Heritage Site soinformation was obtained from a horizontal core drilled from thestalagmite, an approach that minimized damage to the stalagmiteand cave (Brook et al., 2006).

2. Wonderwerk Cave

Wonderwerk Cave (27� 500 4600 S; 23� 330 1900 E; w1680 ma.s.l.) is 45 km south of Kuruman in the Northern Cape Provinceof South Africa (Fig. 1). It extends horizontally about 140 m intothe base of a hill on the eastern flank of the Kuruman Hills of theGaap Escarpment. The cave is a large (w2400 m2) solution cavity,averaging 17 m wide, that erosion has exposed at its northernend (Fig. 2). The cave is developed in stratified dolomitic lime-stones overlain by banded ironstones of early Proterozoic–lateArchaean (2–3 Ga) age (Kent, 1980). Wonderwerk is an important

Fig. 1. Location of Wonderwerk Cave and other sites mentioned in the text. WW ¼Wonderwerk; CA ¼ Cold Air Cave; WO ¼Wonderkrater; WI ¼Witpan; AL ¼ Alexandersfontein;CC ¼ Cango Caves (adapted after Rutherford, 1997).

G.A. Brook et al. / Journal of Arid Environments 74 (2010) 870–884 871

archaeological site that was used as far back as the Oldowan(ca. 1.8 Ma) (Chazan et al. 2008). It contains evidence of fire useat 1 Ma and it appears that grasses were brought into the cave tocreate a bedding surface around 400 ka ago (Beaumont andVogel, 2006). The cave may have been abandoned from ca. 70 to12.5 ka, possibly due to a decline of regional rainfall by up to 60%of present values (Beaumont and Vogel, 2006).

Wonderwerk lies near the boundary between the Nama-Karoo,Grassland, and Savanna ecosystems (Fig. 1). The vegetation type isKuruman Mountain Bushveld (SVK10) with typical small trees andshrubs Rhus lancea, Rhus pyroides, Rhus tridactyla, Rhus ciliata,

Fig. 2. Map and section of Wonderwerk Cave showing the location of the large entrance st1992. The small arrows show the coring site on the stalagmite and indicate the direction of dlocations and extent of all seven excavations in the cave.

Diospyros autro-africana, Euclea crispa, Olea europaea, Tarchonan-thus camphoratus, Anthospermum rigidum, Helichrysum zeyheri,Wahlenbergia nodosa and a variety of grass species (Mucina andRutherford, 2006). The climate is semiarid mesothermal (Schulze,1984) with a mean annual rainfall of 420 mm coming primarily(80%) in the summer months.

Stalagmite W-1 is located 20 m into the 7 m high and 15 m wideentrance to the cave (Figs. 2 and 3A). It rises 2.8 m above the cavefloor and is 2 m in diameter at the base (Fig. 3A). In the walls ofexcavation 1 it can be seen to grade into cemented clastic sedi-ments (Fig. 3B).

alagmite and archaeological excavation 1 that was dug at different times from 1948 torilling. The map is modified from Fig. 2 of Beaumont and Vogel (2006), which shows the

Fig. 3. The large entrance stalagmite (W-1) in Wonderwerk Cave and drilling the core. (A) View into the cave showing the irregular shape of W-1. The cave is a horizontal, bedding-plane tunnel developed at the intersection of the vertical joint and a major bedding surface in dolomite. (B) The electrical drilling rig set up in excavation 1 to drill a core from theback of the stalagmite. During drilling the drill stem is cooled with water that has flowed down the north wall of the excavation.

Fig. 4. Variations in age, color, petrography, and stable isotopes along the Wonderwerkcore, and the locations of pollen samples. L ¼ layered fabric; C ¼concretionary fabric;M ¼microstromatolitic fabric; A ¼ layers of aragonite. Note the significant gaps in ageat 45 cm (ca. 33–23 ka) and at 7.5 cm (ca. 13.4–4 ka).

G.A. Brook et al. / Journal of Arid Environments 74 (2010) 870–884872

3. Methods

In 1999 a core was obtained by drilling horizontally into theback of the W-1 stalagmite (side facing into the cave) from the floorof excavation 1, which at the time of drilling was only about 1 mdeep (Figs. 2 and 3B). The 0.6 m long and 5 cm diameter core wascut vertically in the laboratory and one half was cut horizontallyinto two quadrants. One quadrant was cut into 32, w2 cm longslabs (9.3–23.3 g) for pollen analysis; thin sections were preparedfrom the other quadrant (Fig. 4). The pollen samples were dissolvedin 10% HCl and the organic fraction was separated by means ofheavy liquid (ZnCl2, specific gravity 2).

In view of the low pollen concentrations, a small degree ofcontamination of modern airborne pollen during sample handlingwas expected (Scott and Bonnefille, 1986). These included exoticPlatanus grains presumably from trees near the University of theFree State laboratory where the samples were processed. However,contaminants had a fresh appearance (light color and cell inclu-sions that were not removed by the mild chemical treatment) andwere easily distinguished from fossil pollen grains. For comparisonwith the stalagmite pollen spectra and improvement of the generalpollen sequence in the cave, two urine-impregnated dung depositsfrom deeper in the cave were included in the study. DUNG-A isa previously dated dung deposit about 17 cm thick that containedseveral bone fragments more than 1 cm long (Scott et al., 1995).DUNG-B is about 7 cm thick and contained only minute specks ofbone. The larger bones in DUNG-A suggest porcupine activity butboth deposits could be partly derived from hyraxes, rats or othersmall mammals.

Seventeen samples were cut for radiocarbon dating (14 radio-metric and three AMS) from the remaining intact half of the core(Fig. 4). Assuming a linear growth rate during the late Holocenesection of the core, we obtained a regression relationship of age(103 yr BP) ¼ 0.966 þ 0.521 (distance in cm) using Libby agescorrected for isotopic fractionation. Therefore, the most recentlydeposited carbonate gives an apparent age of about 966 14C yr BPdue to incorporation of old carbon into the carbonate. Based on this,all radiocarbon ages for the core were corrected for the addition ofabout 12% old carbon from the overlying bedrock by subtracting1000 years from the Libby age before calibration. Sample ages were

calibrated using OxCal version 4 (Ramsey 1995, 2001, 2009). TheSouthern Hemisphere (SHCal04) atmospheric calibration curve ofMcCormac et al. (2004) was used for ages in the range 0–11 ka butbeyond this range it was necessary to use the Northern HemisphereIntCal04 curve of Reimer et al. (2004). Ages beyond the range ofIntCal04 data were corrected using the Fairbanks 0107 coralcalibration curve (Fairbanks et al., 2005). In comparing our data

G.A. Brook et al. / Journal of Arid Environments 74 (2010) 870–884 873

with information from other sites, we first calibrated any publisheduncalibrated ages using the same methods.

Samples for isotope analysis were drilled at intervals of 0.2 cmor less in the outer, most recent, proximal part of the core, and thenabout every 1.0 cm from 11 to 54 cm. The distal part of the core(the inner part of the stalagmite) was not sampled due to thepredominance of clastic material. Isotope samples were reactedunder vacuum with distilled 100% orthophosphoric acid (H3PO4) at50 �C following McCrea (1950) and Al-Aasm et al. (1990). CO2 wascollected by conventional cryogenic methods and analyzed ona Finnegan Delta E stable isotope ratio mass spectrometer. Instru-ment precision (1s) was 0.05–0.07& for d18O and 0.01–0.08& ford13C and method precision (1s) 0.12& for d18O and 0.05& for d13C.

Fig. 5. Age–distance relationships in the Wonderwerk core and periods of low or nogrowth at the core location. The hiatuses in growth lasted from ca. 33 to 23 ka and ca.13.4 to 4 ka.

4. Results

4.1. Chronology and rates of deposition

Radiocarbon ages show that the core was deposited from 35 kato the present but not continuously (Table 1). In fact, stratigraphicand chronologic data indicate very slow deposition or no deposi-tion at w33–23 ka (48–42 cm) and w13.3–4 ka (8.25–7 cm) andalong with the lack of pollen in carbonate dating to w13.3 ka thismay suggest drier conditions at these times (Fig. 5). If W-1 wasdeposited only under wetter climatic conditions, the age dataindicate increased moisture at 35–33 ka, 23–13.3 ka and 4 ka topresent. Ages for the core indicate that rates of deposition alongone horizontal radius of the stalagmite were 4.67 cm/ka from 33.3to 34.8 ka, 3.45 cm/ka from 22.8 to 13.3 ka, and 1.79 cm/ka from3.9 ka to present, implying slightly drier conditions in the lateHolocene than during the other two phases of growth. DUNG-B wasdeposited from 14.5 to 13.1 ka when the stalagmite was activelygrowing. By contrast, DUNG-A falls in a hiatus period of thestalagmite sequence (Table 1). Ages for pollen samples from the

Table 1Radiocarbon ages for the Wonderwerk stalagmite core and dung deposits.

Sample ID Lab ID Distance/depth(cm)

d13C(& PDB)

Stalagmite agesWW3-0 UGA-6385/1 0.5 �0.9WW3-1 UGA-6385 1.5 �2.0WW3-3 R13729 2.75 �1.5WW3-5 R13730 5.25 0.1WW3-7 UGA-6385/2 7.0 �0.2WW3-8 R13731 8.25 �1.0WW3-10 CEEA-1 9.5–10.5 �0.1WW3-11 CEEA-2 10.5–11.5 �0.7WW3-14 UGA-6386 14 �0.1WW3-20 CEEA-3 19.5–21 �2.3WW3-22 UGA-6397 22 �5.2WW3-22.5 Beta-108650 22.5 �1.1WW3-32 CEEA-4 31.5–33.5 �4.2WW3-41 CEEA-5 40–42 �2.3WW3-48 UGA-6385/3 48.0 �1.8WW3-55 CEEA-6 55 �2.0

Dung agesDUNG-A1 Pta-6626 0–5DUNG-A2 Pta-6273 15–20

DUNG-B4685.5 UGA-R02306 6–7 �18.9DUNG-B4685.4 UGA-R02305 1–2 �21.1

a Stalagmite sample ages were corrected for incorporation of old carbon by subtractinb Calibrated using using the IntCal04 Northern Hemisphere atmospheric data set of Rc Calibrated using the SH04 Southern Hemisphere atmospheric data set of McCormacd Calibrated using the Fairbanks 0107 calibration curve (Fairbanks et al., 2005).

W-1 core and dung samples were interpolated by assumingconstant deposition rates between bracketing ages.

4.2. Petrography

Stalagmite W-1 is largely spelean calcite, with two layers ofspelean aragonite in the outermost and thus latest part of the core.There is also abundant fine-grained (clay-sized) detrital material, aswell as scattered silt-to-sand size detrital tectosilicate (quartz andfeldspar) grains. Some detrital carbonate grains in the size range ofsilt to sand can also be recognized where, for example, twinningand/or rounding distinguishes them from untwinned spelean

Libby age(yr BP)

Libby agecorrected forold carbona

Calibratedcorrected Libbyages (cal yr BP)(95.4%)

Centralcalibrated age(ka BP)

970 � 39 Recent Recent Recent2061 � 93 1061 � 93 1167–733c 0.92429 � 45 1429 � 45 1372–1180c 1.33593 � 48 2593 � 48 2757–2368c 2.64633 � 48 3633 � 48 4069–3706c 3.9

12458 � 67 11458 � 67 13439–13195b 13.312950 � 220 11950 � 220 14576–13313b 13.913500 � 225 12500 � 225 15275–13939b 14.614259 � 104 13259 � 104 16178–15297b 15.713850 � 150 12850 � 150 15720–14669b 15.212097 � 111 11097 � 111 13201–12866b 13.015420 � 120 14420 � 120 17875–16789b 17.317100 � 140 16100 � 140 19496–18996b 19.220050 � 275 19050 � 275 23551–22114b 22.828968 � 173 27968 � 173 33332 � 240d 33.3 � 0.230400 � 900 29400 � 900 34798 � 914d 34.8 � 0.9

10300 � 100 12611–11709b 12.210400 � 45 12587–12086b 12.3

11198 � 58 13216–12960b 13.112394 � 63 14824–14116b 14.5

g 1000 years from the Libby age.eimer et al. (2004).et al. (2004).

G.A. Brook et al. / Journal of Arid Environments 74 (2010) 870–884874

calcite (Fig. 6). Such grains may be abundant, but only occasionallyrecognized, amidst the spelean calcite of the entire stalagmite.

The core can be divided into three kinds of fabric on the basis ofpetrography and structure. ‘‘Layered’’ fabric is typical of the mostrecent portion of the core and is present in lesser abundancethroughout the core (Fig. 6A and ‘‘L’’ in Fig. 4). It consists of planarlaminae typically 0.015–0.20 mm thick. Thicker layers are typically

Fig. 6. Photomicrographs of the Wonderwerk stalagmite, all at the same scale. (A) Layered fmarked with a black arrow. (B) Microstromatolitic fabric. C ¼ clear calcite; V ¼ void spacefeldspar); V ¼ void space. (D) Surface (marked with black arrow) at which underlying laye

clearer, whereas many thin layers contain more fine detritalmaterial or are more commonly capped by distinct layers of finedetrital material. Detrital tectosilicate grains as large as 0.15 mm indiameter (the size of fine sand) are present but constitute less than1% of this type of fabric.

A second type of fabric consists of small columns of layeredcalcite and can be described as ‘‘microstromatolitic’’ (Fig. 6B and

abric of planar laminae. All of the CaCO3 shown is calcite, except for a layer of aragonite. (C) Concretionary fabric of spheroidal structures. S ¼ silicate grains (either quartz orrs are truncated.

G.A. Brook et al. / Journal of Arid Environments 74 (2010) 870–884 875

‘‘M’’ in Fig. 4). The columns are 0.3–1.2 mm wide and 2.1–10.8 mmhigh. The laminae forming them are sharply concave downward, inthe manner of a stromatolite. Spaces between columns were voidsthat were filled with clear calcite, or with detrital tectosilicategrains.

A third type of fabric consists of laminae that curve locally and,in some cases, curve to form spheroidal structures up to 4.1 mm indiameter. This fabric is termed ‘‘concretionary’’ (Fig. 6C and ‘‘C’’ inFig. 4). Laminae curve irregularly and are in some places truncatedat surfaces resembling the angular unconformities of large-scalestratigraphy. In transmitted light, clay-rich laminae in the concre-tionary fabric are much more opaque than in the layered ormicrostromatolitic fabrics, suggesting that clay-sized detritalmaterial is more abundant in the concretionary fabric. Detritaltectosilicate grains as large as 0.2 mm in diameter locally make upas much as 3% of concretionary fabric, but overall they are at most1% of that fabric.

These fabrics are not distributed uniformly through the core. Forexample, concretionary fabric constitutes 68% of the innermost(earliest) 40 cm of the core but it is not present in the outer (latest)24 cm. Layered fabric, on the other hand, is the only fabric presentin the final 11 cm of the core, and it is locally present throughoutthe rest of the core. Microstromatolitic fabric is highly localized,being present only in one continuous zone 11 cm thick in the outerand thus later half of the core, between two zones of layered fabric.

At least some petrologic zones can be correlated with variationsin ratios of stable isotopes (Fig. 4). Most strikingly, the longest zoneof concretionary fabric, which is in the middle of the core, coincideswith the interval with sustained low values of d13C from 38 to23 cm from the outer surface of the core and is within the intervalof low d18O values from 38 to 18 cm from the outer surface. Bycontrast, d13C and d18O are generally greater and have much greatervariance in parts of the core that include layered and micro-stromatolitic fabric.

The layered fabric in the Wonderwerk speleothem is typical ofstalagmites and presumably reflects growth above the cave floor.The layered fabric’s low content of detrital grains and greatestabundance late in the core are consistent with that hypothesis. Thelayered fabric would thus seemingly represent periods in whichdrip water was sufficient to maintain at least some flow over thespeleothem that precipitated layers of generally even thickness.

The microstromatolitic fabric appears to be a modification oftypical stalagmite growth but with a surface expression like that ofcave popcorn. Development of cave popcorn is commonly the resultof evaporation (Hill and Forti, 1997, pp. 60––61), and so themicrostromatolitic fabric may represent conditions drier than thoseunder which layered fabric formed. The microstromatolitic fabric’shigh content of detrital grains may be the result of trapping ofgrains on the very irregular speleothem surface left after develop-ment of that fabric’s topography.

The irregular nature of the concretionary fabric is reminiscentof the fabric of many calcretes (pedogenic carbonates). That,combined with the concretionary fabric’s high content of detritalmaterial, suggests that it may have originated in precipitation ofCaCO3 within sediment on the cave floor, and in sediment thatperiodically covered the stalagmite while it was small. Truncationof speleothem layers in the concretionary fabric (Fig. 6D) suggestsabrasion of the surface of the speleothem, perhaps by flowingwater, and inclusion of tectosilicate grains in the size range of veryfine to fine sand so far back in the cave (beyond the range of aeoliantransport) suggests either transport of sand by water flowingthrough the cave or delivery of sand by gushing ‘‘drip’’ waters fromthe ceiling of the cave. Such wetter conditions would also beconsistent with lower values of d18O, in that many studies haveshown a correlation between lower d18O of rainfall and greater

amounts of rainfall. (Araguas-Araguas et al., 1998; Gonfiantini et al.,2001; Lachniet and Patterson, 2006; Njitchoua et al., 1999; Rietti-Shati et al., 2000; Vuille and Werner, 2005). Wetter conditions forthe formation of concretionary fabric might also be consistent withlower values of d13C, for two reasons. Firstly, wetter winter oryear-round conditions might allow a greater proportion of C3

vegetation, which has a lower d13C than the C4 vegetation commonin hotter, drier or summer-rain climates (Brook, 1999; Vogel et al.,1978). Alternatively, wetter conditions might allow more produc-tion of biologically-fractionated soil CO2, and thus a greaterproportion of 13C-poor CO2 mixed with atmospheric CO2 andbedrock carbon, in the dissolved bicarbonate delivered by dripwater to the speleothem.

In summary, petrologic characteristics indicate three principalfabrics in the W-1 stalagmite that were deposited under differenthydrologic conditions. Layered fabric is considered to representrelatively dry conditions when flow of at least a thin film of dripwater over the speleothem produced regular spelean layers, butwater delivered only a few detrital grains larger than clay particles.Microstromatolitic fabric suggests a modification of those dryconditions, either when climate was slightly drier or whenevaporation on the speleothem was enhanced by local patterns ofair flow. In contrast, concretionary fabric appears to record timeswhen water flowing or gushing at least episodically through thecave deposited large quantities of sediment. The presence ofmicrostromatolitic fabric only between intervals of layered fabric,rather than in continuity with concretionary fabric, is also consis-tent with the notion that microstromatolitic and concretionaryfabrics represent extremes of at least local, if not regional, deposi-tional conditions and that layered fabric represents an intermediatecase between the two.

4.3. Isotopes

4.3.1. Carbon isotopesStalagmite 13C is influenced by: (1) hydrological conditions above

the cave that affect the exchange of C isotopes between meteoricwaters and the bedrock; (2) the composition and biomass of thevegetation above the cave; and (3) kinetic fractionation of carbon inprecipitating waters, particularly due to rapid CO2 outgassing(McDermott, 2004; Quade, 2004). Open-system groundwater flowconditions promote the exchange of carbon dissolved from thebedrock (d13C ¼ þ1&) with carbon in soil air derived from plantrespiration and decomposition. This minimizes enrichment of 13C indissolved species (particularly CO3

� and HCO3�). Under closed-system

conditions, contact with soil CO2 is quickly shut off as the water flowsrapidly into the limestone. There is no further exchange with soil CO2

after limestone dissolution and so dissolved species are enriched in13C relative to the open-system case.

The d13C of cave drip waters can also be affected by the d13C ofthe CO2 in the soil above the cave (e.g. Talma and Vogel, 1992),which depends on vegetation characteristics (Quade, 2004).Well-mixed air above soil has a d13C of about �6 to �8& (Mongeret al., 1998). The d13C of soil air depends on the photosyntheticpathway used by the plants in the vegetation cover. C4 plantsgenerate cellulose with a modal d13C of �13& and C3 plants�27&;CAM plants have intermediate values (Cerling, 1984). Cerling (1984)estimates limits of �2.2& and �8.5& for the d13C of soil CO2

beneath pure C4 and pure C3 biomasses. Waters percolatingthrough soil equilibriate with soil CO2 and then dissolve limestone,which has a d13C of about þ1&. Under pure C3 or C4 biomasses thefirst speleothem calcite deposited from seepage waters should havea d13C of �12 to�8& or �2.3 toþ1.5&, respectively, depending onwhether dissolution was under open- or closed-system conditions(Brook, 1999).

G.A. Brook et al. / Journal of Arid Environments 74 (2010) 870–884876

These estimates assume no kinetic fractionation of isotopes.However, stalagmite W-1 has probably always been close to theentrance to Wonderwerk Cave in an area where the inflow ofoutside air might cause rapid degassing of CO2 and evaporation,both leading to higher d13C values in the W-1 stalagmite. In fact,W-1 d13C values range from �5.1& to þ4.2& and average �1.4&

(s ¼ 2.1&). The lowest values in the core are for carbonate witha concretionary fabric deposited from ca. 23 to 17 ka and suggestthat a significant amount of the carbon was derived from C3 plantsabove the cave and that there was limited kinetic fractionation.Both the d13C values and the type of fabric suggest cooler andwetter conditions, and an increase in open-system groundwaterflow due to increased biomass on the hill above the cave that mayhave included more C3 shrubs and C3 grasses. If the lower d13Cvalues are due to an increase in C3 grasses on the hill this wouldimply an increase in winter rainfall.

By contrast, warmer and drier conditions might lead to a sparservegetation cover above the cave with fewer C3 shrubs and anincrease in C4 grasses. The reduced plant cover would produce lessCO2 in the soil so that after periodic heavy rains meteoric waterwould pick up very little soil CO2 and be affected more by evapo-transpiration at the surface and in the cave. As a result, drip watersin the cave and stalagmite carbonate would be enriched in 13C dueto the higher d13C of soil CO2, lower levels of CO2 in the soil, andincreased evaporation. The highest values of d13C in the W-1 coreare at ca. 32, 24, 15, and 4 ka. The deposits at 32, 24, and 4 ka occurat the start of or end of a growth hiatus assumed to have beentriggered by extremely dry conditions. Deposition at 15 ka was atthe time of the H1 interval when carbonate with a micro-stromatolitic fabric was deposited indicating very dry conditions.

Currently the Wonderwerk area is dominated by C4 grassspecies (95–100%) and these predominate throughout South Africaexcept where the mean daily maximum temperature during thegrowing (rainy) season is less than about 25 �C, and then C3 grassesare more common (Vogel et al., 1978). Hence, an increase in C3

grasses at Wonderwerk in the past, due to an increase in winterrainfall, should be recorded by a marked shift towards lower 13C inthe W-1 carbonate. Values of d13C for tooth enamel from fourspecies of grazers at Equus Cave, 50 km from Wonderwerk, suggestpast periods with more C3 grasses and enhanced winter rainfall butprovide no evidence for the northward migration of the winterrainfall belt into the area, even during the LGM (Last GlacialMaximum) (Lee-Thorp and Beaumont, 1990, 1995).

The relative difference in mass between 12CO2 and 13CO2 ismuch less than that between H2

16O and H218O, so that carbon is less

affected by kinetic processes than oxygen. As a result, wheninterpreting the Wonderwerk d13C data more negative values ofd13C are considered to be evidence of: (1) an increase in C3 plantsabove the cave, (2) cooler and moister conditions that supportedmore biomass and therefore more CO2 in the soil atmosphere, (3)more regular rains that produced more open-system flow to thecave rather than occasional heavy rains that lead to rapid closed-system flow, and (4) cooler conditions that reduced evaporation onthe stalagmite surface. As more C3 plants, higher levels of soil CO2,

Table 2Mean monthly temperature and rainfall at Kimberley and Pretoria, South Africa.

J F M A M J

Kimberley (elev. 1198 m)a

Temperature (�C) 25.5 24.0 22.0 18.0 14.0 10.5Rain (mm) 57 76 65 49 16 7

Pretoria (elev. 1330 m)a

Temperature (�C) 23.5 22.5 21.5 18.0 15.0 12.0Rain (mm) 136 75 82 51 13 7

a Data from South African Weather Service web site http://www.weathersa.co.za/Clim

reduced evaporation, and an increase in open-system dissolutionare all more likely under cooler and moister conditions, we assumethat lower d13C values indicate such conditions, and possibly alsorecord increased winter rainfall.

4.3.2. Oxygen isotopesThe d18O of speleothem carbonate is influenced by: (1) varia-

tions in atmospheric and cave temperature; (2) variations in oceand18O, which was 1.3–1.8& higher during glacial maxima; (3) thesource of moisture supplying drip water to the cave; (4) the inverserelationship with precipitation amount; (5) the dominance ofsummer versus winter precipitation (colder temperatures meanwinter rain is often more depleted in 18O); and (6) the magnitude ofkinetic fractionation (evaporation or rapid outgassing of CO2) ofdrip water or water films precipitating carbonate (McDermott,2004; Quade, 2004).

Data on d18O in precipitation are available for Pretoria (IAEA:http://isohis.iaea.org/) about 500 km NE of Wonderwerk Cave,while the nearest long rainfall record is for Kimberley 200 km to theSE. Average rainfall at Kimberley is 414 mm/year and at Pretoria674 mm/year with 76.3% of rain at Kimberley falling in the sixwarm-season months October–March and 84.9% falling in thesemonths at Pretoria (Table 2). The oxygen isotope data for Pretoria(Fig. 7) reveal a weak relationship between monthly temperatureand mean monthly d18O (R2 ¼ 0.05) for all months of the year buta somewhat stronger relationship with monthly precipitation(R2 ¼ 0.25). For the six warm-season months there is no relation-ship between monthly rainfall d18O and monthly temperature(R2 ¼ 0.0003) and the same is the case for the six cold-seasonmonths (R2 ¼ 0.01). However, there are weak relationshipsbetween d18O and warm-season precipitation amount (R2 ¼ 0.19)and cold-season precipitation amount (R2 ¼ 0.31) confirming the‘amount effect’ that d18O decreases with precipitation amount. Thisrelationship between d18O and precipitation amount was used tointerpret the d18O time series from the Wonderwerk W-1 core.

Average annual weighted (230 months) precipitation, warm-season (151 months) precipitation, and cold-season (79 months)precipitation at Pretoria is �3.8&, �3.9&, and �3.1&, respectively.The lower values for warm-season rainfall suggest that any increasein warm-season precipitation at Pretoria, and therefore also atWonderwerk, should be accompanied by a decrease in the d18O ofthe rainfall and of any stalagmite carbonate precipitated from it. Onthe other hand, a decrease in warm-season rainfall accompanied byan increase in cold-season rainfall should see an overall increase inthe average d18O of rainwater and any resulting carbonate. As mostrainfall at Pretoria and Kimberley is derived from summer rainsbrought by air masses moving westwards from the Indian Ocean,rainfall at Wonderwerk must have had lower d18O than rainfall atPretoria due to the greater distance traveled by the moisture andthe resulting rainout of 18O. Rainfall at Windhoek in Namibia, forexample, has a weighted monthly mean d18O value of �5.1&

(135 months) compared with �3.8& (230 months) for Pretoria(IAEA: http://isohis.iaea.org/). As Windhoek is longitudinally about1140 km west of Pretoria (direct distance 1180 km), and assuming

J A S O N D Year

11.0 13.0 17.5 20.0 22.5 24.5 18.57 7 12 30 42 46 414

12.5 15.0 19.0 20.5 21.5 22.5 18.53 6 22 71 98 110 674

at/Climstats/

Fig. 7. Oxygen isotopes in precipitation at Pretoria, South Africa in relation to monthly temperature and precipitation amounts. The summer wet season extends from October toMarch and the winter dry season from April to September. Data are from the International Atomic Energy Agency’s (IAEA) GNIP/ISOHIS website at http://isohis.iaea.org/.

G.A. Brook et al. / Journal of Arid Environments 74 (2010) 870–884 877

a linear relationship between distance and d18O, rainfall atWonderwerk should have a d18O value around �4.3& as thelongitudinal distance of Wonderwerk from Pretoria is 480 km(direct distance ca. 520 km).

Lower d18O values in the Wonderwerk core are thought toprimarily reflect: (1) increased summer rainfall in the region withisotopes being influenced by the amount effect, (2) reducedevaporation or rapid outgassing of CO2 from waters dripping orflowing over the stalagmite surface due to cooler and possiblywetter conditions, (3) an increase in summer over winter precipi-tation, and (4) lower d18O values in surrounding oceans duringwarmer (interglacial and interstadials) climate phases due tomelting of ice sheets and other ice bodies leading to lower values inatmospheric moisture. As cooler and wetter conditions are alsolikely to be associated with reduced evaporation, lower d18O valuesare interpreted as being indicative of such conditions. Holmgrenet al. (2003) have interpreted the rainfall and stalagmite d18O signalfrom Cold Air Cave stalagmite T8 somewhat differently. They arguethat in wetter periods the high frequency of persistent warm

rainfall from middle-level stratiform clouds produces less 18Odepletion in the rain than occurs during dry years that arecharacterized by increased thunderstorm and hail activity. Conse-quently, they argue that at Cold Air Cave higher d18O reflectsgenerally warmer, wetter conditions, while lower values implycooler, drier conditions. In using the T8 stalagmite record, Partinet al. (2008) followed our interpretation, assuming that lower d18Ovalues mean more rainfall and higher values mean less. In dryyears, rain from short convectional storms is subjected to strongevaporation at the ground surface and in the soil zone so that lowd18O values increase in waters percolating to caves as they lose 16Opreferentially in the evaporative process. In contrast, d18O values ofrainfall during cool, wet years change only minimally in the soilzone due to low evaporative effects.

4.3.3. Interpreting d18O and d13C: the pollen evidenceVariations in speleothem carbonate d18O and d13C values can be

difficult to interpret climatically because they are influenced by somany factors. In this study both isotope and pollen data were

G.A. Brook et al. / Journal of Arid Environments 74 (2010) 870–884878

obtained from the W-1 stalagmite allowing trends in the isotopedata to be compared with the pollen evidence. Isotope and pollendata from stalagmite W-1 are compared in Fig. 9 with stalagmiteisotope data from Cold Air Cave and with pollen data from theWonderkrater spring peat site, both in Northern Province. Thecomparisons show that lower/higher values of both d18O and d13Cin the stalagmites correspond with evidence of wetter/drierconditions in the pollen records. For example, the high isotopevalues in the Cold Air Cave record from about 9 to 7 ka correspondwith a marked early Holocene dry interval in the Wonderkraterpollen record, and the low isotopic values at Wonderwerk from 23to 17 ka and 4 to 0 ka correspond with evidence of wetter condi-tions in both the Wonderwerk and Wonderkrater pollen records.Therefore, it appears that the pollen evidence supports how wehave interpreted the stalagmite isotope data.

4.4. Pollen

Pollen preservation in stalagmites in Africa is discussed, forexample, by Scott and Bonnefille (1986); Brook et al. (1990a,b);Burney et al. (1994), and Carrion and Scott (1999). Pollen concen-trations in samples from the Wonderwerk stalagmite wereextremely low (0–ca. 250 grains/g, Table 3) compared with thedung samples. Two DUNG-B samples averaged nearly100,000 pollen grains/g measured by the exotic spike method,while four DUNG-A samples were also comparatively rich in pollenbut concentrations were not measured. Twelve of the 32 stalagmitesamples had enough pollen for counts of more than 200 grainswhile eight had fewer than 200; 12 were considered unproductive(Table 3). Pollen spectra from 20 stalagmite samples were used

Table 3Palynology samples from the stalagmitea with their estimated ages, pollen countsand concentrations.

Samplenumber

Depth(cm)

Age(years)

Pollen count(number ofgrains)

Minimumnumber ofpollen grains/g

1 0.7 349 250 2522 2.2 1187 211 193 4.0 2192 252 234 5.9 3225 257 255 7.5 13428 0 36 9.4 13932 116 87 11.5 14489 0 08 13.4 15006 0 09 15.3 15496 0 010 17.2 16000 0 011 19.4 16583 32 312 21.5 17153 0 013 23.4 17643 261 5514 25.3 18160 135 815 27.3 18690 290 2516 29.2 19194 40 217 31.0 19671 270 5718 33.0 20202 43 219 35.6 20891 227 1720 38.0 21527 0 021 40 22044 266 9022 41.5 22442 95 1123 42.6 22746 0 724 45.3 32766 250 2225 47.4 33216 265 8526 49.5 33645 115 827 51.3 34033 0 328 54.6 34713 0 0.129 56.65 35142 0 430 58.4 35509 0 0.131 60.45 35938 220 1632 62.8 36430 99 7

a Urine-impregnated dung samples not shown.

together with the six samples of dung to create a pollen sequence.Pollen percentages in stalagmite samples at 9.4, 29.2 and 33.0 cmwere the only ones based on counts lower than 95 grains (Table 3).Poaceae pollen dominates the whole sequence but the upper fourHolocene levels have higher concentrations than the pre-Holocenesection (Fig. 8), suggesting that the vegetation of the Holocene

Fig. 8. Variations in pollen assemblages through the stalagmite core.

G.A. Brook et al. / Journal of Arid Environments 74 (2010) 870–884 879

period had a high proportion of grass. These samples also show lowbut consistent numbers of tree pollen (e.g. Olea), shrubby elements(Asteraceae and Anthospermum), succulents (Aizoaceae type),halophytes (Chenopodaceae/Amaranthaceae) and sedge pollen(Cyperaceae). The other most prominent pollen types in thesequence, Passerina and Asteraceae (including undifferentiated andStoebe types) represent low shrubs and these were relativelyprominent during the pre-Holocene phase. These types, togetherwith Poaceae pollen, suggest dry grassy karroid vegetation withmarginal fynbos elements during the Last Glacial Maximum period(LGM), agreeing with previous results in the region including EquusCave, and the rest of southern Africa (Scott, 1987; Scott et al., 1995).Peaks of Stoebe type (ca. 17–22 ka and earlier phases) may recordthe coldest periods of the LGM given past and modern pollendistributions in the South African interior (Scott, 1982, 1989; Scottet al., 2003). Passerina, which is also prominent between 17 and22 ka, is not found in the area today and currently occurs 400 km tothe east on the cooler, wetter Drakensberg ca. 700 m higher inC3-dominated grassland and far to the south in the Cape fynbosvegetation. Increases in the proportions of Cyperaceae may be theresult of moderate moisture conditions during the LGM, probablysub-humid rather than semiarid, and this is supported by thepresence of fern spores and small numbers of Restionaceae (fynbos)and Podocarpus (long distance transported yellow-wood) pollen.

The pollen data for 20 stalagmite and four dung samples weresubjected to principal components analysis (PCA) using 22 selectedpollen taxa. Two significant components or factors related tomoisture (WW-PC1, ca. 28% of the variance) and temperature(WW-PC2, ca. 17% of the variance) explained much of the variationin the original data. Taxa that are negatively correlated withWW-PC1 are Poaceae, Podocarpus and Stoebe type, which aredependent on moisture conditions. Taxa that are positively corre-lated with WW-PC1 include typical semiarid forms like succulents(Aizoaceae type, Euphorbia), halophytes (Cheno/Ams), Acanthaceaeand Asteraceae. Olea, and Euclea, which are currently prominent inthe wider surroundings of the site, are also included in the lattergroup, probably because their pollen becomes relatively moreprominent when grass cover declines. WW-PC2 is strongly influ-enced negatively by Passerina and Stoebe pollen, which are asso-ciated with cool temperature conditions, and positively by Rhus,Aloe and Euclea, indicating more frost-free conditions.

The pollen data suggest a generally cool and wet LGM equivalentbetween 17 and 22 ka but in comparison with pollen sequencesfrom the eastern part of South Africa (Scott, 1989, 1999; Scott et al.,2003; Norstrom et al., 2009), the absence of Ericaceae indicate thatthe current east–west moisture gradient still applied. Majortemporal gaps occur in the stalagmite pollen sequence but fortu-nately the dung deposits extend the middle part of this to ca. 12 ka(the W-1growth hiatus lasted from 13.3 to 3.9 ka). In fact, the dungpollen suggests that after the stalagmite stopped growing at 13.3 kathe climate became very dry, confirming our belief that the reasonfor the cessation in growth was aridity. The dry conditions indi-cated by the dung pollen appear to coincide with a cool YoungerDryas equivalent. However, before the onset of dryness there isevidence of a relatively moist spell ca. 13.3 ka, and this sequenceseems to be almost coeval with moisture fluctuations recorded ina swamp pollen spectrum covering the same period from theeastern Free State (Norstrom et al., 2009). However, we did notrecord an equivalent for the prominent short wet spell ca. 10 ka thatis also indicated in the swamp sequence since it corresponds to thehiatus period when the stalagmite did not grow.

The W-1 stalagmite pollen record contributes significantly toother pollen records for Wonderwerk despite low pollen counts. Itprovides a longer and more detailed sequence than previousreports that include Holocene spectra from cave floor sediments

(van Zinderen Bakker, 1982) and terminal Pleistocene/Holocenespectra from porcupine dung and urine (Scott et al., 1995).

5. Paleoclimatic inferences from the Wonderwerk data andcomparison with Cold Air Cave and Wonderkrater in NorthernProvince

Analysis of the Wonderwerk core and dung deposits hasprovided a fragmented record of climate change for the last ca.35 ka. The data are compared in Fig. 9 with information from theCold Air Cave T8 stalagmite (Holmgren et al., 2003), Wonderkraterspring peat (e.g. Scott, 1982; Scott and Thackeray, 1987), andGreenland Ice Sheet GISP2 ice core (Alley, 2004). Although Cold AirCave and Wonderkrater are about 800 km northeast of Wonder-werk, all three sites have preserved remarkably similar records ofclimate change over the last 25 ka that also parallel variations inGreenland Ice Sheet GISP2 paleotemperature (Fig. 9). This suggeststhat past climate changes in southern Africa were linked to changesin global atmospheric and oceanic circulation patterns possiblytriggered by conditions in the North Atlantic. That the Cold Air Caverecord is based on data along the vertical growth axis of a stalag-mite (T8), while the Wonderwerk record comes from a horizontalcore drilled into one flank of a stalagmite (W-1), suggests thatisotopic and other data from horizontal cores can provide usefulpaleoenvironmental information despite precipitating watersbeing more prone to kinetic fractionation of isotopes.

Holmgren et al. (2003) argue that the upper, aragonite part ofthe Cold Air Cave T8 stalagmite was deposited much faster (11 mm/100 year from 10.2 to 0 ka) than the basal calcite section (2 mm/100 year from 24.4 to 12.7 ka), indicating that the Holocene wasmuch wetter than the late Pleistocene. However, if the calcite isprimary and not altered aragonite, the presence of the calcite ismore likely to indicate wetter conditions during deposition ratherthan drier (Cabrol and Coudray, 1982; Murray, 1954; Pobeguin,1955; Reams, 1972; Siegel, 1965; Siegel and Dort, 1966; Thrailkill,1971). This would be particularly true in a dolomite cave wherepercolating waters have high Mg/Ca ratios that favor deposition ofaragonite rather than calcite. These conditions would be met byheavy rainfall during periods of cooler and wetter climate with lowrates of evaporation. Stalagmite growth rates would be low becausemuch of the water entering the cave would be undersaturated withrespect to both calcite and aragonite and the lack of significantevaporation of water on the stalagmite would not change thissituation. By contrast, aragonite is typically deposited under drierconditions from waters with high ionic concentrations and highMg/Ca ratios. Heavy rains that produce cave drip waters with lowionic concentrations are unlikely to precipitate aragonite. Instead,aragonite deposition would be favored during periods with modestrainfall and high temperatures when increased evaporation mightincrease ionic concentrations.

The frequent age reversals in the basal calcite of T8 (six reversalsin a sequence of 11 ages) suggest that the calcite formed byrecrystallization from aragonite, as is commonly the case in olderspelean material (e.g. Railsback et al., 2002). If this happened, itquestions the validity of the U-series ages for the older part of theT8 stalagmite. In addition, if the calcite was originally aragonite,there is no need to correct the isotopic values from the aragonitesection of the stalagmite so that they can be compared with valuesfrom the calcite section. Holmgren et al. (2003) subtracted 0.6&

from d18O values and 1.8& for d13C values). In fact, these changesmake the Holocene values appear lower than the late Pleistocenevalues, giving the impression (by our interpretation of the isotopevalues) that the Holocene was wetter. Although alteration fromaragonite to calcite probably altered the d18O values of the lowerpart of the T8 stalagmite, this would probably not have affected

Fig. 9. The Wonderwerk Cave, Cold Air Cave, and Wonderkrater paleoenvironmental records compared with the GISP2 temperature record. Ages of Heinrich events H0 to H3 followHemming (2004). (A) GISP2 temperature record; (B) variations in d13C – Cold Air Cave stalagmite; (C) variations in d13C – Wonderwerk stalagmite; (D) variations in d18O – Cold AirCave stalagmite; (E) variations in d18O – Wonderwerk stalagmite; (F) paleoclimate interpretation of the Wonderwerk data; (G) first component (WW-PC1) of Wonderwerkstalagmite pollen PCA reflecting moisture; (H) second component (WKR-PC2) of Wonderkrater pollen PCA reflecting moisture; (I) second component (WW-PC2) of Wonderwerkstalagmite pollen PCA reflecting temperature; (J) first component (WKR-PC1) of Wonderkrater pollen PCA reflecting temperature. Data in (A) are from Alley (2004) and data in (B, D,I, and J) are from Holmgren et al. (2003). The Cold Air Cave isotope data are raw values corrected for the different fractionation coefficients between calcite and aragonite andsmoothed by us using a nine-point binomial filter with weights of 0.2270, 0.1946, 0.1216, 0.0541, and 0.0162.

G.A. Brook et al. / Journal of Arid Environments 74 (2010) 870–884880

d13C values significantly because of the low water–rock ratio forcarbon. Thus we believe that the d13C record for Cold Air Cave inFig. 9 is probably a more accurate reflection of the magnitude ofchanges that occurred than are the d18O values.

In the period 24–12 ka the GISP2 temperature record showswarmer periods at ca. 23, 19, and 14 ka and colder periods at ca. 21,17, and 12 ka. The most recent and most prominent of the warmerperiods is the Bølling–Allerød interval from 14.7 to 12.7 ka. Thecolder periods at 17 and 12 ka are at the time of the H1 event andYD or HO event, respectively. In the Cold Air Cave and Wonderwerk

isotope records the three GISP2 warm periods are intervals withlower d18O and d13C values (ca. 2& lower than during interveningperiods) and the colder intervals have higher values. Holmgrenet al. (2003) have interpreted the warmer intervals of the GISP2record as being drier at Cold Air Cave. For reasons given earlier, weinterpret them at Wonderwerk and Cold Air Cave as periods ofincreased moisture and slightly warmer temperature. The isotoperecords suggest slightly drier conditions during the H1 event whilethe dung pollen data indicate significantly drier conditions duringthe YD when deposition of both stalagmites ceased around 13 ka

G.A. Brook et al. / Journal of Arid Environments 74 (2010) 870–884 881

(Fig. 9G,H). The absence of pollen in W-1 carbonate dating to ca.13.3 ka may also indicate a very dry climate at this time. In contrast,the colder period at 21 ka, centered on the LGM, is not as prominentan isotopic peak in the stalagmite records as the H1 or YD,indicating that conditions remained relatively wet. Pollen data for23–17 ka suggest relatively high moisture levels and cooltemperatures.

The petrography of the W-1 core supports the above conclu-sions. From 23 to 17 ka the core has a concretionary fabricindicating wetter conditions, thus conforming with the generalinterpretation of increased moisture in the western half of SouthAfrica during this cool phase, although it is not clear to what extentthis was due to winter or summer rain regimes or lower evapo-transpiration (Chase and Meadows, 2007). At 17.3 ka the concre-tionary fabric gave way to layered fabric indicating less moistureand later to microstromatolitic calcite during the H1 event,showing that the drying trend continued. However, at the start ofthe Bølling–Allerød warm period ca. 14.6 ka this gave way tolayered carbonate, indicating increased moisture until the onset ofthe YD ca. 13.3 ka when deposition ceased, possibly due to muchdrier conditions. Simultaneous growth hiatuses in the Wonderwerkand Cold Air Cave stalagmites, along with the Wonderwerk dungpollen data, strongly suggest a very dry YD or H0 period throughmuch of southern Africa. The T8 and W-1 stalagmites continued togrow during the H1 event but both stopped growing during the YD,suggesting that the H1 event was not as dry as the YD.

Concretionary and layered carbonate on the W-1 stalagmite at35–33 ka, lower d18O and d13C values, and pollen taxa of cold-adapted plants, suggest wetter and colder conditions at Wonder-werk when the GISP2 record shows warm and cold oscillations(Fig. 9A). The isotope and pollen data, along with layered carbonateon the W-1 stalagmite, suggest that the late Holocene climate waswarm and wet after a brief dry interval around 5–4 ka.

An obvious similarity between the Cold Air Cave and Wonder-werk Cave stalagmites is that both stopped growing around 13 kaand deposition did not resume until 10.2 ka at Cold Air Cave and4.5 ka at Wonderwerk. Cessation of growth corresponds with theonset of the YD or H0 event at ca. 12 ka (Fig. 9). The hiatus indeposition at Wonderwerk from 13.3 to 4 ka, along with pollenevidence from DUNG-A, suggests very dry conditions during atleast part of this interval. A growth hiatus in a Cango Cavesstalagmite (Fig. 1) from ca. 15 to 5 ka may indicate that the areaaffected by dry conditions was very extensive (Talma and Vogel,1992). Ages for the Wonderwerk core indicate an earlier deposi-tional hiatus from ca. 33 to 23 ka. Significantly, the T8 stalagmite inCold Air Cave began growing (ca. 24.4 ka) at about the same timethat growth of W-1 resumed, suggesting that prior to ca. 25 ka theclimate was dry enough to severely limit the amount of waterentering the cave. This stopped the growth of W-1 and did notallow T8 to start growing until conditions improved. In fact, T8 andW-1 began to grow at the start of a major wet interval from ca. 25 to17 ka that followed an earlier dry interval from 32 to 25 ka (Fig 9).

There is a striking similarity between moisture and temperaturecomponent scores for pollen at Wonderkrater based on 26 pollentaxa (Holmgren et al., 2003; Scott, 1982, 1989; Scott et al., 2003;Scott and Thackeray, 1987) and the pollen and isotope records forthe Wonderwerk stalagmite (Fig. 9G–J). The Wonderkrater recordshows a marked dry interval during the early Holocene from ca. 10to 6.5 ka, which might explain why the growth hiatus in theWonderwerk core extended beyond the middle Holocene. Today,Cold Air Cave receives more rainfall than Wonderwerk (521 vs.420 mm) and if this was also the case in the past this may explainwhy the T8 stalagmite continued to grow during the early Holocenewhen there was no deposition at the W-1 coring location. The W-1stalagmite became active again from ca. 4 to 3 ka when layered

carbonate with high d18O and d13C values was deposited, indicatingwetter but still dry conditions. This was followed by carbonate withlower d18O and d13C values suggesting somewhat wetter conditionsbetween 3 and 1.2 ka but with higher values around 1.3 karecording a short interval of drier climate. Pollen factor scoressuggest warm and relatively moist conditions throughout the lateHolocene.

Similarities between the Wonderwerk Cave, Cold Air Cave, andWonderkrater data indicate regional-scale changes in climateduring the last 35 ka. It is not clear how much of the increasedmoisture during the late Pleistocene was due to increased precip-itation and how much due to reduced evapotranspiration.However, water balance estimates for the large lake that occupiedAlexandersfontein Pan some time before 19 ka ago (Butzer et al.,1978; Butzer, 1984a, b) strongly suggest that precipitation wassignificantly higher than today when d18O and d13C values of theWonderwerk stalagmite were low.

6. Discussion

There is a strong correlation between dry intervals recorded inthe W-1 stalagmite and North Atlantic Heinrich events (Bond andLotti, 1995; Hemming, 2004). The hiatus in stalagmite growth fromca. 33 to 23 ka may have been triggered by the onset of the H3 eventat ca. 31 ka and prolonged by the H2 event, corresponding with theLGM at around 24 ka. The T8 stalagmite at Cold Air Cave began togrow and the Wonderwerk stalagmite resumed growth after the H2event as temperatures began to rise ca. 24–23 ka, as indicated bydata from the GISP2 ice core (Fig. 9A). The H0 event or YD hada similar effect on the two stalagmites, stopping growth for a few toseveral thousand years. In contrast, the H1 event did not triggera growth hiatus in either deposit, suggesting that it was not asmarked or as abrupt as Heinrich events H3, H2 and H0.

Periods of no deposition at the W-1 coring site at 33–23 and13–4 ka correspond with evidence of dune activity at Witpan from35 to 27 and 15 to 9 ka (Telfer and Thomas, 2007), suggesting thatthe hiatuses were caused by increased aridity near the cave. Afterthe H2 event, from 24 to 22 ka, layered carbonate was deposited onW-1 and d18O and d13C values increased by ca. 5&, suggestingslightly warmer and drier conditions at the same time as temper-atures increased over the Greenland Ice Sheet. Microstromatoliticcarbonate, with higher d18O and d13C values, was deposited duringthe H1 event ca. 16.8 ka, providing further evidence that Heinrichevents brought dry conditions to the Wonderwerk area.

Vidal et al. (1999) argue that reduced North Atlantic Deep Water(NADW) production associated with Heinrich-like event HL1(equivalent to Heinrich event H0) would have generated cooling inthe Northern Hemisphere and warming in the Southern Hemi-sphere climate superimposed on the global deglaciation warmingtrends in both hemispheres. NADW is associated with a consider-able inter-hemispheric northward heat transport in the Atlantic.The southward export of NADW is compensated by a return flow ofwarm, near-surface water from the South Atlantic. They argue thatreduced NADW production during Heinrich events couldcontribute to early warming in the South Atlantic and identify twoperiods of ocean warming in the Equatorial and South Atlanticsurface waters at 43 ka and 33 ka that they say follow Heinrich-likeevents HL 5 and HL 4 (H4 and H3). Reducing this transport wouldlead to a cooling of the (high latitude) Northern Hemisphere anda warming of at least a part of the Southern Hemisphere.

The beginning of the H1 event, lasting from ca. 17 to 15.5 ka,corresponds in the Wonderwerk record with a change from layeredto microstromatolitic carbonate suggesting increased aridity at thecave. The end of H1, at around 16 ka in the stalagmite record, ismarked by an increase in d18O and d13C values and by pollen PC

G.A. Brook et al. / Journal of Arid Environments 74 (2010) 870–884882

scores for dung that indicate much warmer and much drierconditions by ca. 14.6 ka. This was followed by a warm and very dryclimate at 14 ka before the onset of cool, moist conditions around13.2 ka. These changes appear to record the rapid warming thatoccurred after the H1 event that reached a peak ca. 14.5 ka duringthe Bolling–Allerod interval. They also reflect the equally rapidcooling that occurred just a few hundred years later with the onsetof the Antarctic Cold Reversal (ACR), which lasted from about 14 to13 ka. Pollen in the Wonderwerk dung deposits dated to 12 kaimplies cold and very dry conditions at the time of the YoungerDryas (YD) or H0 event centered at 12.5 ka. If the mid-latitudewesterlies and sub-tropical highs were further north duringHeinrich events this might have resulted in less annual rainfall inthe southern African summer rainfall zone and a slight increase inwinter rainfall (Holmgren et al., 2003).

The Holocene Altithermal was triggered by an 8% increase insummer solar radiation in the Northern Hemisphere at ca. 10 ka(deMenocal et al., 2000; Kerwin et al., 1999). It peaked in theSouthern Hemisphere ca. 10.5–8 ka (Fig. 9B,C,H) and broughthigher sea surface temperatures (SSTs) to the North and SouthAtlantic Ocean and reduced Antarctic sea ice (Hodell et al., 2001).The increased summer radiation may have dampened ENSOactivity until ca. 6 ka (Moy et al., 2002) so that El Nino-like condi-tions dominated because of an almost permanent warm pool in thewestern Pacific. This may explain why the North African monsoonwas most intense from 14.8 to 5.5 ka (deMenocal et al., 2000). ElNino brings drought to the summer rainfall zone of southern Africatoday (e.g. Diaz and Kiladis, 1992; Ropelewski and Halpert, 1987),possibly explaining evidence of a drier climate at Wonderwerk,Cold Air Cave, and Wonderkrater during the early Holocene (Fig. 9)(Holmgren et al., 2003; Scott et al., 2003).

The Holocene Altithermal came to an abrupt end ca. 4.5 ka asdeclining Northern Hemisphere summer solar radiation at the startof the Iron Age Neoglacial led to cooler South and North AtlanticSSTs, expanded Antarctic sea ice (Bard 2003; Hodell et al., 2001),and heightened ENSO activity (Moy et al., 2002). These changesaffected global climates through a variety of teleconnections.Increased ENSO activity probably led to a more variable climate insouthern Africa due to alternating dry (El Nino) and wet (La Nina)periods. However, the more frequent La Nina conditions must haveincreased rainfall over much of southern Africa just as these eventsdo today. Higher SSTs and less Antarctic sea ice ca. 2 ka (Hodellet al., 2001) led to a higher frequency of El Nino events (Moy et al.,2002) and drier conditions in the southern Africa summer rainfallzone. This period is represented in the Wonderwerk Cave record bya sharp increase in d18O and d13C values (Fig. 9C,E).

7. Conclusions

A 0.6-m-long core from the large stalagmite in the entrance areaof Wonderwerk Cave, a National Heritage Site, has provided animportant record of conditions in the interior of southern Africaover the last 35 ka. Depositional hiatuses at 33–23 and 13–4 kaindicate dry periods possibly initiated by North Atlantic Heinrichevents H3 and H0, with the former prolonged by H2. Variations inspeleothem d18O and d13C values are difficult to interpret climati-cally but pollen from the Wonderwerk stalagmite confirmed thatlower/higher values of d18O and d13C are indicative of wetter/drierconditions at the cave. In fact, pollen from the core and from twoanimal dung deposits has provided a longer, more detailed, andbetter-dated sequence for the end of the Pleistocene than previouspalynological records for the southern Kalahari (e.g. Beaumont et al.,1984; Scott, 1987; Scott et al., 1995; van Zinderen Bakker, 1982).

Variations in d18O and d13C values in the Wonderwerk stalag-mite match those in a stalagmite from Cold Air Cave (Holmgren

et al., 2003), and variations in pollen match variations in pollen atthe Wonderkrater spring site. All three records mirror fluctuationsin GISP2 paleotemperature, suggesting that past climate changes insouthern Africa were linked to changes in global atmospheric andoceanic circulation patterns possibly triggered by conditions in theNorth Atlantic. The Wonderwerk data suggest wetter conditions at33, 23–17, and 4–0 ka. Drier conditions are indicated by depositionof microstromatolitic carbonate at 17–13 ka and by depositionalhiatuses at 33–23 and 13–4 ka.

This study has shown that pollen may be preserved in stalag-mites even when it is not well preserved in adjacent clasticsediments. Furthermore, although the W-1 stalagmite was not richin pollen it produced a paleovegetation record comparable withthat obtained from Wonderkrater and based on a more traditionalpollen source – a peat. The isotope record from the horizontalWonderwerk core is very similar to the record from Cold Air Cavethat comes from a stalagmite vertical growth axis. This indicatesthat horizontal cores from stalagmites can provide useful isotopicinformation despite precipitating waters being more prone tokinetic fractionation of isotopes. Coring allows access to largestalagmites while minimizing damage to the cave.

Acknowledgements

We thank the previous owners (the Bosman family) of Won-derwerk Cave, especially Susan Joubert, for their permission towork at the cave and for their friendship and hospitality during thedrilling of the core. We also thank Lloyd Rossouw, Liora Horwitzand Michael Chazan for supplying hyrax urine deposits and PeterBeaumont who arranged for the work at Wonderwerk in 1999 andassisted with the drilling of cores. The research was supported byNSF grant 0725090 to Brook. The National Research Foundation(NRF, GUN 2053236) supported L. Scott. Any opinions, findings, andconclusions are those of the authors and the NSF and NRF do notaccept any liability in regard thereto.

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