Age-Related Variation in Isotopic Indicators of Diet at Medieval Kulubnarti, Sudanese Nubia

International Journal of Osteoarchaeology Int. J. Osteoarchaeol. 17: 1–25 (2007) Published online 22 September 2006 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/oa.862

Age-related Variation in Isotopic Indicators of Diet at Medieval Kulubnarti, Sudanese Nubia

B. L. TURNER,a* J. L. EDWARDS,b E. A. QUINN,c J. D. KINGSTONa AND D. P. VAN GERVENd a Department of Anthropology, Emory University, 1557 Dickey Drive, Atlanta, GA 30322, USA b Department of Anthropology, University of Massachusetts at Amherst, Amherst, MA 01003, USA c Department of Anthropology, Northwestern University, Evanston, IL 60208, USA d Department of Anthropology, University of Colorado at Boulder, Boulder, CO 80309, USA

ABSTRACT This study compares trends in dietary composition in two large cemetery populations from the site of Kulubnarti (AD 550–800) in Sudanese Nubia. Bone collagen and bone apatite carbonate were analysed to characterise stable carbon, nitrogen and oxygen isotopes. Previous research on these cemeteries has suggested marked differences in nutritional status and health between the populations. Contrary to expectations, there were no significant relationships between any isotopic indicators related to sex or cemetery of burial, suggesting no isotopically-measurable differences in diet. However, collagen 13C and 15N were significantly related to age, suggesting age-related differences in protein intake or other factors. Weaning trends are gradual and variable, with the range in 15N values exceeding 4% among infants/young children (0–3 yrs) and standard deviations exceeding 1% in collagen 13C and 15N for both infants/young children and subadults (4–17 yrs). This suggests varied weaning strategies among both populations and variable diets prior to adulthood. Also observed was a distinct range of isotopic carbon and nitrogen values among individuals classified as subadults (4–17 yrs), who are depleted in collagen 13C and 15N relative to adults. However, both infants/young children and subadults are slightly enriched in 18O relative to adults, which suggests the presence of non-local individuals or age-related variation in water sources. While most isotopic studies of age-related dietary trends have focused on reconstructing the weaning process, this study presents findings that indicate tripartite isotopic trends distinguishing infancy, subadulthood and adulthood as separate dietary categories. Broad similarities are evident between the results presented here and those from several earlier studies of smaller populations and to nutritional studies of modern communities. These findings suggest that further research into health disparities at Kulubnarti should focus on non-dietary causal factors, and more generally, that greater attention should be paid to subadulthood in palaeodiet studies. Copyright 2006 John Wiley & Sons, Ltd.

Key words: Kulubnarti; weaning; subadult; diet; Nubia; isotopes; collagen; apatite

Introduction of bioarchaeological research, utilising biochem- ical measures of the relative importance of consti- Isotopic reconstructions of palaeodiet in archae- tuent food types to individual diets (DeNiro ological populations constitute an important area & Schoeninger, 1983; Schwarcz & Schoeninger, 1991; Katzenberg, 1992; Schoeninger & Moore, 1992; Ambrose, 1993; Katzenberg et al., 1995; * Correspondence to: Department of Anthropology, Emory University, 1557 Dickey Drive, Atlanta, GA 30322, USA. Fogel et al., 1997). Such techniques provide e-mail: [email protected] insights into patterns of subsistence and resource

Copyright # 2006 John Wiley & Sons, Ltd. Received 4 April 2004 Revised 2 August 2005 Accepted 28 November 2005 2 B. L. Turner et al. utilisation, and measure inter- and intra-group Weber, 1999; Aufderheide & Santoro, 1999; variation in dietary composition, such as the White et al., 2001; Richards et al., 2003; Papatha- relative abundance of different forms of protein nasiou, 2003; Yoneda et al., 2004). Oxygen iso- and carbohydrate in the overall diet (reviewed topes in bone and enamel apatite, expressed as in Katzenberg & Harrison, 1997). 18O, reflect the isotopic composition of sources Palaeodietary analyses using stable isotopes of consumed water, and can be used to recon- have grown increasingly sophisticated with the struct seasonality, geographical origin and pat- refinement of analytical techniques, increased terns of migration in several species of animals resolution and greater understanding of the com- (Koch et al., 1989; Kohn et al., 1998; Gadbury plex and variable cycling of stable isotopes et al., 2000) and humans (Fricke et al., 1995; White in biological systems. Carbon isotopes in bone et al., 1998, 2002). 13 and tooth apatite, expressed as CAP, generally Isotopic markers of dietary composition reflect the relative abundance of 13C:12C related to developmental age or assigned sex in the overall diet (Ambrose & Norr, 1993). are useful in discussing less tangible cultural Carbon and nitrogen isotope ratios in bone characteristics such as gender variation in diet 13 collagen, expressed respectively as CCOL and (Reinhard et al., 1994) and constructions of dif- 15N, primarily reflect the contribution and ferent life stages within a context of differential source of dietary protein. Nitrogen isotopes subsistence strategies. An example is the distinct also reflect trophic-level effects in protein intake range of isotopic values commonly found in the associated with the position of organisms in food tissues of infants who subsist primarily on protein webs (Lee-Thorp et al., 1989; Ambrose & Norr, sources such as breastmilk or herbivore milk 1993; Ambrose et al., 1997). Calculated offsets during the first months of life. Preserved infant 13 13 15 between apatite and collagen C( CAP- tissues commonly show an enrichment of N 13 18 CCOL, i.e. ÁAP-COL) estimate the relative and O in their skeletal tissues by as much as dependence on animal versus vegetable protein 3–5% relative to the tissues of juveniles and and is used to measure the extent of carnivory in adults (Jenkins et al., 2001; Bocherens & Drucker, the diet or changes in dietary macronutrients 2003), reflecting trophic-level fractionation (Lee-Thorp et al., 1989). Early interpretations of effects between the maternal diet, breastmilk these offsets suggested that values of 4% or less and infant tissues. Population-specific weaning indicated diets in which the bulk of carbon was trends in humans and other animals can be drawn from animal protein, indicating a more characterised isotopically as the introduction of carnivorous subsistence pattern, while values of supplementary foods through enrichment in 6–7% indicated a more herbivorous diet, and 13C and the cessation of breastfeeding through values intermediate between the two indicated an depletion of 15N as the diet becomes more like omnivorous diet (Krueger & Sullivan, 1984). that of associated adults (Katzenberg, 1992; More recent interpretations, however, suggest Schoeninger, 1995; Katzenberg et al., 1996; that dietary differences only account for part of Balasse et al., 2001). Recently, 18O has been this herbivore–carnivore effect and must be con- characterised in human enamel carbonate to sidered along with processes such as methano- track changes in water intake associated with genesis and bone formation (Hedges, 2003), the weaning process, as infants are supplemented pointing to the need to consider metabolic varia- with water directly after getting their water tion across taxa when interpreting offset values. exclusively from maternal milk during breastfeed- From these premises, carbon and nitrogen iso- ing (Wright & Schwarcz, 1998, 1999). topes have been used to explore further the The importance of infant and weanling diets as trophic-level effects between isotopic signatures correlated to short-term and long-term health in tissues of consumers and their prey (Sullivan & outcomes is well documented in clinical literature Krueger, 1983), the metabolic effects of water (Cunningham, 1995; Oddy, 2002), and the tim- stress (Ambrose, 1991), and human subsistence ing of the process as well as the composition of variation in a wide variety of ecological contexts weaning foods often influences rates of infant (Larsen et al., 1992; Pate, 1997; Katzenberg & morbidity and mortality (McDade & Worthman,

Copyright # 2006 John Wiley & Sons, Ltd. Int. J. Osteoarchaeol. 17: 1–25 (2007) Age-related Isotopic Variation in Nubia 3

1998). Isotopic studies of archaeological popula- Sudan (Figure 1). The samples are from riverine tions have demonstrated shifts in 15N and 13C cemeteries less than 1 km apart, both dated to AD among the remains of the very young and 550–800 and encompassing the Early Christian allowed researchers to estimate the timing and phase of the medieval period (Adams et al., 1999). nature of introduced supplemental foods (Kat- Previous studies have suggested differential nutri- zenberg et al., 1996; Schurr, 1997; Herring et al., tional and occupational stress between the two 1998; Dupras et al., 2001). Such studies have samples, possibly reﬂecting differential status, brought new dimensions to studies of the detri- based on pathological indicators such as cribra mental effects of dietary change in archaeological orbitalia and reduced cortical thickness (Mittler & populations, measured primarily through ana- Van Gerven, 1994; Van Gerven et al., 1995). The lyses of enamel hypoplasia and other dental non-speciﬁc nature of these indicators and the pathology (Katzenberg et al., 1996). number of possible causes means that the extent To that end, this study seeks to identify to which these indicators are the result of varia- and describe isotopic weaning trends in two tions in diet is unclear. Therefore, this study also large cemetery populations (n ¼ 137) from the seeks to test the hypothesis that the two Kulubnarti archaeological site in modern-day cemetery populations differed in their dietary

Figure 1. Map of Nubia.

Copyright # 2006 John Wiley & Sons, Ltd. Int. J. Osteoarchaeol. 17: 1–25 (2007) 4 B. L. Turner et al. composition, a critical parameter in assessing cross-culturally, but it is reasonable to assume metabolic stress variation between the two popu- that such patterns could have existed in archaic lations. In doing so, this study is the ﬁrst to societies as well. Studies of catch-up growth directly investigate age-related patterning of and malnutrition-related health consequences in dietary composition across both Kulubnarti cem- children (Martorell, 1989, 1995) illustrate the etery samples, which includes large numbers of important effects that dietary composition and well-preserved infants/young children, juveniles nutritional status during childhood have on mor- and adults (Figure 2). bidity, mortality and health later in life. Dietary The data generated in this study also reveals reconstruction among both younger and older isotopic variation at Kulubnarti that suggests subadults in archaeological populations may dietary patterns among subadults distinct from therefore critically inform population-level ana- infants/young children and adults, with several lyses of resource access and health outcomes, and possible interpretations. A less-recognised poten- such a reconstruction is presented here. tial dietary pattern in bioarchaeological literature Isotopic markers of age-related dietary is the post-weaning, juvenile diet as a separate changes such as weaning were assessed using category, with its own cultural implications and analyses of the stable isotopic compositions of 13 health outcomes. Ethnographic data from extant carbon and nitrogen in bone collagen ( CCOL, 15 18 populations have identiﬁed distinct, ‘childhood’ N) and oxygen and carbon in apatite ( OAP, 13 diets in several cultures resulting from differential CAP). These values were used to reconstruct food allocation within households (Gittelsohn individual- and group-level variation in dietary et al., 1998; Luo et al., 2001; Adams, 1977; composition and identify predictors of isotopic Graham, 1997; Messer, 1997). It is uncertain ranges such as age, sex and cemetery of inter- as to how household food allocation varies ment.

Figure 2. Age distribution of individuals analysed isotopically.

Copyright # 2006 John Wiley & Sons, Ltd. Int. J. Osteoarchaeol. 17: 1–25 (2007) Age-related Isotopic Variation in Nubia 5

Figure 3. Stable carbon isotopic composition of collagen samples from R and S cemetery groups by age.

The Kulubnarti human remains the island population, and are respectively referred to herein as the R and S cemeteries. The two Kulubnarti skeletal populations were Based on associated architectural features interred in nearby cemeteries located in the and burial styles, Adams (1977) and Van Gerven hyperarid region known as the Batn el-Hajar, or et al. (1981, 1995) originally regarded the S ‘Belly of Rock’, between the second and Dal cemetery sample as chronologically precedent cataracts of the Nile River in modern-day Sudan (AD 550–750) to the mainland R cemetery (AD (Figure 1). This marginal region is characterised 1000–1550). Recent analyses of burial styles, by poorly-developed soils and massive granite associated textiles and grave goods, however, outcrops, with limited riverine maritime activity suggest synchronicity between the two (Adams due to rapids. Despite this inhospitable environ- et al., 1999), resulting in modified dates of AD ment, the Batn el-Hajar has for centuries sup- 550–800 for both cemeteries. The burials in both ported scattered populations based in small cemeteries include minimal adornment or accom- villages and hamlets clustered around the region’s paniment, probably reflecting the Christian few fertile floodplains. The Kulubnarti site ideologies of the population, and therefore there encompasses both cemeteries as well as settle- is no significant variation in burial styles suggest- ments on the western bank of the Nile and on a ing differential status (Adams et al., 1999). small island close to the shore, adjacent to the Interpretations of site features indicate that the modern village of Kulb (Adams, 1977; Adams, two populations engaged in comparable agropas- et al., 1999). The two populations are designated toral subsistence practices, producing millet, 21-R-2, or the mainland population, and 21-S-46, sorghum and vegetable crops and grazing

Copyright # 2006 John Wiley & Sons, Ltd. Int. J. Osteoarchaeol. 17: 1–25 (2007) 6 B. L. Turner et al. goats (Adams, 1977). Evidence of cyclical 13C & Van Gerven, 1997; Mulhern, 2000). After variation from the Nubian site of Wadi Halfa grinding off surface contaminants from the based on human hair (White, 1993), and more bone with a Dremel tool, approximately 300 mg recently single osteons (Schwarcz et al., 2004), of adult cortical bone was removed from the has been used to interpret seasonal variation in lateral end of the blade with a Dremel tool, and subsistence, characterised by the cultivation of then cleaned twice ultrasonically. Less bone, the C4 crop sorghum during dry seasons and C3 approximately 80–100 mg, was taken from sub- plants during rainy seasons. Although the current adults’ and infants’/young children’s ribs to mini- study did not include soft tissue analysis to test mise intrusion. Each sample was then divided whether this seasonal variation was also present for collagen or apatite preparation and analysis. at Kulubnarti, the dietary composition of the S Recent assessments of isolation protocols for and R cemetery populations also may have been archaeological bone collagen (Liden et al., 1995) affected by seasonally variable subsistence stra- suggest that methods of extraction using only tegies involving shifting consumption of C3 and sodium hydroxide (NaOH) to remove lipids can C4 plants. Cyclical dietary variation of this sort decrease collagen yields and fail to remove lipid would not be readily visible in bone collagen due contaminants completely. As the Kulubnarti 13 15 to the averaging effects of CCOL and N remains are exceptionally well preserved, effec- during the slow turnover rate of organic bone tive removal of all non-collagen organic material, components, but among very young individuals including lipids, was a primary concern. Thus, a 13 15 with faster overall tissue turnover rates, such collagen CCOL and N extraction protocol variation could be a factor to consider. Addition- designed to minimise contaminants was adapted ally, seasonal trends may be delineated in tooth from those discussed by Stafford (personal com- enamel and dentine, which do not remodel once munication), Liden et al. (1995) and Ambrose formed and produce isotopic records during the (1993). Samples were crushed with an agate period of tooth development. Future research mortar and pestle and continually ﬂushed for using dental or soft tissues may address these four hours with a 10:5:1 solution of methanol, questions at Kulubnarti. chloroform and water in a soxhlet distillation Because of the substantial number of well- apparatus to remove lipids, then freeze-dried for preserved individuals in both cemeteries, it was 18 hours in a vacuum container. This was fol- possible to select a large sample from each with lowed by demineralisation in 0.5 M HCl in representation of sex and estimated age. Devel- annealed glass test tubes at 4C until translucent opmental age at death was determined by Van in appearance, with periodic replacement of HCl Gerven et al. (1981) for each individual based on using annealed glass pipettes. Samples were then seriated inter-individual variation in multiple age- treated with a 0.2% potassium hydroxide (KOH) ing criteria including stages of dental eruption solution for 48–72 hours (depending on sample and epiphyseal fusion. Excellent preservation of integrity) to remove humic contaminants and the remains, resulting from the hot, arid condi- then solubised in a 0.05 M HCl solution at 90– tions characteristic of the region, provided many 100C for approximately eight hours. The gela- opportunities to determine sex among subadults tinised samples were ﬁltered through 0.045 mm in addition to adults based on preserved genitalia, millipore syringe tips to remove any residual pelvic dimensions and/or cranial robusticity. contaminants, and freeze-dried. 13 Bone apatite carbonate was isolated for CAP 18 and OAP characterisation using methods adapted from van der Merwe et al. (1995), Methods Ambrose (1993) and Schoeninger et al. (1989). Samples were powdered in a Spex 6700 freezer/ Ribs were selected from each individual, with mill, and treated for 24–48 hours with a 2.5% preference given to the right third rib whenever sodium hypochlorite (bleach) solution. Follow- possible to control for variation in remodelling ing neutralisation, samples were soaked for dynamics between different bone types (Mulhern 2 hours in a 0.1 M acetic acid solution, rinsed

Copyright # 2006 John Wiley & Sons, Ltd. Int. J. Osteoarchaeol. 17: 1–25 (2007) Age-related Isotopic Variation in Nubia 7 to neutral with deionised water and freeze-dried samples. C/N ratios ranged between 3.0 and 3.5 for approximately 24 hours. with one exception (3.9) (Table 1). Correlations Carbon and nitrogen stable isotope composi- calculated between estimated C/N ratios and iso- tions of purified collagen samples were analysed tope values are consistently low (13C, C/N ¼ 0.17, on a Carla Erba CNS analyser interfaced with a 15N, C/N ¼ 0.13), indicating that isotopic signa- Micromass Prism Seris II stable isotope ratio mass tures of the collagen are not linked to relative spectrometer at the Center for Isotope Geoscience yields. While C/N ratios were not determined for at the University of Florida, Gainesville. Bone all samples, ion beam ratios of masses 44 and 29 apatite 13C and 18O were measured using a were used to assess alteration in the samples as Mountain Mass Spec. Multiprep system (single they were analysed on the mass spectrometer. acid aliquot per sample) interfaced with the Although these ion beam ratios do not directly Micromass Prism. The analytical precision of reflect atomic ratios, since N2 and CO2 gas pulses the mass spectrometer was 0.20% for 15N flow through different capillary systems in the and 0.14% for collagen 13C. International elemental analyser ConFlo interface system, they and in-house laboratory standards, as well as provide a quantitative indicator of similarity or replicate runs (indicated by multiple collagen dissimilarity of C/N ratios in the samples. Kulub- and/or isotopic values per individual in Table 1) narti runs were assessed for the three days the yielded a standard deviation of 0.05% for samples ran and the ion beam ratios were more apatite 13C and 0.11% for 18O. Raw data invariant than the organic standards, indicating for both cemeteries are presented in Table 1, and that the collagen samples had very similar C/N measured isotope values are expressed as per mil contents. The 16 samples for which weight (%) relative to established international stan- percentage C/N ratios were determined were dards: atmospheric nitrogen for 15N and PDB distributed throughout the various runs to pro- 13 13 marine carbonate for CCOL, CAP and vide calibration and indicate that most, if not all, 18 OAP. samples are within the acceptable C/N ratio range. The excellent preservation of the Kulub- narti skeletal remains, including their fresh Results appearance and texture and the presence of preserved soft tissues, suggests a low risk of Bone collagen and apatite are both susceptible to diagenetic alteration (Dupras et al., 2001). As a diagenetic alteration, which can distort biogenic test of methodological integrity, a subsample of isotopic signals. Percentage yields and carbon: - duplicates was processed and run for 38 indivi- nitrogen (C/N) ratios are commonly used as a test duals, with the majority showing isotopic differ- of collagen integrity, since yields below 5% ences under 1% (Table 1). (DeNiro, 1985) and atomic C/N ratios outside a Shapiro-Wilk tests of normality revealed that range of 2.9 to 3.6 (DeNiro, 1985; Ambrose, while carbonate 18O is distributed normally for 1993) are indicative of post-mortem chemical both the S and R cemeteries (P ¼ 0.095), neither 13 alteration. Collagen yields for the Kulubnarti cemetery is normally distributed by CCOL 13 15 samples were typically above 5% for samples in (P ¼ 0.000), CAP (P ¼ 0.000) or N which yields were determined (64/67). The uti- (P ¼ 0.006), necessitating nonparametric statisti- lity of percentage collagen yield as a criterion for cal analysis for the latter three variables. Conse- assessing diagenesis, however, was compromised quently, Kruskal-Wallis tests of population by the potential of sample loss during the isola- equality were performed to estimate the predic- tion process described above as the protocol for tive value of cemetery membership, sex and age isolating collagen was being developed. As the on variation in isotopic values for apatite carbon process was refined and sample loss limited, yields and collagen carbon and nitrogen, while a one- were consistently greater than 5% (Table 1). way ANOVA (analysis of Variance) was per- Weight percentages of C and N provided by formed to estimate the predictive value of cem- the elemental analyser were used to calculate etery membership, sex and age on the variation in atomic C/N ratios for 16 representative collagen values for apatite oxygen. These tests revealed no

Copyright # 2006 John Wiley & Sons, Ltd. Int. J. Osteoarchaeol. 17: 1–25 (2007) 8 B. L. Turner et al. significant predictive relationship between cem- ment relative to adults with a high standard 13 13 etery membership or sex and CCOL, CAP, deviation (3.90%); however, only two infants/ 15 18 13 Nor OAP, suggesting little difference in young children have CAP values, a fact that dietary composition between males and females. limits further interpretation. Consequently, the S and R samples were pooled As seen in Figures 3 and 4, the distribution of 13 15 in subsequent statistical tests. Perhaps more CCOL and N values by estimated age at importantly, if cemetery membership (S vs R) death displayed an interesting patterning of was not a significant predictor of either organic data points for both S and R cemeteries, although or inorganic isotopic values, then this suggests no significant correlation was found between 13 15 that proportional dietary composition was not CCOL and N. There is apparent enrichment significantly different between the two cemetery among infants/young children and depletion for 13 15 groups. This contrasts with previous osteological subadults in both CCOL and N. Adult values studies that report differential indicators of nutri- are intermediate between the infants/young chil- tional status and infectious stress between the S dren and subadults. The differences in mean 13 15 and R cemeteries based on prevalence of cribra values for CCOL and N between subadults orbitalia (Mittler & Van Gerven, 1994), tibial and adults, however, are small. The mean 13 length (Hummert, 1983; Hummert & Van CCOL among the pooled subadults is Gerven, 1983), cortical thickness (Van Gerven 18.06%, only 0.44% less than the mean adult et al., 1995) and remodelling dynamics of ribs and value, while the mean 15N among subadults is femora. The results from this study do not neces- 9.73%, only 0.57% less than the mean for adults sarily dispute these interpretations, but they do (Table 2). These small differences in mean iso- raise the question of what factors besides overall topic values could suggest little difference in dietary composition, such as parasite load, collagen isotope ratios between subadults and chronic infection, absolute portion size or differ- adults, with only infants/young children showing ences in micronutrient content between isotopi- a difference. However, the standard deviation in cally similar foods, would have differentially isotopic values is also large for subadults, (SD of 13 15 affected the two Kulubnarti populations. CCOL ¼ 0.80%,SDof N ¼ 1.12%), and as As summarised in Table 2, infants/young chil- a result mean values are less powerful measures of 15 13 13 dren are enriched in N, CCOL and CAP between-cohort variation by themselves. The 13 relative to both subadults and adults; however, wide ranges in the raw distribution of CCOL mean 15N in the combined S and R infant/young and 15N point to overlap between these three child cohort is 12.19%, only 2.46% greater than clusters, with minimum and maximum values for mean 15N for the pooled subadults and 1.89% subadults and adults overlapping with each other greater than mean 15N for the pooled adults. and also with minimum values for infants/young This is less than the expected 3% indicative of a children, which can be explained by the sub- 13 trophic-level enrichment expected for breast- stantial range in subadult and adult CCOL and feeding infants/young children, but this can be 15N values. As shown in Figure 3, subadults and explained by the variability within each cohort. adults range within their cohorts by almost 3% in 15 13 Infants/young children and subadults have N values for CCOL. Figure 4 shows that subadults standard deviations of 1.26% and 1.12%, respec- range within their cohorts by almost 4% in 15N, tively, and show a range in within-cohort values while adults range by almost 3%. Taking these of over 4% (Figure 4). Similar trends are seen in wide ranges into account, however, a tripartite 13 mean CCOL values for the pooled S and R distinction is still visible in the raw collagen 13 15 cohorts, where the mean infant/young child value CCOL and N data, especially in the latter, is 16.46% and enriched relative to mean sub- that merits further exploration. 13 13 adult CCOL by 1.6% and mean adult CCOL Based on Kruskal-Wallis tests of population by only 1.16%, but the standard deviation for the equality, it appears that these three age clusters pooled infant/young child cohort is 1.63% and are significantly distinct in their ranges of 13 15 2 13 the range is over 6% (Figure 3). Mean CAP N( ¼ 52.702, P ¼ 0.0001) and CCOL among infants/young children also shows enrich- ( 2 ¼ 36.763, P ¼ 0.0001). In other words, despite

Copyright # 2006 John Wiley & Sons, Ltd. Int. J. Osteoarchaeol. 17: 1–25 (2007) g-eae stpcVraini Nubia in Variation Isotopic Age-related Copyright Table 1. Isotopic data for S and R cemetery individuals.

a 15 b 13 13 18 13 Burial ID Age at death (yrs) Sex C/N ratio % collagen yield N(%) CCOL (%) CAP (%) O(%) Á CAP–COL (%)

# S2** 10 2.9 8.48 7.05 18.86

06Jh ie os Ltd. Sons, & Wiley John 2006 8.43 19.32 S5 24 Male — — 11.86 2.25 S13 12 8.1 18.57 3.93 8.31 18.68 11.82 6.81 S14 10 9.79 17.52 11.81 2.39 5.78 10.25 17.66 S15 1.5 10.80 18.58 10.93 19.22 S16 27 Male 3.3 14.02 11.57 17.51 11.06 17.49 11.08 17.43 S20 51 Female 9.69 17.81 S22 4 11.55 18.03 13.61 5.19 4.24 11.20 17.66 S23 5 11.30 18.15 S25 1 3.3 13.47 15.68 13.51 15.08 13.53 15.21 S26 4 1.02 — — 12.29 3.55 S29 1 — 15.29 S30 13 — — 12.2 1.62 S31 12 — — 11.93 4.62 S35 10 16.33 11.27 16.71 10.84 1.52 5.87 10.91 3.72 10.91 3.69 S36 13 8.87 17.85 12.04 4.54 5.81 ——11.72 4.97 n.J Osteoarchaeol. J. Int. S39 5 11.35 10.18 18.56 12.18 3.62 6.38 S40 4 19.19 — — 13.53 2.98 S41 15 9.34 17.78 S42b 5 9.79 16.34 S43b 14 3.3 8.42 18.71 S43c 6 10.52 10.47 18.26 11.51 3.97 6.75 S44 0.75 3.3 13.98 12.81 14.00 12.76 13.89 13.20 17 S47 8 9.87 18.54

–5(2007) 1–25 : S48 11 — — 13.13 3.57 S49 9 8.85 9.66 18.13 S52 6 3.4 8.78 18.72

Continues 9 Copyright 10 Table 1 Continued.

a 15 b 13 13 18 13 Burial ID Age at death (yrs) Sex C/N ratio % collagen yield N(%) CCOL (%) CAP (%) O(%) Á CAP–COL (%)

# S55 18 Male 7.44 10.17 18.78 13.71 2.63 5.07 13.11 3.35 06Jh ie os Ltd. Sons, & Wiley John 2006 S59 4 — — 10.92 3.15

S66 8 — 17.88 S67 13 11.13 9.65 19.21 S68a 4 Male 6.44 12.48 15.34 12.85 15.42 S70 1 12.97 16.91 13.06 16.96 S72b 10 9.86 9.07 18.78 S74 51 Female 10.94 2.58 10.39 2.37 S80 37 Male — 17.80 12.28 2.24 S81 3 3.9 13.14 17.43 — — 13.39 17.86 14.6 13.69 17.81 S83 3 12.03 16.13 S84 47 Male 0.11 10.07 15.65 11.11 1.92 4.54 10.03 15.66 10.87 2.47 ——11.25 2.44 S86 37 Male 20.42 — — 11.65 2.55 S87 0.5 12.22 16.39 S88 12 9.71 9.24 18.44 S89 0.75 — 17.42 S92 6 16.46 9.57 17.29 S93 5 9.09 18.42 S95 11 8.07 18.26 n.J Osteoarchaeol. J. Int. 8.29 18.26 S99 39 Male 10.19 18.79 12.3 1.13 6.49 ——12.1 2.89 ——12.03 1.92 S100 23 — — 11.39 2.48 S101 11 9.50 18.27 S104 49 18.71 — — 11.42 1.71 S105 5 9.83 17.26 S107 47 13.8 10.36 17.33 Turner L. B. 17 S108 11 10.38 18.25

–5(2007) 1–25 : S109 31 Female 10.12 17.17 S115 3 14.56 11.66 16.20 S118 51 11.66 2.04 10.93 2.5 S121 4 10.18 12.95 16.94 al. et S123 6 9.93 19.44 g-eae stpcVraini Nubia in Variation Isotopic Age-related Copyright S128 7 9.7 10.36 18.52 S130 9 12.32 8.48 18.88 11.7 3.38 7.18 S131b 1.5 3.5 11.63 12.43 11.81 7.36 4.7 4.45 S135 5 10.36 17.31 # S136 4 7.92 10.33 18.09 S138 5 15.27 9.27 18.18 06Jh ie os Ltd. Sons, & Wiley John 2006 S139 6 Female 15.08 8.88 18.20 S145 26 Female 11.70 17.10 S153 0 — 15.55 S159 0.75 9.3 11.46 17.34 S165 37 Male 11.52 17.25 11.8 3.03 5.45 ——10.73 3.43 S173 42 Male 10.08 17.73 10.06 17.81 S174 51 Female — — 11.24 2.00 S176 51 Female — — 10.17 2.52 S177 38 Male — — 11.50 3.00 S178 10 10.97 10.06 18.50 S180 47 Male — — 11.57 2.89 S192 42 Male 10.77 17.28 9.83 2.87 7.45 ——11.46 2.57 S197 6 8.37 18.07 8.28 18.09 S199a 8 3.12 — — 10.84 2.79 S200 38 Male 9.91 17.48 12.26 1.6 5.22 10.01 17.55 S201 3 3.6 10.98 16.39 S202 26 Female 11.94 3.33 12.45 3.54 S204 19 Female 9.89 18.59 10.05 18.17 S206 37 Male — 17.47 S207 49 Female 9.54 18.13 n.J Osteoarchaeol. J. Int. S208 1.5 5.32 14.55 16.67 S210 4 7.52 10.34 18.67 S212 49 3.4 10.36 18.03 10.25 18.21 S218 0.5 12.41 17.72 S222 25 Male — 18.16 S228 47 Female — 17.15 S232 3 11.12 18.26 17 S234 51 Female — 18.88 S235 3 2.9 13.45 14.79 17.06 –5(2007) 1–25 : S236 16 2.8 10.88 19.72 R2 5 8.42 17.67

Continues 11 Copyright 12 Table 1 Continued.

a 15 b 13 13 18 13 Burial ID Age at death (yrs) Sex C/N ratio % collagen yield N(%) CCOL (%) CAP (%) O(%) Á CAP–COL (%)

# R3 36 Male 9.93 17.91 11.85 3.1 6.06 R4 40 Female 12.02 3.01 06Jh ie os Ltd. Sons, & Wiley John 2006 R5 6 9.31 17.97 R6 37 Female 24.62 10.46 17.44 11.67 2.92 5.77 R9 7 7.31 18.13 R11 42 Male 11.47 2.42

R13 35 Male 28.72 10.96 16.98 11.79 2.72 5.19 R14 23 Male 11.98 3.02 R15 22 Male 14.96 12.34 4.02 R16 7 8.79 18.60 R19 37 Male 12.75 2.66 R21 6 — 17.05 12.24 3.81 4.81 R22 36 Female 19.31 9.16 18.05 11.50 3.65 6.53 11.53 3.60 R26 24 Female 21.23 9.35 17.70 R29 27 Female 10.38 18.48 R30 34 Female 10.10 17.84 12.37 3.53 5.47 R32 40 Female 13.09 10.37 17.17 11.64 2.85 5.53 11.15 2.55 R34 31 Male 21.04 10.45 17.53 R35 31 Female 12.08 3.96 R36 17 Female 3.0 7.51 18.65 R37 51 Female 10.16 18.43 R41 3 6.91 12.65 16.78 12.88 2.18 3.9 n.J Osteoarchaeol. J. Int. R46 47 Male 28.84 — — 12.21 2.78 R50 49 Male 10.32 16.15 10.58 16.62 R51 0.5 11.77 12.68 R52 47 Female 10.76 17.27 11.83 2.61 5.44 11.78 3.08 R54 11 5.14 10.60 19.01 R55 26 Female 22.59 — — 11.45 3.15 R56 24 Male 22.47 11.62 15.88 Turner L. B. 17 R57a 0.75 9.86 15.83

–5(2007) 1–25 : 9.97 15.90 R59 9 13.36 10.04 17.26 11.61 3.42 5.65 R68 12 9.12 18.75 R76 5 3.5 5.94 7.59 18.71 R79 4 10.92 16.83 al. et R82 5 8.61 18.45 8.33 18.65 g-eae stpcVraini Nubia in Variation Isotopic Age-related Copyright R83 40 Female 10.01 17.12 R94 12 10.59 10.25 18.34 R95 14 8.62 10.73 18.02 R96 3 10.32 17.61

# R98 4 11.07 18.27 R99 36 Female 21.82 10.83 17.95 06Jh ie os Ltd. Sons, & Wiley John 2006

R100 3 13.78 11.23 18.12 R102 38 Male 23.76 — — 12.77 1.88 R103c 1.5 12.16 17.26 12.13 17.28 R106 38 Female 18.7 10.61 17.53 12.31 1.81 5.22 R107 51 Female 16.72 11.81 18.10 12.75 1.52 5.35 R108 42 Male — — 11.57 3.15 R113 4 9.71 18.42 R114 42 Female 10.53 17.14 R117 4 10.22 18.21 R118 26 Female 12.26 2.72 R119 36 15.48 10.40 17.34 11.81 2.53 5.53 R120 15 14.14 10.29 17.07 11.56 3.17 5.51 11.52 2.72 R123 10 Male 15.37 9.87 18.56 R124 5 3.3 8.69 16.77 R128 8 10.21 17.97 R133 4 8.48 18.32 11.47 2.39 6.85 11.37 1.77 R136 51 17.01 10.97 17.58 R137 1.5 Female 9.06 26.65 R139 31 Female — — 11.64 1.85 R141 22 Male 25.40 — — 12.51 2.5 R142 9 8.56 9.86 18.17 12.18 3.02 5.99 n.J Osteoarchaeol. J. Int. R143 45 Female 20.23 — — 11.88 3.23 R144 34 Female 18.25 — — 11.85 2.01 R146 15 Male 15.36 10.38 17.74 12.23 3.01 5.51 R147 16 Male 16.32 11.40 17.08 11.59 2.53 5.49 R157 4 11.19 15.86 R158 19 Male 10.44 17.54 10.37 17.50 R161 26 Female 9.15 17.94 R165 13 10.70 18.36 17 R166 6 9.38 18.63 –5(2007) 1–25 : R168 19 Male 3.3 7.48 18.69 R169 1.5 10.97 17.91 R170 12 13.25 9.69 18.99 13 Continues 14 B. L. Turner et al. )

% large individual variations within the three age ( cohorts, there are clear distinctions between them. However, there was no signiﬁcant relationship AP–COL 13 2 ¼ C between age category and CAP ( 0.872, 13 P ¼ 0.6466), which is reﬂected in the more ran- Á dom distribution of values in Figure 5. This

) suggests that what are signiﬁcantly different % between the three age groupings are isotopic O(

18 signals of protein intake rather than of overall diet. ) Á13 % To explore this possibility further, C

( AP-

AP COL offsets were calculated for the subset of the C 11.18 2.72 6.33 10.6112.31 4.43 1.69 12.91 3.41 pooled S and R groups for whom both apatite and 13 collagen data were generated (Table 2). These

) offsets (Table 1) also suggest a possible age- % ( related trend in protein intake across the three

COL age categories (Kruskal-Wallis Test of Population 17.51 18.13 15.40 17.15 17.11 17.22 17.22 16.78 C Equality, ¼ 0.02), although only two observa-

13 P tions were present for the infant/young child age cohort. However, the offsets between the juve- b

) nile and adult age cohorts also approaches sig-

% niﬁcance (Kruskal-Wallis Test of Population N( Equality, P ¼ 0.07), further supporting this inter- 15

13 15 pretation. Mean collagen CCOL and N values for the three age clusters are clearly different, although with some overlap in raw values (Table 2). 18 The distribution of OAP data for the S and R cemeteries (Figure 6) is more variable across the three age clusters and indicates a general decline of 3–4% with advancing age, a trend that appears slightly more pronounced in the S cemetery sample. A one-way ANOVA shows a signiﬁcant relationship between age category and 18O (F ¼ 4.5079, P ¼ 0.003), but this decline in oxy-

., 1999). gen isotopic values across the age categories is

et al too gradual to suggest a weaning trend across the Sex C/N ratio % collagen yield two infant/young child and subadult age cohorts, especially given that there are only two infants/ a young children in the infant/young child cohort for oxygen values. Furthermore, the range in 18O among the subadult cohort is large, exceeding 4%, with a standard deviation approaching 1%. If some enrichment in infant/young child . 18O due to isotopic enrichment of maternal body water in breastmilk is assumed, then the two infant/young child isotopic values may be Continued assumed to fall within the substantial range in subadult values. The distribution of 18O seen in Missing values for carbon, nitrogen and oxygen due to insufﬁcient amounts of extracted material. Ages estimated by Van Gerven (Adams Burial ID Age at death (yrs) R176a 20 Female 9.80 **Multiple collagen and/or apatite values given for a single individual indicate replicates. Table 1 a b R178 8 12.82 9.75 R181c 1 13.52 R182 3 10.56 R184 2 12.43 R186 2 12.22 R200 R201 7 9.25 R193 37 Female R204 2 12.98 R203 17Figure Male6 points to the adult 15.25 cohort as the

Copyright # 2006 John Wiley & Sons, Ltd. Int. J. Osteoarchaeol. 17: 1–25 (2007) Age-related Isotopic Variation in Nubia 15

potential source of age-related variation, sup- 18 ) ported by an adult mean O value of % ( 2.71 0.65% that is depleted relative to the subadult mean by 0.63% (Table 2). The sub- 18 AP-COL adult–adult difference in mean O within the S C % 13 group sample is just under 1 , and while the Á difference within the R group means is noticeably different, these differences failed to reach statistical signiﬁcance and are perhaps again due to the wide variation in each cohort. In sum, the above analyses point to signiﬁcant

) relationships between collagen carbon and nitro- % 0.54 (8) 5.69 (7) 1.78 (2) 4.18 (2) 0.65 (46) 5.71 (16) 0.83 (23) 5.91 (15) 0.52 (19) 5.7 (6) 0.70 (27) 5.72 (10) 0.93 (15) 6.10 (8) gen isotopic values and age, including signiﬁcant O(

18 differences between juvenile and adult age - climate carnivory/herbivory in diet ranges, but a wide range of values within each cluster. No signiﬁcant relationship was found between these values and sex or cemetery of interment, suggesting similar dietary patterns or physiological processes between the two popula-

) tions. Bone apatite carbon isotopic values do not 4 % ( 0.64 (46) 2.71 0.75 (23) 3.34 0.51 (27) 2.85 0.75 (19) 2.52 0.87 (15) 3.50 3.90 (2) 3.44 0.51 (8) 3.03 appear signiﬁcantly differentiated by any of the vs C AP 7.36 (1) 4.70 (1)categorical 4.45 (1) variables above such as cemetery 3 12.88 (1) 2.18 (1) 3.90 (1) C 13 location or sex. A signiﬁcant, negative relation- 11.76 12.00 11.92 11.54 12.02 10.12 11.97

ship exists between isotopic oxygen signatures and age category that is perhaps due to depletion among the adult cohort rather than enrichment among infants/young children, although limita- tions in sample size among the infant/young child

) cohort preclude ruling out the presence of a 18O % ( weaning trend. 0.69 (43) 0.77 (19) 0.80 (69) 0.63 (24) 1.47 (12) 0.75 (31) 1.63 (30) 1.75 (18) 0.85 (38) COL C 13 17.62 17.70 18.06 17.56 16.66 17.98 16.46 18.13 16.33 Discussion A number of interesting interpretations can be made regarding the distinct infant/young child,

) subadult and adult dietary ranges outlined above. a The simplest interpretation is that the clustering 15 13 ) in N and CCOL values is due to age-related % 0.79 (39) 0.88 (24) 1.27 (12) 0.64 (15) 1.26 (27) 1.12 (67) 1.10 (30) 1.14 (37) 1.27 (15 differences in dietary intake, especially of animal N(

15 protein. Controlled feeding studies have sup- 13 9.73 9.64 9.81 - trophic level - trophic level - whole dietported - water source the hypothesis - degree of that while apatite C 10.30 10.26 11.73 10.38 12.19 12.56 values reflect overall dietary intake, including - type of dietary protein - carbon from dietary protein - C carbohydrates, protein and fats, collagen 13C and 15N primarily reflect consumed protein (Ambrose & Norr, 1993). The lack of statistical yrs yrs yrs significance in apatite isotopic values versus the þ þ þ significance of collagen values suggests that it is 18–51 18–51 0–3 yrs 4–17 yrs 0–3 yrs 4–17 yrs 18–51 0–3 yrs 4–17 yrs dietary animal protein intake, rather than whole Numbers in parentheses equal the number of observations for each mean value (single observations indicate an individual isotopic value). 21-R-2 (R group) Total (both S & R) 21-S-46 (S group) Application Table 2. Mean isotopic values by age cluster for s and R groups a diet composition, that varies by age, with

Figure 4. Stable nitrogen isotopic composition of collagen samples from R and S cemetery groups by age. subadults eating less of it. Within the infant/ et al., 2001; Holman & Grimes, 2003). Anecdotal young child (0–3 yrs) and juvenile (4–17 yrs) reports during the 1960–70s, when Kulubnarti clusters, however, there exists substantial varia- and other Nubian sites such as Wadi Halfa were tion. Such wide intragroup ranges suggest several excavated, identified millet gruel as a commonly possible causal factors. administered supplementary food for nursing Firstly, regarding the infant/young child infants, a recipe that could have ancient origins. (0–3 yrs) category, it is possible that the Kulub- The use of gruels as weaning foods in ancient narti populations engaged in several weaning populations was hypothesised by Buikstra et al. practices rather than one uniform standard, (1986), and could have been employed at Kulub- which influenced the timing and level of dietary narti. However, if gruels made of millet, a C4 supplementation and the duration and intensity plant, were the primary weaning foods at Kulub- 13 of breastfeeding. These strategies could depend narti, infant/young child CCOL values should on resource access or individual variation in be enriched relative to those observed here, feeding practices, factors which could have which are more indicative of C3-based supple- shifted and altered infant and young child feed- mentary diets. Regarding the observed decline in ing practices over the duration of the Christian 15N, Balasse et al. (2001) demonstrated through period, which spanned anywhere from 200– controlled feeding experiments that 15N deple- 900 þ years and encompassed the period of tion in collagen reflects not the gradual decline in occupation at Kulubnarti (Adams et al., 1999). breastfeeding, but the actual cessation of breast- The wide variability in the timing of supplemen- feeding, unless there is a substantial amount of tation, the types of supplementary foods used, protein in the supplementary food. If the supple- and the duration of breastfeeding in modern mentary diet involved a protein source such as populations supports this interpretation (Abel herbivore’s milk, as was suggested at Wadi Halfa

Copyright # 2006 John Wiley & Sons, Ltd. Int. J. Osteoarchaeol. 17: 1–25 (2007) Age-related Isotopic Variation in Nubia 17

Figure 5. Stable carbon isotopic composition of bone apatite samples from R and S cemetery groups by age. by White & Schwarcz (1994) and at the Dakhleh the three age categories over time, also visible in Oasis by Dupras et al. (2001), then perhaps the a declining range in the raw distributions of overall isotopic decline is indicative of a gradual isotopic values (Figures 3 and 4), supports the shift from maternal milk as the primary protein suggestion of an overall decline in the rate and source to one that included protein from variability of bone turnover after infancy and C3-browser sources. The variation in the infant/ childhood. Such characteristics are difficult to young child category, however, suggests equal test, due to the inherently cross-sectional nature variability in the supplementary diet, which could of skeletal populations and the possible biasing include varying contributions of milk and/or flesh effects of mortality due to acute infectious or from C3 browsers and C4 grazers and of C3 and C4 nutritional stress that precludes many hard-tissue plants, with varying contributions of carbon and symptoms (Wood et al., 1992). The large percen- nitrogen from animal and plant sources. tage of infants/young children and subadults in A second possible interpretation specific to the both cemetery populations suggests that such infant/young child category is that the observed acute stress may have had a strong presence at ranges are due to variation in physiology affect- Kulubnarti. However, infants/young children in ing metabolism and growth rates or reflecting both cemeteries were interred in ceramic con- pre-existing poor health. The category of ‘infant/ tainers, which provided an effective buffer young child’ in this study spans birth through to against taphonomic processes and may have three years of age, and individuals classified as resulted in a substantial infant/young child sam- infants/young children were probably growing ple by virtue of unusually good preservation. and developing at different velocities depending Finally, seasonal variation in maternal dietary on their exact age within this larger categorisa- intake, similar to that argued by White (1993) for tion. The decline in standard deviations between the Wadi Halfa population, may have also played

Figure 6. Stable oxygen isotopic composition of bone apatite samples from R and S cemetery groups by age. an indirect role in the isotopic variation in the represent long-term averages and thus cannot infant/young child age category. Growing infants directly support a suggestion of seasonal variation and young children have markedly higher rates of in the composition of maternal tissues, but the bone turnover and isotopic incorporation com- range of isotopic variation among the infants and pared with adults and, if breastfeeding, would be young children in these populations and the more likely to reflect seasonal shifts in the iso- evidence for seasonal effects at Wadi Halfa topic composition of breastmilk, which in turn make this interesting food for thought. would reflect seasonal shifts in the maternal diet. A separate set of interpretations can be Therefore, the substantial variation in infant/ advanced regarding the distinct range of isotopic young child isotopic values may reflect differ- values for individuals aged 4–17 years at death. ences in the season of individual infant and young The Kulubnarti subadult range in 15N and 13 child deaths. In essence, infants and young chil- CCOL values is slightly but significantly dren who died during different times of the year depleted relative to both younger and older indi- would have skeletal isotopic signatures that viduals, with a mean 15Nof9.73 1.12% and a 13 reflect their mothers’ seasonally-dependent diets. mean CCOL of 18.01 0.80% (Table 2). An interpretation of diverse adult (therefore This could be attributed to a number of possible maternal) diets is supported by the descriptive factors, including differential growth rates or 15 13 N and CCOL data for all individuals aged 18 stress episodes, differential dietary intake, and and older (Table 2), which suggest differential variable levels of water stress. A substantial lit- adult dietary intakes and thus potential variability erature exists that identifies arrested skeletal in the isotopic composition of maternal tissues growth relative to dental or absolute age as a and breastmilk. Bone collagen isotopic data marker of nutritional and/or infectious stress

Copyright # 2006 John Wiley & Sons, Ltd. Int. J. Osteoarchaeol. 17: 1–25 (2007) Age-related Isotopic Variation in Nubia 19

(Martorell, 1983, 1989), a stress response that are complex, and the effects of these processes on also affects rates of bone protein turnover and the incorporation of isotopic signatures in skeletal micronutrient metabolism (May et al., 1993; Liu & tissues merit further research. Barrett, 2002; Martorell, 2002; Robins, 2003). The age-related trends seen in both 15N and 13 The presence of pathological stress markers CCOL values at Kulubnarti may be due in part such as cribra orbitalia in both cemetery popula- to a marked difference in subsistence options at tions at Kulubnarti lends support to the claim that the site. Unlike Wadi Halfa, the Kulubnarti site at least some individuals experienced stress dur- yielded no evidence of irrigation, but could have ing childhood, although the prevalence was supported the cultivation of C3 staples such as much higher in very young individuals and wheat and barley without such technology due to declined in adolescents (Mittler & Van Gerven, the flood pattern particular to the alluvial plains 1994). Because of this high stress load indicated of the Batn el-Hajar (Adams, 1977: 178–9). at Kulubnarti, the depleted 15N among suba- However, this region contained fewer floodplains dults could represent protein-poor diets that overall, which would make it advantageous to contributed to an early death. Under this ratio- herd C4 grazers such as goats and produce C4 nale, the higher 15N among adults could reflect staples such as millet and sorghum due to their better diets consumed by individuals who sur- higher survivability in hot, dry soils (Ambrose, vived subadulthood. Even if these differences are 1991; Tieszen, 1991). An archaeobotanical sur- skewed by mortality bias, however, this interpre- vey of common plant remains dated to the tation nevertheless leans towards variation in Christian period at Qasr Ibrim in Sudanese Nubia diet. (Rowley-Conwy, 1989, in White & Schwarcz, Interestingly, while White & Schwarcz (1994) 1994) suggested that sorghum and barley were found significant correlations of 15N with age, most prominent among cultigens. An additional 13 including a depletion in values among subadults, contributing factor to CCOL levels in the 13 they found no such relationship for CCOL in Kulubnarti remains would be the isotopic com- the Christian period remains at Wadi Halfa. This position of consumed herbivore tissues such as suggests that aside from the changes undergone meat and milk, which would also reflect C4 or C3 during weaning, there was little variation in diet- plant-based herbivore diets (Dupras et al., 2001). ary isotopic composition across the Wadi Halfa Taking all of these issues into consideration, skeletal sample. However, the juvenile 15N the diet at Kulubnarti appears to have been trend found at Kulubnarti is similar to that found roughly similar to those from nearby contempor- by Richards et al. (2002) at the Wharram Percy ary sites, consisting of mostly C3 (barley, site in England, by White & Schwarcz (1994) at legumes, wheat) with some C4 (sorghum, millet) the Nubian site of Wadi Halfa, and by Katzenberg plants and leguminous and/or animal protein. & Pfeiffer (1995) in Canada. Differences in Trace element analyses of hair from the S and R sample size and the actual shape of the 15N cemeteries have suggested a primarily plant- distribution by age between these data-sets make based diet, suggesting a reliance on legumes interpretations of isotopic composition related to such as beans for protein (Sandford & Kissling, growth and development difficult. They do, 1994). However, the range of 15N values in however, raise interesting questions regarding adults for both the S and R cemeteries is between age-based differences in macronutrient metabo- 7.5% and 11.8%. The range for most legumes is lism, and their effects on the isotopic composi- 0.4–5.0% (van der Merwe, 1982; Ambrose, tion of skeletal tissues. It has been suggested that 1993), although 15N enrichment in arid soils is high juvenile rates of growth and development known to enrich the 15N of many plants, includ- relative to adults would result in altered levels of ing nitrogen-fixers such as legumes (Schwarcz 15N discrimination in metabolic pathways and et al., 1999). Even taking a 3–5% trophic level subsequent rates of 15N routing to bone collagen, enrichment into consideration (Bocherens & producing depleted values in juvenile bone relative Drucker, 2003), it is possible that at least some to adults (Hare et al., 1991). However, the factors animal protein was included in adult diets to involved in skeletal growth and development produce the 15N values observed in their cohort.

However, because low levels of rainfall charac- among the S group, means that the possibility terise the surrounding environment, 15N values of differential protein consumption by juveniles throughout the local foodweb would potentially should not be ruled out. have been enriched by up to 3% (Ambrose, This interpretation is complicated by the 1991), and 13C values by approximately 2–3% potential enriching effect of aridity throughout (Ambrose, 1993). When one takes into account the Kulubnarti food web. If all individuals shared the enrichment of 15N values expected in an arid equal access to water sources, however, the locale such as Kulubnarti, these adult isotopic differences between the juvenile and adult group- ranges could reflect dietary protein intake domi- ings suggest a subadult dietary pattern charac- 13 15 nated by leguminous sources. While it is also terised by lighter CCOL and N values. Even possible that riverine products such as fish con- if it is assumed that preferential access to potable tributed to the diet at Kulubnarti, the range of water was given to juveniles aged 4–17 years in isotopic values, coupled with ethnographic evi- this sample, which would buffer them from dence of long-present fish taboos and a lack of water-stress induced 15N enrichment compared archaeological evidence of fish consumption with adults, such a practice would still constitute (Adams, 1977), suggest a more terrestrially-based a separate, intermediate overall subsistence cate- diet. gory. With these factors in mind, it appears as The implications of these age-related trends though a variable but distinctly age-dependent are unclear. Modern nutritional and ethnographic set of subsistence strategies was pursued at research has identified substantial variation in Kulubnarti. Depending on rates of delay between differential intra-household food allocation dietary shifts and the incorporation of new iso- among numerous populations, with beneficial topic ratios into collagen and apatite, young (Gittelsohn et al., 1997; Graham, 1997) and children were probably completely weaned harmful results (reviewed in Messer, 1997). These soon after age three and were consuming a studies emphasise not only the variability in subadult diet after age four. The gradual decline intrahousehold allocation strategies, but also in 15N across infants/young children aged six the importance of measuring protein and micro- months to four years at death may have reflected nutrient intake in addition to overall caloric supplementation with protein sources such as intake, to more accurately assess overall nutri- bean gruel or animal products, the latter of which tional status. This is especially salient to this may have been present at the Wadi Halfa site study, as the Kulubnarti data suggest age-related (White & Schwarcz, 1994). Supplementation differences specifically in protein intake versus with a protein source could create a more gradual merely the overall diet, allowing an assessment of 15N isotopic decline in infant/young child tis- childhood dietary composition with a more sues because those individuals would be shifting clearly defined set of dietary variables. Further- to a lower trophic level nonetheless characterised more, ethnographic studies point to belief sys- by different protein intakes relative to subadults tems centred on definitions of childhood, and adults. Individuals with relatively low values vulnerability and/or gender bias at various age 13 15 of CCOL and N, which in the Kulubnarti levels as strong predictors of allocation strategies, samples were primarily subadults, may have con- perhaps more so than household food security or sumed disproportionately less protein or different household economy (Messer, 1997). Applying forms of protein with lower 15N values, such as this to the Kulubnarti data, the lack of predictive increased consumption of legumes and decreased value of sex on inorganic or organic 13Cor15N consumption of milk, blood, meat or other animal suggests that, within the resolving power of protein. While a comparison of the calculated isotopic discrimination, sex is not a markedly 13 Á CAP-COL offsets between the pooled age contributing factor to dietary intake and nutri- cohorts reveals only very small differences tional access. However, the variation between between the juvenile and adult age cohorts (less the subadult and adult cohorts suggests a set of than 1), the relatively small subsample size and dietary practices centred on childhood as distinct slightly larger offset for juveniles, especially from adulthood. The range of isotopic variation

Copyright # 2006 John Wiley & Sons, Ltd. Int. J. Osteoarchaeol. 17: 1–25 (2007) Age-related Isotopic Variation in Nubia 21 within the subadult cohort suggests that these and different sources of water. It is therefore practices were not narrowly defined or perhaps possible that the presence of non-local immi- varied by season or food availability. grants at Kulubnarti was responsible for the An alternate interpretation is that this trend is differences in isotopic dietary indicators, rather not indicative of food allocation differentiating than culturally-mediated dietary variation within juveniles from infants and young children and a stable, local population. Future research on the adults, but is rather an artefact of two mortuary Kulubnarti S and R populations will examine populations, an interpretation that could be bone carbonate 18O variation in a larger sample extended to the clustering of values in the of the population in order to address this ques- infant/young child (0–3 yrs) age category. tion more directly. Wright & Schwarcz (1999: 1160) suggested that ages of supplementation and weaning among infants/young children in mortuary samples are Conclusion earlier than those of survivors, due to the protec- tive effects of prolonged breastfeeding. The very This study has produced isotopic dietary profiles nature of infant/young child and subadult mor- for two large skeletal populations with known tuary samples, essentially an assemblage of non- burial contexts and a substantial background of survivors, could mean that the trends seen here osteological and archaeological research, permit- represent subsistence strategies that ‘failed’, in the ting an in-depth interpretive analysis of palaeo- sense that the affected individuals were unable to dietary trends within a larger framework of survive early-to-mid childhood. The adult isoto- behavioural and environmental interaction. Several pic range, therefore, may more accurately reflect interesting trends emerged from the isotopic common diets at Kulubnarti in that such diets data-set, most notably a distinct age-based pat- 15 13 permitted survivorship past infancy and subadult- terning of N and CCOL values between hood. The fact that the infants/young children infants/young children, juveniles and adults. and subadults in both cemeteries, despite marked The causal factors for this tripartite patterning intra-group variation, were clearly different at the are difficult to identify. However, it is suggested inter-group level suggests that whether the sub- here that a ‘childhood’ diet may have existed at sistence patterns were successful or not, they Kulubnarti that consisted of isotopically depleted were still distinct. protein and plant sources relative to the diets of A final interpretive possibility is that the iso- infants/young children and adults, with the immi- topic distinction between subadults and adults at gration of non-local adults further contributing to Kulubnarti is influenced by the presence of non- the variation in dietary composition in the years local immigrants in the adult cohort. As shown in leading up to death. Figure 6, 18O values in the adult cohort are As the range of available food resources depleted relative to the infant/young child and included a variety of C3 and C4 cereal plants subadult cohorts, especially among adults aged and both animal and vegetable protein, it is over 35 years at death. Moreover, a range of reasonable to postulate heterogeneity in dietary approximately 3% within the pooled adult composition according to age. The wide range of cohort supports the notion that some of the isotopic values among the infant/young child adults interred at Kulubnarti were not from the subgroup suggests the absence of a uniform area, or were and had relocated elsewhere during process of supplementation and weaning, and life. White et al. (2004) posit immigration as a possibly seasonally variable maternal diets. The source of 18O variation at the nearby site of gradual decline in infant/young child 15N values Wadi Halfa, while Dupras & Schwarcz (2001) up to age four also suggests varying degrees of described similar trends in Egypt, suggesting a supplementation with high protein foods or pro- greater degree of population movement in the longed breastfeeding with supplementation. region than previously considered. Residence in Also interesting is the lack of significant dif- an ecologically distinct area would imply subsis- ference in any isotopic dietary indicator between tence strategies that utilised different foodwebs the S and R cemeteries. This suggests that the

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