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Stable isotope palaeodietary study of humans and fauna from the multi-period (Iron Age, Viking and Late Medieval) site of Newark Bay, Orkney
Journal of Archaeological Science 33 (2006) 122e131 http://www.elsevier.com/locate/jas
Stable isotope palaeodietary study of humans and fauna from the multi-period (Iron Age, Viking and Late Medieval) site of Newark Bay, Orkney M.P. Richards a,b,*, B.T. Fuller c,d, T.I. Molleson e a
Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany b Department of Archaeological Sciences, University of Bradford, Bradford, West Yorkshire BD7 1DP, UK c Research Laboratory for Archaeology and the History of Art, 6 Keble Road, Oxford OX1 3QJ, UK d Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK e Department of Palaeontology, Natural History Museum, Cromwell Road, London SW7 5BD, UK Received 9 August 2004; received in revised form 24 June 2005; accepted 1 July 2005
Abstract We report here on stable carbon and nitrogen isotope measurements of human and faunal bone collagen from the Iron Age, Viking Age, and Late Medieval site of Newark Bay, Orkney, Scotland. We found a wide range of results for humans in both d13C (ÿ15.4& to ÿ20.3&) and d15N (8.6&e15.6&) values. The enriched carbon and nitrogen values indicate the consumption of significant amounts of marine protein, which is very unusual for post-Mesolithic (e.g. 4000 cal BC) UK and European populations. Also of interest is a statistically significant difference in d13C (t Z ÿ2.48, p Z 0.011) and d15N (t Z ÿ2.44, p Z 0.011) values, and therefore diets, between adult males and females at this site, with males (d13C Z ÿ17.8 G 1.2&, d15N Z 13.2 G 1.6&) having, on average, a higher proportion of marine protein than females (d13C Z ÿ18.9 G 1.1&, d15N Z 11.8 G 1.8&). The weaning age of the sub-adults was difficult to interpret due to the large isotopic variation in the adult females, but nearly all individuals between birth and 1.25 years have elevated d15N values indicating that they were breastfed to some extent. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Palaeodiet; Weaning; d13C; d15N; Orkney; Pictish; Viking Age; Late Medieval
1. Introduction Stable isotope analysis of carbon (d13C) and nitrogen (d N) in human and faunal bone collagen from archaeological contexts is an established method for determining past diets, and is increasingly used to determine past human diets at a range of archaeological sites from different time periods and regions. In the United Kingdom, a relatively large number of isotopic 15
* Corresponding author. Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany. Tel.: C49 341 3550 0. E-mail address: [email protected] (M.P. Richards). 0305-4403/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jas.2005.07.003
studies have been undertaken, especially in recent years, on prehistoric [20,21,23,24,26,28,29] and historic [2,3,17,18,19,25,27] collections. One of the surprising findings of this research, and one which is echoed in isotopic studies of Holocene sites in other areas of Europe, is that the only evidence of the significant consumption of marine foods is during the Mesolithic period, which dates from the start of the Holocene to approximately 4000 cal BC in the UK [21,23,26,28,29]. The study reported here was undertaken for two reasons. Firstly, the time periods represented at this site, (Iron Age, or ‘Pictish’, Viking Age and Late Medieval periods) are relatively unrepresented in the body of isotopic data so far produced for Holocene Europe.
M.P. Richards et al. / Journal of Archaeological Science 33 (2006) 122e131
Secondly, the main impetus for this study was to explore the dietary adaptation of humans in what is a fairly unique environment, where farming is possible although the site is located in the far north of Europe (a latitude of 59 N), but also where there is easy access to relatively abundant marine food resources. In hunteregatherer societies, such as in the Mesolithic period, it may be easier to predict the adaptive strategy of humans in a context such as this, where only wild resources are available (i.e. marine resources are the logical dietary choice). However, it is more difficult to predict the adaptive dietary strategy in complex historic societies which have a long established tradition (and dependence on) of agriculture and animal husbandry. We therefore initiated this study to explore whether historic populations in such an environment would largely be constrained by cultural practices and would therefore maintain a subsistence strategy based on husbandry and agriculture, or would instead revert to the use of available and abundant marine resources, a practice which has not yet been observed in isotopic studies of post-Mesolithic sites in the UK and elsewhere in Europe. As so few studies have been undertaken in environmental contexts such as these we also measured the isotopic values of faunal species. This was done to provide baseline values for interpreting the human values, with a special focus on whether there were any unusual isotope effects due to this site’s location (such as elevated nitrogen isotope values that might come from sea spray), and particularly if animals were being foddered on and fed marine foods such as seaweed. Additionally, the large number of infant and juvenile skeletons also allowed the investigation of breastfeeding and weaning patterning in this population.
2. The site of Newark Bay The site is located on the eastern edge of Newark Bay, a south facing bay in Deerness, East Mainland, Orkney, Scotland. The site was excavated by Brothwell during several rescue seasons from 1968 to 1972, and over 200 individuals were recovered making the Newark Bay collection the most important sample of human remains recovered in Orkney [5]. The burials were mostly single interments, aligned eastewest, and without grave goods. As part of a comprehensive dating project of Pictish and Medieval sites in this region, Barrett et al. [2,3] obtained radiocarbon dates and stable carbon isotope values on a number of burials from this site. Broadly, the uncalibrated radiocarbon dates range from 550 to 1200 BP, representing the Iron Age (‘Pictish’), Viking Age and Late Medieval burials. Barrett et al. [3] found
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a wide range of carbon isotope values with many earlier individuals having terrestrial signatures (ca. ÿ21.0&), and a number of later (Viking Age and Medieval) individuals with more marine values (ca. ÿ16.0&).
3. Stable isotopes and dietary reconstruction The isotopic composition of body tissues such as bone collagen reflects the isotopic signatures of the foods and liquids consumed during life [16]. In archaeological research, bone collagen is routinely analyzed for its carbon (d13C) and nitrogen (d15N) stable isotope ratios. The results obtained from this analysis are quantitative and reflect the origin of the protein portion of the diet during the last years of an individual’s life [1,33]. Stable isotope results are measured as the ratio of the heavier isotope to the lighter isotope (13C/12C or 15N/14N) and reported as d values in parts per 1000 or ‘‘permil’’ (&) relative to internationally defined standards for carbon (vPDB) and nitrogen (AIR). For recent comprehensive reviews see Sealy [32], Katzenberg [12] and Mays [17]. In Holocene Europe, where there is little use of C4 plants, the ratio of carbon isotopes in human bone collagen is primarily used to distinguish between the consumption of marine protein (e.g. d13C of ca. ÿ12 G 1& for 100% marine protein) and terrestrial C3 protein (e.g. d13C ca. ÿ20& G 1& for a 100% terrestrial protein). Human bone collagen d13C values that fall between these two theoretical end points are therefore interpreted as reflecting relative consumption of marine vs. terrestrial protein using a simple linear mixing model. The nitrogen isotope ratio of mammal bone collagen has been shown to be enriched in 15N over the protein consumed, with enrichment between consumer and diet d15N values of 2e4& [14,31]. When baseline herbivore and carnivore values are known for a site, it is then possible to see how the humans, as omnivores, compare and then use the d15N values to determine whether the humans were obtaining their protein from mainly plant sources (e.g. similar values to the herbivores) or animal protein (e.g. similar to the carnivores) or the more usual, somewhere in between reflecting a diet with a mix of both animal (meat or milk products) and plant proteins. 3.1. Breastfeeding and weaning patterns When infants are breastfeeding they are one level above their mothers in the food chain as they are essentially consuming their mother’s tissue through the ingestion of breast milk. Thus, the d15N values of nursing infants are elevated by 2e4& compared to the mother [8,30]. During the weaning process, the
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Table 1 d13C and d15N results for the fauna from Newark Bay (Mean G SD) Species
d13C G SD
d15N G SD
N
Cattle Sheep/goat Pigs Fish Seals
ÿ21.8 G 0.2& ÿ21.8 G 0.8& ÿ20.6 G 1.3& ÿ11.8 G 1.2& ÿ12.0 G 0.5&
5.5 G 0.8& 7.0 G 0.9& 8.4 G 1.6& 13.6 G 1.0& 17.2 G 1.5&
9 5 6 4 8
consumption of supplementary foods results in declining infant body tissue d15N values, as they are a product of the combination of 15N-enriched mother’s milk and weaning foods with lower d15N values. When a child is fully weaned (cessation of breastfeeding), its protein d15N values are then similar to those of its mother, assuming that the child’s diet is similar to that of the mother’s. In archaeological contexts, the age of weaning and the end of breastfeeding has been estimated by measuring the d15N of bone collagen from different age classes of infants and children and noting the age at which the d15N values return to those of the adult female population [9,10,25,30]. While this method yields a general time frame for the duration of breastfeeding, a precise calculation of the introduction of weaning foods is not possible as uncertainty exists about the amount of time needed for the infant skeleton to fully incorporate the isotopically depleted post-weaning nitrogen. In addition, d15N values obtained from infants who died during breastfeeding and weaning need to be interpreted with caution as these individuals might have been fed different diets or died of malnutrition, and this could potentially alter the expected d15N values [11]. Despite these potential problems, measurement of subadult d15N values has become an established method of estimating the timing of weaning and duration of breastfeeding in past populations.
4. Methods Bone collagen was extracted from human adults (n Z 40), juveniles (n Z 88) and faunal species (n Z 32; cattle, pigs, sheep, goats, seals, fish) from the Newark Bay site. The faunal samples were interred, or closely associated, with the human burials. For the humans, we sampled ribs and selected a sub-sample of the total population that had representative numbers of adult males and females as well as juveniles from the various age classes. The complete extraction protocol is described in Richards and Hedges [22] with the addition of a final stage of ultrafiltration before lyopholisation following Brown et al. [6]. The collagen was generally very well preserved, and all samples reported here had collagen yields of over 1% and C:N ratios between 2.9 and 3.6, which are believed to be indicators of good quality collagen [7].
5. Results 5.1. Fauna The faunal isotope data are given in Table 1 and plotted in Fig. 1. As discussed above, faunal samples were measured to establish local baseline food-web stable isotope values and to explore whether domesticated animals, such as sheep/goat, cattle, and pigs were being fed marine foods such as seaweed. The d13C results from the cattle (ÿ21.8 G 0.2&) and sheep/goat (ÿ21.8 G 0.8&) samples do not indicate the consumption of any significant amounts of marine protein. The cattle d15N values (5.5 G 0.8&) are typical of those found in the UK during the Holocene [23,24]. The sheep/goat d15N values (7.0 G 0.9&) are somewhat
20 18 16 14
15N
12 10 8 Cattle Deer Pigs Seals Fish Sheep/goat
6 4 2 0 -25
-23
-21
-19
-17
-15
-13
-11
13C
Fig. 1. Plot of the bone collagen d13C and d15N values of fauna from Newark Bay.
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higher than expected, and this might be due to a seaspray effect where marine nitrogen, which is enriched compared to most soil nitrogen, is deposited near the coast and is taken up by plants. This possible reason, however, does not explain why the d15N values of the cattle are not elevated as well, unless the cattle fed on specific foods that grow away from the coast, whereas perhaps the sheep/goats grazed on plants near the ocean. There are a range of pig values, and the average values d13C (ÿ20.6 G 1.3&) and d15N (8.4 G 1.6&) differ markedly from the sheep/goat and cattle averages. As can be seen in the individual data points (Fig. 1) a number of the pigs are considerably shifted in d13C and d15N, indicating an input from marine foods and this is the cause of the overall difference in the pig average values. It is unlikely (although not impossible) that the pigs could obtain significant marine protein themselves; therefore these isotopic results most likely indicate that the pigs were consuming human refuse. The fish (species unidentified) (d13C Z ÿ11.8 G 1.2&; 15 d N Z 13.6 G 1.0&) and seal (d13C Z ÿ12.0 G 0.5&; d15N Z ÿ17.2 G 1.5&) values are as expected, with average marine d13C values and elevated d15N values. The seal d15N values are approximately 3& higher than the fish values, indicating that these fish, and perhaps others at the same trophic level, were the main protein source for the seals. 5.2. Adults The adult human data are given in Table 2. There is a large range of both d13C (ÿ15.4& to ÿ20.3&) and d15N (8.6&e15.6&) values, which means that there was a range of diets at this site, with some individuals obtaining a major portion of their dietary protein (up to 50%) from marine sources. Fig. 2 is a plot showing the adult data along with average faunal data. The human data plot in a clear line, with a regression r2 value of 0.85. Therefore, the most parsimonious explanation for the human data is that it lies along a mixing line between a marine and terrestrial end point. The likely candidates for these end points are cattle meat (and milk) for the terrestrial input, and marine mammals, such as seals. The marine contribution may also have been from higher trophic level fish than those we measured here. Of course, not all individuals lie along this line, and it is likely that this is due to the contribution of other protein sources with higher d15N values, such as sheep/goat and pigs, in addition to lower trophic level marine organisms. The isotopic values for both the adult males (average d13C Z ÿ17.8 G 1.2&, average d15N Z 13.2 G 1.6&) and females (average d13C Z ÿ18.9 G 1.1&, average d15N Z 11.8 G 1.8&) confirm a statistically significant difference between the sexes for both d13C (t Z ÿ2.48, p Z 0.011) and d15N (t Z ÿ2.44, p Z 0.011) (Fig. 3,
Table 2 d13C and d15N results from the adult humans at Newark Bay (YA Z young adult; MA Z mature adult; OA Z older adult) Sample
Age
Sex
d13C (&)
d15N (&)
C:N
NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB
YA YA YA YA YA YA YA YA MA MA MA MA MA MA MA MA MA MA MA MA MA MA MA MA MA MA MA MA MA OA OA OA OA OA OA OA OA OA OA OA
F M ? ? M M F F F ? F ? M M F F F M F F M F M M M F F F F M M F F F F F F F F F
ÿ19.7 ÿ16.9 ÿ19.3 ÿ17.8 ÿ19.5 ÿ18.7 ÿ18.4 ÿ20.3 ÿ16.9 ÿ18.6 ÿ19.6 ÿ17.3 ÿ18.0 ÿ15.4 ÿ19.6 ÿ20.0 ÿ18.5 ÿ17.5 ÿ17.1 ÿ19.2 ÿ17.5 ÿ19.6 ÿ17.8 ÿ17.3 ÿ17.7 ÿ18.9 ÿ19.4 ÿ16.3 ÿ20.2 ÿ20.0 ÿ17.7 ÿ19.1 ÿ17.9 ÿ19.6 ÿ19.5 ÿ18.4 ÿ19.4 ÿ19.8 ÿ17.7 ÿ17.5
10.9 14.4 10.8 13.7 10.1 11.6 13.0 8.6 13.5 12.7 9.9 13.9 13.4 15.6 10.4 10.5 12.0 13.7 14.6 12.0 13.8 10.8 13.4 14.4 13.8 12.8 11.0 15.6 10.1 10.9 13.7 10.4 12.1 10.6 11.5 14.4 11.5 10.5 12.9 14.4
3.4 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.2 3.3 3.3 3.2 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.4 3.3 3.3 3.3 3.3 3.3 3.4 3.3 3.3 3.3 3.3
69/34 68/12 69/33 69/8 69/2 69/105 68/2 69/36 70/15 70/30 69/11 70/35 68/14 71/1 68/20 69/4A 69/99 70/37 71/2 70/1 69/83 69/85 68/5 70/39 71/8 70/38 69/104B 69/104A 68/16 68/16A 69/67A 71/3 69/107 69/84 69/104 70/6 69/NO 71/9 71/7 69/69
Table 4). These results indicate that, on average, the males were generally consuming a diet with more marine protein than the females. 5.3. Infants and juveniles The d13C and d15N values for the infants, young children, and adolescents are presented in Table 3 and plotted in Fig. 4a, b. For the sub-adults aged between 0 and 1.25 years, there is a large spread in the d13C (ÿ16.3& to ÿ20.7&) and d15N (10.1& to 17.2&) values. In Fig. 5, the d13C and d15N results for the adult females and different age categories of the infants are plotted. The perinatal/stillborn/neonate and 1- to 6-month individuals have slightly higher d15N values
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M.P. Richards et al. / Journal of Archaeological Science 33 (2006) 122e131 24 22
R2 = 0.86
20 18 16
15N
14 12 10
Cattle Sheep/Goat
8
Pig
6
Fish
4
Seal Adult humans
2
Linear (Adult)
0 -23.0 -22.0 -21.0
-20.0 -19.0 -18.0 -17.0 -16.0 -15.0 -14.0 -13.0 -12.0 -11.0 -10.0 13C
Fig. 2. Plot of the human adult bone collagen d13C and d15N values from Newark Bay, with a regression line. Also included are the mean values of fauna from the site.
than the adult females indicating that they were breastfeeding to some extent before death. In addition, the infants in the age category of 9 months to 1.25 years have significantly elevated d15N values (2e4&) when compared to the adult females (Fig. 4). This high 15Nenrichment suggests that these older infants were being primarily breastfed before death.
6. Discussion The isotopic results from this site are significant for a UK population, since previous stable isotope studies
of Neolithic [20,21,23,28], Iron Age/Roman [27], AngloSaxon [19], and Medieval [17,18] humans have shown almost no, or very little (d13C % ÿ18&), marine foods in the diets. The Newark Bay data, with clear marine isotopic signals are most similar to much earlier Mesolithic humans from coastal sites in the UK, who also consumed a significant amount of marine protein [22,23,26,28,29]. At Newark Bay, some inhabitants had a diet where 50% of the protein was from marine sources (assuming end points of approximately ÿ21& for 100% terrestrial and ÿ12& for 100% marine). There is a large range in the d13C (ÿ15.4& to ÿ20.3&) and d15N (8.6&e15.6&) adult isotopic values.
18 16 14
15N
12 10 8 6 4
Females Female mean Males Male mean
2 0 -21
-20.5
-20
-19.5
-19
-18.5
-18
-17.5
-17
-16.5
-16
-15.5
13C
Fig. 3. Adult human d13C and d15N values plotted by sex.
-15
-14.5
-14
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M.P. Richards et al. / Journal of Archaeological Science 33 (2006) 122e131 Table 3 d13C and d15N results from infants and juveniles from Newark Bay (P Z perinatal; S/N Z stillborn/neonate; N Z neonate; m Z months; a Z years) Sample
Age
d13C (&)
d15N (&)
C:N
NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB
P P P S/N S/N S/N S/N S/N S/N S/N S/N S/N N N N N N N N N N N N N N N 1m 1m 1m 1m 1m 3m 3m 3m 3m 3m 3m 3m 3m 3m 3m 3m 3m 3m 3m 3m 3m 6m 6m 6m 6m 6m 6m 6m 6m 6m 6m 6m 6m 9m 9m
ÿ18.5 ÿ16.4 ÿ18.2 ÿ19.0 ÿ20.2 ÿ17.7 ÿ19.9 ÿ19.5 ÿ19.1 ÿ19.2 ÿ16.3 ÿ20.0 ÿ19.5 ÿ18.9 ÿ18.1 ÿ19.8 ÿ19.4 ÿ17.5 ÿ16.9 ÿ20.2 ÿ19.5 ÿ20.2 ÿ17.4 ÿ18.6 ÿ17.7 ÿ19.8 ÿ20.7 ÿ18.4 ÿ18.3 ÿ17.0 ÿ17.9 ÿ19.9 ÿ17.6 ÿ18.8 ÿ18.4 ÿ20.5 ÿ17.5 ÿ19.7 ÿ20.0 ÿ19.2 ÿ18.1 ÿ19.6 ÿ20.2 ÿ19.8 ÿ19.7 ÿ18.0 ÿ20.0 ÿ18.8 ÿ18.1 ÿ20.7 ÿ19.7 ÿ20.5 ÿ20.1 ÿ20.3 ÿ18.7 ÿ19.6 ÿ19.4 ÿ19.6 ÿ20.7 ÿ18.2 ÿ18.8
14.6 16.4 16.3 14.8 11.6 14.8 12.4 13.0 12.5 13.0 15.6 11.6 13.4 13.7 14.7 12.7 13.7 14.8 15.6 10.5 13.4 11.0 15.8 13.9 15.8 10.2 10.6 13.7 14.3 17.2 13.5 12.3 15.3 13.2 15.1 10.7 15.3 11.0 10.5 13.2 14.3 12.0 12.0 11.5 12.2 15.5 10.5 13.2 13.7 10.1 11.8 10.5 10.9 10.3 14.3 11.3 15.1 14.5 11.7 16.1 17.2
3.3 3.3 3.3 3.4 3.4 3.3 3.4 3.4 3.4 3.3 3.4 3.4 3.4 3.3 3.3 3.3 3.4 3.3 3.4 3.3 3.3 3.3 3.3 3.5 3.3 3.3 3.4 3.1 3.4 3.3 3.4 3.4 3.3 3.4 3.3 3.3 3.4 3.3 3.3 3.4 3.4 3.3 3.3 3.5 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.5 3.3 3.3 3.4 3.3 3.4 3.4 3.4 3.3 3.3
69/54 69/52A 69/31 70/21 68/25 69/60 69/109 69/96 70/32 70/4 70/26 68/19 69/41 69/79 69/37 70/11 70/14 69/109 69/19 69/68 69/97 69/103 69/53 70/27 69/40 69/76 70/13 69/95 70/127 70/16 69/43 68/21 69/2 69/88 69/94 69/44 69/56 69/80 69/67X 69/5 70/18 70/33 69/78 69/100 69/30 70/17 71/4 69/92 70/7 69/93 69/70 69/13 71/10 71/5 69/71 69/108 69/63 69/38 69/77 69/57 69/15
Table 3 (continued) Sample
Age
d13C (&)
d15N (&)
C:N
NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB
9m 9m 9m 9m 1a 1.25 a 1.25 a 3a 3a 3a 6a 8a 8a 9a 11 a 11 a 11 a 11 a 12 a 13 a 13 a 15 a 15e16 a 16 a 16 a 17 a 17 a
ÿ18.1 ÿ19.9 ÿ18.3 ÿ19.2 ÿ17.6 ÿ17.3 ÿ19.5 ÿ18.4 ÿ20.9 ÿ20.5 ÿ20.2 ÿ16.9 ÿ19.7 ÿ20.3 ÿ18.7 ÿ18.9 ÿ19.0 ÿ17.3 ÿ19.6 ÿ19.1 ÿ17.9 ÿ19.4 ÿ19.9 ÿ17.8 ÿ17.0 ÿ18.1 ÿ19.9
16.3 13.7 16.5 15.0 17.1 17.0 14.7 13.8 10.1 11.6 10.7 14.5 10.0 10.2 13.0 12.3 10.3 13.9 10.3 12.2 11.5 10.8 10.3 13.8 14.1 13.1 10.5
3.3 3.3 3.3 3.3 3.2 3.4 3.4 3.3 3.4 3.3 3.4 3.3 3.3 3.4 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.4 3.4
69/57 70/10 69/51 70/3 69/42 70/25 69/73 70/20 69/64 69/82 68/36 69/101 69/75 69/17 70/28 69/89 69/55 70/2 69/32 70/5 69/26 69/91 68/13 69/1 69/CC4 69/46 69/16
This indicates that the dietary adaptation was not uniform. While relatively modest isotopic, and therefore dietary, variations between adults have been found at other UK archaeological sites [19,27], the large spread in the isotopic results from Newark Bay is particularly striking. One possible explanation for this is that the isotopic results are not indicating exceptional variation in diets within a contemporary society, but are instead due to dietary changes over time. Research by Barrett et al. [2,3] has identified three different occupation periods at the site (Pictish/Viking Age/Late Medieval). Through the analysis of d13C values and associated radiocarbon dates, Barrett et al. [2] found that dietary habits changed over time with later periods (starting in the Viking Age) having an increasingly more marine diet. Recent research by Barrett and Richards [4] confirmed this earlier result, and found that actually many of the individuals with the more marine isotopic values dated to the Medieval period, between the 11th and 14th centuries AD. We have plotted the d13C values against the radiocarbon ages (Table 5) in Fig. 6. We did not calibrate these ages, nor did we account for the marine reservoir correction that would be required for a number of the individuals, as this is beyond the scope of this paper, and are provided in Barrett and Richards [4]. This plot demonstrates that although there is a peak in the number of individuals with a strong marine d13C
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The observed d13C and d15N differences between the males and females, with the males, on average, having more marine protein in their diets, is also significant since isotopic differences between the sexes are rarely found in stable isotope research. In the UK, male/female isotopic variations (d15N only) have only been found during the late Roman period ([28], Fuller et al., unpublished data). This variation in marine protein consumption between the sexes could be associated with different work activities such as males spending more time at sea fishing. It is also possible that the dietary variations indicate differential access to food resources associated with individual status and social class. Nutritional consumption based on social stratification is unfortunately impossible to identify at Newark Bay, as the burials did not contain grave goods which could have been used to further identify identities and social positions. The use of stable isotopes to determine breastfeeding and weaning practices is dependent on the fact that adult diets need to be fairly uniform [25]. The inhabitants of Newark Bay do not conform to this
Table 4 Student t-tests between the mean d13C and d15N values of the adult males and females from Newark Bay Isotope Female G SD Male G SD (n Z 24) (n Z 12) d13C d15N
Degrees t-Value Significance of level freedom
ÿ18.9 G 1.1& ÿ17.8 G 1.2& 21 11.8 G 1.8& 13.2 G 1.6& 25
ÿ2.48 ÿ2.44
0.011 0.011
value in the Viking and Medieval period, there are also many individuals with clearly terrestrial signatures in this period (and all periods). Therefore, there is no shift in diet through time by all individuals, merely an increase in the frequency of individuals with marine isotopic values in the Viking and Medieval periods. As it is impossible to determine the ages of each burial without directly radiocarbon dating, it is not possible to divide all of our study population into distinct chronological groups. Therefore we have combined all of the isotopic results from this site and consider it a single population for this study.
-14 -15 -16
13C
-17 -18 -19 -20 Adult Females
-21 -22 0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20
Age (years) 18 17 16 15 15N
14 13 12 11 10 Adult Females
9 8 0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20
Age (years) Fig. 4. d13C (a) and d15N (b) bone collagen values for infants and juveniles plotted against age at death. Also included are the adult female mean G SD isotope values.
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M.P. Richards et al. / Journal of Archaeological Science 33 (2006) 122e131 18 17 16 15
15N
14 13 12 11
Perinatal/Stillborn/Neonate
10
1-6 months 9 months - 1.25 years
9
Adult Females
8 -22
-21
-20
-19
-18
-17
-16
-15
-14
13C
Fig. 5. Plot of infant and adult female bone collagen d13C and d15N values. Note that nearly all infants have elevated d15N results compared to the adult females indicating that they were still being breastfed to some extent before death.
pattern, as there is a large range in the diets of the adult females. Thus, it is difficult to determine the age of weaning and the cessation of breastfeeding for this population (Fig. 4a, b). The infants aged from newborn to 1.25 years show elevated d15N values compared to the Table 5 AMS radiocarbon dates and associated isotopic values for adults from the Newark Bay site Skeleton
Lab no
d13C
d15N
AMS date
NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB
TO-6940 TO-7173 GU-10955 TO-7174 AA-54931 AA-54930 TO-7188 TO-7189 TO-7190 TO-7191 TO-7180 TO-7181 TO-7182 TO-7183 TO-7184 TO-7178 TO-7185 AA-54932 TO-7186 TO-7187 TO-7192 AA-54933 AA-54934 AA-54935 TO-6937 AA-54936 AA-54937 TO-7193 TO-6934 AA-54938
ÿ18.4 ÿ16.9 ÿ18.0 ÿ20.0 ÿ19.6 ÿ17.8 ÿ16.3 ÿ19.4 ÿ18.7 ÿ17.9 ÿ19.6 ÿ19.8 ÿ20.3 ÿ17.7 ÿ17.5 ÿ17.8 ÿ17.5 ÿ17.5 ÿ19.6 ÿ18.5 ÿ19.2 ÿ16.9 ÿ17.5 ÿ17.3 ÿ18.4 ÿ15.4 ÿ17.1 ÿ19.1 ÿ17.7 ÿ17.7
13.0 14.4 13.4 10.9 10.4 13.4 15.6 11.0 11.6 12.1 9.8 10.9 8.6 13.7 14.4 13.7 13.8 13.8 10.8 12.0 12.0 13.5 13.7 14.4 14.4 15.6 14.6 10.4 13.8 13.8
550 G 40 930 G 40 630 G 50 1190 G 40 1055 G 40 590 G 40 1030 G 40 1130 G 50 990 G 50 1340 G 60 1380 G 30 930 G 40 1090 G 40 990 G 40 910 G 40 830 G 30 1060 G 40 1070 G 45 1000 G 40 1060 G 40 1010 G 60 1060 G 35 1130 G 40 965 G 40 700 G 40 1075 G 35 1075 G 35 1200 G 40 1160 G 60 1020 G 45
68/2 68/12 68/14 68/16A 68/20 68/5 69/104A 69/104B 69/105 69/107 69/11 69/34 69/36 69/67a 69/69 69/8 69/83 69/83 69/85 69/99 70/1 70/15 70/37 70/39 70/6 71/1 71/2 71/3 71/8 71/8
Radiocarbon dates are from [4].
adult females, and this suggests that breastfeeding was continuing in some form until at least this age (Fig. 6). It is interesting to note that there are only a few juveniles older than 1.25 years at the site, which suggests that there was high infant mortality in the first two years of life. The introduction of solid foods or the weaning process is often linked to an increased risk of infant mortality and morbidity [13,15]. Reduced breast milk consumption decreases the level of immunity for infants, and the weaning diet has the potential to expose children to new pathogens and nutritional stress [13]. Perhaps there are a high number of juveniles in this age class because this may have been an age when the children were weaned onto a possibly nutritionally poor diet and were especially susceptible to infections during this time.
7. Summary and conclusions Stable carbon and nitrogen isotope ratio analysis was undertaken on bone collagen extracted from humans and fauna from the multi-period site of Newark Bay, Orkney, UK. The results indicate that there was a large amount of dietary variation with some individuals having an entirely terrestrial protein diet and others with a high input (ca. 50% of dietary protein) of marine protein. This high level of marine protein in the diet is unusual for the UK, especially for this time period, and has previously only been found during the Mesolithic period. It is especially interesting to observe this high level of ‘wild’ foods in such a recent, historic, complex society in Europe, where food is usually derived from animal husbandry and agriculture. A statistically significant variation in isotopic values was found between males and females, which is also a rare occurrence in isotopic studies. The data indicate that,
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M.P. Richards et al. / Journal of Archaeological Science 33 (2006) 122e131 -14.0 -15.0 -16.0
13C
-17.0 -18.0 -19.0 -20.0 -21.0 -22.0 -23.0 400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
Radiocarbon Age BP Fig. 6. Bone collagen d13C values of adults from Newark Bay plotted against uncalibrated radiocarbon ages BP. Dates are from [4]. For samples NB 69/83 and NB 71/8, where there are two dates on the same individual, the dates were combined for the plot.
on average, males had more marine protein that the females and this may be related to specific activities (i.e. fishing/sealing) or part of a larger change in dietary habits over time. Isotopic measurements were also undertaken on subadults (infants and juveniles) at Newark Bay. Due to the large variation in the adult female diet, it was difficult to determine the weaning age, but elevated d15N values indicate that breastfeeding continued in some form until at least 1.25 years of age. Isotopic studies of European populations are usually undertaken on prehistoric collections, where generally little is known about past diets and where, perhaps, they are easier to undertake as potential dietary inputs are limited only to wild food sources. Isotopic studies of more recent, late prehistoric and historic populations often do not show much variation in isotope values, although there are far fewer studies of these periods. Perhaps this is because isotopic analysis is too blunt a tool to tease out subtle dietary variations in societies that rely almost entirely on domesticated plants and animals obtained through animal husbandry and agriculture. However, this study has shown that in the right circumstances isotope analysis can make a significant contribution to our knowledge even in complex historic societies. The results presented here show that contrary to expectations there was a significant input of wild foods, namely marine foods, into the diets of the people buried at Newark Bay. Therefore, hopefully this study has helped demonstrate the utility of the isotopic method even in more recent historical period complex societies, providing more evidence of the wide range and variety of human dietary adaptations.
Acknowledgements We would like to thank James Barrett, Gundula Mu¨ldner, Mandy Jay two anonymous referees for helpful comments on the paper. We would like to thank the Wellcome Trust and the Max Planck Society for funding.
References [1] S.A. Ambrose, L. Norr, Experimental evidence for the relationship of the carbon isotope ratios of whole diet and dietary protein to those of bone collagen and carbonate, in: J. Lambert, G. Grupe (Eds.), Prehistoric Human Bone: Archaeology at the Molecular Level, Springer-Verlag, 1993, pp. 1e37. [2] J.H. Barrett, R.P. Beukens, D.R. Brothwell, Radiocarbon dating and marine reservoir correction of Viking Age Christian burials from Orkney, Antiquity 74 (2000) 537e542. [3] J.H. Barrett, R.P. Beukens, R.A. Nicholson, Diet and ethnicity during the Viking colonization of northern Scotland: evidence from fish bones and stable carbon isotopes, Antiquity 75 (2001) 145e154. [4] J.H. Barrett, M.P. Richards, Identity, gender, religion and economy: new isotope and radiocarbon evidence for marine resource intensification in early historic Orkney, Scotland, U.K., European Journal of Archaeology, in press. [5] D. Brothwell, D. Tills, V. Muir, Biological characteristics, in: R.J. Berry, H.N. firth (Eds.), The People of Orkney, Aspects of Orkney, vol. 4, The Orkney Press, Kirkwall, 1986, pp. 54e88. [6] T.A. Brown, D.E. Nelson, J.R. Southon, Improved collagen extraction by modified Longin method, Radiocarbon 30 (1988) 171e177. [7] M.J. DeNiro, Post-mortem preservation and alteration of in vivo bone collagen isotope ratios in relation to paleodietary reconstruction, Nature 317 (1985) 806e809.
M.P. Richards et al. / Journal of Archaeological Science 33 (2006) 122e131 [8] M.L. Fogel, N. Tuross, D. Owsley, Nitrogen isotope tracers of human lactation in modern and archaeological populations, Annual Report of the Director, Geophysical Laboratory, 1988e 1989, Carnegie Institution of Washington, Washington, D.C, 1989, pp. 111e116. [9] B.T. Fuller, M.P. Richards, S. Mays, Stable carbon and nitrogen isotope variations in tooth dentine subsections from Wharram Percy, Journal of Archaeological Science 30 (2003) 1673e1684. [10] D.A. Herring, S.R. Saunders, M.A. Katzenberg, Investigating the weaning process in past populations, American Journal of Physical Anthropology 105 (1998) 425e439. [11] K.A. Hobson, R.T. Alisauskas, R.G. Clark, Stable nitrogen isotope enrichment in avian tissues due to fasting and nutritional stress: implications for isotopic analyses of diet, The Condor 95 (1993) 388e394. [12] M.A. Katzenberg, Stable isotope analysis: a tool for studying past diet, demography and life history, in: M.A. Katzenberg, S.R. Saunders (Eds.), The Biological Anthropology of the Human Skeleton, John Wiley and Sons, New York, 2000, pp. 305e327. [13] M.A. Katzenberg, D.A. Herring, S.R. Saunders, Weaning and infant mortality: evaluating the skeletal evidence, Yearbook of Physical Anthropology 39 (1996) 177e199. [14] J.F. Kelly, Stable isotopes of carbon and nitrogen in the study of avian and mammalian trophic ecology, Canadian Journal of Zoology 78 (2000) 1e27. [15] J. Knodel, H. Kintner, The impact of breast feeding patterns on the biometric analysis of infant mortality, Demography 14 (1977) 391e409. [16] M.J. Kohn, You are what you eat, Science 283 (1999) 335e336. [17] S.A. Mays, Carbon stable isotope ratios in mediaeval and later human skeletons from northern England, Journal of Archaeological Science 24 (1997) 561e568. [18] G. Mu¨ldner, M.P. Richards, Fast or feast: reconstructing diet in Later Medieval England by stable isotope analysis, Journal of Archaeological Science 32 (2005) 39e48. [19] K.L. Privat, T.C. O’Connell, M.P. Richards, Stable isotope analysis of human and faunal remains from the Anglo-Saxon cemetery at Berinsfield, Oxfordshire: dietary and social implications, Journal of Archaeological Science 29 (2002) 779e790. [20] M.P. Richards, Human consumption of plant foods in the British Neolithic; direct evidence from bone stable isotopes, in: A. Fairbairn (Ed.), Plants in Neolithic Britain and Beyond, Oxbow Monograph, Oxford, 2000, pp. 123e135. [21] M.P. Richards, R.E.M. Hedges, A Neolithic revolution? New evidence of diet in the British Neolithic, Antiquity 73 (1999) 891e897.
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[22] M.P. Richards, R.E.M. Hedges, Stable isotope evidence for similarities in the types of marine foods used by Late Mesolithic humans at sites along the Atlantic coast of Europe, Journal of Archaeological Science 26 (1999) 717e722. [23] M.P. Richards, R.J. Schulting, R.E.M. Hedges, Sharp shift in diet at onset of Neolithic, Nature 425 (2003) 366. [24] M.P. Richards, R. Jacobi, A. Currant, C. Stringer, R.E.M. Hedges, Gough’s Cave and Sun Hole Cave human stable isotope values indicate a high animal protein diet in the British Upper Palaeolithic, Journal of Archaeological Science 27 (2000) 1e3. [25] M.P. Richards, S.A. Mays, B.T. Fuller, Stable carbon and nitrogen isotope values of bone and teeth reflect weaning at the Mediaeval Wharram Percy Site, Yorkshire, UK, American Journal of Physical Anthropology 199 (2002) 205e210. [26] M.P. Richards, P. Mellars, Stable isotopes and the seasonality of the Oronsay middens, Antiquity 72 (1998) 178e184. [27] M.P. Richards, T.I. Molleson, J.C. Vogel, R.E.M. Hedges, Stable isotope analysis reveals variations in human diet at the Poundbury Camp Cemetery site, Journal of Archaeological Science 25 (1998) 1247e1252. [28] R.J. Schulting, M.P. Richards, The wet, wild and the domesticated: the MesolithiceNeolithic transition on the West coast of Scotland, European Journal of Archaeology 5 (2002) 147e189. [29] R.J. Schulting, M.P. Richards, Finding the coastal Mesolithic in Southwest Britain: AMS dates and stable isotope results on human remains from Caldey Island, South Wales, Antiquity 76 (2002) 1011e1025. [30] M.R. Schurr, Using stable nitrogen isotopes to study weaning behaviour in past populations, World Archaeology 30 (1998) 327e342. [31] M.J. Schoeninger, M.J. DeNiro, Nitrogen and carbon isotopic composition of bone collagen from marine and terrestrial animals, Geochimica et Cosmochimica Acta 48 (1984) 625e639. [32] J. Sealy, Body tissue chemistry and Palaeodiet, in: D.R. Brothwell, A.M. Pollard (Eds.), Handbook of Archaeological Sciences, John Wiley and Sons, Chichester, 2001, pp. 269e 279. [33] L. Tieszen, T. Fagre, Effect of diet quality and composition on the isotopic composition of respiratory CO2, bone collagen, bioapatite and soft tissues, in: J. Lambert, G. Grupe (Eds.), Prehistoric Human Bone: Archaeology at the Molecular Level, Springer-Verlag, 1993, pp. 121e155.
Stable isotope palaeodietary study of humans and fauna from the multi-period (Iron Age, Viking and Late Medieval) site of Newark Bay, Orkney M.P. Richards a,b,*, B.T. Fuller c,d, T.I. Molleson e a
Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany b Department of Archaeological Sciences, University of Bradford, Bradford, West Yorkshire BD7 1DP, UK c Research Laboratory for Archaeology and the History of Art, 6 Keble Road, Oxford OX1 3QJ, UK d Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK e Department of Palaeontology, Natural History Museum, Cromwell Road, London SW7 5BD, UK Received 9 August 2004; received in revised form 24 June 2005; accepted 1 July 2005
Abstract We report here on stable carbon and nitrogen isotope measurements of human and faunal bone collagen from the Iron Age, Viking Age, and Late Medieval site of Newark Bay, Orkney, Scotland. We found a wide range of results for humans in both d13C (ÿ15.4& to ÿ20.3&) and d15N (8.6&e15.6&) values. The enriched carbon and nitrogen values indicate the consumption of significant amounts of marine protein, which is very unusual for post-Mesolithic (e.g. 4000 cal BC) UK and European populations. Also of interest is a statistically significant difference in d13C (t Z ÿ2.48, p Z 0.011) and d15N (t Z ÿ2.44, p Z 0.011) values, and therefore diets, between adult males and females at this site, with males (d13C Z ÿ17.8 G 1.2&, d15N Z 13.2 G 1.6&) having, on average, a higher proportion of marine protein than females (d13C Z ÿ18.9 G 1.1&, d15N Z 11.8 G 1.8&). The weaning age of the sub-adults was difficult to interpret due to the large isotopic variation in the adult females, but nearly all individuals between birth and 1.25 years have elevated d15N values indicating that they were breastfed to some extent. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Palaeodiet; Weaning; d13C; d15N; Orkney; Pictish; Viking Age; Late Medieval
1. Introduction Stable isotope analysis of carbon (d13C) and nitrogen (d N) in human and faunal bone collagen from archaeological contexts is an established method for determining past diets, and is increasingly used to determine past human diets at a range of archaeological sites from different time periods and regions. In the United Kingdom, a relatively large number of isotopic 15
* Corresponding author. Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany. Tel.: C49 341 3550 0. E-mail address: [email protected] (M.P. Richards). 0305-4403/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jas.2005.07.003
studies have been undertaken, especially in recent years, on prehistoric [20,21,23,24,26,28,29] and historic [2,3,17,18,19,25,27] collections. One of the surprising findings of this research, and one which is echoed in isotopic studies of Holocene sites in other areas of Europe, is that the only evidence of the significant consumption of marine foods is during the Mesolithic period, which dates from the start of the Holocene to approximately 4000 cal BC in the UK [21,23,26,28,29]. The study reported here was undertaken for two reasons. Firstly, the time periods represented at this site, (Iron Age, or ‘Pictish’, Viking Age and Late Medieval periods) are relatively unrepresented in the body of isotopic data so far produced for Holocene Europe.
M.P. Richards et al. / Journal of Archaeological Science 33 (2006) 122e131
Secondly, the main impetus for this study was to explore the dietary adaptation of humans in what is a fairly unique environment, where farming is possible although the site is located in the far north of Europe (a latitude of 59 N), but also where there is easy access to relatively abundant marine food resources. In hunteregatherer societies, such as in the Mesolithic period, it may be easier to predict the adaptive strategy of humans in a context such as this, where only wild resources are available (i.e. marine resources are the logical dietary choice). However, it is more difficult to predict the adaptive dietary strategy in complex historic societies which have a long established tradition (and dependence on) of agriculture and animal husbandry. We therefore initiated this study to explore whether historic populations in such an environment would largely be constrained by cultural practices and would therefore maintain a subsistence strategy based on husbandry and agriculture, or would instead revert to the use of available and abundant marine resources, a practice which has not yet been observed in isotopic studies of post-Mesolithic sites in the UK and elsewhere in Europe. As so few studies have been undertaken in environmental contexts such as these we also measured the isotopic values of faunal species. This was done to provide baseline values for interpreting the human values, with a special focus on whether there were any unusual isotope effects due to this site’s location (such as elevated nitrogen isotope values that might come from sea spray), and particularly if animals were being foddered on and fed marine foods such as seaweed. Additionally, the large number of infant and juvenile skeletons also allowed the investigation of breastfeeding and weaning patterning in this population.
2. The site of Newark Bay The site is located on the eastern edge of Newark Bay, a south facing bay in Deerness, East Mainland, Orkney, Scotland. The site was excavated by Brothwell during several rescue seasons from 1968 to 1972, and over 200 individuals were recovered making the Newark Bay collection the most important sample of human remains recovered in Orkney [5]. The burials were mostly single interments, aligned eastewest, and without grave goods. As part of a comprehensive dating project of Pictish and Medieval sites in this region, Barrett et al. [2,3] obtained radiocarbon dates and stable carbon isotope values on a number of burials from this site. Broadly, the uncalibrated radiocarbon dates range from 550 to 1200 BP, representing the Iron Age (‘Pictish’), Viking Age and Late Medieval burials. Barrett et al. [3] found
123
a wide range of carbon isotope values with many earlier individuals having terrestrial signatures (ca. ÿ21.0&), and a number of later (Viking Age and Medieval) individuals with more marine values (ca. ÿ16.0&).
3. Stable isotopes and dietary reconstruction The isotopic composition of body tissues such as bone collagen reflects the isotopic signatures of the foods and liquids consumed during life [16]. In archaeological research, bone collagen is routinely analyzed for its carbon (d13C) and nitrogen (d15N) stable isotope ratios. The results obtained from this analysis are quantitative and reflect the origin of the protein portion of the diet during the last years of an individual’s life [1,33]. Stable isotope results are measured as the ratio of the heavier isotope to the lighter isotope (13C/12C or 15N/14N) and reported as d values in parts per 1000 or ‘‘permil’’ (&) relative to internationally defined standards for carbon (vPDB) and nitrogen (AIR). For recent comprehensive reviews see Sealy [32], Katzenberg [12] and Mays [17]. In Holocene Europe, where there is little use of C4 plants, the ratio of carbon isotopes in human bone collagen is primarily used to distinguish between the consumption of marine protein (e.g. d13C of ca. ÿ12 G 1& for 100% marine protein) and terrestrial C3 protein (e.g. d13C ca. ÿ20& G 1& for a 100% terrestrial protein). Human bone collagen d13C values that fall between these two theoretical end points are therefore interpreted as reflecting relative consumption of marine vs. terrestrial protein using a simple linear mixing model. The nitrogen isotope ratio of mammal bone collagen has been shown to be enriched in 15N over the protein consumed, with enrichment between consumer and diet d15N values of 2e4& [14,31]. When baseline herbivore and carnivore values are known for a site, it is then possible to see how the humans, as omnivores, compare and then use the d15N values to determine whether the humans were obtaining their protein from mainly plant sources (e.g. similar values to the herbivores) or animal protein (e.g. similar to the carnivores) or the more usual, somewhere in between reflecting a diet with a mix of both animal (meat or milk products) and plant proteins. 3.1. Breastfeeding and weaning patterns When infants are breastfeeding they are one level above their mothers in the food chain as they are essentially consuming their mother’s tissue through the ingestion of breast milk. Thus, the d15N values of nursing infants are elevated by 2e4& compared to the mother [8,30]. During the weaning process, the
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Table 1 d13C and d15N results for the fauna from Newark Bay (Mean G SD) Species
d13C G SD
d15N G SD
N
Cattle Sheep/goat Pigs Fish Seals
ÿ21.8 G 0.2& ÿ21.8 G 0.8& ÿ20.6 G 1.3& ÿ11.8 G 1.2& ÿ12.0 G 0.5&
5.5 G 0.8& 7.0 G 0.9& 8.4 G 1.6& 13.6 G 1.0& 17.2 G 1.5&
9 5 6 4 8
consumption of supplementary foods results in declining infant body tissue d15N values, as they are a product of the combination of 15N-enriched mother’s milk and weaning foods with lower d15N values. When a child is fully weaned (cessation of breastfeeding), its protein d15N values are then similar to those of its mother, assuming that the child’s diet is similar to that of the mother’s. In archaeological contexts, the age of weaning and the end of breastfeeding has been estimated by measuring the d15N of bone collagen from different age classes of infants and children and noting the age at which the d15N values return to those of the adult female population [9,10,25,30]. While this method yields a general time frame for the duration of breastfeeding, a precise calculation of the introduction of weaning foods is not possible as uncertainty exists about the amount of time needed for the infant skeleton to fully incorporate the isotopically depleted post-weaning nitrogen. In addition, d15N values obtained from infants who died during breastfeeding and weaning need to be interpreted with caution as these individuals might have been fed different diets or died of malnutrition, and this could potentially alter the expected d15N values [11]. Despite these potential problems, measurement of subadult d15N values has become an established method of estimating the timing of weaning and duration of breastfeeding in past populations.
4. Methods Bone collagen was extracted from human adults (n Z 40), juveniles (n Z 88) and faunal species (n Z 32; cattle, pigs, sheep, goats, seals, fish) from the Newark Bay site. The faunal samples were interred, or closely associated, with the human burials. For the humans, we sampled ribs and selected a sub-sample of the total population that had representative numbers of adult males and females as well as juveniles from the various age classes. The complete extraction protocol is described in Richards and Hedges [22] with the addition of a final stage of ultrafiltration before lyopholisation following Brown et al. [6]. The collagen was generally very well preserved, and all samples reported here had collagen yields of over 1% and C:N ratios between 2.9 and 3.6, which are believed to be indicators of good quality collagen [7].
5. Results 5.1. Fauna The faunal isotope data are given in Table 1 and plotted in Fig. 1. As discussed above, faunal samples were measured to establish local baseline food-web stable isotope values and to explore whether domesticated animals, such as sheep/goat, cattle, and pigs were being fed marine foods such as seaweed. The d13C results from the cattle (ÿ21.8 G 0.2&) and sheep/goat (ÿ21.8 G 0.8&) samples do not indicate the consumption of any significant amounts of marine protein. The cattle d15N values (5.5 G 0.8&) are typical of those found in the UK during the Holocene [23,24]. The sheep/goat d15N values (7.0 G 0.9&) are somewhat
20 18 16 14
15N
12 10 8 Cattle Deer Pigs Seals Fish Sheep/goat
6 4 2 0 -25
-23
-21
-19
-17
-15
-13
-11
13C
Fig. 1. Plot of the bone collagen d13C and d15N values of fauna from Newark Bay.
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higher than expected, and this might be due to a seaspray effect where marine nitrogen, which is enriched compared to most soil nitrogen, is deposited near the coast and is taken up by plants. This possible reason, however, does not explain why the d15N values of the cattle are not elevated as well, unless the cattle fed on specific foods that grow away from the coast, whereas perhaps the sheep/goats grazed on plants near the ocean. There are a range of pig values, and the average values d13C (ÿ20.6 G 1.3&) and d15N (8.4 G 1.6&) differ markedly from the sheep/goat and cattle averages. As can be seen in the individual data points (Fig. 1) a number of the pigs are considerably shifted in d13C and d15N, indicating an input from marine foods and this is the cause of the overall difference in the pig average values. It is unlikely (although not impossible) that the pigs could obtain significant marine protein themselves; therefore these isotopic results most likely indicate that the pigs were consuming human refuse. The fish (species unidentified) (d13C Z ÿ11.8 G 1.2&; 15 d N Z 13.6 G 1.0&) and seal (d13C Z ÿ12.0 G 0.5&; d15N Z ÿ17.2 G 1.5&) values are as expected, with average marine d13C values and elevated d15N values. The seal d15N values are approximately 3& higher than the fish values, indicating that these fish, and perhaps others at the same trophic level, were the main protein source for the seals. 5.2. Adults The adult human data are given in Table 2. There is a large range of both d13C (ÿ15.4& to ÿ20.3&) and d15N (8.6&e15.6&) values, which means that there was a range of diets at this site, with some individuals obtaining a major portion of their dietary protein (up to 50%) from marine sources. Fig. 2 is a plot showing the adult data along with average faunal data. The human data plot in a clear line, with a regression r2 value of 0.85. Therefore, the most parsimonious explanation for the human data is that it lies along a mixing line between a marine and terrestrial end point. The likely candidates for these end points are cattle meat (and milk) for the terrestrial input, and marine mammals, such as seals. The marine contribution may also have been from higher trophic level fish than those we measured here. Of course, not all individuals lie along this line, and it is likely that this is due to the contribution of other protein sources with higher d15N values, such as sheep/goat and pigs, in addition to lower trophic level marine organisms. The isotopic values for both the adult males (average d13C Z ÿ17.8 G 1.2&, average d15N Z 13.2 G 1.6&) and females (average d13C Z ÿ18.9 G 1.1&, average d15N Z 11.8 G 1.8&) confirm a statistically significant difference between the sexes for both d13C (t Z ÿ2.48, p Z 0.011) and d15N (t Z ÿ2.44, p Z 0.011) (Fig. 3,
Table 2 d13C and d15N results from the adult humans at Newark Bay (YA Z young adult; MA Z mature adult; OA Z older adult) Sample
Age
Sex
d13C (&)
d15N (&)
C:N
NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB
YA YA YA YA YA YA YA YA MA MA MA MA MA MA MA MA MA MA MA MA MA MA MA MA MA MA MA MA MA OA OA OA OA OA OA OA OA OA OA OA
F M ? ? M M F F F ? F ? M M F F F M F F M F M M M F F F F M M F F F F F F F F F
ÿ19.7 ÿ16.9 ÿ19.3 ÿ17.8 ÿ19.5 ÿ18.7 ÿ18.4 ÿ20.3 ÿ16.9 ÿ18.6 ÿ19.6 ÿ17.3 ÿ18.0 ÿ15.4 ÿ19.6 ÿ20.0 ÿ18.5 ÿ17.5 ÿ17.1 ÿ19.2 ÿ17.5 ÿ19.6 ÿ17.8 ÿ17.3 ÿ17.7 ÿ18.9 ÿ19.4 ÿ16.3 ÿ20.2 ÿ20.0 ÿ17.7 ÿ19.1 ÿ17.9 ÿ19.6 ÿ19.5 ÿ18.4 ÿ19.4 ÿ19.8 ÿ17.7 ÿ17.5
10.9 14.4 10.8 13.7 10.1 11.6 13.0 8.6 13.5 12.7 9.9 13.9 13.4 15.6 10.4 10.5 12.0 13.7 14.6 12.0 13.8 10.8 13.4 14.4 13.8 12.8 11.0 15.6 10.1 10.9 13.7 10.4 12.1 10.6 11.5 14.4 11.5 10.5 12.9 14.4
3.4 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.2 3.3 3.3 3.2 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.4 3.3 3.3 3.3 3.3 3.3 3.4 3.3 3.3 3.3 3.3
69/34 68/12 69/33 69/8 69/2 69/105 68/2 69/36 70/15 70/30 69/11 70/35 68/14 71/1 68/20 69/4A 69/99 70/37 71/2 70/1 69/83 69/85 68/5 70/39 71/8 70/38 69/104B 69/104A 68/16 68/16A 69/67A 71/3 69/107 69/84 69/104 70/6 69/NO 71/9 71/7 69/69
Table 4). These results indicate that, on average, the males were generally consuming a diet with more marine protein than the females. 5.3. Infants and juveniles The d13C and d15N values for the infants, young children, and adolescents are presented in Table 3 and plotted in Fig. 4a, b. For the sub-adults aged between 0 and 1.25 years, there is a large spread in the d13C (ÿ16.3& to ÿ20.7&) and d15N (10.1& to 17.2&) values. In Fig. 5, the d13C and d15N results for the adult females and different age categories of the infants are plotted. The perinatal/stillborn/neonate and 1- to 6-month individuals have slightly higher d15N values
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M.P. Richards et al. / Journal of Archaeological Science 33 (2006) 122e131 24 22
R2 = 0.86
20 18 16
15N
14 12 10
Cattle Sheep/Goat
8
Pig
6
Fish
4
Seal Adult humans
2
Linear (Adult)
0 -23.0 -22.0 -21.0
-20.0 -19.0 -18.0 -17.0 -16.0 -15.0 -14.0 -13.0 -12.0 -11.0 -10.0 13C
Fig. 2. Plot of the human adult bone collagen d13C and d15N values from Newark Bay, with a regression line. Also included are the mean values of fauna from the site.
than the adult females indicating that they were breastfeeding to some extent before death. In addition, the infants in the age category of 9 months to 1.25 years have significantly elevated d15N values (2e4&) when compared to the adult females (Fig. 4). This high 15Nenrichment suggests that these older infants were being primarily breastfed before death.
6. Discussion The isotopic results from this site are significant for a UK population, since previous stable isotope studies
of Neolithic [20,21,23,28], Iron Age/Roman [27], AngloSaxon [19], and Medieval [17,18] humans have shown almost no, or very little (d13C % ÿ18&), marine foods in the diets. The Newark Bay data, with clear marine isotopic signals are most similar to much earlier Mesolithic humans from coastal sites in the UK, who also consumed a significant amount of marine protein [22,23,26,28,29]. At Newark Bay, some inhabitants had a diet where 50% of the protein was from marine sources (assuming end points of approximately ÿ21& for 100% terrestrial and ÿ12& for 100% marine). There is a large range in the d13C (ÿ15.4& to ÿ20.3&) and d15N (8.6&e15.6&) adult isotopic values.
18 16 14
15N
12 10 8 6 4
Females Female mean Males Male mean
2 0 -21
-20.5
-20
-19.5
-19
-18.5
-18
-17.5
-17
-16.5
-16
-15.5
13C
Fig. 3. Adult human d13C and d15N values plotted by sex.
-15
-14.5
-14
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M.P. Richards et al. / Journal of Archaeological Science 33 (2006) 122e131 Table 3 d13C and d15N results from infants and juveniles from Newark Bay (P Z perinatal; S/N Z stillborn/neonate; N Z neonate; m Z months; a Z years) Sample
Age
d13C (&)
d15N (&)
C:N
NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB
P P P S/N S/N S/N S/N S/N S/N S/N S/N S/N N N N N N N N N N N N N N N 1m 1m 1m 1m 1m 3m 3m 3m 3m 3m 3m 3m 3m 3m 3m 3m 3m 3m 3m 3m 3m 6m 6m 6m 6m 6m 6m 6m 6m 6m 6m 6m 6m 9m 9m
ÿ18.5 ÿ16.4 ÿ18.2 ÿ19.0 ÿ20.2 ÿ17.7 ÿ19.9 ÿ19.5 ÿ19.1 ÿ19.2 ÿ16.3 ÿ20.0 ÿ19.5 ÿ18.9 ÿ18.1 ÿ19.8 ÿ19.4 ÿ17.5 ÿ16.9 ÿ20.2 ÿ19.5 ÿ20.2 ÿ17.4 ÿ18.6 ÿ17.7 ÿ19.8 ÿ20.7 ÿ18.4 ÿ18.3 ÿ17.0 ÿ17.9 ÿ19.9 ÿ17.6 ÿ18.8 ÿ18.4 ÿ20.5 ÿ17.5 ÿ19.7 ÿ20.0 ÿ19.2 ÿ18.1 ÿ19.6 ÿ20.2 ÿ19.8 ÿ19.7 ÿ18.0 ÿ20.0 ÿ18.8 ÿ18.1 ÿ20.7 ÿ19.7 ÿ20.5 ÿ20.1 ÿ20.3 ÿ18.7 ÿ19.6 ÿ19.4 ÿ19.6 ÿ20.7 ÿ18.2 ÿ18.8
14.6 16.4 16.3 14.8 11.6 14.8 12.4 13.0 12.5 13.0 15.6 11.6 13.4 13.7 14.7 12.7 13.7 14.8 15.6 10.5 13.4 11.0 15.8 13.9 15.8 10.2 10.6 13.7 14.3 17.2 13.5 12.3 15.3 13.2 15.1 10.7 15.3 11.0 10.5 13.2 14.3 12.0 12.0 11.5 12.2 15.5 10.5 13.2 13.7 10.1 11.8 10.5 10.9 10.3 14.3 11.3 15.1 14.5 11.7 16.1 17.2
3.3 3.3 3.3 3.4 3.4 3.3 3.4 3.4 3.4 3.3 3.4 3.4 3.4 3.3 3.3 3.3 3.4 3.3 3.4 3.3 3.3 3.3 3.3 3.5 3.3 3.3 3.4 3.1 3.4 3.3 3.4 3.4 3.3 3.4 3.3 3.3 3.4 3.3 3.3 3.4 3.4 3.3 3.3 3.5 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.5 3.3 3.3 3.4 3.3 3.4 3.4 3.4 3.3 3.3
69/54 69/52A 69/31 70/21 68/25 69/60 69/109 69/96 70/32 70/4 70/26 68/19 69/41 69/79 69/37 70/11 70/14 69/109 69/19 69/68 69/97 69/103 69/53 70/27 69/40 69/76 70/13 69/95 70/127 70/16 69/43 68/21 69/2 69/88 69/94 69/44 69/56 69/80 69/67X 69/5 70/18 70/33 69/78 69/100 69/30 70/17 71/4 69/92 70/7 69/93 69/70 69/13 71/10 71/5 69/71 69/108 69/63 69/38 69/77 69/57 69/15
Table 3 (continued) Sample
Age
d13C (&)
d15N (&)
C:N
NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB
9m 9m 9m 9m 1a 1.25 a 1.25 a 3a 3a 3a 6a 8a 8a 9a 11 a 11 a 11 a 11 a 12 a 13 a 13 a 15 a 15e16 a 16 a 16 a 17 a 17 a
ÿ18.1 ÿ19.9 ÿ18.3 ÿ19.2 ÿ17.6 ÿ17.3 ÿ19.5 ÿ18.4 ÿ20.9 ÿ20.5 ÿ20.2 ÿ16.9 ÿ19.7 ÿ20.3 ÿ18.7 ÿ18.9 ÿ19.0 ÿ17.3 ÿ19.6 ÿ19.1 ÿ17.9 ÿ19.4 ÿ19.9 ÿ17.8 ÿ17.0 ÿ18.1 ÿ19.9
16.3 13.7 16.5 15.0 17.1 17.0 14.7 13.8 10.1 11.6 10.7 14.5 10.0 10.2 13.0 12.3 10.3 13.9 10.3 12.2 11.5 10.8 10.3 13.8 14.1 13.1 10.5
3.3 3.3 3.3 3.3 3.2 3.4 3.4 3.3 3.4 3.3 3.4 3.3 3.3 3.4 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.4 3.4
69/57 70/10 69/51 70/3 69/42 70/25 69/73 70/20 69/64 69/82 68/36 69/101 69/75 69/17 70/28 69/89 69/55 70/2 69/32 70/5 69/26 69/91 68/13 69/1 69/CC4 69/46 69/16
This indicates that the dietary adaptation was not uniform. While relatively modest isotopic, and therefore dietary, variations between adults have been found at other UK archaeological sites [19,27], the large spread in the isotopic results from Newark Bay is particularly striking. One possible explanation for this is that the isotopic results are not indicating exceptional variation in diets within a contemporary society, but are instead due to dietary changes over time. Research by Barrett et al. [2,3] has identified three different occupation periods at the site (Pictish/Viking Age/Late Medieval). Through the analysis of d13C values and associated radiocarbon dates, Barrett et al. [2] found that dietary habits changed over time with later periods (starting in the Viking Age) having an increasingly more marine diet. Recent research by Barrett and Richards [4] confirmed this earlier result, and found that actually many of the individuals with the more marine isotopic values dated to the Medieval period, between the 11th and 14th centuries AD. We have plotted the d13C values against the radiocarbon ages (Table 5) in Fig. 6. We did not calibrate these ages, nor did we account for the marine reservoir correction that would be required for a number of the individuals, as this is beyond the scope of this paper, and are provided in Barrett and Richards [4]. This plot demonstrates that although there is a peak in the number of individuals with a strong marine d13C
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M.P. Richards et al. / Journal of Archaeological Science 33 (2006) 122e131
The observed d13C and d15N differences between the males and females, with the males, on average, having more marine protein in their diets, is also significant since isotopic differences between the sexes are rarely found in stable isotope research. In the UK, male/female isotopic variations (d15N only) have only been found during the late Roman period ([28], Fuller et al., unpublished data). This variation in marine protein consumption between the sexes could be associated with different work activities such as males spending more time at sea fishing. It is also possible that the dietary variations indicate differential access to food resources associated with individual status and social class. Nutritional consumption based on social stratification is unfortunately impossible to identify at Newark Bay, as the burials did not contain grave goods which could have been used to further identify identities and social positions. The use of stable isotopes to determine breastfeeding and weaning practices is dependent on the fact that adult diets need to be fairly uniform [25]. The inhabitants of Newark Bay do not conform to this
Table 4 Student t-tests between the mean d13C and d15N values of the adult males and females from Newark Bay Isotope Female G SD Male G SD (n Z 24) (n Z 12) d13C d15N
Degrees t-Value Significance of level freedom
ÿ18.9 G 1.1& ÿ17.8 G 1.2& 21 11.8 G 1.8& 13.2 G 1.6& 25
ÿ2.48 ÿ2.44
0.011 0.011
value in the Viking and Medieval period, there are also many individuals with clearly terrestrial signatures in this period (and all periods). Therefore, there is no shift in diet through time by all individuals, merely an increase in the frequency of individuals with marine isotopic values in the Viking and Medieval periods. As it is impossible to determine the ages of each burial without directly radiocarbon dating, it is not possible to divide all of our study population into distinct chronological groups. Therefore we have combined all of the isotopic results from this site and consider it a single population for this study.
-14 -15 -16
13C
-17 -18 -19 -20 Adult Females
-21 -22 0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20
Age (years) 18 17 16 15 15N
14 13 12 11 10 Adult Females
9 8 0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20
Age (years) Fig. 4. d13C (a) and d15N (b) bone collagen values for infants and juveniles plotted against age at death. Also included are the adult female mean G SD isotope values.
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M.P. Richards et al. / Journal of Archaeological Science 33 (2006) 122e131 18 17 16 15
15N
14 13 12 11
Perinatal/Stillborn/Neonate
10
1-6 months 9 months - 1.25 years
9
Adult Females
8 -22
-21
-20
-19
-18
-17
-16
-15
-14
13C
Fig. 5. Plot of infant and adult female bone collagen d13C and d15N values. Note that nearly all infants have elevated d15N results compared to the adult females indicating that they were still being breastfed to some extent before death.
pattern, as there is a large range in the diets of the adult females. Thus, it is difficult to determine the age of weaning and the cessation of breastfeeding for this population (Fig. 4a, b). The infants aged from newborn to 1.25 years show elevated d15N values compared to the Table 5 AMS radiocarbon dates and associated isotopic values for adults from the Newark Bay site Skeleton
Lab no
d13C
d15N
AMS date
NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB NB
TO-6940 TO-7173 GU-10955 TO-7174 AA-54931 AA-54930 TO-7188 TO-7189 TO-7190 TO-7191 TO-7180 TO-7181 TO-7182 TO-7183 TO-7184 TO-7178 TO-7185 AA-54932 TO-7186 TO-7187 TO-7192 AA-54933 AA-54934 AA-54935 TO-6937 AA-54936 AA-54937 TO-7193 TO-6934 AA-54938
ÿ18.4 ÿ16.9 ÿ18.0 ÿ20.0 ÿ19.6 ÿ17.8 ÿ16.3 ÿ19.4 ÿ18.7 ÿ17.9 ÿ19.6 ÿ19.8 ÿ20.3 ÿ17.7 ÿ17.5 ÿ17.8 ÿ17.5 ÿ17.5 ÿ19.6 ÿ18.5 ÿ19.2 ÿ16.9 ÿ17.5 ÿ17.3 ÿ18.4 ÿ15.4 ÿ17.1 ÿ19.1 ÿ17.7 ÿ17.7
13.0 14.4 13.4 10.9 10.4 13.4 15.6 11.0 11.6 12.1 9.8 10.9 8.6 13.7 14.4 13.7 13.8 13.8 10.8 12.0 12.0 13.5 13.7 14.4 14.4 15.6 14.6 10.4 13.8 13.8
550 G 40 930 G 40 630 G 50 1190 G 40 1055 G 40 590 G 40 1030 G 40 1130 G 50 990 G 50 1340 G 60 1380 G 30 930 G 40 1090 G 40 990 G 40 910 G 40 830 G 30 1060 G 40 1070 G 45 1000 G 40 1060 G 40 1010 G 60 1060 G 35 1130 G 40 965 G 40 700 G 40 1075 G 35 1075 G 35 1200 G 40 1160 G 60 1020 G 45
68/2 68/12 68/14 68/16A 68/20 68/5 69/104A 69/104B 69/105 69/107 69/11 69/34 69/36 69/67a 69/69 69/8 69/83 69/83 69/85 69/99 70/1 70/15 70/37 70/39 70/6 71/1 71/2 71/3 71/8 71/8
Radiocarbon dates are from [4].
adult females, and this suggests that breastfeeding was continuing in some form until at least this age (Fig. 6). It is interesting to note that there are only a few juveniles older than 1.25 years at the site, which suggests that there was high infant mortality in the first two years of life. The introduction of solid foods or the weaning process is often linked to an increased risk of infant mortality and morbidity [13,15]. Reduced breast milk consumption decreases the level of immunity for infants, and the weaning diet has the potential to expose children to new pathogens and nutritional stress [13]. Perhaps there are a high number of juveniles in this age class because this may have been an age when the children were weaned onto a possibly nutritionally poor diet and were especially susceptible to infections during this time.
7. Summary and conclusions Stable carbon and nitrogen isotope ratio analysis was undertaken on bone collagen extracted from humans and fauna from the multi-period site of Newark Bay, Orkney, UK. The results indicate that there was a large amount of dietary variation with some individuals having an entirely terrestrial protein diet and others with a high input (ca. 50% of dietary protein) of marine protein. This high level of marine protein in the diet is unusual for the UK, especially for this time period, and has previously only been found during the Mesolithic period. It is especially interesting to observe this high level of ‘wild’ foods in such a recent, historic, complex society in Europe, where food is usually derived from animal husbandry and agriculture. A statistically significant variation in isotopic values was found between males and females, which is also a rare occurrence in isotopic studies. The data indicate that,
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M.P. Richards et al. / Journal of Archaeological Science 33 (2006) 122e131 -14.0 -15.0 -16.0
13C
-17.0 -18.0 -19.0 -20.0 -21.0 -22.0 -23.0 400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
Radiocarbon Age BP Fig. 6. Bone collagen d13C values of adults from Newark Bay plotted against uncalibrated radiocarbon ages BP. Dates are from [4]. For samples NB 69/83 and NB 71/8, where there are two dates on the same individual, the dates were combined for the plot.
on average, males had more marine protein that the females and this may be related to specific activities (i.e. fishing/sealing) or part of a larger change in dietary habits over time. Isotopic measurements were also undertaken on subadults (infants and juveniles) at Newark Bay. Due to the large variation in the adult female diet, it was difficult to determine the weaning age, but elevated d15N values indicate that breastfeeding continued in some form until at least 1.25 years of age. Isotopic studies of European populations are usually undertaken on prehistoric collections, where generally little is known about past diets and where, perhaps, they are easier to undertake as potential dietary inputs are limited only to wild food sources. Isotopic studies of more recent, late prehistoric and historic populations often do not show much variation in isotope values, although there are far fewer studies of these periods. Perhaps this is because isotopic analysis is too blunt a tool to tease out subtle dietary variations in societies that rely almost entirely on domesticated plants and animals obtained through animal husbandry and agriculture. However, this study has shown that in the right circumstances isotope analysis can make a significant contribution to our knowledge even in complex historic societies. The results presented here show that contrary to expectations there was a significant input of wild foods, namely marine foods, into the diets of the people buried at Newark Bay. Therefore, hopefully this study has helped demonstrate the utility of the isotopic method even in more recent historical period complex societies, providing more evidence of the wide range and variety of human dietary adaptations.
Acknowledgements We would like to thank James Barrett, Gundula Mu¨ldner, Mandy Jay two anonymous referees for helpful comments on the paper. We would like to thank the Wellcome Trust and the Max Planck Society for funding.
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