古骨胶原硫含量和同位素比值的测定及其考古学意义

人(动物)骨胶原蛋白的硫稳定同位素比值,不仅可区分个体食物来源的差异,也可判断其迁徙行为。然而,受限于硫元素在骨胶原蛋白中的低含量(约0.2%),硫元素含量和其同位素比值的准确测定,一直是制约同位素生物考古研究的瓶颈。近些年来,国际学界新出现的质谱分析技术,虽已可实现对低样品量骨胶原S同位素比值的测定,但因缺乏低含量硫标准物质造成硫元素含量测定困难的问题依然存在。目前,我国尚未见到专门用于古骨胶原S含量和同位素测试方法的相关报道。为此,本研究利用基于具有程序升温气相色谱(GC)的元素分析-稳定同位素比值质谱仪(EA-IRMS)联机系统以磺胺和面团参考物质(pasta reference material,S含量为0.14%)为S元素含量测定的标准物质;以国际稳定同位素参考物质USGS42和USGS89为同位素标准物质,对2例古骨胶原中S含量和碳氮硫稳定同位素比值进行了多次测定;并以国际稳定同位素标样IAEA-S-1和IAEA-S-2对骨胶原数据校正,首次建立了骨胶原S含量和同位素比值的分析技术。该技术以低S含量参考物质为元素含量标准物质实现了古骨胶原S含量的准确测定(标准偏差约为0.02%);在保证硫稳定同位素测试精度、准度(<0.4‰)和仪器稳定的情况下,古骨胶原的用量(5.2~5.8 mg)较常用量(10 mg)大幅降低。该分析技术的建立,对于在我国重建先民(动物)的食谱和生存环境、探讨其迁徙行为具有重要的应用价值。     

Carbon isotope measurement techniques for bone collagen: Notes for the archaeologist

Stable carbon isotope analysis of archaeological human bone collagen is becoming increasingly useful in diet reconstructions. This paper describes, for archaeologists, the techniques that we have found useful in carrying out such analyses, and discusses the requirements for measurement accuracy and inter-laboratory calibration.     

Investigation of the ‘canopy effect’ in the isotope ecology of temperate woodlands

Anomalously ¹³C-depleted carbon stable isotope values from closed forest ecosystems have been termed the ‘canopy effect’. Originally this was ascribed to recycling of depleted carbon from forest floor decomposition of organic material, although others have suggested that it is equally likely to be due to variations in leaf-level processes in response to increased shade. This depletion in the heavier carbon isotope is passed on to woodland herbivores feeding within the forest environments. A similar isotopic depletion has also been reported in the archaeological literature from more open temperate woodland settings, but no measurements have been made on the plants at the base of the food chain in order to quantify the effect. In this study we attempt this by examining the carbon and nitrogen stable isotopic values of different species of grasses from a range of open to closed habitat settings within Wytham Wood, Oxfordshire, UK. We find a strong relationship between carbon isotopic depletion of plant tissue and lowered light intensity with an up to 5‰ shift between grass grown in open and closed locations. In order to follow this up the food chain, we also report data on wool from sheep grazing in open pastures near the Wood, and on fallow deer living within the woodland, but which turn out not to show a strong canopy effect, probably related to their feeding strategies. We conclude that there is indeed a strong ‘canopy effect’ in temperate woodland, probably related to differential light levels, but that not all apparently woodland-dwelling mammals show such an effect. We also show considerable isotopic variation at the base of the food chain, which should counsel caution when attempting to interpret dietary isotopes using mixing models.     

Archaeological collagen: Why worry about collagen diagenesis?

DNA appears to decay by random chain scission resulting in a predictable range of fragment lengths. Collagen decay has also been modelled in this same way, although it has become increasingly evident that collagen decay does not follow this same pattern. Radiocarbon and stable isotope analysis now use ultra-filtration to isolate large fragments (>30% of original polymer length) even in Pleistocene bone. How then does collagen decay? This study contrasts experimentally degraded samples with collagen extracted from forensic, archaeological and fossil bone. In experimentally degraded bone, values for amino acid and elemental (C:N) composition, bulk δ ¹³C, δ ¹⁵N, and aspartic acid racemisation (AAR) changed very little until 99% of the collagen was lost, suggesting that the collagen triple helix and polypeptide chains remained remarkably intact. This suggestion was demonstrated directly by examining the integrity of individual polypeptide chains using cyanogen bromide (CNBr) cleavage followed by SDS-PAGE electrophoresis. In ancient samples, AAR values remain remarkably stable and the pattern of CNBr-cleavage was only replaced with a smear of smaller polypeptides in the oldest (Pleistocene) bones investigated. Smearing may reflect both modification of the methionine resides (the sites of CNBr-cleavage) and/or partial hydrolysis of the collagen molecule. The findings reveal why it is not usually necessary to worry about collagen diagenesis; it is mostly intact. However, evidence of partial deterioration of the oldest bone samples suggests that alternative purification strategies may increase yields in some samples.     

Stable isotopes in human skeletons of Southern Ontario: reconstructing Palaeodiet

Most native plants of Ontario use the C₃ photosynthetic mechanism and therefore have relatively low ${}^{13}\text{C}{}^{12}\text{C}$ ratios; maize is a C₄ plant and is relatively enriched in ¹³C. The proportion of maize in the diet of a human can therefore be estimated from the ¹³C-content of collagen of fossil bone. We have used this method to follow the increase in consumption of maize in ancient native populations over the interval from AD 400 to 1650, and to quantify the amount of maize consumed. Maize consumption rose gradually to a maximum of 50% of the diet by AD 1400. These data agree with archaeologically derived data for this region, and with previous isotope studies in the northeastern U.S.A. In some of the latter, however, the maximum percentage of maize consumed has been overestimated because maize was assumed to have a δ¹³C value of ?12·5‰; our studies of archaeological specimens show the correct value to be closer to ?9‰. The introduction of beans into the native diet about AD 1100, should have caused a decrease in the ¹⁵N content of human bone collagen because legumes are deficient in this isotope, with respect to meat and fish. However, we observe no significant change in the ${}^{15}\text{N}{}^{14}$N ratio of human bone collagen over the period from 2300 BC to AD 1640. We conclude that meat and fish remained the main sources of protein even after the advent of agriculture into this region.     

Carbon and nitrogen stable isotope analysis on the diet of Jomon populations from two coastal regions of Japan

We report on a stable isotope paleodietary reconstruction of Jomon populations in Japan during the Middle to Final Jomon period (ca. 5000–2300 years BP), focusing on dietary differences within and among populations and between regions. Carbon and nitrogen isotope analysis was performed on human and faunal bone collagen from six coastal sites along the Inland Sea in the Sanyo (Ota, Funamoto, and Tsukumo) region and along Mikawa Bay and the Pacific Ocean in the Tokai (Kawaji, Yoshigo, and Inariyama) region. We found that carbon and nitrogen isotope ratios were positively correlated, indicating that the Jomon people consumed a mixed diet of marine (shellfish and marine fish) and terrestrial (C₃ plants and terrestrial mammals) protein. In the Ota samples (n = 25, during the Middle Jomon period, 5000–4000 years BP), sex was one of the main reasons for the intra-population dietary variation. Ota males consumed greater amounts of marine food, while Ota females consumed greater amounts of terrestrial food; these dissimilar diets may have been related to the sexual division of labor. Significant inter-population dietary differences were found, which may have been related to differences in age or site location. Notably, the two coastal regions showed clear isotopic differences. Nitrogen isotope ratios of individuals from the Sanyo region were significantly higher than ratios of individuals from the Tokai region. The individuals in the Sanyo region might have consumed a diet high in aquatic foods, particularly high trophic level marine fish, whereas the individuals in the Tokai region might have consumed a lot of marine shellfish. Another possible reason for the regional isotopic difference might have been different baseline of nitrogen isotope ratios of the marine ecosystems.     

Radiocarbon dating of bone by accelerator mass spectrometry

A companion article describes the sample preparation method used in the production of graphite targets for the Oxford accelerator mass spectrometer (AMS) system. The chemical pretreatment developed for the dating of bone, ivory and tooth samples is described in this paper.     

Prehistoric Fijian diet and subsistence: integration of faunal, ethnographic, and stable isotopic evidence from the Lau Island Group

We explore subsistence practices and dietary change on islands in the central Lau Group of Fiji with zooarchaeological methods and stable isotopic analysis of human and animal skeletal material interpreted through an ethnoarchaeological lens. Our dataset combines detailed identifications of fauna, especially fishes, with stable isotopic (δ¹³C, δ¹⁵N) values of human and animal bone collagen and apatite carbonate spanning approximately three thousand years of human occupation on three study islands. Additionally, over fifty inshore and offshore contemporary fishing expeditions were observed on all study islands over a six-year period. We integrate these separate lines of evidence to form robust interpretations of Lauan subsistence patterns over a broad temporal scale. We add to the existing literature on stable isotopic analysis of archaeological bone from Remote Oceania and compare all of these groups through time. Our results indicate that Lauans differentially relied on nearshore reef resources rather than pelagic fishes, and terrestrial endemic species may have served as a portion of the diet during the early prehistoric period. Root crops (e.g., taro, yam) provided the majority of calories to the diet; however, sea grapes likely contributed to the early diet. Our isotopic results differ from previous studies of Fijian diet and that of Remote Oceania at a time of probable marine ecosystem shifts (AD 1300) illustrating diet breadth and variability in subsistence strategies potentially due to climatically influenced resource depletion.