Novel isotopic approaches to investigating human palaeoecology: An introduction

Stable isotope analyses started being performed on archaeological materials more than 50 years ago, to the best of our knowledge, when geochemists such as Cesare Emiliani applied oxygen isotope analyses on marine mollusc remains from prehistoric Mediterranean sites. This scientist, who was one of the founders of palaeoceanography and a key figure in the development of the Marine Isotope Stage timescale, along with his colleagues analyzed shells of intertidal marine gastropods from Upper Palaeolithic deposits at the cave sites of Arene Candide in Italy and Haua Fteah in Libya (Emilani et al. 1964). This work found that oxygen isotope ratios (δO) in the prehistoric shell carbonates were noticeably higher than those of modern limpets and topshells from the Mediterranean and, thereby, that sea surface temperatures during the Late Pleistocene must have been a few degrees colder than at present. This initial study was followed, almost a decade later, by that of another prominent palaeoceanographer and palaeoclimatologist, Shackleton (1973), who for the first time used the potential offered by oxygen isotope analysis as a valuable source of information on the season of collection of marine molluscs. Only a few years later, carbon isotope analysis started to be applied on mammalian skeletal tissues to reconstruct past human diets (DeNiro and Epstein 1978; van der Merwe and Vogel 1978; Vogel and van der Merwe 1977). This was made possible by the finding that stable carbon isotope ratios (δC) are useful proxies for the ecosystem of origin of macronutrients, be it terrestrial, freshwater or marine (e.g. Tauber 1981). At that same time, it was also realised that nitrogen isotope ratios (δN) in the same bone collagen analyzed for δC constituted a unique source of evidence on the trophic level of the protein consumed by an individual (DeNiro and Epstein 1981; Schoeninger and DeNiro 1984). This prolific period of essential background scientific work and pioneering applications on archaeological materials led to the development of isotope-based palaeodietary studies, as described in more detail in reviews on the topic by Lee-Thorp (2008) and Makarewicz and Sealy (2015). The definitive expansion of this field of archaeological science, however, was only made possible by the development of continuous-flow mass spectrometry during the 1990s. It was this technical advance that made the cost of analyses more affordable for archaeological budgets and that led to increasing numbers of isotopic studies both in archaeology and anthropology. Isotope analyses are key techniques in human palaeoecology, although many challenges still lay ahead of us in terms of how these methods can be improved in archaeology (Makarewicz and Sealy 2015). Nevertheless, we share the enthusiasm manifested by Bogaard and Outram (2013) in labelling what we have briefly summarised above as the ‘isotope revolution’. Bogaard and Outram (2013, 333) stated that this revolution is ‘comparable in impact to the advent of radiocarbon dating and of calibration curves in archaeology (cf. Renfrew 1973)’; on this point, we think that the full potential of isotope analyses in archaeology is yet to be achieved. Most isotopic applications have aimed at the direct reconstruction of past human diets, a topic that is of great importance in archaeology because what people ate in the past was influenced both by their environment and their culture. Isotope-based palaeodietary studies, thereby, provide us with clues on how cultures adapted to past environments and, specifically, on the proportions in which different foodstuffs contributed to human diet (Lee-Thorp 2008). However, the findings of such investigations are not always adequately contextualised within the rest of the archaeological record and because it is equally important to reach an understanding of subsistence (i.e. the activities carried out by people to acquire the necessities of life), it could be argued that the Correspondence to: Marcello A. Mannino, Department of Archaeology, School of Culture and Society, Aarhus University, Moesgaard Alle 20, 8270 Højbjerg, Denmark. Email: marcello.mannino@cas.au. dk