IAP2-23-101

Refining dietary interpretation of archaeological humans in the Holocene of northwestern Europe using paired apatite and collagen carbon isotopes

The use of carbon isotopes measured in mammalian apatite was first explored by Krueger & Sullivan1,2 over 40 years ago. Their work focused primarily on fossils in African ecosystems and they presented theoretically derived relationships between the δ13C apatite (which reflects whole diet) and the δ13C collagen (which derives primarily from ingested protein) suggesting it was a simple offset of +7‰ for herbivores and +3‰ for carnivores (Figure 1). A subsequent paper by Lee-Thorp et al.3 explored more complex, empirically derived, regression lines from modern African fauna from different trophic levels, i.e. herbivore, omnivore and carnivore (Figure 1). A key observation in this study was that the difference between δ13C apatite and δ13C collagen is smaller for carnivores than for herbivores which could be useful when assessing degrees of omnivory in archaeological humans although a small case study demonstrated it was not a simple relationship. A further paper by Froehle et al.4 explored how different diets, i.e. marine, C3 or C4 based could be distinguished using combined apatite and collagen δ13C values in animals. None of these seminal studies, however, addressed how apatite δ13C values varied in archaeological humans in the C3-dominated, temperate, maritime foodwebs of north-western Europe.

The rapid increase since the late 1990s of the use of oxygen isotopes to track human residential mobility in the past, and the more recent switch from phosphate to carbonate as the ion of choice, primarily due to lower cost and sample preparation that does not require the use of HF, has by default, made a large amount δ13C data available. Often, in publications, this data is either not reported, not discussed, or briefly mentioned almost in passing in broad terms of whether the diet is marine, C3 or C4 based; the majority of studies investigating human diet still rely solely, or predominantly, on the measurement of collagen. Moreover, if studies based in NW Europe attempt to interpret the apatite δ13C data using one of the aforementioned seminal papers, the data do not always appear to fit: possibly due to a disconnect between the climate, environment, food web or period of the model and the case study (Figure 1). As a result, no serious attempt has yet been made to explore and understand what the much larger range (~8‰ compared to ~3‰ in collagen) of apatite δ13C values that we observe in humans consuming terrestrial C3-based diets in NW Europe is telling us about their diet, particularly predator-prey relationships and the consumption of fats and carbohydrates. Moreover, although we have a robust δ13C collagen upper limit of c. -20‰ for C3-based 100% terrestrial diets of humans in NW Europe, we have yet to establish this for δ13C of apatite or how human values may vary with mixed C3 and marine diets based on fish consumption which have different body temperatures to the warm-blooded mammals on which Kreuger and Sullivan based their models.

Using paired, co-genetic δ13C apatite and δ13C collagen data from teeth of humans and their domestic and prey animals, this project aims to address this gap and produce climate and environment-specific models to permit the construction of finer-grained food webs and interpretations of the δ13C data from humans and their animals during the Holocene in NW Europe.

The main research methods employed in this PhD will be:
database production and manipulation;
stable isotope analysis of organic samples (bone and teeth);
data analysis and visualisation;
contextualisation and interpretation of data to identify diachronic and geographic trends and patterns.

Year 1

Conduct and write an archaeological, ecological and geochemical literature review for publication and presentation at UK conference. Compilation of database of δ13C apatite measurements of humans and animals from Europe throughout the Holocene along with any accompanying co-genetic δ13C collagen data.
Data analysis.
Assessment of sample preparation methods.
Identification of case studies and applications for destructive analysis submitted.
Collection of samples.

Year 2

1st phase of sample preparation and measurement by IRMS.
Data analysis, contextualisation, interpretation and review.
Identification of follow-on studies.
2nd phase of sample preparation and measurement by IRMS.
Data analysis, contextualisation and interpretation.
Identify and draft suitable case studies for publication and presentation at UK conference.

Year 3

Exploration of data visualisation and analysis methods.
Statistical analysis
Drafting of background, methods, results and discussion chapters and submit to supervisors.
Presentation of findings at international conference.

Year 3.5

Revise main chapters following feedback.
Draft introductory and concluding chapters.
Submit full draft for review.
Submit thesis.
Preparation for viva.

The candidate will have a background in stable isotope analysis of modern or archaeological humans and/or animals. Training will be given in sampling strategies, site and case study selection and identification, and how to prepare apatite and collagen samples for isotope analysis and measurement by IRMS.
The candidate will undertake data visualization and analysis training to enable them to use various statistical packages and produce high quality academic and public-facing outputs.