Refining Estimates for the Season of Shellfish Collection on the Pacific Northwest Coast: Applying High‐resolution Stable Oxygen Isotope Analysis and Sclerochronology

Abstract

Stable oxygen isotopes from estuarine bivalve carbonate from Saxidomus gigantea were analysed combined with high‐resolution sclerochronology from modern and archaeological shells from British Columbia, Canada, to determine the seasonality of shellfish collection from the archaeological site of Namu. The combination of high‐resolution sclerochronology and a micro‐milled sampling strategy for δ18O analysis permits a precise estimate of archaeological seasonality, because seasonal freshwater influxes and changes in temperature have dual effects on the δ18O value of the shell. Sclerochronological analysis identifies the timing and duration of growth that is temporally aligned to stable oxygen isotope results, since δ18Oshell appears to be strongly influenced by seasonal inputs of very low δ18O snowmelt‐water from adjacent coastal mountain ranges. The results show that shellfish were collected year‐round at this site over a 4000‐year period, and these data combined with other zooarchaeological lines of evidence support the interpretation of year‐round occupation.

Sclerochronological analysis of archaeological mollusc assemblages: methods, applications and future prospects

“…Aspects of the ambient environment are recorded within the sequential growth structures of accreting skeletal tissues, preserving high-resolution time series information (potentially r e a c h i n g s u b -d a i l y s c a l e s ) i d e a l f o r l o c a l i s e d palaeoenvironmental reconstruction. Studies of a wide range of accreting skeletal tissues, including fish otoliths (Andrews et al 2003;Hufthammer et al 2010;Patterson 2001, 2003), teeth (Pike-Tay and Cosgrove 2002), coralline sponges (Böhm et al 2000), some mammalian bone-including deer (Frankel et al 2013) and wallaby (Pike-Tay and Cosgrove 2002)-and molluscan shell (Burchell et al 2013b;Hallmann et al 2009), show the rapidly expanding application of these techniques into a range of archaeological materials and investigations. Here, we focus on one class of materials that is ubiquitous in coastal archaeological contexts-molluscan shell.…”

“…While the selection of appropriate material assists in ameliorating interpretations from erroneous data (Burchell et al 2013b;Hallmann et al 2013;Kingston et al 2008), a nuanced understanding of the biology, ecology and potential limitations associated with the chosen proxy is essential in generating meaningful and robustly interpretable results. Archaeologists are increasingly employing calcium carbonates derived from accreting skeletal tissues as a staple palaeoenvironmental proxy.…”

“…Therefore, employing high-resolution data recovery techniques, such as sclerochronology, to systematically analyse molluscan shell allows the generation of detailed chronological life histories and reconstructions of the ambient environment. The application of these methods to archaeological assemblages provides the opportunity to address broader questions regarding palaeoenvironments, climate change and their effects on human behaviour (Burchell et al 2013b;Clark 1974;Schöne and Surge 2005).…”

From coral reefs to whale teeth: estimating mortality from natural accumulations of skeletal materials

“…As well as standard cohort and length frequency analyses of population structures (Caddy 1989, Mannino & Thomas 2002, analysis of stable oxygen isotopes from the most recently formed shell section can be applied to determine the season of collection and to give a timeframe to mortality (Mannino et al 2003, Burchell et al 2013. As with the shells of live collected bivalves, sclerochronological techniques such as direct ageing of shells can also be employed on midden samples to extract a wealth of information regarding historical ecological and environmental conditions (see Andrus 2011 for review).…”

Stable isotopes in zooarchaeology: an introduction

“…Sampling shells for palaeoenvironmental information has become a well-established practice (e.g. Burchell et al 2012Burchell et al , 2013Mannino et al 2003Mannino et al , 2007Milner 2002). Early analyses of carbon (δ 13 C) and nitrogen (δ 15 N) from archaeological human bone collagen (e.g.…”