Mussels with Meat: Bivalve Tissue-Shell Radiocarbon Age Differences and Archaeological Implications

Abstract

ABSTRACT. Local reservoir ages are often estimated from the difference between the radiocarbon ages of aquatic material and associated terrestrial samples for which no reservoir effect is expected. Frequently, the selected aquatic material consists of bivalve shells that are typically well preserved in the archaeological record. For instance, large shell middens attest to the importance of mussel consumption at both coastal and inland sites. However, different physiological mechanisms associated with tissue and shell growth may result in differences in reservoir effects between the surviving component (shell) and the component relevant to dietary reservoir effects in consumers (tissue). The current study examines bivalve tissue-shell age differences both from freshwater and marine contexts close to archaeological sites where human consumption of mollusks has been attested. Results exhibited significant ,4 C age differences between bivalve tissue and shell in a freshwater context. In a marine context, no significant bivalve tissue-shell age differences were observed. The results also showed that riverine and lacustrine shells show large and variable freshwater reservoir effects. The results have important implications for establishing local reservoir effects especially in a freshwater environment. For good a priori knowledge of expected 14 C differences in organic and inorganic water, carbon is thus necessary. Furthermore, the high variability in freshwater shell 14 C ages implies the need for representative sampling from the archaeological record.

Potential Use of Archaeological Snail Shells for the Calculation of Local Marine Reservoir Effect

“…The MRE has also a local component, a ΔR value, that represents the difference between the reservoir age and the mean global age (Stuiver et al 1986;Stuiver and Braziunas 1993) and takes into account time and space variations, which depend on many factors like the carbon exchange between ocean carbonates and atmospheric CO 2 , upwelling currents, circulation patterns, and coastal topography (Gordon and Harkness 1992;Ascough et al 2004). Quantification of the local marine reservoir effect is important in the establishment of accurate archaeological chronologies (Fernandes et al 2012). …”

Radiocarbon in ecology: Insights and perspectives from aquatic and terrestrial studies

“…For bivalves, it is also possible to distinguish between carbon contributions from algal and detrital organic matter by analysing shells and soft tissues: 14 C concentrations of shells mostly reflect inorganic carbon sources, and soft tissues reflect organic metabolic carbon sources (Fernandes & Dreves, ). Thus, significant 14 C differences between tissue and shells would indicate that the bivalves’ food sources were imported from a different habitat (Fernandes et al., ). The ability of 14 C to track carbon fluxes and identify herbivore‐ and detritivore‐based food chains shows how it can be used to investigate the effect of eutrophication and intensive land use on primary production sources in lacustrine ecosystems.…”

Potential Freshwater Reservoir Effects in a Neolithic Shell Midden at Riņņkalns, Latvia

“…Such organic carbon inputs may be more seasonally variable, and less relevant to prehistoric conditions, than DIC and shell 14 C ages. Nevertheless, it is carbon from the flesh of mollusks, not from their shells, which enters the food chain, so it is important to assess whether there may be large 14 C-age discrepancies between these tissues (Fernandes et al 2012). …”