A Model for Calculating Freshwater Reservoir Offsets on AMS-Dated Charred, Encrusted Cooking Residues Formed from Varying Resources

Abstract

The freshwater reservoir effect (FRE) hypothesis suggests that ancient carbon from aquatic organisms incorporated into AMS-dated charred, encrusted cooking residues on interior pottery walls produces old apparent radiocarbon ages. This hypothesis has been used primarily in northern European final Mesolithic contexts to explain 14 C ages on cooking residues that are thought to be too old relative to 14 C ages obtained on terrestrial samples, resulting in so-called freshwater reservoir offsets (FROs). More recently, the hypothesis has been cited in interpretations of 14 C ages from residues in the North American Plains and elsewhere. This article presents a model using an Excel spreadsheet that allows calculation of FROs with varying inputs of dead carbon and aquatic and terrestrial resources.

Fishing for Dog Food: Ethnographic and Ethnohistoric Insights on the Freshwater Reservoir in Northeastern North America

“…The results suggest that in only very few cases is there a statistically significant difference that might Figure 6). Fishing for Dog Food: Freshwater Reservoir in NE North America indicate the presence of an FRO, although archaeological context issues may be the critical factors in the noted offsets (Hart andLovis 2007b, 2014).…”

“…While it was subsequently demonstrated that cooking time affected carbon mobilization (Hart et al 2009), the carbon fraction remains the primary determinant. Finally, it is the fraction of ancient carbon contribution by freshwater resources relative to contemporary carbon of freshwater and terrestrial resources that is critical in producing an FRO (Hart 2014). While we focus here on the potential contributions of freshwater fish, it is in fact the relative contribution of carbon, both ancient and contemporary, by all components of a mix that must be considered in assessing FRO potential.…”

“…By way of entrée, it is important to briefly contextualize our research within the framework of this volume. Our work has focused on various facets of carbonized food residue formation, and on the systematic evaluation of the freshwater reservoir effect (FRE) as it might be manifested in such residues (Hart andLovis 2007a,b, 2014;Hart et al 2007Hart et al , 2009Lovis et al 2011;Hart 2014;Upton et al 2014).…”

“…Further, given that 14 C ages are estimates with distributions, which allow for varying probabilities that the estimate accurately reflects the age of the datable substance, any 14 C assay may not capture the true age of the material or event in question regardless of whether an FRO is present. Among the outcomes of our research program are protocols for evaluation of both the potential for an FRE, the order of magnitude of an FRO, and various means to evaluate the relative likelihood that datable material might result in an inaccurate ages Hart 2014;Hart and Lovis 2014).…”

Developing inorganic carbon-based radiocarbon chronologies for Holocene lake sediments in arid NW China

“…A number of studies have examined the RE on 14 C ages on bulk, aquatic organic matter and biological remains of aquatic organisms that feed on aquatic material, based on general comparative estimates (Hendy and Hall, 2006;Shishlina et al, 2007Shishlina et al, , 2012Zhou et al, 2009;Olsen et al, 2010;Ascough et al, 2010Ascough et al, , 2011Wood et al, 2013;Zhao et al, 2013), calculations based on carbon (C) and nitrogen (N) isotopes (Lanting and van der Plicht, 1998;Cook et al, 2001;Watanabe et al, 2010;Bronk Ramsey et al, 2014), N/C ratios (Bertrand et al, 2012) or models (Soulet et al, 2011;Watanabe et al, 2013;Yu et al, 2007Yu et al, , 2014Groot et al, 2014;Hart, 2014). However, as inorganic carbon is less frequently dated for radiocarbon estimates, the RE of inorganic carbon dates in lake sediments is not fully understood.…”