Marine Reservoir Effects in Eastern Oyster (Crassostrea Virginica) from Southwestern Florida, USA

Abstract

In southwestern Florida, USA, terraformed landscapes built almost entirely of oyster shells (Crassostrea virginica) reflect a unique pre-Columbian tradition of shell-built architecture. The ability to reliably date oyster shells is essential to identifying spatial, temporal, and functional relationships among shellworks sites, yet to date there has been no systematic attempt to quantify or correct for carbon reservoir effects in this region. Here we present 14 radiocarbon (14C) ages for 5 known-age, pre-bomb oyster shells collected between AD 1932–1948, as well as 6 14C ages for archaeological oyster/charcoal pairs from the Turner River Mound Complex, Everglades National Park. We report our current best estimate of ΔR = 92 ± 74 yr for Greater Southwest Florida, and ΔR = –15 ± 42 yr for the Turner River archaeological site. Future research should focus on paired archaeological specimens to obtain spatially and temporally relevant estimates of ΔR.

Dating Marine Shell: A Guide for the Wary North American Archaeologist

“…The result is a probability distribution for ΔR limited by the initial range specified and all other model parameters. A North American example of this application (with OxCal code) can be found in Hadden and Schwadron (2019).…”

“…Even where data are available, correctly calculating or applying ΔR values is not always straightforward. ΔR can vary over short- and long-term time scales (e.g., Culleton et al 2006; Deo et al 2004; Hadden and Schwadron 2019), over short distances (Hadden and Cherkinsky 2017a; Rick and Henkes 2014), and among species at the same time and place (Dury et al 2021; Hadden and Cherkinsky 2015). The ΔR term inevitably adds uncertainty to the calibrated 14 C date, meaning that dates on shell and other marine organisms are generally less precise than dates on terrestrial materials.…”

Late Holocene interaction of natural processes and human activity at two archaeological sites in the Ten Thousand Islands area of southwest Florida, USA

“…Summary of radiocarbon data collected from Turner River (TR) and Pumpkin Key (PK) study site samples obtained using a vibracore (C) or from an excavation trench (T). All marine dates (oyster and marl) calibrated using ΔR = 92 ± 74 yr for greater southwest Florida (Hadden and Schwadron 2019) cores consisted of a basal red mangrove peat, oyster rudstone (core 3), and overlying mudstone that contained marine molluscs, including articulated oysters. The sequence was previously described by Parkinson (1989) (TR-C3, TR-C8) plot near or below the contemporaneous sea level elevation and this observation provides additional support for an intertidal to subtidal palaeoenvironmental interpretation.…”

Marine Biogenic Carbonates and Radiocarbon—a Retrospective on Shells and Corals With an Outlook on Challenges and Opportunities

“…As a first approximation, ΔR was assumed to be a constant for a given region . However, researchers have demonstrated considerable variability over short-and longterm timescales (Austin et al 1995;Deo et al 2004;Culleton et al 2006;Hadden and Schwadron 2019). In the Arabian Sea, for example, ΔR declined by over 400 14 C yr over the period ca.…”

“…Here, also species-specific values can be modeled in one run, which is quite convenient. Examples of this application can be found in Hadden and Schwadron (2019), Lindauer et al (2017), Macario et al (2015), Milheira et al (2017), and Zazzo et al (2016.…”