Radiocarbon age offsets in post-bomb terrestrial snails from the Florida Peninsula, USA

Abstract Terrestrial gastropods can incorporate carbon from multiple sources, including 14 C-depleted carbonate from limestone, known as the “Limestone Problem” (Goodfriend and Stipp 1983). This affects the reliability of 14 C dating on terrestrial snails, and varies by species, habitat, and physiography, necessitating local validation studies. This study assessed whether two land snail taxa common in carbonate terrains of Florida (USA) accurately reflect atmospheric 14 C concentration at the time of biomineralization, a necessary condition for accurate dating, or if they incorporate pre-aged carbon, leading to radiocarbon ages that are “too old.” Radiocarbon measurements were made on 11 modern, known-age specimens (collected 1967–2015) of the rosy wolfsnail ( Euglandina rosea ) and flatcoil ( Polygyra spp.) snails, and results were compared to expected atmospheric values based on the Bomb21 NH2 calibration dataset (Hua et al. 2022). Specimens from carbonate terrains had significantly lower 14 C activity than the contemporaneous atmosphere, while those from sandy terrains showed no such offsets. The magnitude of the offset varied by taxon. Flatcoils from carbonate terrains had the most unreliable dates, overestimated by 1350 ± 740 14 C yr on average. Rosy wolfsnails from carbonate terrains had smaller offsets, overestimating by 270 ± 130 14 C yr on average. The results suggest land snails from Florida will incorporate significant and variable amounts of pre-aged or “dead” carbonate in their shells if it is present in the landscape.