Seasonal Variations in Peruvian Marine Reservoir Age from Pre-Bomb Argopecten Purpuratus Shell Carbonate

Abstract

Marine upwelling along coastal Peru can be intense and variable, making radiocarbon dating marine and coastal systems complex. Historical and proxy records of upwelling along coastal Peru are few, and long-lived species such as corals do not grow in the cold coastal waters. Mollusk shell carbonate, however, can record both the magnitude of the local marine reservoir correction, ΔR, and of seasonal oscillations in the ventilation age of coastal waters. If large, these seasonal

oscillations would complicate radiocarbon dating of marine organisms. To examine this possibility, we sampled for d13C, d18O, and 14C content a set of pre-bomb Argopecten purpuratus shells collected from coastal Peru during 1908 and 1926. Intrashell variations of up to 216 14C yr were noted, but these were not consistently correlated with seasonal changes in d18O or d13C. Only an 11 yr difference was observed in the weighted average ΔR of Callao Bay shells collected during normal (1908) and El Nio (1926) years. Despite the intrashell 14C variation noted, weighted average ΔR values from all 3 sample sites and from normal and El Nio years all overlap at 1 s. We report ΔR values of 183 18 and 194 23 yr from Callao Bay

(124'S), 165 24 yr from Salaverry (814'S), and 189 23 yr from Sechura Bay (545'S).