Kevin B. Jones

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

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, Δ R, and of seasonal oscillations in the ventilation age of coastal waters. If large, these seasonalnnoscillations 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 Δ R of Callao Bay shells collected during normal (1908) and El Nio (1926) years. Despite the intrashell 14C variation noted, weighted average Δ R values from all 3 sample sites and from normal and El Nio years all overlap at 1 s. We report Δ R values of 183 18 and 194 23 yr from Callao Baynn(124S), 165 24 yr from Salaverry (814S), and 189 23 yr from Sechura Bay (545S).

Marine radiocarbon reservoir age variation in Donax obesulus shells from northern Peru: Late Holocene evidence for extended El Niño

For at least 6 m.y., El Nino events have posed the greatest environmental risk on the Peruvian coast. A better understanding of El Nino is essential for predicting future risk and growth in this tropical desert. To achieve this we analyzed archaeological and modern pre-bomb shells from the surf clam Donax for the radiocarbon reservoir effect (ΔR) to characterize late Holocene coastal upwelling conditions in northern Peru (8°14′S). Mean ΔR values from these shells suggest that modern upwelling conditions in this region were likely established between A.D. 539 and A.D. 1578. Our radiocarbon data suggest that upwelling conditions ca. A.D. 539 were less intense than those in modern times. The observed coastal water enrichment in 14 C may be consequence of frequent strong El Nino events or extended El Nino–like conditions. These ΔR-inferred marine conditions are in agreement with proposed extended El Nino activity in proxy and archaeological records of ca. A.D. 475–530. Extended El Nino conditions have been linked to political destabilization, societal transformation, and collapse of the Moche civilization in northern Peru. A return to such conditions would have significant impacts on the dense population of this region today and in the near future.

Radiocarbon Chronometry of Site QJ-280, Quebrada Jaguay, a Terminal Pleistocene to Early Holocene Fishing Site in Southern Peru

ABSTRACT Excavations in 1970, 1996, and 1999 at Site QJ-280, Quebrada Jaguay, in southern Peru, yielded enough dateable terrestrial plant material to establish an extensive radiocarbon chronology for the site. QJ-280 is one of oldest well-dated fishing sites in the Americas: it was occupied from the terminal Pleistocene to the mid-Holocene (about 13,000–8,300 calibrated years BP) based on 42 terrestrial radiocarbon dates, encompassing the Jaguay and Machas Phases of the local archaeological sequence. In addition to the terrestrial dates, radiocarbon measurements on valves of two marine surf clam (Mesodesma donacium) individuals from a single, well-dated mid-Holocene Manos Phase archaeological context have provided insight into marine upwelling conditions during the occupation of Quebrada Jaguay. The marine reservoir age varied between 130 and 730 14C years during the brief lives of the two clams (up to 5 years each), and varied by up to 530 14C years within an individual valve, suggesting strong and variable deep marine upwelling; conditions broadly similar to those that exist in coastal Peru today. These rapid variations in marine radiocarbon age suggest that marine radiocarbon dates from environments with variable upwelling could be skewed by up to hundreds of years.