Radiocarbon and stable isotopes in Palmyra corals during the past century

Annual samples from two Palmyra Atoll corals ( Porites lutea ) that lived during the past 110 years were analyzed for radiocarbon (Δ 14 C) and δ 18 O. The Δ 14 C values decreased 7.6‰ from 1896 to 1953, similar to other coral records from the tropical and subtropical Pacific. Δ 14 C values rose from ∼−60‰ to ∼+110‰ by 1980 due to the input of bomb radiocarbon from the atmosphere. Elevated Δ 14 C values were observed for the mid- to late-1950s, suggesting early input of bomb radiocarbon, possibly from the largest Marshall Islands bomb tests in 1954. Secondary aragonite precipitation was identified in a portion of one core using scanning electron microscopy and X-radiography, and was responsible for high δ 18 O and δ 13 C values and a correlation between them. The Δ 14 C results were more resistant to alteration, except when contamination was from the bomb era (>1956).