Annual samples from two Palmyra Atoll corals (Porites lutea) that lived during the past 110 years were analyzed for radiocarbon (D 14 C) and d 18 O. The D 14 C values decreased 7.6& from 1896 to 1953, similar to other coral records from the tropical and subtropical Pacific. D 14 C values rose from $À60& to $+110& by 1980 due to the input of bomb radiocarbon from the atmosphere. Elevated D 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 d 18 O and d 13 C values and a correlation between them. The D 14 C results were more resistant to alteration, except when contamination was from the bomb era (>1956).
We report measurements of near monthly Δ 14 C and δ 18 O during selected decades from an east equatorial Pacific coral that grew during the past four centuries. We find that El Niño events occurred regularly during the late 1700s. During the early 1800s, El Niño events occurred less often, and La Niña conditions prevailed, which were accompanied by unprecedented, low cool season Δ 14 C values and high cool season δ 18 O values. These results indicate that shallow overturning water (e.g., Central Mode Water) from the North Pacific was likely an important source of water to the Galapagos area during the early 1800s.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.