Variability of monthly radiocarbon during the 1760s in corals from the Galapagos Islands

Abstract

Radiocarbon (Delta(14)C) measurements of monthly samples from a Galapagos surface coral are among the first data sets from the new Keck Carbon Cycle Accelerator Mass Spectrometry laboratory at the University of Califomia, Irvine. An average Delta(14)C value of -62parts per thousand is obtained for 144 measurements of samples from monthly coral bands that lived from about AD 1760-1771 (+/-6 yr). High Delta(14)C values were found during January through March, when upwelling was weak or absent at the Galapagos Islands. Low Delta(14)C values were obtained mid-year during strong upwelling. The average seasonal variability of Delta(14)C was 15-25parts per thousand, which is greater than that at other tropical and subtropical locations in the Pacific Ocean because of intense seasonal upwelling at this site. Periods of sustained high Delta(14)C values were found during 1762-1763 and 1766. A spectral analysis revealed that the spectral density for the Delta(14)C data displays most of its variance at the 5-yr cycle, which is reflective of El Nino periodicity during the 20th century.