Investigation of Past Variations In Surface Ocean Radiocarbon During The Holocene

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9314691 DRUFFEL The major goal of this continuing research is to construct time histories of high-precision 14C in past surface ocean water regimes using annual coral bands from fossil and living corals. These data, when coupled with stable oxygen and carbon isotope measurements (18 O and 13C), reveal important information regarding the cycling of 14CO2 in the upper ocean and the exchange of 14CO2 between air and sea. Four experiments will be conducted 1) To determine whether decade time-scale variations in 14C were present in ancient oceans using fossil coral sequences that have been absolutely dated using 230 Th by thermal ionization mass spectrometry. Two time periods will be studied in corals from Vanuatu and from Biscayne National Park, Florida. This will allow for the comparison of 14C in two major ocean currents (the South Equatorial Current and the Gulf Stream, respectively), during extreme thermal conditions that existed in the Holocene: the Little Ice Age and the Hypsithermal. 2) To determine the presence or absence of decade time-scale variations in 14C in the North Pacific during the late Little Ice Age (AD 1680-1730), and compare this record to that obtained from the southwestern Pacific where large 14C variations correlated with ancient El Nino events. Corals from the North Atlantic will also be studied, to examine the extent to which the 14C variability was world-wide. 3) The Suess effect (lowering of 14C due mainly to 14C-free fossil fuel CO2 since late 1800s) will be measured at three sites in the northern Pacific, where no measurable Suess effect was found 4)Collection and high-precision 14C analyses are proposed for a coral from Fernando de Noronha. The equatorial Atlantic is presently the only location in the temperate and tropical oceans for which a post-bomb 14C record is not available. Its importance for parameterizing tracer penetration into the Atlantic cannot be overstated. A limited number of high-precision 14C analyses will b e made using Accelerator Mass Spectrometry (AMS) techniques, with multiple graphite target analysis for each sample. The remainder of the samples (75%) will be measured to high- precision at the UCI Radiocarbon Laboratory using conventional, gas-counting techniques.