An Evaluation of Variability in the 14co2 Cycle in the UpperOcean

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This research will examine carbon and oxygen isotope ratios in annual samples of banded corals from several sites in the Atlantic and Pacific Oceans. The goals are to establish the vriability of the ventilation of the main thermocline with respect to CO2 and to determine the cause and spatial extent of decade time scale changes in surface ocean 1 4 C during the past 500 years. First, high precision (+2 / ) 1 4 C records will be reconstructed for the post-bomb period (1953-present) for banded corals from the equatorial and South Atlantic. Isopycnal mixing models for the upper ocean, similar to that used previously, will be constructed for these locations and for the North and South Pacific. Second, high precision 1 4 C records will be reconstructed for the Little Ice Age (A.D. 1400-1850) from four sites in the world's ocean - North Atlantic (Florida), North Central Pacific (Hawaii), eastern equat Pacific (Galapagos) and Southwest Pacific (Great Barrier Reef). It will be determined whether the decade time scale changes noticed in surface ocean 1 4 C during the Maunder minimum in the Southwest Pacific (Abrahams Reef) were an ocean- wide phenomena, and the potential impact of these changes on surface circulation and on the cycling of CO2 will be assessed. Third, the Suess effect and the changes in 1 8 O and 1 3 C in banded corals from the North Central and Southwestern Pacific will be measured in order to assess the input of fossil fuel CO2 into the ocean. Fourth, high precision 1 4 C will be measured on fossil corals that have been accurately dating using 230 Th by mass spectrometry from the raised reefs of the Huon Peninsula, Papua New Guinea. The goal here is to develop a method to extend the radiocarbon chronology past that available from known-aged tree rings (9,700 calendar yrs BP), into the early Holocene and deglaciation periods when atmospheric pCO2 was substantially lower than nineteenth century levels.