Variability of surface ocean radiocarbon and stable isotopes in the southwestern Pacific

We present high-precision radiocarbon (Delta(14)C) results and stable isotope (delta(18)O and delta(13)C) records for a coral from Heron Island (23 degrees S, 152 degrees E) and new stable isotope (delta(18)O and delta(13)C) records for annual coral bands from Abraham Reef (22 degrees S, 153 degrees E) in the southern Great Barrier Reef studied earlier [Druffel and Griffin, 1993]. These tracers provide unique information on the regional water mass history, and together these data allow us to constrain the variability of circulation in the upper Pacific over the past four centuries. First, we observe decreases in delta(18)O of coral from Abraham Reef and Heron Island, indicating an increase in sea surface temperature and/or a decrease in surface salinity since 1850. Second, the small Suess effect value (Delta(14)C decrease from 1880 to 1955, due mostly to fossil fuel CO2) observed previously at Abraham Reef[Druffel and Griffin, 1993] is confirmed in the measurements reported here from the Heron Island coral. This value is low compared to those observed in other areas of the ocean [Druffel 1997; Druffel and Linick, 1978; Nozaki et al., 1978] between 1880 and 1955. Third, we report alterations in the correlation between Fl Nino events and the occurrence of low Delta(14)C, which is indicative of long-term change(s) in circulation in the SW Pacific. The Delta(14)C shifts reported here are not large, but even small temporal changes in prebomb Delta(14)C suggest that important changes in the large-scale state of the ocean have occurred, such as a temporal change in circulation.