Regional variability of surface ocean radiocarbon from southern great barrier reef corals

High-precision Delta(14)C and stable isotope (delta(18)O and delta(13)C) records are reported for post-bomb corals from three sites off the eastern Australian coast. We observe that Delta(14)C values increased from ca. -50 parts per thousand in the early 1950s to +130 parts per thousand by 1974, then decreased to 110 parts per thousand by 1991. There is general agreement between the coral results and Delta(14)C of dissolved inorganic carbon (DIC) in seawater measured previously for locations in the South Pacific. Delta(14)C values at our southern hemisphere sites increased at a slower rate than those observed previously in the northern hemisphere. Small variations in the Delta(14)C records among our three sites are likely due to differences in circulation between the shallow coastal waters and the open ocean influenced by seasonal upwelling. Low Delta(14)C is associated with most El Nino/Southern Oscillation (ENSO) events after 1970, indicating input of low C-14 waters from the southern-shifted South Equatorial Current. The exception is the severe ENSO event of 1982-1983 when upwelling in the South Equatorial Current could have ceased, causing normal Delta(14)C values in the corals during this time.