Regional Variability of Surface Ocean Radiocarbon from Southern Great Barrier Reef Corals

Abstract

High-precision Delta-14C and stable isotope (delta-18O and delta-13C) records are reported for post-bomb corals from three sites off the eastern Australian coast. We observe that Delta-14C values increased from ca. -50 per mil in the early 1950s to +130 per mil by 1974, then decreased to 110 per mil by 1991. There is general agreement between the coral results and Delta-14C of dissolved inorganic carbon (DIC) in seawater measured previously for locations in the South Pacific. Delta-14C values at our southern hemisphere sites increased at a slower rate than those observed previously in the northern hemisphere. Small variations in the Delta-14C 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-14C is associated with most El Niño/Southern Oscillation (ENSO) events after 1970, indicating input of low 14C 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-14C values in the corals during this time.