Radiocarbon evidence for mid-late Holocene changes in southwest Pacific Ocean circulation

摘要

Variability in the southwest (SW) Pacific Ocean circulation is influenced by the changes in the South Pacific subtropical gyre and its western boundary current, the East Australian Current (EAC). The EAC plays a significant role in transporting warm, well-ventilated, nutrient-poor waters to more temperate higher latitudes. Recent climate changes associated with EAC intensification have led to anomalous warming in the South Tasman, with implications for marine ecosystems and environment. A clear understanding of the significance of these changes requires knowledge of past natural variability. Here we have reconstructed a 4500year record of regional sea surface radiocarbon reservoir ages (R) and local reservoir effects (R). Our results reveal the centennial-scale variability over the last 4500years, with R ranges as large as 390(14)Cyr. Older R (similar to 410(14)Cyr) between 1610 to 1860 A.D. in our record, corresponding to the Little Ice Age, suggests a weaker influence of the EAC in the South Tasman. Between 4000 and 1900cal years B.P., R and R were significantly younger than the modern, with values of similar to 170 and -130(14)Cyr, respectively, indicating increased EAC transport of tropical waters into the South Tasman. We propose that the large R variability was influenced by strong and abrupt El Nino events which punctuated the muted El Nino-Southern Oscillation (ENSO) period in the mid-late Holocene and enabled increased westward flow of gyre waters into the SW Pacific. The strengthening of the EAC extension appears to have been a response to the precession-modulated ENSO-Southern Annular Mode interactions.