The East Australian Current (EAC) is the Western Boundary Current (WBC) of the South Pacific Subtropical Gyre that transports warm tropical water to higher southern latitudes and therefore has a significant impact on the climate of Australia and New Zealand. A weaker EAC transport causes anomalous cool conditions in New Zealand, and a stronger EAC is shown to promote rainfall along the east coast of Australia. Modern observations show that the EAC has strengthened and extended further southward with rising global temperatures over the past decades. However, little is known about the pre-industrial variability of the EAC and its forcing mechanisms and climatic impact on the region. In this study, we analyzed marine sediment samples of three multiple cores recovered offshore northeastern Australia between 15°S and 26°S, spanning the past four thousand years. We present planktic foraminifera Globigerinoides ruber (white) Mg/Ca-based sea surface temperature (SST) reconstructions, which reveal an increase in SST by ~1.2°C after ~1400 CE. The increase in SST is consistent with land temperature reconstructions as inferred from borehole temperatures for northeastern Australia. We infer the increase in temperature after ~1400 CE is related to a stronger EAC heat transport that is likely driven by a spin-up of the Southern Hemisphere subtropical gyre circulation due to a progressive shift of the Southern Annular Mode (SAM) towards its positive phase. An equatorward shift of the bifurcation latitude of the South Equatorial Current because of more El Niño-like conditions may also contribute to the intensification of EAC. Our results reveal an already intensifying EAC prior to its intensification associated with greenhouse-gas-induced anthropogenic climate change and shed light on the complex behavior of the WBCs of the major oceanic gyres.
 

East Australian Current,Western Boundary Current,Mg/Ca-based sea surface temperature,common era