Abstract
We present a paleoceanographic perspective on the North Pacific subtropical gyre circulation during the last two glacial cycles and also discuss the linkage of the subtropical gyre circulation with the tropical ocean-atmosphere dynamics and the East Asian monsoon. Comparison of the sea surface temperature (SST) differences between ODP sites 1014 and 1016 (ΔSSTnortheastern Pacific(NEP)=SSTODP1014-SSTODP1016) and the SST from Core MD01-2421 revealed anti-phase variation : high ΔSSTNEP (indicating weakening of the California Current) corresponded to low SST at the Japan margin (indicating the southward displacement of the northwestern Pacific subarctic boundary and weakening of the Kuroshio Extension), and vice versa. This finding suggests that the intensity of the North Pacific subtropical gyre circulation has varied in response to precessional forcing and that this response has been linked with changes in tropical ocean-atmosphere interactions. In the precessional cycle, the SST variation derived from Core MD01-2421 lags ca. 2.5-4 kyr behind the variations shown by Hulu and Sanbao stalagmite δ18O records and by the pollen temperature index from Core MD01-2421, suggesting out-of-phase variations of the North Pacific subtropical gyre circulation and the East Asian summer monsoon. These findings indicate that the behavior of interactions between tropical oceanatmosphere dynamics and the East Asian summer monsoon may have varied in response to the precessional cycle.
