A 150-year variation of the Kuroshio transport inferred from coral nitrogen isotope signature

The Kuroshio Current is a major global ocean current that drives the physical ocean-atmosphere system with heat transport from tropical to temperate zones in the North Pacific Ocean. We reconstructed the variability of the Kuroshio transport over the past 150 years using coral skeletal nitrogen isotopic composition (δ¹⁵N_coral). A 150 year δ¹⁵N_coral record (1859–2008 A.D.) is 4 times the length of the observational record (1971 to present) and could provide a direct comparison with global climate change, such as the Pacific Decadal Oscillation (PDO) index and El-Niño–Southern Oscillation (ENSO), through recent global warming. Coral cores from Porites were collected from Tatsukushi Bay in 2008 on the Pacific coast of Japan, which is located on the northern front of the Kuroshio Current. δ¹⁵N_coral was used as a proxy to record the δ¹⁵N of nitrate (δ¹⁵N_nitrate) controlled by the upwelling of subtropical subsurface water (δ¹⁵N_nitrate; ~ +2 − +3‰), and δ¹⁵N_coral was negatively correlated with observations of the Kuroshio transport (R = −0.69, P < 0.001) and the 2 year lagged PDO index (R = −0.63, P < 0.005) from 1972 to 2007. The 150 year record of δ¹⁵N_coral suggested that the Kuroshio transport varied with ~25 year cycle, and the amplitude became more stable, and the volume was intensified through the twentieth century. The Kuroshio transport was intensified by the La Niña state in the early 1900s and by the El Niño-PDO state after the 1920s. Our results suggested that the Kuroshio transport was influenced by the combined climate modes of ENSO and PDO during the last century.