Anthropocene North Western Pacific Oceanography Recorded as Seasonal-Resolution Radiocarbon in Coral From Kikai Island, Japan

Radiocarbon (¹⁴C) in corals can be used as a relatively high-sensitivity indicator of vertical and horizontal advection of water masses, which contributes to the understanding of ocean circulation. In this study, we reconstruct Kuroshio and Ryukyu current transport with a seasonal resolution Δ¹⁴C record spanning 1947–2009. This record covers the beginning of the atomic era and was obtained from a coral on Kikai Island in the south of Japan. The Kikai Δ¹⁴C curve features a newly discovered Δ¹⁴C spike in July 1955, a rapid increase after 1962, and a steady decrease after 1980. The spike in 1955 may directly reflect ocean current transport. The lack of periodicity in the Δ¹⁴C record suggests the existence of mesoscale eddies and the complexity of Kuroshio and Ryukyu current transport. In addition, comparing the high-resolution Δ¹⁴C of Kikai and Ishigaki islands, both situated along the path of the Kuroshio, reveals the influence of Pacific Decadal Oscillation and El Niño-Southern Oscillation on the Kuroshio and Ryukyu currents. This suggests that seasonally resolved Δ¹⁴C in corals along an ocean current can produce a long-term record of ocean mixing that responds to climate variability.