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

Abstract

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.