Multidecadal oceanographic changes in the western Pacific detected through high‐resolution bomb‐derived radiocarbon measurements on corals

• Published in: Geochemistry, geophysics, geosystems : G3 Vol. 18; no. 4; pp. 1608 - 1617
• Main Authors: Hirabayashi, S., Yokoyama, Y., Suzuki, A., Miyairi, Y., Aze, T.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 01.04.2017
• Subjects: Atolls; Boundary currents; Carbon 14; coral; Coral reefs; Corals; Eddies; Equatorial currents; Ishigaki; Latitude; Mesoscale eddies; mesoscale eddy; Migration; Nuclear tests; Ocean circulation; Oceanography; Pacific Decadal Oscillation; Physical oceanography; Propagation; radiocarbon; Radiocarbon dating; Resolution; Subtropical countercurrent; Variability; western Pacific; Guam; Ishigaki Island; Palau; United States > US
• ISSN: 1525-2027; 1525-2027
• DOI: 10.1002/2017GC006854

High‐resolution measurements of radiocarbon (14C) in corals can be used to reconstruct past variability in ocean conditions. Here we report seasonal Δ14C changes in coral from Ishigaki Island, Japan, and compare with previously reported data from Palau and Guam. Our data clearly indicate a significant increase in Δ14C from 1947 to 1998 related to atmospheric nuclear bomb testing. The three early Δ14C spikes related to the atmospheric nuclear bomb tests in the US Proving Grounds at Bikini and Enewerak atoll conducted in 1954, 1956, and 1958 were detected from the Ishigaki coral. After 1976, variability in the Mindanao Dome region related to North Equatorial Current (NEC) bifurcation latitude migration affected the Δ14C difference between Palau and Guam, whereas the difference between Ishigaki and Guam was not correlated with the bifurcation latitude. The Δ14C difference between Ishigaki and Guam may be due to mesoscale eddies in the Kuroshio area. On the decadal scale, the northward shift of NEC bifurcation latitude after 1976, the year as known as Pacific Decadal Oscillation regime shift from negative to positive, was concurrent with the abundant westward‐propagating mesoscale eddies in the Subtropical Countercurrent region and stronger Kuroshio transport off the east Taiwan, which may be represented by a smaller Δ14C difference between Ishigaki and Guam after 1976. Key Points High‐resolution radiocarbon measurements were performed on corals from 1947 to 1998 from Ishigaki Island south of Japan Existence of three early Δ14C spikes of nuclear bomb tests in 1950s was confirmed in the North Pacific western boundary current area We demonstrated corals can reconstruct migration of NEC bifurcation latitude related to physical oceanographic changes and mesoscale eddies