Decadal timescale shift in the 14C record of a central equatorial Pacific coral

Abstract

Coral skeletal radiocarbon records reflect seawater Δ14C and are useful for reconstructing the history of water mass movement and ventilation in the tropical oceans. Here, we reconstructed the inter-annual variability in central equatorial Pacific surface water Δ 14C from 1922-1956 using near-monthly 14C measurements in a Porites sp. coral skeleton (FI5A) from the windward side of Fanning Island (3°54′32″N, 159°18′88″W). The most pronounced feature in this record is a large, positive shift in the Δ14C between 1947 and 1956 that coincides with the switch of the Pacific Decadal Oscillation (PDO) from a positive to a negative phase in the mid-1940s. Although the absolute Δ14C values from 1950-1955 in FI5A differ from the Δ14C values of another coral core collected from the opposite side of the island, both records show a large, positive shift in their Δ14C records at that time. The relative increase in the AΔ14C of each record is consistent with the premise that a common mechanism is controlling the Δ14C records within each coral record. Overall, the Fanning Δ14C data support the notion that a significant amount of subtropical seawater is arriving at the Equator, but does not allow us to determine the mechanism for its transport.