Seasonal Radiocarbon Variation of Surface Seawater Recorded in a Coral from Kikai Island, Subtropical Northwestern Pacific

Abstract

A coral radiocarbon (Delta-14C) investigation with a high time-resolution is crucial for reconstructing secular and seasonal Delta-14C changes in the surface seawater which potentially reflect ocean circulations and dynamic ocean-atmosphere interactions. The Delta-14C values of a modern coral (Porites sp.) from Kikai Island, southern Japan, in the subtropical northwestern Pacific, were determined for the period of 1991-1998 at a monthly resolution. A coral Delta-14C time series for the 8 yr indicated seasonal cycles superimposed on a secular decreasing trend of 3.8 per mil per yr. The seasonal amplitude of the coral Delta-14C was about 18 per mil on the average and the minimum Delta-14C was observed in late spring and summer. The Delta-14C changes were tentatively explained by horizontal oceanic advections around Kikai Island or over the wide range of the equatorial and subequatorial Pacific.