Preliminary results of radiocarbon monitoring in the surface waters of the North Pacific

Surface waters samples between Japan and US for radiocarbon measurement have been collected since summer 2003 by cargo ship with the help of a shipping company. As a first step, to investigate regional Δ14C distribution in the North Pacific, the samples collected in the summer season of 2003-2006 were measured using an accelerator mass spectrometer (AMS) at the National Institute for Environmental Studies (NIES) in Japan. Although during 2003-2006, a distinct decreasing trend of Δ14C in the subtropical region of the North Pacific was not observed, the average values of Δ14C in the subtropical region (Kuroshio Current, North Pacific Current and California Current regions) for the 4 years were 72 ± 12, 69 ± 10 and 47 ± 11 per mille , respectively, and indicate that the long-term decreasing trend of Δ14C in the surface waters since the 1970's is still continuing.