Radiocarbon in the water column of the southwestern north Pacific Ocean - 24 years after geosecs

In the framework of the Worldwide Marine Radioactivity Studies (WOMARS) project, water profile samples for radiocarbon measurements were taken during the IAEA'97 cruise at 10 stations in the southwestern North Pacific Ocean. While C-14 concentrations were rapidly decreasing from the surface (Delta(14)C about 100parts per thousand) down to about 800 in at all visited stations (Delta(14)C about -200parts per thousand), the concentrations below 1000 in were almost constant. Some stations were in proximity to the GEOSECS stations sampled in 1973; thus, C-14 profiles could be compared after a 24-yr interval. Generally, C-14 concentrations had decreased in surface waters (by 50-80%o) and increased (by about the same amount) in intermediate waters when compared with GEOSECS data. In deep waters (below 1000 m), the observed C-14 concentrations were similar to GEOSECS values. The bomb-produced C-14 inventory had increased by more than 20% over the 24 yr from 1973 to 1997 and was estimated to be about (32 +/- 5) 10(12) atom m(-2), with an annual C-14 flux of (1.3 +/- 0.3) 10(12) atom m(-2) yr(-1). The results suggest that bomb-produced C-14 has been advected northwards by the Kuroshio Current and the Kuroshio Extension and stored in the intermediate layer as North Pacific. Intermediate Water.