Japan Marine Science and Technology Center, Ocean Research Department, 2-15 Nat- sushima, Yokosuka, Kanagawa 237 Japan
ABSTRACT. In order to verify sediment trap samples as indicators of upper ocean 14C concentrations, particulate inorganic radiocarbon (PIOCΔ14C) collected by time-series sediment traps in the Sea of Okhotsk and the Bering Sea was measured by accelerator mass spectrometry (AMS). All of the PIOCΔ14C measurements were < 0%o, in contrast to GEOSECS 14C data in the upper ocean from the northwestern North Pacific. This difference is attributed to the upwelling of deepwater that contains low Δ14C of dissolved inorganic carbon (DIOCΔ14C) and to the decrease over time of surface DIOCΔ14C owing to the decrease of atmospheric Δ14C values. In addition, PIOCΔ14C values showed significant seasonal variability: PIOCΔ14C collected in the fall was the greatest (-22%o on average), whereas PIOCΔ14C collected in winter showed an average minimum of -48%o. It is likely that this difference was caused by changes in mixed layer thickness. Although some uncertainties remain, further study on PIOCΔ14C will enable us to estimate seasonal variability in DIOCΔ14C and air-sea CO2 exchange rate.
[Radiocarbon Volume 38, Number 3, 1996]