Inorganic Radiocarbon in Time-Series Sediment Trap Samples: Implication of Seasonal Variation of 14 C in the Upper Ocean

• Published in: Radiocarbon
• Main Author: Honda, Makio C.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 1996
• Subjects: General Earth and Planetary Sciences; Archeology; Bering Sea; Okhotsk; Pacific
• Online Access: http://dx.doi.org/10.1017/s0033822200030113; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0033822200030113

In order to verify sediment trap samples as indicators of upper ocean 14 C concentrations, particulate inorganic radiocarbon (PICΔ 14 C) 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 PICΔ 14 C measurements were < 0‰, in contrast to GEOSECS 14 C data in the upper ocean from the northwestern North Pacific. This difference is attributed to the upwelling of deepwater that contains low Δ 14 C of dissolved inorganic carbon (DICΔ 14 C) and to the decrease over time of surface DICΔ 14 C owing to the decrease of atmospheric Δ 14 C values. In addition, PICΔ 14 C values showed significant seasonal variability: PICΔ 14 C collected in the fall was the greatest (-22‰ on average), whereas PICΔ 14 C collected in winter showed an average minimum of −48‰. It is likely that this difference was caused by changes in mixed layer thickness. Although some uncertainties remain, further study on PICΔ 14 C will enable us to estimate seasonal variability in DICΔ 14 C and air-sea CO 2 exchange rate.