科研之友
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摘要
The excess radiocarbon produced by nuclear bomb testing in the atmosphere in the 1950s-1960s (bomb-C-14) is used as a tracer in the surface ocean, extending our understanding of geophysics and biogeochemical cycles. However, there is no bomb-C-14 record for the high-latitude western North Pacific Ocean because of the paucity of long-lived marine calcifying organisms equivalent to reef-building corals. The shells of Stimpson's hard clam, Mercenaria stimpsoni, potentially provide such a record because the clam's lifespan is very long (>100 years). We analyzed C-14 in six live-caught M. stimpsoni shells from the western North Pacific (39.4 degrees N, 142 degrees E) and report, for the first time, the bomb-C-14 record with robust calendar ages based on annual growth increments. The value was constant in 1934-1952 (C-14=-66), with a sudden increase in 1959, a peak in 1974 (107), which was 60 lower than that of the Kuroshio Current, a gradual decline after 1974, and a current value of 16-18, which is approximate to 10 parts per thousand higher than the atmospheric value. The bomb-C-14 values are between the Kuroshio Current (the northwestern subtropical gyre) and Oyashio Current (the Western Subarctic Gyre) values, suggesting that the Tsugaru Current, downstream from the Kuroshio Current, mixes with the Oyashio Current after passing through Tsugaru Strait.
- 出版日期2018-4
