Seasonal Radiocarbon Variation of Surface Seawater Recorded in A Coral from Kikai Island, Subtropical Northwestern Pacific

Morimoto, Maki; Kitagawa, Hiroyuki; Shibata, Yasuyuki

doi:10.1017/s0033822200035694

Cited by 17 publications

(16 citation statements)

References 14 publications

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“…Considering possible large seasonal/annual variations in surface ocean 14 C [ Druffel et al , 2004; Hua et al , 2005; Morimoto et al , 2004], we also analyzed 7 decadal samples (each sample covering ∼10 years). The ΔR values derived from these decadal samples are also presented in Table 2 and plotted in Figure 3 (shown as solid symbols).…”

Section: Resultsmentioning

confidence: 99%

Holocene marine¹⁴C reservoir age variability: Evidence from²³⁰Th-dated corals in the South China Sea

Hua

Zhao

et al. 2010

Paleoceanography

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[1] The South China Sea (SCS) is well connected with the western Pacific and influenced by the East Asian monsoon. We have examined temporal variations in radiocarbon marine reservoir ages (R) and regional marine reservoir corrections (DR) of the SCS during the Holocene using paired measurements of AMS 14 C and TIMS 230Th on 20 pristine corals. The results show large fluctuations in both R and DR values over the past 7500 years (yrs) with two distinct plateaus during 7.5-5.6 and 3.5-2.5 thousand calendar years before present (cal ka BP). The respective weighted mean DR values of these plateaus are 151 ± 85 and 89 ± 59 yrs, which are significantly higher than its modern value of −23 ± 52 yrs. This suggests that using a constant modern DR value to calibrate 14 C dates of the SCS marine samples will introduce additional errors to the calibrated ages. Our results provide the first database for the Holocene R and DR values of the SCS for improved radiocarbon calibration of marine samples. We interpret the two DR plateaus as being related to two intervals with weakened El Niño -Southern Oscillation (ENSO) and intensified East Asian summer monsoon (EASM). This is because the 14 C content of the SCS surface water is controlled by both the 14 C concentration of the Pacific North Equatorial Current (NEC) which is in turn influenced by ENSO-induced upwelling along the Pacific equator and vertical upwelling within the SCS as a result of moisture transportation to midlatitude region to supply the EASM rainfall.

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Section: Resultsmentioning

confidence: 99%

Holocene marine¹⁴C reservoir age variability: Evidence from²³⁰Th-dated corals in the South China Sea

Hua

Zhao

et al. 2010

Paleoceanography

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“…We compiled observations of Δ 14 C in DIC from large‐scale hydrographic surveys [ Broecker and Peng , 1982; Key et al , 2004; Kumamoto et al , 2011a, 2011b; R. Key and A. McNichol, unpublished data, 2012] and individual cruises [ Nydal et al , 1998; Graven et al , 2012b; Broecker et al , 1960; Fairhall and Young , 1985; Linick , 1978; Aramaki et al , 2010; Bien et al , 1960, 1965; Druffel et al , 1989; Gamo et al , 1987; Delibrias , 1980; Guilderson et al , 2006; Kumamoto et al , 2002; Leboucher et al , 2004; Masiello et al , 1998; Povinec et al , 2004; Ribbe and Tomczak , 1997; Tsunogai et al , 1995], as well as observations of Δ 14 C in coral records [ Brown et al , 1993; Druffel and Griffin , 1995; Druffel , 1996; Druffel et al , 2001; Grumet et al , 2002, 2004; Guilderson and Schrag , 1998a, Guilderson et al , 1998b; Guilderson et al , 2000a, 2004; Morimoto et al , 2004; Mitsuguchi et al , 2004; Schmidt et al , 2004].…”

Section: Methodsmentioning

confidence: 99%

Changing controls on oceanic radiocarbon: New insights on shallow‐to‐deep ocean exchange and anthropogenic CO₂ uptake

Graven¹,

Gruber²,

Key³

et al. 2012

J. Geophys. Res.

120

146

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The injection of radiocarbon (14C) into the atmosphere by nuclear weapons testing in the 1950s and 1960s has provided a powerful tracer to investigate ocean physical and chemical processes. While the oceanic uptake of bomb‐derived 14C was primarily controlled by air‐sea exchange in the early decades after the bomb spike, we demonstrate that changes in oceanic 14C are now primarily controlled by shallow‐to‐deep ocean exchange, i.e., the same mechanism that governs anthropogenic CO2 uptake. This is a result of accumulated bomb 14C uptake that has rapidly decreased the air‐sea gradient of 14C/C (Δ14C) and shifted the main reservoir of bomb 14C from the atmosphere to the upper ocean. The air‐sea Δ14C gradient, reduced further by fossil fuel dilution, is now weaker than before weapons testing in most regions. Oceanic 14C, and particularly its temporal change, can now be used to study the oceanic uptake of anthropogenic CO2. We examine observed changes in oceanic Δ14C between the WOCE/SAVE (1988–1995) and the CLIVAR (2001–2007) eras and simulations with two ocean general circulation models, the Community Climate System Model (CCSM) and the Estimating the Circulation and Climate of the Ocean Model (ECCO). Observed oceanic Δ14C and its changes between the 1980s–90s and 2000s indicate that shallow‐to‐deep exchange is too efficient in ECCO and too sluggish in CCSM. These findings suggest that mean global oceanic uptake of anthropogenic CO2 between 1990 and 2007 is bounded by the ECCO‐based estimate of 2.3 Pg C yr−1 and the CCSM‐based estimate of 1.7 Pg C yr−1.

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“…The Tsushima Current splits from the Kuroshio Current southwest of Japan, flows northeastward in the south part of the Sea of Japan, and connects to the Tsugaru Current after passing through Tsugaru Strait. Collection points are shown for M. stimpsoni shell samples and seawater in Otsuchi (red star; this study), reef-building corals in Okinawa and Kikaijima (green circles;Konishi et al, 1981;Morimoto et al, 2004) and Iki (light green circle;Mitsuguchi et al, 2016), and mollusk shells in Kunashiri (white circles;Kuzmin et al, 2001), Etorofu (white square;Yoneda et al, 2000), Shikotan (white diamond;Yoneda et al, 2007), Habomai (white triangle;Kuzmin et al, 2007), Hakodate (black circle;Yoneda et al, 2007), Hachinohe (black squares;Yoshida et al, 2007), and Shiogama (black diamond;Yoshida et al, 2007). Seawater observation points in the open ocean, sampled by research vessels (pink, within the Sea of Japan; closed/open purple symbols, north/south of 41.58N in the western subtropical gyre), are shown…”

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confidence: 93%

Bomb‐¹⁴C Peak in the North Pacific Recorded in Long‐Lived Bivalve Shells (Mercenaria stimpsoni)

et al. 2018

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The excess radiocarbon produced by nuclear bomb testing in the atmosphere in the 1950s–1960s (bomb‐14C) is used as a tracer in the surface ocean, extending our understanding of geophysics and biogeochemical cycles. However, there is no bomb‐14C 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 14C in six live‐caught M. stimpsoni shells from the western North Pacific (39.4°N, 142°E) and report, for the first time, the bomb‐14C record with robust calendar ages based on annual growth increments. The value was constant in 1934–1952 (Δ14C = −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 ∼10‰ higher than the atmospheric value. The bomb‐14C 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.

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Seasonal Radiocarbon Variation of Surface Seawater Recorded in A Coral from Kikai Island, Subtropical Northwestern Pacific

Cited by 17 publications

References 14 publications

Holocene marine¹⁴C reservoir age variability: Evidence from²³⁰Th-dated corals in the South China Sea

Holocene marine¹⁴C reservoir age variability: Evidence from²³⁰Th-dated corals in the South China Sea

Changing controls on oceanic radiocarbon: New insights on shallow‐to‐deep ocean exchange and anthropogenic CO₂ uptake

Bomb‐¹⁴C Peak in the North Pacific Recorded in Long‐Lived Bivalve Shells (Mercenaria stimpsoni)

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Seasonal Radiocarbon Variation of Surface Seawater Recorded in A Coral from Kikai Island, Subtropical Northwestern Pacific

Cited by 17 publications

References 14 publications

Holocene marine14C reservoir age variability: Evidence from230Th-dated corals in the South China Sea

Holocene marine14C reservoir age variability: Evidence from230Th-dated corals in the South China Sea

Changing controls on oceanic radiocarbon: New insights on shallow‐to‐deep ocean exchange and anthropogenic CO2 uptake

Bomb‐14C Peak in the North Pacific Recorded in Long‐Lived Bivalve Shells (Mercenaria stimpsoni)

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Holocene marine¹⁴C reservoir age variability: Evidence from²³⁰Th-dated corals in the South China Sea

Holocene marine¹⁴C reservoir age variability: Evidence from²³⁰Th-dated corals in the South China Sea

Changing controls on oceanic radiocarbon: New insights on shallow‐to‐deep ocean exchange and anthropogenic CO₂ uptake

Bomb‐¹⁴C Peak in the North Pacific Recorded in Long‐Lived Bivalve Shells (Mercenaria stimpsoni)