In this study, a sea-surface water Δ14C record of AD 1966–2000 (i.e., after the atmospheric nuclear-bomb testing period of the mid-1950s to early 1960s) was reconstructed from a coral sample collected from Iki Island, western Japan. The island is located in the Tsushima Strait where the Tsushima Current flows from the East China Sea (ECS) continental shelf into the Sea of Japan, indicating a strong influence of the ECS shelf water on the island. It is widely accepted that the Tsushima Current originates in the area between the ECS shelf break and the Nansei Islands further offshore as a branch of the Kuroshio Current, although another possible origin is the Taiwan–Tsushima Current System. The Δ14C record from Iki Island shows the following evidence of a response to the atmospheric nuclear testing: (1) an increase from ~55‰ in 1966 to ~133‰ in 1970, (2) a plateau ranging between ~123 and ~142‰ during the 1970s to the late 1980s, and (3) a gradual decrease from ~115‰ in 1990 to ~83‰ in 2000. Comparison of this record with coral Δ14C records from the Nansei Islands (Okinawa Island, Ishigaki Island and Kikai Island), located ~160–280 km off the ECS shelf break and little influenced by the shelf water, suggests that the surface-water Δ14C around Iki Island was ~30–45‰ lower than that of the Nansei Islands from the mid-1960s to late 1970s, and that the Δ14C difference between Iki Island and the Nansei Islands decreased from the end of the 1970s to ~0–15‰ in the mid-1980s to 2000. The lower Δ14C around Iki Island can be explained as follows: (1) in contrast to the Nansei Islands area, the ECS shelf area is a vertically mixed, highly concentrated carbon reservoir significantly connected to subsurface and deeper waters outside the shelf area, strongly suggesting that the surface-water Δ14C of the shelf area (perhaps excepting very shallow innermost shelf areas) was significantly less sensitive to the atmospheric nuclear-bomb 14C spike than that of the Nansei Islands area; (2) the shelf-surface water is conveyed from the northern ECS to Iki Island by the Tsushima Current. Thus, it can be suggested that the post-bomb coral Δ14C record from Iki Island reflects oceanographic conditions of the northern ECS shelf.
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Chen CTA (1996) The Kuroshio intermediate water is the major source of nutrients on the East China Sea continental shelf. Oceanol Acta 19:523–527
Chou WC, Gong GC, Tseng CM, Sheu DD, Hung CC, Chang LP, Wang LW (2011) The carbonate system in the East China Sea in winter. Mar Chem 123:44–55. doi:10.1016/j.marchem.2010.09.004
Druffel ERM (1987) Bomb radiocarbon in the Pacific: annual and seasonal timescale variations. J Mar Res 45:667–698
Fang G, Zhao B, Zhu Y (1991) Water volume transport through the Taiwan Strait and the continental shelf of the East China Sea measured with current meters. In: Takano K (ed) Oceanography of Asian marginal seas. Elsevier, Amsterdam, pp 345–348
Grottoli AG, Eakin CM (2007) A review of modern coral δ18O and Δ14C proxy records. Earth Sci Rev 81:67–91. doi:10.1016/j.earscirev.2006.10.001
Guilderson TP, Schrag DP (1998) Abrupt shift in subsurface temperatures in the tropical Pacific associated with changes in El Niño. Science 281:240–243
Guilderson TP, Schrag DP, Kashgarian M, Southon J (1998) Radiocarbon variability in the western equatorial Pacific inferred from a high-resolution coral record from Nauru Island. J Geophys Res 103(C11):24641–24650
Guo XH, Zhai WD, Dai MH, Zhang C, Bai Y, Xu Y, Li Q, Wang GZ (2015) Air–sea CO2 fluxes in the East China Sea based on multiple-year underway observations. Biogeosciences 12:5495–5514. doi:10.5194/bg-12-5495-2015
Isobe A (1999) On the origin of the Tsushima Warm Current and its seasonality. Cont Shelf Res 19:117–133
Kim D, Choi SH, Shim JH, Kim KH, Kim CH (2013) Revisiting the seasonal variations of sea-air CO2 fluxes in the northern East China Sea. Terr Atmos Ocean Sci 24:409–419. doi:10.3319/TAO.2012.12.06.01(Oc)
Konishi K, Tanaka T, Sakanoue M (1982) Secular variation of radiocarbon concentration in seawater: sclerochronological approach. Proc 4th Int Coral Reef Symp 1:181–185
Levin I, Kromer B, Schoch-Fischer H, Bruns M, Münnich M, Berdau D, Vogel JC, Münnich KO (1985) 25 years of tropospheric 14C observations in central Europe. Radiocarbon 27:1–19
Levin I, Kromer B, Schoch-Fischer H, Bruns M, Münnich M, Berdau D, Vogel JC, Münnich KO (1994) Δ14CO2 records from sites in central Europe. In: Boden TA, Kaiser DP, Sepanski RJ, Stoss FW (eds) Trends ’93: A Compendium of Data on Global Change. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee, ORNL/CDIAC-65:203–222
Manning MR, Melhuish WH (1994) Atmospheric Δ14C record from Wellington. In: Boden TA, Kaiser DP, Sepanski RJ, Stoss FW (eds) Trends ’93: A Compendium of Data on Global Change. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee, ORNL/CDIAC-65:193–202
Matsuno T, Lee JS, Yanao S (2009) The Kuroshio exchange with the South and East China Seas. Ocean Sci 5:303–312
Mitsuguchi T (2000) Reconstruction of palaeoceanic environment from multi-element analysis of annually-banded coral skeletons. PhD thesis, Nagoya University
Mitsuguchi T, Matsumoto E, Abe O, Uchida T, Isdale PJ (1997) Magnesium/calcium ratio of coral skeletons as a palaeothermometer. Proc 8th Int Coral Reef Symp 2:1701–1706
Mitsuguchi T, Kitagawa H, Matsumoto E, Shibata Y, Yoneda M, Kobayashi T, Uchida T, Ahagon N (2004) High-resolution 14C analyses of annually-banded coral skeletons from Ishigaki Island, Japan: implications for oceanography. Nucl Instrum Methods Phys Res B 223–224:455–459
Mitsuguchi T, Dang PX, Kitagawa H, Yoneda M, Shibata Y (2007) Tropical South China Sea surface 14C record in an annually-banded coral. Radiocarbon 49:905–914
Morimoto M, Kitagawa H, Shibata Y, Kayanne H (2004) Seasonal radiocarbon variation of surface seawater recorded in a coral from Kikai Island, subtropical northwestern Pacific. Radiocarbon 46:643–648
Park S, Chu PC (2006) Thermal and haline fronts in the Yellow/East China Seas: surface and subsurface seasonality comparison. J Oceanogr 62:617–638
Seo I, Lee YI, Watanabe T, Yamano H, Shimamura M, Yoo CM, Hyeong K (2013) A skeletal Sr/Ca record preserved in Dipsastraea (Favia) speciosa and implications for coral Sr/Ca thermometry in mid-latitude regions. Geochem Geophys Geosyst 14:2873–2885. doi:10.1002/ggge.20195
Stuiver M, Polach HA (1977) Discussion: reporting of 14C data. Radiocarbon 19:355–363
Tsunogai S (2002) The western North Pacific playing a key role in global biogeochemical fluxes. J Oceanogr 58:245–257
Tsunogai S, Watanabe S, Sato T (1999) Is there a “continental shelf pump” for the absorption of atmospheric CO2? Tellus 51B:701–712
Watanabe T, Oba T (1999) Daily reconstruction of water temperature from oxygen isotopic ratios of a modern Tridacna shell using a freezing microtome sampling technique. J Geophys Res 104(C9):20667–20674. doi:10.1029/1999JC900097
Yamano H, Hori K, Yamauchi M, Yamagawa O, Ohmura A (2001) Highest-latitude coral reef at Iki Island, Japan. Coral Reefs 20:9–12. doi:10.1007/s003380100137
Yamano H, Sugihara K, Watanabe T, Shimamura M, Hyeong K (2012) Coral reefs at 34°N, Japan: exploring the end of environmental gradients. Geology 40:835–838. doi:10.1130/G33293.1
Yang D, Yin B, Liu Z, Feng X (2011) Numerical study of the ocean circulation on the East China Sea shelf and a Kuroshio bottom branch northeast of Taiwan in summer. J Geophys Res 116, C05015. doi:10.1029/2010JC006777
Zhao BR, Ren GF, Cao DM, Yang YL (2001) Characteristics of the ecological environment in upwelling area adjacent to the Changjiang River estuary. Oceanol Limnol Sin 32:327–333
The authors thank Dr. Kaoru Sugihara for identifying the species of the coral sample (Dipsastraea speciosa) used in this study. The authors also thank the reviewers (J.R. Toggweiler and two anonymous) and the editors for their comments and suggestions on the manuscript.
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The authors declare that there is no conflict of interest with third parties.
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Mitsuguchi, T., Hirota, M., Group, P.L.A.D. et al. Post-bomb coral Δ14C record from Iki Island, Japan: possible evidence of oceanographic conditions on the northern East China Sea shelf. Geo-Mar Lett 36, 371–377 (2016). https://doi.org/10.1007/s00367-016-0456-4
- Kuroshio Current
- Shelf Area
- Coral Skeleton
- Tsushima Current
- Nansei Island