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Tropical South China Sea Surface 14C Record in an Annually-Banded Coral

Published online by Cambridge University Press:  18 July 2016

Takehiro Mitsuguchi ,
Phong X Dang ,
Hiroyuki Kitagawa ,
Minoru Yoneda  and
Yasuyuki Shibata
Takehiro Mitsuguchi*
Affiliation:
National Institute for Environmental Studies, Tsukuba 305–8506, Japan Institute for Asian PaleoClimate, Konan 483–8226, Japan
Phong X Dang
Affiliation:
Institute of Geography, Vietnamese Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Hanoi, Vietnam. Also: Japan Society for the Promotion of Science Graduate School of Environmental Studies, Nagoya University, Nagoya 464–8601, Japan
Hiroyuki Kitagawa
Affiliation:
Graduate School of Environmental Studies, Nagoya University, Nagoya 464–8601, Japan
Minoru Yoneda
Affiliation:
National Institute for Environmental Studies, Tsukuba 305–8506, Japan
Yasuyuki Shibata
Affiliation:
National Institute for Environmental Studies, Tsukuba 305–8506, Japan
*
Corresponding author. Email: aal53740@nyc.odn.ne.jp
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Abstract

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A surface-water Δ14C record of AD 1948–1999 in the tropical South China Sea (SCS) has been reconstructed from accelerator mass spectrometric radiocarbon measurements of annual bands of a Pontes coral collected from Con Dao Island, Vietnam. Results gave the following Δ14C time series: a steady state of −47.8 ± 2.8‰ (mean ± SD, n = 8) during 1948–1955 (i.e. in the pre-bomb period); a sharp increase during 1956–1966; a gradual increase during 1967–1973; a relatively high maximum value of ∼174‰ in 1973; and a gradual decrease for the following period to ∼86‰ in 1999. This Δ14C record having a sharp increase and a relatively high peak is similar to the records of subtropical corals (latitudes 21–27°) and is distinctly different from the records of equatorial/tropical corals (latitudes <10°), although our coral sample was collected from an equatorial/tropical region (8°39′N, 106°33′E). This can be explained by the geographic, oceanographic, and climatic setting of our study site. The SCS is a semi-enclosed marginal sea in the far western tropical Pacific and is little influenced by equatorial upwelling or related ocean currents. Our study site is located in the southwestern SCS, where an enormous submerged plain (the Sunda Shelf) spreads out with very shallow waters (mean depth <100 m). Furthermore, in the SCS, the East Asian monsoon (a strong, seasonally reversing wind system) enhances air-sea gas exchange especially in the mainland coastal waters, including our study site. Such semi-enclosed shallow waters with enhanced ventilation were probably very sensitive to the atmospheric nuclear explosions in the late 1950s and early 1960s and caused the sharp increase and high peak in the coral Δ14C record. Our coral Δ14C values in the southwestern SCS are significantly higher than the values in the northwestern SCS (Xisha Islands), which seems to suggest that meridional mixing of surface waters is not active in the SCS and that the open-ocean water intruding into the northern SCS (i.e. the Kuroshio intrusion) has only a limited influence on the southern SCS.

Type
Articles
Information
Radiocarbon , Volume 49 , Issue 2 , 2007 , pp. 905 - 914
Copyright
Copyright © 2007 by the Arizona Board of Regents on behalf of the University of Arizona 

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