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

Abstract

A surface-water A 14 C 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 A 14 C time series: a steady state of -47.8 ± 2.8%o (mean ± SD, η -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%c in 1973; and a gradual decrease for the following period to ~86%c in 1999. This A I4 C 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°33Έ). This can be explained by the geographic, océanographie, 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 A ,4 C record. Our coral A 14 C 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 openocean water intruding into the northern SCS (i.e. the Kuroshio intrusion) has only a limited influence on the southern SCS.'National Institute for Environmental Studies, Tsukuba 305-8506, Japan. institute for Asian PaleoClimate, Konan 483-8226, Japan. Corresponding author.

Radiocarbon variability recorded in coral skeletons from the northwest of Luzon Island, Philippines

“…3a). The average Δ 14 C value in the 1970s was 146.7 ‰, which lies between the average Δ 14 C values in Guam (Andrews et al 2016) and Ishigaki (Hirabayashi et al 2017a) and is lower than that in Con Dao (Mitsuguchi et al 2007) (Fig. 2).…”

“…Con Dao Island lies on the Sunda Shelf in the southwestern SCS, where the waters are very shallow (Mitsuguchi et al 2007). Mitsuguchi et al (2007) suggested that the ∆ 14 C record in Con Dao is primarily related to monsoon-induced air-sea gas exchange in the semienclosed shallow waters.…”

“…We also compare these data with the coral data reported from Ishigaki (Hirabayashi et al 2017a), Guam (Andrews et al 2016), Con Dao (Mitsuguchi et al 2007), and Hon Tre Island (Bolton et al 2016) to understand the relationship between North Pacific western boundary currents and SCS circulation around the Luzon Strait.…”

“…However, post-bomb 14 C data are scarcely available for the SCS (e.g., Mitsuguchi et al 2007;Shen et al 2003). Recent studies employed Iodine-129 ( 129 I) in coral skeleton obtained from SCS as a tracer of 1950s nuclear bomb test (Bautista et al 2016;Chang et al 2016 (Chang et al 2016).…”

Upwelling of Pacific Intermediate Water in the South China Sea Revealed by Coral Radiocarbon Record

“…Dang et al (2004) and Mitsuguchi et al (2007Mitsuguchi et al ( , 2008 have attributed this early rise and the enriched values to the shallow location of the coral on the Sunda shelf. Indeed, its location is isolated as it lies 300 km from the deeper SCS basin.…”