A monthly resolved coral δ13C and δ18O record of changes in the Kuroshio Current into the South China Sea via the Luzon Strait

Abstract

The Kuroshio Current enters the South China Sea (SCS) via the Luzon Strait and exerts significant effects on circulation and water mass properties of this marine basin. However, because of a lack of continuous oceanographic observations, multi-decadal variations in Luzon Strait Transport (LST) remain uncertain. In this study, monthly resolved coral δ13C and δ18O data from Xiaoliuqiu Island, located offshore of southwestern Taiwan and along the Kuroshio Current intrusion route, are used to reconstruct LST from 1977 to 2003 and investigate interannual and decadal variability. On an interannual timescale, greater LST leads to stronger upwelling, which brings deep low-temperature and high-salinity sub-surface waters containing 13C-depleted dissolved inorganic carbon to the surface; this is reflected in lower coral δ13C and higher coral δ18O values. The interannual variability in the upper (0–745 m) and surface (0–1 m) layers of LST during 1977–2003 is also reconstructed using the coral δ18O record. Coral δ18O data indicate that LST has weakened since the 1990s. The upper layer of LST has decreased by nearly 25%, and the surface layer of LST has decreased by 60% over the 27 years of observation. Our results show that coral δ13C and δ18O data can be used to reconstruct interannual variations in LST.