U-series dating of dead Porites corals in the South China sea: Evidence for episodic coral mortality over the past two centuries

High-precision (up to ±1–2 years) U-series dating of dead in situ massive Porites corals on the reef flats of Yongshu and Meiji Reefs, Nansha area, southern South China Sea reveals that mortality of these massive corals occurred many times over the past two centuries, many of which appear to correlate in time with historic El Niño events. Despite different habitats of corals, at least six mortality events occurred simultaneously on both reefs (e.g. in 1869–1873, 1917–1920, 1957–1961, 1971, 1982–1983 and 1999–2000 AD), reflecting the occurrence of large-scale regional events. We speculate that many of such mortality events, especially those dated at 1998–2000, 1991, 1982–1983, 1971, and 1957–1958 AD with an overall uncertainty of ±1–2 years, are probably due to high temperature bleaching during El Niño years (e.g. 1997–1998, 1991–1992, 1982–1983, 1972–1973 and 1957–1959 AD). This study demonstrates that individual colonies of massive corals have died at different times over the past two centuries and mass spectrometric U-series dating of very young corals with a precision of up to ±1–2 years is likely to become a powerful tool for reconstruction of past coral mortality history and investigation of global warming and coral bleaching.