Timing and duration of growth hiatuses in mid Holocene massive Porites corals from the northern South China Sea

Growth hiatuses in massive corals are usually indicative of past ecological or environmental stresses. Among 37 fossil Porites colonies surveyed from the reef flat of Dadonghai fringing reef at Sanya, Hainan Island, northern South China Sea, seven of them were found to show clear evidence of past mortality, representing a population of similar to 19%. Among these samples, two of them (SYO-13 and SYO-28) display clear growth hiatuses reflecting mortality followed by subsequent recruitment, and five others exhibit a well-preserved mortality surface and no subsequent recruitment. The growth hiatuses were dated using high-precision thermal ionisation mass spectrometry U-series techniques. The age results suggest all the dated corals formed and died in the mid Holocene. Multiple dates below the growth hiatuses suggest that SYO-13 and SYO-28 died at 6298 +/- 11 and 6929 +/- 19 a BP (i.e. years before AD 1950), respectively. Multiple dates above the growth hiatuses indicate that growth in SYO-13 and SYO-28 resumed at 6257 +/- 14 and 6898 +/- 20 a BP, respectively. The calculated durations of growth hiatuses are therefore 41 +/- 18 a for SYO-13 and 31 +/- 28 a for SYO-28, respectively, implying growth resumed within decades after the mortality events. U-series dating of four other samples with dead heads suggests that they died at 6035 +/- 53, 6059 +/- 23, 6127 +/- 22 and 6474 +/- 24 a BP, respectively. In addition, using solution inductively coupled plasma mass spectrometry (ICP-MS), monthly resolution Sr/Ca and Mg/Ca ratios were determined for the annual growth bands below and above the growth hiatuses for three of the dated samples. The Sr/Ca and Mg/Ca profiles indicate that the three corals probably died in different seasons (from spring to autumn), and the mortality appears to be unrelated to anomalous sea surface temperature-induced bleaching. Copyright (C) 2010 John Wiley & Sons, Ltd.