Mg/Ca and Sr/Ca ratios in a coral from Koh Chueak, Surat Thani, Thailand

Abstract

The Mg/Ca and Sr/Ca ratios were determined for Porites lutea specimens that were collected from Koh Chueak, Surat Thani Province, Thailand, using inductively coupled plasma optical emission spectrometry. The elemental analyses were performed from the surface to the interior of the coral specimen along its growth axis at 1-mm intervals, generating the near-monthly resolved time series for the Mg/Ca and Sr/Ca ratios. The ratios demonstrate clear annual cycles, which are assumed to refl ect variations in the sea surface temperature (SST). Comparing with the annual maximum and minimum values of SST, the following Mg/Ca-SST and Sr/Ca-SST relations were determined: Mg/Ca (mmol/mol)＝－1.72＋0.193×SST and Sr/Ca (mmol/mol)＝11.83－0.098×SST. These relations are different than those of previously published studies. The reason for this difference is unclear; however, it may be related to vital effects that have been observed for geochemical proxies in coral skeletons and to differences in chemical composition of seawater and in sampling procedure.