Mg/Ca, Sr/Ca and U/Ca ratios of a porites coral from Sanya Bay, Hainan Island, South China Sea and their relationships to sea surface temperature

Abstract

High-resolution Mg/Ca, Sr/Ca and U/Ca ratios are reported in the skeleton of Porites sp. collected from Sanya Bay, on the south coast of the Hainan Island, China using inductively coupled plasma mass spectrometry combined with isotope dilution technique (ICP-MS-ID). The coralline Mg/Ca ratios covary with sea-surface temperatures (SST) for the 10 year interval, giving the relationship between Mg/Ca and SST as T (°C)=(-14.13±0.31)+ (8.846±0.068) x 103Mg/Ca with the mean square weighted deviation (MSWD) of 9.7. Using this equation, we are able to reconstruct SST record with a precision better than ±0.5°C. Several Sr/Ca and U/Ca ratios show poor linear relationships with the measured SST. This study indicates that the growth rates of the coral do not significantly affect coralline Mg/Ca, Sr/Ca and U/Ca ratios. However, the high meteoric precipitation in this area, which may cause a heavy run-off from the Island, may change seawater Sr/Ca and U/Ca ratios and ruin the relationships between coralline Sr/Ca or U/Ca ratios and SST. This implies that in coastal areas like Hainan, coralline Mg/Ca ratios are valid for reconstructing the SST records, but Sr/Ca and U/Ca ratios may be suspected. (C) 2000 Elsevier Science B.V.