Strontium/calcium ratios (Sr/Ca) in reef coral skeletons have been used for sea surface temperature (SST) proxy. Because skeletons of reef corals are accumulated throughout more than 100 years, SST records from coral skeletons were important archives to reveal climate mechanisms. Here, we improved the coral Sr/Ca analytical method using an inductively coupled plasma optical emission spectrometer which method has advantages in terms of initial/running cost and analysis time. We checked variations of Sr and Ca sensitivities as increases of Ca concentrations using various wavelengths of Sr and Ca. Our results suggested that sensitivities of Sr/Ca in a range of coral skeletons were modulated by selections of wavelengths and sensitivity changes of Sr and Ca. A combination of Sr(421.5 nm) and Ca(373.6 nm) is stable for the Sr/Ca analysis at a low Ca concentration. A SD of Sr/Ca(421.5/373.6 nm) was 0.006 mmol mol−1 (1σ, n = 40) based on the replicate measurement of the reference material (JCp-1) using our new method. By applying a Porites colony from Kikai island, Japan, a precision of reconstructed SST was over ± 0.3°C at weekly resolution.
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