A Quick, Simple, and High-Throughput Method for Determining Li/Mg, Mg/Ca, Sr/Ca, and U/Ca Ratios in Coral Skeleton Using Quadrupole ICP-MS.

Abstract

Information about sea surface temperature (SST) allows both local and global climate reconstructions dating back centuries to millennia. To determine SST variations over time, including the deep past, a number of proxies are used. Li/Mg, Mg/Ca, Sr/Ca, and U/Ca ratios in coral skeletons are the most commonly used high-resolution temperature proxies. Various methods, using different types of instrumentation, are employed to obtain high-precision data on the variation of these ratios in coral skeletons. Generally, each method has its own advantages and disadvantages; however, a common drawback of most is that they are time-consuming. This article presents a quick, simple, and high-throughput method for determining mentioned ratios in coral skeletons using quadrupole ICP-MS. The reduction of calcium concentration to 3 ppm in the analytical solutions, combined with optimized operating conditions and quasi-simultaneous measurement of each element pair, ensures excellent signal sensitivity and stability of ratio values during sample runs. The drift of ratio values was investigated using the in-house coral secondary standard NEP-3b. During some runs, the drift of ratios during the analysis was so low that it provided excellent repeatability of results without off-line mathematical correction of the obtained data. Due to the selected ICP-MS operating conditions, this high-sensitivity method enables for the analysis of all studied isotopes in a single measurement, whereas typical procedures require two sample preparations and separate measurements. As a result, this method doubles the throughput compared to the previous procedures while demonstrating comparable short- and long-term precisions, both of which were assessed using the international standard sample JCp-1.