EVALUATING CORAL SR/CA USING ICP-AES AS A COST-EFFECTIVE GEOCHEMICAL ANALYSIS FOR PALEOTEMPERATURE RECONSTRUCTIONS

Geochemical records from modern and fossil corals are excellent proxies of environmental conditions. Coral strontium/calcium ratios (Sr/Ca) are reliable recorders of sea surface temperature, and, when paired with coral oxygen isotopes (δ18O), we can also determine sea surface salinity. Corals incorporate both Sr and Ca into their aragonite (CaCO3) skeleton and the Sr/Ca distribution coefficient between the aragonite and seawater is dependent on the temperature of the seawater at the time the coral was living. However, most methods require costly analyses using inductively coupled plasma mass spectrometry (ICP-MS) or laser ablation technique, instruments not commonly available at smaller undergraduate-focused Universities. Alternatively, an inductively coupled plasma atomic emission spectrometer (ICP-AES), a less expensive instrument with a smaller per sample cost, may provide appropriate sensitivities of Sr/Ca in the range commonly found in coral skeletons. Here, we test the sensitivity of Sr and Ca measurements using a Thermo iCAP 6000 ICP-AES at the University of Mary Washington with the goal of developing a reliable but cost-effective Sr/Ca analytical method for coral-based paleotemperature reconstructions. We first create and test synthetic standards derived from known Sr/Ca present in modern coral skeletons (8.7-8.8 mmol/mol). We check the variations in Sr and Ca sensitivities using calibration standards with Ca concentrations between 20 and 60 ppm. We also check consistency between runs using a natural standard derived of coral powder at 30 ppm. Lastly, we compare tropical Pacific coral Sr/Ca measurements from the ICP-AES with measurements from Florida State University’s ICP-MS. If our results are proven successful, it will help make Sr/Ca and potentially other trace metal analyses of carbonates, such as magnesium/calcium (Mg/Ca), more accessible to undergraduate students where research resources are limited.