The Sr/Ca ratio of coral carbonate is a widely used proxy for reconstructing paleo surface seawater temperatures. Some corals e.g., Porites sp. Build colonies that can exist for more than 300 years and, hence, represent valuable archives for past climate conditions, even in very remote areas of the tropical oceans where no instrumental records exist. Such paleo-temperature data sets are urgently needed for validating models that are developed for predicting the future of Earth climate. Sr/Ca directly compares to the temperature where carbonate crystallized from seawater. Consequently, a small uncertainty of Sr/Ca ratio determinations accomplishes temperature estimates with high resolution. Here, simultaneous ‘multi-collector’ data acquisition is the gold standard for a high precision determination of elemental/ isotopic ratios and superior to instruments with sequential data acquisition like ICP-MS. MC-ICP-MS instruments do not have the dispersion needed for a simultaneous analysis of Ca and Sr.

Conventional Sr/Ca analysis is based on micro-drilled coral carbonate powder with a spatial resolution of ~ 300 µm for a seasonal resolution of paleo temperatures. This approach is extremely time-consuming and labour-intensive given sample numbers of 2-4.000 samples for a typical temperature record of ~ 200 years from a large Porites coral colony.

In the presentation we will show the typical stability from an ICP-OES measurement over several 4 days runs and the uncertainty of a reference material. We routinely determine Sr/Ca ratios by liquid sample introduction ICP-OES with measurement uncertainties of ∼ 0.05%rel., which corresponds to temperature uncertainties of ∼ 0.1°C.