Rhodoliths can act as daily resolution paleotemperature archives in the Red Sea

Abstract

Long-term, high-frequency temperature records are critical for evaluating the vulnerability of marine ecosystems to ongoing ocean warming. Commonly used paleoceanographic archives, such as corals and bivalves, face regional and ecological constraints. Rhodoliths, free-living coralline red algal nodules, are established and globally accessible alternatives, yet their complex three-dimensional growth structures hinder the construction of continuous age models. Here we present a workflow combining staining-based growth calibration, semi-automated increment detection using micro-computed tomography, and dynamic time warping to assemble a daily chronology spanning 133 days (March–July) from seven fruticose thalli of a single rhodolith from the central Red Sea. The resulting multi-thallus chronology, combined with a multi-element temperature proxy (Magnesium-to-Strontium), yields closer agreement with in-situ logger temperatures (R² = 0.91, RMSE = 0.63 °C) than individual thalli or single-element proxies, establishing a proof-of-concept framework for daily-resolved paleotemperature reconstructions from tropical rhodoliths.