Beyond bleaching: thermal stress changes the atomic structure of a shallow-water coral skeleton

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Supplementary data for manuscript submitted to Nature Climate Change on 3/02/2023 titled "Beyond bleaching: thermal stress changes the atomic structure of a shallow-water coral skeleton". ABSTRACT: Anthropogenic warming is linked to more frequent coral bleaching events across the globe. Previous work has shown that marine heatwaves cause the expulsion of photosynthetic symbionts from coral tissue (i.e., bleaching) and alter the geochemistry of the coral skeleton, calling into question the reliability of skeletal trace element-based paleo-proxies through periods of stress. Here we show---for the first time---that the mineralogical properties of a Porites sp. coral from Butaritari atoll (3°N, 173°E) reflect the coral's health and are linked to measured trace-element concentrations through time. Furthermore, we find that while trace-element content alone can partially explain the changes in coral aragonite crystallography, other related factors such as skeletal organic material are also likely contributors. Our findings indicate that marine heatwaves can alter the properties of the fundamental building blocks of the coral's aragonite skeleton, with potential implications for the structural integrity of the reef.

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