Aragonite in fossil corals doesn’t guarantee original preservation

PUBLICATION — Stolarski, J., Cisneros-Lazaro, D., Adams, A., Janiszewska, K., Meibom, A. 2025. Rapid isotopic exchange in mineralogically unaltered coral skeletons. Scientific Reports 15:20986, doi:10.1038/s41598-025-06327-9.  

Figure: Four scleractinian coral taxa with fundamentally different skeletal architectures were subjected to isotopic exchange experiments (top row). Microstructural organization of sectioned coral skeletons overlaid with NanoSIMS maps showing some skeletal regions highly enriched in ¹⁸O isotopes.

Aragonite under scrutiny: Is the foundation of paleoclimatology starting to crumble?
Aragonitic skeletons of modern and fossil corals are widely regarded as diagenetically unaltered and as preserving the original isotopic signals of the environment in which they formed. However, experiments on modern coral skeletons have shown that even those retaining aragonitic mineralogy can alter their isotopic composition when exposed to water enriched in oxygen ¹⁸O isotopes. The intensity of isotopic alteration across various coral species differs according to microstructures and organic content. These findings challenge the long-standing assumption that the preservation of aragonitic mineralogy guarantees a “pristine state of preservation”.