[Coral-List] Lack of evidence supporting amorphous CaCO3 in coral skeletons

Thomas DeCarlo thomas.decarlo at uwa.edu.au
Tue Dec 18 23:29:51 UTC 2018

Dear Coral-List,

I would like to draw your attention to my recent Comment piece in Nature Communication: https://www.nature.com/articles/s41467-018-07601-3

Several high-profile papers have recently claimed that corals build their skeletons from amorphous calcium carbonate (ACC) particles. If true, this would have critical implications for understanding coral responses to ocean acidification and for interpreting geochemical climate proxies within coral skeletons.

Raman spectroscopy is a key technique used in these studies claiming to find ACC. However, as I show in the linked Comment article, the Raman data have been mis-interpreted because they definitely do not support the presence of ACC. Rather, all the published Raman data indicate crystalline calcium carbonates. In corals older than a few days, the skeleton is always aragonite. For example, I have posted several hundred thousand Raman spectra online (https://zenodo.org/communities/calcifierraman) from our recent papers, and these clearly show aragonite. There may be tiny amounts of high-Mg calcite in the initial basal plates of newly settled polyps (see linked Comment article), but this is not representative of the bulk skeleton-building process.

Whether corals use ACC at all remains an interesting hypothesis, but one that currently has very little supporting evidence. I look forward to seeing future work on the subject, but I encourage everyone to view these recent claims with scrutiny.

Thomas DeCarlo

Dr. Thomas DeCarlo
Postdoctoral research associate
School of Earth Sciences and Oceans Institute, University of Western Australia
ARC Centre of Excellence for Coral Reef Studies
Office (08) 6488-4486

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