5:15 PM - 7:15 PM
[MZZ42-P11] Detection of amorphous calcium carbonate from coral skeletons
Keywords:Geochemistry, Calcification, Coral, ACC, Synchrotron radiation analysis
Marine organisms that form calcium carbonate, such as sea urchins and bivalves, are called calcifying organisms. Among these, reef-building corals are widely used in reconstructing paleoclimatic and paleoceanographic environments because the chemical composition and isotopic ratios of trace elements in their skeletons serve as proxies for sea water temperature and salinity. However, the biomineralization process is still largely unknown. Therefore, elucidating the mechanisms of skeletal formation in calcifying organisms is a significant focus, not only in biology perspective but also from a geoscientific viewpoint.
Calcifying organisms are known to have polymorph depending on the species, and are broadly classified into two categories: calcite and aragonite. Reef-building corals are a group that precipitates aragonite. In addition, recent studies found the presence of ACC (amorphous calcium carbonate) in sea urchins whose main skeletal component is calcite. They suggested that ACC could serve as a precursor of calcium carbonate crystals, especially in the early stages of biomineralization. Although multiple studies have observed the presence of ACC in sea urchin, that from corals has been limited. Therefore, the primary objective of this study is to investigate whether ACC is produced during the early stages of coral calcification, which is essential for understanding the mechanisms underlying coral calcification.
In this study, mineral composition and crystal structure of synthesized ACC standards and juvenile coral polyp skeletons were measured using photoelectron emission microscopy (PEEM) and scanning soft X-ray microscopy (SFXM) at the SPring-8 synchrotron radiation facility. For PEEM, polyp skeletons were embedded in resin and polished until a smooth surface, while ACC standards were in powder form. Both samples were coated with of 1 to 2 nm in platinum coating to prevent charging during observation. On the other hand, the polyp skeleton sample for SFXM was fixed to a substrate with adhesive or carbon tape.
In PEEM measurements, the majority of the ACC standard samples were confirmed to be ACC. Some crystal structures that appeared to be calcite were also observed, but these were considered to be ACC crystallized under inorganic conditions. On the other hand, crystal structures of aragonite could not be confirmed in this study, suggesting that calcite, rather than aragonite, may be formed during crystallization from ACC. As for the polyp skeleton, it was confirmed that it is mostly formed of aragonite, which is consistent with the results of previous studies. However, localized crystalline structures that appeared to be calcite or ACC were also observed, suggesting that corals in the early stages of skeletal formation were not uniformly calcified. Compared to sea urchins, there have been limited reports on the presence of ACC in coral skeletons, suggesting that ACC may be present in this study.
SFXM revealed areas of localized Mg concentration. These findings suggest that the biomineralization process during the early stages of coral calcification is driven by a complex system.
Calcifying organisms are known to have polymorph depending on the species, and are broadly classified into two categories: calcite and aragonite. Reef-building corals are a group that precipitates aragonite. In addition, recent studies found the presence of ACC (amorphous calcium carbonate) in sea urchins whose main skeletal component is calcite. They suggested that ACC could serve as a precursor of calcium carbonate crystals, especially in the early stages of biomineralization. Although multiple studies have observed the presence of ACC in sea urchin, that from corals has been limited. Therefore, the primary objective of this study is to investigate whether ACC is produced during the early stages of coral calcification, which is essential for understanding the mechanisms underlying coral calcification.
In this study, mineral composition and crystal structure of synthesized ACC standards and juvenile coral polyp skeletons were measured using photoelectron emission microscopy (PEEM) and scanning soft X-ray microscopy (SFXM) at the SPring-8 synchrotron radiation facility. For PEEM, polyp skeletons were embedded in resin and polished until a smooth surface, while ACC standards were in powder form. Both samples were coated with of 1 to 2 nm in platinum coating to prevent charging during observation. On the other hand, the polyp skeleton sample for SFXM was fixed to a substrate with adhesive or carbon tape.
In PEEM measurements, the majority of the ACC standard samples were confirmed to be ACC. Some crystal structures that appeared to be calcite were also observed, but these were considered to be ACC crystallized under inorganic conditions. On the other hand, crystal structures of aragonite could not be confirmed in this study, suggesting that calcite, rather than aragonite, may be formed during crystallization from ACC. As for the polyp skeleton, it was confirmed that it is mostly formed of aragonite, which is consistent with the results of previous studies. However, localized crystalline structures that appeared to be calcite or ACC were also observed, suggesting that corals in the early stages of skeletal formation were not uniformly calcified. Compared to sea urchins, there have been limited reports on the presence of ACC in coral skeletons, suggesting that ACC may be present in this study.
SFXM revealed areas of localized Mg concentration. These findings suggest that the biomineralization process during the early stages of coral calcification is driven by a complex system.