Seashell Formation Provides Understanding of Historic Oceanographic Conditions

The Science

Marine organisms such as corals and some plankton build calcium carbonate (CaCO3) shells. The elements that make up these shells play a key role in global elemental cycling, which means the shells contain a record of historical ocean chemistry and associated global climate conditions. A recent study shed light on shell formation by combining several advanced imaging techniques to provide information about the chemical composition of these shells at different spatial scales.

The Impact

The findings reveal that shell formation could be influenced by high levels of elements such as sodium and magnesium, which could bias geochemistry measurements used to estimate historical oceanographic conditions. This new information could be used to develop more accurate methods for assessing climate.

Summary

Foraminifera are a group of marine protozoans with a fossil record that extends back to the earliest Cambrian period, offering one of the most comprehensive geochemical archives of past ocean chemistry and climate. Scientists routinely perform geochemical analyses on ancient foraminifera CaCO3 biomineral skeletons to estimate historical oceanographic conditions. However, interpretation of these analyses has been limited by incomplete understanding of the nucleation of biominerals at the appropriate spatial scales. In particular, relatively little is known about chemical properties of the organic template, a structure around which biominerals grow during shell formation. To address this knowledge gap, a team of researchers from the University of California, Davis; University of Washington; Department of Energy’s (DOE) Environmental Molecular Sciences Laboratory (EMSL); and Columbia University combined advanced imaging techniques that span atom-level and submicron spatial resolutions. They mapped the chemical composition of the organic mineral template preserved within the carbonate skeleton of the foraminifera Orbulina universa, a model organism used extensively for studying biomineralization and geochemistry. The researchers used atom probe tomography and time-of-flight secondary ionization mass spectrometry at EMSL, a DOE Office of Science user facility. By linking the two sets of observations, the researchers found the organic mineral template embedded within the carbonate shell is enriched in sodium and magnesium, suggesting elements other than calcium play an unexpectedly important role in biomineral shell formation. Under some circumstances, the prevalence of sodium and magnesium in the organic template could bias geochemistry measurements used to estimate historical oceanographic conditions, such as temperature and salinity. The new findings could be used to develop more accurate methods for assessing past climate.

Principal Investigator(s)

Oscar Branson
University of California
[email protected]

Alexander Gagnon
University of Washington
[email protected]

Funding

This work was supported by the U.S. Department of Energy’s (DOE) Office of Science, Office of Biological and Environmental Research, including support of the Environmental Molecular Sciences Laboratory, a DOE Office of Science user facility; and the U.S. National Science Foundation.

References

O. Branson, E. Bonnin, D. Perea, H. J. Spero, Z. Zhu, M. Winters, B. Honisch, A. D. Russell, J. S. Fehrenbacher, and A.C. Gagnon, “The nanometer-scale chemistry of a calcite biomineralization template: Implications for skeletal composition and nucleation.” Proceedings of the National Academy of Sciences (USA) 113(46), 12934-12939 (2016). [DOI: 10.1073/pnas.1522864113]