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. The study combined advanced imaging techniques to provide information about the chemical composition of these shells at different spatial scales.
Scientists study the shells of certain marine organisms to understand the chemical composition of marine environments, but they need more details about how shells form to obtain a more accurate understanding of ocean chemistry. The findings reveal that high levels of certain elements, such as sodium and magnesium, could influence shell formation. The incorporation of these elements could bias measurements used to estimate historical oceanographic conditions. Scientists could use this new information to improve the accuracy of climate models.
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 calcium carbonate (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, scientists know relatively little 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; U.S. Department of Energy's (DOE) Environmental Molecular Sciences Laboratory (EMSL); and Columbia University combined advanced imaging techniques that span atomic-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. The enrichment suggests 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 conditions.
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This work was supported by the U.S. Department of Energy's (DOE's) 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 National Science Foundation.
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EMSL research highlight: Seashell Formation Provides Understanding of Historic Oceanographic Conditions