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 the shell formation could be influenced by high levels of non-CaCO3 related ion species 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, the interpretation of these analyses has been limited by our 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 gap in knowledge, a team of researchers from the University of California Davis; the University of Washington; EMSL, the Environmental Molecular Science Laboratory; and Columbia University combined advanced imaging techniques that span atom-level and sub-micron spatial resolutions. They mapped the chemical composition of the organic mineral template preserved within the carbonate skeleton of the foraminifera Orbulina universa. Orbulina universa, extensively used as a model organism 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 together 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.
PI Contacts
Oscar Branson
University of California
oscarbranson@gmail.com
Alexander Gagnon
University of Washington
gagnon@uw.edu
Funding
This work was supported by the U.S. Department of Energy’s Office of Science (Office of Biological and Environmental Research), including support of the Environmental Molecular Sciences Laboratory (EMSL), a DOE Office of Science User Facility, and the U.S. National Science Foundation.
Publication
O. Branson, E. Bonnin, D. Perea, H.J. Spero, Z. Zhu, M. Winters, B. Hönisch, 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 (2016). doi: 10.1073/pnas.1522864113.