Nanometer-Scale Chemistry of a Calcite Biomineralization Template: Implications for Skeletal Composition and Nucleation

Abstract

Plankton, corals, and other organisms produce calcium carbonate skeletons that are integral to their survival, form a key component of the global carbon cycle, and record an archive of past oceanographic conditions in their geochemistry. A key aspect of the formation of these biominerals is the interaction between organic templating structures and mineral precipitation processes. Laboratory-based studies have shown that these atomic-scale processes can profoundly influence the architecture and composition of minerals, but their importance in calcifying organisms is poorly understood because it is difficult to measure the chemistry of in vivo biomineral interfaces at spatially relevant scales. Understanding the role of templates in biomineral nucleation, and their importance in skeletal geochemistry requires an integrated, multiscale approach, which can place atom-scale observations of organic-mineral interfaces within a broader structural and geochemical context. Here we map the chemistry of an embedded organic template structure within a carbonate skeleton of the foraminifera Orbulina universa using both atom probe tomography (APT), a 3D chemical imaging technique with Ångström-level spatial resolution, and time-of-flight secondary ionization mass spectrometry (ToF-SIMS), a 2D chemical imaging technique with submicron resolution. We quantitatively link these observations, revealing that the organic template in O. universa is uniquely enriched in both Na and Mg, and contributes to intraskeletal chemical heterogeneity. Our APT analyses reveal the cation composition of the organic surface, offering evidence to suggest that cations other than Ca 2+ , previously considered passive spectator ions in biomineral templating, may be important in defining the energetics of carbonate nucleation on organic templates. biomineralization | templating | foraminifera | geochemistry | paleoceanography

Overcoming Challenges Associated with the Analysis of Nacre by Atom Probe Tomography

“…This behaviour has also been reported by Branson et al . (), who conducted experiments on calcium carbonates of foraminifera.…”

“…), and calcium carbonate from foraminifera (Branson et al . , Pérez‐Huerta and Laiginhas ). Difficulties in running materials containing organics, namely the evaporation of complex ions (Gordon et al .…”

“…), difference in field evaporation between organic and inorganic areas of the sample (Branson et al . ), potential peak overlaps (La Fontaine et al . ) and frequent fracturing (Langelier et al .…”

Calcium carbonates: induced biomineralization with controlled macromorphology

“…Morphological variations of crystal shapes revealed a microbial impact on mineral precipitation (compare Branson et al, 2016). Crystal colors by impurities incorporated into the lattice such as salts or secreted pigments were clearly observed, as calcite can incorporate metal ions in its crystal structure (Kang et al, 2014).…”

Combined Effects of Gametogenic Calcification and Dissolution on δ18O Measurements of the Planktic Foraminifer Trilobatus sacculifer

“…Why PREGAM calcite is more susceptible to dissolution than GAM calcite remains unclear, but the selectivity of this dissolution is likely related to the oxidation of organic matter within internal domains and/or the microcrystalline structure and higher Mg composition of PREGAM calcite (Branson et al, 2016;Johnstone et al, 2010Johnstone et al, , 2011Nouet & Bassinot, 2007). Moreover, previous study has shown that diurnal variation in the biological activity of algal symbionts hosted by many mixed layer dwelling planktic foraminifers imparts sequential day-night banding to the PREGAM calcite, with the night bands having higher Mg content (Eggins et al, 2004;Spero et al, 2015;Fehrenbacher et al, 2017).…”