Compositional Analysis of Cultured Biominerals
Mineral composition is influenced by a host of environmental, chemical, and biological factors during growth. To accurately interpret these signals we need to separate the impact of each parameter on tracer behavior. These data can then be used to build a chemical-scale understanding of mineral growth. Biomineral culture and inorganic precipitation experiments, where growth parameters are isolated and manipulated independently, are uniquely suited to address these questions.
Culture and precipitation experiments often involve overgrowth on an initial material. For example, seed crystals are used to control mineralogy, avoid nucleation, and access low growth rates during inorganic precipitation. Similarly, biomineral culture experiments typically start from wild specimens with preexisting and poorly characterized skeletons. In both classes of experiments, new growth corresponding to experimental conditions must be separated from initial material.
We developed a new method of compositional analysis during mineral growth. The method relies on growth from a solution enriched in multiple stable isotopes and is an adaptation of the isotope-dilution technique, however in this case isotope dilution occurs within a growing mineral. The new technique has several advantageous characteristics: (1) it requires neither the amount nor the composition of the initial material to be known, (2) it harnesses the precision, sensitivity, and accessibility typically associated with bulk analysis, and (3) it works even when it is impossible to physically identify and separate newly grown material. Furthermore, the method allows new modalities. For example, it can be used to isolate different events through time. Amongst other applications, this feature can be used to answer an important question in biomineralization and paleoceanography: the effect of light and photosymbionts on skeletal composition. Finally, the method can be extended to resolve stable isotope fractionation during mineral growth for select systems of non-traditional stable isotopes.