About this Research Topic
Biominerals often display periodic chemical heterogeneities in (i) major or trace elements, and (ii) stable or radiogenic isotopes. These patterns provide information on the mechanisms of biomineral growth, and they are often used to reconstruct past-environmental conditions. Biominerals made of carbonates are widespread in marine organisms and display a large range of chemical compositions as calcite or aragonite can accommodate a variety of impurities (such as metal cations, anions, organic molecules) in relatively large amounts. In the case of calcitic biominerals, little is known about how some organisms produce low-magnesium calcite, while others make calcite with high magnesium contents under similar marine environments. On another hand, in the skeleton or shell of a given species, uncertainties remain on the origin of internal chemical oscillations: are they the product of extrinsic environmental variables such as seawater temperature, salinity, pH, nutrient availability, concentration of elements in the seawater or intrinsic parameters associated with crystal growth such as growth kinetics, diffusion in the crystal or in the calcifying fluid, presence of defects induced by the incorporation of impurities? Several models are considered to explain these fluctuations: (1) mixing of various carrier phases, (2) specific pumping of cations to sites of calcification or mixing between direct seawater transport and ionic pumping, (3) growth rate, via direct influence on the partition coefficient or via modification of the crystal structure, (4) Rayleigh fractionation in a closed or semi-closed reservoir, (5) pH variation in the calcifying fluid (6) compartmentalized precipitation with the possible role of amorphous calcium carbonate (ACC) precursors, and (7) total or partial control by the organic factory.
The last three decades have shown the emergence of techniques allowing 2D mapping of chemical heterogeneities in minerals (electron microprobe, SIMS, LA-ICPMS, EDX on SEM or TEM). Recently, technical developments on these techniques considerably expanded, and the quality of the 2D images of major/trace elements, stable/radiogenic elements improved, allowing spatial scale bridging from the centimeter to the nanometer. In addition new instruments, in laboratory or on synchrotrons, were developed and allow 2D or 3D imaging of (i) organic matter, (ii) specific organic molecules, (iii) chemical bonds typical of proteins, sugars or lipids, (iv) vibration modes characteristic of specific molecules or atomic environments, (v) oxidation states of chemical species (e.g. nano-SIMS, Scanning transmission X-ray microscopy; micro X-ray fluorescence; X-ray absorption near edge spectroscopy; UV-, FTIR-, Raman micros spectroscopies).
The scope of the proposed Research Topic in Frontiers in Earth Science is to gather articles related to the quantification and imaging of chemical compositions in biominerals obtained with (and preferably with a combination of) the best available analytical techniques. Analyzed compounds include major/trace elements, stable/radiogenic isotopes. Special emphasis will be put on the challenging imaging of organic matter and identification of specific molecules within it. Experimental studies on parameters influencing the incorporation of elements are particularly welcome. The data should be interpreted in terms of (i) mechanisms of biomineral formation and (ii) potential applications (or limitations) to environmental reconstructions. The articles will be evaluated on the basis of the innovation and quality of analyses and images, the innovation and adequacy of the method used, and originality and soundness of the interpretation.
Keywords: Biomineral, Chemical imaging, Major and trace elements, Stable and radiogenic isotopes, Crystal growth
Important Note: All contributions to this Research Topic must be within the scope of the section and journal to which they are submitted, as defined in their mission statements. Frontiers reserves the right to guide an out-of-scope manuscript to a more suitable section or journal at any stage of peer review.