Influences of saturation state, temperature, precipitation rate, Mg/Ca and amino acid inclusion on the aragonite Raman ν1 band: implications for interpreting marine calcifier biomineralisation

The full width half maximum (FWHM) of the aragonite Raman ν1 band is a potential proxy of the saturation state (ΩAr) of the media from which the aragonite precipitates, and is used to infer changes in the biomineralisation environment of marine calcifiers. However, controls on the FWHM are not fully understood. Here, we analyse the FWHM of a suite of aragonite samples synthesised in vitro under tightly controlled conditions. We vary temperature, ΩAr and pH independently during precipitation and determine how these parameters individually influence the FWHM. We also explore how the FWHM relates to aragonite precipitation rate, trace/minor element composition and biomolecule inclusion. The FWHM is positively related to ΩAr, aragonite growth rate and aragonite Mg/Ca. Although it is unclear which metric controls the FWHM, all likely increase structural disorder in the aragonite lattice. The incorporation of aspartic and glutamic acids in aragonite also significantly increases the FWHM, although it is unclear how inclusion of these amino acids in the proteins, which occur in biogenic aragonite, acts to alter FWHM. The sensitivity of the FWHM to ΩAr change is small (i.e. 0.0105 cm−1 for every 1 unit increase in ΩAr) suggesting that the FWHM has limited application in tracking the effects of ocean acidification on biogenic aragonite over decade to century time scales.