Geochemical and microstructural characterisation of two species of cool-water bivalves (<i>Fulvia tenuicostata</i> and <i>Soletellina biradiata</i>) from Western Australia

Abstract

Abstract. The shells of two marine bivalve species (Fulvia tenuicostata and Soletellina biradiata) endemic to south Western Australia have been characterised using a combined crystallographic, spectroscopic and geochemical approach. Both species have been described previously as purely aragonitic; however, this study identified the presence of three phases, namely aragonite, calcite and Mg-calcite, using XRD analysis. Data obtained via confocal Raman spectroscopy, electron probe microanalysis and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) show correlations between Mg / S and Mg / P in F. tenuicostata and between Sr / S and S / Ba in S. biradiata. The composition of the organic macromolecules that constitute the shell organic matrix (i.e. the soluble phosphorus-dominated and/or insoluble sulfur-dominated fraction) influences the incorporation of Mg, Sr and Ba into the crystal lattice. Ionic substitution, particularly Ca 2+ by Mg 2+ in calcite in F. tenuicostata, appears to have been promoted by the combination of both S-and P-dominated organic macromolecules. The elemental composition of these two marine bivalve shells is species specific and influenced by many factors, such as crystallographic structure, organic macromolecule composition and environmental setting. In order to reliably use bivalve shells as proxies for paleoenvironmental reconstructions, both the organic and inorganic crystalline material need to be characterised to account for all influencing factors and accurately describe the "vital effect".

Mineralogy of Deep-Sea Coral Aragonites as a Function of Aragonite Saturation State

“…Comparing our crystallographic findings of deep-sea corals to previous studies, unit cell volumes of live deep-sea corals (227.719-227.927 Å 3 ) fall slightly above the range of previous X-ray diffraction studies on mollusk (226.4277-227.774 Å 3 ) and coral biogenic aragonites (227.488-227.603 Å 3 ) (Pokroy et al, 2004(Pokroy et al, , 2006(Pokroy et al, , 2007Stolarski et al, 2007;Roger et al, 2017) (Figure 2 and Supplementary Table S3). Average anisotropic axis elongations in corals from this study compared to geological aragonite (Pokroy et al, 2007) agree with elongation ratios from Pokroy et al (2007) along the aand c-axes ( a/a Pokroy = 0.000967, a/a This study = 0.001086; c/c Pokroy = 0.0019, c/c This study = 0.00199), but not along the b-axis in which we observe elongations rather than a shortening as reported by Pokroy et al (2007)…”

Coral calcifying fluid aragonite saturation states derived from Raman spectroscopy

“…When light interacts with a material, a small percentage (typically < 0.0001 %) of the photons are scattered inelastically (referred to as Raman or Stokes scattering), resulting in a change of energy and frequency (Smith and Dent, 2005). The frequency shifts associated with Raman scattering are characteristic of both the internal vibrations of a molecule and the lattice vibrations between molecules in a crystal, which makes Raman spectroscopy a valuable tool for mineral identification (Urmos et al, 1991;Dandeu et al, 2006;Brahmi et al, 2010;Clode et al, 2011;Nehrke et al, 2011;Stock et al, 2012;Foster and Clode, 2016;Stolarski et al, 2016;Roger et al, 2017). Importantly, Raman peaks can also provide information regarding the chemical composition of crystals and the conditions of the fluid from which they formed.…”

Coral calcifying fluid aragonite saturation states derived from Raman spectroscopy

“…The frequency shifts associated with Raman scattering are characteristic of both the internal vibrations of a molecule and the lattice vibrations between molecules in a crystal, which makes Raman spectroscopy a valuable tool for mineral identification (Urmos et al, 1991;Dandeu et al, 2006;Brahmi et al, 2010;Clode et al, 2011;Nehrke et al, 2011;Stock et al, 2012;Stolarski et al, 2016;Roger et al, 2017). Importantly, Raman peaks can also provide information regarding the chemical composition of crystals and the conditions of the fluid from which they formed.…”