Optimising a method for aragonite precipitation in simulated biogenic calcification media

Abstract

Resolving how factors such as temperature, pH, biomolecules and mineral growth rate influence the geochemistry and structure of biogenic CaCO3, is essential to the effective development of palaeoproxies. Here we optimise a method to precipitate the CaCO3 polymorph aragonite from seawater, under tightly controlled conditions that simulate the saturation state (Ω) of coral calcification fluids. We then use the method to explore the influence of aspartic acid (one of the most abundant amino acids in coral skeletons) on aragonite structure and morphology. Using ≥200 mg of aragonite seed (surface area 0.84 m2), to provide a surface for mineral growth, in a 330 mL seawater volume, generates reproducible estimates of precipitation rate over Ωaragonite = 6.9–19.2. However, unseeded precipitations are highly variable in duration and do not provide consistent estimates of precipitation rate. Low concentrations of aspartic acid (1–10 μM) promote aragonite formation, but high concentrations (≥ 1 mM) inhibit precipitation. The Raman spectra of aragonite precipitated in vitro can be separated from the signature of the starting seed by ensuring that at least 60% of the analysed aragonite is precipitated in vitro (equivalent to using a seed of 200 mg and precipitating 300 mg aragonite in vitro). Aspartic acid concentrations ≥ 1mM caused a significant increase in the full width half maxima of the Raman aragonite v1 peak, reflective of increased rotational disorder in the aragonite structure. Changes in the organic content of coral skeletons can drive variations in the FWHM of the Raman aragonite ν1 peak, and if not accounted for, may confuse the interpretation of calcification fluid saturation state from this parameter.

Unexpected increase in structural integrity caused by thermally induced dwarfism in large benthic foraminifera

“…It is important to note that our experiment, like most FEA, does not consider the role of organics between calcite layers or around individual crystals which could play a role in enhancing hardness [ 60 ]. It has been shown in taxa with very different calcification processes and mineralogy that they increase skeletal organic content under conditions of ocean acidification [ 61 – 63 ] though this does not appear to impact hardness significantly [ 64 ]. Moreover, as foraminifera have very low organic content in their shells, ranging between 0.04% and 0.1% [ 65 , 66 ], we assume that this is not likely to have a significant effect.…”

Ocean alkalinity enhancement approaches and the predictability of runaway precipitation processes – Results of an experimental study to determine critical alkalinity ranges for safe and sustainable application scenarios

“…However, under the conditions of this study, i.e., with liquid alkaline material, the Ωaragonite threshold for the initiation of spontaneous pseudo-homogeneous carbonate formation in particle-free seawater is approximately 11.3 at a salinity of 32.6 and ~11°C (Marion et al, 2009based on data from Morse & He, 1993. Most ocean surface waters are naturally oversaturated with carbonates (Ωaragonite ~2-5, Olsen et al, 2018), yet no obvious spontaneous inorganic carbonate formation is occurring., as the presence of Mg 2+ (Berner, 1975;Pan et al, 2021), phosphate (Burton & Walter, 1990), and dissolved organic matter species (Chave & Suess, 1970;Kellock et al, 2022) are known to delay or inhibit precipitation of CaCO3. Since Mg 2+ in an open ocean context correlates to salinity, its concentration could vary depending on the local conditions (Moras et al, 2023), while phosphate and DOM concentrations are related to biological processes and seasonal changes.…”

A Simplified Model for Shear Behavior of Mortar Using Biomimetic Carbonate Precipitation

“…Studies have shown that Asp is a broad-spectrum mediator that can act on almost all phases of calcium carbonate in vitro. It can stabilize and extend the lifetime of amorphous calcium carbonate (ACC) [ 6 , 7 ], increase the hardness of calcite single crystals [ 8 ], and even promote or inhibit aragonite precipitation under certain conditions [ 9 , 10 ]. However, the most reported effect of Asp is that it can induce the formation of vaterite [ 11 , 12 ], even though this is usually thermodynamically disfavored.…”