School of Earth and Environmental Sciences, University of St. Andrews, St. Andrews, United Kingdom.
Department of Chemistry, University of York, York, United Kingdom.
PLoS One. 2022 Dec 2;17(12):e0278627. doi: 10.1371/journal.pone.0278627. eCollection 2022.
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.
确定温度、pH 值、生物分子和矿物生长速率等因素如何影响生物成因碳酸钙的地球化学和结构，对于有效开发古代用指标至关重要。在这里，我们优化了一种从海水中沉淀碳酸钙多晶型文石的方法，该方法在严格控制的条件下模拟珊瑚钙化液的饱和状态（Ω）。然后，我们使用该方法来探索天冬氨酸（珊瑚骨骼中最丰富的氨基酸之一）对文石结构和形态的影响。使用≥200mg 的文石种子（表面积 0.84m2）为矿物生长提供表面，在 330ml 海水体积中，可在 Ω文石=6.9-19.2 范围内产生可重复的沉淀速率估计值。然而，未播种的沉淀在持续时间上变化很大，并且不能提供一致的沉淀速率估计值。低浓度的天冬氨酸（1-10μM）促进文石的形成，但高浓度（≥1mM）抑制沉淀。通过确保至少 60%的分析文石是在体外沉淀的（相当于使用 200mg 的种子并在体外沉淀 300mg 的文石），可以将体外沉淀的文石的拉曼光谱与起始种子的特征区分开来。天冬氨酸浓度≥1mM 会导致拉曼文石 v1 峰的全宽半最大值显著增加，反映出文石结构中旋转无序度增加。珊瑚骨骼中有机物质含量的变化会导致拉曼文石 ν1 峰的 FWHM 发生变化，如果不加以考虑，可能会混淆从该参数解释钙化液饱和状态的解释。
