Amino acid compositions of aragonite samples precipitated from seawater, using a pH stat titrator using the constant composition technique between September 2021 and December 2022. Samples were precipitated from 330 mL of seawater with no biomolecules (control) or with a seawater concentration of 2 mM of aspartic acid (Asp), 2 mM glycine (Gly), 2 mM of both amino acids (Asp+Gly) or 2 mM dipeptide glycyl-L-aspartic acid (Asp-Gly) or from 33 mL of seawater with variable concentrations of aspartic acid (Asp) or tetra-aspartic acid (Asp4). Protein was extracted from the samples and run as free amino acids (to detect amino acids in free form) and as hydrolysed samples (to detect peptides). Data were collected to determine how changes in the calcification fluids of calcareous organisms affect aragonite precipitation. Data were collected by Giacomo Gardella, Sam Presslee and Nicola Allison and interpreted by Giacomo Gardella, Cristina Castillo Alvarez, Nicola Allison, Adrian Finch, Kirsty Penkman, Roland KrÓ§ger, Sam Presslee and Matthieu Clog