UNDER EMBARGO - This dataset contains marine organic matter source samples, artificial mixtures of known composition, and compound-specific nitrogen stable isotope data of amino acids (δ¹⁵N-AA). Source materials include phytoplankton, zooplankton, and faecal pellets from the marine fouling species Mytilus edulis and Metridium senile.Samples were collected and processed in the laboratory under controlled conditions. Artificial mixtures were prepared by combining source materials in defined proportions to generate experimental samples representing multiple marine organic matter source combinations. Metadata describing sample collection, preparation, and mixture composition are included.Compound-specific nitrogen isotope ratios of individual amino acids were measured using stable isotope analysis. The dataset includes isotopic measurements for all source samples and artificial mixtures, along with associated metadata required to document sampling, laboratory preparation, and analytical procedures.