This dataset contains the data generated for publication "Organic Phases in Bivalve (Arctica islandica) Shells: Their Bulk and Amino Acid Nitrogen Stable Isotope Compositions", including the following files: Specimen_ID_shell_morphology_measurement: Description of locality of collection, shell ID, shell working ID and the shell morphology measurement which can be referred to Section 2.1 of the manuscript. EA_IRMS_raw_error_propagate: This file contains data showing the m/z 28 signal intensities of all measurements and the error propagation that mentioned in Section 2.3 of the manuscript. It also includes the calculation of analytical accuracy and precision. Statistics: The file contains the summary of statistical analyses performed in this manuscript. Refer to Section 2.7 and 3.3. Recovery: It contains the recovery of the total nitrogen contents or amino acid concentrations after different treatments and this was mentioned in Section 4.1 of the manucript. Mass_balance: The computation procedure that showed in Section 3.4 and discussed in Section 4.3 can be traced in this file. GC-C-IRMS_long_term_sd: The file shows the long-term precision of GC-C-IRMS computed from the mixed standard of amino acids BSIA_d15N: The file contains all the bulk d15N data that used in this manuscript. CSIA_d15N: The file contains all the amino acid d15N data that used in this manuscript. AA_Composition: The file shows AA percent data that used in this manuscript. For details see main text of the manuscript.

This research has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement No 856488).