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.