The radiocarbon isotope data of aragonite, calcite, and dolomite veins and whole-rock total carbon and total non-carbonate carbon from serpentinized peridotites recovered during IODP Expedition 357 (October to December 2015) from the Atlantis Massif, Mid-Atlantic Ridge was examined to characterize carbon sources and the fate of dissolved organic (DOC) and inorganic carbon (DIC) in seawater during long-lived hydrothermal circulation and serpentinization. The measurements were performed at the ETH Zurich from 2017 to 2020 using an Elemental Analyzer interfaced to a MICADAS Accelerator Mass Spectrometer (AMS) equipped with a gas-ion source or by direct injection of CO2, from carbonate dissolution, into the ion source of the AMS