Warm airmass intrusions (WAIs) from the mid-latitudes significantly impact the Arctic water budget. Here, we combine water vapor isotopes measurements from the MOSAiC expedition, with a Lagrangian-based process attribution diagnostic to track moisture origin and transformation in the central Arctic Ocean during two WAIs, under contrasting sea-ice concentrations (SIC). During winter with high SIC, two moisture states emerge: the local in-Arctic moisture, for which the isotope signal is influenced by kinetic processes in ice-cloud formation, is rapidly overprinted by low-latitude moisture advected poleward during WAI. In summer under low SIC, moisture is supplied through evaporation from land and ocean, with moisture distillation via liquid-cloud formation. The isotopic composition reflects the influence of higher humidity at the evaporation sites. Given the projected increase of frequency and duration of WAIs, our study contributes to assess process changes in the Arctic water cycle.