We present the isotopic dataset of near-surface water vapour, continuously surveyed from the Polarstern research vessel during the Leg 4 of the Multidisciplinary Drifting Observatory for the Study of Arctic Climate (MOSAiC). The isotopic measurements were acquired continuously by a Cavity Ring-Down Spectrometer (CRDS) installed onboard the RV Polarstern; the ambient inlet was located at 29m asl. A custom-designed calibration module, including four water standards, was operated in parallel to the CRDS. The data is quality controlled and the measurements are calibrated against humidity dependency and deviation from the VSMOW standard values. Knowingly affected or erroneous data were removed.

Corresponding authors: Camilla F. Brunello (camilla.brunello@awi.de), Martin Werner (martin.werner@awi.de)