These maps display sea ice concentrations (SIC) and 96-hour air mass back-trajectories arriving at the German research ship Polarstern during the MOSAiC expedition (Legs 1-4, October 2019 – August 2020), shown hourly at three arrival heights: 50 m (red), 250 m (purple), and 1000 m (pink). The 96-hour air mass back-trajectories were calculated using the NOAA HYSPLIT model (Stein et al., 2015) with meteorological data from the GDAS1 system (Global Data Assimilation System; 1° latitude/longitude; 3-hourly). Sea ice concentration data were sourced from ERDDAP (Environmental Research Division’s Data Access Program), managed by NOAA (National Oceanic and Atmospheric Administration). The marginal ice zone (MIZ) is defined here as the oceanic region with SIC between 15% and 80%.