Markus Rex and Stefanie Arndt have respectively led and participated in the MOSAiC expedition. Between 2019 and 2020 the German icebreaker Polarstern spent a year drifting through the Arctic Ocean trapped in ice. The goal was to improve the understanding of the full seasonal cycle of processes and interactions in the coupled polar climate systems between the atmosphere, sea ice, ocean, and ecosystem to provide guidance for improving climate models.