This dataset captures the yearlong evolution of physical properties of the snow cover over Arctic sea ice during the MOSAiC expedition (October 2019-September 2020). It also includes the surface scattering layer that is typical of the melting summer sea ice surface. This dataset is specifically for measurements that were logged as “snowpit events” during MOSAiC. The snowpit events were either detailed point-measurements of vertical snow profiles or horizontally repeated transects, measured at selected locations in designated undisturbed areas. One snowpit event corresponds to one site visit. The snowpits are often co-located with measurements from other MOSAiC teams to improve our understanding of how snow cover affects and interacts with the atmosphere-sea ice-ocean-ecology system. Most snowpits were measured at least bi-weekly to capture the temporal evolution of physical properties of snow. Some snowpits were one-off events to capture interesting and unplanned-for surface conditions. This dataset includes 576 snowpit events, and describes the snow conditions during the entire expedition.Please direct inquiries to; David Wagner (PS122/1), Martin Schneebeli (PS122/2), Amy Macfarlane (PS122/3 and PS122/4), Ruzica Dadic (PS122/5).