Geographic location and imagery of field site for sea-ice samples collected. (a) Map of field site location near Utqiaġvik with zoom-out inset of Alaska; (b) photo by A. Torstensson of sampled ice core with visible bottom algal layer; and (c) microscopic image by A. Torstensson of Nitzschia frigida, the dominant alga present by visual identification. DOI: https://doi.org/10.1525/elementa.421.f4