Basal melt of ice shelves leads to an accumulation of disc-shaped ice platelets (platelet layer) beneath a nearby sea-ice cover. Here we present the seasonal cycle of fast ice attached to the Ekström Ice Shelf and the underlying platelet layer in 2012. Ice platelets emerge from the cavity and interact with the fast-ice cover of Atka Bay as early as June. Episodic accumulations throughout the winter lead to an average platelet-layer thickness of 4 m in December, with local extrema of 10 m. The additional buoyancy partly prevents surface flooding and snow-ice formation despite a thick snow cover. Subsequent thinning of the platelet layer in December is associated with an inflow of warm water masses. The combination of model studies with observed fast-ice thickness reveals an average ice-volume fraction in the platelet layer of 0.26. We �nd that nearly half of the combined solid sea-ice and ice-platelet volume in this area is generated by heat loss to the ocean rather than to the atmosphere. The total ice-platelet volume underlying Atka Bay fast ice is equivalent to more than one �fth of the annual basal melt volume under the Ekström Ice Shelf.