Here we present results from our investigation on the influence of the Ekström Ice Shelf on the land-fast sea ice of Atka Bay, eastern Weddell Sea. • Ice platelets emerge from the cavity and interact with the fast-ice 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. • Additional buoyancy prevents surface flooding and snow-ice formation despite thick -now cover. • The seasonal cycle shows a maximum thickness in December, and a subsequent thinning, which 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 of the platelet layer of 0.26. • 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, equivalent to more than one fifth of the annual basal melt volume under the Ekström Ice Shelf.