The echo-free zone occurs in the basal region of ice sheets (e). We linked it to disturbances on the micro-scale caused by ice dynamics (Drews et al., TC, 2009). Although layer power reflection coefficient (c) based on EDML ice-core conductivity (a) and crystal orientation fabric (b) are above detection threshold, coherent reflections vanish. Suitable explanation: larger-scale roughness, as indicated by the
small-scale roughness of line-scan images (d).

Line-scan images of the EDML ice core showing cloudy bands. EFZ onset is at 2100 m depth. Cloudy band stratigraphy appears undisturbed (zoom 1) above EFZ with small-scale undulations (zoom 2) slowly developing. Intra-EFZ layers appear partly dipped parallel (zoom 3) and partly rough as dips point into opposite directions.