Submarine eskers preserved on Adler Grund, south-western Baltic Sea

The position of offshore ice margins, especially in the Baltic Sea, is poorly known. Based on hydroacoustic surveys, we mapped a field of submarine eskers on the seafloor of the shoal Adler Grund, southwestern Baltic Sea. The eskers comprise discontinuous, branching ridge structures with zigzag-shaped crests. These features are elevated up to 7 m above the surrounding seafloor with slope angles approaching 26o. The ridges are composed of gravel and boulders. Their interpretation as glacio-tectonic features is unlikely due to branching ridge crests and a continuous reflector at the base of several ridges. Based on their morphology and distribution, the ridges are interpreted as concertina eskers formed by meltwater outbursts close to an ice margin. Their good state of preservation indicates that the eskers were most likely formed during the last advance of the Weichselian glaciation across the study region.