Submarine end moraines on the continental shelf off NE Greenland Implications for late glacial dynamics

Favourable sea-ice conditions gave way to an acoustic survey offshoreNE Greenland during RV Polarstern ARK-XXIV/3 leg in 2009. The acquired data set clearly depicts sediment ridges in an area of app.189km. The ridges are found in water depths between 270 and 350 m. The sediment ridges are 2.5e9 kmlong, 50e250 m wide and 5e25 m high. In profile, most of these ridges are characterized by steep slopes towards Northwest and gentle slopes towards Southeast. Their internal structure, imaged by parametric echo-sounding data, shows that they are positive sedimentation features rather than erosive remnant structures. Arcuate shape, joint orientation and position on a basal till are indicative for endmoraines. Because they are positioned within the Westwind Trough on a basal till that extends further east, we consider these ridges endmoraines of theWestwind ice stream reported by Evans et al. (2009),Marine geophysical evidence for former expansion and flow of the Greenland Ice Sheet across the northeast Greenland continental shelf. Based on our hydro-acoustic data, we interpret these endmoraines to be formed by short-lived re-advances during an overall recession of the ice margin. However, they could also be deposited during halts of thegrounding line (comparable to De Geer moraines) though theirmorphological characteristics are slightly different from most published De Geer moraines. The ages for the moraine deposition can be inferred from a thin sedimentary drape indicating timing between Lateglacial and early Holocene. This set of end moraines is direct evidence for a dynamic behaviour of the marine-based ice stream during the last deglaciation on the NE Greenland shelf.