Tidally influenced iceberg motion: sub-metre resolution imaging of iceberg ploughmarks using autonomous underwater vehicles in the Weddell Sea

Linear to curvilinear depressions interpreted as iceberg ploughmarks are identified on the continental shelf beyond Larsen C Ice Shelf in about 350 m water depth using multibeam echo-sounding at sub-metre horizontal resolution. Detailed imaging of ploughmark morphology demonstrates the presence of irregularly spaced ridges extending across the full ploughmark width. These ridges have an arcuate shape in plan-view, are up to 2 m high, 20-40 m wide, show occasional presence of subdued debris-flow lobes on their distal side and have an asymmetric cross-profile in which the seafloor deepens beyond their slightly steeper side. The ridges are interpreted to have been produced when the iceberg moved backwards under the falling tide, which pushed up a ridge of sediment behind the iceberg keel, before it continued on its original trajectory under the rising tide. Similar features, which we term ‘iceberg tidal ridges’, can be identified at lower resolution on bathymetric and three-dimensional seismic data from the mid-Norwegian margin, suggesting the broader implications of the interpretations presented here. For example, the mapping of delicate ridges preserved within iceberg ploughmarks can be used to reconstruct past oceanic circulation including the former direction and strength of ocean currents.