Geophysical evidence of deep-keeled icebergs on the Rockall Bank, Northeast Atlantic Ocean

Abstract

High resolution multibeam swath bathymetric data acquired from the Rockall Bank reveal an abundance of linear to slightly sinuous seabed incisions. These features, interpreted as relict iceberg scours, provide for the first time evidence that the Rockall Bank was intensively scoured by iceberg keels. While the shallower portion of the Rockall Bank lacks evidence of iceberg scouring, on the western and southern flanks (between 250 and 450m water depth) the seabed is almost completely covered by thousands of cross-cutting scours. More isolated scours, up to 800m wide and 25km long are also observed down to nearly 600m water depth. Based on a full glacial sea level low stand of 120m, these isolated scour marks must have been carved by gigantic icebergs with keels up to 500m deep and able to create incisions up to 15m deep in the seabed. Analysis of scour orientation, length, width, and depth indicates that these mega-icebergs were likely calved from large, fast-flowing ice sheet outlets draining circum-North Atlantic ice sheets. Prevailing scour orientations suggest a number of possible ice sheet sources, including southeast and southern Greenland and the Donegal-Barra ice stream of the last British–Irish Ice Sheet. The bimodal distribution of the scour depth observed across the Rockall Bank suggest either different icebergs provenances or physical and climatic controls on icebergs draft.