Sea-floor scour at the mouth of Hudson Strait by deep-keeled icebergs from the Laurentide Ice Sheet

Physical evidence on the dimensions of icebergs released from the mouth of Hudson Strait into the northwest Atlantic during the last Heinrich event (H-0) is presented. Side-scan sonar imagery shows scour marks up to 700 m wide and longer than 28 km. These scour marks were carved by gigantic icebergs (megabergs) with keel drafts possibly as great as 660 m capable of scouring trenches 20 to 25 m deep into the seabed. These icebergs were likely calved from the grounding margin of a thick (possibly as thick as 640 m) rapidly-flowing glacial margin during the H-0 Heinrich event (11 ka BP). Along with the relatively few megabergs released were large numbers of smaller icebergs that calved from the ice margin at the same time and were also produced from break-up of the megabergs. Scouring of the seabed by the large and smaller icebergs happened at the same time, with megabergs scouring only in the deep waters of Hatton Basin, and the smaller bergs scouring only on the eastern, shallow margin of the Basin at the continental shelf break.