1. 1 Atlantic Geoscience Centre, Geological Survey of Canada (Atlantic), Bedford Institute of Oceanography, PO Box 1006, Dartmouth, Nova Scotia B2Y 4A2, Canada (E‐mail: ), 2IFREMER, Géosciences Marines, BP 70, 29280 Plouzané, France, 3Department of Earth Sciences, Memorial University of Newfoundland, St Johns, Newfoundland A1X 3B5, Canada