Asbjorn J Breivik, University of Oslo, Center for Earth Evolution and Dynamics (CEED), Oslo, Norway, Jan Inge Faleide, University of Oslo, Centre for Earth Evolution and Dynamics (CEED), Oslo, Norway, Rolf Mjelde, Univ Bergen, Bergen, Norway, Ernst Flueh, GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany and Yoshio Murai, Hokkaido Univ, Sapporo, Japan