Peter L Croot, iCRAG (Irish Centre for Research in Applied Geosciences), Earth and Ocean Sciences, School of Natural Sciences and the Ryan Institute, National University of Ireland Galway, Galway, Ireland, Eva-Maria Brodte, Alfred Wegener Institute, Helmholtz-Zentrum für Polar- und Meeresforschung, Helgoland, Germany, Peter Lemke, Alfred Wegener Institute, Helmholtz-Zentrum für Polar- und Meeresforschung, Bremerhaven, Germany and Karen Wiltshire, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, List/Sylt, Germany