1. GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany.
2. Faculty of Mathematics and Natural Sciences, Kiel University, Kiel, Germany.
3. Laboratoire d'Etudes en Géophysique et Océanographie Spatiale (LEGOS), CNRS/IRD/UT3/CNES, Toulouse, France.
4. Department of Oceanography, University of Cape Town, Cape Town, South Africa.
5. Lamont-Doherty Earth Observatory, Columbia University, New York, NY, USA.
6. Geophysical Institute, University of Bergen and Bjerknes Centre for Climate Research, Bergen, Norway.