[1] TU Dortmund Univ, Inst Appl Math LS 3, Vogelpothsweg 87, D-44227 Dortmund, Germany
[2] Helmholtz Ctr Polar & Marine Res, Alfred Wegener Inst, Handelshafen 12, D-27570 Bremerhaven, Germany
[3] Univ Erlangen Nurnberg, Appl Math 1, Cauerstr 11, D-91058 Erlangen, Germany