1. Kitami Institute of Technology; 165 Koen-cho,; Kitami; 090-8507; Japan
2. Limnological Institute, Siberian Branch; Russian Academy of Sciences; 3, Ulan-Batorskaya Street,; P.O. Box 4199,; Irkutsk; 664033; Russia
3. Renard Centre of Marine Geology; Ghent University; Krijgslaan 281-S8,; Ghent; B-9000; Belgium
4. Methane Hydrate Research Center; National Institute of Advanced Industrial Science and Technology; 2-17 Tukisamu Higashi Toyohira-ku,; Sapporo; 062-8517; Japan