1. Graduate School of Advanced Science and Engineering Hiroshima University Higashi‐Hiroshima 739‐8526 Japan
2. National Institute of Polar Research Tokyo 190‐8518 Japan
3. Department of Polar Science School of Multidisciplinary Science SOKENDAI (The Graduate University for Advanced Studies) Tokyo 190‐8518 Japan
4. Department of Earth Sciences Graduate School of Science Tohoku University Sendai 980‐8578 Japan
5. Kochi Institute for Core Sample Research Japan Agency for Marine‐Earth Science and Technology (JAMSTEC) Nankoku Kochi 783‐8502 Japan
6. Marine Works Japan Nankoku Kochi 783‐8502 Japan