Kenji Kawamura^1,2, Ikumi Oyabu¹, Shuji Aoki³, Takakiyo Nakazawa³, Ayako Abe-Ouchi⁴ and Fuyuki Saito⁵, (1)National Institute of Polar Research, Tokyo, Japan, (2)SOKENDAI Graduate University for Advanced Studies, Kanagawa, Japan, (3)Tohoku University, Sendai, Japan, (4)University of Tokyo, Atmosphere and Ocean Research Institute, Bunkyo-ku, Japan, (5)Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokohama, Japan