[M-IS14] 古気候・古海洋変動

[MIS14-P33] 気候モデルによる全球凍結と海洋深層循環のシミュレーション

*小長谷 貴志¹、小玉 貴則²、川崎 高雄³、シェリフ多田野 サム⁴、高須賀 大輔⁵、阿部 彩子³、藤井 昌和⁶ (1.海洋研究開発機構、2.東京科学大学地球生命研究所、3.東京大学大気海洋研究所、4.琉球大学、5.東北大学、6.国立極地研究所)

キーワード：全球凍結、海洋深層循環、気候モデル

It is considered that the Earth has experienced snowball events in the past, where the surface is covered with ice. Previous studies have investigated the snowball onset and climate of the snowball using general circulation models. This study used a coupled atmosphere-ocean climate model MIROC4m and focused on the ocean circulation changes during the onset of snowball and their evolution to steady-states under snowball climate, under modern configuration of the Earth. If solar constant is abruptly changed to $94 \%$ of the present-day, climate of the modern Earth turned into a snowball state after 1300 years, and the sea ice thickness start to increase. During the onset of snowball, extensive sea ice formation and melting of sea ice in the mid-latitude contributes substantial freshening in the surface water and salinity stratification. In contrast, such salinity stratification was absent if the duration necessary for snowball onset was short because of stronger solar constant forcing. After snowball onset, the global sea ice cover reduces air-sea flux and leads to drastic weakening in the deep ocean circulation, but as the ocean temperature and salinity fields approach to a nearly constant field, the meridional overturning circulation resumed in the steady-state snowball climate. Although the evolution of ocean circulation would depend on the model setting, particularly for the treatment of air-sea fluxes or continental distribution, our results suggest the importance of ocean circulation and associated biogeochemical changes in climate system feedback and sequence of snowball events.