[M-IS18] 古気候・古海洋変動

[MIS18-07] Transient simulations of the last two deglaciations and abrupt climate changes related to different Northern ice sheet discharge and insolation

*小長谷 貴志¹、阿部 彩子¹、齋藤 冬樹² (1.東京大学大気海洋研究所、2.海洋研究開発機構)

There were significant differences between the last two deglaciations, particularly in Atlantic Meridional Overturning Circulation (AMOC) and Antarctic warming in the deglaciations and the following interglacials. Here, we present transient simulations of deglaciation using a coupled atmosphere–ocean general circulation model for the last two deglaciations focusing on the impact of ice sheet discharge on climate changes associated with the AMOC in the first part, and the sensitivity studies using a Northern Hemisphere ice sheet model in the second part. We show that a set of abrupt climate changes of the last deglaciation, including Bolling–Allerod warming, the Younger Dryas, and onset of the Holocene were simulated with gradual changes of both ice sheet discharge and radiative forcing. On the other hand, penultimate deglaciation, with the abrupt climate change only at the beginning of the last interglacial was simulated when the ice sheet discharge was greater than in the last deglaciation by a factor of 1.5. One additional deglaciation experiments using realistic T2 orbital and GHG forcing indicate that a weak AMOC during the middle and later stages of the deglaciation was sufficient for the Antarctic warmth of T2, which can be explained by the fact that the typical response time of Antarctic warming to the AMOC. These results, together with Northern Hemisphere ice sheet model experiments suggest the importance of the transient climate and AMOC responses to the different orbital forcing conditions of the last two deglaciations, through the mechanisms of mass loss of the Northern Hemisphere ice sheet and meltwater influx to the ocean.