17:15 〜 18:30
[MIS05-P13] Analysis of the abrupt climate change during the last deglaciation
キーワード：AMOC、退氷期、氷期気候、大気海洋結合モデル
Abrupt climate changes in the deglaciation share many features with glacial abrupt climate changes, i.e. DO events. However, we do not know much about how global temperature changes in response to this, the exact changes in the interior of the ocean, or similarities between the deglaciation and DO events. In this study, we compared the experimental results of the last deglaciation and the DO oscillations using MIROC-4m, an atmosphere-ocean general circulation model (AOGCM), focusing on changes in the air surface temperature, ocean temperature and ocean salinity. By comparing model results to proxy records, we showed the challenges of interpreting model and proxy data, and by comparing the last deglaciation and the DO oscillations, we discussed the ocean-wide feedbacks, including those of the deep ocean.
As a result, a comparison of the model results and proxy data for the last deglacial period shows that the warming during the last deglaciation was moderate in the Southern Hemisphere but rapid in the Northern Hemisphere. The model also shows that the tropics warm gradually at first, like Antarctica, and then warm rapidly when the northern hemisphere warms rapidly. A comparison of mid-glacial and deglacial experiments shows that the rapid climate change during the deglaciation has much in common with those of the DO oscillations, specifically, in terms of how the temperature and ocean density change. In both experiments, the temperature changes in the sub-surface ocean due to the AMOC mode change spread eastward from the Atlantic Ocean to the Pacific Ocean via the Southern Ocean. Also, while the AMOC was in the same mode, the density change at the bottom ocean, which is caused by changes in sea ice formation over the Southern Ocean proceeded to affect the vertical density gradient in the Atlantic Ocean.
It is thought that the behavior of the Southern Ocean and the deep ocean is deeply involved not only in DO oscillation with a period of several thousand years but also in the AMOC oscillation during deglaciation. This suggests that the rapid climate change during deglaciation is part of the rapid climate change during glaciation and that similar mechanisms are at work.
As a result, a comparison of the model results and proxy data for the last deglacial period shows that the warming during the last deglaciation was moderate in the Southern Hemisphere but rapid in the Northern Hemisphere. The model also shows that the tropics warm gradually at first, like Antarctica, and then warm rapidly when the northern hemisphere warms rapidly. A comparison of mid-glacial and deglacial experiments shows that the rapid climate change during the deglaciation has much in common with those of the DO oscillations, specifically, in terms of how the temperature and ocean density change. In both experiments, the temperature changes in the sub-surface ocean due to the AMOC mode change spread eastward from the Atlantic Ocean to the Pacific Ocean via the Southern Ocean. Also, while the AMOC was in the same mode, the density change at the bottom ocean, which is caused by changes in sea ice formation over the Southern Ocean proceeded to affect the vertical density gradient in the Atlantic Ocean.
It is thought that the behavior of the Southern Ocean and the deep ocean is deeply involved not only in DO oscillation with a period of several thousand years but also in the AMOC oscillation during deglaciation. This suggests that the rapid climate change during deglaciation is part of the rapid climate change during glaciation and that similar mechanisms are at work.