17:15 〜 18:45
[MIS12-P23] Impact of surface boundary conditions on the stability diagram of the Atlantic meridional overturning circulation under the glacial climate
キーワード：氷期-間氷期サイクル、大西洋子午面循環、気候モデル
The Atlantic meridional overturning circulation (AMOC) is considered to have repeated abrupt transitions between different states during the glacial period which contributed to abrupt climate changes. Previous studies have investigated the structure of the AMOC modes by means of hysteresis experiments in which continuously changing freshwater flux is imposed at high latitudes in the North Atlantic in climate models. Some studies suggested that the glacial AMOC has a different hysteresis diagram from that in the present-day AMOC. However, there are discrepancies in the modes and their hysteresis behaviors of the AMOC among the previous studies, and its mechanism has not been investigated.
In this study, we investigated the hysteresis behaviors of the AMOC and its robustness under modern and glacial climates using an earth system model of intermediate complexity. We conducted hysteresis experiments with various surface boundary conditions based on the output of the climate models in the Paleoclimate Modelling Intercomparison Project (PMIP) 2, 3, and 4. In the modern climate, the bistability between the on and off modes was commonly found. However, the hysteresis diagram of the glacial AMOC was divided into three types depending on the choice of surface boundary conditions; the cold type, which has the cold mode with the shallow AMOC, the modern type, which shows similar behavior to the modern hysteresis, and the linear type, which shows no abrupt mode transitions but gradual changes of the AMOC. These three categories can encompass different behaviors of the glacial AMOC in previous research. The mode transitions of the AMOC in the cold-type hysteresis were driven by the thermal and sea ice feedback, while those in the modern-type hysteresis were due to the salinity feedback.
In this study, we investigated the hysteresis behaviors of the AMOC and its robustness under modern and glacial climates using an earth system model of intermediate complexity. We conducted hysteresis experiments with various surface boundary conditions based on the output of the climate models in the Paleoclimate Modelling Intercomparison Project (PMIP) 2, 3, and 4. In the modern climate, the bistability between the on and off modes was commonly found. However, the hysteresis diagram of the glacial AMOC was divided into three types depending on the choice of surface boundary conditions; the cold type, which has the cold mode with the shallow AMOC, the modern type, which shows similar behavior to the modern hysteresis, and the linear type, which shows no abrupt mode transitions but gradual changes of the AMOC. These three categories can encompass different behaviors of the glacial AMOC in previous research. The mode transitions of the AMOC in the cold-type hysteresis were driven by the thermal and sea ice feedback, while those in the modern-type hysteresis were due to the salinity feedback.