[M-IS12] 古気候・古海洋変動

[MIS12-25] Multi-model assessment of the deglacial climatic evolution at high southern latitudes

*小長谷 貴志¹、Menviel Laurie²、阿部 彩子¹、Vadsaria Tristan^1,3、Ivanovic Ruza⁴、Snoll Brooke⁴、シェリフ多田野 サム^4,5、Valdes Paul⁶、Gregoire Lauren⁴、Kapsch Marie-Luise⁷、Mikolajewicz Uwe⁷、Bouttes Nathaelle⁸、Roche Didier⁸、Lhardy Fanny⁸、He Chengfei⁹、Otto-Bliesner Bette¹⁰、Liu Zhengyu¹¹、陳 永利¹ (1.東京大学大気海洋研究所、2.University of New South Wales、3.UiT The Arctic University of Norway, Tromsø、4.School of Earth & Environment, University of Leeds、5.琉球大学、6.School of Geographical Sciences, University of Bristol、7.Max Planck Institute for Meteorology、8.Laboratoire des Sciences du Climat et de l’Environnement/Institut Pierre-Simon Laplace, UMR CEA-CNRS-UVSQ, Université Paris-Saclay、9.Rosenstiel School of Marine, Atmospheric, and Earth Science, University of Miami、10.Climate and Global Dynamics Laboratory, National Center for Atmospheric Research、11.Atmospheric Science Program, Department of Geography, Ohio State University)

キーワード：最終退氷期、気候モデル

The quaternary climate is characterised by glacial-interglacial cycles, with the most recent transition from the last glacial maximum to the present interglacial (the last deglaciation) occurring between ~ 21 and 9 ka. While the deglacial warming at southern high latitudes is mostly in phase with atmospheric CO₂ concentrations, some proxy records have suggested that the onset of the warming occurred before the CO₂ increase. In addition, southern high latitudes exhibit a cooling event in the middle of the deglaciation (15–13 ka) known as the Antarctic Cold Reversal (ACR). In this study, we analyse transient simulations of the last deglaciation performed by six different climate models as part of the 4th phase of the Paleoclimate Modelling Intercomparison Project (PMIP4) to understand the processes driving southern high latitude surface temperature changes. While proxy records from West Antarctica and the Pacific sector of the Southern Ocean suggest the presence of an early warming before 18 ka, only half the models show a significant warming (~1 °C or ~10 % of the total deglacial warming). All models simulate a major warming during Heinrich stadial 1 (HS1, 18–15 ka), greater than the early warming, in response to the CO₂ increase. Moreover, simulations in which the AMOC weakens show a more significant warming during HS1 as a result. During the ACR, simulations with an abrupt increase in the AMOC exhibit a cooling in southern high latitudes, while those with a reduction in the AMOC in response to rapid meltwater exhibit warming. We find that all climate models simulate a southern high latitude cooling in response to an AMOC increase with a response timescale of several hundred years, suggesting the model’s sensitivity of AMOC to meltwater, and the meltwater forcing in the North Atlantic and Southern Ocean affect southern high latitudes temperature changes. Thus, further work needs to be carried out to understand the deglacial AMOC evolution with the uncertainties in meltwater history. Finally, we do not find substantial changes in simulated Southern Hemisphere westerlies nor in the Southern Ocean meridional circulation during deglaciation, suggesting the need to better understand the processes leading to changes in southern high latitude atmospheric and oceanic circulation as well as the processes leading to the deglacial atmospheric CO₂ increase.