17:15 〜 18:30
[MIS16-P25] A study on the responses of the climate field in the Cretaceous to orbital parameter changes
★Invited Papers
キーワード：白亜紀、地球軌道要素、極域気温増幅、アジアモンスーン
Insolation changes to the orbital parameters, such as the eccentricity, obliquity, and precession, have a great impact on the climate. In particular, it is well-known that there have been periodic changes in ice sheets and climatic fields in the past hundreds of thousands of years, related to changes in orbital parameters. The physical mechanism of these changes has been investigated by using numerical simulations. The Cretaceous is known as one of the warmest periods in the Phanerozoic due to increased levels of greenhouse gases, and the proxies indicate the striking temperature amplifications in the high-latitude and polar regions, resulting in a smaller equator-to-pole temperature difference. Also, the Cretaceous cyclic sediments recording signals related to changes in the orbital parameters have been found in many parts of the world. In this study, we investigated the response of the Cretaceous climate field to changes in the orbital parameters using an atmospheric-ocean vegetation coupling model, MIROC4m-LPJ and also compared it with the proxy data and orbital parameter sensitivity experiments using the present-day configuration.
In the high latitude regions, the change in temperature with respect to the change in the orbital parameters is noticeable in the Cretaceous experiment. In particular, in conditions where the northern hemisphere summer is at perihelion and the obliquity is higher than the present-day value, polar amplification as shown by Cretaceous proxy data is obtained. By comparing the hydrological cycle responses in the present day and the Cretaceous, it was found that the fluctuation of the precipitation in East Asia due to orbital parameter changes is larger in the Cretaceous. This is attributed to the major structural changes in the East Asian summer monsoon in the Cretaceous. Furthermore, as a result, the variety of vegetation across East Asia in the Cretaceous has increased.
In the high latitude regions, the change in temperature with respect to the change in the orbital parameters is noticeable in the Cretaceous experiment. In particular, in conditions where the northern hemisphere summer is at perihelion and the obliquity is higher than the present-day value, polar amplification as shown by Cretaceous proxy data is obtained. By comparing the hydrological cycle responses in the present day and the Cretaceous, it was found that the fluctuation of the precipitation in East Asia due to orbital parameter changes is larger in the Cretaceous. This is attributed to the major structural changes in the East Asian summer monsoon in the Cretaceous. Furthermore, as a result, the variety of vegetation across East Asia in the Cretaceous has increased.