A GCM Study on Effects of Continental Drift on Tropical Climate at the Early and Late Cretaceous

Abstract

Simulations of the Early Cretaceous (120,000,000 years before the present day: 120 Ma) and the Last Cretaceous (65 Ma) have been performed using an atmospheric general circulation model (AGCM) coupled with a 1.5-layer reduced-gravity ocean model. After the initial spin-up period, both the runs are integrated for approximately 70 years. The simulation results confirm the occurrence of first-order changes in tropical atmospheric circulation in response to changes in the land/sea distribution. The simulation results show that the continental drift during the Cretaceous strongly affects the Walker and Hadley circulations. The birth of the Atlantic resulting from the breakup of the Gondwana continent causes splitting of a Walker circulation cell into two, and this in turn reduces the zonal gradient of the equatorial SST over the Pacific. The resultant SST warming in the equatorial Pacific enhances the Hadley circulation. The northward drift of the Indian continent causes significant SST warming in the Indian Ocean and intensifies the monsoon precipitation over Asia. It is also shown that the seasonal variations in the Asian monsoon are much stronger in the 65-Ma run than in the 120-Ma run. Interestingly, continental breakups cause the mega-monsoon system to split into distinct monsoon systems such as the Indian, South American, and African monsoon systems.