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 a¤ects 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.

Astronomically Driven Variations in Depositional Environments in the South Atlantic During the Early Cretaceous

“…We argue that Aptian organic‐rich black shales (with high HI values) in Site 364 represent the strong influence of continental runoff from tropical South Africa, whereas carbonate horizons with low organic content (and low HI values) formed when the basin was influenced from the SW trade winds and more oxic conditions developed (when the Intertropical Convergence Zone was located in a relatively northern position). Climate model simulations support our hypothesis, demonstrating that the appearance of the Atlantic Ocean led to significant changes in the hydrological cycle and modulated the monsoonal‐influenced regions (Ohba & Ueda, ).…”

Mid-Pliocene global climate simulation with MRI-CGCM2.3: set-up and initial results of PlioMIP Experiments 1 and 2

“…Yukimoto et al, 2006b;Kitoh et al, 2007;Ohba and Ueda, 2010;Ueda et al, 2011). We employ a version with a triangular truncation at zonal wave number 42 (T42; an approximately 280 km transform grid) and a 30-layer hybrid sigma-pressure coordinate system with the top at 0.4 hPa.…”

Hadley circulation and precipitation changes controlling black shale deposition in the Late Jurassic Boreal Seaway

“…[]. Studies for the Cretaceous (highlighted below) provide some general insight on the dominant processes and feedback under the paleo‐Hadley cells during global greenhouse conditions that may well also have operated in the Jurassic and during other time periods of global warmth: Paleogeography affected the global large‐scale atmospheric and marine circulation via modulations (strength and position) of the Hadley‐Walker circulation and this affected regional precipitation [ Ohba and Ueda , ]. Lower latitudinal temperature gradients and poleward expansion of the Hadley cells, with the descending, subtropical limbs located at around 25–30° [ Hay et al ., ]. Large latitudinal net moisture changes associated with an intensification of Hadley cell circulation [ Manabe and Bryan , ]. A more vigorous terrestrial hydrological cycle leading to an increased nutrient flux to the oceans with implications for marine productivity and enhanced OC burial [ Hofmann and Wagner , ]. …”