Evolution of the Atlantic Intertropical Convergence Zone, and the South American and African Monsoons Over the Past 95-Myr and Their Impact on the Tropical Rainforests
Acosta, R. Paul; Ladant, Jean-Baptiste; Zhu, Jiang; Poulsen, Christopher J.
2022-07
Citation
Acosta, R. Paul; Ladant, Jean-Baptiste ; Zhu, Jiang; Poulsen, Christopher J. (2022). "Evolution of the Atlantic Intertropical Convergence Zone, and the South American and African Monsoons Over the Past 95- Myr and Their Impact on the Tropical Rainforests." Paleoceanography and Paleoclimatology 37(7): n/a-n/a.
Abstract
The widening of the South Atlantic Basin led to the reorganization of regional atmospheric and oceanic circulations. However, the response of the Atlantic Intertropical Convergence Zone (ITCZ), and South American and African monsoons across paleoclimate states, especially under constant paleogeographic and climatic changes, has not been well understood. Here we report on paleoclimate simulations of the Cenomanian (∼95 Ma), early Eocene (∼55 Ma), and middle Miocene (∼14 Ma) using the Community Earth System Model version 1.2 to understand how the migration of the South American and African continents to their modern-day positions, uplift of the Andes and East African Rift Zone, and the decline of atmospheric CO2 changed the Atlantic ITCZ, and the South American and African monsoons and rainforests. Our work demonstrates that the South Atlantic widening developed the Atlantic ITCZ. The South Atlantic widening and Andean orogeny led to a stronger South American monsoon. We find the orogeny of the East African Rift Zone is the primary mechanism that strengthened the East African monsoon, whereas the West African monsoon became weaker through time as West Africa migrated toward the subtropics and CO2 levels fell below 500 ppm. We utilize the Köppen-Geiger Climate Classification as an indicator for maximum rainforest extent. We find that during the Cenomanian and early Eocene, a Pan-African rainforest existed, while the Amazon rainforest was restricted toward the northwestern corner of South America. During the middle Miocene, the Pan-African rainforest was reduced to near its modern-day size, while the Amazon rainforest expanded eastward.Plain Language SummaryThe rifting of the West Gondwana supercontinent from the middle Cretaceous led to the opening of the South Atlantic Basin and the reorganization of regional atmospheric and oceanic circulations. However, the evolution of the South American and African continents under constant paleogeographic and climatic changes has not been well understood. Here we report on paleoclimate simulations since the middle Cretaceous using the Community Earth System Model version 1.2 to understand how the widening of the South Atlantic Basin, uplift of the Andes and East African Rift Zone, and CO2 decline through time influenced the Atlantic Intertropical Convergence Zone (ITCZ), and the South American and African monsoons and rainforests. Our results suggest that both changes in geography and topography have a first-order control on the rainfall distribution of the Atlantic ITCZ, South American, and African monsoon. Increased atmospheric CO2 in the past enhanced tropical precipitation, but it does not determine where it occurs. Our work shows that when the South Atlantic Basin was narrowed, the eastern Amazon rainforest did not exist, while a Pan-African rainforest expanded toward the subtropics. As the South Atlantic Basin widened, the eastern Amazon rainforest formed, while the Pan-African rainforest shrunk to its modern-day size.Key PointsRifting of West Gondwana initiated the Atlantic Intertropical Convergence Zone and altered the South American and African monsoonsSimulations of Cenomanian, early Eocene, and middle Miocene indicate paleogeography instead of CO2 control monsoon distributionThrough time, changes in South American and African monsoon circulation influenced the evolution of the Amazon and African rainforestsPublisher
Wiley Periodicals, Inc. Springer
ISSN
2572-4517 2572-4525
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