[A-OS23] Atlantic climate variability, and its global impacts and predictability

[AOS23-P06] Investigating South American monsoon during mid-Pliocene

*Andrea Taschetto¹, Gabriel Pontes², Ilana Wainer², Alex Sen Gupta¹ (1.Climate Change Research Centre and ARC Centre for Excellence in Climate Extremes, University of New South Wales, Australia, 2.Department of Physical Oceanography, University of São Paulo, Brazil)

Keywords:mid-Pliocene, South America, precipitation, South Atlantic Convergence Zone, Atlantic ITCZ

South America receives more than 50% of its total annual rainfall from November to March, when convection increases over the Amazon Basin and the South Atlantic Convergence Zone (SACZ) strengthens, forming the South American Monsoon System (SAMS). Extreme SAMS events have great economical and societal impacts (e.g. agriculture, housing subject to flooding, water supply). Evaluation of possible changes in South America rainfall associated with warmer scenarios is of urgent demand. Here we investigate how Southern Hemisphere rainfall may had been different during the mid-Pliocene Warm Period (~3Ma), a time of mean global warming between 2-3ºC that share characteristics of the currently CO2-induced warming. We examine simulations undertaken as part of the Pliocene Model Intercomparison Project and performed climate model experiments using the atmospheric component of the NCAR Community Earth System Model (CESM) to understand the mid-Pliocene climate as well as to provide insights on possible rainfall changes in a warmer world. We show that higher rates of warming in the North Atlantic compared to the South Atlantic generated an interhemispheric temperature gradient that in turn enhanced the southward cross-equatorial energy flux by up to 48%. The enhanced energy flux equator resulted in a strengthening of the Southern Hemisphere Hadley circulation, that in turn intensified the South Atlantic Subtropical High. These atmospheric changes weakened and displaced the SACZ poleward. In addition, the intensified energy flux equator shifted the Atlantic Inter-Tropical Convergence Zone northward, weakening the contribution of oceanic moisture advection to the Amazon Basin and the SACZ. Curiously those changes in the mid-Pliocene relative to present day climate are not accompanied by significant variations in the Atlantic Meridional Overturning Circulation. The evaluation of the mid-Pliocene adds a constraint associated with differing rates of warming between hemispheres.