Past Amazon precipitation under different Atlantic Meridional Overturning Circulation and sea surface temperature scenarios of the last deglaciation

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Grigolato, Julia ; Chiessi, Cristiano M. ; Bertassoli Jr, Dailson J. ; Campos, Marilia C. ; Shimizu, Marilia H. ; Magalhaes, Rene H. ; Nace, Trevor ; Sawakuchi, Andre O. ; Wahnfried, Ingo D. ; Neri, Rafael ; Cunha, Alan C. ; Silva, Cleverson G. ; Baker, Paul A. ; Govin, Aline ; Zabel, Matthias

• Document type: Journal article
• Source: QUATERNARY SCIENCE REVIEWS; v. 362, p. 14-pg., 2025-08-15.

Abstract

Changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC) have been suggested to affect the mean latitude of the tropical rain-belt and the intensity of the South American Monsoon System. These changes impact Amazonian precipitation patterns, which play a critical role in sustaining the most biodiverse ecosystem on Earth. Consequently, the projected decrease in AMOC strength in response to anthropogenic climate change may constitute a serious risk to the stability of the Amazon rainforest. AMOC strength was significantly reduced during most millennial-scale stadials (e.g., Heinrich Stadials (HS)) of the last glacial and deglacial periods. These stadials offer valuable opportunities to understand the impact that slowdowns of the AMOC, as well as other concurrent changes of large-scale ocean and atmospheric conditions (e.g., sea ice extent, surface winds, ice sheet height and extent, sea level), had on Amazonian precipitation. Here we reconstruct precipitation changes that occurred in the Amazon Basin from 27.4 to 3.6 cal ka BP with a focus on Heinrich Stadial 1 (HS1, 18.6-14.6 cal ka BP) and the Younger Dryas (YD, 12.9-11.7 cal ka BP, also known as Heinrich stadial 0). To achieve this, two marine sediment cores collected from the slope of the western equatorial Atlantic were radiocarbon dated and analyzed for major elemental composition. To support the interpretation of our data, we employed (i) a comprehensive evaluation of major elemental composition in suspended sediments from the major rivers of the Amazon Basin, (ii) a regional compilation of tropical South American hydroclimate records, and (iii) outputs from a transient fully-coupled climate model run covering the last 21 ka. Our results reveal different precipitation patterns in the Amazon Basin during HS1 and the YD that were related to heterogenous displacements of the Intertropical Convergence Zone (ITCZ) and heterogenous sea surface temperature (SST) anomalies in the western equatorial Atlantic and the eastern equatorial Pacific. These changes were at least in part associated to different AMOC scenarios. Furthermore, two distinct phases are discernible within HS1 (i.e., HS1a from 18.6 to 16.6 cal ka BP and HS1b from 16.6 to 14.6 cal ka BP), each being characterized by variations in the relative concentrations of Al, K, Ca, Ti, and Fe. We interpret these sediment composition changes to be related to a shift in the main precipitation locus, that moved from the central Andes (HS1a) to southeastern Amazonia (HS1b). During HS1b, the low-pressure region over the eastern equatorial Pacific (due to a stronger positive SST anomaly in the eastern equatorial Pacific relative to the western equatorial Atlantic) produces, together with a shift further south in the ITCZ position, a positive precipitation anomaly over the southern and eastern Amazon Basin. Precipitation anomalies during the YD were apparently less conspicuous, located in the eastern Amazon Basin, but we cannot exclude the possibility of major elemental signals to be affected by a significant sea level rise that increased accommodation space for terrigenous sediments on the continental shelf. The heterogeneous response of precipitation under different AMOC scenarios reinforces the importance of hightemporal resolution paleoclimate studies from the Amazon Basin and the need to spatially compartmentalize the precipitation responses to these events due to the continental dimension of the basin. (AU)

• FAPESP's process: 22/06452-0 - The South Atlantic on a 2°C warmer planet
• Grantee: Marília de Carvalho Campos Garcia
• Support Opportunities: Generation Project Research Grant
• FAPESP's process: 23/05764-0 - The South Atlantic on a 2°C warmer planet
• Grantee: Marília de Carvalho Campos Garcia
• Support Opportunities: Scholarships in Brazil - Generation Project
• FAPESP's process: 22/07285-0 - Assessing the sources of terrigenous sediments deposited in the western equatorial Atlantic via ICP-OES analyses
• Grantee: Júlia Grigolato Iani
• Support Opportunities: Scholarships abroad - Research Internship - Master's degree
• FAPESP's process: 18/23899-2 - Trans-Amazon Drilling Project: origin and evolution of the forests, climate, and hydrology of the South American tropics
• Grantee: André Oliveira Sawakuchi
• Support Opportunities: Research Program on Global Climate Change - Thematic Grants
• FAPESP's process: 18/15123-4 - Past perspectives on tipping elements of the climate system: the Amazon Rainforest and the Atlantic Meridional Overturning Circulation (PPTEAM)
• Grantee: Cristiano Mazur Chiessi
• Support Opportunities: Research Grants - Research Program on Global Climate Change - Young Investigators - Phase 2
• FAPESP's process: 19/24349-9 - Assessing the effects of past and future climate change on Amazonian biodiversity (CLAMBIO)
• Grantee: Cristiano Mazur Chiessi
• Support Opportunities: BIOTA-FAPESP Program - Regular Research Grants
• FAPESP's process: 22/06440-1 - Wetland expansion in Amazonia during the late Holocene and its implications to the global methane budget
• Grantee: Dailson José Bertassoli Junior
• Support Opportunities: Generation Project Research Grant
• FAPESP's process: 19/24977-0 - Environmental signals recorded in modern sediments of tropical South American rivers
• Grantee: Dailson José Bertassoli Junior
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 21/08085-1 - Abrupt changes in the strength of the Atlantic meridional overturning circulation and its impacts over Amazonian precipitation and vegetation during the last two glacial periods
• Grantee: Renê Hamada Magalhães
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)
• FAPESP's process: 21/00853-0 - Modern terrigenous sediment sources and past changes in precipitation over tropical South America recorded in terrigenous sediments deposited in the western tropical Atlantic
• Grantee: Júlia Grigolato Iani
• Support Opportunities: Scholarships in Brazil - Master