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

Abstract

Part of the uncertainties of a possible future dieback of the Amazon Rainforest are related to another similarly uncertain tipping element of the climate system: the Atlantic Meridional Overturning Circulation (AMOC). Indeed, a shutdown/marked slowdown event of the AMOC may significantly redistribute surface heat in the Atlantic Ocean strongly affecting Amazonian precipitation and vegetation. Marine sediment cores from the Atlantic Ocean recorded repeated shutdown/marked slowdown events of the AMOC during the last glacial period, holding a wealth of much-needed information not available in the instrumental record. Yet, the paucity of records hampers the detailed characterization of the consequences of such AMOC shutdown/marked slowdown events to Amazonian precipitation and vegetation. Here, we will investigate abrupt changes in the upper Western tropical Atlantic Ocean as well as in Amazonian precipitation and vegetation during all AMOC shutdown/marked slowdown events of the last two glacial periods. Therefore, we will perform the following analyses in a carefully selected marine sediment core influenced by the Amazon River discharge: (I) radiocarbon in planktonic foraminifera and stable oxygen isotopes in epibenthic foraminifera (for the production of an age model); (II) paired stable oxygen isotopes and Mg/Ca in planktonic foraminifera (proxies for the stratification of the upper water column, temperature and salinity); and (III) stable hydrogen and carbon isotopes of plant-wax-derived long-chain n-alkanes (proxies for the amount of rainfall and the main types of vegetation, respectively). By doing this, we will provide an in-depth understanding of the responses and internal feedbacks of 2 Amazonia and the Western tropical Atlantic for abrupt climate changes of the last two glacial periods, helping to constrain possible future scenarios for Amazonia and the Atlantic Ocean. (AU)