Wetland expansion in Amazonia during the late Holocene and its implications to the global methane budget

• Grant number: 22/06440-1
• Support Opportunities: Generation Project Research Grant
• Duration: March 01, 2023 - February 29, 2028
• Field of knowledge: Physical Sciences and Mathematics - Geosciences - Geology
• Principal Investigator: Dailson José Bertassoli Junior
• Grantee: Dailson José Bertassoli Junior
• Host Institution: Instituto de Geociências (IGC). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated researchers: André Oliveira Sawakuchi ; Cristiano Mazur Chiessi ; Enno Schefuß ; Francisco William da Cruz Junior
• Associated scholarship(s): 23/15362-7 - The distribution of seasonally flooded areas in lowland Amazonia during the Holocene, BP.DR; 24/00766-8 - A multiproxy approach to reconstruct hydrological changes in Eastern Amazonia during the late Holocene;, BP.MS

Abstract

The 2.5-fold increase in atmospheric concentrations of methane (CH4) is thought to have been responsible for up to 0.5°C of anthropogenic global warming. In 2007, CH4 concentrations resumed rising at expressive rates after almost a decade of near-zero growth. The mechanisms behind this erratic behavior remain unclear. Still, several lines of evidence suggest that wetland areas, which account for roughly two thirds of natural CH4 emissions, played an important role. On a different time-scale, a similar debate has surrounded an anomalous increase in atmospheric CH4 concentrations during the mid- to late Holocene transition (ca. 4-5 ka). According to the IPCC AR5 and AR6, evidences for either natural or anthropogenic causes for this surge are still equivocal. Disentangling the impacts of different forcings is critical to understand the observed events and project future trends for atmospheric CH4 concentrations. Thus, we will test the hypothesis that the enlargement of floodplains and archipelagos within valleys of major Amazonian rivers drove the increase in global atmospheric CH4 concentrations during the late Holocene. We present an innovative approach based on biomarkers from marine sediment records and floodplains chronology to assess changes on CH4-producing land cover during the studied period. The obtained data will help to constrain confidence intervals for floodplain emissions during different time-frames. Results will also be compared to geochemical, isotopic and molecular signals to determine if changes in the hydrology of the Amazon River Basin are linked to the observed trends in CH4 emissions. This will shed new light onto potential feedback mechanisms of seasonally flooded areas under future climate scenarios. Meanwhile, the outcomes of this research initiative will provide derivative insights into pressing topics such as the improvement of natural emission scenarios in climate models and constraining the boundaries of the beginning of large-scale anthropogenic impacts (the 'Anthropocene'). It will also foster the training of high-level human resources and support the development of a new research line at the Institute of Geosciences of the University of São Paulo (IGc/USP). This research line will be mainly focused on the application of biomarkers to investigate climate change in tropical areas. (AU)