Modern pollen signatures of Amazonian rivers and new insights for environmental reconstructions

Author(s)

Akabane, Thomas Kenji ^[1] ; Sawakuchi, Andre Oliveira ^[1] ; Chiessi, Cristiano Mazur ^[2] ; Kern, Andrea K. ^[1] ; Diaz Pinaya, Jorge Luiz ^[3] ; Tapias Ceccantini, Gregorio Cardoso ^[4] ; De Oliveira, Paulo Eduardo ^{[4, 1, 5]}

Affiliation

^[1] Univ Sao Paulo, Inst Geosci, Rua Lago 562, BR-05508080 Sao Paulo, SP - Brazil

^[2] Univ Sao Paulo, Sch Arts Sci & Humanities, Sao Paulo, SP - Brazil

^[3] Univ Sao Paulo, Polytech Sch, Sao Paulo, SP - Brazil

^[4] Univ Sao Paulo, Inst Biosci, Sao Paulo, SP - Brazil

^[5] Field Museum Nat Hist, Keller Sci Act Ctr, Chicago, IL 60605 - USA

• Document type: Journal article
• Source: PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY; v. 554, SEP 15 2020.
• Web of Science Citations: 0

Abstract

Paleoenvironmental reconstructions based on Amazonian fluvial and marine pollen data are often hindered due to the scarcity of modern calibration data. In Amazonia, rivers are the main pathways for pollen from upland and flooded forests to continental and marine sediment sinks. Linking pollen assemblages transported by rivers to watershed vegetation is crucial to interpret palynological archives. In order to constrain the interpretation of palynological archives, we analysed the pollen content of 36 riverbed sediment samples distributed from the mouth of the Ica River (ca. 68 degrees W) to the Amazon estuary (ca. 49 degrees W) with support of grain size and major element analyses of the inorganic sedimentary content. The palynological analysis shows a strong imprint of the lowland floodplain vegetation as the main source of the riverborne pollen. The upper reaches of the Amazon River present abundant Cecropia, reflecting early-successional stages induced by intense floodplain disturbance. The middle and lower reaches of the Amazon River exhibit a progressive increase in herbs mainly represented by Poaceae and Cyperaceae, related to wider floodplains covered by seasonally inundated vegetation. Floodplain forests of whitewater rivers (varzeas) are palynologically characterized by Iriartea, Mauritia, Ilex, Pseudobombax, Acalypha, and Luehea/Laetia, with high frequency of Cecropia or herbs, and montane taxa. At the black- and clearwater rivers, the igapo floodplain forests provide high percentages of Symmeria, Myrtaceae, and Alchornea, and can be distinguished by Sapium/Sebastiana, Piranhea, Amanoa, Pouteria, Ferdinandusa/Genipa, Attalea/Astrocatyum, and Eschweilera which suggest conditions of higher stability and mature forests. Contribution from the non-flooded uplands, Andean Mountains, and savannas/Cerrado occur, but their signals are blurred by the high pollen production of the lowland floodplains. Our data provide a calibration set for environmental reconstructions of river-influenced deposits across the Amazon including offshore areas of the most iconic riverine dominated landscape in the world. (AU)

• FAPESP's process: 12/50260-6 - Structure and evolution of the Amazonian biota and its environment: an integrative approach
• Grantee: Lúcia Garcez Lohmann
• Support Opportunities: BIOTA-FAPESP Program - Thematic Grants
• FAPESP's process: 11/06609-1 - Provenance, transport and storage of sediments in Amazon rivers
• Grantee: André Oliveira Sawakuchi
• Support Opportunities: Regular Research 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