ENSO-Orchestrated Carbon Supply and Sequestration in Amazonian River Basins by Erosion-Sedimentation Processes
Rolf
Aalto, University of Washington, Seattle, USA, aalto@u.washington.edu
(Presenting)
Anthony
K
Aufdenkampe, Stroud Water Research Center, PA, USA, aufdenkampe@stroudcenter.org
Laurence
Maurice-Bourgoin, IRD, French Research Institute for the Development, Brasilia, Brazil, lmaurice@unb.br
Application of a new geochronological method quantifies century-scale floodplain sedimentation rates across a pristine 720,000 km2 basin covering the principal sediment and water sources for the Madeira River, the largest sediment source for the Amazon. Large, rapid-rise, cold-phase ENSO floods account for the preponderance of sediment accumulation and dominate sediment discharge from Andean tributaries into the large rivers of the Amazonian lowland, indicating considerable inter-annual variation of sediment supply and transport resulting from the interaction of Andean erosion and the dynamics of extreme climate. Transient, ENSO-driven processes control the formation of floodplains and sedimentary strata, and modulate the efflux, transport, floodplain storage, exchange due to channel migration, and downstream delivery of sediment and associated (adsorbed) carbon, nutrients, and pollutants to the Amazon main stem.
Such infrequent, extreme mechanisms of sediment and carbon transport suggest a three-step process could represent a major carbon sink in Amazonian foreland basins: 1) extensive Andean hillslope failure and channel migration during large La Niña associated storms mobilizes vast quantities of fresh organic matter and sediment with low organic carbon (OC) content; 2) within the river, mineral surfaces acquire normal OC loadings via sorption as they are rapidly evacuated from the mountainous source basins to adjacent foreland depocenters; and 3) deposited sediments preserve “fresh” carbon within organo-mineral complexes and by deep burial in point bars and “crevasse-splay” deposits that have little potential for exchange with the biosphere and atmosphere. Calculations suggest that this process could sequester 300-500 Mtonnes of carbon per event in the Amazonian foreland and regulate the supply of particulate OC to the lower Amazon.
Submetido por Rolf Erhart Aalto em 25-MAR-2004
Tema Científico do LBA: CD (Armazenamento e Trocas de Carbono)