Collaborative Research: Episodic, ENSO-Orchestrated Carbon Sequestration in Amazonian River Basins by Erosion-Sedimentation Processes

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Abstract - Hernes - 0403478 This interdisciplinary group proposal addresses a three-step process that could represent a majorcarbon sink in Amazonian foreland basins. Stated as hypotheses, the proposal suggests: 1) extensiveAndean hillslope failure and channel migration during large La Nina associated storms mobilizes vastquantities of fresh organic matter and sediment with low organic carbon (OC) content ; 2) within theriver, mineral surfaces acquire normal OC loadings via sorption as they are rapidly evacuated from themountainous 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" depositsthat have little potential for exchange with the biosphere and atmosphere. Calculations presented in theProject Description (C.1.2) suggest that this process could sequester ~ 300 Mtonnes of carbon per event inthe Amazonian foreland. When extrapolated globally to other humid tropical regions, these estimates areequivalent to 50-100% of the average annual "missing carbon sink" or 50-100% of atmospheric CO2anomalies typically observed during La Nina.To explore these hypothesis, proposers will study 1) the rates and mechanics of sedimentmobilization, transport, and deposition of river sediment during extreme events, 2) the associations oforganic carbon with sediments at erosional and depositional sites, and 3) the transfer of OC from rapid(5 y) to slower (50 y) turnover pools, via sorption and deep burial processes. We will employ acombination of GIS analysis of satellite images to map changes associated with individual large storms(hillslope failures and river migration); field surveys of sediment transport processes; and laboratoryanalysis of archived and newly collected samples to determine organic carbon concentrations, sources andturnover times; sediment characteristics; and transport/deposition timing and rates (geochronology).The proposed project is a collaborative, multi-disciplinary, multi-national research effort thatbuilds upon a record of prior and current NSF-funded results of decadal-scale sediment fluxes and organiccarbon dynamics within river basins of the Amazon. In close coordination with sediment-flux,geochronological, geochemical, and process-mapping (GIS) studies conducted by scientists from Univ. ofWashington, scientists at Stroud Water Research Center and Univ. of California Davis will investigate thequantities, sources, and sequestration of organic carbon mobilized during by these geomorphologicalprocesses. In addition, this project benefits from a close working collaboration with the French Institut deRecherche pour le Developpement (IRD), with whom we will conduct fieldwork in the Andes andforeland basins of Bolivia and Peru during both the dry and wet seasons. Additional collaborations arewith the Univ. Nacional Agraria La Molina (UNALM) and the Univ. of California Santa Barabara. Thesecontinuing international collaborations offer considerable scientific and logistical advantages and costsavings for this current proposal to study the carbon transported and deposited by extreme storm events.If this research effort substantiates the primary hypothesis, such continental-scale, climate-driven,erosion-sedimentation processes will be demonstrated to represent substantial, previously unrecognizednatural carbon sinks of global significance. Furthermore, these processes could potentially result in thesequestration of similar quantities of carbon by anthropogenically accelerated erosion-sedimentation.Additionally, this research benefits anyone interested in the geochemical processes of organic carbonpreservation in sediment and soils or the timing/rates/mechanics of landsliding, sediment transport,channel-floodplain interaction, and sedimentary basin dynamics during extreme, ENSO-orchestratedfloods.The strong bridging between the disciplines of geomorphology, biogeochemistry and organicgeochemistry has broader impacts on earth science as a whole, by offering new perspectives that willfacilitate the development of new geochemical and GIS techniques. Enhanced collaboration with IRDsupports a productive and visible international, interdisciplinary scientific partnership. For example, ourprevious collaborative research with IRD resulted in new understandings of mercury contaminationdynamics within riparian food sources to indigenous human populations. The PIs have a record of publicoutreach, and this project will generate data products useful to educators and researchers, including ourown teaching and public presentations to both scientists and general audiences. Furthermore, this willprovide valuable research experience to many undergraduate and some graduate students in the USA andSouth America, including funds for these students to publish and present results at meetings