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

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0403722MontgomeryThis interdisciplinary group proposal addresses a three-step process that could represent a major carbon 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 vast quantities 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 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 presented in theProject Description (C.1.2) suggest that this process could sequester ~ 300 Mtonnes of carbon per event in the 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 CO2 anomalies typically observed during La Nina.To explore these hypothesis, proposers will study 1) the rates and mechanics of sediment mobilization, 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 a combination 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 laboratory analysis 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 that builds 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. of Washington, scientists at Stroud Water Research Center and Univ. of California Davis will investigate thequantities, sources, and sequestration of organic carbon mobilized during by these geomorphological processes. 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 and foreland 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. These continuing 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 unrecognized natural 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 organic geochemistry has broader impacts on earth science as a whole, by offering new perspectives that will facilitate the development of new geochemical and GIS techniques. Enhanced collaboration with IRDsupports a productive and visible international, interdisciplinary scientific partnership. For example, our previous collaborative research with IRD resulted in new understandings of mercury contamination dynamics 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 our own teaching and public presentations to both scientists and general audiences. Furthermore, this will provide valuable research experience to many undergraduate and some graduate students in the USA and South America, including funds for these students to publish and present results at meetings." VMATHIS PFRM1036 04/20/2004 14:26:40:33 1