HR: 13:40h
AN: B13G-01 INVITED    [Abstracts]
TI: Rejuvenation and aging of carbon in rivers: Sources, exports and interactions among fractions in the Amazon and other systems
AU: * Mayorga, E
EM: emiliomayorga@gmail.com
AF: Rutgers, The State University of New Jersey, Institute of Marine and Coastal Sciences 71 Dudley Rd., New Brunswick, NJ 08901-8521, United States
AU: Aufdenkampe, A
EM: aufdenkampe@stroudcenter.org
AF: Stroud Water Research Center, Avondale, Avondale, PA 000, United States
AU: Masiello, C
EM: masiello@rice.edu
AF: Rice University, Department of Earth Science, Houston, TX 000, United States
AU: Krusche, A
EM: alex@cena.usp.br
AF: Centro de Energia Nuclear na Agricultura, Piracicaba, Piracicaba, SP 000, Brazil
AU: Quay, P
EM: pdquay@u.washington.edu
AF: University of Washington, School of Oceanography, Seattle, WA 000, United States
AU: Richey, J
EM: jrichey@u.washington.edu
AF: University of Washington, School of Oceanography, Seattle, WA 000, United States
AU: Seitzinger, S
EM: sybil@marine.rutgers.edu
AF: Rutgers, The State University of New Jersey, Institute of Marine and Coastal Sciences 71 Dudley Rd., New Brunswick, NJ 08901-8521, United States
AB: Carbon in all its forms plays a key role in riverine ecosystems. Organic carbon (OC) sustains heterotrophic activity that produces CO2 and interacts with minerals through sorptive processes. Dissolved inorganic carbon (DIC) serves as a source for carbon fixation by autotrophs and as a key control on geochemical reactions. Organic and inorganic carbon are subject to interconversion through biologically mediated processes. In turn, they are part of an open fluvial system that receives exports from terrestrial environments in the form of OC, respired soil CO2, and weathering products; processes allocthonous carbon within its channels; sequesters OC for tens to thousands of years through floodplain sediment deposition; interacts with the atmosphere via gas exchange; and ultimately transports carbon to the oceans or inland lakes. Natural 13C and 14C isotopes provide a unique capability to identify the sources of carbon to rivers, processes leading to its transformation in transit, and residence times on land and within rivers. They can also provide an indicator of the degree of biologically mediated coupling between DIC and OC fractions, We illustrate the downstream evolution of DIC and OC fractions in the Amazon river system, discussing the extent and controls on coupling among fractions. Previous results demonstrate that: respiratory generation of CO2 in the lowlands can come to dominate the isotopic composition of DIC, essentially flushing out and replacing DIC via evasion; the OC fueling this respiration is often a very small, labile component effectively decoupled from bulk OC fractions; and in turbid systems with abundant sediment supplies, sorptive protection on mineral surfaces may decouple DOC and POC and couple POC to the upstream sediment erosion and depositional cycles. As a result, we observe longitudinal trends towards DIC equilibration with the labile fraction of OC, reaching or approaching 14C values close to the atmosphere's. POC responds strongly to sediment dynamics, which may result in strong seasonal and longitudinal variability in age overprinted over a broader long-term trend towards younger POC downstream. In contrast, bulk DOC often appears distinct from DIC and POC and displays a remarkable uniformity in age (decades) across all systems, unless autotrophic production is pervasive. Finally, we assess global patterns in riverine carbon fraction age and coupling among fractions, comparing them to those in the Amazon and framing them in the context of global patterns of carbon fraction distribution and flux to the oceans.
DE: 1030 Geochemical cycles (0330)
DE: 1040 Radiogenic isotope geochemistry
DE: 1615 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912)
DE: 1806 Chemistry of fresh water
DE: 9360 South America
SC: Biogeosciences [B]
MN: 2007 Fall Meeting