A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

Organic and inorganic carbon dynamics within waters of the AmazonBasin: Stable and radio-isotope constraints on sources ofoutgassed carbonAnthony Aufdenkampe , School of Oceanography, University of Washington, SeattleWA 98195-5351, USA. anthonya@u.washington.eduMayorga, E., School of Oceanography, University of Washington, Seattle, WA USAMasiello, C. A., Center for Accelerator Mass Spectrometry, Lawrence LivermoreNational Laboratory, Livermore, CA, USAQuay, P. D., School of Oceanography, University of Washington, Seattle, USAHedges, J. I., School of Oceanography, University of Washington, Seattle, USARichey, J. E., School of Oceanography, University of Washington, Seattle, USAKrusche, A. V., Centro de Energia Nuclear na Agricultura (CENA), Universidade de SaoPaulo, BrazilLlerena, C. A., Facultad de Ciencias Forestales, Universidad Nacional Agraria LaMolina, Lima, PeruForsberg, B. R., Instituto Nacional de Pesquisas da Amazonia (INPA), Manaus, BrazilQuintanilla, J., Instituto de Investigaciones Quimicas, Universidad Mayor de San Andres,La Paz, BoliviaParallel Session: River water as a medium for transport in AmazoniaABSTRACT:Recently, Richey et al. (2002, Nature Vol. 416, p.617) demonstrated that outgassingof carbon dioxide from river and wetland waters of the central is a significant fluxrelative to terrestrial carbon sequestration. An outstanding issue raised by this study isthat the source of this outgassed carbon remains largely unconstrained. Stable and radioisotopescompositions of river-borne carbon offers one approach to constraining sources.As part of the CAMREX project studying the riverine biogeochemistry of the Amazonbasin, we have recently surveyed 14 C and 13 C isotopic compositions of four principalfractions – dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), fineparticulate organic carbon (FPOC) and coarse particulate organic carbon (CPOC). The~30 sites surveyed for these four coexisting fractions cover a wide range of environments– from both Andean and lowland headwaters to the mainstem Amazon – at several stagesof the hydrograph. These preliminary data yield a number of important insights topotential sources. Perhaps most striking are downstream trends of decreasing ages forcarbon in all fractions, indicating that river-borne carbon is remineralized and replaced ontime scales that are short with respect to transit down the river system.