title: Young organic matter as a source of carbon dioxide outgassing from Amazonian rivers.
abstract: Rivers are generally supersaturated with respect to carbon dioxide, resulting in large gas evasion fluxes that can be a significant component of regional net carbon budgets. Amazonian rivers were recently shown to outgas more than ten times the amount of carbon exported to the ocean in the form of total organic carbon or dissolved inorganic carbon. High carbon dioxide concentrations in rivers originate largely from in situ respiration of organic carbon, but little agreement exists about the sources or turnover times of this carbon. Here we present results of an extensive survey of the carbon isotope composition (13C and 14C) of dissolved inorganic carbon and three size-fractions of organic carbon across the Amazonian river system. We find that respiration of contemporary organic matter (less than five years old) originating on land and near rivers is the dominant source of excess carbon dioxide that drives outgassing in medium to large rivers, although we find that bulk organic carbon fractions transported by these rivers range from tens to thousands of years in age. We therefore suggest that a small, rapidly cycling pool of organic carbon is responsible for the large carbon fluxes from land to water to atmosphere in the humid tropics.
authors.affiliation: School of Oceanography, University of Washington, Seattle, Washington 98195, USA. emiliomayorga@alum.mit.edu
authors.forename: Emilio
authors.initials: E
authors.lastname: Mayorga
authors.forename: Anthony K
authors.initials: AK
authors.lastname: Aufdenkampe
authors.forename: Caroline A
authors.initials: CA
authors.lastname: Masiello
authors.forename: Alex V
authors.initials: AV
authors.lastname: Krusche
authors.forename: John I
authors.initials: JI
authors.lastname: Hedges
authors.forename: Paul D
authors.initials: PD
authors.lastname: Quay
authors.forename: Jeffrey E
authors.initials: JE
authors.lastname: Richey
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Brown
mesh_terms: D001272:Atmosphere / Q000737:chemistry; D001938:Brazil; D002245:Carbon Dioxide / Q000032:analysis / Q000378:metabolism*; D002247:Carbon Isotopes; D005740:Gases / Q000032:analysis / Q000378:metabolism; D009792:Oceans and Seas; D009930:Organic Chemicals / Q000737:chemistry / Q000378:metabolism*; D045483:Rivers / Q000737:chemistry*; D012623:Seawater / Q000737:chemistry; D013997:Time Factors; D014329:Tropical Climate; D014835:Volatilization
chemical_list: D002247:Carbon Isotopes; D005740:Gases; D009930:Organic Chemicals; D002245:Carbon Dioxide