@article{fdi:010063736,
  title = {{I}nsights into iron sources and pathways in the {A}mazon {R}iver provided by isotopic and spectroscopic studies},
  author = {{M}ulholland, {D}. {S}. and {P}oitrasson, {F}. and {B}oaventura, {G}. {R}. and {A}llard, {T}. and {V}ieira, {L}. {C}. and {S}antos, {R}. {V}. and {M}ancini, {L}. and {S}eyler, {P}atrick},
  editor = {},
  language = {{ENG}},
  abstract = {{T}he present study investigated the weathering and transport mechanisms of {F}e in the {A}mazon {R}iver. {A} particular emphasis was placed on {F}e partitioning, speciation, and isotopic fractionation in the contrasting waters of the {S}olimoes and {N}egro rivers and their mixing zone at the beginning of the {A}mazon {R}iver. {S}amples collected in the end-member rivers and thirteen sites distributed throughout the mixing zone were processed through frontal vacuum filtration and tangential-flow ultrafiltration to separate the different suspended solid fractions, i.e., particulate ({P} > 0.45 mu m and {P} > 0.22 mu m), colloidal (0.22 mu m > {C} > 5 k{D}a) and truly dissolved elements ({TD} < 5 k{D}a). {T}he {F}e isotopic composition and electron paramagnetic resonance ({EPR}) species were measured on these different pore-sized fractions. {T}he acidic and organo-{F}e-rich waters of the {N}egro {R}iver displayed dissolved and colloidal fractions enriched in heavy isotopes (similar to 1.2 parts per thousand, in delta {F}e-57 values relative to {IRMM}-14), while the particulate fractions yielded light isotopic compositions of -0.344 parts per thousand for {P} > 0.22 mu m and -0.104 parts per thousand for {P} > 0.45 mu m fractions). {T}he mineral particulate-rich waters of the {S}olimoes {R}iver had dissolved and colloidal fractions with light isotopic composition (-0.532 parts per thousand and -0.176 parts per thousand, respectively), whereas the particulate fractions yielded delta {F}e-57 values close to those of the continental crust (i.e., -0.029 parts per thousand for {P} > 0.22 mu m and 0.028 parts per thousand for {P} > 0.45 mu m). {T}en kilometers downstream from the {N}egro and {S}olimoes junction, the concentrations of colloidal and dissolved {F}e species deviate markedly from conservative mixing. {A} maximum {F}e loss of 43 mu g/{L} (i.e., 50% of the dissolved and colloidal {F}e) is observed 110 km downstream from the rivers junction. {T}he contrasting {N}egro and {S}olimoes {R}ivers isotopic compositions along the pore-sized water fractions is attributable to the biogeochemical processes involving different types of upland soils and parental materials. {F}or instance, the isotopic composition of colloidal and dissolved {F}e from the {N}egro {R}iver are consistent with {F}e oxidation and complexation mechanisms at the interface between waterlogged podzols and river networks, as supported by strong organo-{F}e complexes signals observed by {EPR}. {C}onversely, the particulate and colloidal fractions from the {S}olimoes {R}iver have delta {F}e-57 consistent with strong mechanical erosion in the {A}ndean {C}ordillera and upland soils, as evidenced by high concentrations of {F}e3+-oxides sensu lato measured by {EPR}. {T}he massive dissolved and colloidal {F}e removal is associated with the evolution of the physical and chemical composition of the waters (i.e., ionic strength) during mixing, which influences organo-{F}e3+ and {F}e3+-oxyhydroxides stability. {S}everal models are discussed to explain {F}e non-conservative behavior, including dissociation of organo-{F}e complexes and the subsequent formation of solid {F}e3+-oxyhydroxides and semiquinone free radicals, as evidenced by {EPR} spectra demonstrating that organo-{F}e signals decrease as {F}e3+-oxyhydroxides and free radicals signals increase. {A}s in estuarine regions, the mechanisms involving {F}e transfer and loss in the mixing zone has a negligible effect on the bulk water {F}e isotopic composition. {T}his result suggests that a tropical basin similar to the {A}mazon {R}iver {B}asin delivers to the ocean waters with an {F}e isotopic composition similar to that of the {E}arth's continental crust.},
  keywords = {{AMAZONE} ; {BRESIL}},
  booktitle = {},
  journal = {{G}eochimica et {C}osmochimica {A}cta},
  volume = {150},
  numero = {},
  pages = {142--159},
  ISSN = {0016-7037},
  year = {2015},
  DOI = {10.1016/j.gca.2014.12.004},
  URL = {https://www.documentation.ird.fr/hor/fdi:010063736},
}