@article{PAR00002675,
  title = {{L}imited iron isotope variations in recent lateritic soils from {N}simi, {C}ameroon : implications for the global {F}e geochemical cycle},
  author = {{P}oitrasson, {F}. and {V}iers, {J}. and {M}artin, {F}. and {B}raun, {J}ean-{J}acques},
  editor = {},
  language = {{ENG}},
  abstract = {{L}aterites are oxidized {F}e-rich soils covering one third of the continents and are drained by half of the continental waters. {T}hey therefore represent a key component of the iron geochemical cycle at the {E}arth's surface, yet no iron isotope study has been conducted on recent laterites so far. {B}uilding on previous integrated morpho-pedological studies of soils located in an equatorial rainforest, {S}outhern {C}ameroon, we have undertaken a mineralogical, elemental and isotopic study of iron in two lateritic profiles. {O}ne is a borehole 3620 cm deep going to the parent granodioritic rock, located at the top of a hill, whereas the other is 675 cm deep and is located downhill. {M}ossbauer spectroscopy reveals that typically >= 96% of the soil's iron is held in nanocrystalline hematite and goethite. {I}ron isotope measurements performed by plasma source mass spectrometry show that {F}e isotopic equilibrium was rarely reached between these iron oxide and hydroxide despite their small size. {O}verall, it is found that most samples display iron isotope signatures very close to the mean crustal value, with a maximum range of 0.2 parts per thousand in delta {F}e-57. {G}iven that lateritic soils evolve over millions of years, show large variations in {F}e concentrations and mineralogical abundances, this range is surprisingly small when compared to other {F}e isotope studies of soils from different climatological contexts, that can easily show delta {F}e-57 ranges in excess of 1 parts per thousand. at the bulk sample scale. {T}he most likely explanation of this finding is that despite notable vertical and lateral {F}e mobility in the studied laterites from {C}ameroon, as computed using the open-system mass fraction transport function, tau({F}e,w), iron remained mostly in the oxidized form as shown by {M}ossbauer spectroscopy. {T}his probably results from the strong bioturbation and pedoturbation of these lateritic soils that lead them to remain porous over a large thickness and facilitated the flow of oxygenated waters from the surface down to the saprolite horizon. {T}his study therefore reveals that soils that remained as an open system for iron do not necessarily show large {F}e isotopic variations. {I}t is suggested that the {F}e drained from such lateritic soils should have delta {F}e-57 values within similar to 0.1 parts per thousand. of that of the continental crust. {T}his is in contrast with previous soil studies, notably from sites located at higher latitudes, that imply that these soils should release isotopically more variable {F}e to surface waters. {S}uch possible contrasted isotopic signatures from different surface waters will likely lead to an isotopically heterogeneous ocean given the short residence time of {F}e in seawater.},
  keywords = {{L}aterite ; {S}oil ; {G}oethite ; {H}ematite ; {I}ron isotopes ; {C}ontinental surfaces},
  booktitle = {},
  journal = {{C}hemical {G}eology},
  volume = {253},
  numero = {1-2},
  pages = {54--63},
  ISSN = {0009-2541},
  year = {2008},
  DOI = {10.1016/j.chemgeo.2008.04.011},
  URL = {https://www.documentation.ird.fr/hor/{PAR}00002675},
}