TY - JOUR
T1 - Iron isotopic fractionation during continental weathering
AU - Fantle, Matthew S.
AU - DePaolo, Donald J.
N1 - Funding Information:
This work was partially supported by a NASA ESS Graduate Fellowship to MSF and by NSF Grant EAR-9909639. Major funding was provided by the Director, Office of Science, Basic Energy Sciences, Chemical Sciences, Biosciences, and Geosciences Division of the U.S. Department of Energy under Contract No. De-AC03-76SF00098. Samples of core LL44-GPC3 were provided by Dr. Frank Kyte (UCLA). Tom Owens helped with mass spectrometric analyses. The authors also thank Ryan Petterson for assistance with river sampling and Ron Amundson for advice and help with soil sampling.
PY - 2004/12/15
Y1 - 2004/12/15
N2 - The effect of continental weathering on the iron isotope compositions of natural materials is investigated. Unweathered igneous rocks, pelagic clay, and dust fall within the range δ56 Fe=0±0.3‰. Rivers with large suspended loads also have δ56Fe values near zero. Dilute streams have δ56Fe values that trend towards lower δ56Fe (∼-1) suggesting that dissolved riverine iron is isotopically light relative to igneous rocks. Bulk soil and soil leaches display systematically different δ56Fe profiles, indicating that isotopically distinct Fe pools are generated during pedogenesis. Nannofossil ooze, which contains Fe scavenged from the ocean water column, has δ56Fe≉0, but is consistent with seawater dissolved Fe having negative δ56Fe. It is inferred that continental weathering under modern oxidizing Earth surface conditions preferentially releases dissolved Fe with negative δ56Fe, which is transported in rivers to the ocean. A preliminary analysis of the marine Fe budget suggests that riverine Fe has a substantial role in determining the δ56Fe of both the modern and ancient oceans, but other inputs, particularly that from diagenesis of marine sediments, may also be important. Since the chemical pathways of Fe processing during weathering are dependent on oxidation state and biological activity, Fe isotopes may prove useful for detecting changes in these parameters in the geologic past.
AB - The effect of continental weathering on the iron isotope compositions of natural materials is investigated. Unweathered igneous rocks, pelagic clay, and dust fall within the range δ56 Fe=0±0.3‰. Rivers with large suspended loads also have δ56Fe values near zero. Dilute streams have δ56Fe values that trend towards lower δ56Fe (∼-1) suggesting that dissolved riverine iron is isotopically light relative to igneous rocks. Bulk soil and soil leaches display systematically different δ56Fe profiles, indicating that isotopically distinct Fe pools are generated during pedogenesis. Nannofossil ooze, which contains Fe scavenged from the ocean water column, has δ56Fe≉0, but is consistent with seawater dissolved Fe having negative δ56Fe. It is inferred that continental weathering under modern oxidizing Earth surface conditions preferentially releases dissolved Fe with negative δ56Fe, which is transported in rivers to the ocean. A preliminary analysis of the marine Fe budget suggests that riverine Fe has a substantial role in determining the δ56Fe of both the modern and ancient oceans, but other inputs, particularly that from diagenesis of marine sediments, may also be important. Since the chemical pathways of Fe processing during weathering are dependent on oxidation state and biological activity, Fe isotopes may prove useful for detecting changes in these parameters in the geologic past.
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U2 - 10.1016/j.epsl.2004.10.013
DO - 10.1016/j.epsl.2004.10.013
M3 - Article
AN - SCOPUS:10644251963
SN - 0012-821X
VL - 228
SP - 547
EP - 562
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
IS - 3-4
ER -