Abstract
The Fe isotope composition of Proterozoic to modern clastic sedimentary rocks and aerosols defines a range ind 56 Fe values that is only slightly more variable than the range of Fe isotope com- positions measured in terrestrial igneous rocks, indicating that chemical weathering, sedimentary transport, and diagenesis play only a minor role in producing Fe isotope variations in environ- ments where Fe redox conditions have been controlled by current levels of atmospheric oxygen. In contrast, the Fe isotope composi- tions of hot fluids ( .300 8C) from mid-ocean-ridge (MOR) spread- ing centers define a narrow range that is shifted to lower d 56 Fe values by 0.2‰-0.5‰ as compared to igneous rocks. These new data allow a conceptual model for the Fe isotope composition of the oxic oceans that predicts large ranges in Fe isotope composition under conditions of changing aerosol and MOR Fe fluxes, such as during periods of major worldwide glaciation.
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