High-Temperature Fe Isotope Geochemistry

Linking Chemical Heterogeneity to Lithological Heterogeneity of the Samoan Mantle Plume With Fe‐Sr‐Nd‐Pb Isotopes

“…(2007), the mixing of ∼6% of a recycled upper continental crust component and ∼94% of a depleted peridotite source (Ta'u source) can reproduce the 87 Sr/ 86 Sr value of the most extreme EM2 lava (ALIA‐D115‐21) from Samoa. The differentiated high‐silica igneous rocks (e.g., rhyolites, granites), which are primary component of the upper continental crust (UCC), have δ 57 Fe values of up to 0.9‰ but the average δ 57 Fe of all reported samples with SiO 2 > 60 wt.% is ∼0.3‰ (Johnson et al., 2020). The ancient (e.g., Proterozoic or late Archean) sedimentary rocks mainly show average UCC‐like (δ 57 Fe = 0.13 ‰, Gong et al., 2017) or much lighter Fe isotopic compositions (Johnson et al., 2008).…”

Biogeochemistry of iron in coastal Antarctica: isotopic insights for external sources and biological uptake in the Amundsen Sea polynyas

“…Indeed, van Manen et al (2022) found the mCDW outflow was enriched in refractory particulate Fe (most likely lithogenic Fe) compared to labile particulate Fe and dissolved Fe. Further, +5.78 ‰ is much heavier than any δ 56 Fe values reported for any dFe source in the marine system (Fitzsimmons and Conway, 2023;Johnson et al, 2020). If we instead assign a crustal signature to δ 56 Fe icemelt (+0.09 ‰), the constrained contribution of 0.6 % from ice shelf melt could not result in the δ 56 Fe outflow as observedthe estimated overall δ 56 Fe signal in the outflow would be -0.61 ‰, which is much lighter than the observed δ 56 Fe outflow (-0.23 ± 0.15 ‰).…”

“…Typically, RD-derived dFe initially ranges from − 2 to − 1.5 ‰; but the values can become even lower following precipitation of relatively heavy Fe(III) oxyhydroxides (typically ≥ − 3.5 ‰) (Crosby et al, 2007;Fitzsimmons and Conway, 2023;Homoky et al, 2009;Severmann et al, 2010). To date, a range of endmember δ 56 Fe compositions have been previously reported or assumed for the signature of the benthic flux of Fe derived from RD into bottom waters (-3.5 to -0.93 ‰ as summarised by Johnson et al (2020) and Fitzsimmons and Conway (2023)), with variability likely dependent on sediment and bottom water conditions (e.g., redox cycles in porewater particulates).…”

“…For example, reductive dissolution (RD) leads to elevated concentrations of reduced Fe in porewater that can diffuse into bottom waters, where the size of the flux depends on the absence/ presence (and thickness) of an overlying oxygenated surface sediment layer where Fe 2+ can be oxidized prior to diffusion. However, likely due to differences in the intensity of reduction processes within sediments and oxidation of Fe in an oxygenated surface sediment layer or in near bottom seawater, reductive dissolution is characterized by a wide range of isotopically light signatures (-3.5 to -1‰, e.g., Homoky et al, 2021;Johnson et al, 2020;Severmann et al, 2006). Conversely, nonreductive dissolution (NRD) induced via particle and colloid weathering and ligand mediated dissolution, often facilitated by sediment resuspension, have been suggested to exhibit a relatively consistent isotopic signature (~+0.1 ‰, e.g., Homoky et al, 2013;Homoky et al, 2021;Radic et al, 2011) compared to RD.…”