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Very low isotope ratio of iron in fine aerosols related to its contribution to the surface ocean
Author(s) -
Kurisu Minako,
Takahashi Yoshio,
Iizuka Tsuyoshi,
Uematsu Mitsuo
Publication year - 2016
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2016jd024957
Subject(s) - aerosol , isotope fractionation , hematite , ferrihydrite , isotope , fractionation , seawater , fraction (chemistry) , iron oxide , environmental chemistry , evaporation , chemistry , yield (engineering) , analytical chemistry (journal) , mineralogy , materials science , geology , oceanography , metallurgy , physics , organic chemistry , adsorption , quantum mechanics , thermodynamics
Seven size‐fractionated aerosol samples were collected from Hiroshima, Japan, and were analyzed in terms of chemical composition, soluble fraction of iron (Fe), Fe species, and Fe isotope ratios. The results suggested that Fe in fine particles contained a larger fraction of anthropogenic aerosols than coarse particles did. Iron in the fine particles was more soluble in simulated seawater (up to 25%) than that in the coarse particles and was in the form of Fe (hydr)oxide species, such as ferrihydrite or hematite. The Fe isotope ratios (δ 56 Fe) of the coarse particles (+0.04‰ to +0.30‰) were close to the crustal mean value (0.0‰). By contrast, the δ 56 Fe values of fine particles were much lower and ranged from −2.01‰ to −0.56‰. δ 56 Fe values of the soluble Fe fraction in the fine particles were remarkably low (−3.91 to −1.87‰), suggesting that anthropogenic aerosols yield soluble Fe with low δ 56 Fe values. Such low values could be explained by kinetic isotope fractionation during evaporation of Fe at high temperatures, coupled with the refractory characteristics of Fe. Marine aerosols from the Northwest Pacific were also analyzed. The δ 56 Fe values in the fine particles were also lower than those in the coarse particles. These results may be important to quantitatively estimate the contribution of anthropogenic Fe deposited on the surface ocean on the basis of the Fe isotopes.