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Volume 14, issue 22
Atmos. Chem. Phys., 14, 12415–12428, 2014
https://doi.org/10.5194/acp-14-12415-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 14, 12415–12428, 2014
https://doi.org/10.5194/acp-14-12415-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 27 Nov 2014

Research article | 27 Nov 2014

Chemistry and mineralogy of clay minerals in Asian and Saharan dusts and the implications for iron supply to the oceans

G. Y. Jeong1 and E. P. Achterberg2 G. Y. Jeong and E. P. Achterberg
  • 1Department of Earth and Environmental Sciences, Andong National University, Andong 760-749, Republic of Korea
  • 2GEOMAR Helmholtz Centre for Ocean Research, Kiel, 24148 Kiel, Germany

Abstract. Mineral dust supplied to remote ocean regions stimulates phytoplankton growth through delivery of micronutrients, notably iron (Fe). Although attention is usually paid to Fe (hydr)oxides as major sources of available Fe, Fe-bearing clay minerals are typically the dominant phase in mineral dust. The mineralogy and chemistry of clay minerals in dust particles, however, are largely unknown. We conducted microscopic identification and chemical analysis of the clay minerals in Asian and Saharan dust particles. Cross-sectional slices of dust particles were prepared by focused ion beam (FIB) techniques and analyzed by transmission electron microscopy (TEM) combined with energy dispersive X-ray spectroscopy (EDXS). TEM images of FIB slices revealed that clay minerals occurred as either nano-thin platelets or relatively thick plates. Chemical compositions and lattice fringes of the nano-thin platelets suggested that they included illite, smectite, illite–smectite mixed layers, and their nanoscale mixtures (illite–smectite series clay minerals, ISCMs) which could not be resolved with an electron microbeam. EDXS chemical analysis of the clay mineral grains revealed that the average Fe content was 5.8% in nano-thin ISCM platelets assuming 14% H2O, while the Fe content of illite and chlorite was 2.8 and 14.8%, respectively. In addition, TEM and EDXS analyses were performed on clay mineral grains dispersed and loaded on micro-grids. The average Fe content of clay mineral grains was 6.7 and 5.4% in Asian and Saharan dusts, respectively. A comparative X-ray diffraction analysis of bulk dusts showed that Saharan dust was more enriched in clay minerals than Asian dust, while Asian dust was more enriched in chlorite. Clay minerals, in particular nanocrystalline ISCMs and Fe-rich chlorite, are probably important sources of Fe to remote marine ecosystems. Further detailed analyses of the mineralogy and chemistry of clay minerals in global mineral dusts are required to evaluate the inputs of Fe to surface ocean microbial communities.

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Mineral dust supplies iron to remote oceans, stimulating phytoplankton growth and carbon dioxide decrease. Iron-bearing clay minerals are the dominant phase in mineral dust. However, their mineralogical properties are largely unknown. We first determined microstructures and chemical compositions of the clay minerals in individual dust particles by transmission electron microscopy. Nanocrystalline illite-smectite series clay minerals and iron-rich chlorite are probably important sources of iron.
Mineral dust supplies iron to remote oceans, stimulating phytoplankton growth and carbon dioxide...
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