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| Titel |
Chemistry and mineralogy of clay minerals in Asian and Saharan dusts and the implications for iron supply to the oceans |
| VerfasserIn |
G. Y. Jeong, E. P. Achterberg |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 14, no. 22 ; Nr. 14, no. 22 (2014-11-27), S.12415-12428 |
| Datensatznummer |
250119187
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| Publikation (Nr.) |
 copernicus.org/acp-14-12415-2014.pdf |
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| Zusammenfassung |
| 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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