Authigenic iron oxide formation in the estuarine mixing zone of the Yangtze River |
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| Authors: | D J Fan R D Neuser X G Sun Z S Yang Z G Guo S K Zhai |
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| Institution: | (1) Key Lab of Submarine Geosciences and Technology, Ministry of Education, Ocean University of China, 238 Songling Road, Qingdao, 266100, China;(2) Institute of Geology, Mineralogy and Geophysics, Ruhr-University Bochum, Bochum, 44801, Germany;(3) Chinese Academy of Meteorological Sciences, Beijing, 100081, China |
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| Abstract: | Estuaries are elementary geochemical fronts where river water and seawater mix. Within this mixing zone, iron and other non-conservative
elements can undergo complex reactions to form new solid phases. In order to understand authigenic iron oxide formation in
the Yangtze River Estuary, two onsite water-mixing sets of experiments were conducted, one by mixing variable amounts of unfiltered
Yangtze River water with filtered East China Sea water of different salinity (set 1), the other by mixing variable amounts
of filtered Yangtze River water with filtered East China Sea water of different salinity (set 2). In set 2, the minerals newly
formed in the course of mixing were investigated by means of a scanning electron microscope fitted with an energy-dispersive
X-ray analytical system. It was found that ferrihydrite and lepidocrocite were formed in these mixing experiments, coexisting
in nearly equal amounts. These iron oxides appear as aggregated particles with a large grain-size range of several microns
to more than 100 μm. The electrolytic properties of seawater played an important role in the formation of these authigenic
iron oxides. Kaolinite and organic aggregates were also found in the experimentally mixed pre-filtered waters. Amounts of
newly formed suspended matter (set 2) were one to three orders of magnitude lower than those of total suspended matter (TSM)
(set 1). This implies that newly formed minerals represent only a very small proportion of TSM in the estuarine mixing zone
of the Yangtze River. |
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