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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Acknowledgements
The authors thank Prof. Jan Veizer and Dr. Thomas Steuber for providing research facilities, Prof. Werner Schreyer for constructive discussions on iron oxide identification, and the crews of the R/V Dongfanghong 2 for their help in sampling during the June 2003 cruise. This study was supported by the Ministry of Science and Technology of China (2002CB412404 and 2005CB422304), and the National Natural Science Foundation of China (40676035).
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Fan, D.J., Neuser, R.D., Sun, X.G. et al. Authigenic iron oxide formation in the estuarine mixing zone of the Yangtze River. Geo-Mar Lett 28, 7–14 (2008). https://doi.org/10.1007/s00367-007-0084-0
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DOI: https://doi.org/10.1007/s00367-007-0084-0