Abstract
Abstract. In the North Pacific, transport and deposition of mineral dust from Asia appear to be one of major sources of iron which can regulate growth of phytoplankton in the ocean. In this process, it is essential to identify chemical species of iron contained in Asian dust, because bioavailability of iron in the ocean is strongly influenced by the solubility of iron, which in turn is dependent on iron species in the dust. Here, we report that clay minerals (illite and chlorite) in the dusts near the source collected at Aksu (western China) can be transformed into ferrihydrite by atmospheric chemical processes during their long-range transport to eastern China (Qingdao) and Japan (Tsukuba) based on the speciation by X-ray absorption fine structure (XAFS) and other methods such as X-ray diffraction and chemical extraction. As a result, Fe molar ratio in Aksu (illite : chlorite : ferrihydrite = 70 : 25 : 5) was changed to that in Tsukuba (illite : chlorite : ferrihydrite = 65 : 10 : 25). Moreover, leaching experiments were conducted to study the change of iron solubility. It was found that the iron solubility for the dust in Tsukuba (soluble iron fraction: 11.8 % and 1.10 % for synthetic rain water and seawater, respectively) was larger than that in Aksu (4.1 % and 0.28 %, respectively), showing that iron in the dust after the transport becomes more soluble possibly due to the formation of ferrihydrite in the atmosphere. Our findings suggested that secondary formation of ferrihydrite during the transport should be considered as one of important processes in evaluating the supply of soluble iron to seawater.
Highlights
Iron (Fe) is an essential micronutrient and has been identified as a limiting factor for growth of phytoplankton in highnitrate low-chlorophyll (HNLC) regions of the ocean (Martin and Fitzwater, 1988; de Baar et al, 1995; Jickells et al, 2005; Boyd and Ellwood, 2010)
The results were consistent with observations at these sites (Shao et al, 2003; Kanai et al, 2003, 2005), showing that the Taklimakan Desert in China was one of important source areas of mineral dust for the dust event transported to eastern China and Japan in March 2002
This study focuses on the speciation of Fe in mineral dusts transported from Aksu to Qingdao and Tsukuba (Japan)
Summary
Iron (Fe) is an essential micronutrient and has been identified as a limiting factor for growth of phytoplankton in highnitrate low-chlorophyll (HNLC) regions of the ocean (Martin and Fitzwater, 1988; de Baar et al, 1995; Jickells et al, 2005; Boyd and Ellwood, 2010). It has been suggested that atmospheric processes can change the solubility of Fe as it moves from the source to the deposition area in oceans, actual chemical processes affecting Fe species in the solid phase in the mineral dusts are not clear. Large scale dust storms frequently occur in the western China and a large amount of dusts can be transported long distances over the HNLC region of the North Pacific under the influence of westerly winds. We describe the increase of Fe solubility caused by transformation of initially stable atmospheric Fe into more soluble phase during the long-range transport from western China to Japan and subsequently discuss the anthropogenic effect on the transformation of Fe species in the dust
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
