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Environmental problems - Chemical approaches

Aeolian iron mobilisation by dust–acid interactions and their implications for soluble iron deposition to the ocean: a test involving potential anthropogenic organic acidic species

Chao Luo A B C and Yuan Gao A D

A Department of Earth and Environmental Sciences, Rutgers University, Newark, NJ 07102, USA.

B Department of Earth and Atmospheric sciences, Cornell University, Ithaca, NY 14853, USA.

C Present address: School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332, USA.

D Corresponding author. Email: yuangaoh@andromeda.rutgers.edu

Environmental Chemistry 7(2) 153-161 http://dx.doi.org/10.1071/EN09116
Submitted: 9 November 2009  Accepted: 17 February 2010   Published: 22 April 2010

Environmental context. Studying the input of atmospheric soluble iron to the ocean is important as the soluble form of iron is bioavailable for phytoplankton uptake in the surface ocean to support photosynthesis. In this paper, the effect of organic acidic species on atmospheric iron dissolution is addressed through a global model for the first time. The new results contribute to a better understanding of iron dissolution processes in the atmosphere and the role of atmospheric iron in ocean biogeochemical cycles.

Abstract. Dust deposition is a major source of iron in certain oceanic regions. Many atmospheric processes, such as heterogeneous reactions with acidic species, may convert insoluble iron in dust to soluble forms that become bioavailable for phytoplankton uptake in the surface ocean. Here we report for the first time the effects of organic acidic species on iron dissolution using laboratory-measured conversion rates by oxalate, simulated in a global model to estimate soluble iron fluxes to the ocean. With the complexity and limited data from measurements relating to different sources for oxalate, we focus on the effect of oxalate of anthropogenic origin in this work as a first-step testing, and we apply a scaling factor for oxalate based on its relationship with aerosol sulfate observed by in situ measurements in the continental sites. The results show better correlation with the observations than the work including inorganic acids alone, suggesting the contribution of organic acids to Fe dissolution. However, the simulated iron solubility is lower than that derived from measurements, suggesting additional processes may contribute to Fe dissolution that should be included in the model. Total deposition of soluble iron to the global ocean including the effect by anthropogenic oxalate is ~0.34 Tg year–1.


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