Abstract
Abstract. It has been shown that volcanic ash fertilizes the Fe-limited areas of the surface ocean through releasing soluble iron. As ash iron is mostly insoluble upon the eruption, it is hypothesized that heterogeneous in-plume and in-cloud processing of the ash promote the iron solubilization. Direct evidences concerning such processes are, however, lacking. In this study, a 1-D numerical model is developed to simulate the physicochemical interactions of the gas–ash–aerosol in volcanic eruption plumes focusing on the iron mobilization processes at temperatures between 600 and 0 °C. Results show that sulfuric acid and water vapor condense at ~ 150 and ~ 50 °C on the ash surface, respectively. This liquid phase then efficiently scavenges the surrounding gases (> 95 % of HCl, 3–20 % of SO2 and 12–62 % of HF) forming an extremely acidic coating at the ash surface. The low pH conditions of the aqueous film promote acid-mediated dissolution of the Fe-bearing phases present in the ash material. We estimate that 0.1–33 % of the total iron available at the ash surface is dissolved in the aqueous phase before the freezing point is reached. The efficiency of dissolution is controlled by the halogen content of the erupted gas as well as the mineralogy of the iron at ash surface: elevated halogen concentrations and presence of Fe2+-carrying phases lead to the highest dissolution efficiency. Findings of this study are in agreement with the data obtained through leaching experiments.
Highlights
In 2010, sockeye salmon unexpectedly reached record numbers in British Columbia’s Fraser River after low numbers during recent decades (Larkin, 2010)
It has been hypothesized that the soluble iron contained in the volcanic ash from the eruption of Kasatochi Volcano, Aleutian Islands, in 2008, could have indirectly provided a feast for the salmon (Parsons and Whitney, 2012) through an enhanced marine primary productivity (MPP) and phytoplankton bloom upon ash deposition into Fe-limited ocean surface waters (Olgun et al, 2013a)
The 1-D numerical model introduced in this study simulates the heterogeneous interactions of the gases, liquid phase and the ash surface within the volcanic eruption plume in the temperature range of 600–0 ◦C
Summary
In 2010, sockeye salmon unexpectedly reached record numbers in British Columbia’s Fraser River after low numbers during recent decades (Larkin, 2010). It has been hypothesized that the soluble iron contained in the volcanic ash from the eruption of Kasatochi Volcano, Aleutian Islands, in 2008, could have indirectly provided a feast for the salmon (Parsons and Whitney, 2012) through an enhanced marine primary productivity (MPP) and phytoplankton bloom upon ash deposition into Fe-limited ocean surface waters (Olgun et al, 2013a). This phytoplankton bloom was the first direct evidence of a fertilization effect of volcanic ash iron on the surface ocean (Langmann et al, 2010; Hamme et al, 2010).
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