Chemical and mineralogical composition of Icelandic Dust: Implications for the climate

Abstract:

Iceland is among the most active sources of natural dust in the world, but there is limited knowledge on its chemical composition, mineralogy and optical properties, which prevents an accurate assessment of its impact on the climate. In this study, surface sediments were collected from five major dust hotspots in Iceland. Dust aerosols were generated using atmospheric chambers, and PM₁₀ and PM₂₀ were collected for further analysis. The dust samples primarily consist of amorphous basaltic material (glass) ranging from 8 wt% (Hagavatn hotspot) to 60-90 wt%, with high total Fe (10-13 wt%). About 80-90% of total Fe is contained in aluminosilicate minerals, mainly pyroxene, and in the amorphous glass. Dithionite Fe (Fe oxides such as hematite and goethite), ascorbate Fe (amorphous Fe), and magnetite contribute respectively 1-6%, 0.3-1.4% and 7-15% of the total Fe. We found that the initial Fe solubility is 0.08-0.6% (ammonium acetate extraction, pH 4.7), which is comparable to low latitude dust such as Saharan dust. The Fe solubility at pH 2 is significantly higher than typical low latitude dust (up to 30%).

Our results quantify the differences in composition and mineralogy of Icelandic dust from low latitude dust. We attribute these differences to the low degree of chemical weathering, to the basaltic composition of the parent sediments, and to glacial processes. In particular, the high magnetite content (1-2 wt%) indicates a potentially significant impact of Icelandic dust on the radiation balance in the sub-polar and polar regions. Wavelength dependence absorption and scattering properties of Icelandic dust on its mineralogical composition, and particularly on the iron speciation will be evaluated. This new dataset on chemical and mineralogical composition, and optical parameters will be fed to global model(s) to estimate the radiative impact of Icelandic dust and its role on Arctic climate.