ALBERT

Description: The 2010 eruption of Eyjafjallajökull produced volcanic ash that was mostly deposited to the south and east of the volcano with the thickest deposits closest to the eruption vents. For months following the eruption there were numerous reports of resuspended volcanic ash made by weather observers on the ground. A saltation sensor (SENSIT) and an Optical Particle Counter (OPC) located on the southern side of Eyjafjallajökull measured post-eruptive particulate matter (PM) saltation and suspension events, some of which were also observable by satellite imagery. During the fall/winter following the eruption visible satellite images and the SENSIT show that PM measured by the OPC were only detected by the when winds had a northerly component, making the source on the slopes of Eyjafjallajökull. During the largest observed events, particles 〉10 μm were suspended but measured in extremely low concentrations (〈 1 particle/cm3). The saltation measurements, however, show high concentrations of particles 〉100 μm in size during these events. During the largest events, winds were at least 5 ms-1 with a relative humidity 〈 70%. Ground conditions in Iceland change quickly from unfavorable to favorable for the suspension of particles. It is hypothesized that this is due to the porosity of the surface material allowing water to filter through quickly, as well as the fast-drying time of surface material. The high moisture content of the atmosphere and the ground do not appear to be a deterrent for large PM events to occur in Iceland.

Description: Iceland is a highly active source of natural dust. Icelandic dust has the potential to directly affect the climate via dust–radiation interaction and indirectly via dust–cloud interaction, the snow/ice albedo effect and impacts on biogeochemical cycles. The impacts of Icelandic dust depend on its mineralogical and chemical composition. However, a lack of data has prevented an accurate assessment of the role of Icelandic dust in the Earth system. Here, we collected surface sediment samples from five major Icelandic dust hotspots. Dust aerosols were generated and suspended in atmospheric chambers, and PM10 and PM20 fractions were collected for further analysis. We found that the dust samples primarily consist of amorphous basaltic materials ranging from 8 wt % (from the Hagavatn hotspot) to 60 wt %–90 wt % (other hotspots). Samples had relatively high total Fe content (10 wt %–13 wt %). Sequential extraction of Fe to determine its chemical form shows that dithionite Fe (Fe oxides such as hematite and goethite) and ascorbate Fe (amorphous Fe) contribute respectively 1 %–6 % and 0.3 %–1.4 % to the total Fe in Icelandic dust. The magnetite fraction is 7 %–15 % of total Fe and 1 %–2 wt % of PM10, which is orders of magnitude higher than in mineral dust from northern Africa. Nevertheless, about 80 %–90% of the Fe is contained in pyroxene and amorphous glass. The initial Fe solubility (ammonium acetate extraction at pH 4.7) is from 0.08 % to 0.6 %, which is comparable to low-latitude dust such as that from northern Africa. The Fe solubility at low pH (i.e. pH 2) is significantly higher than typical low-latitude dust (up to 30 % at pH 2 after 72 h). Our results revealed the fundamental differences in composition and mineralogy of Icelandic dust from low-latitude dust. We attribute these differences to the low degree of chemical weathering, the basaltic composition of the parent sediments and glacial processes. Icelandic dust contributes to the atmospheric deposition of soluble Fe and can impact primary productivity in the North Atlantic Ocean. The distinct chemical and mineralogical composition, particularly the high magnetite content (1 wt %–2 wt %), indicates a potentially significant impact of Icelandic dust on the radiation balance in the subpolar and polar regions.