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.
Bibliographical noteFunding Information:
Acknowledgements. Clarissa Baldo is funded by the Natural Environment Research Council (NERC) CENTA studentship (grant no. NE/L002493/1). This paper is partly funded by the NERC highlight topic project (NE/S00579X/1). This project has received funding from the European Union’s Horizon 2020 research and innovation programme through the EUROCHAMP-2020 Infrastructure Activity under grant agreement No 730997. Part of this work was sup- ported by the COST Action inDust (CA16202) supported by COST (European Cooperation in Science and Technology). This work was carried out with the support of the Icelandic Research Fund (Ran-nís) grant no. 207057-051. We acknowledge Diamond Light Source for time on Beamline/Lab I18 under the Proposals: SP22244-1; SP12760-1; SP10327-1. The authors gratefully acknowledge Gau-tier Landrot (SAMBAA SOLEIL), who provided his expertise for the analysis of the XANES spectra and results. Thanks also to Gi-annantonio Cibin (Diamond Light Source), who provided the magnetite standard for the XANES measurements.
ASJC Scopus subject areas
- Atmospheric Science
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Baldo, C. (Creator), University of Birmingham, 3 Nov 2020