Characterization of aerosol trace elements over the polar regions
Creators: name: Fan, Songyun
Publisher: name: No Publisher Supplied
Year: 2022

description: Atmospheric deposition of dust is an important pathway supplying nutrient trace elements to the surface water of remote oceans. Recent warming in the sensitive polar regions might potentially enhance the regional dust emission. Bulk and size-segregated aerosol samples were collected in the western Antarctic Peninsula and the Arctic Ocean to characterize atmospheric trace elements and to evaluate the importance of aeolian dust input to the high latitude marine ecosystems. The objectives of this study are to (1) characterize atmospheric trace elements in aerosols and identify their major sources, (2) quantify the atmospheric dust deposition, and (3) assess the aerosol iron bioavailability through characterizing the aerosol Fe mineralogy and oxidation states. Sampling of both size-segregated and bulk aerosol particles was carried out at Palmer Station in the western Antarctic Peninsula and during a cruise in the Arctic Ocean. Results from the western Antarctic Peninsula showed that trace elements in aerosols over this region are primarily derived from (1) regional crustal emissions, (2) long-range transport, and (3) sea salt aerosols. Elements derived from crustal sources (Al, P, Ti, V, Mn, Ce) with crustal enrichment factors (EFcrust) &lt;10 were dominated by the coarse-mode particles (&gt;1.8 µm) and peaked around 4.4 µm in diameter. Other elements including Ca, Ni, Cu, Zn, and Pb showed EFcrust &gt; 10. The particle size distribution of aerosol Pb was dominated by fine particles and peaked at 0.14–0.25 µm, suggesting an anthropogenic contribution through long-range transport. The estimated dry deposition fluxes of mineral dust during the 2016-2017 austral summer in the Antarctic Peninsula ranged from 0.65 to 28 mg m−2 yr−1 with a mean of 5.5±5.0 mg m−2 yr−1, which were lower than most fluxes reported previously in coastal Antarctica. The Fe minerals in the dust particles over the Antarctic Peninsula were predominantly hematite and biotite with a minor fraction of pyrite and ilmenite. The aerosol Fe oxidation state was higher during the austral summer than the winter due to a higher fraction of biotite. Multivariate linear models involving meteorological data indicated that the wind speed, relative humidity, and solar irradiance were the factors that significantly controlled the percentage of Fe(II) in the austral summer. In addition, the snow depth was significantly (p &lt; 0.05) correlated with the aerosol Fe concentrations, suggesting the effects of snow/ice cover on the regional dust emissions. Samples from the Arctic cruise showed aerosol Fe mineralogy could be dominated by biotite, ferrihydrite, and hematite, varying spatially. Results from the Arctic cruise showed that aerosol particles collected near coastal Alaska were heavily affected by the biotite-enriched glacial flour, whereas ferrihydrite was the most enriched Fe-containing mineral in the remote Arctic Ocean. A few samples impacted by air masses from the inland North American and Eurasian contained a high fraction of hematite with minor Fe(III) sulfate, biotite, and ferrihydrite. The aerosol Fe fractional solubility demonstrated a positive linear relationship with the Fe oxidation state, suggesting that the atmospheric aging processes (e.g., acidic reactions) could modify the Fe bioavailability during long-rang transport. Although the dust deposition fluxes over polar regions are small, the dust derived from high latitude could potentially be more bioavailable than the tropical and subtropical dust. That can be attributed to the high fraction of Fe(II) minerals, mostly biotite from glacial flour. The atmospheric processes such as photoreduction and acidic reactions can further improve the Fe solubility. Therefore, dust sources in high latitudes are expected to be increasingly important under the rapid warming conditions.