Distinct chemical and mineralogical composition of Icelandic dust compared to northern African and Asian dust
Distinct chemical and mineralogical composition of Icelandic dust compared to northern African and Asian dust
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DOI：
10.5194/acp-20-13521-2020
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发表时间：
2020-11-12
影响因子：
6.3
通讯作者：
Shi, Zongbo
中科院分区：
文献类型：
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作者：
Baldo, Clarissa;Formenti, Paola;Shi, Zongbo
冰岛是一个高度活跃的天然粉尘来源。冰岛沙尘有可能通过尘-辐射相互作用直接影响气候，并通过尘-云相互作用、雪/冰反照率效应和对生物地球化学循环的影响间接影响气候。冰岛尘埃的影响取决于它的矿物学和化学成分。然而，数据的缺乏阻碍了对冰岛尘埃在地球系统中的作用的准确评估。在这里，我们收集了冰岛五个主要尘埃热点的地表沉积物样本。在大气室中产生和悬浮粉尘气溶胶，并收集PM10和PM20组分进行进一步分析。我们发现尘埃样品主要由无定形玄武岩物质组成，从8wt %（来自Hagavatn热点）到60wt %（其他热点）到90wt %（其他热点）。样品的总铁含量相对较高（10 wt %-13 wt %）。连续提取铁以确定其化学形态表明，二硫代铁（铁氧化物如赤铁矿和针铁矿）和抗坏血酸铁（无定形铁）分别占冰岛粉尘中总铁的1% - 6%和0.3% - 1.4%。磁铁矿部分占总铁的7% - 15%，占PM10的1% - 2%，比来自北非的矿物粉尘高出几个数量级。然而，约80% -90%的铁含有辉石和非晶玻璃。初始铁溶解度（pH值为4.7的乙酸铵萃取）为0.08% ~ 0.6%，与北非等低纬度粉尘相当。铁在低pH（即pH 2）下的溶解度明显高于典型的低纬度粉尘（72小时后在pH 2下可达30%）。我们的研究结果揭示了冰岛尘埃与低纬度尘埃在成分和矿物学上的根本差异。我们将这些差异归因于化学风化程度低、母沉积物的玄武岩成分和冰川作用。冰岛沙尘有助于大气中可溶铁的沉积，并可能影响北大西洋的初级生产力。独特的化学和矿物组成，特别是高磁铁矿含量（1 wt %-2 wt %），表明冰岛尘埃对亚极地和极地地区的辐射平衡有潜在的重大影响。
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.