Chemistry and mineralogy of clay minerals in Asian and Saharan dusts and the implications for iron supply to the oceans

Jeong, Gi Young; Achterberg, Eric P.

doi:10.5194/acp-14-12415-2014

Cited by 47 publications

(72 citation statements)

References 67 publications

(84 reference statements)

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“…The maximum and mean of the mineral data are tabulated (Table 3) (Table 3), with typically higher contributions at higher dust loadings ( Figure 7). The calcite content was up to 90.7%, with a mean of 28.4%, and compared with a mean of 8.2% by Glaccum and Prospero (1980) and lower values by Avila et al (1997) and Jeong and Achterberg (2014). The uncertainty regarding the gypsum contribution in our samples may well have contributed to the observed differences between our data and literature values.…”

Section: Mineralogycontrasting

confidence: 56%

“…Leaching experiments have demonstrated that aerosol Fe solubility is highly dependent on the chemical form and reactivity of Fe in each sample and, in particular that Fe is significantly more labile in clay minerals than in more refractory phases such as quartz which has a low Fe content of typically only a few µg g -1 (Götze et al, 2004) compared to 3-4 % for illite clays (Jeong and Achterberg, 2014;Journet et al, 2008;Schroth et al, 2009). The octahedral sites of clays in the crystal structures of clay minerals can accommodate a significant quantity of Fe.…”

Section: Accepted M Manuscriptmentioning

confidence: 99%

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Aerosol time-series measurements over the tropical Northeast Atlantic Ocean: Dust sources, elemental composition and mineralogy

et al. 2015

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The North Atlantic receives the largest dust loading of any of the world's oceans due to its proximity to North African deserts and prevailing wind patterns. The supply of biologically important trace elements and nutrients via aerosols has an important influence on biogeochemical processes and ecosystems in this ocean region. In this study we continuously sampled aerosols between July 2007 and July 2008 at the Cape Verde Atmospheric Observatory (CVAO), which is situated on an island group close to the North African continent and under the Saharan/Sahelian dust outflow path. The aim of our work was to investigate temporal variations in aerosol concentration, composition and sources in the Cape Verde region over a complete seasonal cycle, and for this purpose we undertook mineralogical and chemical (42 elements ). These observations have been attributed to dust transport occurring in higher altitude air layers and mainly north of the Cape Verde during summer, whilst in winter the dust transport shifts south and occurs in the lower altitude trade winds with consequent greater influence on the Cape Verde region. The elemental composition of the aerosols closely agreed with mean upper crustal abundances, with the exception of elements with pronounced anthropogenic sources (e.g. Zn and Pb) and major constituents of sea water (Na and Mg). A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT3 Mineral analysis showed that clays were the most abundant mineral fraction throughout the whole sampling period, with an increase in quartz and clays during strong dust events and an associated decrease in calcite. This could have important implications for the estimation of release of for exampleFe from mineral dust with clays having a higher Fe solubility than quartz.The elemental composition and mineralogy of aerosol samples collected during the cruise were indistinguishable from those collected at the CVAO during the same period, although mean atmospheric Al was 65% higher at the CVAO than those measured on the ship due to the irregular and uneven nature of dust transport.Air mass back-trajectories showed an important role for southern source regions of the NorthAfrican deserts during summer, with 92.5% of the samples indicating a contribution from the Sahel.Significantly elevated ratios of V, Ni, Cu, Zn, Cd and Pb with Al were present in samples originating from the Sahel compared with samples with a more northerly origin. This was likely due to enhanced anthropogenic emissions related to the greater population densities in the Sahel compared with the less developed Saharan regions further north.Ratios of other elements and trends in rare earth elements could however not be used to distinguish differences in source regions. Similar source material compositions, the mixing of dust from different regions during transport, and the pooling of samples over a 1-3 day collection period appears to have diluted specific signals from source regions.

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Section: Mineralogycontrasting

confidence: 56%

Section: Accepted M Manuscriptmentioning

confidence: 99%

Aerosol time-series measurements over the tropical Northeast Atlantic Ocean: Dust sources, elemental composition and mineralogy

et al. 2015

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“…Overall, the average Fe content for all clay minerals analyzed here is 3.84 wt%. If one considers that there is also chlorite, which has a typical Fe content of 14.8 wt % in desert dust (Jeong and Achterberg, 2014), then the average Fe content in our studied clays rises to 5.7 wt %. This later value is in very good agreement with the average 5.4 wt% Fe content of clay minerals in Saharan dust analyzed by Jeong and Achterberg (2014).…”

Section: Tem-aem Analysesmentioning

confidence: 86%

“…If one considers that there is also chlorite, which has a typical Fe content of 14.8 wt % in desert dust (Jeong and Achterberg, 2014), then the average Fe content in our studied clays rises to 5.7 wt %. This later value is in very good agreement with the average 5.4 wt% Fe content of clay minerals in Saharan dust analyzed by Jeong and Achterberg (2014). 10 Further detailed textural and compositional insights were obtained using the HAADF and EDX detectors of the 15 Titan TEM operated in STEM mode.…”

Section: Tem-aem Analysesmentioning

confidence: 86%

“…This is typically a major fraction in desert dust, is considered responsible for most of the scattering of sun light, includes most of the bioavailable iron, and due to its long 30 atmospheric residence time is the one that can affect most distant locations (Tegen and Lacis, 1996;Sokolik and Toon, 1999;Lafon et al, 2006;Journet et al, 2008;Formenti et al, 2014a,b;Jeong and Achterberg, 2014;Jeong et al, 2016). Another goal of our study was to compare the mineralogy and physicochemical properties of the clay fraction with those of the two other relevant size fractions: i.e., sand and silt, an aspect that has been generally neglected in previous studies.…”

Section: Introductionmentioning

confidence: 99%

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Mineralogy and physicochemical features of Saharan dust wet deposited in the Iberian Peninsula during an extreme red rain event

Rodríguez-Navarro¹,

Lorenzo²,

Elert³

2018

Preprint

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Abstract. The mineralogy and physicochemical features of Saharan dust particles help to identify source areas and determine their biogeochemical, radiative and health effects, but their characterization is challenging. Using a multianalytical approach, here we characterized with unprecedented level of detail the mineralogy and physicochemical properties of Saharan dust particles massively wet deposited (~18 g m -2 ) following an extreme "red rain" event triggered by a north African cyclone that affected the southern Iberian Peninsula during February 21-23, 2017. Abundant palygorskite and illite, 10 and relatively high carbonate contents, well-known northern and north-western Saharan dust indicators, along with low chlorite content and significant amounts of smectites and kaolinite, whose abundance increases southwards in the western Sahara, complemented by satellite imagery and back/forward trajectories, show that the most probable dust source areas were (i) south/central Algeria, north Mali and northwest Niger, and (ii) north Algeria, south Tunisia and north-west Libia.Scanning and transmission electron microscopy analyses, including Z-contrast high angle annular dark field (HAADF) 15 imaging and analytical electron microscopy (AEM) show that clay minerals include abundant structural Fe (57 % of the total Fe) and typically form nanogranular aggregates covered or interspersed with amorphous/poorly crystalline iron oxyhydroxide nanoparticles (ferrihydrite), which account for 28 % of the free Fe, the rest being goethite and hematite. These nanogranular aggregates tend to form rims lining large silicate and carbonate particles. Such internally mixed iron-containing phases are main contributors to the observed absorption of solar and thermal radiation, and along with the abundant 20 coarse/giant particles (>10 μm), strongly affect the dust direct radiative forcing. The lack of secondary sulfates in aggregates of unaltered calcite internally mixed with clays/iron-rich nanoparticles shows that iron-rich nanoparticles did not form via atmospheric (acid) processing but were already present in the dust source soils. Such iron-rich nanoparticles, in addition to iron-containing clay (nano)particles, are an important source for bioavailable (soluble) iron. The dust particles are a potential health hazard, specially the abundant and potentially carcinogenic iron-containing palygorskite fibers. Ultimately, we show 25 that different source areas are activated over large desert extensions, and large quantities of complex dust mixtures are transported thousands of kilometers and wet-deposited during such extreme events, which thwart any other Saharan dust event affecting south-western Europe. The past, present, and future trends, as well as impacts, of such extreme events must be taken into account when evaluating and modeling the manifold effects of the desert dust cycle.Atmos. Chem. Phys. Discuss., https://doi

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Iron Mineralogy and Speciation in Clay‐Sized Fractions of Chinese Desert Sediments

Zhao

Balsam

et al. 2017

JGR Atmospheres

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Iron released from Asian desert dust may be an important source of bioavailable iron for the North Pacific Ocean and thereby may stimulate primary productivity. However, the Fe species of the fine dusts from this source region are poorly characterized. Here we investigate iron species and mineralogy in the clay‐sized fractions (<2 μm), the size fraction most prone to long‐distance transport as dust. Samples were analyzed by sequential chemical extraction, X‐ray diffraction, and diffuse reflectance spectrometry. Our results show that Fe dissolved from easily reducible iron phases (ferrihydrite and lepidocrocite) and reducible iron oxides (dominated by goethite) are 0.81 wt % and 2.39 wt %, respectively, and Fe dissolved from phyllosilicates extracted by boiling HCl (dominated by chlorite) is 3.15 wt %. Dusts originating from deserts in northwestern China, particularly the Taklimakan desert, are relatively enriched in easily reducible Fe phases, probably due to abundant Fe contained in fresh weathering products resulting from the rapid erosion associated with active uplift of mountains to the west. Data about Fe speciation and mineralogy in Asian dust sources will be useful for improving the quantification of soluble Fe supplied to the oceans, especially in dust models.

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Chemistry and mineralogy of clay minerals in Asian and Saharan dusts and the implications for iron supply to the oceans

Cited by 47 publications

References 67 publications

Aerosol time-series measurements over the tropical Northeast Atlantic Ocean: Dust sources, elemental composition and mineralogy

Aerosol time-series measurements over the tropical Northeast Atlantic Ocean: Dust sources, elemental composition and mineralogy

Mineralogy and physicochemical features of Saharan dust wet deposited in the Iberian Peninsula during an extreme red rain event

Iron Mineralogy and Speciation in Clay‐Sized Fractions of Chinese Desert Sediments

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