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Constraining dust models to understand and quantify the effect of dust upon climate and ecosystems requires comprehensive analyses of the physiochemical properties of dust-emitting sediments in arid regions. Building upon previous studies in the Moroccan Sahara and Iceland, we analyse a diverse set of crusts and aeolian ripples (n=55) from various potential dust-emitting basins within the Mojave Desert, California, USA. Our focus is on characterizing the particle size distribution (PSD), mineralogy, aggregation/cohesion state, and Fe mode of occurrence. Our results show differences in fully and minimally dispersed PSDs, with crusts exhibiting average median diameters of 92 and 37 µm , respectively, compared to aeolian ripples with 226 and 213 µm , respectively. Mineralogical analyses unveiled strong variations between crusts and ripples, with crusts being enriched in phyllosilicates (24 % vs. 7.8 %), carbonates (6.6 % vs. 1.1 %), Na salts (7.3 % vs. 1.1 %), and zeolites (1.2 % and 0.12 %) and ripples being enriched in feldspars (48 % vs. 37 %), quartz (32 % vs. 16 %), and gypsum (4.7 % vs. 3.1 %). The size fractions from crust sediments display a homogeneous mineralogy, whereas those of aeolian ripples display more heterogeneity, mostly due to different particle aggregation. Bulk Fe content analyses indicate higher concentrations in crusts (3.0 ± 1.3 wt %) compared to ripples (1.9 ± 1.1 wt %), with similar proportions in their Fe mode of occurrence: nano-sized Fe oxides and readily exchangeable Fe represent ∼1.6 %, hematite and goethite ∼15 %, magnetite/maghemite ∼2.0 %, and structural Fe in silicates ∼80 % of the total Fe. We identified segregation patterns in the PSD and mineralogy differences in Na salt content within the Mojave basins, which can be explained by sediment transportation dynamics and precipitates due to groundwater table fluctuations described in previous studies in the region. Mojave Desert crusts show similarities with previously sampled crusts in the Moroccan Sahara in terms of the PSD and readily exchangeable Fe yet exhibit substantial differences in mineralogical composition, which should significantly influence the characteristic of the emitted dust particles. [ABSTRACT FROM AUTHOR]

Characterising the physico-chemical properties of dust-emitting sediments in arid regions is fundamental to understanding the effects of dust on climate and ecosystems. However, knowledge regarding high-latitude dust (HLD) remains limited. This study focuses on analysing the particle size distribution (PSD), mineralogy, cohesion, iron (Fe) mode of occurrence, and visible–near infrared (VNIR) reflectance spectra of dust-emitting sediments from dust hotspots in Iceland (HLD region). Extensive analysis was conducted on samples of top sediments, sediments, and aeolian ripples collected from seven dust sources, with particular emphasis on the Jökulsá basin, encompassing the desert of Dyngjunsandur. Both fully and minimally dispersed PSDs and their respective mass median particle diameters revealed remarkable similarities (56 ± 69 and 55 ± 62 µ m, respectively). Mineralogical analyses indicated the prevalence of amorphous phases (68 ± 26 %), feldspars (17 ± 13 %), and pyroxenes (9.3 ± 7.2 %), consistent with thorough analyses of VNIR reflectance spectra. The Fe content reached 9.5 ± 0.40 wt %, predominantly within silicate structures (80 ± 6.3 %), complemented by magnetite (16 ± 5.5 %), hematite/goethite (4.5 ± 2.7 %), and readily exchangeable Fe ions or Fe nano-oxides (1.6 ± 0.63 %). Icelandic top sediments exhibited coarser PSDs compared to the high dust-emitting crusts from mid-latitude arid regions, distinctive mineralogy, and a 3-fold bulk Fe content, with a significant presence of magnetite. The congruence between fully and minimally dispersed PSDs underscores reduced particle aggregation and cohesion of Icelandic top sediments, suggesting that aerodynamic entrainment of dust could also play a role upon emission in this region, alongside saltation bombardment. The extensive analysis in Dyngjusandur enabled the development of a conceptual model to encapsulate Iceland's rapidly evolving high dust-emitting environments. [ABSTRACT FROM AUTHOR]

Understanding the effect of dust upon climate and ecosystems needs comprehensive analyses of the physiochemical properties of dust-emitting sediments in arid regions. Here, we analyse a diverse set of crusts and aeolian ripples (n=55) from various dust-hotspots within the Mojave Desert, California, USA, with focus on their particle size distribution (PSD), mineralogy, aggregation/cohesion state and iron mode of occurrence characterization. Our results showed differences in fully and minimally dispersed PSDs, with crusts average median diameters (92 and 37 µm, respectively) compared to aeolian ripples (226 and 213 µm, respectively). Mineralogical analyses unveiled variations between crusts and ripples, with crusts enriched in phyllosilicates (24 vs 7.8 %), carbonates (6.6 vs 1.1 %), Na-salts (7.3 vs 1.1 %) and zeolites (1.2 and 0.12 %), while ripples enriched in feldspars (48 vs 37 %), quartz (32 vs 16 %), and gypsum (4.7 vs 3.1 %). Bulk Fe content analyses indicate higher concentrations in crusts (3.0±1.3 wt %) compared to ripples (1.9±1.1 wt %), with similar Fe speciation proportions; nano Fe-oxides/readily exchangeable Fe represent ~1.6 %, hematite/goethite ~15 %, magnetite/maghemite ~2.0 % and structural Fe in silicates ~80 % of the total Fe. We identified segregation patterns in PSD and mineralogy differences within the Mojave basins, influenced by sediment transportation dynamics and precipitates due to groundwater table fluctuations. Mojave Desert crusts show similarities with previously sampled crusts in the Moroccan Sahara for PSD and readily exchangeable Fe, yet exhibit differences in mineralogical composition, which could influence the emitted dust particles characteristics. [ABSTRACT FROM AUTHOR]

Characterizing physico-chemical properties of dust-emitting sediments in arid regions is fundamental to understand the effect of dust on climate and ecosystems. For high-latitude dust (HLD), this knowledge is scarce. This study focuses on the particle size distribution (PSD), mineralogy, cohesion, iron (Fe) mode of occurrence and Visible Near Infra-Red (VNIR) reflectance spectra of dust-emitting sediments from dust-hotspots in Iceland (HLD region). Extensive analysis was conducted on top sediments collected from seven dust-sources and an intensive at Jokulsá basin including top sediments, sediments and aeolian ripples. Fully and minimally dispersed PSDs evidenced remarkable similarities with an average median diameter of 56±69 and 55±62 µm. Mineralogical analyses showed the prevalence of amorphous phases (68±26 %), feldspars (17±13 %), and pyroxenes (9.3±7.2 %), aligned with the reflectance spectra. Fe content reached 9.5±0.40 wt %, mainly in silicate structures (80±6.3 %), complemented by magnetite (16±5.5 %), hematite/goethite (4.5±2.7 %), and readily exchangeable Fe-ions or Fe nano-oxides (1.6±0.63 %). Icelandic top sediments have coarser PSD compared to the high dust-emitting crusts from mid-latitude arid regions, distinctive mineralogy, and threefold bulk Fe content, with a large presence of magnetite. The congruence between fully and minimally dispersed PSDs underscores a reduced particle aggregation and cohesion of Icelandic top sediments, suggesting that aerodynamic entrainment of dust may also play a role upon emission in this region, aside of saltation bombardment. The analysis of an extensive sampling in Dyngjusandur allowed this study to present a conceptual model to encapsulate Iceland's rapidly evolving high dust-emitting environments. [ABSTRACT FROM AUTHOR]

The effects of desert dust upon climate and ecosystems depend strongly on its particle size and size-resolved mineralogical composition. However, there is very limited quantitative knowledge on the particle size and composition of the parent sediments along with their variability within dust-source regions, particularly in dust emission hotspots. The lower Drâa Valley, an inland drainage basin and dust hotspot region located in the Moroccan Sahara, was chosen for a comprehensive analysis of sediment particle size and mineralogy. Different sediment type samples (n= 42) were collected, including paleo-sediments, paved surfaces, crusts, and dunes, and analysed for particle-size distribution (minimally and fully dispersed samples) and mineralogy. Furthermore, Fe sequential wet extraction was carried out to characterise the modes of occurrence of Fe, including Fe in Fe (oxyhydr)oxides, mainly from goethite and hematite, which are key to dust radiative effects; the poorly crystalline pool of Fe (readily exchangeable ionic Fe and Fe in nano-Fe oxides), relevant to dust impacts upon ocean biogeochemistry; and structural Fe. Results yield a conceptual model where both particle size and mineralogy are segregated by transport and deposition of sediments during runoff of water across the basin and by the precipitation of salts, which causes a sedimentary fractionation. The proportion of coarser particles enriched in quartz is higher in the highlands, while that of finer particles rich in clay, carbonates, and Fe oxides is higher in the lowland dust emission hotspots. There, when water ponds and evaporates, secondary carbonates and salts precipitate, and the clays are enriched in readily exchangeable ionic Fe, due to sorption of dissolved Fe by illite. The results differ from currently available mineralogical atlases and highlight the need for observationally constrained global high-resolution mineralogical data for mineral-speciated dust modelling. The dataset obtained represents an important resource for future evaluation of surface mineralogy retrievals from spaceborne spectroscopy. [ABSTRACT FROM AUTHOR]

The effect of mineral dust emitted from arid and semiarid surfaces upon climate and ecosystems depends fundamentally on their particle size distribution (PSD) and size-resolved mineralogical composition. However, soil mineralogy atlases used for mineral-speciated dust modelling are highly uncertain as they are derived extrapolating mineralogical analyses of soil samples that are particularly scarce in dust-source regions. This extrapolation neglects the processes affecting the formation of different dust-emitting surface sediments, such as dunes, crusts, and paved sediments. The Lower DrÃa Valley, an inland drainage basin and preferential dust-source located in southern Morocco, was chosen for a comprehensive analysis of sediment grain size and mineralogy. Different sediment types samples were collected, including paleo-sediments, paved surfaces, crusts, and dunes, and analysed through PSD analysis of minimally and fully dispersed samples, and X-ray diffraction mineralogical analysis of bulk samples. We also performed Fe sequential wet extraction to characterize Fe mineralogy, including the contents of (oxyhydr)oxides (goethite and hematite), key to dust radiative effects, and poorly crystalline pool of Fe (readily exchangeable ionic Fe and nano-Fe-oxides), relevant to dust impacts upon ocean biogeochemistry. Based on the results we propose a conceptual model where both particle size and mineralogy are segregated by transport and deposition of sediments during runoff of water across the basin, and by the precipitation of salts, which causes a sedimentary fractionation. Coarser particles substantially richer in quartz are more present in elevated areas, and finer particles rich in clay, carbonates, and Fe-oxides are present in depressed areas, where dust emission is maximized. When water ponds and evaporates, secondary carbonates and salts precipitate, and the clays are enriched in readily exchangeable ionic Fe, due to sorption of dissolved Fe by illite. Our results differ from currently available mineralogical atlases and highlight the need for observationally-constrained global high-resolution mineralogical data for mineral-speciated dust modeling. [ABSTRACT FROM AUTHOR]