Characterization of the particle size distribution, mineralogy and Fe mode of occurrence of dust-emitting sediments across the Mojave Desert, California, USA.

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]