07 Jun 2023
 | 07 Jun 2023

Variability in grain size, mineralogy, and mode of occurrence of Fe in surface sediments of preferential dust-source inland drainage basins: The case of the Lower Drâa Valley, S Morocco

Adolfo González-Romero, Cristina González-Florez, Agnesh Panta, Jesús Yus-Díez, Cristina Reche, Patricia Córdoba, Andres Alastuey, Konrad Kandler, Martina Klose, Clarissa Baldo, Roger N. Clark, Zong Bo Shi, Xavier Querol, and Carlos Pérez García-Pando

Abstract. 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 Drâa 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.

Adolfo González-Romero et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-1120', Ali Al-Dousari, 02 Aug 2023
    • AC1: 'Reply on RC1', Adolfo Gonzalez Romero, 28 Aug 2023
  • RC2: 'Comment on egusphere-2023-1120', Anonymous Referee #2, 07 Aug 2023
    • AC2: 'Reply on RC2', Adolfo Gonzalez Romero, 28 Aug 2023

Adolfo González-Romero et al.

Adolfo González-Romero et al.


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Short summary
The effect of dust emitted from desertic surfaces upon climate and ecosystems depends on their size and mineralogy, but, data from soil mineral atlases of desert soils is scarce. We performed particle size distribution, mineralogy and Fe speciation at S Morocco. Results show coarser particles, with high quartz proportion are near the elevated areas, meanwhile in depressed areas, finer sizes and higher proportions of clays and nano Fe-oxides. This differences are important for dust modelling.