Dust deposits in Souss–Massa basin, South-West of Morocco: granulometrical, mineralogical and geochemical characterisation

Khiri, Fouad; Ezaidi, Abdelkrim; Kabbachi, Belkacem

doi:10.1016/j.jafrearsci.2004.07.019

Cited by 29 publications

(13 citation statements)

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“…Figure 8 shows that both source areas display Ca / Al and Mg / Al ratios higher than the mean crustal composition. The high Ca / Al are related to the elevated carbonate contents in the Saharan sediments, found in north-western (Morocco and Atlas region; Criado and Dorta, 2003;Khiri et al, 2004;Linke et al, 2006;Moreno et al, 2006;Castillo et al, 2008) and north-eastern Africa (Egypt, Libya; Linke et al, 2006, Israel, Ganor and Foner, 1996, Jordan, Abed et al, 2009. Intermediate values were reported for southern Egypt and northern Sudan (Tomadin et al, 1989;Sharif, 1995), while lower Ca contents (Ca / Al<0.5) were found in samples from central and southern Algeria and the Sahel zone.…”

Section: Source Areas Of Saharan Dust Aerosolmentioning

confidence: 99%

Saharan dust aerosol over the central Mediterranean Sea: PM<sub>10</sub> chemical composition and concentration versus optical columnar measurements

et al. 2014

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Abstract. This study aims to determine the mineral contribution to PM 10 in the central Mediterranean Sea, based on 7 yr of daily PM 10 samplings made on the island of Lampedusa (35.5 • N, 12.6 • E).The chemical composition of the PM 10 samples was determined by ion chromatography for the main ions, and, on selected samples, by particle-induced X-ray emission (PIXE) for the total content of crustal markers. Aerosol optical depth measurements were carried out in parallel to the PM 10 sampling.The average PM 10 concentration at Lampedusa over the period June 2004-December 2010 is 31.5 µg m −3 , with low interannual variability. The annual means are below the EU annual standard for PM 10 , but 9.9 % of the total number of daily data exceeds the daily threshold value established by the European Commission for PM (50 µg m −3 , European Community, EC/30/1999).The Saharan dust contribution to PM 10 was derived by calculating the contribution of Al, Si, Fe, Ti, non-sea-salt (nss) Ca, nssNa, and nssK oxides in samples in which PIXE data were available. Cases in which crustal content exceeded the 75th percentile of the crustal oxide content distribution were identified as elevated dust events. Using this threshold, we obtained 175 events. Fifty-five elevated dust events (31.6 %) displayed PM 10 higher than 50 µg m −3 , with dust contributing by 33 % on average.The crustal contribution to PM 10 has an annual average value of 5.42 µg m −3 , and reaches a value as high as 67.9 µg m −3 (corresponding to 49 % of PM 10 ) during an intense Saharan dust event.The crustal content estimated from a single tracer, such as Al or Ca, is in good agreement with the one calculated as the sum of the metal oxides. Conversely, larger crustal contents are derived by applying the EU guidelines for demonstration and subtraction of exceedances in PM 10 levels due to high background of natural aerosol. The crustal aerosol amount and contribution to PM 10 showed a very small seasonal dependence; conversely, the dust columnar burden displays an evident annual cycle, with a strong summer maximum (monthly average aerosol optical depth at 500 nm up to 0.28 in June-August). We found that 71.3 % of the dust events identified from optical properties over the atmospheric column display a high dust content at the ground level. Conversely, the remaining 28.7 % of cases present a negligible or small impact on the surface aerosol composition due to the transport processes over the Mediterranean Sea, where dust frequently travels above the marine boundary layer, especially in summer.Published by Copernicus Publications on behalf of the European Geosciences Union. M. Marconi et al.: Saharan dust aerosol over the central Mediterranean SeaBased on backward trajectories, two regions, one in Algeria-Tunisia, and one in Libya, are identified as main source areas for intense dust episodes occurring mainly in autumn and winter. Data on the bulk composition of mineral aerosol arising from these two source areas are scarce; results on characteristic ratios between ele...

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Section: Source Areas Of Saharan Dust Aerosolmentioning

confidence: 99%

Saharan dust aerosol over the central Mediterranean Sea: PM<sub>10</sub> chemical composition and concentration versus optical columnar measurements

et al. 2014

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“…Thus 'dry' deposition can be a very efficient sorter of particles. In this way, Saharan dust transported across the Atlantic is seen to be much finer at distance from source, with median deposited particle sizes in Morocco measured at 22.0-37.0 µm (Khiri, Ezaidi and Kabbachi, 2004) and those deposited in the Caribbean at 4.0 µm (Petit et al, 2005). In contrast 'wet' deposition, where particles are drawn out of the airflow by rain, cleanses the atmosphere and results in a much less sorted deposit ( Figure 20.5).…”

Section: Dust Sinksmentioning

confidence: 96%

Desert Dust

Washington¹,

Wiggs²

2011

Arid Zone Geomorphology

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The arid zone contains few perennial lakes; examples such as the Caspian Sea, the Dead Sea and Lake Aral invariably have inflowing rivers rising in fringing uplands or distant humid areas. Instead, the majority of arid and semi-arid regions are characterised by endoreic (internal) drainage or, in extreme cases, may lack integrated surface drainage altogether. Under these circumstances surface depressions become important local and regional foci for the accumulation of water in episodic (termed here ephemeral) lakes. Due to the negative balance between rainfall and evaporation (often exceeding 10:1), these water bodies are often highly saline and, in some cases, supersaturated with salts. Such salt lakes, which have a minimum salinity of 5,000 mg l -1 , in turn lie at one end of a spectrum of otherwise ephemeral and often relict closed basins of varying scales and origins frequently termed playas or pans. Pans and playas have been identified and studied throughout the world's arid lands. In Africa they have been described from the Sahara (Boulaine 1954; Coque 1962); Senegal (Tricart 1953), the Kalahari (Passarge 1904; Lancaster 1978a) and neighbouring regions (de Bruiyn 1971). Holm (1960), Powers et al. (1966) and others have described Arabian sebkhas, both coastal and inland. Playas in many Asian arid environments have been discussed: in Mongolia (Cotton 1942); in Iran (Krinsley 1970); in India (Godbole 1972); in China (Chen and Bowler 1986) and in the USSR (Zemljanitzya 1973). There is a considerable literature on the Australian basins extending from the early works such as Woodward (1897) through to the results of detailed research programmes such as SLEADS (Saline Lakes, Evaporites and Aeolian Deposits; Torgersen et al. 1986; Chivas and de Dekker 1991; Chivas 1995). Playas and pans of the United States received the early attentions of geomorphological pioneers (Russell 1885; Gilbert 1895) and have been subjectto considerable interest ever since especially those in the southwestern deserts (Reynolds et al., 2007), and the Texas High Plains (Wood and Ostercamp, 1987), while those in South America have been given less attention (Tricart 1969, Dargám, 1995. Pans have also been described in areas which experience cold climates, for example, Taylor Valley in Antarctica (Lyons et al. 1998) and the numerous salt lakes of the Pallisers Triangle region of the Canadian Prairies (Last 1994).The identification of pans and playas within arid environments has suggested to some authors that there may be climatic controls on their development (e.g. Tricart 1954, reported in Cooke andWarren 1973). The majority of southern Kalahari and peri-southern Kalahari pans, for example, occur on the arid side of the 500 mm mean annual isohyet and the 1000 mm free evaporation isoline (Goudie and Thomas 1985). However, comparable features are found beyond the limits of modern aridity, for example the Bays of Carolina,

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“…Continental dust studies in northern Morocco revealed that dust is produced predominantly locally (Khiri et al, 2004;Kandler et al, 2009). For instance, a high percentage of quartz and feldspar and a low amount of micas in the dust samples were interpreted as representing mostly local dust sources and the availability of calcite sources from proximal coastal dunes in Morocco (Khiri et al, 2004). Further, also in Morocco, dust was sampled in Tinfou at a height of 4 m during the SAMUM 2006 field campaign.…”

Section: Introductionmentioning

confidence: 99%

“…Formenti et al, 2008), on research ships (Chester et al, 1971(Chester et al, , 1972Stuut et al, 2005;Aston et al, 1973;Chester and Johnson, 1971a, b) and with gravity cores off NW Africa (Biscaye, 1964(Biscaye, , 1965Lange, 1982;Rateev et al, 1969;Griffin et al, 1968;Diester-Haass and Chamley, 1978;Meyer et al, 2013). Continental dust studies in northern Morocco revealed that dust is produced predominantly locally (Khiri et al, 2004;Kandler et al, 2009). For instance, a high percentage of quartz and feldspar and a low amount of micas in the dust samples were interpreted as representing mostly local dust sources and the availability of calcite sources from proximal coastal dunes in Morocco (Khiri et al, 2004).…”

Section: Introductionmentioning

confidence: 99%

“…The source regions of Saharan dust have been studied frequently by analysing the mineralogical composition of dust collected at continental sites (e.g. Skonieczny et al, 2013Skonieczny et al, , 2011Schütz and Sebert, 1987;Kandler et al, 2009;Khiri et al, 2004), during aircraft flights (e.g. Formenti et al, 2008), on research ships (Chester et al, 1971(Chester et al, , 1972Stuut et al, 2005;Aston et al, 1973;Chester and Johnson, 1971a, b) and with gravity cores off NW Africa (Biscaye, 1964(Biscaye, , 1965Lange, 1982;Rateev et al, 1969;Griffin et al, 1968;Diester-Haass and Chamley, 1978;Meyer et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Seasonal provenance changes of present-day Saharan dust collected on- and offshore Mauritania

Friese¹,

Hateren²,

Vogt³

et al. 2017

Preprint

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Abstract. Saharan dust has a crucial influence on the earth climate system and its emission, transport and deposition are intimately related to, e.g., wind speed, precipitation, temperature and vegetation cover. The alteration in the physical and chemical properties of Saharan dust due to environmental changes is often used to reconstruct the climate of the past. However, to better interpret possible climate changes the dust source regions need to be known. By analysing the mineralogical composition of transported or deposited dust, potential dust source areas can be inferred. Summer dust transport off northwest Africa occurs in the Saharan air layer (SAL). In continental dust source areas, dust is also transported in the SAL; however, the predominant dust input occurs from nearby dust sources with the low-level trade winds. Hence, the source regions and related mineralogical tracers differ with season and sampling location. To test this, dust collected in traps onshore and in oceanic sediment traps off Mauritania during 2013 to 2015 was analysed. Meteorological data, particle-size distributions, back-trajectory and mineralogical analyses were compared to derive the dust provenance and dispersal. For the onshore dust samples, the source regions varied according to the seasonal changes in trade-wind direction. Gibbsite and dolomite indicated a Western Saharan and local source during summer, while chlorite, serpentine and rutile indicated a source in Mauritania and Mali during winter. In contrast, for the samples that were collected offshore, dust sources varied according to the seasonal change in the dust transporting air layer. In summer, dust was transported in the SAL from Mauritania, Mali and Libya as indicated by ferroglaucophane and zeolite. In winter, dust was transported with the trades from Western Sahara as indicated by, e.g., fluellite.

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Dust deposits in Souss–Massa basin, South-West of Morocco: granulometrical, mineralogical and geochemical characterisation

Cited by 29 publications

References 7 publications

Saharan dust aerosol over the central Mediterranean Sea: PM<sub>10</sub> chemical composition and concentration versus optical columnar measurements

Saharan dust aerosol over the central Mediterranean Sea: PM<sub>10</sub> chemical composition and concentration versus optical columnar measurements

Desert Dust

Seasonal provenance changes of present-day Saharan dust collected on- and offshore Mauritania

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Dust deposits in Souss–Massa basin, South-West of Morocco: granulometrical, mineralogical and geochemical characterisation

Cited by 29 publications

References 7 publications

Saharan dust aerosol over the central Mediterranean Sea: PM&lt;sub&gt;10&lt;/sub&gt; chemical composition and concentration versus optical columnar measurements

Saharan dust aerosol over the central Mediterranean Sea: PM&lt;sub&gt;10&lt;/sub&gt; chemical composition and concentration versus optical columnar measurements

Desert Dust

Seasonal provenance changes of present-day Saharan dust collected on- and offshore Mauritania

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Saharan dust aerosol over the central Mediterranean Sea: PM<sub>10</sub> chemical composition and concentration versus optical columnar measurements

Saharan dust aerosol over the central Mediterranean Sea: PM<sub>10</sub> chemical composition and concentration versus optical columnar measurements