Abstract
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.
Highlights
Mineral dust influences global climate through many feedback mechanisms and is in turn influenced by variations in environmental parameters
The fluxes, grain-size distributions and the mineral assemblages of the continental trap samples and oceanic sediment trap samples were well comparable to the characteristics of Saharan dust reported for the region
– A clear seasonal variability in the particle size of mineral dust deposited on land could be observed with generally coarser modal grain sizes during summer compared to winter
Summary
Mineral dust influences global climate through many feedback mechanisms and is in turn influenced by variations in environmental parameters. The emission, transport and deposition of mineral dust reacts sensitively to parameters of climate change like rainfall, wind, temperature and vegetation cover (Knippertz and Stuut, 2014). The emission, transport and deposition of mineral dust have an impact on the atmospheric energy balance (Haywood and Boucher, 2000), precipitation distribution and amplitude (Yoshioka et al, 2007), sea surface temperatures (Lau and Kim, 2007), and the oceanic carbon pump (Martin et al, 1991; Martin, 1990; Jickells et al, 2005; Iversen et al, 2010; Iversen and Robert, 2015; Ploug et al, 2008a).
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