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

Abstract

Abstract. Saharan dust has a crucial influence on the earth climate system and its emission, transport, and deposition are intimately related to environmental parameters. The alteration in the physical and chemical properties of Saharan dust due to changes in environmental parameters 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 offshore Northwest Africa occurs in the Saharan air layer (SAL). In contrast, dust transport in continental dust source areas occurs predominantly with the 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 offshore 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 ferryglaucophane and zeolite. In winter, dust was transported with the Trades from the Western Sahara as indicated by e.g. sepiolite and fluellite.