The 7–13 March 2006 major Saharan outbreak: Multiproxy characterization of mineral dust deposited on the West African margin

Abstract

Mineral dust deposits were collected at Mbour, Senegal, throughout the spring of 2006 and especially during the well‐documented March 7–13 large Saharan dust outbreak. During this 7‐day period, significant changes in mass flux, grain‐size, clay mineralogy and Sr and Nd isotopic compositions were recorded, indicating distinct provenances for the dust transported and deposited during and outside the event. All these terrigenous proxies, as well as freshwater diatom taxa, also showed significant temporal variations during the outbreak, implying contributions from at least two different provenance regions. Tri‐dimensional back‐trajectories and satellite imaging enabled us to link those distinct signatures to regions increasingly to the southeast within a large area covering Mauritania, Mali and southern Algeria, identified by the Total Ozone Mapping Spectrometer (TOMS) as the main source of the prominent winter/spring plume over the tropical Atlantic. The multiproxy characterization of the March 7–13 dust fall therefore enables us to typify the terrigenous signature of two different regions supplying dust off West Africa, and provide valuable clues for the interpretation of Northeastern Tropical Atlantic Ocean dust sedimentary records in terms of changes in provenance regions and transport systems. Additionally, because dust deposition data are scarce, flux and grain size data obtained in this study, among other parameters such as clay assemblages, provide important constraints for atmospheric transport models and dust deposition budget estimates in this area.

Climatically-controlled siliceous productivity in the eastern Gulf of Guinea during the last 40 000 yr

“…Similarly, investigation of diatom assemblages in a dust collector located at Mbour, Senegal, indicated that A. granulata and Hantzschia amphioxys are the two dominant diatoms in eolian dust coming from central and northern Sahara, respectively (Skonieczny et al, 2011). It is worth noting that H. amphioxys is absent from the diatom assemblages in core GeoB4905-4, which agrees well with an origin from the central Sahara of the eolian dust reaching the eastern Gulf of Guinea (Stuut et al, 2005).…”

“…This suggests a significant aeolian transport of opal phytoliths from the Namib desert to the ocean by southeast trade winds. Phytoliths were also found in aeolian dust collected at Mbour, Senegal (Skonieczny et al, 2011) along with Aulacoseira spp. and Hantzschia amphioxys and in sediment traps off western Africa (Romero et al, 1999).…”

Mineralogy and physicochemical features of Saharan dust wet deposited in the Iberian Peninsula during an extreme red rain event

“…Overall, and in agreement with previous studies that pointed out that major Saharan dust outbreaks affecting large desert areas typically involve mixing of dust entrained from different active dust source areas (Skonieczny et al, 2011;Formenti et al, 2014a), our mineralogical analysis, in combination with satellite imagery, BSC dust forecast, and forward-30 and backward-trajectory analyses, shows that this is the case here too, with PSA1 and PSA3 as the most probable dust source areas. Despite the difficulty in accurately pin-pointing the different source areas down to a local scale during such an extreme event, our results show that it is still possible to identify different regional dust signatures that help constraint potential dust source areas.…”

“…Most models of dust radiative forcing typically consider the smallest particles only (geometric diameter <10 µm) (Tegen and Lacis, 1996;Tegen, 2003). Such small sizes, however, do not represent the actual size of dust particles in major dust events, which in turn are the ones that most significantly contribute to entrain and transport desert mineral dust 25 (Skonieczny et al, 2011;Mahowald et al, 2014;Kok et al, 2017). Indeed, one of the causes of uncertainty in climate models is that the size distribution of dust particles is poorly constrained and typically the amount of smaller particles is overestimated (Kok, 2011).…”

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

“…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).…”