Elemental and isotopic composition of surface soils from key Saharan dust sources

Abstract

Saharan dust contains significant amount of P, an important macronutrient to all living organisms, which has been shown to exert large effects on nearby and remote ecosystems located across the dust transport pathways. The biological effect of Saharan dust depends on the amount and nature of the P speciation of the dust. However, thus far relatively small numbers of samples frompotential source areas (PSA) has been analyzed. Here we report the P speciation (resin-P, HCl-P, Fe-bound-P and organic-P), the 18OP values, the elemental composition, and the 87Sr/86Sr and 143Nd/144Nd of the fine fraction and bulk soil from 5 important PSAs across Northern Africa. We found the HCl-P concentrations between different source areas were relatively constrained but that these concentrations were higher in the fine fraction, which here is used a surrogate for dust. The 18OP values for soils fromsand dunes varied from15.0 to 21.4 ,which is in the range of phosphate minerals fromsedimentary origin. The 18OP values of soils from dry lakes were significantly higher (24.0 28.5 ), probably since their P is derived from fossilized plankton that lived in the lake as it dried up. The 87Sr/86Sr and Nd values ranged from 0.7219 to 7276 and 12.7 to 14.0 in eastern samples and from 0.7146 to 0.7185 and 11.9 to 13.4 inwestern samples, suggesting a different source for the siliciclastic material of eastern and western samples. Our analysis indicates that the 18OP values are decoupled from the Sr and Nd isotopic systems. Together, the new chemical and isotope data are specific for different PSAs and thus are used for source apportionment purposes. Such data can be used to provide more accurate estimates of the flux of potentially bioavailable P to marine and terrestrial ecosystems. These estimates can be used in global climatemodels to determine themagnitude and distribution of P control on carbon uptake.

Linking Barbados Mineral Dust Aerosols to North African Sources Using Elemental Composition and Radiogenic Sr, Nd, and Pb Isotope Signatures

“…Our Nd isotopic behavior agrees well with previous reports for summertime Barbados aerosols during 2003-2011 (À14.1 ≤ ε Nd ≤ À11.4; average À 12.7 ± 0.78) (Pourmand et al, 2014). They are also in the range of values reported for the dust derived in North Africa (À17.9 to À10.1) Borg & Banner, 1996;Gross et al, 2016;Grousset et al, 1998;Grousset & Biscaye, 2005;Skonieczny et al, 2011;Skonieczny et al, 2013), over the North Atlantic (À14.2 to À11.2) (Aarons et al, 2013;Grousset et al, 1988), over the Mediterranean Sea (À12.4 to À10.9) (Grousset et al, 1988), and from different locations in the world under the influence of African dust events (À15.3 to À11.1) (Chauvel et al, 2014;Grousset et al, 1988Grousset et al, , 1998Kumar et al, 2014).…”

Kinetics of enzyme‐catalysed oxygen isotope exchange between phosphate and water revealed by Raman spectroscopy

“…However, knowledge about the kinetics of enzyme‐catalysed oxygen isotope exchange is of important value for environmental sciences. The oxygen isotope composition of phosphate has been used as a tracer of sources and processes of phosphorus in aquatic ecosystems, along soil chronosequences and rainfall gradients in terrestrial ecosystems, in arable soils or as a tracer of atmospheric phosphorus inputs to ecosystems . Most studies found that the oxygen isotope composition of bioavailable phosphate in environmental systems is close to equilibrium with the surrounding water.…”

Origin of calcium in pedogenic carbonate nodules from silicate watersheds in the Far North Region of Cameroon: Respective contribution of in situ weathering source and dust input

“…6) and Sr and Nd signatures measured in aerosols and dust deposits may show contrasted signatures, regarding their departure dust sources (Abouchami et al, 2013). To approximate a representative signature of the regional dust, we only considered aerosols and dust deposits, and selected data from specific regions expected to be dust sources for the study area as it is located along specific wind trajectories: i) the Harmattan deposits in Faya Largeau and Mao in Chad, as well as in N'guigmi and Niamey, Niger (Abouchami et al, 2013); ii) dust deposits in Niamey (Grousset et al, 1998); iii) two soil samples composed mainly of dust from the Bodélé Depression (Gross et al, 2016); and finally, iv) a calculated value for the aeolian end-member that contributed to soils recovered from the Mount Cameroon (Dia et al, 2006). The calculated average value is 0.716 ± 0.001 (n = 8) and − 11.5 ± 1.0 (n = 6) for 87 Sr/ 86 Sr and ε(Nd), respectively, and the Ca/Sr ratio and the Sr/Nd ratio are 179 ± 81 (n = 4) and 3.8 ± 1.6 (n = 6), respectively.…”

“…Error bars are the same as symbols. *Average data from Grousset et al (1998), Dia et al (2006), Abouchami et al (2013), and Gross et al (2016). 1 Grousset et al (1998); 2 Grousset et al (1992); 3 Grousset and Biscaye (2005); 4 Bory (1997); 5 Cole et al (2009);6 Skonieczny et al (2011);7 Borg and Banner (1996) Abouchami et al (2013); 10 Pelt et al (2013); 11 Dia et al (2006); 12 Gross et al (2016).…”

“…The black lines draw the hyperbolas between the "optimized" end-member/Saharan dust and the two bedrocks. 1 Grousset et al (1998), Dia et al (2006), Abouchami et al (2013) and Gross et al (2016). Where not shown, error bars are the same as symbols.…”