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.

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Northern and eastern Africa were exposed to significantly wetter conditions relative to present during the early Holocene period known as the African Humid Period (AHP), although the latitudinal extent of the northward expansion of the tropical rain belt remains poorly constrained. New records of 230 Th xs -normalized accumulation rates in marine sediment cores from the Red Sea and Gulf of Aden are combined with existing records of western Africa dust and terrestrial records across the Sahara Desert, revealing that fluxes of dust transported east from the Sahara decreased by at least 50% during the AHP, due to the development of wetter conditions as far north as ~22°N. These results provide the first quantitative record of sediment and dust accumulation rates in the Red Sea and the Gulf of Aden over the past 20 kyrs and challenge the paradigm of vast vegetative cover across the north and northeastern Sahara Desert during the AHP.