Seasonal radiogenic isotopic variability of the African dust outflow to the tropical Atlantic Ocean and across to the Caribbean

•Seasonality of dust radiogenic isotope signal at Cape Verde and Barbados.•Cape Verde summer dust fingerprints the Saharan Air Layer.•Shift in dust provenance during winter dust outbreak.•Long-range transport of African dust isotopic signal to the Caribbean.•Minor contribution of Bodélé Depression to dust outflow at Cape Verde and Barbados.