Measurements of windblown dust characteristics and ocean fertilization potential: The ephemeral river valleys of Namibia

Delivery of nutrients to the ocean by mineral aerosol deposition involves complex biogeochemical interactions that include atmospheric processing, dissolution and biotic uptake of available nutrients in the surface waters. Research into the fertilization potential of aeolian dust is currently constrained by a lack of understanding of the nutrient composition and bioavailability in dust source areas. Further, research into hot-spots of dust emission has largely focused on paleo-lacustrine sources and pans, to the detriment of other potential sources such as ephemeral river valleys in desert regions. Here, we investigate the sediment characteristics and nutrient content of windblown and surface sediments of a largely overlooked southern African dust source, Namibia's ephemeral river valleys. We deployed monitoring equipment in three river valleys to capture deflated sediments and monitor airborne dust concentration and meteorological conditions throughout an annual dust season. Our results show that windblown dust within the river valleys is easily transportable offshore from Namibia over the Benguela Upwelling System, an intensely productive region of the South Atlantic Ocean. We demonstrate that the windblown dust contains iron, phosphorus and nitrogen nutrients, each of which may positively impact primary production rates when deposited in the complex upwelling system. The river valley dust has a significantly higher content of nutrients than either of southern Africa's major dry lake bed dust sources, Etosha and Makgadikgadi Pans. This aeolian work builds on previous source sediment findings proposing the ephemeral river valleys of Namibia as regionally important sources of dust with enhanced ocean fertilisation potential.