Namib desert dust affects phytoplankton biomass in the Benguela upwelling region: Insights from first mesocosm study

The Benguela upwelling system (BUS) is frequently subject to dust deposition from southern Africa, which supplies macronutrients and trace metals to the ocean. The impact of these nutrients on chlorophyll-a (Chl-a) in the BUS was investigated using the first-ever mesocosm study from 29 September to October 12, 2022. The study employed a single triplicate treatment where mesocosms were seeded with dust (DG) from the Kuiseb ephemeral riverbed, one of the leading dust sources in southern Africa and one unamended control (CM). All mesocosms were also seeded with equal amounts of Chaetoceros, Pavlova, and Tetraselmis, species of phytoplankton commonly found in the BUS. Temporal dynamics in Chl-a, iron (Fe), nitrate (NO₃⁻), silicon (Si), orthophosphate (PO₄³⁻), and light intensity were measured. The data suggests that adding dust from the Namib desert elicited a positive response from the phytoplankton in the BUS, as evidenced by higher Chl-a concentrations in the DG compared to the CM. This study demonstrates the likely importance of southern African dust emission and deposition for phytoplankton productivity in the adjacent BUS.