ROLE OF EXTREME WINDS SHAPING COASTAL ARID ECOSYSTEMS: RELATION BETWEEN SOIL AND DUST IN COASTAL NAMIBIA

Diffusion and absorption of radiation are directly impacted by mineral dust aerosols, currently representing the greatest uncertainty of the radiative forcing in global climate models. Dust production models in global circulation models are based on parameterized theoretical models and idealized laboratory of field experiments. Consequently, this can lead to a misrepresentation of the size and composition of dust particles when evaluating their distribution and subsequent radiative effects. This project is part of a series of campaigns to better understand the influence of mineral aerosols in the southeast Atlantic. Therefore, the objective is to quantify the enrichment of soils from dust particles locally transported to better assess the biological cycling and the radiative effects related to the parent soil material. Three valleys (Huab, Omaruru, Kuiseb) have been selected, considering their importance in potential soil and oceanic fertilisation derived from their active aeolian transport; all with a currently unknown net sediment transport direction between the consistent southwesterly trade wind and episodic easterlies. For each valley, data were collected in August-September 2017 from: surface soil samples throughout the valley deposited behind vegetation, horizontal transport traps, and PM₁₀ aerosol filters. In addition, meteorological data were collected to better understand the influence of wind direction, frequency and intensity. Between May and June 2018, experiments with a resuspension chamber have been performed, coupled with size distributions (Coulter method), as well as XRF and XRD analyzes, to compare the impact of sediment derived from several transport modes on their radiative and chemical properties. Theses various approaches aim to improve the performance and the standard procedures for measuring dust particles. Though satellite imagery has been helpful to investigate the main emission sources in the coast of Namibia, the relation between soil and airborne dust for theses several valleys are not well understood. Hence, these results aim to look at the relation of parent material versus emitted particles, as well as the differences of the environmental component for the three valleys. This is achieved by comparing size distributions and resuspension chamber resulting elemental and mineralogy analyses, all which are necessary to better understand the role of particle characteristics as part of an influence on its environment and dust transport.