Determining controls on aeolian dust emissions: analysis of dynamic processes at Etosha Pan, Namibia.

The emission, transport, and deposition of windblown mineral aerosols (aeolian dust) represents a critical component in the Earth's land-atmosphere-ocean-biosphere system; impacting climate [1], ocean fertilisation [2], nutrient transport [3], air quality and human health [4]. Sophisticated numerical models offer the principal means of forecasting future global atmospheric dust loading and transport pathways of nutrient-laden dust plumes [5].As the relative impact of dust depends on the mineralogical and geochemical composition of theparticles, which is primarily determined by the terrestrial sources from which they are initially entrained, an accurate knowledge of the origin of erodible material, the identification of emission source areas, and data on the drivers governing eroding processes are a prerequisite for global dust emissions modelling [6]. Geomorphological studies dedicated to the detection and mapping of large-scale dust source areas using remote sensing data have identified ephemeral lakes in their dry phases (pans or playas) as regionally and globally significant dust sources [7,8]. Within these regions, stores of fine sediment are frequently replenished during flooding periods which, on drying, can become susceptible to aeolian erosion [9]. However, the relative sophistication of existing numerical models remains limited in representing dust emissions from these significant source regions [10].Whilst research to date has provided a general understanding of the windblown dust system, the processesby which sediment is eroded from the playa surface by wind areinherently complex [11]. This is due to dynamic variability in the environmental drivers that control sediment availabilityforerosion (i.e., the creation and breakdown of crusting, heaving, etc.) in response to variations in sediment geochemistry and atmospheric conditions [12]. Thus, inherent complexities in dynamic sediment availability through flooding events generate high spatial (i.e., sub-model grid) and temporal (i.e., seasonal and interannual) heterogeneityin emission sources, which are poorly depicted in model parametrisations developed from existing coarse-scale remote sensing observations [13]. The purpose of this research is to investigatethecomplex controls on sediment availability to refine our understanding of what defines the local-scale emissivity of sediment from ephemeral lakes. With the recent launch of new satellite sensors with high spatial and temporal resolution (e.g., PlanetScopeand ESA's Sentinel), a novel opportunity exists to identify specific 'hot-spot' dust emissionlocations and to characterise the spatio-temporal dynamics of controls on sediment availability for aeolian erosion. Combined with analysis of the mineralogical and geochemical composition of eroded sediment, this willallow for improvements in constraining control parameters of dust production from these significant source regions and thus improve assessments of the effects of emissions in response to changing environmental conditions in the future.