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Stellenbosch University (2021)

Southern African dust characteristics and potential impacts on the surrounding oceans

Kangueehi, Kaukurauee Ismael

Titre : Southern African dust characteristics and potential impacts on the surrounding oceans

Auteur : Kangueehi, Kaukurauee Ismael

Université de soutenance : Stellenbosch University

Grade : Doctoral Degree (Earth Sciences) 2021

Résumé partiel
This study supports understanding the potential impact of dust aerosols from southern Africa have on the proximal ocean ecosystems. Dust can release essential nutrients and thus fertilize the ocean, which affects the food-web and the carbon dioxide concentrations in ocean waters, i.e. climate. Dust that fertilizes the phytoplankton communities in open oceans stimulates the drawdown of carbon dioxide from the atmosphere through the process of photosynthesis. Key here is that the nutrients must be released from the aerosol particles, as they can only be uptaken by biological organisms in soluble form. However, mineral dust emitted from arid environments differ from dust emitted through industrial activities ; as a result the solubility and, by extent, potential impact on the ocean may also differ. In this study, I investigated mineral characteristics and solubility of dust from three distinct regions, one with a strong human footprint (Saldanha Bay), one with mostly natural mineral dust (Namib Desert) and one off shore over the Southern Ocean. The first study targeted Saldanha Bay, a town that hosts the largest port in South Africa, with exports of up to 60 million tons of iron and manganese ore annually and is home of a steel plant and a smelter. Satellite images and photos from the area have shown extensive dispersion of dust from the area. Solubility leaching experiments revealed that dust collected in this town is highly soluble (bioaccessible) for trace metals such as Fe (up to 28%), Cu (up to 33%), Pb (up to 45%) and Zn (up to 38%). Phytoplankton communities in open oceans are sometimes depleted in these trace metals, and thus, such high solubility of dust from Saldanha Bay can prove to be an important nutrient supplier to surrounding oceans. In addition, air mass trajectories revealed that this readily available dust most likely affects the southeast Atlantic and Indian Ocean. The major implication was that harbour towns can be essential sources of trace metals to proximal oceans. Secondly, I present results from the largest non-playa environment in the Namib Desert. Some of the prominent dust emitters located in the Namib Desert provide, feed and source of hundreds of tons of mineral dust to proximal surface ocean waters.

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Page publiée le 17 avril 2022