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Accueil du site → Doctorat → Royaume-Uni → 2017 → The role of windblown dust from ephemeral river valleys in the fertilisation of the Benguela Upwelling System

University of Oxford (2017)

The role of windblown dust from ephemeral river valleys in the fertilisation of the Benguela Upwelling System

Dansie, Andrew

Titre : The role of windblown dust from ephemeral river valleys in the fertilisation of the Benguela Upwelling System

Auteur : Dansie, Andrew

Université de soutenance : University of Oxford

Grade : Doctor of Philosophy (PhD) 2017

Résumé
The deposition of dust on the global ocean provides essential nutrients for biological primary production. Research into aeolian dust has focused on dust sources identified at the global scale by the emission of mineral aerosols a minimum of one kilometre into the atmosphere. The deflation origins of these global hot-spots of dust are major topographical pan features providing paleolacustrine sources of fine, desiccated sediment that is highly susceptible to wind erosion. However, small-scale geomorphological features are being increasingly identified as significant emitters of dust. Namibia’s twelve western ephemeral river valleys are known to regularly produce dust but have remained largely overlooked as a regionally significant source of dust and as a contributor to ocean fertilisation. The depositional area of the river valley dust is the adjacent marine Benguela Upwelling System which hosts one of the highest primary production rates in the world’s oceans. In this research correlation between terrestrial airborne dust concentrations, aeolian dust and oceanic chlorophyll levels is assessed and the fertilisation potential of dust from three river valleys is investigated. The results provide the first direct evidence of the contribution of river valley dust to ocean fertilisation within the highly productive Benguela upwelling system. The research further shows that Namibia’s river valleys provide an enriched source of aeolian nutrients, most importantly for bioavailable iron, with windblown dust and source sediments having a higher fertilisation potential than either of southern Africa’s major pan dust source areas. These enriched sediments in the dust-emitting lower regions of the three river valleys are shown to occur irrespective of upper catchment rainfall, land use or geology. This suggests that similarly enriched dust source sediments would be common to all twelve valleys, resulting from comparable geomorphological processes, and the river valleys are therefore a regionally significant source of ocean fertilising dust. This research demonstrates the impact that small-scale dust sources can have and that riverine dust sources can be a source of highly fertile mineral aerosols that warrant increased research attention.

Présentation (ETHOS)

Page publiée le 29 novembre 2019