Holocene fluvial valley fill sources of atmospheric mineral dust in the Skeleton Coast, Namibia. Issue 12 (4th May 2017)

• Record Type: Journal Article
• Authors: Thomas, David S.G.; Durcan, Julie A.; Dansie, Andrew; Wiggs, Giles F.S.
• Is Part Of: Earth surface processes and landforms. Volume 42:Issue 12(2017)
• Page Start: 1884
• Page End: 1894
• Publication Date: 2017-05-04
• Subjects: mineral dust -- valley fill -- Holocene -- Aeolian -- Namibia; Geomorphology -- Periodicals; 551.4
• DOI: 10.1002/esp.4151
• Languages: English
• ISSNs: 0197-9337

Abstract

Abstract: Western Namibia is a significant global source of atmospheric mineral dust. We investigate the relationship between dust and source sediments, assessing the sustainability of dust flux. Remote sensing studies have highlighted specific ephemeral fluvial systems as important contributors to dust flux, including highlighting sections of valleys that are the origins of dust plumes in the period 2005–2008. Little is known however about the specific within‐valley dust sediment sources, particularly whether dust is derived from modern ephemeral channel floors or older valley fill sediments, many of which have been reported in the region. As part of a region‐wide analysis of aeolian dust flux, we investigate the sediment properties of atmospheric dust samples and valley sediments from the Huab valley, one of the principal regional dust sources. Trapped dust samples contain up to 88% very fine sand and silt when collected samples are disaggregated prior to analysis. Valley fill surface samples comprise 80% very fine sand and silt, and the surface of the modern ephemeral channel 30%. Valley fill sediments were sampled at depths up to 3.6 m below the present surface and reveal Holocene depositional ages from 0.6 ± 0.03 ka back to 9.79 ± 0.73 ka. These sediments contain 30% to 6% very fine sand and silt, with levels decreasing with depth and age. Aeolian bedforms in the valley system (nebkhas on the fill surface and climbing dunes on valley margins) indicate that aeolian processes under the influence of strong seasonal easterly winds likely result in dust being winnowed out of the valley fill surfaces, with sandy bedforms being constructed from the coarser component of the fill sediments. The volume of valley fill sediment suggests dust sourced from Holocene sediments is likely to continue into the future regardless of flow conditions in the modern channel system. Copyright © 2017 John Wiley & Sons, Ltd.