Evaluating the relative importance of northern African mineral dust sources using remote sensing

Natalie L Bakker,Nick A Drake,Charlie S Bristow

doi:10.5194/acp-19-10525-2019

Abstract

Abstract. Northern African mineral dust provides the Amazon Basin with essential nutrients during the boreal winter months, when the trajectory of the Saharan dust plume is towards South America. This process, however, is still poorly understood. There is little knowledge of where the dust is coming from, and, thus, little information regarding the concentration of nutrients in the dust. This information is vital to assess the impact it will have on the Amazon. In order to further our understanding of the problem, this study analyses northern African dust sources of the boreal winter dust seasons between the years 2015 and 2017. It utilises high spatio-temporal resolution remote sensing data from SEVIRI, MODIS, VIIRS, and Sentinel-2 to identify dust sources, classify them according to a geomorphic dust source scheme, and quantify the relative importance of source regions by calculating the total dust mass they produce. Results indicate that palaeolakes emit the most dust, with the Bodélé Depression as the single largest dust source region. However, alluvial deposits also produce a substantial amount of dust. During the boreal winter dust seasons of 2015–2017, ∼36 % of the total dust mass emitted from northern Africa was associated with alluvial deposits, yet this geomorphic category has been relatively understudied to date. Furthermore, sand deposits were found to produce relatively little dust, in contrast to the results of other recent studies.

Highlights

Mineral dust is an important component of the Earth system, affecting radiative forcing, cloud properties, and playing a key role in terrestrial, oceanic, atmospheric, and biogeochemical exchanges (Harrison et al, 2001; Jickells et al, 2005; Mahowald et al, 2010)
The dust point sources per geomorphological class are shown in Table 1; the vast majority were associated with alluvial deposits (51.11 %) or palaeolakes (42.85 %)
This study provides a quantitative analysis of wintertime northern African mineral dust sources

Summary

Introduction

Mineral dust is an important component of the Earth system, affecting radiative forcing, cloud properties, and playing a key role in terrestrial, oceanic, atmospheric, and biogeochemical exchanges (Harrison et al, 2001; Jickells et al, 2005; Mahowald et al, 2010). The Sahara and the Sahel are the world’s largest dust source regions, emitting several hundred teragrams of mineral dust yearly (Ridley et al, 2012). Most of this dust is carried over large distances and transported west and southwest across the Atlantic Ocean (Chiapello et al, 1997). In order to better understand past, current, and future impacts of northern African mineral dust on the Amazon Basin, the biogeochemical properties of the dust need to be determined. It has been shown that these properties differ significantly based on the geology and geomorphology of the terrestrial source (Gross et al, 2015, 2016); it is critical to precisely identify dust sources and their geomorphic nature

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