Contribution of the world's main dust source regions to the global cycle of desert dust

Abstract

Abstract. Even though desert dust is the most abundant aerosol by mass in Earth's atmosphere, the relative contributions of the world’s major dust source regions to the global dust cycle remain poorly constrained. This problem hinders accounting for the potentially large impact of regional differences in dust properties on clouds, the Earth's energy balance, and terrestrial and marine biogeochemical cycles. Here, we constrain the contribution of each of the world’s main dust source regions to the global dust cycle. We use an analytical framework that integrates an ensemble of global model simulations with observationally informed constraints on the dust size distribution, extinction efficiency, and regional dust aerosol optical depth. We obtain a data set that constrains the relative contribution of each of nine major source regions to size-resolved dust emission, atmospheric loading, optical depth, concentration, and deposition flux. We find that the 22–29 Tg (one standard error range) global loading of dust with geometric diameter up to 20 μm is partitioned as follows: North African source regions contribute ~50 % (11–15 Tg), Asian source regions contribute ~40 % (8–13 Tg), and North American and Southern Hemisphere regions contribute ~10 % (1.8–3.2 Tg). Current models might on average be overestimating the contribution of North African sources to atmospheric dust loading at ~65 %, while underestimating the contribution of Asian dust at ~30 %. However, both our results and current models could be affected by unquantified biases, such as due to errors in separating dust aerosol optical depth from that produced by other aerosol species in remote sensing retrievals in poorly observed desert regions. Our results further show that each source region's dust loading peaks in local spring and summer, which is partially driven by increased dust lifetime in those seasons. We also quantify the dust deposition flux to the Amazon rainforest to be ~10 Tg/year, which is a factor of 2–3 less than inferred from satellite data by previous work that likely overestimated dust deposition by underestimating the dust mass extinction efficiency. The data obtained in this paper can be used to obtain improved constraints on dust impacts on clouds, climate, biogeochemical cycles, and other parts of the Earth system.

Interannual Variability in the Source Location of North African Dust Transported to the Amazon

“…Our finding that there is interannual variability in the source of dust transported to Cayenne agrees with a recent modeling study showing Cayenne is located near (within ∼1°) a transition zone whereby both Western and Central African dust sources contribute equally to dust deposition in the Amazon (Kok et al, 2021). Model runs in Kok et al show that the Central PSA (which in their study includes the Sahel region) can contribute between 16% and 53% of dust deposition to the Amazon while the Western PSA (which in their study combined the Western-PSA2 and Western-PSA3) can contribute between 28% and 53% of the annual deposition flux.…”

“…A shift toward more radiogenic ε Nd values in transported dust collected at Amazon Tall Tower Observatory (ATTO) in summer and fall is observed and the authors suggest this dust originated from southern Africa (Nogueira et al, 2021). In our samples, however, we see no comparable shift in ε Nd values, which suggests dust transport to Cayenne is not from southern Africa during summer and fall, in agreement with findings from previous modeling and remote sensing studies (Kok et al, 2021;Prospero et al, 2020). The reason for the seasonal differences between Amazon Tall Tower Observatory (ATTO) and Cayenne is likely due to the location of Cayenne, approximately 1,000 km northeast of ATTO (Figure 1).…”

Present‐Day Patagonian Dust Emissions: Combining Surface Visibility, Mass Flux, and Reanalysis Data

“…Persistent cloud cover makes remote sensing of dust activity difficult (Gassó & Stein, 2007; Gassó et al., 2010; Johnson et al., 2011) and Aerosol Optical Depth is underestimated compared to surface‐based Aerosol Robotic Network measurements in the Southern Hemisphere (Schutgens et al., 2020). In turn, high uncertainties still persist in modeled dust emissions for southern South America (Kok et al., 2021; Takemura et al., 2009), in part due to underrepresentation of source areas (e.g., Ohgaito et al., 2018; Takemura et al., 2009) which are too small to be realistically parameterized in degree‐scale global models (Bullard et al., 2016). Thus, observational surface constraints of dust activity are key to informing dust models and reanalyzes such as NASA's Modern‐Era Retrospective analysis for Research and Applications, Version 2 (MERRA‐2) on source location and both intensity and temporal variability of emissions in Patagonia.…”

Airborne Bacterial Community Composition According to Their Origin in Tenerife, Canary Islands

“…Desert dust that originates in the arid and desert environments of our planet are one of the main sources of aerosolized particles. The Sahara–Sahel region itself accounts for about 50% of that dust, contributing 11–15 Tg of dust per year ( Kok et al, 2021 ).…”