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Volume 16, issue 21 | Copyright

Special issue: The Saharan Aerosol Long-range Transport and Aerosol-Cloud-interaction...

Atmos. Chem. Phys., 16, 13697-13710, 2016
https://doi.org/10.5194/acp-16-13697-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 04 Nov 2016

Research article | 04 Nov 2016

Particle size traces modern Saharan dust transport and deposition across the equatorial North Atlantic

Michèlle van der Does1, Laura F. Korte1, Chris I. Munday1, Geert-Jan A. Brummer1,2, and Jan-Berend W. Stuut1,3 Michèlle van der Does et al.
  • 1NIOZ, Royal Netherlands Institute for Sea Research, Department of Ocean Systems, and Utrecht University, Texel, the Netherlands
  • 2Faculty of Earth and Life Sciences, Vrije Universiteit Amsterdam, Amsterdam, the Netherlands
  • 3MARUM, Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany

Abstract. Mineral dust has a large impact on regional and global climate, depending on its particle size. Especially in the Atlantic Ocean downwind of the Sahara, the largest dust source on earth, the effects can be substantial but are poorly understood. This study focuses on seasonal and spatial variations in particle size of Saharan dust deposition across the Atlantic Ocean, using an array of submarine sediment traps moored along a transect at 12°N. We show that the particle size decreases downwind with increased distance from the Saharan source, due to higher gravitational settling velocities of coarse particles in the atmosphere. Modal grain sizes vary between 4 and 32µm throughout the different seasons and at five locations along the transect. This is much coarser than previously suggested and incorporated into climate models. In addition, seasonal changes are prominent, with coarser dust in summer and finer dust in winter and spring. Such seasonal changes are caused by transport at higher altitudes and at greater wind velocities during summer than in winter. Also, the latitudinal migration of the dust cloud, associated with the Intertropical Convergence Zone, causes seasonal differences in deposition as the summer dust cloud is located more to the north and more directly above the sampled transect. Furthermore, increased precipitation and more frequent dust storms in summer coincide with coarser dust deposition. Our findings contribute to understanding Saharan dust transport and deposition relevant for the interpretation of sedimentary records for climate reconstructions, as well as for global and regional models for improved prediction of future climate.

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We studied seasonal and spatial variations in particle size of Saharan dust deposition along a transect in the Atlantic Ocean, using an array of moored submarine sediment traps. We show a downwind decrease in particle size, but seasonal changes are also prominent. In addition, the dust is much coarser than previously suggested and incorporated into climate models.
We studied seasonal and spatial variations in particle size of Saharan dust deposition along a...
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