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Volume 17, issue 9 | Copyright

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

Atmos. Chem. Phys., 17, 6023-6040, 2017
https://doi.org/10.5194/acp-17-6023-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 16 May 2017

Research article | 16 May 2017

Downward particle fluxes of biogenic matter and Saharan dust across the equatorial North Atlantic

Laura F. Korte1, Geert-Jan A. Brummer1,2, Michèlle van der Does1, Catarina V. Guerreiro3, Rick Hennekam1, Johannes A. van Hateren1,2, Dirk Jong1, Chris I. Munday1, Stefan Schouten4,5, and Jan-Berend W. Stuut1,6 Laura F. Korte 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, the Netherlands
  • 3University of Bremen, Faculty of Earth Sciences, Bremen, Germany
  • 4NIOZ – Royal Netherlands Institute for Sea Research, Department of Marine Microbiology and Biogeochemistry, and Utrecht University, Texel, the Netherlands
  • 5Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Utrecht, the Netherlands
  • 6MARUM – Center for Marine Environmental Sciences, University of Bremen, Germany

Abstract. Massive amounts of Saharan dust are blown from the coast of northern Africa across the Atlantic Ocean towards the Americas each year. This dust has, depending on its chemistry, direct and indirect effects on global climate which include reflection and absorption of solar radiation as well as transport and deposition of nutrients and metals fertilizing both ocean and land. To determine the temporal and spatial variability of Saharan dust transport and deposition and their marine environmental effects across the equatorial North Atlantic Ocean, we have set up a monitoring experiment using deep-ocean sediment traps as well as land-based dust collectors. The sediment traps were deployed at five ocean sites along a transatlantic transect between north-west Africa and the Caribbean along 12°N, in a downwind extension of the land-based dust collectors placed at 19°N on the Mauritanian coast in Iouîk. In this paper, we lay out the setup of the monitoring experiment and present the particle fluxes from sediment trap sampling over 24 continuous and synchronized intervals from October 2012 through to November 2013. We establish the temporal distribution of the particle fluxes deposited in the Atlantic and compare chemical compositions with the land-based dust collectors propagating to the downwind sediment trap sites, and with satellite observations of Saharan dust outbreaks.

First-year results show that the total mass fluxes in the ocean are highest at the sampling sites in the east and west, closest to the African continent and the Caribbean, respectively. Element ratios reveal that the lithogenic particles deposited nearest to Africa are most similar in composition to the Saharan dust collected in Iouîk. Downwind increasing Al, Fe and K contents suggest a downwind change in the mineralogical composition of Saharan dust and indicate an increasing contribution of clay minerals towards the west. In the westernmost Atlantic Ocean, admixture of re-suspended clay-sized sediments advected towards the deep sediment trap cannot be excluded. Seasonality is most prominent near both continents but generally weak, with mass fluxes dominated by calcium carbonate and clear seasonal maxima of biogenic silica towards the west. The monitoring experiment is now extended, with autonomous dust sampling buoys for better quantification of Saharan dust transport and deposition from source to sink and their impact on fertilization and carbon export to the deep ocean.

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We collected Saharan dust at the Mauritanian coast as well as in the deep the North Atlantic Ocean, along a transect at 12 °N, using an array of moored sediment traps. We demonstrated that the lithogenic particles collected in the ocean are from the same source as dust collected on the African coast. With increasing distance from the source, lithogenic elements associated with clay minerals become more important relative to quartz which is settling out faster. Seasonality is prominent, but weak.
We collected Saharan dust at the Mauritanian coast as well as in the deep the North Atlantic...
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