Environmental factors controlling the seasonal variability in particle size distribution of modern Saharan dust deposited off Cape Blanc

Carmen A. Friese*, Michèlle van der Does, Ute Merkel, Morten H. Iversen, Gerhard Fischer, Jan Berend W. Stuut

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

The particle sizes of Saharan dust in marine sediment core records have been used frequently as a proxy for trade-wind speed. However, there are still large uncertainties with respect to the seasonality of the particle sizes of deposited Saharan dust off northwestern Africa and the factors influencing this seasonality. We investigated a three-year time-series of grain-size data from two sediment-trap moorings off Cape Blanc, Mauritania and compared them to observed wind-speed and precipitation as well as satellite images. Our results indicate a clear seasonality in the grain-size distributions: during summer the modal grain sizes were generally larger and the sorting was generally less pronounced compared to the winter season. Gravitational settling was the major deposition process during winter. We conclude that the following two mechanisms control the modal grain size of the collected dust during summer: (1) wet deposition causes increased deposition fluxes resulting in coarser modal grain sizes and (2) the development of cold fronts favors the emission and transport of coarse particles off Cape Blanc. Individual dust-storm events throughout the year could be recognized in the traps as anomalously coarse-grained samples. During winter and spring, intense cyclonic dust-storm events in the dust-source region explained the enhanced emission and transport of a larger component of coarse particles off Cape Blanc. The outcome of our study provides important implications for climate modellers and paleo-climatologists.

Original languageEnglish
Pages (from-to)165-179
Number of pages15
JournalAeolian Research
Volume22
DOIs
Publication statusPublished - 1 Sept 2016

Funding

We thank the captains, crews and scientific teams of the research cruises with RV Meteor in 2003 (M58/2), RV Poseidon in 2004 (POS310), RV Meteor in 2005 (M65/2) and RV Poseidon in 2006 (POS344), during which the sediment traps were serviced. In addition, we thank Marco Klann for preparing and splitting the samples. JBS acknowledges funding from ERC Grant 311152 DUSTTRAFFIC. Funding is acknowledged from the German Science Foundation ( DFG ) through the DFG-Research Center/Cluster of Excellence “The Ocean in the Earth System”. For fruitful scientific discussions we further thank Prof. Dr. Dierk Hebbeln, Dr. Peter Knippertz and Dr. Gerlinde Jung.

Keywords

  • Dust-storm
  • Gravitational settling
  • Particle size spectrum
  • Saharan dust
  • Sediment trap mooring
  • Wet deposition

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