Major Element Signatures of Silicate Dust Deposited on the West African Margin: Links With Transport Patterns and Provenance Regions

Abstract

AbstractMineral dust deposition characteristics are poorly constrained, even in the Northeastern Tropical Atlantic Ocean, which is immediately downwind of the Saharan desert and the largest marine repository of aeolian dust in the world. Here, we report on a 2‐year (March 2013–February 2015) time series of deposited dust on the Senegalese margin. This record enables us to document the chemical variability (major elements) of the settling Saharan dust (<30 µm silicate fraction, i.e., carbonate‐free) at a resolution varying from one week to one day, along with the deposition flux. This continuous time series reveals a greater geochemical diversity than previously reported, particularly during the dry winter‐spring season when continental trade winds sweep across vast regions of West Africa at low atmospheric levels before reaching the sampling site. By contrast, during major deposition events, which make up for most of the yearly flux, our record shows that Saharan dust chemical composition displays much narrower ranges. Trajectory analyses indicate that these relatively well‐defined chemical signatures are due to the limited number of provenance sectors involved during major deposition occurrences. The chemical characterization of the dust deposited during these events, hence, allows identifying the major element fingerprint of the related source regions, the most important one being a sizable area at the border of Algeria and Mali including the Tanezrouft desert north of the Taoudeni basin. Also, since these major events are associated with major Saharan outbreaks, they provide estimations of the prevailing elemental signatures for Saharan dust impacting the Northeastern Tropical Atlantic Ocean.