North African mineral dust across the tropical Atlantic Ocean: Insights from dust particle size, radiogenic Sr-Nd-Hf isotopes and rare earth elements (REE)

Abstract

Large amounts of mineral dust are exported from North Africa across the Atlantic Ocean, impacting the atmosphere and ocean during transport and after deposition through biogeochemical processes. In order to characterize the isotopic signature of dust from different seasons and years, in relation to their bulk particle size, and to obtain a general idea of its provenance, Saharan dust was collected using subsurface sediment traps moored in the tropical North Atlantic Ocean in 2012-2013, and by shipboard aerosol collection during three trans-Atlantic research cruises in 2005, 2012 and 2015. The samples were analysed for radiogenic Strontium (Sr), Neodymium (Nd), and Hafnium (Hf) isotopes, rare earth element (REE; La-Lu) abundances and particle size. In addition, soil sediments from Mauritania, a potential source area, were analysed and compared to the Atlantic dust samples. The results indicate no relation between Sr and Nd isotopic compositions and dust particle size. In contrast, Hf isotopic compositions show a strong relation with particle size, associated to the so-called zircon effect. We explored alternative sources of lithogenic particles to the sediment traps such as Amazon River sediments. Our results reveal that the sediment-trap samples bear distinctly different geochemical signatures from sediments from the Amazon Basin and Amazon River tributaries, and confirm that the primary source of lithogenic particles is northern Africa. The collected dust samples show close relations to African dust aerosols collected at Barbados and samples from the Bodélé Depression, although differences between seasons are observed, which we relate to differences in source areas.

Mineral phosphorus drives glacier algal blooms on the Greenland Ice Sheet

“…The REE (rare earth element) signatures of the mineral fraction in our surface samples were used to assess dust source. The REE signatures were homogenous and exhibited a positive Eu/Eu* anomaly analogous to local sources (Supplementary Note 6 , Supplementary Table 14 ) 29 – 31 thereby excluding distal sources characterized by a negative Eu/Eu* anomaly (Asian 32 and African 33 dust) as significant contributors (Fig. 6a, b ).…”

The antiquity of the Sahara Desert: New evidence from the mineralogy and geochemistry of Pliocene paleosols on the Canary Islands, Spain

“…6). Van der Does et al (2016Does et al ( , 2018, however, have recently documented aeolian transport of sand-sized particles to the open ocean, so the earlier finding of Thiede et al (1982) may not necessarily exclude an aeolian origin for mica. Nevertheless, although studies of marine sediments have suggested a relatively great age (Pliocene or Miocene) for the Sahara, there are limitations on the interpretation of an African origin for what is thought to be the aeolian component of such sediments.…”

Examination of the ocean as a source for atmospheric microplastics

“…It could be possible the triboelectric effect [52] of air passing over the plastic will statically charge the particle and make it attract dust. Van der Does et al (2018) [57] suggest this effect could assist particles to remain aloft. The triboelectric effect may also potentially increase plastic particle's potential to be entrained after ocean expulsion (bubble burst/jet expulsion) and transported, similar to ultragiant dust [52].…”