Aerosol time-series measurements over the tropical Northeast Atlantic Ocean: Dust sources, elemental composition and mineralogy

• Published in: Marine Chemistry
• Main Authors: Patey, Matthew D., Achterberg, Eric P., Rijkenberg, Micha J.A., Pearce, Richard
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2015
• Subjects: North Atlantic; Northeast Atlantic
• Online Access: https://eprints.soton.ac.uk/378077/; https://eprints.soton.ac.uk/378077/1/Patey_Aerosol.pdf

The North Atlantic receives the largest dust loading of any of the world's oceans due to its proximity to North African deserts and prevailing wind patterns. The supply of biologically important trace elements and nutrients via aerosols has an important influence on biogeochemical processes and ecosystems in this ocean region. In this study we continuously sampled aerosols between July 2007 and July 2008 at the Cape Verde Atmospheric Observatory (CVAO), which is situated on an island group close to the North African continent and under the Saharan/Sahelian dust outflow path. The aim of our work was to investigate temporal variations in aerosol concentration, composition and sources in the Cape Verde region over a complete seasonal cycle, and for this purpose we undertook mineralogical and chemical (42 elements) analyses of the aerosol samples and air mass back-trajectory calculations. Aerosol samples were also collected during a research cruise in the (sub-) tropical Northeast Atlantic Ocean in January 2008. The concentration of atmospheric Al, a proxy for mineral aerosol concentration, at CVAO was in the range of 0.01–66.9 ?g m? 3 (maximum on 28–30 January 2008) with a geometric mean of 0.76 ?g m? 3. It showed distinct seasonal variations, with enhanced Al concentrations in winter (geometric mean 1.3 ?g m? 3), and lower concentrations in summer (geometric mean 0.48 ?g m? 3). These observations have been attributed to dust transport occurring in higher altitude air layers and mainly north of the Cape Verde during summer, while in winter the dust transport shifts south and occurs in the lower altitude trade winds with consequent greater influence on the Cape Verde region. The elemental composition of the aerosols closely agreed with mean upper crustal abundances, with the exception of elements with pronounced anthropogenic sources (e.g. Zn and Pb) and major constituents of sea water (Na and Mg). Mineral analysis showed that clays were the most abundant mineral fraction throughout the whole sampling period, with ...