Oxygen isotopes in single micrometer-sized quartz grains: tracing the source of Saharan dust over long-distance atmospheric transport |
| |
| Authors: | Jérôme Aléon Marc ChaussidonBernard Marty Lothar SchützRuprecht Jaenicke |
| |
| Institution: | 1 Centre de Recherches Pétrographiques et Géochimiques-Centre National de la Recherche Scientifique, 15 rue Notre-Dame des Pauvres, BP 20, 54501 Vandoeuvre-lès-Nancy, France
2 Institut für Physik der Atmosphäre-Johannes Gutenberg Universität, Postfach 3980, Becherweg 21, D-55099 Mainz, Germany |
| |
| Abstract: | Oxygen isotope compositions were measured by ion microprobe in individual micrometer-sized quartz grains extracted from one aerosol sample collected on the Cape Verde Islands and from four surface samples (three soils and one sediment) representing potential source regions of aerosols in Western and Central Africa (Morocco, Algeria, Niger, and Chad). A large range of δ18O values, from +6.2‰ to +39.3‰ is present within the aerosol quartz grains. The different size fractions of the quartz grains from the surface samples overlap nearly entirely this range but show significant differences in their δ18O distributions for the different size fractions of the grains (i.e., different modes, different proportions of grains with low or high δ18O, ...). These differences in δ18O distributions can be related to different geological formations (i.e., mantle-derived magmatic rocks, crustal magmatic rocks, or sedimentary rocks) outcropping in each region, thus giving a fingerprint of the source region. Quartz grains with unusually high δ18O values between +30‰ and +40‰ were attributed to lacustrine cherts formed in evaporitic environments (Chad basin).The existence of distinct δ18O distributions for the surface samples, which reflect regional geology but indicate some transport of the grains, enables the characterization of mixing processes during dust emission in the atmosphere. Particles are mixed at a regional scale in the dust reservoir, but injection of fine particles into the high troposphere occurs as a discrete and localized event with no mixing during the subsequent long-range transport by the easterlies. The comparison of the δ18O distribution of the quartz from the aerosol sample with the equivalent size fractions in surface samples shows that the Niger area is the more probable source region for the aerosol although the Moroccan source cannot be excluded. This method gives a valuable tool to trace the source region of dust into the atmosphere or into sediment samples, allowing the reconstruction of air mass circulations. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
