Atmospheric deposition across the Atacama Desert, Chile: Compositions, source distributions, and interannual comparisons

Abstract

Hyper-arid areas such as the Atacama Desert accumulated significant amounts of insoluble dust and soluble salts from the atmosphere, providing minable salt deposits as well as mimicking the surface processes on Mars. The deposition rates, compositions and sources, however, were poorly constrained. Especially, the variabilities of atmospheric deposition in the Atacama Desert corresponding to a changing climate were unassessed. In this work, the atmospheric depositions collected using dust traps across a west-east elevation gradient in the Atacama (~23°S) from 1/2/2010 to 12/31/2011 were analyzed and compared to previous results in 2007–2009. The insoluble dust deposition rates in our sampling period were significantly higher than those of 2007–2009 in most dust traps, which was attributed to the changes in wind, highlighting the importance of long-term monitoring of insoluble dust fluxes. Soluble salts, instead, showed less distinct interannual variations in deposition rates, geochemical compositions or source contributions. At the coastal site (T1), soluble salts were originated from both primary sea-salt (SS) aerosols and non-sea-salt (NSS) sources such as anthropogenic emission, marine biogenic emission and biomass burning; the deposition rates of these salts largely depended on the wind speed and the amount of anthropogenic emissions. Sulfur isotopic evidence further showed that NSS sulfate at T1 was mainly originated from local SO2 emission from local power plants. The inland sites (T2-T8) displayed much lower soluble salts deposition rates, and the salts were primarily sourced from entrainment of local surface minerals, including Na(Cl, NO3), CaSO4, and nitrate formed via atmospheric oxidation of anthropogenic NOx. Sulfur isotopic compositions of sulfate deposited at T2-T8 were similar to those in local surface soil; however, three sites near the Chuquicamata mine showed slightly lower δ34Ssulfate values, indicating the presence of secondary sulfate originated from mining activities. The soluble salts deposited at the Andean site (T10) were dominantly from wet deposition that incorporated local lake salts, and therefore, the deposition rates were mainly controlled by the amount of precipitation.