Earth's driest regions act as a planetary "dustbin" for certain products of atmospheric photochemistry, and hence may inform us about changes in atmospheric chemistry and climate over the previous few million years. More specifically, significant end-products of atmospheric chemistry are oxidized aerosol particles including nitrates, sulfates, and perchlorates. These particles (or their gas-phase precursors) leave the atmosphere via rainout or dry deposition, but retain telltale signatures of their atmospheric origin in their isotopic compositions. In the driest places on Earth, these atmospherically-derived salts accumulate in soils (Ewing, 2006), and form an underexplored paleoclimate/paleochemistry record. Signals to be understood include changing sources of biogenic and volcanic chlorine, variations in ozone chemistry, paleo-rainfall rates, and identifying the dry-limit for microbial life in these desiccated soils. The rational for studying these hyper-arid areas is further motivated by the detection of perchlorate as the dominant soluble salt on Mars by NASA's Phoenix lander (Hecht, 2009), which remain difficult to explain from a theoretical perspective (Smith, 2011).

This project is primarily focused on numerical modelling of atmospheric chemistry, but also involves field work and geochemical analyses.  An existing 1-D photochemical model (Catling, 2010) will be developed to include expanded treatment of rainwater chemistry, particle formation, halogen chemistry, along with the inclusion of oxygen (17O and 18O) and chlorine (37Cl) isotopes. The multiple oxygen isotopes in particular will enable exploration of an extra degree of freedom evident in the data, helping reduce uncertainties in aerosol formation pathways. The model will be used to interpret vertical soil profiles obtained by the adviser in 2010 along an aridity gradient through Chile's Atacama desert, intersecting the regions with the lowest recorded rainfall rates on Earth (< 1mm/yr). This ground-truthed model will be of interest to additional studies in Earth Sciences, and so has the potential to lead to additional publications/collaborations beyond the scope of the project.

In addition to numerical modelling, the project includes field work in the Atacama to obtain additional samples needed to constrain the model, and laboratory training in Ion Chromatography to measure nitrates, chlorides, bromates, and (per)chlorates salts. Depending on student interest, the project could also include isotopic analysis, soil modelling, or modelling related to understanding perchlorate formation on Mars. The student will be actively encouraged to network through attendance at conferences, workshops and meetings at institutional, national and international levels. The project will be co-advised by Professor Roland von Glasow and would form a solid foundation for a career in Earth or planetary sciences.
 

Catling, D, Claire, M., Zahnle, K. et al. "Atmospheric origins of perchlorate on Mars and in the Atacama." JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS 115 (E00E11), 2010.

Ewing, SA, et al. "A threshold in soil formation at Earth's arid-hyperarid transition. "GEOCHIMICA ET COSMOCHIMICA ACTA, 70 (21), pp. 5293-5322, 2006.

Hecht, MH, et al. "Detection of Perchlorate and the Soluble Chemistry of Martian Soil at the Phoenix Lander Site." SCIENCE, 325 (5936), pp. 64-67, 2009.

Smith, M., Catling, D., Claire, M, Zahnle, K. "The Photochemistry of Early Mars: Implications for Sedimentary Minerals and Life" THE INTERNATIONAL CONFERENCE ON EXPLORING MARS HABITABILITY, Lisbon, Portugal 13-15 June, 2011.