The identification of perchlorate on Mars by the Phoenix mission (Hecht et al. 2009 Science vol 325, 64) encouraged those who favored the Atacama Desert as an analog. However, in the Atacama, nitrate predominates wherever perchlorate is found and the extreme aridity is unlike the Phoenix landing site, where there is ice. In Israel, the site of a former ammonium perchlorate factory was investigated because of environmental concerns about perchlorate in both groundwater and the unsaturated zone but it is also a valuable Mars analog. The unsaturated zone comprises 40 m of sands with sandy clay and clay-rich layers in which bacteria with perchlorate reducing capability had been detected. Microbial perchlorate reduction occurs under anaerobic conditions, not those expected in the unsaturated zone, and the process needs water and an electron donor (e.g. trace organic matter). Chlorine stable isotope analyses quantitatively characterize both partially reduced perchlorate and the resultant chloride product. Our analyses show varying extents of perchlorate reduction in the unsaturated zone, up to 10%, but not correlated with depth, clay content, or water content. We assume that the reduction is occurring in microenvironments in a generally aerobic system but the precise source of the electron donor is still enigmatic; organic coatings on clays would be one possibility. This site, despite having been modified by human activity, is a valuable analog for possible microbial processes on Mars. The microbial activity has given another example of the persistence of life in an extreme environment where nutrients are extremely limited. Although not analogous in terms of Mars temperatures, this site offers the potential for new understanding of life processes (and new challenges for Mars exploration).
- 0448 BIOGEOSCIENCES / Geomicrobiology
- 5200 PLANETARY SCIENCES: ASTROBIOLOGY