Biogeochemical Heterogeneity in Mars Analog Soils from the Atacama Desert

Water is ubiquitous on Earth and plays a fundamental role in all aspects of biogeochemical cycling. Our existence on an aqua planet hampers our ability to interpret a planet like Mars where it may not have rained for a billion years. Soils from the hyperarid core of Chile's Atacama Desert may represent the closest geochemical analog to Martian soils, as this region has the lowest precipitation on Earth. The extreme lack of rainfall (a few mm per decade) limits both weathering and biological activity to the point where soils are effectively sterile. Oxidized end products of atmospheric chemistry such as nitrate and perchlorate build up to values approaching those measured on Mars by NASA's Phoenix Lander. In June 2012, we collected soil samples from 8 locations along an aridity gradient from the hyperarid core of the Atacama (rainfall < 1 mm/yr) towards the arid (5-100 mm/yr) surrounding areas where microbial community activity is sufficient to support the hardiest of desert plant species. Field observations indicate that microbial activity and geochemical heterogeneity are anti-correlated. We will present our quantitative results coupling geochemical heterogeneity (salt concentrations, org C/N, trace metals) and microbial community activity (TRFLP, nitrogen cycling) along this transect, and argue that geochemical heterogeneity (which could be measured by a rover or lander on Mars) may be a proxy for lifeless soils.