SOIL GEOCHEMISTRY IN THE PRESENCE OF LIFE, OR LACK OF IT, ALONG A HYPERARID PRECIPITATION GRADIENT IN THE ATACAMA DESERT, CHILE

The biogeochemistry of soil development in much of the world is characterized by the weathering of silicates, depletion of major elements, volumetric collapse, and eventual nutrient impoverishment. In contrast, soils in arid regions become repositories for chemical weathering products and atmospheric inputs. In the most extreme hyperarid regions, soils appear to retain virtually all atmospheric inputs, including soluble constituents such as nitrates and sulfates, resulting in large volumetric expansion during soil development. Under these conditions, biological incorporation of C and N into soil profiles (primary production) may be absent, or restricted to limited activity of endemic organisms. As a case study in extremely arid desert soils, we report on our initial investigations of soil and microbial biogeochemistry along a precipitation gradient (~15mm to ~2 mm yr^-1, south to north) in the Atacama Desert of northern Chile. Primary research sites were chosen on the oldest recognizable stream terraces/alluvial fans along the gradient (Pleistocene-aged ?). We characterize biogeochemical processes at these sites by focusing on the cycling/transport of C, N, and other major elements in the soils. Additionally, we focus on the size and character of the soil microbial community, with a goal of understanding how, or if, soil microbiological processes occur in extreme hyperarid soils that lack observable above-ground primary production. Our work will be presented in context with on-going research in the region by other geoscientists.