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Habitability of hyperarid Atacama Desert soil and implication on Martian habitats

Abstract

The hyperarid core of the Atacama Desert is one of the driest places on Earth and has been for more than 10 million years, rendering the soils a suitable analog environment for Mars, where today´s life detection methods come to their limit of sensitivity. However, a recent study has shown that after rare rainfall events these Mars-like soils can temporarily support an active microbial community. Our goal is to characterize the physicochemical properties of these soils habitats, giving indications on the presence of water and its pathways within the soil (rain water infiltration vs. ground water evaporation). Therefore, we investigated within the hyperarid core multiple soil profiles along a few kilometer long transect using sedimentological and geochemical methods (e.g. grain size analysis, X-ray diffraction, ion chromatography and mass spectrometry of sulfur isotopes). The data show that highly soluble salts (e.g. halite, nitratine) are concentrated in the base of soil profiles located at low altitudes. Sulfates are abundant as calcium sulphate throughout the entire profiles and are concentrated in the upper parts of the investigated soil. These sulfates shift from the hydrated gypsum turning into anhydrate with depth, which also correlates with the sulfate δ34S values, showing a fractionation within the gypsum containing soil profile. Our findings confirm an infiltration of water by rain events to a limited depth (ranging from 0.3 to 0.7 m) keeping the calcium sulfate hydrated. This shows that only above the transition of gypsum to anhydrite, water might be sufficiently available for the soil to be habitable, whereas below the transition the water activity is presumably too low for microbial activity. We aim to extend this study to all Atacama soil types and to combine these findings with remote sensing data to create a habitability map for the Yungay Valley in the Atacama Desert which is well suited as a test bed for Mars exploration.
Habitability of hyperarid Atacama Desert soil
and implications on Martian habitats
ARENS, FELIX L.; Airo, Alessandro; Sager, Christof; Schulze-Makuch, Dirk
Center of Astronomy & Astrophysics, Technical University Berlin, 10623 Berlin
The hyperarid core of the Atacama Desert, Chile, is one of the driest places on Earth and has been for
more than 10 million years, rendering the soils a suitable analog environment for Mars, where today´s
life detection methods come to their limit of sensitivity. However, a recent study has shown that after
rare rainfall events these Mars-like soils can temporarily support an active microbial community
(Schulze-Makuch et al. 2018). Our goal is to characterize the physicochemical properties of these soils
habitats, giving indications on the presence of water and its pathways within the soil (rain water
infiltration vs. ground water evaporation). Therefore, we investigated within the hyperarid core
multiple soil profiles along a few kilometer long transect using sedimentological and geochemical
methods (e.g. grain size analysis, X-ray diffraction, ion chromatography and mass spectrometry of
sulfur isotopes). The data show that highly soluble salts (e.g. halite, nitratine) are concentrated in the
base of soil profiles located at low altitudes. Sulfates are abundant as calcium sulphate throughout the
entire profiles and are concentrated in the upper parts of the investigated soil. These sulfates shift
from the hydrated gypsum turning into anhydrate with depth, which also correlates with the sulfate
δ34S values, showing a fractionation within the gypsum containing soil profile. Our findings confirm an
infiltration of water by rain events to a limited depth (ranging from 0.3 to 0.7 m) keeping the calcium
sulfate hydrated. This shows that only above the transition of gypsum to anhydrite, water might be
sufficiently available for the soil to be habitable, whereas below the transition the water activity is
presumably too low for microbial activity. We aim to extend this study to all Atacama soil types and to
combine these findings with remote sensing data to create a habitability map for the Yungay Valley in
the Atacama Desert which is well suited as a test bed for Mars exploration.
REFERENCES:
Schulze-Makuch, D. et al. (2018) Transitory microbial habitat in the hyperarid Atacama Desert. Proc.
Natl. Acad. Sci. (USA) 115: 2670-2675.
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