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Soils at the hyperarid margin: The isotopic composition of soil carbonate from the Atacama Desert, Northern Chile

Jay Quade·Jason A. Rech·Claudio Latorre·Julio L. Betancourt·Erin Gleeson·Mary T.K. Kalin
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Abstract

We evaluate the impact of exceptionally sparse plant cover (0–20%) and rainfall (2–114 mm/yr) on the stable carbon and oxygen composition of soil carbonate along elevation transects in what is among the driest places on the planet, the Atacama Desert in northern Chile. δ 13 C and δ 18 O values of carbonates from the Atacama are the highest of any desert in the world. δ 13 C (VPDB) values from soil carbonate range from -8.2% at the wettest sites to +7.9% at the driest. We measured plant composition and modeled respiration rates required to form these carbonate isotopic values using a modified version of the soil diffusion model of [Cerling (1984) Earth Planet. Sci. Lett. 71 , 229–240], in which we assumed an exponential form of the soil CO 2 production function, and relatively shallow (20–30 cm) average production depths. Overall, we find that respiration rates are the main predictor of the δ 13 C value of soil carbonate in the Atacama, whereas the fraction C 3 to C 4 biomass at individual sites has a subordinate influence. The high average δ 13 C value (+4.1%) of carbonate from the driest study sites indicates it formed-perhaps abiotically—in the presence of pure atmospheric CO 2 . δ 18 O (VPDB) values from soil carbonate range from -5.9% at the wettest sites to +7.3% at the driest and show much less regular variation with elevation change than δ 13 C values. δ 18 O values for soil carbonate predicted from local temperature and δ 18 O values of rainfall values suggest that extreme (>80% in some cases) soil dewatering by evaporation occurs at most sites prior to carbonate formation. The effects of evaporation compromise the use of δ 18 O values from ancient soil carbonate to reconstruct paleoelevation in such arid settings.

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Geochimica et Cosmochimica ActaArticle
90° N90° S · 180° W ← longitude → 180° E
Source-reported bounding extent: -30.44867367928756° to -17.644022027872712° latitude; -71.71875° to -66.796875° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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Jay Quade, Jason A. Rech, Claudio Latorre, Julio L. Betancourt, Erin Gleeson, Mary T.K. Kalin. 2007. Soils at the hyperarid margin: The isotopic composition of soil carbonate from the Atacama Desert, Northern Chile. https://doi.org/10.1016/j.gca.2007.02.016

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