Identifying water availability in the Atacama Desert (Chile) by triple oxygen isotope analyses of sulfates

2020 ◽  
Author(s):  
Swea Klipsch ◽  
Daniel Herwartz ◽  
Michael Staubwasser
Keyword(s):  
Oxygen Isotope ◽  
Water Availability ◽  
Isotope Composition ◽  
Atacama Desert ◽  
Soil Surface ◽  
Desert Soil ◽  
Sea Spray ◽  
Alluvial Fans ◽  
Coastal Cordillera ◽  
Silver Sulfate

<p>Ca-Sulfates (Gypsum and Anhydrite) are the most common salts accumulating in the soil of the Chilean Atacama Desert. Sulfate sources include sea spray, redeposition of playa sediments, terrestrial weathering, and deposition of sulfate formed in the atmosphere (secondary atmospheric sulfate = SAS). Sulfate from sea spray, playa lakes, and terrestrial weathering have a triple oxygen isotope composition (Δ<sup>17</sup>O<sub>SO4</sub>) at or slightly below zero reflecting reaction with water and oxygen. Positive Δ<sup>17</sup>O<sub>SO4</sub> are generally the result of atmospheric SO<sub>2</sub> oxidation by ozone or hydrogen peroxide. Sulfate oxygen is only altered with ambient water by cycling through biological activity resulting in Δ<sup>17</sup>O<sub>SO4</sub> ≈ 0‰. Therefore, Δ<sup>17</sup>O<sub>SO4</sub> aids in quantifying the relative contribution of SAS to the desert soil and in identifying bioactivity and water availability in the hyperarid Atacama Desert. The spatial quantification of different sulfate sources may serve to improve the understanding of sulfate deposition in this region.</p><p>Samples were analysed by continuous flow IRMS using the pyrolysis of Ag<sub>2</sub>SO<sub>4</sub> to determine Δ<sup>17</sup>O<sub>SO4</sub> from O<sub>2</sub>. An optimized sample preparation to form clean silver sulfate and intra-day calibration against two in-house standards resulted in an external reproducibility of 0.12‰. An inter laboratory comparison including data derived from the laser-fluorination method confirmed the accuracy of our analyses.</p><p>We analyzed desert soil surface samples from four E-W transects in the Atacama Desert reaching from the Pacific coast across the Coastal Cordillera, the Central Depression, and up the alluvial fans protruding from the Pre-Andean Cordillera. Transects begin at Pisagua (19.5°S), Salar Grande (21.0°S), Antofagasta (24.0°S), and Paposo (25.0°S). Values of Δ<sup>17</sup>O<sub>SO4</sub> vary between 0.3 and 1.1‰. The lowest Δ<sup>17</sup>O<sub>SO4 </sub>values were measured near Salar Grande and on the Pre-Andean alluvial fans. The highest Δ<sup>17</sup>O<sub>SO4 </sub>values are observed at the highest altitudes in the Coastal Cordillera - east of Paposo - well above the coastal fog zone (> 1200 m). At similar or higher altitudes on the Pre-Andean fans, Δ<sup>17</sup>O<sub>SO4</sub> converge towards zero.</p><p>The spatial distribution is the result of source contributions and subsequent biological reset. Positive Δ<sup>17</sup>O<sub>SO4</sub> values throughout suggest a significant contribution from SAS. We quantified sea spray contributions using Cl- concentration, which drop dramatically above the fog-zone [1]. Furthermore, salt distribution suggests minimal weathering and redistribution in recent times. The lowest contribution from such near zero Δ<sup>17</sup>O<sub>SO4</sub> sulfate sources are expected in the Coastal Cordillera, which is consistent with our data. Within the Coastal Cordillera there is a north to south Δ<sup>17</sup>O<sub>SO4 </sub>trend, which is also an elevation trend. Increased water availability from fog at lower elevations facilitates more efficient resetting of Δ<sup>17</sup>O<sub>SO4</sub> via microbial activity. These observations suggest that the driest place in the Atacama Desert is situated within the Coastal Cordillera above the fog zone.</p><p>[1] Voigt et al. (2020) Global and Planetary Change <strong>184</strong></p>

scholarly journals Non-destructive estimates of soil carbonic anhydrase activity and soil water oxygen isotope composition

2017 ◽  
Author(s):  
Sam P. Jones ◽  
Jérôme Ogée ◽  
Joana Sauze ◽  
Steven Wohl ◽  
Noelia Saavedra ◽  
...  
Keyword(s):  
Oxygen Isotope ◽  
Soil Water ◽  
Isotope Composition ◽  
Soil Surface ◽  
Bulk Water ◽  
Oxygen Isotope Composition ◽  
Spatial And Temporal Variability ◽  
Co2 Fluxes ◽  
Carbonic Anhydrases ◽  
Water Pool

Abstract. The contribution of photosynthesis and soil respiration to net land-atmosphere carbon dioxide (CO2) exchange can be estimated based on the differential influence of leaves and soils on budgets of the oxygen isotope composition (δ18O) of atmospheric CO2. To do so, the activity of carbonic anhydrases (CA), a group of enzymes that catalyse the hydration of CO2, in soils and plants needs to be understood. Measurements of soil CA activity typically involve the inversion of models describing the δ18O of CO2 fluxes to solve for the apparent, potentially catalysed, rate of CO2 hydration. This requires information about the δ18O of CO2 in isotopic equilibrium with soil water, typically obtained from destructive, depth-resolved sampling and extraction of soil water. In doing so, an assumption is made about the soil water pool that CO2 interacts with, that may bias estimates of CA activity if incorrect. Furthermore, this can represent a significant challenge in data collection given the potential for spatial and temporal variability in the δ18O of soil water and limited a priori information with respect to the appropriate sampling resolution and depth. We investigated whether we could circumvent this requirement by inferring the rate of CO2 hydration and the δ18O of soil water from the relationship between the δ18O of CO2 fluxes and the δ18O of CO2 at the soil surface measured at different ambient CO2 conditions. This approach was tested through laboratory incubations of air-dried soils that were re-wetted with three waters of different δ18O. Gas exchange measurements were made on these soils to estimate the rate of hydration and the δ18O of soil water, followed by soil water extraction to allow for comparison. Estimated rates of CO2 hydration were 6.8 to 14.6 times greater than the theoretical un-catalysed rate of hydration, indicating that CA were active in these soils. Importantly, these estimates were not significantly different among water treatments suggesting that this represents a robust approach to assay the activity of CA in soil. As expected, estimates of the δ18O of the soil water that equilibrates with CO2 varied in response to alteration to the δ18O of soil water. However, these estimates were consistently more negative than the composition of the soil water extracted by cryogenic vacuum distillation at the end of the gas measurements with differences of up to −3.94 ‰ VSMOW. These offsets suggest that CO2 may be principally interacting with water pools associated with particle surfaces rather than the bulk water pool under the incubation conditions of this study.

scholarly journals Non-destructive estimates of soil carbonic anhydrase activity and associated soil water oxygen isotope composition

2017 ◽  
Vol 21 (12) ◽  
pp. 6363-6377 ◽  
Author(s):  
Sam P. Jones ◽  
Jérôme Ogée ◽  
Joana Sauze ◽  
Steven Wohl ◽  
Noelia Saavedra ◽  
...  
Keyword(s):  
Oxygen Isotope ◽  
Soil Water ◽  
Isotope Composition ◽  
Soil Surface ◽  
Carbonic Anhydrase Activity ◽  
Co2 Exchange ◽  
Oxygen Isotope Composition ◽  
Spatial And Temporal Variability ◽  
Co2 Fluxes ◽  
Carbonic Anhydrases

Abstract. The contribution of photosynthesis and soil respiration to net land–atmosphere carbon dioxide (CO2) exchange can be estimated based on the differential influence of leaves and soils on budgets of the oxygen isotope composition (δ18O) of atmospheric CO2. To do so, the activity of carbonic anhydrases (CAs), a group of enzymes that catalyse the hydration of CO2 in soils and plants, needs to be understood. Measurements of soil CA activity typically involve the inversion of models describing the δ18O of CO2 fluxes to solve for the apparent, potentially catalysed, rate of CO2 hydration. This requires information about the δ18O of CO2 in isotopic equilibrium with soil water, typically obtained from destructive, depth-resolved sampling and extraction of soil water. In doing so, an assumption is made about the soil water pool that CO2 interacts with, which may bias estimates of CA activity if incorrect. Furthermore, this can represent a significant challenge in data collection given the potential for spatial and temporal variability in the δ18O of soil water and limited a priori information with respect to the appropriate sampling resolution and depth. We investigated whether we could circumvent this requirement by inferring the rate of CO2 hydration and the δ18O of soil water from the relationship between the δ18O of CO2 fluxes and the δ18O of CO2 at the soil surface measured at different ambient CO2 conditions. This approach was tested through laboratory incubations of air-dried soils that were re-wetted with three waters of different δ18O. Gas exchange measurements were made on these soils to estimate the rate of hydration and the δ18O of soil water, followed by soil water extraction to allow for comparison. Estimated rates of CO2 hydration were 6.8–14.6 times greater than the theoretical uncatalysed rate of hydration, indicating that CA were active in these soils. Importantly, these estimates were not significantly different among water treatments, suggesting that this represents a robust approach to assay the activity of CA in soil. As expected, estimates of the δ18O of the soil water that equilibrates with CO2 varied in response to alteration to the δ18O of soil water. However, these estimates were consistently more negative than the composition of the soil water extracted by cryogenic vacuum distillation at the end of the gas measurements with differences of up to −3.94 ‰ VSMOW–SLAP. These offsets suggest that, at least at lower water contents, CO2–H2O isotope equilibration primarily occurs with water pools that are bound to particle surfaces and are depleted in 18O compared to bulk soil water.

MUDFLOW ALLUVIAL FANS OF THE ATACAMA DESERT IN CHILE

2016 ◽  
Author(s):  
Alan D. Howard ◽  
◽  
William E. Dietrich ◽  
Rebecca M.E. Williams ◽  
Alex M. Morgan ◽  
...  
Keyword(s):  
Atacama Desert ◽  
Alluvial Fans

Oxygen isotope composition of Holocene dolomite formed in a humid hypersaline setting: Comment and Reply

Geology ◽  
1993 ◽  
Vol 21 (3) ◽  
pp. 281 ◽  
Author(s):  
Gerald M. Friedman ◽  
R. P. Major ◽  
R. Michael Lloyd ◽  
F. Jerry Lucia
Keyword(s):  
Oxygen Isotope ◽  
Isotope Composition ◽  
Oxygen Isotope Composition

scholarly journals Calcium Biogeochemical Cycle in a Typical Karst Forest: Evidence from Calcium Isotope Compositions

Forests ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 666
Author(s):  
Guilin Han ◽  
Anton Eisenhauer ◽  
Jie Zeng ◽  
Man Liu
Keyword(s):  
Soil Depth ◽  
Isotope Composition ◽  
Soil Surface ◽  
Natural Soil ◽  
Calcium Isotope ◽  
Karst Forest ◽  
Content Ratio ◽  
The Difference ◽  
Preferential Uptake ◽  
Vital Factor

In order to better constrain calcium cycling in natural soil and in soil used for agriculture, we present the δ44/40Ca values measured in rainwater, groundwater, plants, soil, and bedrock samples from a representative karst forest in SW China. The δ44/40Ca values are found to differ by ≈3.0‰ in the karst forest ecosystem. The Ca isotope compositions and Ca contents of groundwater, rainwater, and bedrock suggest that the Ca of groundwater primarily originates from rainwater and bedrock. The δ44/40Ca values of plants are lower than that of soils, indicating the preferential uptake of light Ca isotopes by plants. The distribution of δ44/40Ca values in the soil profiles (increasing with soil depth) suggests that the recycling of crop-litter abundant with lighter Ca isotope has potential effects on soil Ca isotope composition. The soil Mg/Ca content ratio probably reflects the preferential plant uptake of Ca over Mg and the difference in soil maturity. Light Ca isotopes are more abundant in mature soils than nutrient-depleted soils. The relative abundance in the light Ca isotope (40Ca) is in the following order: farmland > burnt grassland > forests > grassland > shrubland. Our results further indicate that biological fractionation in a soil–plant system is a vital factor for Ca–geochemical transformations in soil surface systems.

Stable Hydrogen and Oxygen Isotope Composition of Waters from Mine Tailings in Different Climatic Environments

2007 ◽  
Vol 41 (6) ◽  
pp. 1870-1876 ◽  
Author(s):  
Jorge E. Spangenberg ◽  
Bernhard Dold ◽  
Marie-Louise Vogt ◽  
Hans-Rudolf Pfeifer
Keyword(s):  
Oxygen Isotope ◽  
Mine Tailings ◽  
Isotope Composition ◽  
Oxygen Isotope Composition ◽  
Hydrogen And Oxygen Isotope

Oxygen isotope composition of kaolinite rocks as an indicator of different stages of their lithogenesis

2011 ◽  
Vol 438 (1) ◽  
pp. 697-700
Author(s):  
N. S. Bortnikov ◽  
V. M. Novikov ◽  
E. O. Dubinina ◽  
A. D. Savko ◽  
A. G. Berketa ◽  
...  
Keyword(s):  
Oxygen Isotope ◽  
Isotope Composition ◽  
Oxygen Isotope Composition
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