Universität zu Köln

Klipsch, Swea (2021). Identifying Sulfate Sources and Recycling Processes in the Atacama Desert with Sulfur, Strontium and Triple Oxygen Isotopes. PhD thesis, Universität zu Köln.

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Abstract

Sulfate is the dominating salt in soils of the Atacama Desert, one of the oldest and driest deserts on Earth. Sulfate sources include marine sulfate, terrestrial weathering (e.g., redistribution of surface material), and sulfate that is formed within the atmosphere by oxidation of reduced sulfur species. The stable isotopic composition of sulfate (D17OSO4 , d18OSO4 , and d34SSO4) is characteristic for each formation process, wherefore it serves as a tool to identify respective sulfate sources. The classical stable isotope proxies (d18OSO4 and d34SSO4) mainly help to distinguish between marine and terrestrial sulfate. In addition to these, the novel triple oxygen isotope tool (D17OSO4) also allows to identify sulfate formed in the atmosphere. Under Earth’s surface conditions, the isotopic composition of sulfate only alters when the sulfate is processed by microbes or plants. Hence, the isotopic composition of sulfate allows identifying the sulfate sources and enables to draw conclusions on biological alteration processes. This is especially interesting for areas, where biological activity is limited due to the low water availability, like the Atacama Desert. The first study presents a fast and easy to use method to determine D17OSO4 of natural sulfate samples. It includes a protocol for the quantitative dissolution of natural Ca- and Na-sulfates samples and subsequent conversion into sufficiently pure Ag-sulfate for pyrolysis analyses. Determined D17OSO4 values from multiple in-house standards are compared to previously published results from different laboratories using different methods (pyrolysis and fluorination). A normalization procedure results in excellent reproducibility of standards, comparable to other laboratories including those using those using the fluorination method, verifying the accuracy and precision of the presented method. The second study aims to improve the understanding of sulfate deposition and the spatial distribution of hyperaridity. Samples taken along four E-W transects are analyzed for their isotopic compositions (D17OSO4 , d18OSO4 , d34SSO4 , and 86Sr/88Sr). Throughout positive D17OSO4 values, determined using the method developed in the first study, suggest a significant contribution from atmospheric sulfate for all Atacama Desert sediments. The combination of D17OSO4 and d34SSO4 allows distinguishing between marine sulfate and sulfate that derived from atmospheric oxidation of biogenic sulfur gases emitted from the Ocean. In addition, a clear trend is visible in the triple oxygen isotopic composition (D17OSO4 and d18OSO4) of all samples, pointing from the isotopic composition of atmospheric sulfate to that of biological cycled sulfate. This trend reflects a gradient in the degree of biological activity and can therefore be used as indicator for water availability in the Atacama Desert. This work provides an optimized pyrolysis method for triple oxygen isotope analysis of sulfate from desert environments and expands our knowledge of sulfate source contribution, sulfate deposition, biological sulfate cycling, and water availability within the hyperarid Atacama Desert.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Klipsch, Swea s.klipsch@uni-koeln.de UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-639300
Date:	2021
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Geosciences > Institute of Geology and Mineralog
Subjects:	Earth sciences
Uncontrolled Keywords:	Keywords Language Triple Oxygen Isotopes UNSPECIFIED Atacama Desert UNSPECIFIED Sulfate Sources UNSPECIFIED
Date of oral exam:	12 November 2021
Referee:	Name Academic Title Staubwasser, Michael Prof. Dr. Münker, Carsten Prof. Dr.
Funders:	CRC 1211
Projects:	Earth - Evolution at the dry limit
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/63930