Evaluating Spatial Heterogeneity and Vertical Stratification of  Brine Pools in the Salar de Llamara, Atacama Desert, Northern Chile

Tianshu Kong

Brines are believed to host life in extreme environments on Earth and evaporite deposits associated with these brines are a target for the search for extraterrestrial life. Brine pools can be found in the Salar de Llamara and one example of such brine pool systems is locally known as the Puquios in the Salar de Llamara in the Atacama Desert of Northern Chile. While many studies have investigated the microbial communities living in polyextreme environments, the characterization of the environmental conditions is often limited to a few sampling stations, lacking detailed studies of factors such as vertical stratification in brine chemistry. Previous work in the Puquios suggests that the lagoons are periodically stratified and exhibit heterogeneity across the main lagoons; this variability has been proposed to be related to the geometrical description of the lagoon (ie depth, slope gradient, fetch).  As a result, the Puquios in the Salar de Llamara provide an ideal system to conduct measurements of spatial heterogeneity in brine chemistry and stratification to better quantify environmental conditions in lagoons forming at the "edge of habitability". In this thesis, I address this knowledge gap about the chemical ‘"edge of habitability" by conducting a high-resolution analysis, including in situ and laboratory-based measurements of brine chemistry, statistical analyses (z-test, Mann Whitney U test, p-values and coefficient of variation) of the datasets, and generate maps of spatial heterogeneity and vertical stratification of brine chemistry parameters in each of the four main lagoons. I compare this characterization of the brines with in situ meteorological data, including wind speed, wind direction, temperature, photosynthetically active radiation, relative humidity, and dew point.  I assess diurnal variability in the patterns of spatial heterogeneity and stratification by conducting repeat measurements of two lagoons, Puquio 1 and Puquio 4, in both the morning and afternoon, enabling an evaluation of how wind and temperature variability throughout a day in this extreme environment impact brine characteristics. Finally, I assess intra-weekly variability in stratification and spatial heterogeneity of brine chemistry by comparing similar datasets collected a week apart in November 2019. The results of these analyses suggest that lagoons with shallow, low slope gradients, like Puquio 1 and 3, are easily mixed by afternoon winds and lack stratification. These lagoons, which are dominated by microbial mats (Puquio 1 and 3), also exhibit the highest degree of spatial heterogeneity in the Puquios system, especially in biologically relevant aspects such as the sulfur isotope (d34S values) composition of the dissolved sulfate. By contrast, lagoons with crystalline bottom types (Puquios 2 and 4) exhibit minimal spatial heterogeneity, and stronger vertical stratification. Finally, comparison of diurnal and weekly variability demonstrates that such polyextreme systems are highly dynamic, further suggesting that limits of environmental conditions for ecosystems persisting at the edge of habitability may need to be expanded.<o:p></o:p></div><o:p></o:p>

Evaluating Spatial Heterogeneity and Vertical Stratification of Brine Pools in the Salar de Llamara, Atacama Desert, Northern Chile

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