Searching for Biosignatures in Mars Analogue Sites: An Analysis of Microbial Carbon Cycling and Biosignatures within Acid-sulfate and Hypersaline Lake Environments

Abstract

<p>By studying signatures of life within extreme environments on Earth we better understand signatures of life that may be found within the geologic record on Earth as well as elsewhere in the universe. This thesis research utilized phospholipid fatty acid analysis (PLFA) in combination with carbon isotopic analysis (δ¹³C) to understand microbial carbon cycling and biosignatures within two Mars analogue environments.</p> <p>The Golden Deposit was an acid sulfate environment that was an analogue to the acid-sulfate conditions present on early Mars. Mixing of inflowing surface water and upwelling acidic groundwater on the deposit caused variations in water chemistry. Such variations resulted in differences in the microbial communities and carbon isotopic compositions within the Golden Deposit. The most acidic groundwater seep on the deposit had a distinct geochemistry, which selected for a unique microbial community and distinct carbon isotopic signatures. Variations detected within the small spatial area of the Golden Deposit indicated that biosignatures preserved on Mars might be highly variable making the unambiguous identification of past life on the planet more difficult.</p> <p>Three saline lakes of the Cariboo Plateau were used for this study and were analogues to environmental conditions present on early Earth as well as the alkaline, evaporitic conditions present on early Mars. All three lakes contained benthic microbial mat communities dominated by cyanobacteria. Photosynthetic influences by cyanobacteria resulted in an isotopic enrichment of the DIC pool. Enriched lake DIC values were preserved in precipitated carbonates (δ¹³C_carb) and the ∆¹³C_DIC-TOC(avg) was similarly preserved in ∆¹³C_carb-TOCvalues and were biosignatures of photosynthetic activity. The preservation of these biosignatures suggested that concentrations of CO₂ on early Earth did not necessarily exceed modern levels and that measuring the carbon isotopic compositions of carbon pools within saline, carbonate-rich deposits on Mars could lead to the identification of past life on the planet.</p>