With the landing of the Mars2020 rover Perseverance, a new generation of Martian research is possible. This mission will return samples from Jezero crater, including those from settings that were likely wet (e.g., as evidenced by smectite clays and carbonate sequences) and therefore possibly habitable in the Martian past. Tremendous strides in proxy development have opened up windows to reconstructing past microbial ecology, pH and alkalinity on Earth. We propose to extend these advances to Martian samples, but such efforts will require a new generation of paleo-proxy validation and calibration in terrestrial analogues. These analogue locations include famous alkaline settings that remain unexplored using the planned methods: Lake Myvatn in Iceland, the Coorong coastal lagoon in Australia, and Lake Salda in Turkey. The student will use i) organic biomarkers to reveal ecologies associated with highly alkaline setting and ii) boron and nitrogen isotope analysis to provide perspectives of pH and alkalinity conditions. Additional biomarkers (e.g. glycerol ether lipids) will provide further constraints on pH. These parameters will help define the conditions of potential past life on Mars and expanded possibilities for biosignatures, particularly once Martian samples are returned and analysed in our labs in the coming years. The overarching goal is to develop an interdisciplinary strategy for exploring possible microbial ecology on ancient Mars, emphasizing alkaline settings that are hypothesised from Mars’ wet past and shown on Earth are known to harbour large and diverse microbial communities. This study also speaks broadly to habitability on high-pH bodies such as Enceladus and exoplanetary water worlds as targets in the search for extraterrestrial life.
High-pH lakes are among the most biologically productive natural aquatic systems on Earth, and pH estimates can place constraints on the partial pressure of CO2 [pCO2] in ancient and exotic planetary atmospheres. Terrestrial analogue sites will include the shallow Lake Myvatn related to active volcanism, the Coorong lagoons noted for novel pathways of carbonate mineral (dolomite) formation and highly variable pH (e.g., circumneutral to high) in a marginal marine setting, and Lake Salda known for its remarkable microbial structures. The student will use biomarkers to infer ecological and redox conditions. This includes: i) C30 steranes (24-n-propyl cholestanes; 24-npc) for pelagophytes; ii) gammacerane for stratification; iii) the 2-methylhopane index for cyanobacteria and α-proteobacteria; and, iv) C27-29 steranes for the algal community. Compound-specific isotopic techniques will be used to further deconvolve sources of organic matter (Whiteside and Grice, 2016). To reconstruct pH and alkalinity, the student will use: i) the boron isotopic composition (δ11B) of carbonate (c.f. Liu et al., 2014), ii) the nitrogen isotopic composition (δ14N) of bulk rock; Stüeken et al., 2020) and iii) the distribution of bacterial and archaeal ether lipids (e.g. GDGTs). Each proxy has its own strengths and weaknesses and the student will use a combined approach to provide the most accurate reconstructions to characterise the potential habitability.
The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted at the School of Ocean and Earth Science. The student will receive expert training in  organic geochemical techniques (Whiteside),  compound specific stable isotope techniques (Whiteside/Bray),  sample collection from field sites (Whiteside/Lyons), and  inorganic geochemical techniques, including nitrogen and boron isotope analysis using gas source isotope ratio mass spectrometry and multicollector inductively coupled plasma mass spectrometry, respectively (Lyons/Stueken/Rae). The student will present at national and international conferences and NASA working groups, write peer-reviewed publications and a PhD thesis. The research training addresses field, numerical, statistical and laboratory skills, equipping the student for a career across a range of professions.
Liu, W.G. et al. 2014. Late Miocene episodic lakes in the arid Tarim Basin, western China.
Proceedings of the National of Sciences of the United States of America, 111 (46): 16292-16296.
Stüeken, E. et al. 2020. Nitrogen isotope ratios trace high-pH conditions in a terrestrial Mars analog site. Science Advances, 6, eaay3440.
Whiteside, J.H., and Grice, K., 2016. Review of biomarker records associated with mass extinction events. Annual Review of Earth and Planetary Science. 44:581-612.