Characterizing Biomarkers along Subsurface to Surface Gradients of the Paradox Basin: Implications for Astrobiology and Mars Exploration

Abstract

Subsurface environments are increasingly recognized as crucial astrobiological analogs for studying Martian habitability. Where subsurface fluids meet surface conditions, we often observe an explosion of life, harvesting energy from the geochemical disequilibrium produced by this convergence. However, it remains unclear how biosignatures change across this transition. This study examines lipid biomarker compositions from sediment and biofilm samples in the Paradox Basin, a geologically complex area with significant paleofluid flow records. An abundance of even carbon n-alkanes in the hydrocarbon fraction indicates a microbial origin in samples. By cataloging these biomarkers, we aim to enhance the identification of reliable biosignatures critical for future missions targeting extraterrestrial life.

Introduction

In the search for extraterrestrial life, subsurface environments on Earth serve as crucial analogs for understanding Martian habitability. These environments, shielded from harsh surface conditions like intense radiation, low atmospheric pressure, and extreme temperature fluctuations, offer protection that makes them favorable for life [1]. On Mars, the subsurface is considered a promising target in the search for life or evidence of past life [2]. Understanding how biosignatures change as we move from the depths to the surface is critical for detecting life on Mars. One area of particular interest is the transition zone where subsurface fluids emerge at the surface, creating unique conditions that can support diverse microbial life. Studying these zones in Mars analog environments on Earth can help us identify reliable biomarkers, traces of life, that are essential for future missions aimed at discovering extraterrestrial life. The Paradox Basin, located in the Colorado Plateau (USA), is a geologically complex area located on the border between Utah and Colorado. Known for its hypersaline and sulfide-rich subsurface fluids, the Paradox Basin mimics conditions that might be found on Mars, making it an excellent site to study how microbial and biogeochemical processes operate in similar environments [3]. This study focuses on characterizing lipid biomarkers from various samples within the Paradox Basin to better understand how biomarkers change as they move from subsurface to surface environments, thereby contributing valuable insights to the broader field of astrobiology and informing future Mars exploration missions.

Methodology

(Above) Workflow for sample preperation.

Samples were collected from two locations within the Paradox Basin: Salt Creek (SC) and Stinking Springs (ST). Eighteen samples were collected (eight from SC and ten from SS), including sediment, biofilm, and salt deposits from springs emitting subsurface fluids, as well as from associated runoff channels and two groundwater wells. Samples were characterized by color, texture, smell, and source. For bulk isotope analysis, freeze-dried samples were weighed and treated with MilliQ water to extract salts, which were then freeze-dried and weighed. The pH of the salt extract was measured before freeze-drying. Samples were treated with 1M HCl to remove inorganic carbon and re-weighed. They were then loaded into tin capsules for gas chromatography combustion isotope ratio mass spectrometry analysis (GC-IRMS). Lipids were extracted from freeze-dried samples following a modified Simplex protocol [4]., followed by elemental sulfur removal, hydrolysis, and separation into hydrocarbon (F1), ester/ketone/alcohol (F2/F3), and acid fractions (F4). These fractions were analyzed using gas chromatography-mass spectrometry (GC-MS) and quantified using gas chromatography-flame ionization detection (GC-FID). Sample peaks were quantified relative to the intensity of a known quantity of palmitic acid isobutyl ester (PAIBE), which was added to each sample before analysis.

Example of sediment samples.

Results

(A)n-alkane ratios in Fraction 1 of Salt Creek sediment samples shows abundance of even n-alkane (B)n-alkane ratios in Fraction 1 of Stinking Springs sediment samples shows a similar abundance of even n-alkanes (C)n-alkane ratios in hydrocarbon fraction in all samples arranged from shorter n-alkanes C16 (right) to longer n-alkanes C34 (left) shows an abundance of shorter n-alkanes. Total Lipid Extract (TLE) ranged from 0.43 mg to 53.3 mg per gram of sediment, varying by sample type. Carbonate content in the collected samples ranged from 8.77% to 50.1%, while salt content ranged from 0.1% to 46.6%. In both Salt Creek and Stinking Springs, the hydrocarbon fraction showed an abundance of C16-C22 even carbon n-alkanes, strongly suggesting a microbial origin. This observation aligns with previous DNA sequencing data, which revealed broad similarities at the phylum level among the samples. By continuing to compare lipid profiles with DNA sequencing data, we aim to link specific lipids to the organisms that produce them.

(Above) Microbial communities in samples at phlylum level with 16S rRNA sequencing data.

Discussion

The preservation of lipid biomarkers in subsurface conditions, particularly at the interface where subsurface fluids meet surface conditions, provides valuable insights into the potential for life on Mars. Identifying reliable biosignatures is crucial for future missions aimed at discovering extraterrestrial life. By comparing lipid profiles with DNA sequencing data, we seek to identify potential biosignatures that could be detected by future Mars rovers. This research contributes to the broader field of astrobiology, aiding in hypothesizing about the conditions necessary for life on Mars and other astrobiological targets. Future work will focus on measuring the total organic carbon (TOC) and nitrogen content, as well as the isotopic composition of samples. We will also measure δ13C of lipid biomarkers and inorganic carbon to expand the geobiological context. Continued development of lipid profiles will allow us to track microbial ecology from subsurface to surface depth and compare results with other subsurface environments on Earth.

References

Checinska Sielaff, A.; Smith, S.A. Habitability of Mars: How Welcoming Are the Surface and Subsurface to Life on the Red Planet? Geosciences 2019, 9, 361.
Finkel, P. L., Carrizo, D., Parro, V. & Sánchez-García, L. An Overview of Lipid Biomarkers in Terrestrial Extreme Environments with Relevance for Mars Exploration. Astrobiology 23, 563–604 (2023).
Kim, J.-H. et al. Hydrogeochemical evolution of formation waters responsible for sandstone bleaching and ore mineralization in the Paradox Basin, Colorado Plateau, USA. Geol. Soc. Am. Bull. (2022)
Coman, C. et al. Simultaneous Metabolite, Protein, Lipid Extraction (SIMPLEX): A Combinatorial Multimolecular Omics Approach for Systems Biology. Mol. Cell. Proteomics MCP 15, 1453–1466 (2016).

About Maria

I'm a biology major at Cornell Univerisity with a concentration in microbiology and an interest in astrobiology. I'm interested in studying life in extreme/analog environments! In the future I hope to support the direction of future space missions/research to astrobiological targets of interest such as Mars or Europa. In my free time to love to read, embroider and cook!

Contact Info: mdc289 at cornell.edu, mcalderonmarrero at gmail.com

Let's Connect!: Let's Connect

This material is based upon work supported by the National Science Foundation AST-2149425 Osburn; EAR-2120912 Osburn; EAR-2120733 McIntosh. This material is based upon work supported by the National Science Foundation under grant No. AST 2149425, a Research Experience s for Undergraduates (REU) grant awarded to CIERA at Northwestern University. Any opinions, findings, and conclusions or recommendations expressed in this material a re those of the author(s) and do not necessarily reflect the views of the National Science Foundation.