Search

Modern and ancient hypersaline brines have been identified across the solar system, but the habitability of these environments remains unknown. Here, we evaluate organic matter (OM) production in MgSO4 and Na2CO3 rich hypersaline lakes whose chemistries resemble deposits on Mars such as those identified in Jezero crater. We focus our analysis on lipid biomarkers including fatty acids, alkanes, and ether‐bound lipids in modern brines, salt deposits, and surface sediments. We also report total organic carbon (TOC), carbon/nitrogen (C/N) ratios, and bulk OC (δ13C and δ15N) isotopes to contextualize the lipid biomarker data. In all lakes, the predominant biosignatures include midchain (12 < C < 23) fatty acids and alkanes suggesting microbial origin. Sediments also incorporate a greater diversity of lipids. Ether‐bound lipids derived from archaea and bacteria constitute a minor but measurable fraction of the lipids. This result contrasts with typical findings from other studies with NaCl brines which contain significant archeal biomass. TOC concentrations in all sediments are high, ranging from 0.7% to 12% with sulfate‐rich sediments having the highest concentrations. The isotopic and elemental compositions of TOC corroborate the biomarker results, showing δ13C values and C/N values indicative of aquatic microbial origin. This richness of organic matter and in situ microbial biosignatures differ from previously studied Cl‐dominated Mars‐analog sites which have shown limited OM production and preservation and acidic SO4‐rich hypersaline environments which were dominated by terrestrial inputs. Overall, our results suggest that MgSO4‐rich hypersaline environments are conducive for life and harbor a rich microbial biomarker landscape. Plain Language Summary: The minerals found on Mars suggest that it had abundant hypersaline waters early in its history. However, liquid water no longer persists on its surface. As such, we must use environments on Earth that are similar to Mars and other astrobiological targets to better understand the potential for life elsewhere. Here, we examine fatty molecules and organic carbon from hypersaline lakes on Earth that resemble water compositions thought to have been present on early Mars. We also use bulk carbon isotopic data to help inform the results from our biomarker analysis. Overall, data from these sites shows that circumneutral SO4‐rich environments are conducive for life and harbor a suite of microbial biosignatures. In comparison to other Martian‐analog environments on Earth, this study shows that circumneutral SO4‐dominated lakes produce in situ biological signatures in abundance. Key Points: SO4‐dominated hypersaline lakes produce more abundant organic matter (OM) than a Na2CO3‐dominated site of comparable salinityThe circumneutral MgSO4‐dominated hypersaline lakes studied here harbor abundant microbial biosignatures compared to other Martian analogsLipid biosignatures produced in situ predominate within sedimentary OM rather than biosignatures produced by surrounding vegetation [ABSTRACT FROM AUTHOR]