Molecular biosignatures in planetary analogue salts : implications for transport of organics in sulfate-rich brines beyond Earth

Abstract

Salts formed during evaporation or freezing of brines can potentially incorporate organic matter that can inform about past biological activity. We analysed the lipid fraction preserved within the contemporary Lost Hammer salt deposit (Canadian High Arctic) - an analogue to extraterrestrial salt systems - and paired this with space mission-relevant evolved gas analysis. Our findings show microbial organic matter (fatty acids and n-alkanes) is incorporated into Lost Hammer salts, which comprise polyhydrated sulfates and chlorides. We find a difference in the relative abundance of fatty acids vs. n-alkanes indicating how these biosignatures evolve across active and non-active parts of the spring. We also find differences between pristine salt-organic mixtures and deposits that may have been remobilised by subsequent dissolution and recrystallisation. In this system, n-alkanes have the highest preservation potential, surviving the likely dissolution and recrystallisation of hydrated salt phases. This is important for considering the fate of organic matter on icy moons such as Europa, where salts emplaced on the surface by briny extrusions may have undergone fractional crystallisation, or where subsurface salts are remobilised by localised melting. It is also relevant for once active brine systems on Mars, where cycles of groundwater recharge and/or deliquescence led to dissolution and re-precipitation of evaporitic salts.