Geochemical interactions among water, minerals, microbes, and organic matter in formation of speleothems in volcanic (lava tube) caves

Volcanic (lava tube) caves at Lava Beds National Monument (N. CA, USA) provide a valuable terrestrial analog for volcanic on Mars and the Moon. Terrestrial host diverse microbial life, liquid water, variety of secondary mineral deposits (speleothems) with morphologies chemical compositions. Speleothems may preserve records past present life signatures paleoenvironmental changes in caves. Distinguishing between speleothems via processes microbially-mediated will insights future exploration martian To elucidate formation speleothems, we studied makeup (inorganic organic) cave waters seven variable ages, temperature, moisture content, light intensity, frequency human visitation. Cave water was characterized by stable isotopic composition (δ 18 O δ 2 H), concentrations major trace elements, cations, anions, characteristics dissolved organic matter (DOM). A forward reaction model (PHREEQC) used to test possible pathways precipitation that formed these speleothems. The source primarily regional meteoric entered through openings or overburden fractured basalt walls as indicated floor puddle line H = 8.32*δ + 9.55 parallel global (GMWL, 8.3*δ 10). ceiling drip 3.39*δ – 44.77 intersecting GMWL be undergoing evaporation within Silicate weathering found primary process resulting enriched Si (22 ± 7 mg/L), contained levels Al, Fe, Zn, Li, Sr, Cu, B, V, Ba, Cr Mn. Geochemical calculations were undersaturated respect both amorphous silica (SiO 2am ) calcite (CaCO 3 which components observed Results showed could lower solubility SiO CaCO increasing their saturation ultimately precipitate two minerals forming DOM high carbon (DOC, 12 8 mg/L) molar C/N ratio ranging from 22. aromatic (SUVA 254 , 1.2–2.9 L/mg.m), terrestrially derived humic-like (humification index, 7–26) molecules 100 Da 5000 approximate molecular weight (AMU). Our results carbonaceous transported into not utilized heterotrophic metabolisms DOC accumulated over inorganic (DIC). Both findings suggest minimal heterotrophy, chemo-litho-autotrophy important cycle elements low conditions. Together, this study proposes potential pathway speleothem interaction constituents, where ions are concentrated cyclic condensation-vaporization processes. This work is part multi-disciplinary project Biologic Resource Analog Low Light Environments (BRAILLE) funded NASA PSTAR Program (NNH16ZDA001N), focuses studying analogs Moon Mars. • Source precipitation. Water-rock interactions controlled chemistry. Evaporation played an role 2(am.) . plant-derived matter. Enrichment indicate net lack metabolism.