P31A-2024
Preservation Potential of Life in Little Hot Creek, California: Implications for the use of Hot Spring Systems as Astrobiological Targets
Wednesday, 16 December 2015
Poster Hall (Moscone South)
Kaitlin R. Rempfert1, Danielle Priscilla Santiago Ramos2, Gabriela S. Nascimento3, Feifei Zhang4, Sean J Loyd5, Olivia Piazza6, Emma Bertran7, Blake W. Stamps8, Bradley S. Stevenson8, John R Spear9 and Frank A Corsetti10, (1)University of Colorado at Boulder, Geological Sciences, Boulder, CO, United States, (2)Princeton University, Princeton, NJ, United States, (3)ETH Zurich, ERDW, Zurich, Switzerland, (4)Arizona State University, Tempe, AZ, United States, (5)California State University Fullerton, Fullerton, CA, United States, (6)University of Southern California, Earth Sciences, Los Angeles, CA, United States, (7)Harvard University, Earth and Planetary Sciences, Cambridge, MA, United States, (8)University of Oklahoma Norman Campus, Norman, OK, United States, (9)Colorado School of Mines, Golden, CO, United States, (10)University of Southern California, Department of Earth Sciences, Los Angeles, CA, United States
Abstract:
Hot spring deposits have long been considered astrobiological targets; modern springs display diverse and abundant life and rapid mineralization is thought to increase biosignature preservation potential. Volcano-associated, silica-rich, mineral deposits have been identified on Mars, so the study of terrestrial examples is warranted. We studied a hot spring in Long Valley Caldera near Little Hot Creek, California, as part of the 2015 Geobiology Summer Course to characterize biological diversity and the potential for biosignature preservation in the rock record. Subsurface hydrothermal waters interact with the rhyolitic Bishop Tuff and feed Little Hot Creek, which exhibits progressively decreasing temperatures (~82-71°C) and rising pH (6.7-7.6) along a 23 m spatial transect. Creek water and sediment samples were collected along the entire transect, in addition to rim-encrusting carbonate-silica structures located ~6 m downstream from the creek source. 16S rRNA sequencing of both water and sediment samples yielded operational taxonomic units (OTUs) reflecting the potential capability for autotrophic thiosulfate oxidation and reduction, hydrogen oxidation, and sulfur oxidation near the creek source. Despite the obvious presence of life in the creek, the preservation potential of biosignatures in mineral deposits has proven ambiguous in at least three ways: 1. Sulfur isotope fractionation between aqueous sulfate and sulfide (~0.3‰) is consistent with both biotic and abiotic sulfur oxidation; 2. The increasing d13C of DIC down the transect can be solely explained by CO2 degassing; and 3. The d13C of rim-encrusting carbonates likely record a similar degassing signal. However, amorphous silica precipitates do exhibit textural evidence of life, with low inheritance between layers and lack of isopachous layering. Our results suggest that mineral deposits in Little Hot Creek show little potential for biosignature preservation; hence, further consideration of hot springs as astrobiological targets is necessary.
