P31F-04
Biogenic Carbon on Mars: A Subsurface Chauvinistic Viewpoint
Wednesday, 16 December 2015: 08:45
3014 (Moscone West)
Tullis C Onstott1, Chui Yim Maggie Lau1, Cara Magnabosco1, Rachel Harris1, Yuheng Chen2, Greg Slater3, Barbara Sherwood Lollar4, Thomas L Kieft5, Esta van Heerden6, Gaetan Borgonie7, Hailiang Dong8 and Deep Carbon Cycle Team, (1)Princeton University, Princeton, NJ, United States, (2)Arizona State University, The Biodesign Institute, Phoenix, AZ, United States, (3)McMaster University, Hamilton, ON, Canada, (4)University of Toronto, Toronto, ON, Canada, (5)New Mexico Institute of Technology, Department of Biology, Socorro, NM, United States, (6)University of the Free State, Bloemfontein, South Africa, (7)Extreme Life Isyensya, Gentbrugge, Belgium, (8)Miami University Oxford, Oxford, OH, United States
Abstract:
A review of 150 publications on the subsurface microbiology of the continental subsurface provides ~1,400 measurements of cellular abundances down to 4,800 meter depth. These data suggest that the continental subsurface biomass is comprised of ~1016-17 grams of carbon, which is higher than the most recent estimates of ~1015 grams of carbon (1 Gt) for the marine deep biosphere. If life developed early in Martian history and Mars sustained an active hydrological cycle during its first 500 million years, then is it possible that Mars could have developed a subsurface biomass of comparable size to that of Earth? Such a biomass would comprise a much larger fraction of the total known Martian carbon budget than does the subsurface biomass on Earth. More importantly could a remnant of this subsurface biosphere survive to the present day? To determine how sustainable subsurface life could be in isolation from the surface we have been studying subsurface fracture fluids from the Precambrian Shields in South Africa and Canada. In these environments the energetically efficient and deeply rooted acetyl-CoA pathway for carbon fixation plays a central role for chemolithoautotrophic primary producers that form the base of the biomass pyramid. These primary producers appear to be sustained indefinitely by H2 generated through serpentinization and radiolytic reactions. Carbon isotope data suggest that in some subsurface locations a much larger population of secondary consumers are sustained by the primary production of biogenic CH4 from a much smaller population of methanogens. These inverted biomass and energy pyramids sustained by the cycling of CH4 could have been and could still be active on Mars. The C and H isotopic signatures of Martian CH4 remain key tools in identifying potential signatures of an extant Martian biosphere. Based upon our results to date cavity ring-down spectroscopic technologies provide an option for making these measurements on future rover missions.
