HR: 0800h
AN: B21A-1019    [Abstracts]
TI: Travertine-Depositing Cool-Springs of the Rio Grande Rift, New Mexico: Links Between Geochemistry, Tectonic Setting, and Microbial Diversity
AU: * Newell, D L
EM: dnewell@unm.edu
AF: Dept. Earth and Planetary Sciences, University of New Mexico, Northrop Hall, Albuquerque, NM 87131 United States
AU: Crossey, L J
EM: lcrossey@unm.edu
AF: Dept. Earth and Planetary Sciences, University of New Mexico, Northrop Hall, Albuquerque, NM 87131 United States
AU: Dahm, C N
EM: cdahm@sevilleta.unm.edu
AF: Department of Biology, University of New Mexico, Castetter Hall, Albuquerque, NM 87131 United States
AU: Takacs-Vesbach, C
EM: cvesbach@unm.edu
AF: Department of Biology, University of New Mexico, Castetter Hall, Albuquerque, NM 87131 United States
AB: Travertine-depositing cool springs found within the Rio Grande rift in New Mexico may represent the distal discharges of deep hydrothermal systems related to continental rifting. We hypothesize that these springs represent overlooked ecological niches that host chemolithotrophic microorganisms relying on spring chemistry for metabolism. The geochemistry of these springs is in many ways similar to seafloor and continental hot springs, such as Yellowstone, where thermophilic microbes representing the deepest branches of the universal phylogenetic tree are found. We analyzed cool springs that varied in water type from Ca-Mg-HCO₃ to Na-Cl and Na-SO₄ waters and ranged from dilute to high (23,000 ppm) in total dissolved solids. Carbon dioxide comprised up to 99% of the water-free spring gases. Hydrogen was present up to tenths of percent, equating to 7-3400 nM dissolved H₂. Methane and hydrogen sulfide were detected in some springs up to 0.1 and 4%, respectively. Oxygen was deficient to absent. ³ He⁴He ratios ranged from 0.1 to 0.6 RA (relative to air), equating to 1-7% mantle-derived helium. The δ¹³CO₂ of spring gases ranged from -4.6 to -1.0 permil PDB, overlapping the mantle and marine limestone ranges. Mixing models using carbon and helium isotopes suggest that at least 5% of the CO₂ was mantle derived. We hypothesize that the source of high H₂ levels was mantle-derived magmatism. The lack of oxygen, abundance of hydrogen and carbon (dissolved CO₂), and high concentrations of aqueous species such as sulfate have created an environment suitable for chemolithotrophic microbes. The presence of methane and hydrogen sulfide suggest that methanogenic and sulfate reducing microbes are active. Microbial community analysis using PCR-DGGE will test for microbial diversity and identify potential trends in metabolism related to spring geochemistry. The apparent link between mantle-derived gases and deeply-circulated fluids in a continental rift setting with the presence of chemolithotrophic life make these cool-springs unique and understudied biogeochemical hotspots.
DE: 0448 Geomicrobiology
DE: 0463 Microbe/mineral interactions
DE: 1034 Hydrothermal systems (0450, 3017, 3616, 4832, 8135, 8424)
DE: 1051 Sedimentary geochemistry
SC: Biogeosciences [B]
MN: Fall Meeting 2005