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Geophysical Monograph Series



  • Deep-sea ecology—Congresses
  • Mid-ocean ridges—Congresses



Diversity of life at the geothermal subsurface—surface interface: The Yellowstone example

J. R. Spear and N. R. Pace

Generally, studies of the terrestrial example of Yellowstone National Park indicate that the diversity of microbial life at the geothermal subsurface-surface interface is considerable. On the other hand, experiments in a subsurface well in Biscuit Basin suggest that the Yellowstone subsurface is highly reduced, with minimal in situ subsurface life at this location. The absence of life in the subsurface is likely due to low concentrations of available electron acceptors. Where subsurface thermal waters emerge to the surface, however, in the presence of oxidizing electron acceptors, microbial life blossoms on all growth surfaces at high temperatures. The geothermal subsurface-surface interface in the presence of both electron donors and acceptors, provides the key location for life to thrive and forms the cornerstone of the microbial ecosystem. Through molecular analyses, the identities of organisms present in a community can be determined by their phylogenetic types (phylotypes), their molecular signatures. Molecular sequences allow relationships to other life forms to be inferred. Comparisons of gene sequences of organisms and consideration of the geochemistry of a particular environment can help to explain how this geothermal system functions. Experimental results challenge some popular notions about the kinds of organisms that inhabit the geothermal realms and the energy sources that fuel them. In contrast to the popular notion that representatives of the phylogenetic domain Archaea dominate high-temperature ecosystems, members of the domain Bacteria are most abundant in the Yellowstone ecosystem. Moreover, while sulfur metabolism is generally proposed to be the primary energy source for life in this geothermal system, the main organisms identified by phylotype are related to organisms that utilize hydrogen, not sulfur, for energy. This implies that hydrogen is the main energy source that drives primary productivity in this and potentially other geothermal ecosystems. Primary dependence on hydrogen metabolism could be the common theme for high-temperature life in hydrothermal zones at mid-oceanic ridges, as well as for the earliest life on Earth and, potentially, for life on other planetary bodies.

Citation: Spear, J. R., and N. R. Pace (2004), Diversity of life at the geothermal subsurface—surface interface: The Yellowstone example, in The Subseafloor Biosphere at Mid-Ocean Ridges, Geophys. Monogr. Ser., vol. 144, edited by W. S. Wilcock et al., pp. 343–354, AGU, Washington, D. C., doi:10.1029/144GM21.

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