This study challenges a widespread notion that most global CO2 degassing takes place at mid-ocean ridges and subaerial volcanoes by evaluating degassing in continental extensional areas. The hypothesis to be tested is that there is a substantial and unrecognized upward flux of fluids and gases from deep within the earth that rise through vents in the Rio Grande rift and other tectonically-active regions of the western U.S. These fluids often issue as carbonate-depositing (travertine) springs, degrade regional water quality, release carbon to the atmosphere, and support distinct microbial ecosystems. This study will gather data on time-variations in the geochemical character (including trace element, stable isotope and noble gas analysis) of major spring systems and associated groundwaters to evaluate a hypothesis that microseismicity is triggering advective transport and degassing. Microbial sampling and DNA amplification will be used to compare these ?continental smokers? to black and white smokers known along oceanic spreading centers.
The study will support graduate and undergraduate training, as well as a museum exhibit on travertine springs and their geological and hydrologic significance.
The discovery and characterization of continental smokers accomplished in this grant have transformative potential for the fields of hydrology and geomicrobiology. Three decades ago, the discovery of oceanic black and white smokers provided evidence for direct convective transfer of heat and fluid from the mantle to Earth's surface beneath oceans. Discovery of these underwater hot spring vents also led to discovery of new organisms, ecosystems, and previously unknown biological niches involving non-photosynthetic biological pathways (chemolithotrophy). Even earlier (1969), the discovery of a heat-tolerant bacteria in a Yellowstone hot springs led to the discovery of an enzyme now used for the polymerase chain reaction (PCR) - the foundation for microbiology research on DNA cloning and sequencing. Our model for continental smokers extends many of the same concepts to tectonically active regions of continents such as transfer of mantle fluids to groundwater systems and unique microbial communities around spring vents. Our work identifies travertine-depositing carbonic springs of the western US and other global extensional regimes in continents (for example the Rio Grande Rift in New Mexico) to be sites of mantle degassing based on 4He/3He and other noble gas analyses. Correlation of spring hydrochemistry with mantle tomographic images generated with data from the EarthScope experiment indicates that mantle degassing takes place preferentially above mantle low velocity zones indicating rapid fluid pathways exist for gases to rapidly ascend through the ~ 100 km thick continental lithosphere. Water chemistry modeling indicates that the high CO2 in these springs is derived dominantly from depth (below the aquifer), and likely mainly from the mantle. A main contribution of the continental smokers research is that this class of springs document previously underappreciated and widespread endogenic inputs into groundwater systems that cause deterioration of water quality for water supply. This discovery will assume greater importance for arid regions that rely on groundwater for sustenance of human populations and ecosystems. Additionally, as surface systems receive less surface recharge through anticipated climate change scenarios in the Southwest, deeply-circulated groundwaters emanating from faults as described in this research will have even greater negative impacts on water quality. These springs include both hot springs and cool springs such that hydrochemical data on continental smokers has direct overlap with geothermal exploration and research. Our RNA sequencing analyses of microbes from springs in New Mexico, Colorado, Arizona, and Utah indicates that, like oceanic smokers, many of these spring systems host unique and novel micro-organisms that are very deeply branching on the tree of life. This discovery leads the way for continued studies that promise to better understand: 1) early Earth chemolithotophic microbial life, 2) depth of origin and mobility of the subsurface microbial biosphere, and 3) potentially new organisms that, like the Yellowstone discovery, may lead to improved microbiology techniques. Broader impacts from this grant have been substantial in the realms of student training (all levels), mentoring of Native American and Hispanic geoscience undergraduates, MS and PhD students, and public informal science education through television documentaries (Valles Caldera- the Science), History and Discovery Channel programs about continental smokers, and outreach through the award winning Trail of Time Geoscience Exhibition at Grand Canyon National Park, which reaches 5 million annual visitors with information about springs and travertines of Grand Canyon among other geoscience topics.
