EXPLORATION OF DISSOLVED INORGANIC CARBON AND DISSOLVED ORGANIC CARBON IN HOT SPRINGS WITHIN YELLOWSTONE NATIONAL PARK

Dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) are crucial nutrients for autotrophic and heterotrophic microbial life, respectively, in hydrothermal systems. Biogeochemical processes that control amounts of DIC and DOC in Yellowstone hot springs can be investigated by measuring carbon abundances and respective isotopic values. A decade and a half of field work in 10 regions within Yellowstone National Park and subsequent geochemical lab analyses reveal that sulfate-dominant acidic regions have high DOC (Up to 57 ppm C) and lower DIC (up to 50 ppm C) compared to neutral-chloride regions with low DOC (< 2 ppm C) and higher DIC (up to 100 ppm C). Abundances and isotopic data suggest that sedimentary rock erosion by acidic hydrothermal fluids, fresh snow-derived meteoric water, and exogenous carbon input allowed by local topography may affect DOC levels. Evaluating the isotopic compositions of DIC and DOC in hydrothermal fluids gives insight on the geology and microbial life in the subsurface between different regions. DIC d¹³C values range from -4 ‰ to +5 ‰ at pH 5-9 and from -10 ‰ to +3 ‰ at pH 2-5 with several springs lower than -10 ‰. DOC d¹³C values parkwide range from -10 ‰ to -30 ‰. Within this range, neutral-chloride regions in the Lower Geyser Basin have lighter isotopes than sulfate-dominant acidic regions. In hot springs with elevated levels of DOC, the range only varies between -20 ‰ and -26 ‰ which may be caused by local exogenous organic matter runoff. Combining other geochemical measurements, such as differences in chloride and boron fractionations, demonstrate that some regions contain mixtures of multiple fluids moving through the complex hydrological system in the subsurface. The mixing of these fluids may account for increased levels of DOC in meteoric sulfate-dominant acidic regions. Ultimately, we provide the foundational values of dissolved carbon and their isotopic composition in a parkwide study, so results can be combined with future studies that apply different sequencing analyses to understand specific biogeochemical cycling and microbial communities that occur in individual hot springs.