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Isotope Geochemistry

Andrew Jacobson: Members of the Jacobson group employ radiogenic isotope measurements to study chemical, physical, and biological phenomena occurring at the Earth’s surface. Many activities use isotopes to probe the compositional evolution of the Earth, at timescales spanning the geological to modern-day. Other projects aim to elucidate the fundamental behavior of isotopes, including their distribution, transport, and possible fractionation within and between Earth’s biogeochemical reservoirs. A prime goal is to isotopically track the flow, transformation, and distribution of carbon during gradual and catastrophic environmental change. Presently, the Radiogenic Isotope Laboratory emphasizes the analysis of novel isotope systems (e.g., Ca and stable Sr) to support research in aqueous geochemistry, ground and surface water hydrology, paleoceanography, and climate change, both modern and ancient.

Maggie Osburn’s stable isotope-based research focuses on the hydrogen and carbon isotopic composition of fatty organic molecules called lipids. Biology incorporates signatures from both the environment and an organism’s biochemistry into lipids and different organisms fractionate differently based on what they do for a living. By measuring the isotopic composition lipids from environmental samples, the Osburn group can answer a diverse range of questions about the biogeochemistry of study areas. Active study sites include Yellowstone National Park, the former Homestake Gold Mine in South Dakota and the Kidd Creek Mine in Canada, Mammoth Cave National Park, flooded caves in the Yucatan, and many others. As lipids are often well preserved, these data can be used to understand conditions in past environments as well (see Paleoclimatology and Paleoceanography).

Matt Hurtgen’s research seeks to better understand the complex set of couplings and feedbacks that regulate the chemical composition of the ocean-atmosphere system and how this has changed over the past ~1 billion years.  In particular, the Hurtgen group utilizes carbon and sulfur isotopes preserved in rocks to reconstruct the chemistry of ancient oceans and to identify the processes that influence the marine carbon cycle, the evolution of Earth’s climate system, and the long-term redox balance of the Earth’s surface.

Neal Blair’s research focuses on the cycling of carbon across the Earth’s surface as reflected by particulate organic C pools in streams, rivers, reservoirs, and the ocean. Stable and radio-isotopic measurements are used to track organic C as it moves across land surfaces and the seafloor. This lateral portion of the C-cycle is especially sensitive to anthropogenic impacts such as via land use. Field areas have included the Pacific Rim (California, Oregon, New Zealand, Taiwan, Papua New Guinea), the Midwest, and the Amazon River shelf.

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