CAREER: triple-isotope approach to unraveling subsurface food webs

Overview: The continental subsurface harbors a vast yet understudied microbial biosphere in which geological and biological realms are united through biogeochemistry. While prior work has informed the extent and diversity of subsurface microbes (e.g.1-4), understanding of in situ physiology has lagged far behind. Are subsurface ecosystems dependent on the surface, does this change with depth, and how has this changed with time? I hypothesize that ultra-deep continental ecosystems must live independently of surficial organic matter and signatures of dark primary productivity will be recorded in microbial biomass. I propose to develop a novel amino acid (AA) triple isotope fingerprint and apply it to deconvolve trophic relationships in a range of deep subsurface sites, I will calibrate this fingerprint with relevant heterotrophic and autotrophic microbes (Objective 1), then query biomass from three subsurface localities including shallow (1-150 m), intermediate (250-1500 m), and ultra-deep (2.4-2.9 km) environments (Objective 2). I will integrate my research products into the high school curriculum by building interactive, field-based analytical content modules for Chicago public high school biology classrooms (Objective 3) and creating immersive laboratory experiences for high school students via summer internships and field opportunities (Objective 4). These educational objectives harness the interdisciplinarity of Geobiology to expose new and diverse minds to Earth Science. By incorporating research products into the K-12 classroom and inviting high school interns into research arenas, I directly link research and education objectives and further my career goals. Intellectual Merit:The experiments and field campaigns proposed here are the first of their kind, constituting a novel isotopic approach to investigate a 2.7 km swath of the crust, 2.5 Ga of Earth History, and the oldest fluids on Earth. DeNiro and Epstein (1978) wrote “You are what you eat (plus a few ‰),” but what do subsurface microbes eat? My triple AA isotope approach exploits the distinct biochemical routing of C, N, and H through cells and ecosystems, to provide an answer to this long-standing question that has potentially transformative implications to C-cycling on Earth and biospheric evolution. This newly calibrated isotopic fingerprint will have broad application within the geobiology community, but also ecology, medicine, anthropology, and others. Field studies will transform the state of knowledge on nutrient cycling within individual subsurface sites and the global subsurface biosphere, informing biogeochemical fluxes in the modern and constraining their temporal evolution. Findings from this work will have far reaching utility to the interpretation of marine, freshwater, and soil systems5,6,7, human and animal microbiomes8, and even to the habitability of other planets. Broader Impacts: My educational objectives attempt to simultaneously address two related challenges within the Earth Sciences: the limited Earth Science content in school curricula and the grave lack of diversity in the field. By partnering with a NU outreach organization to develop geobiology-based curriculum modules as part of the implementation of Next Generation Science Standards, I can introduce my research to a diverse population of students. Through a summer internship program for the same pool of students, I can facilitate potentially transformative individual laboratory and field experiences. Meaningful and sustained contact with these students will promote their college readiness an