PhD Dissertation Defense: Adrienne Hoarfrost

The PhD Dissertation Defense of Adrienne Hoarfrost will be presented by the University of North Carolina at Chapel Hill’s Department of Marine Sciences. The main location of this event will be in seminar room G201 on the ground floor of Murray Hall on UNC-CH campus in Chapel Hill, NC. The defense will be streamed live to UNC’s Institute of Marine Sciences room 222 in Morehead City, NC. This event will be held on Wednesday, September 12th from 2:30 pm – 3:30 pm.

Title: Linking environmental and microbial processes from community to global scales

Abstract: The interconnections between life and the environment are inextricably linked. From the scale of a single microbe to the entire Earth system, biological and environmental processes have coevolved over more than four billion years into a complex system of interactions and feedbacks that together produce the geochemical and ecological conditions we observe around us. Community-scale processes produce biogeochemical fluxes, which vary across regional and global scales in predictable patterns. At the community, regional, and global scale, this dissertation addresses a question central to our understanding of environmental microbial systems: How do microbial community interactions with their environment govern their functional and ecological role in the ecosystem, and how do environmental conditions shape the distribution and functional capacities of microbial genetic diversity? I demonstrate that microbial carbon cycling capacities in warm core ring waters originating from the Gulf Stream during an eddy intrusion event on the Mid-Atlantic Bight continental slope are distinct from other shelf and shelf break water masses, illuminating the relationship between marine microbial communities and physical processes at the regional scale. As these eddy intrusion events likely increase in the future, these regional scale interactions have functional and biogeochemical implications in both present and future oceans. At the global scale, I build models to accurately predict genetic diversity of the key marine heterotroph SAR86 from environmental variables, identifying five previously unrecognized ecotypes within the SAR86 clade characterized by distinct environmental distributions, and resulting in the first global-resolution projections of SAR86 ecotype biogeography. From the community to the global scale, each level of inquiry demands solutions tailored to address the key challenges and opportunities unique to it, and new approaches are brought to bear at small and large scales, developing a more effective method to measure microbial activities in sediments to expand the range of environments for which microbial activity measurements are feasible, and providing a data discovery tool that harnesses the potential of publicly available sequencing datasets to scale data-driven discovery to ever more complex microbial systems.