Arctic | Lower Trophic Lev els DOCTORATE POSTER PRESENTATION
Linking microbial and biogeochemical measurements of carbon and nitrogen cycling across seasons in an Arctic lagoon Presenter: Brian Kim , bskim@vims.edu , Virginia Institute of Marine Science
Tasha Griffin , grifnata@oregonstate.edu, Oregon State University Byron Crump , byron.crump@oregonstate.edu , Oregon State University Amber Hardison , akhardison@vims.edu , Virginia Institute of Marine Science
Microbial activity on the Arctic coast drives biogeochemical cycling of terrestrial inputs to the Arctic Ocean, thereby fueling primary production and supporting food webs relied upon by Inupiat communities. As the Arctic warms, Alaska’s northern coastal ecosystems are responding to rapid shifts in ice cover duration and terrestrial influxes from coastline erosion. While rising rates of primary production in the Arctic Ocean are well-defined and appear to be driven by increasing terrestrial inputs, the seasonal trends and microbial processes driving coastal nutrient cycling and productivity remain underexplored. A coastal system of particular interest in Alaska is the Beaufort Sea coast which is bordered by an irregular and discontinuous chain of barrier islands that enclose numerous shallow lagoons. In order to forecast the impacts of a changing Arctic, we must first understand the seasonal and microbial processes that support coastal nutrients and subsequent primary production, particularly during the understudied winter period. In this study, we conducted tracer stable isotope (15N-ammonium, 15N-urea, 13C-bicarbonate) incubations alongside microbial metatranscriptomics (mRNA) sequencing to quantify carbon (C) and nitrogen (N) cycle rates and gene expression across seasons on the Beaufort Sea coast. Incubations showed high rates of light-dependent carbon fixation during break up that were sustained through the open water season. During ice cover, carbon fixation rates were comparable between light and dark treatments, with high gene expression for both autotrophy and heterotrophic CO2 assimilation. This was further supported by 15N stable isotopes and metatranscriptomics which showed high rates of nitrification during ice cover, but not during break up and open water. In addition, nitrification showed a substrate preference for ammonium over urea and exhibited lower rates in light treatments suggesting light inhibition. Our results show that Arctic primary production is primarily driven through photoautotrophy during break up and open water but may rely on chemoautotrophic and heterotrophic carbon assimilation during the long winter months to support the under ice ecosystem .
Alaska Marine Science Symposium 2023 30 6
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