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Abstract
This study used ocean observations, 16 rRNA, and taxonomic insights to understand the relationships between meltwater-modified ocean circulation, iron supply, and pelagic bacterial community structure in the Amundsen Sea Polynya (ASP), Antarctica. Polynyas are marine ecosystems characterized by seasonal sea ice cover and massive phytoplankton blooms; the ASP is one of the most productive polynyas globally. Ocean models of the ASP suggest the importance of an "iron conveyor belt," comprising iron-rich deepwater upwelled via meltwater entrainment under ice-shelf cavities, delivering key micronutrients to the phytoplankton. How the microbial community changes along this “conveyor belt,” and the influence of bacteria on the bioavailability of the iron, was yet to be explored. This research found distinct communities in each water mass, characterized by location within the ASP, suggesting community succession along the route. Aerobic decomposers dominated in the surface waters, within and below the bloom, while bottom-water communities included known siderophore producers. Communities likely performing nitrification and sulfur-oxidization were found near the ice shelf. Our findings indicate a possible coupling of the nitrogen and iron cycle in this system.