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Abstract
The California Current Large Marine Ecosystem (CCLME) experiences seasonal upwelling that drives high productivity but also episodic hypoxia, signaling ecosystem stress. This study examined microbial roles in carbon and nitrogen cycling during hypoxic events off Oregon using stable isotope probing (SIP) with ^13C-NaHCO₃. Results revealed widespread dissolved inorganic carbon assimilation by heterotrophic and autotrophic bacteria, including gamma sulfur oxidizers (SUP05, ARCTIC96BD-19) and organisms involved in nitrogen cycling. qPCR confirmed SUP05 abundance correlated with low oxygen and upwelling. RT-qPCR of amoA transcripts indicated variable ammonia oxidation linked to Columbia River influence. Findings highlight microbial contributions to biogeochemical processes in dynamic coastal margins.