Vertical Structure and Functional Diversity of Microbial Communities in the Ross Sea, Antarctica

The Ross Sea, Antarctica, encompasses distinct water masses, each characterized by unique physicochemical conditions influencing microbial community composition and functional diversity. This study examined microbial communities across five stations covering various water masses, including Antarctic Surface Water (AASW), Circumpolar Deep Water (CDW), and Shelf Water (SW). Despite limited horizontal variability, significant vertical structuring was observed, potentially driven by vertical microbial dispersal from surface waters. Surface communities exhibited lower alpha diversity due to abundant labile organic matter favoring fast-growing heterotrophic taxa, whereas deeper communities displayed increased microbial richness, reflecting adaptation to more refractory organic matter. Functional diversity revealed distinct depth-related patterns, with metabolic pathways associated with organic matter predominantly enriched in surface layers. Concurrently, rare taxa became more abundant with depth, emphasizing their potential role as keystone organisms in deep-ocean nutrient cycling. These findings highlight the critical role of vertical microbial connectivity and organic matter composition in shaping microbial community structure and functional specialization, contributing significantly to our understanding of microbial-mediated biogeochemical processes in polar marine ecosystems.