Abstract
Biogeochemical cycles in the ocean are strongly influenced by microbial activity, which affects nutrient and organic matter cycling. These processes, influenced by factors such as temperature, salinity, density and inorganic nutrients, drive the vertical stratification of microbial communities, which subsequently influence the chemistry at different depth layers. Sequencing technology has expanded our understanding of oceanic prokaryotic communities' taxonomic and functional potential. However, there is limited information on how these communities vary across gradients. In this study, we conducted metagenomic analyses on samples from the eastern North Pacific, collected across a longitudinal transect around 45°N and throughout the entire water column. We assessed taxonomic and functional classification, focusing on the roles of prokaryotic communities in biogeochemical cycling. Our results revealed that the surface community was dominated by the SAR11 clade, followed by Flavobacterales and Rhodobacterales. The deep layers harboured a more diverse community, where Thaumarchaeota accounted for the most significant proportion. This clear taxonomic stratification led to variations in the communities' functional capabilities across different depth layers. Photosynthesis and heterotrophy dominated the surface layers, whereas the deeper layers exhibited a mix of metabolic features, allowing organisms to potentially utilise both inorganic and organic carbon sources.