Abstract
The coastal region of the Western Antarctic Peninsula is considered a biological hotspot with high levels of phytoplankton productivity and krill biomass. Recent in situ observations and particle modeling studies of Palmer Canyon, a deep bathymetric feature in the region, demonstrated the presence of a recirculating eddy that traps particles, retaining a distinct particle layer over the summer season. We applied metagenomic sequencing and Imaging Flow Cytobot (IFCB) analysis to characterize the microbial community in the particle layer. We sampled across the upper water column (< 200 m) along a transect to identify the locations of increased particle density, categorizing particles into either living cells or cellular detritus via IFCB. An indicator species analysis of community composition demonstrated the diatom Corethron and the bacteria Sulfitobacter were significantly highly abundant in samples with high levels of living cells, while the mixotrophic dinoflagellate Prorocentrum texanum and prokaryotes Methanomassiliicoccales and Fluviicola taffensis were significantly more abundant in samples with high detritus within the particle layer. From our metagenomic analysis, the significantly differentially abundant metabolic pathway genes in the particle layer of Palmer Canyon included pathways for anaerobic metabolism, such as methanogenesis and sulfate reduction. Overall, our results indicate that distinct microbial species and metabolic pathway genes are present in the retained particle layer of Palmer Canyon.