Investigation of the seasonal co-occurrence patterns of archaea and bacteria across vertical gradients in the Southern Ocean

<p dir="ltr">The Southern Ocean plays a pivotal role in global climate regulation and biogeochemical cycling, yet the dynamics of its microbial communities remain poorly resolved. This thesis investigates the structure and drivers of microbial communities across spatial and temporal gradients, with a focus on the influence of environmental conditions, seasonal variability, and water column depth. Amplicon sequencing data were analysed using the microeco pipeline to assess community composition, alpha and beta diversity, and co-occurrence network patterns. Results reveal that microbial assemblages are strongly shaped by shifts in light availability, ice cover, and nutrient regimes, which regulate the timing and magnitude of phytoplankton blooms and, in turn, microbial succession. Depth stratification further contributed to community differentiation, reflecting distinct ecological niches in surface, mid-depth, and deep waters. Network analyses highlight both positive and negative associations among taxa, suggesting that cooperative and competitive interactions structure microbial dynamics in this polar environment. Collectively, these findings offer novel perspectives on the ecological processes governing microbial communities in the Southern Ocean and underscore their sensitivity to ongoing environmental change.</p>