Hydrographic fronts shape productivity, nitrogen fixation, and microbial community composition in the southern Indian Ocean and the Southern Ocean

Abstract. Biogeochemical cycling of carbon (C) and nitrogen (N) in the ocean depends on both composition activity underlying biological communities abiotic factors. The Southern Ocean is encircled by a series strong currents fronts, providing barrier to microbial dispersion into adjacent oligotrophic gyres. Our study region straddles boundary between nutrient-rich gyre southern Indian Ocean, an ideal changes productivity. Here, we measured impact C N uptake community diversity, contextualized hydrographic factors local physico-chemical conditions across Ocean. We observed that contrasting characteristics led unique diversity patterns, with significant correlations alpha primary productivity (PP). However, detected no link specific PP (PP normalized chlorophyll-a concentration) beta diversity. Prokaryotic were correlated N2 fixation, which itself prokaryotic process, measurable fixation 60∘ S. While regional water masses have distinct genetic fingerprints eukaryotic fractions, vary more gradually regionally. This suggests phylogenetic strongly bounded physical oceanographic features, while responds chemical conclude concomitant assessments are central understanding dynamics complex responses microorganisms changing environment.