Marine diazotrophs play a critical role in sustaining primary productivity in nitrogen-limited oligotrophic oceans through biological nitrogen fixation, potentially influencing the efficiency of the biological carbon pump (BCP). However, the contribution of diazotroph-derived carbon to deep-ocean sequestration and the microbial mechanisms underlying its export remain poorly understood. This master's thesis, conducted within the ERC-funded HOPE project, investigates the relationship between carbon export intensity and microbial community dynamics associated with marine snow in the Western South Pacific Ocean, a region characterized by high rates of N₂ fixation and significant atmospheric CO₂ uptake. Using samples collected by an autonomous smart buoy equipped with an DNA-RNA sampler and deep-ocean sediment traps, this study will characterize microbial assemblages in both the euphotic and mesopelagic areas of the water column, with a particular focus on diazotroph communities. Molecular analyses, including 18S and 16S rRNA gene sequencing and quantitative PCR, will be employed to assess microbial diversity and abundance. By linking microbial composition to measurements of carbon export, this work aims to identify potential pathways through which diazotrophs contribute to carbon sequestration and improve our understanding of their role in regulating the ocean's response to climate change.
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