Particle-associated diazotrophs drive nitrogen fixation in Arctic subsurface waters of the Barents Sea

Biological dinitrogen (N 2 ) fixation sustains productivity in oligotrophic oceans and is now also thought to contribute substantially to the nitrogen supply in the warming Arctic. Here we demonstrate significant N 2 fixation by particle-associated diazotrophs in subsurface waters of the Barents Sea. Comparing our findings with subtropical studies reveals particle-associated non-cyanobacterial diazotrophs as the primary N 2 fixers in subsurface Arctic waters of the Barents Sea, contrasting with diverse communities in warmer regions. As the Arctic shifts towards oligotrophication, understanding the magnitude and controls of particle-associated N 2 fixation will provide critical insights into future nitrogen supply required to sustain productivity in the rapidly changing Arctic Ocean. However, particle-associated N 2 fixation may be a distinctive feature of the Barents Sea, where in contrast to other Arctic shelves the seasonal and long-term trends in nitrogen dynamics are heterogeneously determined by changes in the external Atlantic Water supply, sea-ice extent, and terrestrial inputs. In this context, the role of particle-associated N 2 fixation across the wider Arctic Ocean will require further investigation.