Enhancing role of nitrogen fixation in biogeochemical cycles of the Pacific Arctic

The Arctic Ocean is warming rapidly, prompting increased attention to the ecosystem’s response to sea-ice loss and the influx of organisms from lower latitudes. Here we found that nitrogen fixation in the Pacific Arctic region was significantly elevated when sea ice in the Chukchi shelf region retreated earlier. UCYN-A2 was determined to be the dominant diazotroph, with numerical simulation and water mass analyses implying its origin to be in the Bering Sea. UCYN-A2 abundance was positively correlated with temperature, and it extended into the Arctic off-shelf region, which is undergoing oligotrophication as a result of sea-ice loss. In this region, nitrogen fixation contributed significantly to new production (4.6– 100%, average: 34%), underscoring its impact on the biogeochemical cycles. This study highlights the increasing importance of nitrogen fixation in the Pacific Arctic region, driven by warming, sea-ice loss, and borealization.