Nitrite Cycling in Warming Arctic and Subarctic Waters

The primary nitrite (NO2-) maximum (PNM) is a typical feature of oceanic nitrogen (N) cycle, yet its characterization in the world ocean remains a gap. By combining the natural abundance of NO2- isotopes with geochemical model, we report for the first time that the formation of Arctic and subarctic PNMs is dominated by ammonia oxidation, while the oxidation of NO2- is the main sink. Notably, NO2- oxidation plays a more important role in Arctic and subarctic waters than in low- and mid-latitude waters. The residence time of NO2- in the PNM further suggests that the NO2- cycle in the Arctic Ocean is more dynamic than in other marine ecosystems. Our findings provide insights into N cycle dynamics in the upper Arctic Ocean ecosystem.