Nitrogen dynamic in Eurasian coastal Arctic ecosystem: Insight from nitrogen isotope

Abstract

Primary productivity is limited by the availability of nitrogen (N) in most of the coastal Arctic, as a large portion of N is released by the spring freshet and completely consumed during the following summer. Thus, understanding the fate of riverine nitrogen is critical to identify the link between dissolved nitrogen dynamic and coastal primary productivity to foresee upcoming changes in the Arctic seas, such as increase riverine discharge and permafrost thaw. Here we provide a field‐based study of nitrogen dynamic over the Laptev Sea shelf based on isotope geochemistry. We demonstrate that while most of the nitrate found under the surface freshwater layer is of remineralized origin, some of the nitrate originates from atmospheric input and was probably transported at depth by the mixing of brine‐enriched denser water during sea ice formation. Moreover, our results suggest that riverine dissolved organic nitrogen (DON) represents up to 6 times the total riverine release of nitrate and that about 62 to 76% of the DON is removed within the shelf waters. This is a crucial information regarding the near‐future impact of climate change on primary productivity in the Eurasian coastal Arctic.