Evidence of dissolved organic Nitrogen assimilation in Arctic Coastal Ecosystem

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 apprehend upcoming changes in the Arctic seas, as increased riverine discharge and permafrost thawing. 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 fresh water 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 about 62% of the dissolved organic nitrogen (DON) released by the Lena River is assimilated within the shelf, which represents up to 28% of the yearly new primary productivity over this region. This is a crucial information regarding the near-future impact of climate change on primary productivity in coastal Arctic.