Inputs of Nutrients and Organic Matter from Land to the Arctic Ocean and their Potential Impact on Ocean Processes

The Arctic Ocean is the most riverine-influenced of all of the world's oceans. Freshwater inputs are great enough to create an estuarine-like environment that has low-salinity surface waters with a clear terrigenous chemical signal. Despite this, the importance of riverine nutrients to the Arctic Ocean is generally poorly understood. This study couples measurements of circumpolar riverine nutrient fluxes from the PARTNERS (Pan-Arctic River Transport of Nutrients, Organic Matter, and Suspended Sediments) Project with the MIT General Circulation Model, to develop estimates of the distribution and availability of riverine N in the Arctic Ocean. These estimates are used to assess the importance of terrigenous dissolved inorganic and organic N (tDIN, tDON) for oceanic processes such as primary and secondary production. We estimate that annually, 0.2 Tg of tDON is lost to remineralization, photodegradation, and biological sequestration, distributed over shelf (85%) and open ocean (15%) regions. In addition, across the full pan-arctic watershed approximately 0.4 Tg of tDIN is delivered to the Arctic Ocean each year. If all of this N were to pass through algal-based food webs and be recycled in the ocean environment, primary production in the range of 4-10 Tg C yr-1 could result. While this is just a fraction of the Arctic Ocean's total primary production, rapid uptake of tDIN in N-limited nearshore regions would lead to localized rates of riverine-supported productivity as great as 17-46 g C m-2 yr-1. This work demonstrates that riverine nutrients have an important effect on productivity in the nearshore zone, and continue to be available for uptake well into the open ocean, albeit at relatively low concentrations.