Delivery of terrigenous nutrients from rivers and coastal erosion sustain up to one third of Arctic Ocean Net Primary Production

Ronny Lauerwald1,2, Jens Terhaar2,3, Pierre A. G. Regnier4, Nicolas Gruber5 and Laurent Bopp6, (1)Université Libre de Bruxelles, Department of Geoscience, Environment and Society, Brussels, Belgium, (2)LSCE Laboratoire des Sciences du Climat et de l'Environnement, Gif-Sur-Yvette Cedex, France, (3)Université Libre de Bruxelles, Department of Earth and Environmental Sciences, Brussels, Belgium, (4)Université Libre de Bruxelles, Brussels, Belgium, (5)ETH Zurich, Environmental Physics, Zurich, Switzerland, (6)Ecole normale supérieure (ENS), Département de Géosciences, Paris, France
The Arctic is more than any other region affected by climate change. Associated warming and sea ice reduction will likely lead to increased marine net primary production (NPP) during the first half of the 21st century, which would then significantly enhance the fishery catch potential in the Arctic Ocean. However, projections of Arctic Ocean NPP diverge strongly over the second half of the 21st century and do not even agree on the sign of future NPP change. More importantly, the models used for these projections often neglect terrigenous nutrient inputs from rivers and coastal erosion, which are believed to be of great importance for the Arctic Ocean.

In our study, we explicitly simulate the impact of terrigenous carbon and nutrient inputs on Arctic NPP, using an ocean-biogeochemical model and a novel, spatially and seasonally resolved, observation-based forcing data set of carbon and nutrient inputs from rivers and coastal erosion. For nitrogen (N), which is the limiting nutrient in the Arctic Ocean, we quantified the average contemporary inputs from Arctic rivers and coastal erosion at 1 Tg N yr-1 and 1.6 Tg N yr-1, respectively. The evaluation of our model results confirms that these inputs are necessary to reproduce the observed Arctic NPP, which is otherwise substantially underestimated. Our simulation results show that terrigenous nutrient inputs sustain 36 ± 14 % (21±8 Tg N yr‑1) of annual Arctic NPP. This proportion significantly exceeds earlier estimates because of high simulated recycling rates and because of the inclusion of inputs from coastal erosion. Our results further suggest that changes in terrigenous nutrient fluxes due to climate change are one of the determining factors of the future of primary production and associated food webs in the Arctic Ocean.