Modeling the seasonal and interannual variations in nitrate flux through Bering Strait

The nutrient flux through Bering Strait has significant impacts on the biomass and community composition of phytoplankton in the western Arctic Ocean. Based on a three-dimensional ocean-sea ice-biogeochemical model, the hindcast simulations from 1998 to 2015 suggest that the nitrate flux through Bering Strait reaches the peak during February?May (-12 kmol N/s) and then decreases to a relatively lower level (-8 kmol N/s) in July and maintains this level until January. The interannual nitrate fluxes in winter and summer were analyzed with winter defined as February?March and summer defined as July?August. The main findings are summarized as follows. (1) Shelf-slope exchange near Cape Navarin plays a key role in poleward nutrient supply since the main nutrient transport belt over the Bering shelf corresponds to the pathway of Anadyr Current from Cape Navarin to Bering Strait. (2) In the winter season, the interannual nitrate flux through Bering Strait has a significant correlation (r = 0.80, p < 0.01) with that through the section adjacent to Cape Navarin (CN section) in the fall season. This remote interannual signal from upstream appears to regulate the Bering Strait nitrate flux via horizontal advection so that it can be considered as a predictor factor. (3) In the summer season, the nitrate budget in the water column from Cape Navarin to Bering Strait indicates that biological activity plays a limited role in the interannual variation in poleward nitrate flux. Instead, this interannual variability is determined by the volume transport through Bering Strait and upstream advection.