Observations of Cross-Shelf Nitrate Fluxes on the Oregon Continental Shelf

The United States Pacific Northwest ocean ecosystems are primarily limited in growth from nitrate supply. The nitrate supply that drives the highly productive marine growth in this region is primarily a result of wind driven coastal upwelling. This work investigates cross-shelf nitrate fluxes over the Oregon continental shelf using new data made available through the installation of the Ocean Observatories Initiative Endurance Array. The primary onshore flow of nitrate-rich water over the continental shelf is found to originate at the middle depths, consistent with previous research in the region. However, the upwelling transport and cross-shelf nitrate fluxes on the continental shelf are found to be in poor agreement with common upwelling indices and a variety of physical forcings (e.g., wind stress). This suggests the need for additional dynamics (e.g., large-scale pressure gradients) to fully explain the observed surface transport and nitrate fluxes. Near the coast, an empirical model is found to be successful at predicting the nearshore nitrate concentrations from onshore wind stress measurements. The primary results from this research are laying the groundwork for future analytical modelling of nitrate and water transport on the Pacific Northwest continental shelf.