The biological reprocessing of organic nitrogen into dissolved inorganic forms, termed remineralization, is an important component of the marine nitrogen and carbon cycles. Since inorganic nitrogen availability commonly limits primary production in the ocean, where and how much nitrogen remineralization takes place in the water column has important feedbacks on oceanic carbon dioxide uptake and carbon sequestration. Despite these important impacts, our understanding of the factors that determine the magnitude and distribution of nitrogen remineralization rates is severely lacking. Recent molecular, isotopic and biogeochemical advancements now allow us to study nitrification, the terminal step in nitrogen remineralization and a significant source of nitrous oxide to the atmosphere, with unprecedented spatial and temporal resolution. This seminar will focus on experimental and observational efforts to identify the primary controls over nitrification rates in nearshore waters of the central California Current System, where upwelling establishes strong spatial and temporal gradients in the physicochemical and biological properties of surface waters.