Optimal Environmental Conditions and Anomalous Ecosystem Responses in the California Current System

In Eastern Boundary Current systems, wind-driven upwelling drives nutrient-rich water to the ocean surface, making these regions among the most productive on Earth. Bottom-up regulation of productivity by changing wind and/or nutrient conditions can dramatically impact ecosystem functioning, though the mechanisms are not well understood beyond broad-scale relationships. Here we quantify the dependence of phytoplankton biomass on wind forcing and nutrient availability and show that the influences of wind and nutrients interact strongly and nonlinearly. Taken together these two influences provide a much more complete view of bottom-up controls on productivity than either does on its own. We describe optimal environmental conditions for phytoplankton biomass and present an integrative framework in which past and future ecosystem change can be evaluated relative to environmental drivers. The utility of this framework includes (i) explaining observed ecosystem responses during several extreme events in the northeast Pacific, and (ii) providing a mechanistic underpinning for potential biological impacts of projected climate change.