Physical and biogeochemical drivers of alongshore pH and oxygen variability in the California Current System

In the California Current System (CCS), the nearshore environment experiences natural exposure to low pH and reduced oxygen in response to coastal upwelling. Anthropogenic impacts further decrease pH and oxygen below biological thresholds, making the CCS particularly vulnerable to ocean acidification and hypoxia. Results from a coupled physical-biogeochemical model reveal a strongly heterogeneous alongshore pattern of nearshore pH and oxygen in the central CCS, both in their long-term means and trends. This spatial structuring is explained by an interplay between alongshore variability in local upwelling intensity and subsequent primary production, as well as changes in the vertical density structure modulated by meanders in the regional ocean circulation. The model solution suggests that the progression of ocean acidification and hypoxia will not be spatially homogeneous, thereby highlighting the need to consider sub-regional processes when assessing natural and anthropogenic impacts on coastal ecosystems in eastern boundary current upwelling regions.