Climate Oscillations Driving Phytoplankton Dynamics and Marine Productivity in Todos Santos Bay: Insights From the Southern California Current System

ABSTRACT This study explores the impacts of climatic phenomena, including the El Niño‐Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), marine heatwaves (MHWs), and the North Pacific Gyre Oscillation (NPGO), on phytoplankton dynamics in Todos Santos Bay (TSB) from 2010 to 2022. Analysis of the anomalies of the sea surface temperature (SSTa), phytoplankton biomass (CHLa), upwelling indices (Bakun and BEUTI), and absolute dynamic topography (ADTa) revealed substantial effects on nutrient dynamics and primary productivity. The results indicate a significant reduction in phytoplankton biomass during El Niño due to increased ADT that weakened nutrient upwelling. In contrast, La Niña periods were associated with enhanced nutrient flow and phytoplankton biomass due to intensified coastal upwelling. The study also highlights the impact of the NPGO’s warm phase in reducing the influx of cold, nutrient‐rich subarctic water, influencing the phytoplankton community structure towards smaller phytoplankton and dinoflagellates. Notably, a positive correlation was found between ADTa and the dominance of smaller phytoplankton and dinoflagellates, suggesting that higher sea levels and increased stratification favor these groups over larger phytoplankton like diatoms. This shift suggests potential long‐term ecological implications, including effects on marine biodiversity and fisheries. The findings underscore the complex interplay between global climatic phenomena and marine ecosystem productivity, emphasizing the necessity of adaptive ecosystem management in the face of climatic variability.