The Effects of PDO on Phytoplankton Primary Production in the Pacific Ocean

Abstract The Pacific Decadal Oscillation (PDO), a dominant low‐frequency climate mode in the North Pacific, modulates sea surface temperature (SST), circulation dynamics, and wind stress, thereby controlling nutrient supply and phytoplankton primary production (PP) in the sunlit ocean layer. However, the mechanisms linking PDO to PP variability remain insufficiently understood, mainly due to limited long‐term observational data sets. Using simulations from the Community Earth System Model Large Ensemble Project (CESM‐LE), which includes both historical and RCP8.5 scenarios (1920–2100), this study investigates PDO impacts on PP across the Pacific Ocean. The PP response to the PDO exhibits strong latitudinal variability driven by regional limiting factors. In subarctic regions, PP exhibits a tripolar pattern associated with the PDO and is primarily controlled by nutrient availability, particularly iron and nitrate. In the mid‐latitude North Pacific, upper‐euphotic PP is positively correlated with PDO, largely regulated by lateral nutrient transport within the mixed layer. In contrast, photosynthetically available radiation (PAR) acts as the dominant linkage between PDO and PP in the lower euphotic zone. The PDO's influence also extends to the tropical Pacific, where its positive phases weaken trade winds and equatorial currents, reducing the zonal nitrate supply and leading to significant PP declines in the western and central tropical Pacific. Together, these results illustrate how the PDO orchestrates marine productivity through distinct regional mechanisms.