Decadal variability of eddy kinetic energy in the subtropical Northeast Pacific

Ocean mesoscale eddies, characterized by substantial eddy kinetic energy (EKE), are ubiquitous throughout the global ocean and play an essential role in ocean circulation, climate, and biogeochemistry. In the North Pacific, high and variable EKE is primarily concentrated in the western Subtropical Gyre. In contrast, the EKE levels in the Subtropical Northeast Pacific are relatively lower. Nevertheless, the EKE in this region remains comparable to the local mean kinetic energy and exhibits significant variability across seasonal to interannual timescales. In this study, we investigated the decadal variability of EKE in the Subtropical Northeast Pacific using observational data from 1993 to 2024. Results reveal that the EKE in this region undergoes remarkable decadal variability with a significant period of 10–11 years. This variability is characterized by a monopole spatial pattern, with the largest amplitude centered northeast of the Hawaiian Archipelago, at approximately 154°W, 26°N. Additionally, the variability is also manifested by decadal changes in the amplitudes of both cyclonic and anticyclonic eddies. Mechanistically, the EKE decadal variability is primarily driven by decadal variations in baroclinic eddy available potential energy (EPE) to EKE conversion through vertical eddy density flux. These decadal variations in baroclinic instability are likely to originate from the Pacific Decadal Oscillation (PDO). The PDO is suggested first to modulate the eddy field of density, subsequently altering the baroclinic EPE to EKE conversion associated with baroclinic instability. Consequently, the EKE fluctuates correspondingly and exhibits significant decadal variability, with the PDO signal leading the observed EKE decadal variability by approximately 15 months. Given the vital role of eddies in the transport of heat and nutrients, the identified decadal variability of EKE is expected to cause significant decadal variations in the coastal ecosystem surrounding the Hawaiian Archipelago.